Catalytic Steam Reforming and Esterification of Bio-oil

University of Calgary

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Graduate Studies The Vault: Electronic Theses and Dissertations

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Catalytic Steam Reforming and Esterification of

Bio-oil

Sampouri, Saeed

Sampouri, S. (2016). Catalytic Steam Reforming and Esterification of Bio-oil (Unpublished

master's thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/25227

http://hdl.handle.net/11023/3029

master thesis

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UNIVERSITY OF CALGARY

Catalytic Steam Reforming and Esterification of Bio-oil

by

Saeed Sampouri

A THESIS

SUBMITTED TO THE FACULTY OF GRADUATE STUDIES

IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE

DEGREE OF MASTER OF SCIENCE

GRADUATE PROGRAM IN CHEMICAL AND PETROLEUM ENGINEERING

CALGARY, ALBERTA

MAY, 2016

© Saeed Sampouri 2016

ii

Abstract

This study investigated two methods of upgrading bio-oil. The first was the production of

hydrogen (H2) via catalytic steam reforming of the aqueous phase of bio-oil. The experiments were

carried out in a fixed bed tubular flow reactor over nickel-based alumina-supported catalysts

promoted with magnesia (Ni-MgO/Al2O3). The impact of time, nickel quantity, preparation

conditions, and the initial bio-oil to water ratio on the yield of various outlet gases including

hydrogen was investigated.

The second method investigated in this study was catalytic esterification of bio-oil with an

acid catalyst and various alcohols. An existing method was modified to measure the esterification

degree and the effect of reaction conditions including temperature, carbon chain length of the

alcohols, catalyst, alcohol content, and reaction time. This study employed a batch reactor for the

reduction of carboxylic acids.

iii

Acknowledgements

I would like to express my sincere appreciations to those who helped me to accomplish this

research. First and foremost, my supervisor Dr. Jalal Abedi for his excellent guidance, support,

immense knowledge and providing me with an excellent atmosphere during the research and

writing this thesis.

Besides my supervisor, I would like to thank my thesis committee: Dr. Alex De Visscher and Dr.

Hassan Hassanzadeh. I am also grateful to Dr. Fakhry Seyeden Azad for her encouragements, and

contribution in this research.

The financial support of the Natural Sciences and Engineering Research Council of Canada

(NSERC), the Centre for Environmental Engineering Research and Education (CEERE), and the

Department of Chemical and Petroleum Engineering are acknowledged.

Last but not least, thanks to my family for their encouraging words and reassuring confidence. And

to my wife, thank you for the patience, love, and respect you had for me during this adventure.

iv

Dedication

I would like to dedicate this work to my wife and my parents.

v

Table of Contents

Abstract ............................................................................................................................... ii Acknowledgements ............................................................................................................ iii

Dedication .......................................................................................................................... iv Table of Contents .................................................................................................................v List of Tables .................................................................................................................... vii List of Figures and Illustrations ....................................................................................... viii

CHAPTER ONE: INTRODUCTION AND LITERATURE REVIEW ..............................1

1.1 Introduction ................................................................................................................1 1.2 Fast Pyrolysis .............................................................................................................3 1.3 Bio-oil ........................................................................................................................3

1.4 Different Techniques for Upgrading Bio-Oil ............................................................6 1.5 Literature Review for Esterification ..........................................................................9 1.6 Literature Review on Steam Reforming ..................................................................19

1.6.1 Hydrogen from Biomass ..................................................................................19 1.6.2 Steam Reforming of Biomass ..........................................................................21

1.6.2.1 Thermodynamic Analysis ......................................................................22 1.6.2.2 Catalysts .................................................................................................23 1.6.2.3 Experimental Conditions .......................................................................25

1.7 Objective of this study .............................................................................................27 1.8 Outline of this thesis ................................................................................................27

CHAPTER TWO: STEAM REFORMING EXPERIMENTAL .......................................29 2.1 Catalyst ....................................................................................................................29

2.2 Aqueous Phase Preparation and Characteristics ......................................................30 2.3 Fixed-bed Steam Reforming Apparatus ..................................................................31

2.4 Procedure .................................................................................................................35 2.5 Data Analysis ...........................................................................................................35 2.6 Results and Discussion ............................................................................................38

CHAPTER THREE: CATALYTIC ESTERIFICATION .................................................49 3.1 Introduction ..............................................................................................................49 3.2 Materials and Chemicals...........................................................................................49 3.3 Apparatus and Equipment ........................................................................................50

3.4 Experimental Procedure ...........................................................................................51 3.4.1 Esterification Reaction ....................................................................................51

3.4.1.1 Catalyst Type .........................................................................................52

3.4.1.2 Alcohol Type .........................................................................................53 3.4.1.3 Reaction Temperature ............................................................................53 3.4.1.4 Reaction Time ........................................................................................53 3.4.1.5 Alcohol Amount ....................................................................................53

3.4.1.6 Catalyst Amount ....................................................................................54 3.4.2 Titration and Recording ...................................................................................54

3.5 Analyzing Method ...................................................................................................58

3.6 Results and Discussion ............................................................................................61

vi

3.6.1 Modifying Titration Procedure ........................................................................61

3.6.2 Catalyst Type ...................................................................................................67 3.6.3 Alcohol Type ...................................................................................................67 3.6.4 Effect of Reaction Temperature ......................................................................69

3.6.5 Effect of Reaction Time ..................................................................................70 3.6.6 Effect of Alcohol/bio-oil Volumetric Ratio ....................................................72 3.6.7 Catalyst Loading Amount ................................................................................73 3.6.8 Effect of Various Alcohols on Viscosity .........................................................74

CHAPTER FOUR: CONCLUSIONS AND RECOMMENDATIONS ............................76

4.1 Conclusions ..............................................................................................................76 4.2 Recommendations ....................................................................................................79

REFERENCES ..................................................................................................................81

vii

List of Tables

Table 1.1 Comparison of the properties of bio-oil and conventional fuels .................................... 5

Table 2.1 Specifications of the Gases Used for GC Calibration ................................................... 35

Table 2.2 Characteristics and composition of the catalysts .......................................................... 38

Table 2.3 Elemental Analysis and Characteristics of Commercial (BTG) Bio-Oil and the

three Aqueous Phases with Various Bio-Oil/Water Ratios .................................................. 39

Table 2.4 CO/CO2 and H2/CO molar ratios obtained by steam reforming of various aqueous

bio-oil samples over various catalysts .................................................................................. 48

Table 3.1 Chemicals used in bio-oil esterification experiments ................................................... 50

Table 3.2 Titration Data ................................................................................................................ 58

viii

List of Figures and Illustrations

Figure 1.1 Main procedures of biofuel production from biomass .................................................. 2

Figure 1.2 Main feedstock resources for biochemical biomass conversion ................................... 2

Figure 1.3 Pyrolysis of biomass ...................................................................................................... 4

Figure 1.4 Deactivation of catalyst with N-containing organics in bio-oil ................................... 16

Figure 2.1 Catalytic steam reforming plant .................................................................................. 32

Figure 2.2 Process flow diagram of the steam reforming plant of bio-oil aqueous phase: ........... 33

Figure 2.3 Micro Gas Chromatograph .......................................................................................... 34

Figure 2.4 Steam reforming of aqueous phase of bio-oil (oil/water ratio = 2/1) over (a) Al2O3,

(b) Ni-MgO/Al2O3-1, (c) Ni-MgO/Al2O3-2, and (d) Ni-MgO/Al2O3-3 catalysts.

Operational conditions: nitrogen flow rate = 200 STP mL/min; bio-oil aqueous phase

feed rate = 0 .......................................................................................................................... 40




feed rate = 0 .......................................................................................................................... 41




feed rate = 0 .......................................................................................................................... 42

Figure 2.7 Comparison among the results obtained for steam reforming of aqueous phase of

bio-oil with various bio-oil to water ratios over Al2O3, Ni-MgO/Al2O3-1, Ni-

MgO/Al2O3-2, and Ni-MgO/Al2O3-3 catalysts. Operational conditions: nitrogen flow

rate = 200 STP mL/min; bio-oil aqueous phase feed rate = 0.1 mL/min; temperature =

850°C. ................................................................................................................................... 45

Figure 3.1 Process flow diagram of esterification and esterification degree detection ................ 51

Figure 3.2 Amberlyst-15 beads ..................................................................................................... 52

Figure 3.3 Manual titration set up ................................................................................................. 55

Figure 3.4 KFD 758 Titrino .......................................................................................................... 57

Figure 3.5 Titration curve of acetic acid with 0.1 N NaOH ......................................................... 59

Figure 3.6 Precipitation after titration: a) KOH 0.1 N, b) KOH 0.5 N, c) NaOH 0.1 N, d)

NaOH 0.5 N .......................................................................................................................... 62

ix

Figure 3.7 Titration results with a) 0.1 N NaOH and b) 0.5 N NaOH .......................................... 64

Figure 3.8 Front panel of titration using LabVIEW ..................................................................... 66

Figure 3.9 Effect of carbon amount of alcohol on the esterification degree in the presence of

sulfuric acid ........................................................................................................................... 68

Figure 3.10 Effect of carbon amount of alcohol on the catalytic esterification of bio-oil ............ 69

Figure 3.11 Effect of temperature on esterification degree .......................................................... 70

Figure 3.12 Effect of reaction time on the total acidity applying Amberlyst 15 .......................... 72

Figure 3.14 Effect of Alcohol/bio-oil ratio on esterification degree ............................................ 73

Figure 3.15 Effect of catalyst amount on reaction conversion ..................................................... 74

Figure 3.16 Effect of different alcohols on the viscosity change ................................................. 75

1

Chapter One: Introduction and Literature Review

1.1 Introduction

Depletion of fossil fuels and increasing environmental concerns such as greenhouse gas

emissions, air pollution, and global warming, make renewable energy sources increasingly

attractive. Biomass, the sun (e.g. photovoltaic solar cells and solar heat collectors), wind, water,

and geothermal resources are all sources of renewable energy. Each source has unique benefits

and costs, but biomass is of particular interest because between renewable resources it is the only

one that can be directly converted into liquid fuel by fast pyrolysis to provide a competitively

priced fuel for power production, transportation, and heat. Biomass is defined as a non-fossil,

biodegradable, organic material obtained from living or recently living microorganism, plant, and

animal cells. Sources of biomass include various natural and derived materials, such as wood

waste, municipal solid waste, waste paper, agricultural residue, sawdust, biosolids, grass, waste

from food processing, animal waste, and algae (Balat, 2011; Blin, et al., 2007; Bridgwater et al.,

1999).

The term bio-fuel refers to solid, liquid, or gaseous fuels that are generally produced from

biomass. A large variety of technologies are available to generate energy from biomass. Figure 1.1

illustrates the two main processes of converting biomass to energy, thermochemical and

biochemical. Each process has advantages and disadvantages. The main advantage of the

thermochemical processes is that the feedstock cannot be considered a food resource. Some of the

feedstock options for biochemical biomass conversion are shown in Figure 1.2 (Bridgwater, 2012;

Chen et al., 2015; Damartzis & Zabaniotou, 2011; Demirbash, 2007) .

2

Figure 1.1 Main procedures of biofuel production from biomass

Figure 1.2 Main feedstock resources for biochemical biomass conversion

Biomas

Thermochemical Conversion

Torrefaction Liquefaction Pyrolysis Gasification

Biochemical Conversion

Biodisel Bioethanol

Biochemical Biofuels

Bioethanol

Wheat Maize Sugar Beet Potatoes

Biodiesel

Soybean Palm Sunflower Rapeseed

Solid Gas Liquid

3

1.2 Fast Pyrolysis

The production of liquid fuel by the fast pyrolysis of biomass is of particular interest

because it is the only thermal process capable of producing usable liquid product directly from

biomass. Liquid fuels such as bio-oil have the advantage of being easy to transport and store as

well as the potential to provide a number of valuable chemicals. The liquid bio-oil produced by

fast pyrolysis has the potential to supply chemicals of much higher value than fuels. Most of these

compounds are in low concentrations. The process of pyrolysis is the thermal decomposition of

biomass in the absence of oxygen. In a biomass pyrolysis three products will be produced: gas,

bio-oil, and biochar (Figure 1.3) (Blin et al., 2007; Bridgwater et al., 1999). The relative

proportions of these products depends on the reaction parameters, the properties of the biomass,

and, the pyrolysis method. The operational conditions including temperature, heating rate, and

vapour residence time can be manipulated to produce more bio-oil or biochar (Balat, 2011; Blin et

al., 2007; Bridgwater et al., 1999). The ideal conditions for to producing bio-oil with high yields

are moderate pyrolysis temperature (≈500 ºC), very high heating rates (103–105 ºC/s), short vapour

residence times (<2 s), and rapid quenching of pyrolysis vapours (Blin et al., 2007; Bridgwater et

al., 1999).

1.3 Bio-oil

The liquid product of biomass pyrolysis is called bio-oil or pyrolysis oil. It is a viscous,

corrosive, dark brown free flowing organic liquid with a smoky odour and a low pH. The properties

of the bio-oil vary depending on the type of biomass feedstock from which it is produced and the

production technology. In a fast pyrolysis process, 70-75 wt % of the feedstock is typically

4

converted into liquid bio-oil. The energy density of bio-oil is about ten times that of biomass.

Figure 1.3 Pyrolysis of biomass

The composition of bio-oils is complex but they share many similar material properties. Bio-oil

contains hundreds of highly oxygenated organic compounds including acids, alcohols, ethers,

ketones, aldehydes, phenols, furans, esters, sugars, nitrogen compounds, multifunctional

compounds, a lot of water (20-30%), and some solid particles (Blin et al., 2007; Bridgwater et al.,

HEAT

Biomass

Vapor Condensation

5

1999; Rout et al., 2009). The derivative chemicals in pyrolysis oil are generally the result of the

thermal decomposition of lignin, cellulose, and hemicellulose. The molecular weights of these

compounds are very different, it changes from low amount as 18 (water) to high amount as 5000

or more (pyrolyticlignins). As a result of the large number of oxygenated compounds and

significant water content, the heating value of bio-oil is approximately half that of fossil oil. Bio-

oil is relatively sensitive to aging and can be unstable (Balat, 2011; Lu , 2009). Table 1.1 illustrates

the different characteristics of bio-oil and conventional oil.

Table 1.1 Comparison of the properties of bio-oil and conventional fuels (Bridgewater and Brammer,

2002)

Properties Bio-oil Diesel Heavy Fuel Oil

Density kg/m3 at 15 °C 1220 854 963

Typical composition % C 48.5 86.3 86.1

% H 6.4 12.8 11.8

% O 42.5 - -

% S - 0.9 2.1

Viscosity cSt at 50 °C 13 2.5 351

Flash Point °C 66 70 100

Pour Point °C 27 20 21

Ash % wt 0.13 0.01 0.03

Sulfur % wt 0 0.15 2.5

Water % wt 20.5 0.1 0.1

Heating Value MJ/kg 17.5 42.9 40.7

Acidity pH 3 - -

6

In conclusion, the most challenging limitations of bio-oil are its low volatility, high

corrosiveness, high viscosity, and poor heat value. Refining and upgrading are necessary to make

bio-oil an attractive fuel or feedstock for value-added chemicals. Several investigations have been

undertaken for this purpose and have proposed methods including catalytic cracking, steam

reforming, emulsification, catalytic hydrogenation, esterification, distillation, extraction with

solvents, supercritical technology extraction, and column chromatography. However, most of

these technologies have various problems due to the complexity and thermal instability of bio-oil.

Several upgrading techniques are described in the following section.

1.4 Different Techniques for Upgrading Bio-Oil

1. Catalytic Hydrogenation

Hydrotreatment is carried out in hydrogen providing solvents in presence of catalysts such as

NiMo/Al2O3. Catalytic hydrogenation requires more extreme conditions such as higher

temperature and hydrogen pressure and stable catalysts but it is an effective way to convert

unsaturated compounds into some more stable compounds (Balat, 2011; Xu et al., 2009).

7

2. Catalytic Cracking

In this method, oxygen containing compounds are catalytically converted to hydrocarbons

by removing the oxygen in the form of H2O, CO2, or CO. Zeolitic catalysts like HZSM-5 are

particularly useful for this purpose. Catalytic cracking does not require hydrogen and the

procedure is carried out at atmospheric pressure, which reduces the operating costs.

Unfortunately, the results are not promising due to high coking (8–25wt %) and the low quality

of the obtained fuels (Balat, 2011; Lu et al., 2009).

3. Emulsification

The goal of emulsification is to combine bio-oil and diesel fuel directly with the aid of

surfactants (Ikura, 2003; Zhang et al., 2013).

4. Distillation

Azeotropic distillation with toluene can be applied to remove the water component of bio-oil.

However, instability of bio-oil from both thermal and chemical point of view and its composition

with components that have similar boiling points make distillation inapplicable to produce various

oxygenated chemicals or well defined fractions (Žilnik & Jazbinšek, 2012; Rout et al., 2009).

5. Solvent Extraction

Bio-oil is a complex mixture of different groups of organic materials. Water-soluble and water-

insoluble fractions of bio-oil can be separated by water extraction, which can be further separated.

Organic solvents such as CHCl3, diethyl ether, and benzene have been studied for bio-oil extraction

but have produced low yields (Žilnik & Jazbinšek, 2012).

8

6. Supercritical CO2 Extraction

Supercritical technology was recently introduced to the field of bio-oil refining. In this

technology bio-oil is upgraded by esterification of carboxylic acids and hydrodeoxygenation of

phenols in supercritical alcohols and in supercritical n-hexane, respectively. Due to the relatively

low critical pressure (73.8 atm) and critical temperature (31.1 °C) of CO2 supercritical CO2

extraction is considered a significant method to separate thermal sensitive chemical compounds in

the past few years (Rout et al., 2009).

7. Column Chromatography

Bio-oil is a complicated mixture of several hundred organic compounds with a large range of

chemical functional groups. Therefore, it is not possible to separate all of the fractions by

distillation, extraction and, other conventional methods. Column chromatography is a new

separation technology and can provide the high sensitivity required in bio-oil separation. For

instance, phthalate esters as a toxic to humans, have been successfully separated from bio-oil using

column chromatography (Zeng et al., 2011).

8. Steam Reforming

Catalytic steam reforming of bio-oils is a technique for producing hydrogen. Hydrogen is an

extremely valuable product for the chemical industry especially in fuel, energy, and agricultural

fields. However, the complex composition of bio-oil and problems caused by deposition of carbon

on the surface of the catalyst during the reaction have led current studies to focus on performing

9

experiments on steam reforming of model bio-oil in presence of reforming catalysts (Czernik et

al., 2007; Seyedeyn-Azad et al., 2011).

(Eq. 1-1)

9. Esterification

Esterification is another technique designed to improve the quality of bio-oil. Large quantities

of carboxylic acids in bio-oil result in high acidity, corrosiveness, and poor stability. The classic

method of removing acids is esterification, a reaction between an acid and an alcohol to produce

water and ester. This reaction which will be discussed in detail in the following section.

1.5 Literature Review for Esterification

When compared with fossil fuels, bio-oil has several undesired properties including:

(1) High viscosity

(2) High acidity

(3) High water content

(4) High ash content

(5) High oxygen content

(6) Low heating value

These undesired properties limit the use of bio-oil as a substitute for fossil fuel. Researchers have

used bio-oil in conventional fuel engines. For instance, Venderbosch and van Helden reviewed the

application of bio-oil in diesel engines. Traditional diesel engines burn acid free diesel and all of

the engine compartments are made of steel. The use of bio-oil in steel engines results in erosion of

10

the injection needles due to its high acidity and abrasive particles. The latter problem could be

overcome by filtration. The formation of carbon deposits in the combustion chamber and exhaust

valves was also reported (Brown, 2011).

The abundance of organic acids in bio-oil results in low pH and high corrosiveness.

Esterification could be a relatively simple way of overcoming this problem to make bio-oil more

attractive as a liquid fuel. The esterification reaction can be performed at low temperatures and

pressures with relatively inexpensive equipment.

Recent studies have demonstrated that an esterification reaction of bio-oil with alcohol in

the presence of an acid catalyst lowered the total acid value of the bio-oil. Esterification also

lowered the water content and increased the high heating value. The use of a controlled

esterification reaction could prohibit other undesired acid catalyzed reactions such as

oligomerization and polymerization, which result in an undesirable increase in viscosity over time.

According to the Fischer esterification reaction, esterification is the result of the reaction

between an alcohol and a carboxylic acid which happens in the presence of an acid catalyst (Eq.

1.2).

(Eq.1.2)

In this reaction, R-COOH shows a carboxylic acid, R’-OH represents an alcohol and R-COOR’ is

an ester. The reaction is reversible and the equilibrium constant (Keq) is given in Eq. 1.3. The value

of Keq shows the favoured side of the reaction. If Keq is greater than 1, the reaction proceeds from

left to right which is exothermic so also energy is generated. When the Keq value is less than 1, the

reaction goes from right to left.

11

(Eq. 1.3)

Where [R-COOH] is the molar concentration of the carboxylic acid, [R’-OH] is the molar

concentration of the alcohol, and [R-COOR’] is the molar concentration of the ester.

A better way to determine the direction of the reaction is to calculate the Gibbs free energy

change (ΔG). The relationship between Keq and ΔG can be calculated as shown in Eq. 1.4. The

equilibrium position may change with pressure, temperature, and concentration. Pressure change

can be ignored if all reactants are in the liquid state.

ΔG°r= -RTln (Keq) (Eq. 1.4)

In Eq. 1.4, ΔG°r is the Gibbs free-energy change of the reaction in the reference conditions, R

stands for the universal gas constant, and T is temperature. ΔG < 0 means that the reaction will

favour the right side and ΔG > 0 favours the left.

Several researcher teams have investigated esterification of bio-oil by applying various

catalysts and alcohols.

Diebold and Czernik (1997) studied the influence of several additives on the viscosity

alteration of pyrolysis-oil during long term storage. In their study acetone, ethyl acetate, methyl

isobutyl ketone, methanol, acetone and methanol, and ethanol were applied. According to the

results, the addition of alcohol significantly decreased the change in bio-oil viscosity over time.

The researchers concluded that low molecular weight, monofunctional alcohols reacted with the

oligomers present in the bio-oil to form polyesters. It was also demonstrated that ketones and

aldehydes reacted with the alcohols to become acetals and ketals. The experiments showed that

the influence of methanol is greater if alcohol was immediately added to newly produced bio-oils,

12

comparing to an aged sample. The effect of the addition of alcohol was greater with lower

molecular weight alcohols (Diebold & Czernik, 1997). A similar investigation published by

Boucher et al. in 2000 showed that adding methanol to the bio-oil reduced the viscosity over time

and also decreased the rate of phase separation compared to crude bio-oil at similar conditions

(Boucher et al., 2000).

Zhang et al. (2006) prepared a solid acid 40SiO2/TiO2-SO4 and solid base 30K2CO3/Al2O3-

NaOH and used them in an esterification reaction of model bio-oil. They used ethanol and acetic

acid in a molar ratio of 2.5: 1(ethanol: acetic acid) and catalyst at 5 wt % of the reaction solution.

It was reported that the acid catalyst increased the esterification reaction rate and 88% of

equilibrium conversion was obtained in 80 minutes of reaction time. The gross calorific value

increased for the both acid and base catalyst, from 15.83 MJ/kg to 23.87 MJ/kg and 24.03 MJ/kg,

respectively. The pH of the upgraded bio-oil was 1.12 after the acid catalyst and 5.93 with the base

catalyst. The viscosity and density were also decreased. GC-MS was used to consider the

conversion of the esterification reaction. It was concluded that both the acid and base catalysts are

capable of catalyzing the reaction between acetic acid and ethanol, but the acid catalyst is more

effective (Zhang et al., 2006).

Lohitharn and Shanks (2009) conducted experiments to determine if in bio-oil model

compounds, the presence of high reactive light aldehydes can affect esterification. They

investigated the effect of acetaldehyde and propionaldehyde on the esterification of acetic acid

with ethanol and presence of SBA-15-SO3H as the catalyst, a mesoporous silica catalyst and an

organic–inorganic which is functionalized with propylsulfonic acid groups. They showed that the

effect of the aldehyde on the esterification of acetic acid with ethanol depended more on

13

temperature than on the quantity of alcohol. At temperatures above 100°C the aldehydes did not

interfere significantly with esterification but at 50°C and 70°C, the presence of aldehydes

decreased the reaction conversion. This decrease is the result of a rapid competitive acetalization

reaction between the aldehydes and ethanol (Lohitharn & Shanks, 2009).

Tang et al. (2009) used a combination of bio-oil esterification with hydroprocessing and

cracking to upgrade bio-oil. At supercritical temperatures, bio-oil was combined with ethanol and

hydrotreatment was conducted with a Pd/SO4-2/ZrO2/SBA-15 catalyst. Mesoporous molecular

sieve SBA-15 was incorporated with superacid SO4-2/ZrO2 to generate acid sites on the surface of

the SBA-15. It was reported that the properties of the bio-oil improved by reduction in the viscosity

and density and increase in the HHV and pH. It was concluded that the quantity of aldehydes and

ketones in the bio-oil decreased while esterification converted the acids to esters.

According to thermogravimetric and differential thermogravimetric analyses, the

macromolecular chemicals decomposed and more volatile compounds were produced (Tang et al.,

2009).

Tang et al (2010) published a paper on a one-step hydrogenation/esterification reaction for

model bio-oil with acetic acid and acetaldehyde as the model reactants. A bifunctional mesoporous

organic-inorganic hybrid silica were synthesized and tested in the experiments. The silica was

promoted with platinum and a propylsulfonic acid group.

The bifunctional Pt/SBA15-PrSO3H catalyst promoted about double the conversion of the

monofunctional SBA15-PrSO3H catalyst in the esterification reaction. The experiment

demonstrated that combining metallic platinum nanoparticles with strong acid sites resulted in

14

production of the hybrid catalyst to achieve one-step hydrogenation/esterification (Tang et al.,

2010).

In 2010, Chang et al. published two papers on bio-oil esterification. They used 732 and

NKC-9 type acidic ion exchange resins as the catalysts and methanol to esterify bio-oil in two

different reactors. They expressed that esterification could be proven by GC-MS or FTIR analysis

but the peaks have overlaps and are hard to discriminate. They conducted a potentiometric titration

with NaOH as the titrant to determine the acid number of the bio-oil before and after esterification.

Following the esterification reaction, the acid of the upgraded bio-oil on 732 resin and NKC-9

resin was decreased by 88.54% and 85.95%, respectively (Wang et al., 2010 a; Wang et al., 2010

b).

Li et al. (2011) studied catalytic esterification of carboxylic acids and acetalisation of

aldehydes in bio-oil production process, simultaneously. They confirmed the results of

experiments by Lohitharn and Shanks (2009) (X. Li et al., 2011). Their experiments employed

commercial Amberlyst-70 as the catalyst with methanol at temperatures between 70°C and 170°C.

They found that increasing temperature significantly accelerate conversion of light organic acids

and aldehydes to esters and acetals. The researchers reported that reactions between bio-oil and

methanol in presence of acid catalyst also decreased the coking formation during the bio-oil

reaction production. GC-MS was applied to quantify the results.

Moens et al. (2009) investigated the esterification and etherification of mixed hardwood

bio-oil. Their experiment determined that the amount of alcohol required for completely

conversion of the acids, aldehydes, and ketones in one kilogram of a typical bio-oil containing 1.5

15

to 2 moles of carboxylic acid groups and 4-6 moles of carbonyl groups is 10-14 moles. According

to their results, high water content (20-30%) of bio-oils results in reverse reaction in equilibrium

of esterification reactions. To complete the esterification reaction, the initial water content in the

bio-oil or the water generated during the esterification reaction must be removed to prevent the

esterification reaction from being reversed. In that case carboxylic acid and alcohol will be

produced. This would have negative effects on the stabilization of the esters produced by the

original esterification reaction (Moens et al., 2009).

Miao and Shanks (2009) performed experiments comparing the esterification of SBA-15-

SO3H. The acidic properties of bio-oil were simulated using 3 M acetic acid with methanol as the

esterification alcohol. The results indicated that SBA-15-SO3H has similar site activity for acetic

acid esterification as sulfuric acid. The water tolerance experiment showed that SBA-15-SO3H

inhibited the esterification reaction less than sulfuric acid for the model compounds. The

researchers concluded that SBA-15- SO3H increased catalyst water tolerance due to the presence

of hydrophobic propyl groups (Miao & Shanks, 2009).

The effect of nitrogen containing compounds on bio-oil esterification was studied by Li et

al. in 2013. They investigated the esterification of bio-oil produced from mallee (Eucalyptus

loxophleba ssp. gratiae) leaves in methanol in presence of Amberlyst 70. The study found that the

presence of nitrogen containing organics in the bio-oil results in formation of neutral salts in the

initial stage of the reaction. It will deactivated the catalyst and this problem had to be resolved by

high catalyst loading to have other acid catalyzed reactions occurred (Hu et al., 2013).

16

Figure 1.4 Deactivation of catalyst with N-containing organics in bio-oil (Hu et al., 2013)

Leahy et al. (2014) synthesized, characterized, and functionalized a ZrO2-TiO2 nanotube

composite with sulfate groups to produce a solid acid catalyst. The catalyst was applied in the

esterification of levulinic acid as an organic acid conversion to ethyl levulinate. According to the

GC-MS results, only esters were produced. The ZrO2-TiO2 nanotube composite was recommended

as a catalyst for the esterification of bio-oil (Li et al., 2014).

The same research group applied sulfated ZrO2−TiO2 to the esterification of a model bio-

oil made up of acetic acid and ethanol in 2015. The effect of different Zr/Ti loading ratios was

considered. This catalyst efficiently and simultaneously reduced the acid and water content. A pH

meter and GC-MS were used to analyze and evaluate esterification (Liu et al., 2015).

In 2014, two studies were conducted on the esterification of bio-oil over ZSM-5 (W. Chen

et al., 2014; Milina et al., 2014). Chen et al. studied the esterification of a mixture of phenol, acetic

acid, and n-butanol in the presence of zeolite ZSM-5.

Yi et al. (2014) conducted upgrading experiments on the water soluble fraction of bio-oil

using online extraction. They reported that the formation of char during the reaction was

17

significantly suppressed and the upgraded oil had less moisture, less acidity, and a higher heating

value (Qin et al. 2014).

Tanneru et al. (2014) pretreated bio-oil with ozone/H2O2 before upgrading it via

esterification. They removed the aldehydes existing in the raw bio-oil by converting them to

carboxylic acids via oxidation of them. Aldehydes are an oxygenate compound. They t react with

phenols in a polymerization process and produces high molecular weight resins. The

polymerization reactions of aldehyde increase the viscosity of bio-oil during storage or after

exposure to heat.

𝑅 − 𝐶𝐻𝑂⏟ 𝐴𝑙𝑑𝑒ℎ𝑦𝑑𝑒

𝑂𝑥𝑖𝑑𝑖𝑧𝑖𝑛𝑔 𝑎𝑔𝑒𝑛𝑡→ 𝑅 − 𝐶𝑂𝑂𝐻⏟

𝐶𝑎𝑟𝑏𝑜𝑥𝑦𝑙𝑖𝑐 𝑎𝑐𝑖𝑑

(Eq 1.5)

The research team applied butanol and Ru/γAl2O3 as the esterification catalyst. The results

show an increase in pH and 5.7% increase in heating value (Tanneru et al., 2014).

Most esterification studies used model bio-oil, often just acetic acid, which is not a good

model for bio-oil because bio-oil is a mixture of different chemicals including acids. Bio-oil can

be esterified with good results. The occurrence of esterification can confirmed by Fourier

transform infrared (FITR) or gas chromatography-mass spectrometry (GC-MS) analysis. Their

spectrum should be applied for the qualitative analysis of both the raw and upgraded bio-oils. Gas

chromatography can be considered as an analyzing instrument to measure the organic acids in bio-

oils and to evaluate the extent of esterification. However, because of the overlapping

chromatographic peaks it is difficult to analyze, often there is a need for complicated pretreatment

operations. Therefore, although these methods are frequently used to analyze bio-oil, their results

18

are not reliable. GC-MS is unable to detect acids with high molecular weight and there is a huge

amount of heavy carboxylic acids (around 50% of total acid content) present in bio-oil.

Chang et al. (2010) determined the acid number change for evaluating the degree of

esterification (Wang et al., 2010) using potentiometric titration. Their method is based on the

American Society for Testing and Materials (ASTM D664). ASTM D664 is a potentiometric

titration standard method used to determine acid number in petroleum products, lubricants,

biodiesel, and mixtures of biodiesel. It is reported in mg/g of KOH. In ASTM D664 a mixture of

toluene, isopropanol, and water is used as the solvent. This method is an accurate way to find the

acid number of compounds soluble in a mixture of toluene and isopropanol. However, significant

challenges are encountered when ASTM D664 is applied to analyze bio-oil.

The first issue is that bio-oil is not very soluble in toluene because of presence of many

polar components such as acids in it. The second challenge is high acidity of isopropanol compared

to other weak acids such as phenol so they cannot be measured because the concentration of solvent

is much more than that of the reagents. Consequently, titration of very weak acid cannot be carried

out with a visible inflection point. The third problem is the competition between water and very

weak acid to donate protons. The fourth issue is that the titrant of ASTM D664 is not suitable for

titration using glass electrodes in bio-oil. During titration, potassium salts are produced which are

usually insoluble in organic solvents. The formation of gelatinous and sticky precipitates on the

surface of the electrode would significantly decrease its sensitivity (Wu et al., 2014).

To address these problems, Wu et al. (2014) developed a non-aqueous titration method

designed to analyze the acidic components of bio-oil. Their titration method employs quaternary

19

ammonium hydroxide as the titrant and a mixture of tert-butanol and acetone as the solvent. The

method resolves the problems encountered by applying the ASTM D664 and can accuratelly

measure the concentrations of both strong and weak acids in bio-oil produced by pyrolysis of

biomass (Wu et al., 2014).

1.6 Literature Review on Steam Reforming

Various investigations have been conducted to determine the influence of different process

parameters such as temperature, steam to carbon ratio, catalyst type, and reactor design on the

hydrogen production yield from bio-oil steam reforming. These studies address some of the

problems encountered in steam reforming bio-oil to produce hydrogen.

1.6.1 Hydrogen from Biomass

Simultaneous gasification and gas-cleanup, water gas shift, and pyrolysis followed by

steam reforming are two of the main pathways by which hydrogen is produced from biomass.

Gasification is a thermochemical process by which biomass is converted to a gaseous mixture via

partial oxidation at high temperatures. The produced gas consists of carbon monoxide, carbon

dioxide, hydrogen, methane, and a small amount of other hydrocarbons (Bridgwater, 2003).

Thermal decomposition and partial oxidation of biomass during gasification is performed by air,

oxygen, or steam. Depending on the weight of the biomass, the hydrogen production yield for air

or oxygen gasification and water gas shift after that is approximately 14%, for steam gasification

it is about 17%. The alternative method of producing hydrogen from biomass is steam reforming

of bio-oil. The main advantage of this approach compared to gasification is the improved

transportability of the bio-oil, which makes it possible to perform pyrolysis where biomass is

available and conduct catalytic steam reforming in a different location. Pyrolysis is performed at

20

lower temperatures with less expensive equipment so it requires lower capital costs than

gasification (Czernik et al., 2007).

Hydrogen is the lightest and one of the most abundant element on the surface of the earth.

It is extremely flammable. Unlike fossil fuels, that produce CO2 during their combustion, burning

hydrogen with pure oxygen produces heat and water. It has the highest energy content of any

known fuel at 120 MJ/kg. Bio-oil contains a large amount of hydrogen and can be used in hydrogen

production (Armaroli & Balzani, 2011).

In addition to being a clean energy resource, hydrogen has applications such as

hydrogenating vegetable oils in the food industry, petroleum refining, ammonia and methanol

synthesis in petrochemical industries, and deoxygenation of bio-oil into hydrocarbons suitable for

fuels and commodity chemicals (Bridgwater, 2003; Chornet and Czernik, 2008). Nowadays,

hydrogen is commercially generated from the steam reforming of natural gas. About 59% of the

global hydrogen production is from catalytic steam reforming of natural gas. In most parts of the

world, natural gas supplies are secure and inexpensive. However the conversion of natural gas to

hydrogen emits greenhouse gases into the atmosphere and the industry is under pressure to find

renewable hydrogen sources. The use of natural gas to produce hydrogen generates about 30

million tons of carbon dioxide each year (Bridgwater, 2003; Levin & Chahine, 2010). Electrolysis

of water using electricity from renewable sources like wind could be a future source of hydrogen,

but the most cost-effective source of renewable hydrogen is thermochemical production from

biomass. Generating hydrogen from biomass does not increase atmospheric carbon dioxide or

cause any other environmental problems. This process has a neutral carbon footprint is neutral

21

because no additional carbon is introduced. The carbon is cycled between biomass growth through

photosynthesis fixation and the application of biomass (Galdámez et al., 2005).

1.6.2 Steam Reforming of Biomass

Catalytic steam reforming is a well-known and well-studied technology that has been

available since 1930 and is currently used to produce hydrogen in industry. This fact makes it

attractive for hydrogen production from bio-oil. The complete steam reforming reaction is the

combination of steam reforming reaction which is endothermic and water-gas shift reaction which

is exothermic. These two reactions are reversible. The steam reforming of bio-oil considering its

molecule as CnHmOk is given below.

(Eq. 1.6)

The produced gas is called synthesis gas or syngas. The presence of excess steam in the system

results in a water-gas shift reaction. In this reaction carbon monoxide reacts with water and carbon

dioxide is produced.

(Eq. 1.7)

The overall reaction is presented in Eq. 1.8.

(Eq. 1.8)

The first step is favoured by high temperature because it is an endothermic reaction and

lower temperature is favoured the second as an exothermic reaction. Therefore, in many cases the

22

first step performs in a high temperature reactor and then the products are sent to a reactor with

lower temperature to accelerate the exothermic reaction (Rioche et al., 2005).

One of the common problems in steam reforming is the formation of carbon (coke) on the

surface of the catalyst and can result in deactivation of the catalyst. Coke formation is due to the

occurrence of unwanted reactions such as thermal decomposition (Eq. 1.9) and the Boudard

reaction (Eq. 1.10) at high temperatures. The formation of carbon deposits on the surface of

catalyst affects bio-oil reforming time and must be removed by frequent regeneration of the

catalyst (Rioche et al., 2005).

CnHmOk ↔ CxHyOz + gas (H2, CO, CO2, CH4…) + coke (Eq. 1.8)

2 CO ↔ CO2 + C (solid) (Eq. 1.9)

1.6.2.1 Thermodynamic Analysis

Thermodynamic analysis assists in predicting the composition of the products and the

effect of different parameters on H2 yield. Vagia and Lemonidou (2007) applied ASPEN plus 11.1

software to conduct a thermodynamic analysis of H2 production via steam reforming. They used

model bio-oil consisting of acetic acid, ethylene glycol, and acetone. The Peng–Robinson property

method and RGibbs reactor were selected to minimize the Gibb’s free energy. The effects of the

reactant and product composition in the feed, inlet temperature, pressure, reaction temperature,

and steam to fuel (S/F) ratio were studied. Their study showed that at atmospheric pressure H2

yield is favoured by increasing temperatures and S/C (steam to carbon ratio). They also concluded

that the concentration of oxygenated compounds in the produced stream are very low and can be

neglected. The optimum conditions were 627°C, atmospheric pressure, and S/C = 3 (steam to

23

carbon ratio). At these conditions, 0.208 kmol/s of the model compound mixture produced about

1 kmol/s of hydrogen. At temperatures higher than 327°C, no coke was formed (Vagia &

Lemonidou, 2007). The same research group performed a similar thermodynamic analysis with

the same model parameters and compound for H2 production by autothermal reforming. They

recovered 20% less H2 with autothermal reforming than steam reforming (Vagia & Lemonidou,

2008).

Aktas et al. (2009) performed a thermodynamic analysis over steam reforming of a model

bio-oil at high pressure. They used a mixture of isopropyl alcohol, lactic acid, and phenol as the

model bio-oil. Their analysis was performed at a pressure of 30 bar and temperatures from 327 °C

to 927 °C with a steam to fuel ratio of 4 to 9. The Gibb’s free energy minimization technique was

used to calculate the amount of each component (in mole) in the stream of produced material and

the composition of products at equilibrium. Sequential quadratic programming method is used to

solve the resulting optimization equations. Their analysis confirmed that H2 yield increased by

increasing temperature and steam to fuel ratio (Aktaş, et al., 2009).

1.6.2.2 Catalysts

Catalyst selection is one of the main concerns of steam reforming. Steam reforming of bio-

oils is usually performed in the presence of a catalyst to increase the reaction rate and achieve

equilibrium more quickly. Several catalysts have been applied in bio-oil steam reforming but

nickel based catalysts are the most common. Various combinations of noble metal catalysts and

support structures have been studied for their performance in bio-oil steam reforming. The

advantages of noble metals over Ni-based catalysts include higher activity per unit volume of metal

24

and better selectivity to hydrogen instead of coke formation when reforming whole crude bio-oil.

However, noble metal catalysts are more expensive.

Rioche et al. (2005) performed experiments using noble metal catalysts such as platinum,

Palladium, and Rhodium oxides promoted on two different types of supports, alumina (Al2O3) and

ceria-zirconia (CeZrO2) in the temperature range of 650-950 °C. Four different model bio-oil

including acetic acid, phenol, acetone, and ethanol were applied to test the effect of the metal

catalyst and support. Each compound represents an organic family found in bio-oil. The

stoichiometric hydrogen yield of the model bio-oils was highest for the combination of Rh-

CeZrO2.

The effect of the Pt and Rh catalysts was studied for steam reforming of a raw bio-oil. The CeZrO2

materials represented more influence on the reaction than the alumina samples (Rioche et al.,

2005).

Marda et al. (2009) reported a hydrogen yield of about 25 % for partial oxidation of whole

bio-oil at 625-850 °C in a non catalytic reaction (Marda et al., 2009). Czernik et al. (2007) applied

commercial catalysts C11-NK and NREL#20 in a bench-scale fluidized bed reactor for steam

reforming of raw bio-oil at 850°C. These catalysts were made by impregnation of alumina based

supports with Ni, K, Ca, and Mg. Using steam-carbon ratio of 5.8, the H2 yield was reported at 70-

80% (Czernik et al., 2007).

Galdámez et al. (2005) investigated the catalytic impact of a nickel-aluminium catalyst

with La in a fluidized bed over the temperature range of 450-700 °C and S/C of 5.58. The

experiments were conducted on a model compound which was acetic acid. The extent to which

25

amount La2O3 onto the Ni–Al catalyst affected hydrogen yield was studied. It was reported that

impregnation with La does not change the H2 yield with Ni-Al. The total gas yield reduced when

the weight of the catalyst decreased. The research team also carried out a non-catalytic steam

reforming reaction and reported that the H2 and CO2 yields were very low when a catalyst was not

used (Galdámez et al., 2005).

Kechagiopoulos et al. (2006) conducted experiments in a fixed bed reactor for the steam

reforming of bio-oil. By applying a commercial nickel catalyst, the effect of various parameters

including reaction temperature, steam-to-carbon ratio in the feed, and space velocity were studied

by them. The aqueous phase of a real bio-oil and a model compound (acetic acid, acetone, and

ethylene glycol) were considered. At higher temperatures of 600°C and steam to carbon ratios of

greater than 3, a 90% hydrogen yield was reported for the model compounds and a 60 % yield was

reported for the aqueous phase of bio-oil. Coking was the most serious problem encountered in the

experiment (Kechagiopoulos et al., 2006).

1.6.2.3 Experimental Conditions

To study process parameters and choosing catalysts for steam reforming of bio-oils, the

aqueous bio-oil fraction, whole bio-oil, and a model compound were considered. In the model

compound, acetic acid was used as the carboxylic acids, phenol as a model of the phenolics from

lignin, acetone as the carbonyl containing ketones and aldehydes, and ethanol as the model alcohol.

1.6.2.3.1 Selection of Reactor Type

The reactor type plays a very important role in steam reforming of bio-oil. Typical reactors

applied in steam reforming include fluidized bed, bench-scale, and fixed bed reactors. The

26

formation of carbonaceous deposits limits operation time making fixed reactors the least desirable

for steam reforming of bio-oils. On the contrary, continuous application of fluidized bed reactors

is made possible by the continuous gasification of carbonaceous deposits on the surface of the

catalyst (Czernik et al., 2007).

Basagiannis et al. (2007) reported that using a nozzle-fed reactor significantly decreases

carbon deposition. In this type of system, the liquid is injected into the reactor by using high flow

rate nozzles (Basagiannis & Verykios, 2007).

Gongxuan et al. (2010) used a “Y” type reactor for bio-oil steam reforming. The process

produces some CO2. The objective of this experiment was to enable a reaction between the

produced CO2 and biomass such that biomass gasification coupled with CO2 reforming of the

biomass decreases the CO2 emissions. These reaction systems were able to efficiently decrease

CO2 emissions produced by various reforming processes (Hu & Lu, 2010).

1.6.2.3.2 Temperature and S/C Ratio

Steam reforming of bio-oil is an endothermic reaction therefore increasing temperature

shifts the equilibrium towards the right and increases H2 yield. The steam to carbon ratio affects

H2 yield significantly as well. H2 production increases with increased temperature and S/C ratio

(Wang et al., 2007).

Yan et al. (2010) performed steam reforming of the bio-oil aqueous fraction in a fixed bed

reactor followed by CO2 capture using CaO and dolomite. At high temperatures and by capturing

CO2, H2 production decreased. They reported that the optimal temperature for H2 production with

CO2 capture is between 550 °C and 650 °C.

27

Kechagiopoulos et al. (2006) reported that H2 yield will by increasing S/C ratio and

decreasing pressure. They reported that the maximum hydrogen yield for their experimental

conditions was between 600°C and 750°C (Kechagiopoulos et al., 2006).

1.7 Objective of this study

The objective of this study was to upgrade a real and commercial crude bio-oil. Two methods

were applied for this purpose, esterification and steam reforming.

Four catalysts were prepared on an alumina support and applied for steam reforming and two for

esterification.

In the first part of this study, Ni-MgO/Al2O3 catalysts are applied for steam reforming of

the aqueous phase of a crude bio-oil using three aqueous phase samples with various water

content. The influence of adjusting the pH during catalyst preparation on hydrogen yield is

also studied.

The purpose of second part was upgrading the bio-oil to a potential fuel by an esterification

reaction to increase the raw bio-oil HHV, lower the acidity and viscosity, and improve its

stability. This study identified the best esterification reaction time, temperature, alcohol,

and catalysts. A sub-objective was to perform the esterification with minimal alcohol and

catalyst to reduce process costs.

1.8 Outline of this thesis

This thesis consists of four chapters in addition of a table of contents, a list of figures, and

a list of tables. Chapter 1 includes introduction, the background of this research and scope of the

work.

28

Chapter 2 presents the experiments conducted to produce hydrogen from catalytic steam

reforming of bio-oil. It introduces the catalysts and the reactor applied. In this chapter the

experimental procedure for and the effect of various factors on hydrogen production are studied

and discussed.

Chapter 3 details the experimental work on esterification of bio-oil and explains the

developing of an evaluation method to measure esterification degree. In this chapter effect of

changing various factor on esterification extent were investigated and discussed.

Chapter 4 discusses the conclusion and recommends future work which would build upon

this study.

29

Chapter Two: Steam Reforming Experimental

Production of hydrogen by catalytic steam reforming of hydrocarbon fuels, especially

natural gas is a well-known and conventional technology. This well-established technology

converts hydrocarbon fuel into a mixture of carbon monoxide, carbon dioxide, and hydrogen. The

reaction occurs at temperatures around 800°C in the presence of steam and a catalyst (e.g. Ni-

based). Unfortunately, the process generates carbon dioxide, a well-known greenhouse gas, and

contributes to the depletion of fossil fuels. These issues make alternative sources such as biomass

feedstock very desirable.

Nickel-based catalysts supported on alumina and promoted by magnesia (Ni-MgO/Al2O3)

were tested for steam reforming of bio-oil. In this study, Ni-MgO/Al2O3 catalysts are applied for

steam reforming of aqueous phase bio-oil using three aqueous phase samples with various water

contents. The effect of adjusting the pH during catalyst synthesizing on hydrogen yield is also

reported.

2.1 Catalyst

Three Ni-MgO/Al2O3 catalysts were synthesized to study the influence of catalyst

preparation and nickel content on the product yield in steam reformation of bio-oil. Nickel is a

common catalyst used in steam reforming processes. Previous investigations by our research group

have demonstrated the preparation and characterization of the catalysts (Salehi et al., 2011;

Seyedeyn-azad et al., 2014).

30

Ni/Al2O3 was promoted with magnesium to improve its efficiency. The acidic properties of

alumina can catalyze reactions producing coke. Magnesium modified catalysts increase hydrogen

production by neutralizing acid sites on the support and controlling the rate of coking.

In this study, alumina and three Ni-MgO/Al2O3 catalysts with different nickel ratios are used

to investigate the effect of catalyst preparation and nickel content on product yields in the steam

reforming of aqueous phase bio-oil. The order of MgO and Ni impregnation was selected based

on experiments by Cheng et al. They demonstrated that impregnating MgO before nickel resulted

in a noticeable increase in syngas generation compared to when magnesia was promoted onto the

nickel/alumina (Cheng, Wu, Li, & Zhu, 1996). Ni-MgO/Al2O3 synthesis is a two-step procedure.

In the first step, pretreated alumina was impregnated with MgO and in the second step, Ni was

impregnated. Ni-MgO/Al2O3-1 and Ni-MgO/Al2O3-2 catalysts were synthesized in different ways

but with the same amount of MgO (12.8%) and Ni (18%). The Ni-MgO/Al2O3-2 and Ni-

MgO/Al2O3-3 catalysts were prepared using exactly the same procedure, but with different Ni

contents (18 and 33.3%, respectively).

A nitrogen physisorption test was performed at 77 K to obtain the textural properties using

a Micromeritics Tristar II 3020 instrument. Brunauer−Emmet−Teller (BET) surface area, pore

volume, and the average pore size of the catalysts were determined. The most efficient reduction

conditions were found by applying the temperature-programmed-reduction (TPR) technique using

a Quantachrome CHEMBET 3000 instrument.

2.2 Aqueous Phase Preparation and Characteristics

A commercial bio-oil was obtained from Biomass Technology Group (BTG) in the

Netherlands. In order to prepare the aqueous fraction, bio-oil and distilled water were mixed in

31

weight ratios of 1:2, 1:1, and 2:1. The mixtures were centrifuged in a Fisher Scientific Marathon

2100 centrifuge for 2 hours at 4500 rpm to form two separate phases. The upper phase is the

aqueous-rich water-soluble fraction of bio-oil (WSBO) and the lower phase is an organic-rich

phase comprised of the water-insoluble fraction of bio-oil (WIFB). The upper phase was decanted

into a different container.

The bio-oil and the aqueous phases were elementally analyzed using a PerkinElmer Model

2400 CHN analyzer. AQ-1, AQ-2, and AQ-3 stand for the aqueous phases of bio-oil obtained from

the 1:2, 1:1, and 2:1 weight ratios of bio-oil to water, respectively. The bio-oil and the aqueous

phase samples were dominantly composed of carbon (C), hydrogen (H), and oxygen (O).

The water content of the bio-oil was measured by the Karl Fischer titration method using a

Mettler Toledo DL32 colorimetric titrator. An Oakton Instruments pH meter was used to measure

the pH of the solutions and the bio-oil. The pH meter was calibrated using buffer solutions at pH

7 and 10. The density of the bio-oil was evaluated with a density measurement bottle and the higher

heating value (HHV) of the bio-oil was meseared using a bomb calorimeter (Parr Model 1266).

The pH, density, and HHV of the bio-oil were 2.10, 1225 kg/m3, and 17.5 MJ/kg, respectively.

2.3 Fixed-bed Steam Reforming Apparatus

The experimental setup used in this research included a fixed bed tubular reactor, a tubular

furnace, a syringe pump, two mass flow controllers, and a micro GC. The setup is illustrated in

figure 2.1 and a process flow diagram of the plant is shown in figure 2.2.

32

Figure 2.1 Catalytic steam reforming plant

The reactor is the most significant part of a steam reforming plant. The tubular reactor in this

study was constructed from stainless steel with an internal diameter of 1 cm and a height of 43 cm.

A cross-shaped stand was welded in the middle of the reactor to prevent the catalyst from moving

down. The stand plays the role of catalyst bed with a thin layer of glass wool. The reactor is located

inside a tubular furnace (Thermolyne, Model F21135) to provide heat for the system. The

temperature of the catalyst bed and the condenser is monitored by two thermocouples (K-type).

The temperature and gas flow rate were controlled and monitored with LabVIEW software

(version 8.5) and the data from each run was saved in a separate data file. The system is equipped

Condenser

Water-glycol

circulatorCircu

lator

Tubular

furnaceF

urnace

33

with two mass flow controllers (MKS, Model M100B) to measure the flow rates of nitrogen

(carrier gas) and hydrogen (reducing gas) to the reactor.

Figure 2.2 Process flow diagram of the steam reforming plant of bio-oil aqueous phase:

(1) gas flow controllers (2) syringe pump (3) metal condenser (4) tubular furnace (5) tubular

reactor (6) glass condenser (7) water collector (8) water-glycol circulator

The aqueous phase of bio-oil is fed to the reactor by a high-pressure syringe pump (ISCO,

Model 500D). At temperatures higher than 80°C, polymerization reactions occur in the bio-oil. In

order to prevent these unwanted reactions, the feed is injected into the reactor through a capillary

tube surrounded by a cooling jacket. The coolant is provided by a water-glycol circulator (VWR,

Model 1150S). A condenser is applied to recover the excess steam. To analyse the effluent gas

from the reactor the produced gases are fed to an online micro gas chromatograph (GC, Varian

Micro GC, Model CP-4900) equipped with a TCD (thermal conductivity detector).

NitrogenCylinder

F1 F1

HydrogenCylinder

3

6

7

8

GC

Fume Hood

2

5

4 4

34

The GC was calibrated with five calibration gas mixtures, H2, N2, methane (CH4), carbon

monoxide (CO), carbon dioxide (CO2), ethane (C2H6), propane (C3H8), and butane (C4H10). The

types and the concentrations of the calibration gas mixtures are shown in Table 2.1. Gas mixtures

1 and 2 were provided by Paxair Inc. in Calgary. Figure 2.3 shows the GC instrument applied in

this study.

Figure 2.3 Micro Gas Chromatograph

35

Table 2.1 Specifications of the Gases Used for GC Calibration

Gas

Mixture

H2

(%) N2 (%)

CH4

(%) CO (%)

CO2

(%) C2H6 (%) C3H8 (%)

C4H10

(%)

1 0.02 85.00 0.974 2.53 7.54 1.00 0.976 0.967

2 15.00 72.50 0.501 7.00 3.00 0.50 0.499 0.499

3 10.00 90.00 − − − − − −

4 20.00 80.00 − − − − − −

5 50.00 50.00 − − − − − −

2.4 Procedure

Each run of the experiment used 200 mg of catalyst. First, a thin layer of glass wool was

placed on the cross-shaped stand. After ensuring that the stand is thoroughly covered with glass

wool, catalyst was loaded into the reactor. The catalyst should be reduced by hydrogen before

running the steam reforming experiments. Considering the TPR results, the reduction step was

performed in situ at 850°C for 2 hours by applying a mixture of hydrogen and nitrogen. Following

the reduction, the catalyst was flushed with nitrogen gas at 850°C for an additional 1 hour. The

aqueous phase was injected into the reactor at a flow rate of 0.1 mL/min (weight hourly space

velocity (WHSV) = 30 1/h). During the experiment, samples were sent to the GC for analysis.

After each run, the reactor was purged with nitrogen until it reached room temperature.

2.5 Data Analysis

Referring to Eq. 1.8 in chapter 1, for the case of bio-oil (CH1.87O0.75), the stoichiometry for the

overall steam reforming reaction is written as follows.

𝑪𝑯𝟏.𝟖𝟕𝑶𝟎.𝟕𝟓 + 𝟏. 𝟐𝟓 𝑯𝟐𝐎 ↔ 𝐂𝑶𝟐 + 𝟐. 𝟏𝟖𝑯𝟐 ( Eq. 2-1)

36

According to this reaction, the maximum stoichiometric hydrogen yield for bio-oil steam

reforming is 16.67 wt %. In actual conditions, side reactions such as the thermal decomposition of

bio-oil (Eq. 1.9), the methanation reaction, and the Boudouard reaction (Eq. 1-10) result in

hydrogen yields lower than the stoichiometric maximum.

Hydrogen yield is defined as the ratio of the number of moles of produced hydrogen to the

stoichiometry amount of hydrogen that could be produced by the complete reforming of bio-oil to

CO2 and H2. It can be calculated using Eq. 2-2. As shown in Eq. 2-1, the generated hydrogen

originates from both steam and bio-oil.

𝐻2 𝑦𝑖𝑒𝑙𝑑 =𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 ℎ𝑦𝑑𝑟𝑜𝑔𝑒𝑛 𝑝𝑟𝑜𝑑𝑢𝑐𝑒𝑑

2.18 ∗ 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑖𝑛𝑙𝑒𝑡 𝑐𝑎𝑟𝑏𝑜𝑛/𝑛∗ 100

(Eq. 2-2)

Calculating the yield of production of other gases (CH4, CO, and CO2) can be defined in

the same way as hydrogen yield, i.e. the number of moles of the gas obtained per mole of carbon

fed into the system (Eq. 2-3).

𝑂𝑡ℎ𝑒𝑟 𝑔𝑎𝑠𝑒𝑠 𝑦𝑖𝑒𝑙𝑑 =𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑔𝑎𝑠 𝑝𝑟𝑜𝑑𝑢𝑐𝑒𝑑

𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑖𝑛𝑙𝑒𝑡 𝑐𝑎𝑟𝑏𝑜𝑛∗ 100

(Eq. 2-3)

It is possible to calculate the carbon conversion by dividing the sum of the carbon moles

in the generated gases by the carbon moles of the bio-oil (Eq. 2-4) or simply adding the yields of

the generated gases. The conversion cannot be 100% because a portion of the carbon in the

products cannot be detected by the micro GC and because of the formation of coke which was

deposited on the catalyst.

𝐶𝑎𝑟𝑏𝑜𝑛 𝐶𝑜𝑛𝑣𝑒𝑟𝑠𝑖𝑜𝑛 =𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑐𝑎𝑟𝑏𝑜𝑛 𝑖𝑛 𝑔𝑎𝑠 𝑝𝑟𝑜𝑑𝑢𝑐𝑡

𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑐𝑎𝑟𝑏𝑜𝑛 𝑓𝑒𝑑∗ 100

(Eq. 2-4)

37

Nitrogen was applied as a carrier gas and its inlet flow rate was used to calculate the number of

moles of various products formed per unit of time using their molar proportions with respect to

those of N2.

The steam to carbon ratio in the feed is defined in Eq. 2-5.

𝑊

𝐶=𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑖𝑛 𝑓𝑒𝑒𝑑

𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑐𝑎𝑟𝑏𝑜𝑛 𝑖𝑛 𝑓𝑒𝑑

(Eq. 2-5)

The weight hourly space velocity (WHSV) was determined by:

𝑊𝐻𝑆𝑉 =𝑚𝑎𝑠𝑠 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 𝑜𝑓 𝑎𝑞𝑢𝑒𝑜𝑢𝑠 𝑝ℎ𝑎𝑠𝑒

𝑚𝑎𝑠𝑠 𝑜𝑓 𝑐𝑎𝑡𝑎𝑙𝑦𝑠𝑡

(Eq. 2-6)

38

2.6 Results and Discussion

The textural properties of the catalysts including BET surface area, pore volume, average

pore size, and the amounts of Ni and MgO are shown in Table 2.2. The Ni-MgO/Al2O3 catalysts

produced similar TPR profiles (Salehi et al., 2011). One reduction peak was observed at 875°C for

the first two catalysts. This phenomenon might be explained by the strong interactions of MgO

and/or Al2O3 with NiOx species resulting in NiOx reduction. Increasing the amount of Ni in the

catalyst moved this peak to lower temperatures. The thermal stability of γ-Al2O3 increased with

the addition of MgO, which could be due to the formation of Mg-Al2O4 spinel and the inhibition

of Ni-Al2O4 spinel formation (Guo et al., 2005).

Table 2.2 Characteristics and composition of the catalysts

catalyst composition

BET surf. area pore vol av pore

catalyst MgO (%) Ni (%) (m2/g) (cm3/g) size (Å)

Al2O3 0 0 255.00 1.14 −

Ni-MgO/Al2O3-1 12.8 18.0 156.30 0.65 125.55

Ni-MgO/Al2O3-2 12.8 18.0 107.36 0.34 96.91

Ni-MgO/Al2O3-3 12.8 33.3 151.63 0.60 114.79

Table 2.3 shows the results of the elemental analysis, the bio-oil to water ratio (B/W), and

the average chemical formula of the oxygenated organic compounds in the bio-oil and aqueous

phase samples. The compositions of the aqueous phases are different from those of the bio-oil

because they contain C, H, and O in different ratios and have different average molecular formulas

(Table 2.3). The impurities present in the bio-oil included nitrogen, sulfur, and traces of metals,

such as potassium, magnesium, and calcium. With the exception of nitrogen, the impurities were

39

not analyzed. As shown in Table 2.3, the water content values for AQ-1, AQ-2, and AQ-3 were

4.14, 3.77, and 3.19, respectively.

Table 2.3 Elemental Analysis and Characteristics of Commercial (BTG) Bio-Oil and the three

Aqueous Phases with Various Bio-Oil/Water Ratios

Elemental Analysis (wt%)

sample name B/W weight ratio water content (wt %) carbon hydrogen nitrogen oxygena formula including water formula

bio-oil − 22.22 45.83 7.15 0.87 46.15 CH1.87O0.75 CH1.23O0.43, 1.23H2O

AQ-1 1:2 74.53 8.83 10.36 0.25 80.56 CH14.08O6.84 CH2.83O1.22, 4.14H2O

AQ-2 1:1 67.94 13.37 9.16 0.11 77.36 CH8.22O4.34 CH1.45O0.95, 3.77H2O

AQ-3 aBy difference.

2:1 57.38 19.24 9.62 0.30 70.84 CH6O2.76 CH2.02O0.77, 3.19H2O

Figures 2.4, 2.5, and 2.6 show the yields of hydrogen, the main effluent carbon-containing

gases including carbon monoxide, carbon dioxide, methane, and other hydrocarbon gases (CHn).

According to the graphs in figure 2.4, the H2 yield from AQ-1 (oil/water ratio = 1/2) was

very low (about 11%) over Al2O3 but increased slightly when Ni-MgO/ Al2O3-1 and Ni-

MgO/Al2O3-2 catalysts with 18% Ni were employed. This figure illustrates that the preparation

method had no significant on the H2 yield or the conversion of bio-oil to carbon-based gases.

Employing Ni-MgO/Al2O3- 3 with a Ni content of 33.3% increased the hydrogen yield by almost

20%, proving that increasing Ni content is more effective for increasing H2 production.

Increasing the Ni content decreased CO and enhanced CO2 yields (figure 2.4).

40

Figure 2.4 Steam reforming of aqueous phase of bio-oil (oil/water ratio = 1/2) over (a) Al2O3, (b)

Ni-MgO/Al2O3-1, (c) Ni-MgO/Al2O3-2, and (d) Ni-MgO/Al2O3-3 catalysts. Operational

conditions: nitrogen flow rate = 200 STP mL/min; bio-oil aqueous phase feed rate = 0.1 mL/min.

41


(b) Ni-MgO/Al2O3-1, (c) Ni-MgO/Al2O3-2, and (d) Ni-MgO/Al2O3-3 catalysts. Operational

conditions: nitrogen flow rate = 200 STP mL/min; bio-oil aqueous phase feed rate = 0.1 mL/min

42

Figure 2.6 Steam reforming of aqueous phase of bio-oil (oil/water ratio = 2/1) over (a) Al2O3, (b)

Ni-MgO/Al2O3-1, (c) Ni-MgO/Al2O3-2, and (d) Ni-MgO/Al2O3-3 catalysts. Operational

conditions: nitrogen flow rate = 200 STP mL/min; bio-oil aqueous phase feed rate = 0.1 mL/min

43

According to figure 2.5, the H2 yield for the AQ-2 aqueous phase (oil/water ratio = 1/1),

was about 25% (excluding the first three points) over Al2O3 support. This yield increased

dramatically for the impregnated catalysts to nearly 50, 40, and 60% when the Ni- MgO/Al2O3-1, Ni-

MgO/Al2O3-2, and Ni-MgO/Al2O3-3 were employed, respectively. The graphs also illustrate that

pH adjustment has an adverse effect on H2 yield decreasing it by 10%. However, increasing the Ni

content from 18 to 33.3% considerably improved the hydrogen yield. Increasing the Ni content

decreased CO and enhanced CO2 yields.

As shown in figure 2.6, using Al2O3 support in the steam reforming of the AQ-3 aqueous

phase (oil/water ratio=2/1), resulted in an H2 yield of almost 22%. The yield increased considerably

when Ni-MgO/Al2O3-1 was applied. Hydrogen yield was 40% at the beginning of the experiment

but decreased to about 20% after 48 min. The average H2 yield over time was 30%. It was also

observed that the H2 yield increased to about 40% and 47% when Ni-MgO/Al2O3-2 and Ni-

MgO/Al2O3-3 were employed, respectively. This result demonstrates that both the addition of Ni

and the adjustment of pH effectively increased the H2 yield when the bio-oil aqueous phase with

greater bio-oil to water ratio was applied. Figure 2.6 also reveals that the average yield of CO2 was

the highest when Ni-MgO/Al2O3-3 was used. These results indicate that larger amounts of nickel

may encourage the water gas shift (WGS) reaction.

To determine the effect of the addition of acid on catalyst activity, both figure 2.4 and

figure 2.5 should be used to compare the H2 yields obtained with the first and second samples of

the Ni- MgO/Al2O3 series. Although the addition of acid in the second step of preparation

decreased the activity of the catalysts in the beginning of the experiment, similar yields were

44

obtained for both catalysts over time. It can be concluded that the addition of acid in the second

preparation step has no effect on the activity of the catalysts for AQ-1 and AQ-2.

Figure 2.6 illustrates that the preparation procedure also effected the activity of the

catalysts in the aqueous phase with a 2/1 bio-oil/water ratio. The addition of acid in both of the

preparation steps resulted in a stable H2 yield.

The figures show that the reactor effluent gas concentrations varied over time. The flow

rate of the aqueous phase of bio-oil was very low and the injection of the feed over the catalysts

could be in the form of droplets. Therefore, the component yields sometimes fluctuated over time

during the experiments. The same phenomena was reported in previous experiments on bio-oil by

our group. Fluctuations in the concentration of the outlet gas were observed due to the addition of

bio-oil in the form of droplets (Salehi et al., 2011). Other researchers also reported this

phenomenon (Czernik et al., 2007). In figures 2.5 and 2.6, although the yields of the outlet gases

fluctuated and did not reach a steady state condition, the trend of the yields was decreasing over

time. This decrease indicates that the activity of the catalysts decreased with time.

Figure 2.7 depicts the average yields of the gases in the reactor effluent stream over a period

of 1 hour. The maximum average hydrogen yield was 61.2%, which was achieved by applying the

Ni- MgO/Al2O3-3 catalyst, while a 29.3% H2 yield was achieved over the support under the same

operational conditions. Figure 2.7 indicates that Ni-MgO/Al2O3-3 was the most effective catalyst

and the activity of the catalyst was always improved by increasing the nickel content. Comparing

the results obtained by the three bio-oil aqueous phase samples indicated that the highest H2 yield

was obtained with a bio-oil to water ratio of 1/1. Although water provides H2, increasing the

45

amount of water also results in an occupation of the active sites of the catalysts by the water

molecules (Yan et al., 2010).

Figure 2.7 Comparison among the results obtained for steam reforming of aqueous phase of bio-

oil with various bio-oil to water ratios over Al2O3, Ni-MgO/Al2O3-1, Ni-MgO/Al2O3-2, and Ni-

MgO/Al2O3-3 catalysts. Operational conditions: nitrogen flow rate = 200 STP mL/min; bio-oil

aqueous phase feed rate = 0.1 mL/min; temperature = 850°C.

Increasing the H2 yield means more carbon conversion. The carbon conversion is relatively

high over the catalysts and even over the alumina when the aqueous phases of bio-oil AQ-2 and

AQ-3 were employed. However, the amount of CH4 decreased when the aqueous phase with the

46

ratio of 2/1 was used. The results also showed that yields of CO and CO2 increase with increasing

Ni content. We believe that the shift reaction rate increased when the Ni content increased. In

conclusion, considering both hydrogen production and carbon conversion, the best catalytic

activity was found over Ni-MgO/Al2O3-3.

In a previous study on the steam reforming of bio-oil, the catalysts turned black because of

the deposition of a soot like substance. In this study, the catalysts were light to dark gray after being

used in steam reforming of the aqueous phase of bio-oil. Iojoiu et al. (2007) reported that the

thermal decomposition of bio-oil (Eq. 1.8) at 700°C was due to the thermal instability of the bio-

oil components (Iojoiu, Domine, Davidian, Guilhaume, & Mirodatos, 2007). They showed that

thermal cracking of the molecules in the bio-oil into smaller gas molecules and coke before

reaching the catalyst bed resulted in carbon deposition on the catalyst.

Coke formation resulted in blockage of the reactor in the steam reforming of the aqueous

phase of bio-oil, but the catalyst colours were lighter than those previously employed because

thermal decomposition occurred in the precatalyst zone of the catalyst bed. This phenomenon was

more pronounced when the AQ-1 aqueous bio-oil sample was applied. In this case, the blockage

of the reactor was more severe and the catalyst was lighter in colour (even bluish) than those used

for the AQ-2 and AQ-3 aqueous phase samples.

Kechagiopoulos et al. (2006) addressed that thermal decomposition leads to lower

hydrogen yield, catalyst deactivation, and blockage of the reactor (Kechagiopoulos et al., 2006).

They also reported that increasing pressure decreases the hydrogen yield. Higher W/C favours

higher hydrogen yield. However, in his study the hydrogen yield was lower over the same catalyst

and under the same conditions for the AQ-1 sample than for AQ-2 and AQ-3 bio-oil samples with

47

lower W/C ratios. This is likely due to higher pressures resulting from the blockage of the reactor

when the AQ-1 sample is used.

Ortiz-Toral (2008) conducted catalytic steam reforming experiments using model

compounds of acetic acid and methanol. He observed severe thermal decomposition of the acetic

acid over the hot reactor walls. Ortiz-Toral also reported that no carbon deposition was observed

when a more stable model compound such as methanol was employed (Ortiz-toral, Pedro, 2008).

It can be concluded that the blockage of the reactor resulted in lower hydrogen yield for AQ-1 due

to the composition of AQ-1, which was different from that of AQ-2 and AQ-3. Coke deposition

on the catalyst is a major drawback to the process of catalytic steam reforming of bio-oil and its

derivatives because it decreases hydrogen yield and results in reactor blockage and catalyst

deactivation.

Thermal decomposition is one reason for the lower hydrogen yield with the AQ-1 aqueous

sample. Another reason is the effect of active site saturation by water molecules. Although W/C

variations in the three samples did not seem large enough to justify such pronounced saturation

effects, a quick saturation of the active sites could occur as a result of insufficient available

oxygenated compounds in AQ-1, as the flow rate was very low.

Comparing figures 2.5 and 2.6 revealed that the addition of acid during the preparation of

the catalyst increased the activity of the catalyst when the water content decreased. Table 2.4

provides the CO/CO2 and H2/CO molar ratios. Comparing the results obtained by steam

reforming various aqueous bio-oil samples over various catalysts shows that the impregnation of

alumina with nickel and magnesia was favoured over the gas shift reaction. The addition of acid

48

during catalyst preparation reduced the extent of the gas shift reaction, whereas the addition of

nickel promoted the gas shift reaction.

Table 2.4 CO/CO2 and H2/CO molar ratios obtained by steam reforming of various aqueous bio-

oil samples over various catalysts

Al2O3 Ni-MgO/Al2O3-1 Ni-MgO/Al2O3-2 Ni-MgO/Al2O3-3

sample name W/C CO/CO2 H2/CO CO/CO2 H2/CO CO/CO2 H2/CO CO/CO2 H2/CO

AQ-1 4.14 1.63 2.02 1.02 2.86 1.12 2.57 0.44 6.36

AQ-2 3.77 2.26 1.62 1.25 2.81 1.38 2.46 1.03 2.98

AQ-3 3.18 2.31 1.25 0.94 3.18 1.46 2.34 1.03 3.16

49

Chapter Three: Catalytic Esterification

3.1 Introduction

Overcoming several obstacles is necessary for bio-oil to be a reliable fuel. These obstacles

and their recommended upgrading procedures were discussed in detail in the previous chapters.

The corrosiveness of bio-oil due to high concentrations of organic acids is one of the primary

issues limiting its direct application as a liquid fuel.

This chapter expresses the catalytic esterification of bio-oil experiments in the presence of

an acid catalyst using various alcohols. During an esterification reaction, carboxylic acids in the

bio-oil such as formic and acetic acid are converted into combustible and stable esters in order to

simplify the subsequent upgrading. In addition, the process of esterification converts highly

reactive aldehydes into their relative acetals. These aldehydes are the reasons for the

polymerization and condensation of bio-oil.

This chapter introduces the chemicals and instruments used in bio-oil esterification and

examines the effect of reaction conditions including temperature, carbon chain length of the

alcohols, and reaction time. Finally, the results of experiments are provided and discussed.

3.2 Materials and Chemicals

Several chemicals were used in this research. They are listed in Table (3.1). The bio-oil was

obtained from Biomass Technology Group (BTG) in The Netherlands. The ion exchange resin

Amberlyst-15 was commercially available and used as the catalyst for the esterification of bio-oil.

50

Table 3.1 Chemicals used in bio-oil esterification experiments

Chemical Manufacturer

Sodium Hydroxide EMD

Sulfuric Acid (95 %) BDH

Methanol EMD

Ethanol BDH

Butanol (n-Butyl Alcohol) Fisher Scientific Company

tert-Butyl Alcohol, 99% Alfa Aesar

Acetone BDH

Tetramethylammonium Hydroxide Solution (25 wt. % in H2O) Sigma-Aldrich

Amberlyst 15 (H), ion exchange resin Alfa Aesar

Buffer Solutions with pH=4 & 7 EMD

3.3 Apparatus and Equipment

The equipment used in this research is as follows.

Glassware such as beakers, pipettes, and Erlenmeyer Flasks

Sample vials with screw cap

Hotplate/stirrer with thermometer

Magnet stirring bars

Refrigerated circulating bath

Digital balance

3-neck flask

51

758 KFD Titrino-Metrohm

Digital pH meter

3.4 Experimental Procedure

A simplified process flow diagram of the esterification plant is shown in Figure 3.1. The

system consists of two main parts, the esterification unit and the titration and recording unit.

3.4.1 Esterification Reaction

This study investigated the possiblility of upgrading crude bio-oil via an esterification

reaction. The experimental reactions were performed in a 250 ml three-neck round bottom flask

applied as the reactor. The reactor was equipped with a thermometer, a magnetic stirrer bar, and a

reflux condenser and placed in a thermostatic water bath. A water-glycol refrigerated circulator

was connected to the condenser and used as the coolant. The crude bio-oil and selected alcohol

were added to the reactor according to the required volume ratio and mixed slightly. Next, the

catalyst was loaded on the weight percent of bio-oil. This procedure is carried out at room

LabVIEW

Titration

PC

Figure 3.1 Process flow diagram of esterification and esterification degree detection

52

temperature. All reactions were performed at a stirring rate of 350 rpm because there would be no

mass transfer limitations at higher stirring rates (Hu et al., 2012).

3.4.1.1 Catalyst Type

The effects of two different catalysts were investigated. Sulfuric acid was the homogenous

catalyst and Amberlyst-15 was the heterogeneous catalyst. Needless to say, the heterogeneous

catalyst has the advantage of recovery and recycling. H2SO4 is considered the best catalyst for the

esterification reaction in biodiesel production (Aranda et al., 2008; Marchetti & Errazu, 2008).

The Amberlyst-15 is in bead form and is a cation-exchange resin with sulfonic acid

functionality. It is strongly acidic and a macroreticular polymer consisting of crosslinked

copolymers of styrene divinylbenzene. It can be applied as a heterogeneous catalyst in both

aqueous and non-aqueous media. The advantages of Amberlyst-15 include optimal balance of

surface area, optimized pore size distribution, nontoxic, reusability, acid capacity, non-corrosive,

chemical and physical stability, and environmental compatibility. These unique properties make

Figure 3.2 Amberlyst- 15 beads

53

Amberlyst-15 a good choice for hydration, etherification, esterification reactions (Fan et al., 2014;

Kadam et al., 2009).

3.4.1.2 Alcohol Type

Three different alcohols, methanol, ethanol, and normal butanol were used to understand

the influence of alcohol carbon chain variety on esterification progress. All of the reactions were

conducted at 50ºC and at a volumetric crude bio-oil to alcohol ratio of 1:2. The catalyst was added

to the mixture by 5 wt.% of bio-oil. The upgrading reaction continued for 3 hours.

3.4.1.3 Reaction Temperature

Experiments were carried out at three different temperatures to study the effect of

temperature on reaction conversion. The experiments were performed for 3 hr at a volumetric bio-

oil to alcohol ratio of 1:2, using a catalyst with 5 wt.% of bio-oil at 20ºC, 50ºC and 60ºC.

3.4.1.4 Reaction Time

The esterification reaction conversion was measured at 1, 3, 5, 8 and 12 hours. The

reactions were carried out at 50ºC and the reactant and catalyst amounts were as above.

3.4.1.5 Alcohol Amount

Three different ratios of ethanol were applied to determine the effect of the amount of

alcohol on the esterification degree. The volumetric ratios of bio-oil to alcohol were 1:1, 1:2, and

1:3. All three reactions were performed at 50ºC and the amount of catalyst was 5 wt.% of the bio-

oil.

54

3.4.1.6 Catalyst Amount

Four experiments were carried out at 50ºC with ethanol and four amounts of Amberlyst-

15. Bio-oil at 5, 10, 15, 20 wt.% was mixed with ethanol at a 1:2 ratio. The reaction was stopped

at 3 hr and the reaction conversion was measured.

3.4.2 Titration and Recording

A TAN test (total acid number) was chosen to determine the extent of the esterification

reaction in terms of reaction conversion. It is worth mentioning that the TAN and pH are different

aspects. The pH indicates apparent acidity but a TAN test measures the concentration of the acids

in the solution. The technique used for a TAN test is called titration. Titration is a volumetric and

quantitative analysis wherein an acid or base with unknown concentration is gradually neutralized

by another base or acid with known concentration.

As bio-oil is a dark fluid, visual indicators cannot be used to detect the end point of the

titration. A potentiometric titration technique was applied to determine the total organic acid

number in the bio-oil and evaluate the degree to which the bio-oil was upgraded through the

esterification reaction. In potentiometric titration, the potential is measured after adding a specific

titrant volume by an electrode. This type of titration can be performed by an automatic titrator or

simple pH meter.

The most challenging part of this investigation was finding suitable methods of titration

and recording to measure the extent of esterification. At the beginning, manual titration was

conducted using a simple pH meter and a burette (Figure 3.2). The titrant was poured into the

burette and the sample into the beaker. Drops of the titrant were added gradually and the mixture

was stirred. Eventually, the mixture reached equilibrium and no further changes in pH, detected

55

pH, or potential were observed (there is a theoretical relation between pH and mV). At this point,

the titration curve was draw with either pH or potential versus volume added.

Figure 3.3 Manual titration set up

This study followed ASTM D664, a common potentiometric titration method of measuring

TAN in petroleum products, lubricants, biodiesel, and blends of biodiesel. Potassium hydroxide

solution is employed as the titrant and isopropyl alcohol as the solvent. We tested KOH with two

concentrations (0.1 N and 0.5 N) in ethanol and water. The results confirm that this standard is not

valid for bio-oil (results and discussion section). Therefore, we conducted several trials with

modifications to the ASTM D664 method. The first modification was the replacement of KOH

with a sodium hydroxide solution in water as the titrant. In addition, toluene was replaced by a

56

mixture of acetone and butanol and the concentration of NaOH was tested. Finally,

tetramethylammonium hydroxide solution (TMAH) was used as a titrant.

An existing Metrohm 758 Titrino (Figure 3.4) and its pH titration template were modified

and used to carry out the titration automatically. This old equipment was actually designed to

report the endpoint of Karl-Fisher titrations and is not compatible with the programs of new

Metrohm Company titrators. However, in the case of the TAN test, all of the point along the

titration curve are required. LabVIEW software (Version 8.6) was employed to make Metrohm

758 usable in this investigation. LabVIEW is a visual programming language for instrument

control, automation, and data gathering, which was employed to connect the titrator to a PC such

that the existing pH template could be used.

Prior to beginning the titration, a solvent composed of butanol and acetone was prepared

at a 9:1 ratio to dilute the samples. In each titration run, 2 ml of sample was added to 18 ml of

solvent in a 100 ml beaker. The beaker was placed on a small plus-shaped magnetic stirrer to stir

the mixture during the TAN measurement.

57

After each titration run, an excel sheet was saved in the PC by LabVIEW. This spreadsheet

contains the volume added in ml, the pH, and the corresponding potential in mV. The end point

was defined manually at pH=12 and 13.7 for the instrument. Meaning that the instrument will

continue to add titrant until the pH of the solution reaches 12 (13.7 in some cases). The maximum

and minimum rates of volume addition were set at 5 ml/min and 25 µl/min, respectively. The

electrodes were calibrated by buffers at pH 4 and pH 7.

Figure 3.4 KFD 758 Titrino

58

3.5 Analyzing Method

A titration graph can be drawn using the pH or potential recorded data versus the volumetric

amount of added titrant from either manual or automatic titration. A sample datasheet and titration

graph for acetic acid with 0.1 N sodium hydroxide solution is provided in Table 3.2 and Figure

3.3. At the beginning of the titration, the pH did not change much with volume added. However,

approaching the end point, the pH varied sharply and then levelled off. The end point is also called

the equivalence point, which is the point where an equivalent amount (moles) of acid and base

have been mixed. It is represented by the steepest section of the curve.

Table 3.2 Titration Data

Volume

(ml)pH ΔpH ΔpH/ΔV

0 2.78

0.4 3.00 0.14 0.35

0.7 3.14 0.16 0.2286

1.1 3.30 0.19 0.1727

. . . .

. . . .

. . . .

25.2 6.36 0.21 0.0083

25.4 6.57 0.56 0.0220

25.6 7.13 1.56 0.0609

25.7 8.69 1.67 0.0650

. . . .

. . . .

. . . .

28.2 12.32 0.06 0.0021

28.5 12.38 0.04 0.0014

28.8 12.42 0.04 0.0014

59

Determining the exact equivalence point cannot be done visually. Mathematically, the

inflection point of the titration curve corresponds to the equivalence point. That is a point where

the curvature changes from concave to convex or vice versa. At this point, the first derivative is at

its maximum or minimum and the second derivative is zero (if it exists).

For example, the red curve in Figure 3.5 depicts the first derivative where the maximum

point (equivalence point) is at a volume of 25.6 ml. The amount of base consumed to reach the

equivalence point is considered the amount of acidity.

Figure 3.5 Titration curve of acetic acid with 0.1 N NaOH

When the acid has more than one hydrogen or is a mixture of various acids (like bio-oil)

there are more than one steep portion in the titration curve and therefore more extreme points. In

60

the TAN test, the last extremum is considered the total volume of titrant required to neutralize all

of the acids in the sample.

To calculate the first derivative, the centered finite-divided-difference formula from

numerical differentiation was applied.

𝑑𝑓

𝑑𝑥=ℎ2 − ℎ1ℎ1ℎ2

𝑓𝑖 −ℎ2

ℎ1(ℎ2 + ℎ1)𝑓𝑖−1 +

ℎ1ℎ2(ℎ2 + ℎ1)

𝑓𝑖+1 (Eq. 3-1)

If ℎ2 = ℎ1 = ℎ:

𝑑𝑓

𝑑𝑥=𝑓𝑖+1 − 𝑓𝑖−1

2ℎ

In this research, a titration was carried out and the total acidity measured immediately

following each esterificatioin reaction. In this case, a lower amount of base consumed represents

a lower amount of carboxylic acid present in the solution and a higher reaction conversion.

Equations 3-3 and 3-4 were employed to calculate the weight of the consumed base. In these

equations, V is the volume in ml, N is normality, and d is the density in g/ml.

mg of TMAH= V × d × 0.25 ×1000 (Eq. 3-3)

mg of NaOH = V × N × 40 (Eq. 3-4)

To make the measured total acidities comparable to data from other titrations with different titrant

concentrations, the acidity is reported in mg of titrant/g of bio-oil.

61

3.6 Results and Discussion

3.6.1 Modifying Titration Procedure

In the first days of this study, ASTM D664 was applied to quantify the acidity. However,

significant problems were encountered. Performing manual titration highlighted the problems with

the ASTM D664 method because it was performed on a larger volume of sample than the automatic

titration. First of all, in the ASTM D664 method, a mixture of 50% toluene, 49.5% isopropanol,

and 0.5% water is used as the solvent despite bio-oil being almost insoluble in toluene. Therefore,

we employed a mixture of n-butanol and acetone as the solvent to dilute the samples before

titration. While the ASTM D664 method used isopropanol, we substituted with a less polar and

less acidic alcohol (n-butanol) to reduce the chance of competition in the reaction between

oxygenated molecules in bio-oil and alcohol. The pH of the solvent (n-butanol and acetone) was

6.97, which can be considered a neutral mixture.

The primary observed problem of the ASTM D664 standard for bio-oil is the formation of

a large lump of gelatinous precipitate that interferes with mixing and, in cases with KOH solutions

as the titrant, completely stopped the magnet from rotating. The worst consequence of the

formation of these sticky precipitates is covering the electrode, which significantly reduces its

sensitivity by blocking the porous membrane. This precipitation is the result of the formation of

insoluble salts, which are the products of a reaction between the titrant with phenol and its

derivative present in bio-oil.

The formation of precipitating salts at different concentrations of NaOH and KOH are

shown in figure 3.6. Increasing the concentration of KOH from 0.1 to 0.5 marginally decreased

62

the precipitation. The KOH solution was replaced by an NaOH solution to determine its suitability

as the titrant.

In the first experiment, a mixture of bio-oil and ethanol (1:2 volume ratio) was titrated with

0.1 N NaOH (Figure 3.7). The experiment was stopped when the pH reached 12. Unfortunately, a

sticky precipitant was formed. Based on the effect of changes in concentration on the KOH case,

we changed the NaOH concentration from 0.1 N to 0.5 N. The precipitation decreased considerably

but was not completely eradicated (Figure 3.6 c, d).

Figure 3.6 Precipitation after titration: a) KOH 0.1 N, b) KOH 0.5 N, c) NaOH 0.1 N, d) NaOH

0.5 N

63

Figure 3.7 illustrates the manual titration curves for 0.1 and 0.5 normal solutions of NaOH

as the titrant. The equivalent points are calculated using formula (3-1). They are 46.2 ml for 0.1 N

and 10 ml for 0.5 N. These results indicate that 10.6 mg and 11.1 mg of NaOH were consumed to

neutralize each gram of bio-oil at each concentration, respectively.

These results lead to the hypothesis that better results could be obtained if an organic base

was applied as the titrant instead of NaOH and KOH. As the result, Carboxylic acids in bio-oil

were quantified using a non-aqueous potentiometric titration method. A quaternary ammonium

hydroxide solution (tetramethylammonium hydroxide 25 wt. % in water) was employed as the

titrant. The linear formula of TMAH is (CH3)4N(OH). Its molecular weight and density at 25ºC

are 91.15 g and 1.016 g/ml, respectively. When TMAH was used as the titrant, no considerable

precipitation was observed on the electrode.

After adding each drop of titrant, the mixture should be allowed to reach an equilibrium

before the next drop is added to avoid noise and fluctuation in the data. This noise is apparent in

figure 3.7 a. In other experiments, we endeavoured to observe a sufficient interval between titrant

additions to avoid data fluctuation. Needless to say, the more points that are recorded, the more

precise the results we can obtain. Therefore, automatic titration was performed following the

manual experiments. In this case, 290-400 points were recorded over several different runs of the

experiments. Other advantages of automatic titration include lower consumption of titrant, time

efficiency, and reduced human error.

64

a)

b)

Figure 3.7 Titration results with a) 0.1 N NaOH and b) 0.5 N NaOH

1

3

5

7

9

11

13

-0.1

0.1

0.3

0.5

0.7

0.9

1.1

0 20 40 60 80 100 120 140 160

Δp

H/Δ

V (

ML)

pH

ml 0.1 N NaOH

0

0.5

1

1.5

2

2.5

3

0 5 10 15 20 25 30

0

2

4

6

8

10

12

14

pH

ml 0.5 N NaOH

Δp

H/Δ

V (

ml)

65

The automatic titrator was connected to a computer by the LabVIEW software. As the

program is not installed on the instrument, it must be run manually on the PC to record the data.

At this point, the ongoing experiment is monitored on the PC screen (Figure 3.8). The data is

available in an excel spreadsheet following the titration. The stopping procedure is automatic for

the instrument and manual for the PC.

66

Figure 3.8 Front panel of titration using LabVIEW

67

3.6.2 Catalyst Type

Two different catalysts were investigated in this study, sulfuric acid and Amberlyst-15.

Separate experiments at 50ºC were run for 3 hours to compare the two catalysts. Both reactions

were carried out on a 1:2 bio-oil/ethanol mixture in the presence of 5% catalyst.

The total acidity after esterification was 4.24 mg of NaOH/g for sulfuric acid and 4.03 mg

of NaOH/g for Amberlyst-15. The results show that homogeneous sulfuric acid is a slightly more

effective catalyst than heterogeneous Amberlyst-15. Mass transfer limitation in the pores of

Amberlyst-15 might be the reason for the observed difference. The sulfuric acid catalyst can

readily contact the large molecules of carboxylic acids in the bulk of the liquid phase while in the

case of Amberlyst-15, the reactants must attach to hydrogen ion sites located in the macroreticular

pore of the catalyst.

3.6.3 Alcohol Type

Three different alcohols, methanol, ethanol, and butanol were investigated to determine the

effect of various alcohols on the degree of catalytic esterification. The reaction was performed at

50°C with a catalyst concentration of 5 wt. % and an alcohol/bio-oil volume ratio of 2:1.

The results of the esterification reaction with H2SO4 and Amberlyst 15 are shown in

figures 3.9 and 3.10. The bio-oil upgraded with methanol shows a much higher degree of

esterification compared to ethanol and butanol in the presence of sulfuric acid with Amberlyst 15

as the catalyst. The sample from the reaction catalysed by H2SO4 was titrated by NaOH and the

sample of Amberlyst 15 was titrated by TMAH. The reaction time was three hours for sulfuric

acid and one hour for Amberlyst 15. The results followed the same trend regarding the number of

68

carbon atoms in the alcohol. Therefore, we conclude that alcohols with fewer carbon atoms are

more effective for bio-oil upgrading via esterification and that changing the catalysts and reaction

time does not interact with the alcohol type on the reaction conversion.

This faster reaction rate can be explained by the higher quantity of active reagent in the

shorter carbon-chain alcohol, the effect of the size of the alkyl group on reaction rate, and the

higher solubility of this alcohol in the raw bio-oil. Our results confirm the results by

Weerachanchai et al. (2012) who tested methanol and ethanol. However, their study focused on

the catalytic esterification of the water soluble part of the bio-oil (Weerachanchai et al., 2012).

Figure 3.9 Effect of carbon number of alcohol on the esterification degree in the presence of

sulfuric acid

0

1

2

3

4

5

6

0 1 2 3 4 5

Tota

l aci

dit

y (b

ase

/bio

-oil

[mg/

g])

Carbon number of alcohol

ButanolEthanol

Methanol

69

Figure 3.10 Effect of carbon number of alcohol on the catalytic esterification of bio-oil in

presence of Amberlyst 15

3.6.4 Effect of Reaction Temperature

The influence of reaction temperature was studied by conducting esterification of the crude

bio-oil and ethanol under the following conditions: 2:1 volume ratio of ethanol to bio-oil, 5 wt. %

sulfuric acid, and 3 hr of reaction time. The results depicted in figure 3.11 indicate that the

conversion of carboxylic acids to their corresponding esters increased with increasing reaction

temperature from 20-60ºC and the highest degree of esterification was achieved at the highest

temperature. Weerachanchai et al. reported the same trend for the water soluble part of bio-oil.

Li et al. (2011) studied the effect of increasing temperature from 70-170°C in the presence

of Amberlyst-70 and methanol. They concluded that esterification increased with increasing

temperature (Li et al., 2011).

0

5

10

15

20

25

30

35

0 1 2 3 4 5

Tota

l aci

dit

y (b

ase

/bio

-oil

[mg/

g])


ButanolEthanol

Methanol

70

However, bio-oil is sensitive to temperature and its properties change at high temperatures.

Therefore, the conditions considered in this study do not exceed 60°C, which is close to the boiling

points of alcohol.

Figure 3.11 Effect of temperature on esterification degree

3.6.5 Effect of Reaction Time

A set experiments were carried out to investigate the reaction duration for the catalytic

esterification of bio-oil. Six experiments were conducted over 1, 3, 5, 8, 12, and 24 hours. The

results of this experiment are depicted in figure 3.12. For each point on the graph, a new experiment

was carried out because in the case of heterogeneous catalysts the results become unreliable if

3

3.5

4

4.5

5

5.5

10 20 30 40 50 60 70

To

tal a

cid

ity

(ba

se/b

io-o

il [m

g/g

])

Temperature (˚C)

71

sampling occurs from one vessel at different times. This is due to a change in the ratio of the

reactants to the catalyst. Furthermore, each experiment was repeated at least three times and

untrusted results were removed. The total acidity was obtained by calculating the first derivative

of the pH versus volume. The points in figure 3.12, like other graphs in this thesis, are the average

of the maximum amount of the first derivative in that condition.

The experiments were performed at 50°C with Amberlyst 15 by wt. 5% of bio-oil. The

reactants were ethanol and bio-oil (2:1). The results are illustrated in figure 3.12. As shown in the

graph, the total acidity decreased with increasing reaction time. This decrease was faster at the

beginning and reached a maximum after 12 hours. The reaction conversion decreased for the

experiments which ran for 24 hr.

The deactivation of resin catalysts in bio-oil esterification was investigated by Hu et al.

(2013). Several mechanisms can be considered responsible including the presence of metal ions,

nitrogen containing organics, and polymer formation. Each of this mechanisms deactivate the

catalyst in a different way. Metal ions, such as calcium, exchange ions with the catalyst and

deactivate it. Some compounds can get into the pores of Amberlyst 15 and be polymerized inside

them, blocking the pores and making them unable to escape from the pores (Hu et al., 2013).

72

Figure 3.12 Effect of reaction time on the total acidity applying Amberlyst 15

3.6.6 Effect of Alcohol/bio-oil Volumetric Ratio

The effect of alcohol content was investigated by monitoring the esterification reaction

with 5 wt. % of Amberlyst 15 at 50°C for 3 hrs. Similar to other reversible reactions, the excess

amount of a reactant in catalytic esterification will encourage the equilibrium towards the direction

which consumes it. Three alcohol/bio-oil ratios (1:1, 2:1, and 3:1) were studied (figure 3.13). As

expected, increasing the alcohol caused the reaction to move in the forward direction and produce

more esters.

10

15

20

25

30

0 5 10 15 20 25 30

Tota

l aci

dit

y (b

ase/

bio

-oil

[mg/

g])

Time (hr)

73

Figure 3.13 Effect of Alcohol/bio-oil ratio on esterification degree

3.6.7 Catalyst Loading Amount

The effect of loading different amounts of Amberlyst 15 is illustrated in figure 3.14. Bio-

oil and ethanol were mixed with 1:2 ratio and underwent catalytic esterification at 50ºC for 3 hrs.

Four different amounts of catalyst were charged to the reactor.

We expected that an increase in catalyst loading would result in an increase in conversion

because of an increase in active sites. However, figure 3.15 illustrates that higher amounts of

catalyst initially resulted in greater esterification but reached an almost constant amount after 10

wt. % of catalyst to bio-oil. This may be the result of the already high mass transfer rate in the

reaction system such that the additional contact between catalyst and the reactants does not

significantly influence the system.

.

0

5

10

15

20

25

30

0 1 2 3 4

Tota

l aci

dit

y (b

ase

/bio

-oil

[mg/

g])

Alcohol/bio-oil ratio (V/V)

74

Figure 3.14 Effect of catalyst amount on reaction conversion

3.6.8 Effect of Various Alcohols on Viscosity

The addition of alcohols and the conduction of an esterification reaction to remove

unwanted carboxylic acids will also result in a decrease in the viscosity of bio-oil. This is important

because bio-oil is a very viscous liquid and for it to be considered as a replacement for fossil fuels

all of its properties must be improved including viscosity.

The viscosity of the samples was measured after the esterification experiments with

methanol, ethanol, and butanol. The effect of methanol on viscosity was greater than that of the

two other alcohols. However, the viscosity of bio-oil decreased at least 8 times after the addition

of alcohols with the volume ratio of 1:2 in the presence of H2SO4 as the catalyst.

18

19

20

21

22

23

0 5 10 15 20

Tota

l aci

dit

y (b

ase

/bio

-oil

[mg/

g])

Mass % of catalyst to bio-oil

75

Figure 3.15 Effect of different alcohols on the viscosity change at 40 °C

0

1

2

3

4

5

0 1 2 3 4 5

Vis

cosi

ty (

cp)


Butanol

Ethanol

Methanol

76

Chapter Four: Conclusions and Recommendations

4.1 Conclusions

This study investigated two methods of upgrading bio-oil. First, we studied the production

of hydrogen (H2) through catalytic steam reforming of a commercial crude bio-oil. The process

was conducted in a fixed bed tubular flow reactor over nickel based alumina supported catalysts

promoted with magnesia (Ni-MgO/Al2O3).

The effects of different factors including time, Ni content, preparation condition, and initial

bio-oil to water ratio on the yield of various outlet gases including hydrogen was investigated. The

experiments were performed at 850°C and the outlet gas concentrations were obtained. The

average H2 yield was very low with a maximum of 30% over the alumina support with the bio-oil

in aqueous phase at a bio-oil to water ratio of 1:1. The hydrogen yield nearly doubled with the

addition of 12.8% nickel and 33.3% magnesia for the three bio-oil aqueous phase samples at

various bio-oil to water ratios. This effect was even more pronounced in the aqueous bio-oil phases

with greater water content. Increasing the nickel content of the catalysts increased their activity.

On the contrary, the effect of preparation method on H2 yield was greater in the aqueous

phase samples with lower water content. The activity of the catalyst for H2 production was

dependent on the preparation of the catalyst for the aqueous phase sample. The addition of acid in

the second step of preparation reduced the activity of the catalyst when the aqueous phase samples

were prepared with bio-oil to water ratios of 1:2 and 1:1. However, the activity of the catalyst

increased for the sample with an initial bio-oil to water ratio of 2:1. While the addition of acid in

the second step of catalyst preparation did not increase the H2 yield in the case of the aqueous

phase samples with lower bio-oil to water ratios, the stability of those catalysts did increase.

77

Among the catalysts tested, the greatest H2 yield (61%) was achieved over Ni-MgO/Al2O3-

3 with the aqueous phase of bio-oil and a bio-oil to water ratio of 1:1. These results indicate that a

greater bio-oil to water ratio does not necessarily provide greater H2 yield.

The second method of bio-oil upgrading investigated in this study is catalytic esterification.

The objective of bio-oil esterification is to upgrade the oil by lowering the acidity and viscosity

and to improve its stability. This study focuses on the catalytic esterification of bio-oil in the

presence of an acid catalyst and various alcohols.

It was determined that ASTM D664 is not a reliable method to measure the acidity of bio-

oil. Bio-oil is not soluble in the solvent applied in this method and the formation of sticky

precipitates reduced the sensitivity of the electrode. Therefore, a non-aqueous titration method was

specially designed to analyze the acidic components in bio-oil using quaternary ammonium

hydroxide as the titrant and a mixture of butanol and acetone as the solvent. The method overcomes

the problems encountered in the ASTM D664 and can successfully quantify strong and weak

acidities in bio-oils from pyrolysis biomass.

Potentiometric titration was undertaken to determine the total organic acid number in the

bio-oil and evaluate the degree to which the bio-oil was upgraded through the esterification

reaction. The acid number of the bio-oil decreased following esterification due to the conversion

of the organic carboxylic acids to neutral esters. The effect of manipulating the reaction conditions

including temperature, carbon chain length of the alcohols, catalyst type, reaction time, amount of

catalyst loading, and alcohol content were studied.

78

Two catalysts, H2SO4 and Amberlyst-15, were applied with the sulfuric acid showing

slightly better conversion. However, it should be noted that Amberlyst-15 is a heterogeneous

catalyst, which could be recycled and recovered through acid and organic solvent wash and then

reused.

Increasing the temperature resulted in a decrease in the total acid number of the samples

and a higher degree of esterification. As bio-oil is a temperature sensitive fluid, the highest

temperature investigated was 60°C to avoid undesired changes in the properties of the bio-oil.

The alcohols investigated were methanol, ethanol, and n-butanol. The esterification

reaction resulted in better conversion in the presence of alcohols with shorter hydrocarbon chains.

Alcohols with a shorter alkyl group are more soluble in bio-oil and more active, which is why the

smaller molecules of methanol produced higher esterification conversion.

The esterification extent increased over time but began to decrease after almost 12 hrs. The

reduction in the reaction conversion reduction is the result of the reduction in the activity of

Amberlyst 15 after about 12 hrs. Three mechanisms can be considered in the deactivation of

Amberlyst 15, the presence of nitrogen containing compounds in the bio-oil, the formation of

polymers in the pores of the catalyst, and ion exchange between the metal ions and the resin.

The esterification reaction is a reversible reaction. Therefore, according to Le Chatelier's

principle, we expect that increasing the alcohol content will disturb the equilibrium towards

esterification. The results confirm this expectation and no inhibition was observed for the amounts

of alcohol applied.

79

According to this research, increasing the catalyst load in the reaction system increased the

esterification degree to a constant amount. Esterification also improved the pH, density, and

viscosity of the bio-oil. The pH increased and the viscosity and density decreased. The greatest

improvement was obtained when methanol was used as the alcohol.

4.2 Recommendations

Upgrading bio-oil using techniques including steam reforming and esterification is a

burgeoning area of study in both the engineering and scientific fields. Compared to steam

reforming of natural gas, bio-oil steam reforming is a relatively new technology and catalysts are

still being developed. Several of the Ni-based catalysts currently employed in the natural gas

industry were tested for use with bio-oil. The influence of production conditions and nickel content

were investigated, but further research is required to improve the hydrogen production yield and

carbon deposition on the catalyst. Another opportunity for further investigation is the possibility

of employing alternative reactors such as fluidized bed systems.

We studied the effect of manipulating various conditions involved in the catalytic

esterification of bio-oil. The experimental approach was one-factor-at-a-time and any interactions

between factors were neglected. Designing a DOE to simultaneously investigate the effect of

multiple factors should be considered as an extension of this research. As mentioned, bio-oil is

sensitive to temperature change and its properties and composition change with time and

temperature. Esterification reactions at higher temperatures can be carried out at supercritical

conditions of the alcohols. An investigation into esterification during pyrolysis and bio-oil

production represents another option to extend this research.

80

The development of alternative catalysts should also considered for future investigation. An

alternative catalyst could be used to make the upgrading process more economical. Another

opportunity is the application of environmentally safe catalysts such as enzymes or whole cells.

81

References

Aktaş, S., Karakaya, M., & Avcı, A. K. (2009). Thermodynamic analysis of steam assisted

conversions of bio-oil components to synthesis gas. International Journal of Hydrogen

Energy, 34(4), 1752–1759.

Aranda, D. A. G., Santos, R. T. P., Tapanes, N. C. O., Ramos, A. L. D., & Antunes, O. A. C.

(2008). Acid-catalyzed homogeneous esterification reaction for biodiesel production from

palm fatty acids. Catalysis Letters, 122, 20-25.

Armaroli, N., & Balzani, V. (2011). The Hydrogen Issue. ChemSusChem, 4(1), 21–36.

Balat, M. (2011). An Overview of the Properties and Applications of Biomass Pyrolysis Oils.

Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 33, 674-689.

Basagiannis, A. C., & Verykios, X. E. (2007). Steam reforming of the aqueous fraction of bio-oil

over structured Ru/MgO/Al2O3 catalysts. Catalysis Today, 127(1-4), 256–264.

Blin, J., Volle, G., Girard, P., Bridgwater, T., & Meier, D. (2007). Biodegradability of biomass

pyrolysis oils: Comparison to conventional petroleum fuels and alternatives fuels in current

use. Fuel, 86, 2679–2686.

Boucher, M. ., Chaala, A., & Roy, C. (2000). Bio-oils obtained by vacuum pyrolysis of softwood

bark as a liquid fuel for gas turbines. Part I: Properties of bio-oil and its blends with methanol

and a pyrolytic aqueous phase. Biomass and Bioenergy, 19(5), 337–350.

Bridgwater, A. V., Meier, D., & Radlein, D. (1999). An overview of fast pyrolysis of biomass.

Organic Geochemistry, 30, 1479–1493.

Bridgwater, A. V. (2003). Renewable fuels and chemicals by thermal processing of biomass.

Chemical Engineering Journal, 91(2-3), 87–102.

Bridgwater, A. V. (2012). Review of fast pyrolysis of biomass and product upgrading. Biomass

82

and Bioenergy, 38, 68–94.

Brown, R. (2011). Thermochemical processing of biomass. Process Engineering, Wiley.

Chen, W., Luo, Z., Yu, C., Li, G., Yang, Y., Zhang, J., & Lu, K. (2014). Catalytic transformations

of acids, aldehydes, and phenols in bio-oil to alcohols and esters. Fuel, 135, 55–62.

Chen, W.-H., Lin, B.-J., Huang, M.-Y., & Chang, J.-S. (2015). Thermochemical conversion of

microalgal biomass into biofuels: a review. Bioresource Technology, 184, 314–27.

Cheng, Z., Wu, Q., Li, J., & Zhu, Q. (1996). Effects of promoters and preparation procedures on

reforming of methane with carbon dioxide over Ni/Al2O3 catalyst. Catalysis Today, 30(1-3),

147–155.

Chornet E. and Czernik S. (2008). Harnessing hydrogen. Professional Engineering, 21(August),

28.

Czernik, S., Evans, R., & French, R. (2007). Hydrogen from biomass-production by steam

reforming of biomass pyrolysis oil. Catalysis Today, 129, 265–268.

Damartzis, T., & Zabaniotou, a. (2011). Thermochemical conversion of biomass to second

generation biofuels through integrated process design-A review. Renewable and Sustainable

Energy Reviews, 15(1), 366–378.

Demirbas, A. (2007). Progress and recent trends in biofuels. Progress in Energy and Combustion

Science, 33(1), 1–18.

Diebold, J. P., & Czernik, S. (1997). Additives To Lower and Stabilize the Viscosity of Pyrolysis

Oils during Storage. Energy Fuels, 11(10), 1081–1091.

Fan, G., Liao, C., Fang, T., Luo, S., & Song, G. (2014). Amberlyst 15 as a new and reusable

catalyst for the conversion of cellulose into cellulose acetate. Carbohydrate Polymers, 112,

203–9.

83

Galdámez, J. R., García, L., & Bilbao, R. (2005). Hydrogen Production by Steam Reforming of

Bio-Oil Using Coprecipitated Ni-Al Catalysts . Acetic Acid as a Model Compound. Energy

& Fuels, 19(3), 1133–1142.

Guo, J., Lou, H., Zhao, H., & Zheng, X. (2005). Improvement of stability of out-layer MgAl2O4

spinel for a Ni/MgAl2O4/Al2O3 catalyst in dry reforming of methane. Reaction Kinetics and

Catalysis Letters, 84(1), 93–100.

Hu, X., Gunawan, R., Mourant, D., Wang, Y., Lievens, C., Chaiwat, W., … Li, C.-Z. (2012).

Esterification of bio-oil from mallee (Eucalyptus loxophleba ssp. gratiae) leaves with a solid

acid catalyst: Conversion of the cyclic ether and terpenoids into hydrocarbons. Bioresource

Technology, 123, 249–55.

Hu, X., & Lu, G. (2010). Bio-oil steam reforming, partial oxidation or oxidative steam reforming

coupled with bio-oil dry reforming to eliminate CO2 emission. International Journal of

Hydrogen Energy, 35(13), 7169–7176.

Ikura, M. (2003). Emulsification of pyrolysis derived bio-oil in diesel fuel. Biomass and

Bioenergy, 24(3), 221–232.

Iojoiu, E. E., Domine, M. E., Davidian, T., Guilhaume, N., & Mirodatos, C. (2007). Hydrogen

production by sequential cracking of biomass-derived pyrolysis oil over noble metal catalysts

supported on ceria-zirconia. Applied Catalysis A: General, 323, 147–161.

Kadam, S. T., Thirupathi, P., & Kim, S. S. (2009). Amberlyst-15: an efficient and reusable catalyst

for the Friedel–Crafts reactions of activated arenes and heteroarenes with α-amido sulfones.

Tetrahedron, 65(50), 10383–10389.

Kechagiopoulos, P. N., Voutetakis, S. S., Lemonidou, A. a, & Vasalos, I. a. (2006). Hydrogen

Production via Steam Reforming of the Aqueous Phase of Bio-Oil in a Fixed Bed Reactor.

84

Energy & Fuels, 20(5), 2155–2163.

Levin, D. B., & Chahine, R. (2010). Challenges for renewable hydrogen production from biomass.

International Journal of Hydrogen Energy, 35(10), 4962–4969.

Li, X., Gunawan, R., Lievens, C., Wang, Y., Mourant, D., Wang, S., … Li, C. Z. (2011).

Simultaneous catalytic esterification of carboxylic acids and acetalisation of aldehydes in a

fast pyrolysis bio-oil from mallee biomass. Fuel, 90, 2530–2537.

Li, Z., Liu, Y., Kwapinski, W., & Leahy, J. J. (2014). ZrO2-modified TiO2 nanorod composite:

Hydrothermal synthesis, characterization and application in esterification of organic acid.

Materials Chemistry and Physics, 145(1-2), 82–89.

Liu, Y., Li, Z., Leahy, J. J., & Kwapinski, W. (2015). Catalytically Upgrading Bio-oil via

Esterification. Energy & Fuels, 29(6), 3691–3698.

Lohitharn, N., & Shanks, B. H. (2009). Upgrading of bio-oil: Effect of light aldehydes on acetic

acid removal via esterification. Catalysis Communications, 11, 96–99.

Lu, Q., Li, W. Z., & Zhu, X. F. (2009). Overview of fuel properties of biomass fast pyrolysis oils.

Energy Conversion and Management, 50, 1376–1383.

Marchetti, J. M., & Errazu, A. F. (2008). Esterification of free fatty acids using sulfuric acid as

catalyst in the presence of triglycerides. Biomass and Bioenergy, 32(9), 892–895.

Marda, J. R., DiBenedetto, J., McKibben, S., Evans, R. J., Czernik, S., French, R. J., & Dean, A.

M. (2009). Non-catalytic partial oxidation of bio-oil to synthesis gas for distributed hydrogen

production. International Journal of Hydrogen Energy, 34(20), 8519–8534.

Miao, S., & Shanks, B. H. (2009). Esterification of biomass pyrolysis model acids over sulfonic

acid-functionalized mesoporous silicas. Applied Catalysis A: General, 359(1-2), 113–120.

Milina, M., Mitchell, S., & Pérez-Ramírez, J. (2014). Prospectives for bio-oil upgrading via

85

esterification over zeolite catalysts. Catalysis Today, 235, 176–183.

Moens, L., Black, S. K., Myers, M. D., & Czernik, S. (2009). Study of the neutralization and

stabilization of a mixed hardwooc bio-oil. Energy & Fuels, 23(13), 2695–2699.

Ortiz-toral, Pedro, J. (2008). Steam reforming of bio-oil : Effect of bio-oil composition and

stability, Master of science thesis.

Qin, F., Cui, H., Yi, W., & Wang, C. (2014). Upgrading the Water-Soluble Fraction of Bio-oil by

Simultaneous Esterification and Acetalation with Online Extraction. Energy & Fuels, 28 (4),

2544-2553.

Rioche, C., Kulkarni, S., Meunier, F. C., Breen, J. P., & Burch, R. (2005). Steam reforming of

model compounds and fast pyrolysis bio-oil on supported noble metal catalysts. Applied

Catalysis B: Environmental, 61(1-2), 130–139.

Rout, P. K., Naik, M. K., Naik, S. N., Goud, V. V., Das, L. M., & Dalai, A. K. (2009). Supercritical

CO 2 fractionation of bio-oil produced from mixed biomass of wheat and wood sawdust.

Energy and Fuels, 23, 6181–6188.

Salehi, E., Azad, F. S., Harding, T., & Abedi, J. (2011). Production of hydrogen by steam

reforming of bio-oil over Ni/Al2O3 catalysts: Effect of addition of promoter and preparation

procedure. Fuel Processing Technology, 92(12), 2203–2210.

Seyedeyn-azad, F., Abedi, J., & Sampouri, S. (2014). Catalytic Steam Reforming of Aqueous

Phase of Bio-Oil over Ni- Based Alumina-Supported Catalysts. Industrial & Engineering

Chemistry, 53(46), 17937–17944.

Seyedeyn-Azad, F., Salehi, E., Abedi, J., & Harding, T. (2011). Biomass to hydrogen via catalytic

steam reforming of bio-oil over Ni-supported alumina catalysts. Fuel Processing Technology,

92(3), 563–569.

86

Tang, Y., Miao, S., Shanks, B. H., & Zheng, X. (2010). Bifunctional mesoporous organic-

inorganic hybrid silica for combined one-step hydrogenation/esterification. Applied Catalysis

A: General, 375(2), 310–317.

Tang, Z., Lu, Q., Zhang, Y., Zhu, X., & Guo, Q. (2009). One step bio-oil upgrading through

hydrotreatment, esterification, and cracking. Industrial and Engineering Chemistry Research,

48(15), 6923–6929.

Tanneru, S. K., Parapati, D. R., & Steele, P. H. (2014). Pretreatment of bio-oil followed by

upgrading via esterification to boiler fuel. Energy, 73, 214–220.

Vagia, E., & Lemonidou, A. (2007). Thermodynamic analysis of hydrogen production via steam

reforming of selected components of aqueous bio-oil fraction. International Journal of

Hydrogen Energy, 32(2), 212–223.

Vagia, E., & Lemonidou, A. (2008). Thermodynamic analysis of hydrogen production via

autothermal steam reforming of selected components of aqueous bio-oil fraction.

International Journal of Hydrogen Energy, 33(10), 2489–2500.

Wang, J., Chang, J., & Fan, J. (2010). Catalytic esterification of bio-oil by ion exchange resins.

Journal of Fuel Chemistry and Technology, 38(5), 560–564.

Wang, J. J., Chang, J., & Fan, J. (2010). Upgrading of bio-oil by catalytic esterification and

determination of acid number for evaluating esterification degree. Energy and Fuels, 24,

3251–3255.

Wang, Z. X., Dong, T., Yuan, L. X., Kan, T., & Zhu, X. F. (2007). Characteristics of Bio-Oil-

Syngas and Its Utilization in Fischer - Tropsch Synthesis. Energy and Fuels, 21(4), 2421–

2432.

Weerachanchai, P., Tangsathitkulchai, C., & Tangsathitkulchai, M. (2012). Effect of reaction

87

conditions on the catalytic esterification of bio-oil. Korean Journal of Chemical Engineering

29 (2), 182-189.

Wu, L., Hu, X., Mourant, D., Wang, Y., Kelly, C., Garcia-Perez, M., … Li, C. Z. (2014).

Quantification of strong and weak acidities in bio-oil via non-aqueous potentiometric

titration. Fuel, 115, 652–657.

Xu, Y., Wang, T., Ma, L., Zhang, Q., & Wang, L. (2009). Upgrading of liquid fuel from the

vacuum pyrolysis of biomass over the Mo-Ni/[gamma]-Al2O3 catalysts. Biomass and

Bioenergy, 33, 1030–1036.

Yan, C.-F., Cheng, F.-F., & Hu, R.-R. (2010). Hydrogen production from catalytic steam

reforming of bio-oil aqueous fraction over Ni/CeO2–ZrO2 catalysts. International Journal of

Hydrogen Energy, 35(21), 11693–11699.

Zeng, F., Liu, W., Jiang, H., Yu, H. Q., Zeng, R. J., & Guo, Q. (2011). Separation of phthalate

esters from bio-oil derived from rice husk by a basification-acidification process and column

chromatography. Bioresource Technology, 102, 1982–1987.

Zhang, L., Liu, R., Yin, R., & Mei, Y. (2013). Upgrading of bio-oil from biomass fast pyrolysis in

China: A review. Renewable and Sustainable Energy Reviews, 24, 66–72.

Zhang, Q., Chang, J., Wang, T. J., & Xu, Y. (2006). Upgrading bio-oil over different solid

catalysts. Energy and Fuels, 20, 2717–2720.

Žilnik, F. L., & Jazbinšek, A. (2012). Recovery of renewable phenolic fraction from pyrolysis oil.

Separation and Purification Technology, 86(86), 157–170.

Catalytic Steam Reforming and Esterification of Bio-oil

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