Impact of Ball-Milling Pretreatment on Pyrolysis PAPER Impact of Ball-Milling Pretreatment on...

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Transcript of Impact of Ball-Milling Pretreatment on Pyrolysis PAPER Impact of Ball-Milling Pretreatment on...

  • ORIGINAL PAPER

    Impact of Ball-Milling Pretreatment on Pyrolysis Behaviorand Kinetics of Crystalline Cellulose

    Amir Sada Khan1,2 Zakaria Man1 Mohammad Azmi Bustam1

    Chong Fai Kait4 Muhammad Irfan Khan1 Nawshad Muhammad3

    Asma Nasrullah4 Zahoor Ullah1 Pervaiz Ahmad5

    Received: 22 July 2015 / Accepted: 8 December 2015 / Published online: 30 December 2015

    Springer Science+Business Media Dordrecht 2015

    Abstract Effect of ball-milling pretreatment on pyrolysis

    characteristics of cellulose was studied by thermogravi-

    metric analysis (TGA) at four different heating rates; 5, 10,

    20, and 40 K/min. Variation in the thermal stability and

    activation energy of cellulose with ball-milling were cal-

    culated by TGA Kinetics using Kissinger, Kissinger

    AkahiraSunose, FlynnWallOzawa and Starink model

    free methods. Results demonstrated that ball-milling

    reduced the thermal stability and activation energy of

    cellulose. The original and ball-milled cellulose were

    thoroughly characterized by Fourier-transform infrared

    spectroscopy, X-ray diffraction, and Scanning electron

    microscopy. X-ray diffraction analysis revealed that ball-

    milling decreased the crystallinity of cellulose from 93 to

    51 %. The results suggested that ball-milling pretreatment

    led to effective disruption of crystalline cellulose to

    amorphous cellulose. It is, therefore, concluded that the

    ball-milled cellulose can easily become a useful source of

    chemicals and energy than crystalline cellulose.

    Keywords Cellulose Ball-milling Crystallinity index Thermokinetics Activation energy

    Abbreviations

    TGA Thermogravimetric analysis

    KAS KissingerAkahiraSunose

    FTIR Fourier-transform infrared spectroscopy

    XRD X-ray diffraction

    NMR Nuclear magnetic resonance spectroscopy

    CV Calorific values

    CC Crystalline cellulose

    BMC Ball-milled cellulose

    b Heating ratesTmax Temperature of the peak

    Ea Activation energy

    cm-1 Wavenumber

    CI Crystallinity index

    a Conversion factorn Reaction order

    A Pre-exponential factor

    R Ideal gas constant

    Introduction

    Industrial revolution is largely dependent on energy

    resources, and existing natural energy resources such as

    natural gas, oils, and coal are exhaustible. Besides the rapid

    consumption of fossil fuel, these conventional energy

    Electronic supplementary material The online version of thisarticle (doi:10.1007/s12649-015-9460-6) contains supplementarymaterial, which is available to authorized users.

    & Amir Sada Khanaamirsada_khan@yahoo.com

    & Nawshad Muhammadnawshadchemist@yahoo.com

    1 Centre of Research in Ionic Liquid, Department of Chemical

    Engineering, Universiti Teknologi PETRONAS,

    31750 Tronoh, Malaysia

    2 Department of Chemistry, University of Science and

    Technology, Bannu 28100, Khyber Pakhtunkhwa, Pakistan

    3 Interdisciplinary Research Centre in Biomedical Materials,

    COMSATS Institute of Information Technology, Lahore,

    Pakistan

    4 Fundamental and Applied Science Department, Universiti

    Teknologi PETRONAS (UTP), 31750 Tronoh, Perak,

    Malaysia

    5 Department of Physics, Faculty of Science, University of

    Malaya, 50603 Kuala Lumpur, Malaysia

    123

    Waste Biomass Valor (2016) 7:571581

    DOI 10.1007/s12649-015-9460-6

    http://dx.doi.org/10.1007/s12649-015-9460-6http://crossmark.crossref.org/dialog/?doi=10.1007/s12649-015-9460-6&domain=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1007/s12649-015-9460-6&domain=pdf

  • resources also threaten our ecosystem by emitting haz-

    ardous gases during their combustion. Thus, the demand

    and search for alternative energy resources are important to

    meet vast energy requirements [1, 2]. Recently, lignocel-

    lulosic biomass is mainly composed of cellulose, has been

    introduced as an alternative to fossil fuel because of its

    abundance, environmental friendliness, and sustainability.

    Therefore, cellulose which is most abundant component of

    biomass can contribute to energy and chemical demands in

    the future [36].

    Cellulose is the homo-polymer consists of glucopyra-

    nose repeating unit. The repeating units are linking toge-

    ther by b-(1?4) glycosidic bonds formed between C-1 andC-4 of the adjacent glucose. The chemical formula of

    cellulose is (C6H10O5) n and structurally it consists of long

    straight chains without branching. The long-chains are

    interlinked through hydrogen bonding (results from inter-

    action of hydrogen atom of one chain with hydroxide group

    of another chain) and van der Waals forces, which cause

    the cellulose to be packed into microfibrils [5, 7]. These

    close packing of chains via intermolecular and

    intramolecular hydrogen bonding limit the solubility and

    conversion/hydrolysis of cellulose into energy and chemi-

    cals [8]. Cellulose is containing both crystalline and

    amorphous components. The amorphous component is

    more important than the crystalline region because of its

    easy degradation and conversion into chemicals and fuels.

    The higher reactivity of amorphous cellulose than crys-

    talline cellulose (CC) can be attributed to the lower cohe-

    sive energy density of the former than the latter [4].

    In the last few years, various chemical and physical

    methods have been applied to decrease the crystallinity

    and molecular weight of cellulose for efficient conversion/

    hydrolysis to glucose and others chemicals. In chemical

    methods, strong acids [912] and ionic liquids [1315] are

    usually used to decrease the crystallinity of cellulose and

    ultimately its hydrolysis to chemicals. Acid and ionic

    liquid treatments decrease the crystallinity and facilitate

    the conversion of cellulose. However, the applications of

    such treatments are limited by the high cost, toxicity,

    corrosive nature, and environmental pollution of ionic

    liquids. Physical treatments are more environmental

    friendly than chemical treatments because the former does

    not need any solvent. Ball-milling is a powerful physical

    technique used to modify the structure of cellulose [16

    18].

    Pyrolysis is one of the most efficient methods in con-

    verting cellulose into valuable chemicals and fuels. It is

    thermal process and conducted in the absence of oxygen.

    During pyrolysis, the molecules of cellulose are broken

    down to low molecular weight gases (volatiles), liquids

    (tars) and solid char. The volatile gases and liquids are both

    very important from energy point of view because of their

    high calorific value (CV). Thermogravimetric analysis

    (TGA) is a rapid and effective quantitative method used to

    understand the pyrolysis under nonisothermal and isother-

    mal conditions, and to determine the kinetic parameters of

    the thermal decomposition of cellulose. These kinetic

    parameters include activation energy (Ea), reaction order

    (n), and pre-exponential factor (A). The activation energy is

    a dominant factor that gives considerable information

    about cellulose reactivity. Determining kinetic parameters

    via TGA is essential to design and establish efficient, safe,

    and reasonable processes. Kissinger [19], Ozawa [20],

    FlynnWall [21], and Friedman [22] proposed model free

    kinetics methods. The model-free methods are extensively

    used because of their simplicity and low error risk. The

    model free kinetics methods are used to evaluate simple

    and complex kinetic reactions without prior knowledge of

    the reaction mechanism [18]. These all models are based

    on the following general expression;

    dadt

    Ae EaRT f a 1

    To the best of our knowledge, there is a very little

    information available on the effect of mechanical treatment

    on the pyrolysis process of cellulose. This study is the first

    systematic study to investigate the effect of a mechanical

    treatment (i.e., ball-milling) on the kinetics of thermal

    decomposition of cellulose. Kinetic parameters were

    determined by using Kissinger, KissingerAkahiraSunose

    (KAS), FlynnWallOzawa (FWO) and Starink methods.

    The effect of ball-milling on the crystallinity and mor-

    phology of cellulose was thoroughly characterized by

    Fourier-transform infrared spectroscopy (FTIR), X-ray

    diffraction (XRD, and scanning electron microscopy

    (SEM). The calorific values (CVs) of the cellulose sample

    before and after ball-milling were determined. Investigat-

    ing the effect of ball-milling on the crystallinity and ther-

    mal decomposition kinetics of cellulose using various

    model free methods is a significant contribution.

    Experimental

    Ball-Milling of Cellulose

    The crystalline cellulose (CC) was supplied by Merck

    Malaysia. The cellulose was milled using planetary ball

    mill (Fristch, Germany, S. No: 05.6000/00594) for 2 h with

    a milling frequency 600 rpm. A 20 g cellulose sample was

    placed in a zirconium oxide bowl (500 mL) with 25 zir-

    conium oxide balls (1 cm diameter) during milling. To

    prevent overheating of cellulose, 5 min of interval was

    provided between every 30 min of milling. This ball-milled

    cellulose (BMC) was used for further analysis.

    572 Waste Biomass Valor (2016) 7:571581

    123

  • Characterizations of Cellulose

    The FTIR spectra of crystalline and ball-milled cellulose

    were recorded using FTIR spectros