Bioresource Technology 237 (2017) 57–63

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Bioresource Technology

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Pyrolysis of agricultural biomass residues: Comparative study of corncob, wheat straw, rice straw and rice husk

http://dx.doi.org/10.1016/j.biortech.2017.02.0460960-8524/� 2017 Elsevier Ltd. All rights reserved.

⇑ Corresponding author at: Thermo-Catalytic Processes Area (TPA), Bio-FuelsDivision (BFD), CSIR-Indian Institute of Petroleum (IIP), Dehradun 248005, Uttarak-hand, India.

E-mail addresses: tbhaskar@iip.res.in, thalladab@yahoo.com (T. Bhaskar).

Bijoy Biswas a, Nidhi Pandey a, Yashasvi Bisht a, Rawel Singh c, Jitendra Kumar a, Thallada Bhaskar a,b,⇑a Thermo-Catalytic Processes Area (TPA), Bio-Fuels Division (BFD), CSIR-Indian Institute of Petroleum (IIP), Dehradun 248005, Uttarakhand, IndiabAcademy of Scientific and Innovative Research (AcSIR), New Delhi, IndiacDepartment of Chemistry, A.S. College, Samrala Road, Khanna 141402, India

h i g h l i g h t s

� Pyrolysis behaviors of four agricultures residue were compared.� Higher bio-oil yield obtained (47.3 wt%) for corn cob.� Optimum temperature 450 �C for CC & RH and 400 �C for RS & WS.� Organic carbon conversion high in CC and RH than WS and RS.

a r t i c l e i n f o

Article history:Received 31 December 2016Received in revised form 9 February 2017Accepted 12 February 2017Available online 24 February 2017

Keywords:Slow pyrolysisAgriculture biomassFixed bedBio-oilBio-char

a b s t r a c t

Pyrolysis studies on conventional biomass were carried out in fixed bed reactor at different temperatures300, 350, 400 and 450 �C. Agricultural residues such as corn cob, wheat straw, rice straw and rice huskshowed that the optimum temperatures for these residues are 450, 400, 400 and 450 �C respectively.The maximum bio-oil yield in case of corn cob, wheat straw, rice straw and rice husk are 47.3, 36.7,28.4 and 38.1 wt% respectively. The effects of pyrolysis temperature and biomass type on the yield andcomposition of pyrolysis products were investigated. All bio-oils contents were mainly composed of oxy-genated hydrocarbons. The higher area percentages of phenolic compounds were observed in the corncob bio-oil than other bio-oils. From FT-IR and 1H NMR spectra showed a high percentage of aliphaticfunctional groups for all bio-oils and distribution of products is different due to differences in the com-position of agricultural biomass.

� 2017 Elsevier Ltd. All rights reserved.

1. Introduction

Biomass has been considered as a potential and renewablesource of energy that can be used for the production of variety ofchemicals and materials (Bridgewater and Grassi, 1991; Chumand Overend, 2001; Antal, 1983). The advantages of biomass overconventional fossil fuels are their low sulfur and nitrogen contentsand no net emissions of CO2 to the atmosphere (Bridgewater andGrassi, 1991; Probstein and Hicks, 1982). Biomass resources covera wide range of materials such as forest residues, energy crops,organic wastes, agricultural residues, etc. Agricultural waste, areadily available biomass, is produced annually worldwide and isvastly underutilized (Williams and Nugranad, 2000).

Agricultural biomass residues are composed of cellulose, hemi-cellulose and lignin and possess a high-energy content(Meshitsuka and Isogai, 1996; Worasuwannarak et al., 2007). Agri-cultural residues such as rice straw and rice husks are abundant inrice growing countries such as Brunei, China and India (Gidde andJivani, 2007) Agriculture residue such as corn cob and wheat straware also being a viable feed for bio-fuels production.

In developing countries, the large quantities of agricultural resi-dues are currently utilised either as raw material for paper indus-try, or as animal feed sources. But generally since the collectionand disposal of these residues are becoming more difficult andexpensive, it is left unused as waste material or simply burned inthe fields, thereby creating significant environmental problems.The conversion methods may be physical, biological, chemical orthermal to give a solid, liquid or gaseous fuel. The most promisingmethod seems to be thermochemical one for the production of bio-oils. Pyrolysis of biomass is one of the most efficient technologiesused to produce biofuels. The process is carried out at elevated

58 B. Biswas et al. / Bioresource Technology 237 (2017) 57–63

temperatures under an inert atmosphere which is maintainedusing either argon or nitrogen gas. The process yields bio-oil, solidresidue, and gaseous products. These products can be used directlyor after processing as fuel (Yin et al., 2013).

Previous work on pyrolysis of corn cob, wheat straw, rice strawand rice husk has been carried out (Balagurumurthy et al., 2015;Park et al., 2014; Pottmaier et al., 2013; Yu et al., 2016; Caoet al., 2004; Ceranic et al., 2016; Shariff et al., 2016). Park et al. usedaround 100 g of rice straw and carried out slow pyrolysis at 300,400, 500, 600 and 700 �C with a heating rate of 10 �C min�1. Almostsame yields of bio-oil and bio-char (39%) have been obtained athigher temperatures above 500 �C. The bio-oil yield slightlydecreased, while the gas yield increased at 700 �C. Rice strawpyrolysis in hydrogen and nitrogen environments has been carriedout by Balagurumurthy et al. and observed maximum bio-oil 31.0%and 12.8% under N2 and H2 atmosphere at 400 �C in both cases. Thehigher amount of bio-oil was observed under the N2 environmentthan H2 environment. Pottmaier et al. carried out slow pyrolysis ofwheat straw and rice straw at 250–900 �C. They observed that slowpyrolysis, in 100 mL�min�1 nitrogen, for RH and WS, at a heatingrate of 50 �C min�1, shows an increase of volatiles release as a func-tion of final pyrolysis temperature for 250, 350, 500, 600, 700,900 �C as follows: 31.5 < 56.7 < 64.1 < 62.6 < 65.9 < 68.1 (wt%) (forwheat straw), 21.3 < 53.4 < 64.6 < 60.9 < 63.9 < 63.4 (wt%) (for ricehusk). Cao et al. has carried out pyrolysis of corn cob and concludedthat the liquid products were approximately 34–40.96 (wt%), thegas products were 27–40.96% (wt%) and the solid products 23.6–31.6 (wt%). There were fewer changes for the yields of these prod-ucts above 600 �C. Shariff et al. were investigated the characteristicof corn cob as a biomass feedstock for slow pyrolysis process andobserved that the weight loss of corn cob feedstock was prominentin the temperature range of 250–350 �C. Two distinct peaks ofderivative thermogravimetric (DTG) curve indicate the difficultyof corn cob feedstock to degrade due to its high fixed carbon con-tent. The overall findings showed that corn cob is suitable to beused as the feedstock for slow pyrolysis because of its high volatilematter and low percentages of nitrogen and sulfur. The main inter-est in pyrolysis process is conversion of biomass to potential fuelssuch as bio-oil and bio-char which can be stored or transportedmuch easier as compared to biomass. In addition, bio-oil obtainedfrom the pyrolysis process can be considered as a source of usefulchemicals and bio-chars can be converted to value added productssuch as activated carbons and potentially can also be used for soilamendment (Meyer et al., 2011).

To the best of our knowledge there is no report on slow pyrol-ysis of agriculture biomass residue and comparisons on productionof bio-oil and bio-char. The focus of this research is to study theeffects of different pyrolysis temperatures (300–450 �C) on theslow pyrolysis of corn cob, wheat straw, rice straw and rice huskto understand comparative studies under identical conditions.The experiments have been carried out at temperatures of 300,350, 400 and 450 �C in nitrogen atmosphere and products suchas bio-oil and bio-char have been obtained. The liquid and solidproducts have been characterized using various analytical tech-niques such as Fourier Transform-Infrared Spectroscopy (FT-IR),Nuclear Magnetic Resonance Spectroscopy (1H NMR), Gas Chro-matography–Mass Spectrometry (GC–MS), Total organic carbon(TOC) and X-ray Diffraction (XRD).

2. Materials and methodology

2.1. Materials

Agriculture biomass residues Corn cob (CC), Wheat straw (WS),Rice straw (RS) and Rice husk (RH) were used in this study

collected from Uttarakhand, Dehradun district (India). They weredried in sun and then crushed and sieved to obtain particle sizebetween 0.5 and 2 mm.

2.2. Characterisation methods

The thermo-gravimetric analysis was carried out in ShimadzuDTG-60 instrument. These tests were conducted using 2–10 mgof the agriculture biomass residue sample material at a heatingrate of 10 �C/min with a temperature range of 25–900 �C in theN2 atmosphere. The gross calorific value was found using Parr6300 Bomb Calorimeter. The elemental composition of C, H, N, Sand O was measured by using an Elementar vario micro cube unit.Moisture content has been obtained using HR-83 Mettler ToledoHalogen Moisture Analyzer. The 1H NMR spectra have beenrecorded in the Bruker Avance 500 Plus instrument using CDCl3as a solvent. Powder X-ray diffraction patterns were collected onBruker D8 advance X-ray diffractometer fitted with a Lynx eyehigh-speed strip detector and a Cu Ka radiation source. Diffractionpatterns in the 2–80� region have been recorded with a 0.04 stepsize (step time = 4 s). The FT-IR spectra were recorded on Nicolet8700 FT-IR spectrometer over a range of 400–4000 cm�1 with thesample powder diluted in KBr plates. The organic fraction of thebio-oil was analyzed using gas chromatography–massspectrometry (GC/MS, Agilent 7890 B). The carrier gas was Heand column flow rate was 1 ml min�1. A HP-1 column(25 m � 0.32 mm � 0.17 lm) was used for the separation. An ovenisothermal program was set at 50 �C for 2 min, followed by a heat-ing rate of 5 �C min�1 till 280 �C where it was held for 5 min. Theinjected volume was 0.4 lL in a split less mode. Compounds wereidentified by way of the National Institute of Standards and Tech-nology (NIST) library of mass spectra. TOC analysis of feed and bio-char was performed for obtaining total organic carbon conversionof the feed by using Shimadzu TOC-L unit with solid sample mod-ule SSM-5000A. Volatile matter has been calculated by measuringthe weight loss in the sample after placing it in a muffle furnace at950 �C for 2 min similar to ASTM-D3175. Volatile matter and ashanalysis of the feed was carried out using oven dried feedstock.

2.3. Experimental procedure

Slow pyrolysis of corn cob, wheat straw, rice straw and ricehusk were performed in a glass reactor (length: 280 mm; i.d.34 mm) under atmospheric pressure of nitrogen and it has shownin Fig. S1. Briefly, 10 g of biomass was loaded into the reactor andthe residual air in the reactor was purged using carrier gas nitrogen(flow rate: 50 ml min�1). The starting temperature was the ambi-ent room temperature at 25 �C and the heating rate to reach thepyrolysis temperature was set around 20 �C min�1. Once finalpyrolysis temperature was attained, the reactor was maintainedat the required temperature for a period of 1 h to ensure that allcondensable vapours were collected. Biomass bed temperaturehas been taken as the pyrolysis temperature and another thermo-couple indicated the skin temperature of the reactor. The vapoursformed after the reaction was condensed using cooling watermaintained at 4 �C (Krishna et al., 2015). Water in bio-oil wasremoved by the addition of anhydrate sodium sulphate and diethylether was used to recover the organic fraction. Conversion asdefined in this process is the amount of solid that has been con-verted into liquid or gaseous products. The remaining solid afterthe reaction left in the reactor is termed as bio-char. Various equa-tions to calculate the yield of various fractions are given below(Krishna et al., 2015).

Bio� oil yield;wt:% ¼ ðW4Þ � ðW3ÞWeight of feed

� 100

B. Biswas et al. / Bioresource Technology 237 (2017) 57–63 59

Bio� char yield;wt:% ¼ ðW2Þ � ðW1ÞWeight of feed

� 100

Gas yield;wt:%¼100%� ðBio�oil yield;wt:%þBio�char yield;wt:%Þ

Conversion;% ¼ 100%� ðBio� char yield;wt:%ÞWhere, W1 = Weight of empty reactor, W2 = Weight of reactor afterreaction, W4 = Weight of measuring cylinder with bio oil, W3 =Weight of empty measuring cylinder.

The experiments have been carried out in duplicates and theaverage values have been reported which are within the standarddeviation of ±1.0%. The organic fraction of the bio-oil was charac-terised using FT-IR, 1H NMR and GC–MS. The solid bio-char hasbeen characterised using TOC, FT-IR and XRD.

3. Results and discussions

3.1. Characterization of agriculture biomass residues

The ultimate and proximate analysis of corn cob, wheat straw,rice straw and rice husk are shown in Table 1. The contents of car-bon and hydrogen in rice husk and corn cob were higher than thatin rice straw and wheat straw. From the elemental compositionperspective, Sulfur and nitrogen were found to be in small amountsin all samples except rice husk that has highest nitrogen and corncob that has highest sulfur content. The estimated moisture con-tents of available agriculture biomass residue showed slightly dif-ferent results for most of the agriculture biomass residue. Themarginal differences in reported values are mainly due to agricul-ture biomass residue obtained from different feed. The lowest vola-tile content was found in the rice husk i.e. 73.41 wt% and thehighest volatile content in the corn cob i.e. 91.16 wt%.

The samples of corn cob, wheat straw had low ash contents thatwere less than 7 wt%, where in the case of rice straw and rice huskhad substantially higher ash content i.e. greater than 15. It is ben-eficial from another perspective that the inorganic compounds pre-sent in the agriculture waste resources with higher ash contentshave potential to be used as catalysts in the thermal conversiontechnologies e.g. gasification and pyrolysis (Kenney et al., 2013).

The calorific values of the samples are reported in the ultimateanalysis (see Table 1). The heating/calorific values of the agricul-ture waste samples determined by Bomb Calorimeter. Corn cobshowed the highest higher heating values (HHV) i.e. about 16 MJ/kg. Whereas, in the case of rice husk showed the lowest HHV valuei.e. about 12.87 MJ/kg. The considerable heating values of the agri-culture waste residues showed that these locally available renew-able resources can potentially be converted to substantial amountof bio-energy products from effective conversion technologies.

Thermal decomposition of four agricultures residue was deter-mined by thermo gravimetric analysis (TGA) under N2 atmosphere.DTG (rate of weight loss) and TGA (weight loss) curves are pre-sented as supplementary figures Fig. S2a, S2b, S2c and S2d. Ther-mal decomposition of residues consist of mainly three stages: theloss of moisture bound by at low temperature around 100 �C, pri-mary pyrolysis in the temperature range (200–500 �C) and sec-ondary decomposition at high temperatures over 700 �C (Brebu

Table 1Ultimate and proximate analysis of Corn cob, wheat straw, Rice straw and Rice husk.

Elements Ultimate analysis (wt%) Proxim

C H N S Moistu

Corn cob 42.10 5.90 0.50 0.48 12.77Wheat straw 38.34 5.47 0.60 0.37 12.81Rice straw 36.07 5.20 0.64 0.26 11.69Rice husk 41.92 6.34 1.85 0.47 10.89

and Vasile, 2010). Below 120 �C, the weight loss in the residuescorresponded to free water evaporation. For lignocellulosicbiomass, the primary classes of thermally degradable biopolymersare cellulose, hemicelluloses and lignin. Hemicellulose decom-poses in the temperature range of 220–315 �C. Cellulose pyrolysisoccurs at higher temperature range (315–400 �C). Among the threecomponents, lignin is the most difficult to decompose, which cov-ers a wider temperature range of up to 900 �C. DTG showed themaximum weight loss in four agriculture residues were between310 and 342 �C. Major decomposition of agricultures residue hap-pened slowly in a wide range (300–450 �C) of temperatures with amaximal mass loss rate at 312, 310, 302 and 342 �C of corn cob,wheat straw, rice straw and rice husk due to the ultimate, proxi-mate and chemical composition were different in the differentagricultures residue. The FT-IR spectra of four agricultures residue(corn cob, wheat straw, rice straw and rice husk) is shown inFig. S3. All the agriculture residues showed sharp peaks corre-sponding to the 3424 cm�1 stretching vibrations is originateddue to stretching of OAH groups for intra-molecular hydrogenbonds between cellulose chains. The bands at around 2914 cm�1,related to asymmetric and symmetric methylene stretching inthe spectra of all the agriculture residues. The band around1380–1430 cm�1 is associated with the amount of the crystallinecellulose and the intensity of this band is more pronounced in corncob as compared to others may be due to high cellulose content.The bands at �1246, �1375 and �1157 cm�1 are assigned toCAH stretching, CH2 wagging and CAO stretching respectively incellulose. Absorption bands at �1638 cm�1 are originated from lig-nin, which includes the aromatic skeleton vibrations involvingboth CAC stretching. Stretching vibrations at 1246 and1732 cm�1 is due to C@O and CAO bonds of the acetyl ester unitspresent in hemicelluloses (Yuan et al., 2015). The bands at 1740–1730 and 1560–1480 cm�1 for the entire four agriculture residuecan be considered due to hemicellulose content and its showedcrystallinity, which is supported by XRD also (Meshitsuka andIsogai, 1996).

3.2. Product yields

Slow pyrolysis of corn cob, wheat straw, rice straw and ricehusk under nitrogen atmosphere has been carried out at 300,350, 400 and 450 �C. The pyrolysis products yield obtained fromcorn cob, wheat straw, rice straw and rice husk consisting of gas,bio-oil and bio-char, is presented in Table 2.

The maximum bio-oil yield of 47.3, 36.7, 28.4 and 38.1 wt%were obtained at 450, 400, 400 and 450 �C for corn cob, wheatstraw, rice straw and rice husk respectively. As the temperatureincreased from 300 to 400 �C, the bio-oil yield increased in the caseof wheat straw and rice straw. With further increase in the temper-ature, bio-oil yield decreased. But for corn cob and rice husk, withthe temperature elevated from 300 to 450 �C, the bio-oil yieldincreases. The yield of solid bio-char of corn cob, wheat straw, ricestraw and rice husk were decreased as the temperature increasesfrom 300 to 450 �C and the gas yield increased steadily from 350to 450 �C . The bio-oil yield increases and conversion was seen toincrease with increase in temperature due to the primary decom-position of holocellulose and lignin. Previous studies showed that

ate analysis (wt.%)

re Volatiles Fixed Carbon Ash HHV (MJ/kg)

91.16 6.54 2.30 16.0083.08 10.29 6.63 14.6878.07 6.93 15.00 14.8773.41 11.44 15.14 12.87

Table 2Product yields of pyrolysis of corn cob, wheat straw, rice straw and rice husk under nitrogen atmosphere at different temperatures.

Temperature, �C Bio-oil, wt% Gas, wt% Bio-char, wt% Conversion, %

CC-300 42.8 24.2 33.0 67.0CC-350 45.0 30.0 25.0 75.0CC-400 45.6 29.4 25.0 75.0CC-450 47.3 28.7 24.0 76.0

WS-300 32.5 31.4 36.1 63.9WS-350 36.0 29.4 34.6 65.4WS-400 36.7 28.9 34.4 65.6WS-450 29.2 38.4 32.4 67.6

RS-300 25.9 39.0 35.1 64.9RS-350 27.1 37.9 35.0 65.0RS-400 28.4 38.1 33.5 66.5RS-450 27.1 39.8 33.1 66.9

RH-300 35.9 20.8 43.3 56.7RH-350 36.2 26.6 37.2 62.8RH-400 37.5 27.2 35.3 64.7RH-450 38.1 26.9 35.0 65.0

CC = Corn cob, WS = Wheat straw, RS = Rice straw, RH = Rice husk and 300, 350, 400 and 450 are the temperatures.

60 B. Biswas et al. / Bioresource Technology 237 (2017) 57–63

bio-oil yields from the pyrolysis of biomass increased incremen-tally as the temperature was raised to a certain temperature(Balagurumurthy et al., 2015; Krishna et al., 2016). After this speci-fic temperature that has been changed depending on the condi-tions (i.e., type of biomass, type of reactor, and type of pyrolysis),further increases in pyrolysis temperatures generated lower yieldsof bio-oils and increasing the yields of non-condensable gas prod-ucts due to secondary cracking. It is believed that each biomass hasthe potential to provide a maximum bio-oil yield at a certain pyrol-ysis temperature. It is clearly seen from Table 2, that each biomasshas the potential to provide a maximum bio-oil yield at a certainpyrolysis temperature. For both wheat straw and rice straw maxi-mum bio-oil yield was observed at 400 �C, whereas in the case ofcorn cob and rice husk maximum bio-oil yield was observed at450 �C. Product distribution obtained at different temperaturesfrom different types of agriculture biomass residues suggested thatit had a significant effect on product distribution due to the struc-tural differences in the different biomass as evident from TGA/DTGand FTIR.

3.3. Total organic carbon (TOC) analysis of corn cob, wheat straw, ricestraw and rice husk and bio-chars

To understand the conversion on the basis of total organic car-bon (TOC), TOC analysis of corn cob, wheat straw, rice straw andrice husk and bio-chars obtained after pyrolysis at different tem-peratures was investigated and results are presented in Table S1.TOC results indicated that rice husk showed better organic conver-sion than corn cob, wheat straw and rice straw. Carbon, the mainelement in all of the produced bio-chars was present in signifi-cantly greater amounts in the bio-chars than in the agricultureresidue. Relatively the total organic conversion is higher in the caseof rice husk bio-chars than the other residues. The highest conver-sion of raw biomass has been occurred (56.62%) in the case of risehusk. The higher amount of organic carbon (54.98, 53.24, 54.41 and51.78%) at 300, 350, 400 and 450 �C were present in the case ofwheat straw bio-chars than other three agriculture residues. Anincrease in the carbon content of bio-chars produced by pyrolysisto makes them suitable precursors for the production of activatedcarbons.

3.4. Bio-oil characterization

3.4.1. Gas chromatography–mass spectrometry (GC–MS) of bio-oilGC–MS analysis has been carried out to identify the compounds

in bio-oils from the pyrolysis of biomass. The effect of temperature

on components of bio-oil from corn cob, wheat straw, rice strawand rice husk pyrolysis and their relative mass contents detectedby GC–MS. Here we have shown only optimum temperaturesbio-oils in Table 3. Small peaks on the chromatograms or peaksbelonging to unidentified compounds are not presented in thetable. As expected, the pyrolysis bio-oils were a complex mixtureof organic compounds containing a mass of highly oxygenatedcompounds, such as phenols, ketones carboxylic acids, etc. It hasbeen reported that bio-oils produced from different types of bio-mass samples under similar conditions have similar composition.Table 3 shows that the corn cob, wheat straw, rice straw and ricehusk bio-oils (450 �C, 400 �C, 400�C and 450 �C) had a large amountof compounds including Phenol, 2-methoxy (relative area were12.4%, 8.5%, 4.4%, 2.0% respectively), Phenol, 2,6-dimethoxy (rela-tive area 7.2%, 6.6%, 2.5%, 1.3% respectively), 2-methoxy-4-vinylphenol, (relative area were 7.9%, 6.2%, 2.8%, 1.9% respectively),Phenol, 4-ethyl-2-methoxy (relative area were 4.9%, 4.1%, 3.1%,1.4% respectively), Furanmethanol (relative area were 4.1%, 3.4%,3.1%, 1.1% respectively), Cathecol (relative area were 5.2%, 4.1%,1.6%, 3.5% respectively), Phenol, 2-methyl (relative area were3.1%, 2.3%, 3.7%, 1.8% respectively), Phenol, 4-ethyl (relative areawere 6.0%, 2.1%, 4%, 4.3% respectively), Benzofuran, 2,3-dihydro-(relative area were 9.1%, 3.7%, 3.4%, 3.2% respectively) and 2-cyclopenten-1-one,3-methyl-(relative area were 2.6%, 1.7%, 1.7%, 1.2%respectively). Furfural was another significant compound foundin corn cob (450 �C) and wheat straw (400 �C) bio-oils with relativearea of 4.9%, 1.9% respectively. 1,2-Benzenediol, 4-methyl wasfound in corn cob(450 �C), wheat straw(400 �C) and rice huskbio-oil(450 �C) with relative area of 1.4%, 1.2%, 2.3% respectively.n-Hexadecanoic acid was the compound with the highest area %in the rise husk bio-oil (450 �C), GC–MS profile with a relative areaof 16.8%. It was also found in the wheat straw bio-oil (400 �C) witha relative area of 1.4%. Thus, bio-oil is a complex mixture with a lotof chemical compounds. Furfural, cyclopenten and phenolic com-pounds are the main chemical compounds in the bio-oil for thefour kinds of biomass (Tsai et al., 2007; Chen et al., 2011).

3.4.2. 1H Nuclear magnetic resonance (NMR) of bio-oilNMR analysis of the bio-oil samples has been done to under-

stand the ratios of chemical environments of the proton. NMRspectra provided complementary functional group information toFT-IR spectra and the ability to quantify and compare integrationareas between spectra (Mullen et al., 2009). Similar to FT-IR, 1HNMR spectra showed a high percentage of aliphatic functionalgroups for all bio-oils and a summary of integrated peak arearegions assigned to different functional group classes are provided

Table 3The chemical composition of Corn cob, Wheat straw, Rice straw and Rice husk bio-oil obtained from gas chromatography–mass spectrometry (GC/MS). CC = Corn cob, WS = Wheatstraw, RS = Rice straw, RH = Rice husk.

Compounds identified in bio-oil obtained under N2 atmosphere Area, %

CC-450 �C WS-400 �C RS-400 �C RH-450 �C

Furfural 4.9 1.9 – –2-Furanmethanol 4.1 3.4 3.1 1.12-Cyclopenten-1-one, 3-methyl- 2.6 1.7 1.7 1.23-Hexen-2-one, 3-methyl- – 0.4 5.3 –Phenol 6 2.4 3.02-Cyclopenten-1-one, 2-hydroxy-3-methyl- 3.9 3.0 – –Phenol, 2-methyl- 3.1 2.3 3.7 1.8Phenol, 3-methyl- – – 3.6 –Phenol, 2-methoxy- 12.4 8.5 4.4 2.0Phenol, 2,4-dimethyl- – – 2.3 1.52-Cyclopenten-1-one, 3-ethyl-2-hydroxy- 1.8 1.6 1.3 –Phenol, 2,5-dimethyl- – 1.1 – –Phenol, 4-ethyl- 6.0 2.1 4.0 4.3Creosol 2.0 1.6 – 1.2Catechol 5.2 4.1 1.6 3.5Benzofuran, 2,3-dihydro- 9.1 3.7 3.4 3.21,2-Benzenediol, 3-methyl- 2.7 1.8 – 1.6Phenol, 4-ethyl-2-methoxy- 4.9 4.1 3.1 1.41,2-Benzenediol, 4-methyl- 1.4 1.2 2.32-Methoxy-4-vinylphenol 7.9 6.2 2.8 1.9Phenol, 2,6-dimethoxy- 7.2 6.6 2.5 1.3Benzaldehyde, 3-hydroxy-4-methoxy- 1.4 1.2 – –3-Hydroxy-4-methoxybenzoic acid – 1.6 – –1,2,3-Trimethoxybenzene 1.2 – – –trans-Isoeugenol – 2.3 – –Apocynin – 1.2 – –Homovanillyl alcohol – 1.4 – 0.4Phenol, 2-methoxy-4-(1-propenyl)-, (Z)- 1.9 – – 1.45-tert-Butylpyrogallol 1.4 – – –n-Hexadecanoic acid – 1.4 – 16.81,2-Cyclopentanedione, 3-methyl- – – 2.7 1.4p-Cresol – – – 2.8Vanillin – – – 1.04-Ethylcatechol – – – 2.01-Penten-3-ol, 2-methyl- – – 1.0 –Hydrazine, 1-(4-ethylphenyl)- – – 1.4 –Octadecanoic acid – – – 2.2

0.5-1.5 1.5-3.0 3.0-4.5 4.5-6.0 6.0-8.0 8.0-10.00

10

20

30

40

50

prot

ons,

%

Chemical shift , ppm

CC-300 0C CC-350 0C CC-400 0C

CC-450 0C

Corn cob

Fig. 1a. 1H Nuclear magnetic resonance (NMR) of Corn cob bio-oil.

0.5-1.5 1.5-3 3-4.5 4.5-6 6-7.2 7.2-8.20

10

20

30

40

Prot

on, %

Chemical shift, ppm

WS-300 0C WS-3500C WS-4000C WS-4500C

Wheat Straw

Fig. 1b. 1H Nuclear magnetic resonance (NMR) of Wheat straw bio-oil.

B. Biswas et al. / Bioresource Technology 237 (2017) 57–63 61

Fig. 1a, b, c and d below. All bio-oils displayed a low percentage ofmethoxy/carbohydrate functionality (4.5–6.0 ppm). The value ofproton percentage of bio-oil was maximum for wheat straw andminimum for rice straw in this region (4.5–6.0 ppm). The regionof the spectrum between 6.0 and 8.5 ppm corresponds to the aro-matic region (Mullen et al., 2010; Biswas et al., 2016). The

maximum proton content of bio-oil was obtained for rice strawat around 21% in this region. The proton percentage correspondingto rice husk was lowest in this region. The downfield spectrumregions (9.5–10 ppm) of the bio-oils arise from the aldehydes.Aromatic/hetero-aromatic functionality was also observed in allbio-oils (6.0–8.5 ppm) in agreement with findings from FT-IR.

0.5-1.5 1.5-3.0 3.0-4.5 4.5-6 6-8 8-100

10

20

30

40

50

Prot

on %

Chemical Shift, ppm

RS-300 0C RS-350 0C RS-400 0C RS-450 0C

Rice Straw

Fig. 1c. 1H Nuclear magnetic resonance (NMR) of Rice straw bio-oil.

0.5-1.5 1.5-3 3-4.5 4.5-6 6-7.2 7.2-8.20

10

20

30

40

50

60

70

Prot

on %

Chemical shift, ppm

RH-3000C RH-3500C RH-4000C RH-4500C

Rice Husk

Fig. 1d. 1H Nuclear magnetic resonance (NMR) of Rice husk bio-oil.

62 B. Biswas et al. / Bioresource Technology 237 (2017) 57–63

Aldehydes functionality (9.5–10.0 ppm) was absent from all sam-ples despite the observed C@O functional groups (1730–1700 cm�1) by FT-IR. The appearance of such FT-IR bands may bedue to other carbonyl-bearing groups like protonated carboxylicacids, carboxylic acid esters, amides, and ketones. The most upfield region of the spectra, from 0.5 to 1.5 ppm represents aliphaticprotons attached to carbon atoms at least two bonds away from aC@C or heteroatom (O or N). The next integral region from 1.5 to3.0 ppm represents protons on aliphatic carbon atoms that maybe bonded to a C@C double bond. All the bio-oils have higher per-centage of protons in the spectral region from 0.5 to 3.0 ppm. Thebio-oils from rice husk showed higher proton percentage than allthe three samples in the region from 0.5 to 3.0 ppm. The regionis further divided into two regions namely, 0.5 to 1.5 and 1.5 to3.0 ppm. The bio-oil from corn cob, rice straw and wheat strawsamples have higher percentage of protons in the region from 1.5to 3.0 than the region from 0.5 to 1.5 which suggests the presenceof unsaturation (C@C) in the bio-oil. The region of the 1H NMRspectrum at 3.0–4.5 ppm represents methoxyl protons (Kosaet al., 2011) or methylene group that joins two aromatic rings.All the bio-oils from corn cob, wheat straw and rice straw showed

high proton percentage than rice husk. The 1H NMR of the bio-oilsobtained from pyrolysis of four agriculture residue indicated thepresence of substitute phenol and aromatic compounds.

3.4.3. Fourier transform-infra red spectroscopy (FT-IR) of bio-oilThe Fourier transform infrared (FT-IR) spectra of the oils are

given in Fig. S4a and S4b. The OAH stretching vibrations between3200 and 3400 cm�1 of the bio-oil indicate the presence of phenolsand alcohols. The presence of alkanes is indicated by the absor-bance peak of CAH vibrations between 2800 and 3000 cm�1 andby 1350 and 1470 cm�1 bands due to the CAH bending. Carbohy-drate content of four biomass produced bio-oil with strong C@Ostretching absorbance between 1650 and 1730 cm�1 indicate thepresence of ketones, aldehydes and carboxylic acids (Serranoet al., 1996). The absorbance peaks between 1600 and 1630 cm�1

indicate the presence of alkenes and aromatics. The peaks between900 and 1300 cm�1 are due to the presence of primary, secondaryand tertiary alcohols and also phenols and they are showing theCAO stretching and OAH bending. Furthermore, the absorptionpeaks between 650–800 and 1420–1610 cm�1 indicate mono andpolycyclic and substituted aromatic groups. Obtained bio-oil hasa typical FT-IR spectrum compared with the previous studies(Balagurumurthy et al., 2015; Krishna et al., 2016). The FT-IR spec-tra of various bio-oil samples from four biomass show the samepeaks indicating the presence of same functional groups in thebio-oil samples. The spectra differ only in the relative intensity ofsome peaks. The FT-IR spectra were in conflict with the variouspeaks obtained in the 1H NMR spectra of the bio-oils.

3.5. Bio-char characterization by powder X-ray diffraction and FT-IR

The stacked powder XRD patterns of corn cob, wheat straw, ricestraw and rice husk feed and bio-chars at optimal final tempera-tures have been shown as Fig. S5a and S5b. From the figure, itcan also be observed that the corn cob, wheat straw, rice strawand rice husk feed has a peak at 2h around 21� attributed to thehkl 101 crystallographic planes of crystalline regions of cellulose.This peak is hardly evident in the bio-char patterns which indicatethe conversion of cellulose in the feed. The peak at 2h around 21�assigned to the crystallographic planes of cellulose are also seento reduce with increase in pyrolysis temperature thus formingamorphous bio-char rich in carbon content. These are in confirma-tion with the results of FT-IR which indicates the conversion offeed cellulose into products. On the contrary, it was found thatthe X-ray diffraction peaks, for the all the four bio-char were char-acterized by a broad band instead of cellulose signals (with thepyrolysis temperatures) indicating a destruction of biomass struc-ture and a highly disordered structure (Meshitsuka and Isogai,1996).

The functional groups in bio-chars from the pyrolysis of corncob, wheat straw, rice straw and rice husk shown in Fig. S6,revealed that the functional groups in bio-chars were similar. Someof the functional groups observed in four bio-chars are as follows:the broad band at 3455 cm�1 was attributed to the hydroxylgroups (OAH) due to the water content in all the bio-chars. Thepresence of water in the bio-chars could be from absorption ofmoisture by the bio-chars or KBr during pellets preparation. Thepeaks at 2918–2853 cm�1 are assigned to CAH vibrations, satu-rated CAC, and CAH; the peaks at 1405 and 1585 cm�1 confirmedthe aromatic ring C@C stretching vibration. The peak at 1095 cm�1

represents CAH out-of-plane bending vibrations of the alkenegroups. For the four biochars, all of them shows the same func-tional groups. That is because the biomass material consists of cel-lulose, hemicellulose and lignin which have a large amount of C, Hand O (Chen et al., 2014). The intensities FT-IR spectra of the pyr-olytic bio-chars of all four corn cob, wheat straw, rice straw and

B. Biswas et al. / Bioresource Technology 237 (2017) 57–63 63

rice husk are weakened, indicating that many cellulose, hemi-cellulose and lignin structural units were broken down inpyrolysis.

4. Conclusions

Pyrolysis of four different agriculture biomass residues has seenthat the product distributions under identical conditions werestrongly affected by the types of biomass samples. The highestbio-oil yield was obtained from corn cob 47.30 wt%. Maximumorganic carbon conversion (56.62%) calculated from TOC measure-ment was observed for rice husk. The contents of the bio-oils infour samples were similar and mainly composed of oxygenatedhydrocarbons, that has agreed with further analysis from FT-IRand 1H NMR. The analysis of four bio-char derived from pyrolysisby XRD and FT-IR, which indicating that biomass components unitswere broken down in pyrolysis and converted into products.

Acknowledgements

The authors thank the Director, CSIR-Indian Institute of Petro-leum, Dehradun, for his constant encouragement and support.The authors thank the Analytical Science Division (ASD) of CSIR-IIP for NMR, FT-IR, and XRD analysis. The authors thank CSIR –India in the form of XII Five Year Plan project (CSC0116/BioEn)and Ministry of New and Renewable Energy (MNRE) for providingfinancial support.

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.biortech.2017.02.046.

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