1

CHEMICAL ENGINEERING FOR ENERGY

TREATMENT OF ODOROUS VOLATILE ORGANIC COMPOUNDS USING UV/H2O2

Master Thesis Project in Chemical Sciences and Engineering

By

Nguo Manases Fuh

Supervisor: Mats Westermark

Industrial Contack: Jack Delin

September 2011

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ABSTRACT

Odorous volatile organic compounds emissions from fried-food industries posed severed pollution

problems both to the workers and the surrounding inhabitants. These industries need to look for cost

effective and efficient methods to reduce these emitted gases. Several solutions such as the use of

centrifugation, scrubbers, ion exchangers, biofiltration, condensation, adsorption, absorption, and

incineration have been exploited to reduce these smelling gases. Centriair in collaboration with KTH

aim at using UV light in combination with ozone and hydrogen peroxide to degrade these odorous

VOCs emitted from the frying of meat balls (SCAN) and chips.

Several volatile organic compounds which are odorants with low threshold values were identified in

the emitted gases from meat frying which includes: aldehydes, sulphur containing compounds,

ketones, pyrazines, and alcohols. The type and concentration of these odorants emitted depends

among other things primarily on the type of oil used during the frying process.

This work focuses on the use of advanced oxidation processes to abate theses odorous gases. The

effect of UV dosage and the use of hydrogen peroxide were tested in a flow reactor. Ozone

producing UV lamps were used for the treatment of 2,4-decadienal, Hexanal, furfural, and 2,5-

dimethylpyrazine. A simultaneous chemical and odour analysis was done using a GC/MS

Olfactometry system.

UV/Ozone/H2O2 was effective in reducing the volatile organic compounds tested thus reducing the

odor concentration. The percent removal was proportional to the energy dosage.

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Table of Contents

Abstract ....................................................................................................................................................2

1. Introduction ...................................................................................................................................4

1.1 Aims and Objectives ....................................................................................................................4

1.2 Methodology ...............................................................................................................................4

2. Odorous Compounds Found during Frying ....................................................................................5

2.1 Threshold Values for Some Odorous Compounds ......................................................................6

3. Ultra Violet Lamps ..........................................................................................................................6

3.1 Low-Pressure Mercury Lamps .....................................................................................................6

3.2 Medium-Pressure Mercury Lamps ..............................................................................................6

3.3 High-Pressure Mercury Lamps ....................................................................................................7

3.4 Factors Affecting the Performance of UV Lamps ........................................................................7

4. Hydrogen Peroxide ........................................................................................................................7

5. Treatment Methods .......................................................................................................................7

5.1 Different Oxidative Treatment Methods.....................................................................................7

5.1.1. Air Ionization ...........................................................................................................................8

5.1.2. Using UV Light .........................................................................................................................8

5.1.3. Advanced Oxidation Processes ................................................................................................9

UV/Ozone .................................................................................................................................... 10

Fenton’s Reaction ....................................................................................................................... 10

UV/Hydrogen Peroxide ............................................................................................................... 11

6. Analytical Methods ..................................................................................................................... 12

6.1. Gas Chromatography Olfactometry ................................................................................................ 12

6.2. Dräger Tubes ................................................................................................................................... 13

7. Experimentation ......................................................................................................................... 13

8. Results and Discussions .............................................................................................................. 14

9. Conclusion ................................................................................................................................... 17

References ................................................................................................................................. 18

Appendix .................................................................................................................................... 20

Appendix 1 .................................................................................................................................. 21

Appendix 2................................................................................................................................... 24

Appendix 3 ............................................................................................................................... ....25

Appendix 4 ....................................................................................................................................27

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1. Introduction

Food processing industries such as SCAN (frying of meat) are continuously faced with the problem of

odorous compound emitted during the manufacture process. Increasing residential area around such

industries leads to a call for concern for the wellbeing of the public and the workers. With a

combination of technologies, centriair produce equipments to abate the various pollutants from the

exhaust air of these industries. The odorants are resistant to the classical methods such as

adsorption, ion exchange, biofiltration, condensation, scrubbers, absorption, and incineration.

Centriair centrifugal technique in association with Technair UV-treatment technology has therefore

been installed in Aviko’s plant aimed for the reduction of odorous compound emitted during deep-

fat frying. [1]

In this paper, the use of UV light in combination with hydrogen peroxide has been investigated. This

advanced Oxidation Process (AOP) is a recent development in air treatment for the removal of

odorous volatile organic compounds (VOCs) from food process industries. This photochemical

oxidation process involves the use of ultra violet light to produce hydroxyl radicals which are strong

oxidizing agents by splitting hydrogen peroxide molecules. This process seems to be very effective as

a polishing step for the treatment of exhaust air from frying industries.

1.1. Aims and Objectives

During industrial frying of meat for example, various volatile organic compounds are been emitted

some of which are odorous. These odorous compounds need to be destroyed before release to the

atmosphere since it posed problems to the surrounding environment and the factory workers. Our

goal is to develop a cost-effective technology in order to reduce the amount of odorous volatile

organic compounds in industrial frying processes. We set to optimize the destruction of odorous

VOCs from frying industries using advanced oxidation technique (UV/H2O2).

1.2. Methodology

Different odorous VOCs compounds will be identified and a few will be treated with UV/H2O2 in a

laboratory scale. Several factors which are known to influence the oxidation process taken place

during the irradiation with the UV/H2O2 will be investigated. These factors include:

Intensity of the light (number of lamps)

UV dose (J/cm2)

Retention time (treatment time)

Initial Concentration of the substances to be oxidized

Gas flow rate

Type of UV device

Temperature

Pressure

Turbulence

Relative Humidity

The distance of the UV light from the odorous compounds [2]

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The number and location of the UV devices and the UV energy required is therefore dependent on

the air volume, concentrations and type of gas phase contaminants and the desired destruction as

well as the construction of the device.

2. Odorous Compounds found during frying

Different compounds which are odorous have been identified to be present in the gaseous mixture

emitted during frying for example meat. Most of these compounds include the aldehydes, volatile

fatty acids (VFAs), pyrazines, sulphur containing compounds, ketones, alcohols, carboxylic acids and

esters which could have originated either from the oil, the meat or the ingredients.

The characteristic odor obtained during the frying of meat is derived from the thermally induced

degradation of lipids and the milliard reactions that occur between amino acids and reducing sugars.

Most of the characteristic odor produced is as a result of the production of volatile compounds.

Several hundred volatile compounds have been identified [3]. Appendix 3 gives some of the odorous

volatile organic compounds from literature. [4, 5]

Depending on the frying conditions and the different ingredient added during the process, the

volatile organic compounds emitted differs. This also have an effect on the odor. Kirsten and Werner

[6] show that frying at 2800C for 3 minutes per side produces significant different in the odor

compared to frying at 3000C for 1 minute per side.

The type of oil use for the frying is the main contribution to the odor produced. The oil quality should be of one with low saturated fat, low linolenic acid content, and high oxidative stability. The free fatty acid content should be less than 0.05 % weight [7]. A study by Stephen et al. [8] shows that some compounds such as 3-cis-hexanal and 2,4-trans, trans-decadienal are produce from the frying oil while others such as dimethyl disulfide and 2,5-dimethyl pyrazine, were produced by the food. A gas chromatogram also indicate the present of 2-methyl mercaptomethyl butanal, 2-methyl mercaptosulfoxide-2-pentenal, 2-methylmercapto-5-methyl-2-hexenal, and 2-methylmercapto-2,4,6-octatrienal which are probably the products of the chemical reactions taking place. The table below gives the composition of a quality frying oil.

Table 1: Composition of Good Frying Oil [7]

Analysis Desired Level Analysis Desired Level

Free Fatty Acid 0.03 (% wt) Iron (ppm) < 0.2

Peroxide Value (meq/Kg) < 0.5 Calcium (ppm) < 0.2

Conjugated Dienes (%) Trace Magnesium (ppm) < 0.2

Polar Compounds (%) < 2.0 Diacylglycerol (%) < 0.5

Polymers (%) < 0.5 Para anisidine Value (%) < 4.0

Phosphorus (ppm) < 0.5 Chlorophyll (ppb) < 30

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2.1. Threshold values for Some Odorous Compounds

Threshold values of odorous compounds vary considerable depending on the measuring method

used. Therefore individual threshold measurement is of primary interest to researcher. Using the

triangular odor bag method, Yoshio Nagata [9] measure the odor threshold values of some 223

compounds. It was observed that the threshold decreases as the molecular weight of the compound

increases. Table 2 presents a selection of the odorants that are produced during industrial frying

process.

Table 2: Possible Malodor Compounds in Industrial Frying Processes [9]

Compound Odor character Odor threshold (ppm, v/v) Molecular weight (g/mol)

Acetaldehyde Pungent, fruity 0.0015 44.05

3-methylbutanal Fruity 0.0002 86.6

2-methylpropanal Pungent, fruity 0.0001 – 0.002 72.12

phenyl acetaldehyde Honey like, sweet 0.004 132.16

Formaldehyde Ester-like, 50 30.03

Acetic Acid Sour wine 0.0060 60.05

Dimethyl Sulfide Onion, garlic 0.0030 62.13

Dimethyl Disulfide Sulfury 0.0022 94.20

Hexanal Grassy, oily, fishy 0.0045 100.16

3. UV Lamps Treatment of odorous compounds depends on the type of UV lamp use with the right wavelength to provide enough energy for the production of hydroxyl radical. Different lamps technologies are available. The ultra violet light source consists of fused silica quartz tube typically of diameter 15 – 25 mm and 100 – 1200 mm long filled with mercury and an inert gas such as argon [10]. The main mechanism of the process is the ionization of mercury atoms to produce electrons that excite other atomic mercury [11]. The mercury is usually mixed with an inert material such as argon that helps to provide the require energy for ionization. The excited mercury atoms return to the ground state with the emission of photons. These photons can be reabsorbed (self-absorption) by another mercury atom. This phenomenon is particularly important when mercury concentration is high in the gas phase and when the diameter of the lamp is higher. The initial discharge is achieved through the application of electrical energy across the electrode of the quartz tube. 3.1. Low-Pressure Mercury Lamps

Generation of UV occurs at a total gas pressure of 102 to 103 Pa. These types of lamps are particularly important for the production of monochromatic wavelength (185 nm and 253.7 nm) of UV light [11]. These lamps are commercially readily available at comparatively low cost in cylindrical shapes with diameter ranges of 0.9 – 4 cm and 10 – 160 cm in length [10]. The problem of reversibility of emission or self-absorption is reduced by increasing the emission rate near the walls than at the inner part of the lamps.

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3.2. Medium-Pressure Mercury Lamps

The total gas pressure for this type of lamps ranges between 1 to 3 bars for UV generation and the emitted radiation is polychromatic. 3.3. High-Pressure Mercury Lamps These lamps operate at a total pressure of up to 106 Pa. The wavelength range of the UV light source is 185 – 480 nm. 3.4. Factors Affecting the Performance of UV Lamps

Temperature: Temperature is a thermodynamic factor that will affect the vapor pressure equilibrium of mercury. For low-pressure lamps, the optimum temperature needed inside the lamp is 400C [11].

Voltage: As voltage increasing, the emitted intensity of low-pressure lamps increases Aging of the lamp: Emission rate decreases over a period of time due to the aging of the

quartz material.

4. Hydrogen Peroxide

Hydrogen peroxide is a powerful, effective, selective, versatile, and widely use oxidant with a relative

simple storage conditions and dosing procedures. It has been use in numerous processes both in the

industries and domestic applications [12]. As compare to ozone, it is a widely commercial available

reagent that have high potential yield for the production of hydroxyl radicals.

At high concentrations, hydrogen peroxide can be unstable and poisonous [13]. But it is use as a

disinfectant and antiseptic in homes at lower concentrations.

5. Treatment Methods

Centriair have developed several pilot plants to assess and control industrial odor. The N.O.S.E.

techniques available for odor abatement include [14]:

Centrifugal separator Venturi Scrubber Packed Tower Scrubber Ultraviolet Light Ozone generator system

5.1. Different Oxidative Treatment Methods

The use of oxidative methods for breaking down organic compounds has been extensively applicable

especially in wastewater treatment plants. Most often, these methods are use as a polishing step to

further remove compounds that escape the classical methods of treatment. These methods include:

Air Ionization

The use of UV

Advanced Oxidation Processes

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5.1.1. Air Ionization

This contributes significantly to the reduction of airborne microbial, neutralization of odor, and

specific volatile organic pollutants. Basically, it involves the formation of reactive air ions such as O2.-,

O.-, O3.- by either using photons, nuclear or electronic ionization systems in the presence of oxygen.

These species undergoes a series of chain reactions with the pollutants involves with a final product

been CO2 and H2O for VOCs [15].

CxHy + (x + y/4)O2 → xCO2 + (y/2)H2O

5.1.2. Using UV light

Ultraviolet irradiations of the right wavelength use to destroy volatile organic compounds should

have sufficient energy (photons) to excite molecules (M) to a higher electronic state which makes

them unstable. The transfer energy cause chemical reactions to take place. Different molecules

absorbed ultra violet photons to different extents depending on the functionality, structure and/or

orientation of the molecule. This leads either to the activation, excitation or decomposition of the

special involve.

M(g) + UV M+(g) + e-

In order for the right amount of UV energy to oxidize the functional majority of organic compounds,

the type of UV device and it position (cross sectional width and/or height) plays an important role.

The figure below shows the region of absorption of UV light by different functional groups. High

irradiation doses will be require if trace concentrations of organic pollutants are present which will

lower the efficiency of the photochemical reaction.

Dust and other particles (oil) will tend to absorbed the UV light and convert it to heat. Therefore, for

effective utilization of the UV light for air cleaning, it should be free of dust particles. Filtration or

absorption of the air to be treated is therefore recommended prior to the use of UV.

The aging of the UV lamp is also an important factor to be considered. This is because intensity

emitted by UV lamps decreases over a period of time. Therefore UV lamps should be selected based

on end-of-life output.

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Figure 1: UV light wavelength absorption range of different functional groups [16]

Table 3: Functional Groups

A Alkanes H Aldehydes

B Alkenes I Carboxylic Acids

C Alkynes J Arenes

D Imines K Napthalenes

E Nitriles L Phenols

F Thiones M Thiols

G Alcohols N Esters

5.1.3. Advanced Oxidation Processes (AOPs)

These are processes based on the oxidative ability of certain chemical such as ozone, oxygen,

hydrogen peroxide, in combination with UV light. Destruction of the organic compound is achieved

by the direct oxidation of the contaminants with the oxidizers. The main mechanism of AOPs is the

production of the hydroxyl radical (.OH) which is a highly reactive electrophile that attacks organic

chemicals by either

Radical addition

o M + HO• → MOH

Hydrogen abstraction

o M + HO• → M• + H2O

Electron transfer

o Mn + HO• → Mn-1 + OH-

M represents an organic compound [17].

150

170

190

210

230

250

270

290

310

330

350

A B C D E F G H I J K L M N

Functional group

Wavelength (nm)

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These methods have been use extensively for wastewater treatment. The list below shows available

AOPs processes that have been developed and some applied for treatment of contaminants.

Hydrogen peroxide/UV light

Hydrogen peroxide/Ozone

Titanium dioxide/UV light

Ozone/UV light

Ozone/Titanium dioxide

Ozone/Hydrogen peroxide/UV light

Ozone/Hydrogen peroxide/Titanium dioxide

Fenton’s Reaction (Fe2+/H2O2, H2O2/Fe2+/UV)

Catalytic Oxidation

Sonolysis (using ultrasound)

Ozone/Sonolysis [18, 19]

The use of UV light in combination with ozone, hydrogen peroxide and /or titanium dioxide reduces

the residence time and requires UV dosage which is far less than when using UV alone.

UV/Ozone

UV/O3 system, Process Technology Inc (PTI), is the only commercial available system for the

treatment of contaminated air [19]. Ozone with a high extinction coefficient (ε254 nm = 3300 M-1cm-1)

compare to hydrogen peroxide (ε254 nm = 20 M-1cm-1) readily absorbed UV radiation at 254 nm to

produce the hydroxyl radical as illustrated below with hydrogen peroxide as intermediate product.

[18]

O3 + hv O2 + O

O + H2O H2O2 2.OH

The combination of UV light with ozone produces hydroxyl (.OH) radicals which act as a strong

oxidizing agent. The addition of hydrogen peroxide accelerates the production of hydroxyl radicals.

Fenton’s Reaction

A powerful oxidizing medium is created when ferrous iron (catalyst) is combined with hydrogen

peroxide. The mechanism of the reaction is given below:

Fe2+ + H2O2 Fe3+ + -OH + HO.

Fe2+ + HO. Fe3+ + -OH

.OH + RH H2O + R.

R. + Fe3+ Fe2+ + R+ (regeneration step)

The hydroxyl radical is generated via catalytically decomposition of hydrogen peroxide by Fe (III).

Fenton process is highly effective for the production of the hydroxyl radical. However, high

concentration of Fe (III) is needed since for each .OH produced, one molecule of Fe (III) is use. The

use of UV increases the efficiency of the process.

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Catalytic Processes

A number of combinations involving metals oxide or metal ions as catalyst accelerate the production

of hydroxyl radicals. Several authors [9, 10, 11, 12] have demonstrated that catalytic assisted

processes are more efficient in the decomposition of organic pollutants. The disadvantage being the

blockage of the reaction surface (catalytic surface) which will require continues cleaning.

Previous studies on odor reduction shows that the fishy/grassy-smelling aldehydes are reduce by UV

photo catalysis to chalky or sweet smell. This is as a result of the formation of shorter chains of

aldehydes which can further be reduced by increasing the exposure time to UV/H2O2.

UV/Hydrogen Peroxide

UV/H2O2 has been widely used for wastewater treatment [20, 21] and dye removal [22]. Organic molecules are broken down to harmless, non-smelling compounds that eventually escape to the atmosphere. The rate determining step of the milliard reactions that leads to the decomposition of organic molecules is the cleavage of the O-O bond in hydrogen peroxide to generate the hydroxyl radical. H2O2 + light energy (UV) .OH + .OH The number of malodor compounds decomposed depends of the amount of hydroxyl radical

produce. The higher the concentrations of hydrogen peroxide, the higher the amount of hydroxyl

radicals produced. Therefore more targeted compounds will be destroyed. The concentration of

hydrogen peroxide is limited by the side reactions that take place. The ∙O2H radical produced is not

active and will slow down the oxidation process [17].

.OH + H2O2 H2O + HO2.

HO2. + H2O2 H2O + .OH + O2

2HO. → H2O2 2ΗΟ2

. → H2O2 + Ο2 HO. + ΗΟ2

. → H2O + Ο2 The allowed concentration of hydrogen peroxide in water as set by European Commission of

Normalization is 17mg/L.

Hydrogen peroxide has poor UV absorption characteristics. Thus specific reactor design is require in

order not to waste the energy from the UV light source. At least 70 % of the energy from the UV

radiation should be absorbed by the hydrogen peroxide molecule. The figure below shows how the

absorptive character of hydrogen peroxide depends on wavelength and temperature.

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Figure 2: Temperature dependence of the absorption of hydrogen peroxide [23, 24] The require UV dose differs depending on the targeted contaminant to be treated and the degree of odour removal to be achieve [25]. UV lamps with lower wavelength increase the absorptivity of H2O2.

6. Analytical Methods Used

The fundamental principle to the measurement of odor concentration is the odor detection threshold. For the human sensory organ to perceive an odorant, its concentration should be above it threshold value. Four sensory parameters are usually recognized by environmentalist

Detectability (Threshold concentration) Intensity Character Hedonic

A sample of exhaust air from frying contains a mixture of odorous compounds generally at low concentrations [26]. To analyze the sample, the composition and concentration of the mixture must be known. Different analytical methods have been use for the identification of odorants.

6.1. Gas Chromatography Olfactometry (GC-Olfactometry)

GC – Olfactometry is a technique that uses humans as detectors to access odor activity in an air

stream. The GC separates each compound in a mixture based on their shape, polarity, partial charge

and/or molecular mass. The results which can either be expressed as a Charm chromatogram, an

odor spectrum chromatogram or odor activity value (OAV) gives both the qualitative and quantitative

analysis of the various odorants found in the mixture [27].

The actual value of odour concentration determined by panelists depends on several factors such as

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The experimental method use

The sex and age of the members of the panel

Experience of the panelists

Medical conditions of the panelists

Four different methods of collection and processing of GC-O data in order to estimate the sensory

contribution of an odorant have been exploited:

Dilution Analysis: This is based on stepwise dilution to the threshold value and sniffing of

particular odour. Both the CharmAnalysis and aroma extraction dilution analysis (AEDA) are

example of odour detections based on this principle. A ratio of the concentration of the

odour active compound to the threshold values (aroma value or OAV) is obtained from such

analysis.

Detection frequency method: A panel of 6-12 persons perceived odour active compounds as

they are eluted from the column.

Posterior intensity method: Odour intensity is measured after a peak has been eluted from a

column.

Time-intensity method.

Ref: Saskia M. van Ruth, Method of Gas Chromatography-Olfactometry: A Review, J.

Biomolecular Engineering, 2001, Vol. 17, 4-5, pp. 121-128

6.2 Dräger Tubes

These tubes are design to change colour when a gaseous substance is absorbed on the material in

the tubes. Different tubes are available depending on the substance to be detected:

Ozone greenish blue to yellow

Acrolein: use for the detection of double bonds red to yellow

Formaldehydes white to yellow

The number of strokes determines the concentration in ppm of the substance in question with an

error margin of 15 %.

7. Experimentation

The procedures used to prepare the samples for the experiment were simple dilution from the stock

solution to the require concentrations. The concentration used depends on the threshold value of

the substance in question and the level at which the substance pose problems to the atmosphere.

Stock solution of 2,4-decadienal (>90 % purity), Hexanal (> 98 % purity), furfural (>98 % purity), 2,5-

dimethylpyrazine were provided by the organic lab at KTH.

The photochemical reactor consists of six parallel low pressure mercury lamps of length 77.5 cm with

a total output of 216 W (36 W per lamp). The quartz tubes lamps were enclosed in a rectangular steel

metal material of total volume 9 liters (76 m * 20 m * 6 m). The lamps emit UV light of wavelength

253.7 nm and 365 nm. Ozone was generated as a result of the emission of the light rays by the UV

lamps. The ozone dräger tubes were use to determine the concentration of ozone in the following

cases:

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All UV lamps on in the reactor

All UV lamps off in the reactor and

The first three UV lamps on

1 mL – 1.5 mL of the sample was dissolved in a 4000 mL boiler containing distilled water. A 2000 W

heater was used to vaporize water/sample mixture into the system with a flow of 3.2 l/h. The water

was in order to maintain the humidity at 600C. The system was operated in a fume cupboard at a

typical temperature range of 25oC – 80oC and at atmospheric pressure. Air flow rate of 400 l/min was

provided by a warm air pistol. The result of flow rate and the number of lamps use (energy dose)

were tested.

1,5 g/4 L solution of hydrogen peroxide was added to the 2000 W boiler together with the samples.

Analytical Method Used: Samples of the odorants after the UV lamps were absorbed onto Tenax

fibers at a gas flow rate of 22 l/h for 15 minutes. The absorbed gas samples were later eluted and

extracted from the Tenax using hexane as an internal standard. The GC/MS instrument was provided

by the Organic Chemistry Lab at KTH. The GC instrument consists of a polar DB Wax column with the

following specification: length 30 m; I.D. 0.25 mm; film (stationary phase) 0.25μm. The MS

equipment was Finnigan SSQ 7000.

Using pure hexane as the experiment control for the GC analysis, separate peaks of compounds in

relation to the chemical nature and their size were identified. The amount of a particular compound

can be calculated from the area under the corresponding peak.

8. Results and Discussion

The tables below shows the extent of destruction of the various selected compounds used for in

this work.

Figure 4: 2,4-decadienal Figure 5: Hexanal

O

OH

Figure 6: Furfural figure 7: 2,5- dimethylpyrazine

Table 4: Percent Odour Reduction with different UV Dosage

0 lamp 3 lamps 6 lamps

Ozone Dosage - 2 mg/m3 50 mg/m3

2,4-decadienal 375 mg/L 100% reduction 100% reduction

Hexanal 375 mg/L 66% reduction 86% reduction

Furfural 250 mg/L - -

2,5- dimethylpyrazine 250 mg/L 31% reduction 60% reduction

CH3 O CH3 O

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A) 2,4 - decadienal B) 2,4 - decadienal

C) Hexanal D) Hexanal

E) 2,5- dimethylpyrazine F) 2,5 - dimethylpyrazine

Inlet (0 lamps) Outlet (UV)

Figure 8: GC/MS Curves with UV

RT: 0,00 - 54,02

0 5 10 15 20 25 30 35 40 45 50

Time (min)

0

10

20

30

40

50

60

70

80

90

100

Re

lative

Ab

un

da

nce

11,39

5,51

3,36

12,38

23,57

53,9852,185,95 14,90 48,1915,83

7,89 40,1639,10 42,2717,21 44,4030,9722,54 23,76

NL:3,97E5

TIC MS Test 11

RT: 0,00 - 54,01

0 5 10 15 20 25 30 35 40 45 50

Time (min)

0

10

20

30

40

50

60

70

80

90

100

Re

lative

Ab

un

da

nce

3,31

3,51

3,96

4,25

4,35

4,72

5,34

6,61

50,556,71

7,458,79 49,70 51,0619,07 45,81

19,6511,50 26,05 44,7513,22 42,8139,8026,6323,97 34,1531,35

NL:2,83E5

TIC MS Test 2

RT: 0,00 - 54,02

0 5 10 15 20 25 30 35 40 45 50

Time (min)

0

10

20

30

40

50

60

70

80

90

100

Re

lative

Ab

un

da

nce

11,49

14,95

5,5524,283,41

48,2423,60 32,2429,46 34,865,82 9,60 53,0037,3415,81 42,42

NL:9,96E6

TIC MS Test 8

RT: 0,00 - 54,02

0 5 10 15 20 25 30 35 40 45 50

Time (min)

0

10

20

30

40

50

60

70

80

90

100

Re

lative

Ab

un

da

nce

3,49

3,29

11,393,61

3,81

12,38

5,50

13,44 32,99

53,8730,9752,335,65

15,786,83 48,27

41,2716,65 38,51 42,4328,8319,75 36,4620,05 24,27

NL:2,14E5

TIC MS Test 12

RT: 0,00 - 54,02

0 5 10 15 20 25 30 35 40 45 50

Time (min)

0

10

20

30

40

50

60

70

80

90

100

Re

lative

Ab

un

da

nce

11,49

24,24

5,53

9,573,69 21,78 48,1018,2312,40 35,806,37 41,21 53,9830,9924,91 43,33

NL:1,46E7

TIC MS Test 7

RT: 0,00 - 54,02

0 5 10 15 20 25 30 35 40 45 50

Time (min)

0

10

20

30

40

50

60

70

80

90

100

Re

lative

Ab

un

da

nce

11,39

5,51

3,36

12,38

23,57

53,9852,185,95 14,90 48,1915,83

7,89 40,1639,10 42,2717,21 44,4030,9722,54 23,76

NL:3,97E5

TIC MS Test 11

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Table 5: Percent Odour Reduction with H2O2 and different UV Dosage

UV Dosage 0 lamp 3 lamps 6 lamps

Ozone Dosage - 2 mg/m3 50 mg/m3

H2O2 Concentration 1,5 g/4 l solution 1,5 g/4l solution 1,5 g/4l solution

2,4-decadienal 375 mg/l 100% reduction 100% reduction

Hexanal 375 mg/l 86% reduction 96% reduction

Furfural 250 mg/l - -

2,5- dimethylpyrazine 250 mg/l 57% reduction 60% reduction

a) 2,4 - decadienal b) 2,4 - decadienal

c) Hexanal d) Hexanal

e) 2,5 - dimethylpyrazine f) 2,5 – dimethylpyrazine

RT: 0,00 - 54,01

0 5 10 15 20 25 30 35 40 45 50

Time (min)

0

10

20

30

40

50

60

70

80

90

100

Re

lativ

e A

bu

nd

an

ce

44,85

44,51

48,72

42,6114,583,36

3,66 50,5726,73 38,4215,74 37,904,33 33,42 50,9718,216,56 13,81 29,9924,27 35,48

NL:1,05E6

TIC MS Test 1

RT: 0,00 - 54,02

0 5 10 15 20 25 30 35 40 45 50

Time (min)

0

10

20

30

40

50

60

70

80

90

100

Re

lativ

e A

bu

nd

an

ce

11,45

3,41 24,293,7014,94 48,33 54,0015,85 31,029,59 19,82 36,88 41,3328,90 42,99

NL:3,98E6

TIC MS Test 9

RT: 0,00 - 54,02

0 5 10 15 20 25 30 35 40 45 50

Time (min)

0

10

20

30

40

50

60

70

80

90

100

Re

lativ

e A

bu

nd

an

ce

5,51

3,27

32,96

30,92

24,24

12,36

11,3748,11

36,805,979,55 13,42

28,8241,17 53,3716,64 43,3417,21

26,6036,00 38,2821,82

NL:4,81E5

TIC MS Test 10

RT: 0,00 - 54,02

0 5 10 15 20 25 30 35 40 45 50

Time (min)

0

10

20

30

40

50

60

70

80

90

100

Re

lative

Ab

un

da

nce

11,39

5,51

3,36

12,38

23,57

53,9852,185,95 14,90 48,1915,83

7,89 40,1639,10 42,2717,21 44,4030,9722,54 23,76

NL:3,97E5

TIC MS Test 11

RT: 0,00 - 54,02

0 5 10 15 20 25 30 35 40 45 50

Time (min)

0

10

20

30

40

50

60

70

80

90

100

Re

lative

Ab

un

da

nce

11,39

5,51

3,36

12,38

23,57

53,9852,185,95 14,90 48,1915,83

7,89 40,1639,10 42,2717,21 44,4030,9722,54 23,76

NL:3,97E5

TIC MS Test 11

RT: 0,00 - 54,02

0 5 10 15 20 25 30 35 40 45 50

Time (min)

0

10

20

30

40

50

60

70

80

90

100

Re

lative

Ab

un

da

nce

11,49

24,24

5,53

9,573,69 21,78 48,1018,2312,40 35,806,37 41,21 53,9830,9924,91 43,33

NL:1,46E7

TIC MS Test 7

17

Figure 9: GC/MS Curves with UV and H2O2

Destruction of 2,4-decadienal was complete (100%) as observed in the GC/MS diagram. This is

probably due to the fact that this compound contains alkenic double (C=C) bonds which is highly

reactive with the hydroxyl radical produced inside the reactor. Both the ozone/UV and

ozone/UV/H2O2 were efficient in degrading 2,4-decandienal.

The combination of ozone and UV light gave 66% degradation of Hexanal. The degradation increases

to 86% when the UV dosage was double. Further degradation (96%) was achieved by the

introduction of hydrogen peroxide to the mixture. The combination of ozone, UV and hydrogen

peroxide, produces the hydroxyl radical which increases the rate of the reaction.

The extents of degradation of furfural and 2,5-dimethylpyrazine were not as efficient as compared to

2,4-decadienal and Hexanal. This is probably due to the ring structures of these compounds.

9. Conclusion

Using a combination of UV/Ozone and UV/Ozone/H2O2, the destruction of 2,4-decadienal was very

efficient (100%). This results to the removal of the fatty smell. UV/Ozone gave Hexanal removal of

66%. Significant increase in the destruction of Hexanal was achieved when the dosage of UV light was

increased. Increase in the destruction rate of Hexanal was also noticed when H2O2 was introduced

into the solution. The degradation of furfural (35%) and 2,5- dimethylpyrazine (27%) also show

marked increase when the number of lamps were increased and when hydrogen peroxide was used.

During the experiment, some problems were encountered. In order to achieved higher degradation

efficiency for Hexanal, furfural, 2,5- dimethylpyrazine, UV lamps of higher dosage capacity are

recommended. In addition to this, an external ozone generation in combination with the UV lamps

should be put to consideration.

18

References

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aroma value from shallow-fried beef, Journal of Agricultural food chemistry, 1994, Vol. 42,

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7. Monoj K. Gupta, Frying Oils, Bailey’s Industrial Oil and Fat Products, 6th Ed., Vol. 6, 2005, John

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by UV/H2O2, Journal of Water Supply: Research and Technology-Aqua, 2009

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www.atmosphere.mpg.de/spectral-atlas-mainz

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Chemistry of Fried Food Flavour by Kathleen Warner and William E. Neff, 2001

20

29. ScienceLab.com, Chemical and Laboratory Equipment, Material Safety Data Sheet, Hydrogen

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21

Appendix

Appendix 1

Peak List A (2,4 – decadienal inlet)

RT Start RT End RT Area %Area Height %Height 5,51 5,34 5,70 1037562,827 25,77 230981,301 26,17 Hexanal 11,39 11,34 11,57 1329505,495 33,02 360827,186 40,88 2,5-dimethylpyrazine 12,38 12,30 12,58 433010,918 10,76 117946,945 13,36 A ketone 13,42 13,36 13,59 168350,959 4,18 30912,596 3,50 Nitro compound 15,83 15,73 16,03 340657,718 8,46 33704,744 3,82 23,57 23,50 23,74 333662,840 8,29 75079,053 8,51 2,4-decadienal 48,19 48,09 48,49 383189,387 9,52 33260,413 3,77 n-hexadecanoic acid

Peak List B (2,4 – decadienal outlet with 3 lamps)

RT Start RT End RT Area %Area Height %Height 6,61 6,52 6,77 164957,650 17,36 26164,612 21,94 ketone 19,07 18,94 19,22 149953,483 15,78 32010,961 26,84 acetic acid 26,05 26,00 26,24 161318,917 16,98 24120,369 20,22 50,55 50,45 50,92 473923,373 49,88 36970,922 31,00 n-hexadecanoic acid

Peak List b (2,4 – decadienal outlet with 6 lamps)

RT Start RT End RT Area %Area Height %Height 6,56 6,40 6,64 197373,259 0,42 25992,553 1,42 pentyl hydroperoxide 14,58 14,43 14,78 568628,799 1,20 130549,777 7,14 ketone 15,74 15,67 15,91 318080,119 0,67 64014,665 3,50 heptyl hydroperoxide 18,21 18,10 18,47 213917,088 0,45 33631,634 1,84 24,27 24,10 24,45 351834,492 0,74 31007,888 1,70 26,73 26,64 26,89 350029,709 0,74 79078,777 4,33 pentyl hydroperoxide 33,42 33,24 33,66 395014,676 0,84 52961,777 2,90 acetic acid 38,42 37,68 38,87 2233764,806 4,73 57527,679 3,15 42,61 42,49 43,27 3138588,974 6,64 119423,442 6,54 octadecanoic acid 44,85 44,21 46,30 34511938,722 73,05 1001571,892 54,81 octadecanoic acid 48,72 48,43 49,26 4035914,543 8,54 170668,847 9,34 50,57 50,38 50,99 930005,527 1,97 60917,431 3,33 n-hexadecanoic acid

22

Peak List C (Hexanal inlet)

RT Start RT End RT Area %Area Height %Height 3,69 3,51 3,74 3171064,365 3,23 413904,913 1,75 pentyl hydroperoxide 5,53 5,39 5,58 11256954,410 11,47 3284098,000 13,86 Hexanal 9,57 9,50 9,74 2541393,110 2,59 583551,000 2,46 1-pentanol 11,49 11,34 11,57 63415363,410 64,61 14551240,00 61,43 2,5-dimethylpyrazine 24,24 24,16 24,51 14773040,760 15,05 4546618,000 19,19 Hexanoic acid 48,10 48,09 48,37 2999612,080 3,06 307101,000 1,30 n-hexadecanoic acid

Peak List D (Hexanal outlet with 3 lamps)

RT Start RT End RT Area %Area Height %Height 5,55 5,39 5,76 2504339,818 4,13 442699,267 3,06 hexanal 11,49 11,29 11,64 41756691,260 68,92 9961075,000 68,96 2,5-dimethylpyrazine 14,95 14,84 15,19 12164782,945 20,08 3571820,000 24,73 furfural 24,28 24,23 24,51 1528866,335 2,52 309919,000 2,15 pentanoic, hexanoic acid 48,24 48,02 48,61 2631912,690 4,34 158211,000 1,10 n-hexadecanoic acid

Peak List d (Hexanal outlet with 6 lamps)

RT Start RT End RT Area %Area Height %Height 5,53 5,34 5,77 1451782,919 7,87 138728,828 3,08 Hexanal 11,45 11,34 11,81 14372112,795 77,94 3981339,000 88,50 2,5-dimethylpyrazine 14,94 14,84 15,07 744606,845 4,04 121593,000 2,70 hexanioc acid 24,29 24,23 24,46 711793,299 3,86 179306,112 3,99 Furfural 48,33 48,21 48,61 1160280,910 6,29 77623,042 1,73 n-hexadecanoic acid

Peak List E (2,5 – dimethylpyrazine inlet)

RT Start RT End RT Area %Area Height %Height 5,51 5,34 5,70 1037562,827 25,77 230981,301 26,17 Hexanal 11,39 11,34 11,57 1329505,495 33,02 360827,186 40,88 2,5-dimethylpyrazine 12,38 12,30 12,58 433010,918 10,76 117946,945 13,36 A ketone 13,42 13,36 13,59 168350,959 4,18 30912,596 3,50 Nitro compound 15,83 15,73 16,03 340657,718 8,46 33704,744 3,82 23,57 23,50 23,74 333662,840 8,29 75079,053 8,51 2,4-decadienal 48,19 48,09 48,49 383189,387 9,52 33260,413 3,77 n-hexadecanoic acid

23

Peak List F (2,5 – dimethylpyrazine outlet with 3 lamps)

RT Start RT End RT Area %Area Height %Height 5,50 5,34 5,58 351626,438 10,89 79481,594 11,74 Hexanal 11,39 11,34 11,57 660012,082 20,44 155659,165 23,00 2,5-dimethylpyrazine 12,38 12,23 12,58 438431,676 13,58 125792,024 18,59 A ketone 13,44 13,42 13,66 338446,828 10,48 82615,451 12,21 Nitro compound 15,78 15,68 16,03 258934,115 8,02 34724,288 5,13 28,83 28,78 29,02 146104,019 4,52 27684,687 4,09 alcohol 30,97 30,92 31,22 268476,295 8,31 54883,786 8,11 butanoic acid 32,99 32,89 33,54 481443,545 14,91 88099,447 13,02 alcohol 48,27 48,14 48,44 285413,065 8,84 27879,388 4,12 n-hexadecanoic acid

Peak List B (2,5 – dimethylpyrazine outlet with 6 lamps)

RT Start RT End RT Area %Area Height %Height 5,51 5,40 5,70 1284149,856 13,39 352217,137 17,92 Hexanal 9,55 9,38 9,74 295703,504 3,08 57512,747 2,93 heptyl hydroperoxide 11,37 11,29 11,52 596054,956 6,21 144792,899 7,37 2,5-dimethylpyrazine 12,36 12,23 12,58 513901,481 5,36 169351,476 8,61 acetic acid 13,42 13,31 13,78 489797,029 5,11 70183,243 3,57 nitro compound 24,24 24,11 24,46 838862,281 8,75 222174,932 11,30 Hexanoic acid 26,60 26,36 26,77 249721,779 2,60 37747,106 1,92 2,3-epoxyhexanol 28,82 28,74 29,21 292961,983 3,05 65357,330 3,32 30,92 30,81 31,34 1094052,650 11,41 261907,199 13,32 n-hexanoic acid 32,96 32,89 33,30 1299369,263 13,55 315874,726 16,07 n-decanoic acid 36,80 36,69 37,10 582862,856 6,08 99210,288 5,05 41,17 41,09 41,56 487112,045 5,08 47769,510 2,43 48,11 48,02 48,68 1566789,285 16,34 121796,131 6,20 n-hexadecanoic acid

24

Appendix 2

Table 6: Some Selected Tested Compounds Using UV Light with TiO2 Catalyst

Compound Tested Trimethylene sulfide propylene sulfide thiophene methyl disulfide

Gas flow rate 262 mL/min 409 mL/min 324 mL/min 474 mL/min

Organic Loading 61 ppm 86 ppm 54 ppm 34 ppm

UV Wavelength 365 nm 365 nm 365 nm 365 nm

UV Intensity 4,5 mW/cm2 4,5 mW/cm2 4,5 mW/cm2 4,5 mW/cm2

Residence Time 1,81 min 0,99 min 1,30 min 0,85 min

% Removal 99 % 99 % 99 % 99 %

Test Conditions 23 % RH 21 % O2 23 % RH 21 % O2 23 % RH 21 % O2 23 % RH 21 % O2

UV irradiation time: 30 minutes Treatment time: 15 minutes TiO2 loading: 9,5*10-4 g/cm2 (14) Table 7: Some Selected Tested Compounds Using UV Light with H2O2

UV dosage: 0 – 2500 mJ/cm2 1 - 30 minutes UV irradiation time [21]

The experimentation was carried out using Rayonet RPR-100 with quartz reactors of light intensity

7.2 mW/cm. The specifications of this model include:

Compact 0.4064 m high and 0.3048 m square

Barrel reactor 0.254 m in diameter and 0.381 m deep

Units weigh 11.34 Kg

Fans

110/277 V and 50/60 cycles

Total consumption 400 watts with watts of 253.7 nm UV = 35, and 1.65 * 106

photons/sec/cm3

Ref: Model RPR-100,

http://www.rayonet.org/word%20pages/Microsoft%20Word%20-%20RPR-100.pdf

Compound Tested Nonadienal Heptadienal Decadienal Hexanal

Odor Threshold 80 ng/L (0,00008 ppm)

25,000 ng/L (0,0025 ppm)

300 ng/L (0,003 ppm)

4,500 ng/L (0,0045 ppm)

Organic Loading 6.5 μg/L 55 μg/L 14 μg/L 90 μg/L

UV Wavelength 253,7 nm 253,7 nm 253,7 nm 253,7 nm

UV Intensity 7.2 mW/cm2 7.2 mW/cm2 7.2 mW/cm2 7.2 mW/cm2

Hydrogen Peroxide Dosage

6 mg/L 6 mg/L 6 mg/L 6 mg/L

UV Dosage 864 mJ/cm2 4320 mJ/cm2 2160 mJ/cm2 2160 mJ/cm2

Residence Time 1 – 10 mins 1 - 10 mins 1 - 10 mins 1 - 10 mins

% Removal 97 % 100 % 86 % 89 %

25

Appendix 3

Odorants

French fries odorants listed by Wagner & Grosch

(1998), without relative order. [5]

Sulfur compounds

Methanethiol (Fig 10).

Aldehydes (E, Z)-2, 4-decadienal

(E, E)-2, 4-decadienal (Fig 11)

trans-4, 5-epoxy-(E)-2-decenal

methylpropanal (Fig 12)

2- and 3-methylbutanal

benzaldehyde

Pyrazines

2-ethyl-3, 5-dimethylpyrazine (Fig 13)

3-ethyl-2, 5-dimethylpyrazine

2,3-diethyl-5-methylpyrazine

3-isobutyl-2-methoxypyrazine

Ketones

4-hydroxy-2,5-dimethyl-3(2H)-furanone.

Alcohols

Pentan-1-ol

Fig 10. methanethiol

Fiure 11: (E,E)-2,4-decadienal

Fig 12. methylpropanal

Potato chip odorants compiled (secondary

source) by Rappert & Müller (2005). [4]

Sulfur compounds

Methanethiol.

Aldehydes

(E, Z)-2, 4-decadienal

(E, E)-2, 4-decadienal

methylpropanal

2-methylbutanal

3-methylbutanal

(Z)-2-nonanal

(E)-2-nonanal

Methional (Fig 10)

Hexanal

Phenyl acetaldehyde (Fig 11).

Hept-2-enal

Pyrazines

2-ethyl-3, 5-dimethylpyrazine

2-ethyl-3, 6-dimethylpyrazine

3-ethyl-2, 5-dimethylpyrazine

2,3-diethyl-5-methylpyrazine

2-ethyl-3-ethyl-5-methylpyrazine.

Ketones

1-octen-3-one

1-penten-3-one.

Fig 10. methional

Fig 11. Phenyl acetaldehyde

26

Fig 13. 2-ethyl-3, 5-dimethylpyrazine

“Negative” flavor odors from degradation of oleic acid (into triolein) and linoleic acid (into trilinolein),

listed in work by Warner and Neff (2001). [28]

Triolein 190°C

Strong “fruity, plastic”

Octanal (Fig 14)

Heptanal

(E)-2-decenal

(E)-2-undecenal.

Weak to moderate “deep fried”

(E, E)-2, 4-decadienal

(E, E)-2, 4-nonadienal

(E, E)-2, 4-undecadienal

(E)-2-octenal.

Fig 14. Octanal

Trilinolein 190°C

Strong “grassy, fruity”

hexanal

2-pentyl furan (Fig 16)

Pentanal.

Moderate “deep fried”

(E, E)-2, 4-decadienal

(E, Z/Z, E)-2,4-decadienal (Fig 15)

(E, E)-2, 4-nonadienal

(E)-2-octenal

(E)-2-heptenal

(E, E)-2, 4-octadienal.

Fig 15. 2,4 Decadienal

Fig 16. 2-pentyl furan

27

Appendix 4

Table 8: Physical and Chemical Properties of 30 % Hydrogen peroxide [29, 30]

Property

Physical State and Appearance Liquid

Molecular Weight 34.0147 g/mol

Density 1.463 g/cm3

Odor Odorless

Taste Slightly acid, bitter

Color Colorless

pH 11.9

Vapour Pressure 3.1 KPa at 200C

Solubility Soluble in cold water and diethyl ether

Boiling Point 1080C

Oxidation Potential 1.8 V

O-O Bond Energy 139 KJ/mol

Corrosivity Non-corrosive

Hazard Severed skin irritation and carcinogenic

Figure 12: Structure of Hydrogen Peroxide