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Pyrolysis of babool seeds (Acacia nilotica) in a fixed bed reactor and bio-oil characterization
Renewable Energy 96 (2016) 167e171
Contents lists available at ScienceDirect
Renewable Energy journal homepage: www.elsevier.com/locate/renene
Pyrolysis of babool seeds (Acacia nilotica) in a fixed bed reactor and bio-oil characterization Rahul Garg, Neeru Anand*, Dinesh Kumar University School of Chemical Technology, GGS IP University, Delhi, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 August 2015 Received in revised form 17 March 2016 Accepted 19 April 2016
With the growing awareness of environmental issues, production of biofuel has a potential to provide an alternative source of renewable energy sources. In the present work, the effect of pyrolysis temperature, particle size and sweep gas flow rate (N2) was investigated for production of bio-oil from pyrolysis of babool seeds (Acacia nilotica). Optimum conditions obtained for the maximum liquid and bio-oil yield (~49% & 38.3%, respectively) were 500 C, 100 cm3/min sweep gas flow rate (N2) and particle size range upto 0.4 mm. Bio-oil with a calorific value of 36.45 MJ/kg was characterized by FT-IR, 1H NMR, GC/MS. The characterization of bio-oil indicates that it can be an alternative fuel for transportation sector. © 2016 Elsevier Ltd. All rights reserved.
Keywords: Babool seed Pyrolysis Bio-oil FT-IR 1 H NMR GC/MS
1. Introduction The demand for energy is increasing at an exponential rate due to population growth in developing countries like India, Brazil and Africa [1]. To overcome this problem clean, domestic and renewable energy is commonly accepted as the key for the future worldwide. Biomass has various environmental and social benefits but these renewable energy technologies are not easily commercialized because of various associated costs. Biomass containing cellulose, hemicellulose and lignin can be converted into many useful products like oil, gas, solid and/or valuable feedstock for chemical industry. Various thermochemical processes like gasification, hydrolysis, pyrolysis and liquefaction are used to convert forest crop, agricultural waste into desired product [2]. Among these processes, pyrolysis has attracted more attention for the conversion of biomass into liquid products as the process conditions are easy to maintain and have low installation/operating cost with respect to liquefaction [3]. The yield of different products and their physiochemical properties depend on process conditions like biomass type, temperature, particle size and inert gas flow rate [4]. In addition to the process conditions, technology type is also another
* Corresponding author. E-mail address: [email protected] (N. Anand). http://dx.doi.org/10.1016/j.renene.2016.04.059 0960-1481/© 2016 Elsevier Ltd. All rights reserved.
important factor, and big efforts are being made to develop new reactors for maximizing bio oil yield. Various reactors that have been used for pyrolysis of biomass includes ablative, entrained, free fall, rotating cone, vacuum, fluidized bed, auger, spouted based on mode of heat transfer and acceptability of feedstock in various sizes [5]. Each reactor has its advantages and limitations. Bio-oil obtained from the pyrolysis has stability, corrosion issues and low calorific value due to high oxygen content. GC/MS analyses by various authors have confirmed that bio-oil contains various organic compounds such as oxygenated hydrocarbons, ketones, alcohols, aldehydes and phenol [6]. The advantage of liquid fuel is that it can be stored until required or readily transported to places where it can be most effectively utilized [7,8]. In the recent, literature study shows that different biomass feedstock like oily seeds can be converted into various useful products using pyrolysis for example hemp seed (liquid yield 40% at 350 C) [9], safflower seed (liquid yield 44% at 500 C) [10], castor seed (liquid yield 64.4% at 550 C) [11], tamarind seed(liquid yield 45% at 400 C) [12], pistacia khinjuk seed (liquid yield 51% at 600 C) [13], Jatropha curcas L. (liquid yield 55% at 550 C) [14]. Above studies show that high liquid yield can be obtained at temperature between 450 and 600 C and short vapor residence time. Babool seed obtained from Babool tree grown in the wasteland of India is a forestry waste. Babool (Acacia nilotica) is a tree of
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5e20 m height with a dense spherical crown, stems and branches. The number of seeds produced by Babool plant is approximately 8000/kg. Seeds contain 35e45% oil. Annually, 6 lakhs tones babool pods and 60,000 tones babool seeds are available in India [15]. Hence, it may be feasible to use babool seeds as a raw material for fuel production besides being used for medicinal application. In this work Babool seeds were pyrolized to produce transportation grade liquid fuel. The effect of important parameters e.g. temperature, sweep gas flow rate and particle size were investigated for obtaining high yield of bio-oil. Further the bio-oil was analyzed using spectroscopic and chromatographic techniques for their candidacy as transportation grade fuel. 2. Materials and methods 2.1. Materials The babool seeds (Acacia nilotica) investigated in this study were acquired from waste land on the banks of Najafgarh drain, Delhi. Physical impurities were removed from seeds by washing, and drying at 100 C to remove the moisture. Further the seeds were crushed in ball mill and sieved into fractions of different particle diameter as (i) upto 0.4 mm (ii) 0.4e0.6 mm (iii) 0.6e0.8 mm, and (iv) 0.8e1.0 mm. Other chemicals for analysis and characterization like KBr, CS2, acetone, CdCl3 etc were purchased from Fischer Scientific, Agfa Acer and CDH with 99% purity. 2.2. Experimental procedure
of temperature from 400 to 700 C in an interval of 100 C at a heating rate of 25 C/min, particle size upto 1 mm (upto 0.4 mm, 0.4e0.6 mm, 0.6e0.8 mm and 0.8e1.0 mm) and sweep gas (N2) flow rate of 100e400 cm3 min1. For every experiment 20 g of seeds were introduced in the reactor. Vapors produced after pyrolysis were condensed using water cooled condenser with the help of chiller maintained at 4 C. The condensed liquid phase was collected from the bottom of a separator. The liquid product comprised of bio-oil (organic) as well as aqueous fraction. To separate the bio-oil from aqueous fraction, the liquid product was mixed with equal quantity of diethyl ether. The obtained bio-oil fraction was dried over anhydrous sodium sulfate, and then filtered and evaporated in a rotary evaporator at 25 C in order to remove diethyl ether [16,17]. Then the organic fraction was weighed, bottled and denoted as bio-oil in the present study. Acetone was added to solid products to separate any heavy hydrocarbons, if any. The product yield was calculated using the following equations
Liquid Yieldð%Þ ¼ YLiquid ¼
Liquid ðgÞ 100 Biomass fed to reactor ðgÞ (1)
Char Yield ð%Þ ¼ YChar ¼
Char ðgÞ 100 Biomass fed to reactor ðgÞ (2)
Gas Yield ð%Þ ¼ YGas ¼ 1 YLiquid YChar
The pyrolysis studies were performed in a SS316 fixed bed reactor with the following dimensions i.d. of 1.8 cm and total length of 18.5 cm (Fig. 1). The experimental setup consists of electrical heated furnace, PID controller and double condenser. K type (Cr: Al) thermocouple (L-2001E) was used for temperature measurement inside the reactor. Experiments were conducted to study the effect
(3)
Bio oil Yield ð%Þ ¼ YBiooil ¼
Bio oil ðgÞ 100 Biomass fed to reactor ðgÞ
Fig. 1. Schematic diagram of experimental setup for bio-oil generation.
(4)
R. Garg et al. / Renewable Energy 96 (2016) 167e171
169
2.3. Characterization of feed and bio-oil The raw material i.e. babool seeds was characterized by proximate and ultimate analysis. Percent Moisture, ash, volatile and fixed carbon content was determined according to ASTM standards D 2016 74, D1102 84, D3174 89 [18]. Ultimate analysis was carried out in Elemental CHNO analyzer to determine the carbon, hydrogen, nitrogen and oxygen content. Lignocellulosic content with extractives of the seeds was obtained using TAPPI standards [19]. Bio-oil was characterized for their functional group compositional analyses by using a Nicolet 6700 Fourier transform infrared (FT-IR) spectrophotometer using KBr pellets of 1 mm thickness. The analysis of the organic compounds in the bio-oil was performed on GC/MS-QP 2010 SHIMADZU, Omega Wax TM 250 (column: 30 mm 0.25 mm, 0.25 mm film thickness). The 1H NMR of bio-oil was obtained at a frequency of 300 MHz, High Resolution NMR spectrometer (BRUKER) instrument by dissolving sample in CdCl3.
3. Result and discussion
Fig. 2. Yield of pyrolysis products at different temperatures (heating rate of 25 C min1, sweep gas flow rate of 100 cm3 min1 and particle size upto 0.4 mm).
3.2. Effect of particle size
The crushed seeds were characterized for ultimate, proximate and lignocellulosic fractions as discussed earlier. As shown in Table 1 it was observed that seed contains 41% of extractives and 20% proteins. High content of oxygen as well as ash was observed which makes it less suitable to be used as fuel.
3.1. Effect of pyrolysis temperature The yield of pyrolysis products at different temperatures with particle size upto 0.4 mm using sweep gas (N2) flow rate of 100 cm3 min1 is shown in Fig. 2. With the increase in temperature from 400 C to 700 C, Char yield was observed to decrease from 21% to 12% whereas an increase in the gas yield was noticed from 32% to 48%. With the increase in temperature char yield decreased because the char materials decompose at higher temperature [4]. Liquid yield was observed to increase initially from 47% at 400 C to 49% upto500 C and thereafter decreased. The decrease in liquid yield can be due to increase of secondary volatile decomposition of intermediate hydrocarbons [20]. Maximum liquid (~49%) as well as bio-oil yield (~38.7%) were obtained at 500 C and hence it was considered as the optimum temperature for further studies. Similar liquid yields 45% and 44% were obtained for the pyrolysis of safflower seed at 500 C [10] and tamarind seed at 400 C [12], respectively. It can be said that the liquid yield is comparable and can be promising for the production of alternative fuel.
The effect of particle size in the range from 0 to 1 mm on the product yield with pyrolysis temperature of 500 C using the sweep gas (N2) flow rate of 100 cm3 min1 was performed and results are shown in Fig. 3. An increase in the char yield from 18% to 25.8% was obtained with the increase of particle size whereas gas yield decreased from 37% to 29%. A reduction in the liquid yield was observed with increase in particle size indicating that large particle do not enhance the heat transfer and mass transfer associated with the cracking mechanism [21,22]. Liquid yield decreased from 42.7% to 41.8% with the increase of particle diameter due to non-uniform heating of particles. Maximum bio-oil yield (~32%) was obtained with particle diameter 0e0.4 mm. This indicates that small particles (below 0.4 mm) are suitable for obtaining a high bio-oil yield. 3.3. Effect of sweep gas (N2) flow rate Fig. 4 shows the yield of pyrolysis products using different sweep gas (N2) flow rate with particle size upto 0.4 mm at pyrolysis
Table 1 Babool seeds characterization. Characteristics
Percentage composition
Extractive (wt %) Hemi-cellulose (wt %) Lignin (wt %) Protein (wt %) Proximate Analysis (wt %) Moisture content Volatile matter Ash content Fixed carbon Ultimate Analysis (%) C H N O
41 24 15 20 12.5 69.1 7.3 11.0 54.1 6.12 5.23 34.53
Fig. 3. Yield of pyrolysis products using different particle size (heating rate of 25 C min1, pyrolysis temperature of 500 C and sweep gas flow rate of 100 cm3 min1).
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Fig. 4. Yield of pyrolysis products using different sweep gas flow rates (heating rate of 25 C min1, pyrolysis temperature of 500 C, particle size upto 0.4 mm).
temperature of 500 C. It can be observed that both liquid and biooil yield were maximum (~44 and 33.5% wt %) at nitrogen flow rate 100 cm3 min1. Liquid yield was observed to decrease continuously from 44% to 30% with the increase in the sweep gas flow rate from 100 to 400 cm3 min1. The decrease may be due to the following reasons: at high sweep rate, low residence time is available for cracking of long polymeric chains of lignin, cellulose and hemicellulose to small hydrocarbons and thus higher char yield was obtained at higher sweep gas rates. The insufficient condensation of the hot vapors by the cooling can also be responsible for higher gas yield [23,24]. The Char yield first decreased from 20% to 19% and then increased to 22% whereas gas yield increased from 36% to 48% as sweep gas flow rate is increased from 100 to 400 cm3 min1. 3.4. Chemical composition of bio-oil Bio-oil used for the analysis was obtained at the following process conditions T ¼ 500 C, Particle size ¼ upto 0.4 mm and Sweep gas flow rate ¼ 100 cm3 min1. HHV analysis indicates a high calorific value of bio-oil ~36.45 MJkg1 which is close to that of transportation grade fuel. Elemental analysis shows a decrease in the oxygen content from 34.5% for Babool seeds to 27.4% for the biooil. The functional groups present in the bio-oil were identified and spectra by FT-IR are shown in Fig. 5. Table 2 shows the peak identification for the different functional groups as reported in literature. The presence of eOH, eNH, water impurities were detected at 3400 cm1 with eCH stretching in CH3 and CH2 at 30002800 cm1. The peak in the range of 1750e1600 cm1 shows the presence of >C]O group in ketones, ester and aldehydes eCH deformation vibration was found at 1500e1400 cm1. CO vibration in alcohols was detected at 1300e1000 cm1. Aromatics and Phenols vibration were observed at 850e650 cm1 [25]. The pyrolytic oil obtained from babool seed was characterized using GC/MS diluted with CS2. More than 100 peaks were observed in the spectra and the compounds were identified from NIST library. Different compounds such as alkanes, alkenes, saturated fatty acids and their derivatives such as esters, amides and nitriles were identified. Nitrogenous compounds were observed due to the presence of proteins within the seeds. The major peaks were identified as Heptadecane (7.3%), Hexadecene (35.4%), 2-Tetradecene (4.2%),
Fig. 5. FT-IR spectra of the bio-oil. Table 2 FT-IR analysis of bio-oil obtained from Babool seeds pyrolysis. Wave number (cm1)
Functional group
3400 3000e2800 1750e1600 1500e1400 1300e1000 850e650
OH, NH, water impurities CH stretching of CH3, CH2 C]O…ketones, esters, aldehydes CH CO…alcohols aromatics, phenols
Trans-7-Pentadecene (1.8%), Tetradecane, 1-Iodo (3.8%), Trans-7Pentadecene (3.9%), Phenol (2%), Tridecene, (Z) (2.4%), 9,10Anthracenediol (9.76%) and 1-Tridecanol (14.17%) as shown in Table 3. Presence of straight chain hydrocarbon could be due to Table 3 GC/MS analysis of bio-oil. Peak
Retention time
% Area
Name
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
4.21 4.54 4.91 5.1 5.27 5.38 5.79 6.19 6.71 7.15 7.79 8.85 10.05 12.18 12.42 13.9 14.8 16.14 17.33 19.4 20.9 22.29 24.92 25.41 25.91 26.67 27.2 29.22 34.18
7.3 0.7 35.4 4.2 0.5 1.8 3.8 3.9 1.2 0.4 0.6 0.18 0.82 2.0 0.4 1.47 1.34 0.23 0.24 0.48 0.59 1.0 1.23 1.37 2.44 0.8 1.2 9.76 14.17
Heptadecane Tetradecanol Hexadecene 2-Tetradecene Ethanone, 1-Phenyl Trans-7-Pentadecene Tetradecane, 1-Iodo Trans-7-Pentadecene 1-Dodecanol 3z)-3-Hexenyl 2-Oxopropanoate Dodecane, 1,1-Difluoro Isoxazole, 3-(3-Butenyl)-5-MethylDodecane, 1,1-Difluoro Phenol 1-Methylbutyl Nitrite Methane, Bis(4-Methylphenoxysulfonyl) Dodecane, 1,1-Difluoro 6-Oxabicyclo[3.2.1]Oct-2-Ene-7-Ethanol Nonanoic Acid, Methyl Ester Octane, 1-Iodo-N-Octyl Iodide Pentadecanal Methyl 2-Hydroxydodecanoate Nonadecanol Pentadecanenitrile Tridecene, (Z) Phthalic Acid, 4-Cyanophenyl Nonyl Ester 1,2-Benzenedicarboxylic Acid, Dibutyl Ester 9,10-Anthracenediol 1-Tridecanol
R. Garg et al. / Renewable Energy 96 (2016) 167e171
cracking of various acids e.g. palmitic, stearic or oleic acid in seed. 1 H NMR was performed for the bio-oil and various components were identified as Paraffinic, olefinic, aromatics and oxygenated compounds. High presence of aliphatic protons attached to carbon atoms removed from C]C or heteroatom was observed in the region 0.5e1.5 ppm. Similarly high concentration of aromatic/olefinic was noticed in the region of 1.5e3.0 ppm. Presence of lignin derived methoxy phenol was confirmed by the peaks between 4.4 and 6.0 ppm. Also peaks between 6.0 and 8.5 ppm confirm the presence of oxygen and nitrogen attached with aromatic compounds. The peaks after 8.5e10 ppm were due to the presence of aldehydes and carboxylic acids [26]. 4. Conclusions Babool seeds, a forestry waste in northern India, can be a suitable candidate for the production of transportation grade fuel for reducing the dependency on fossil fuel in transportation sector. Maximum liquid as well as bio-oil yield (~49% & 38.3%, respectively) of Babool seed pyrolysis were obtained at sweep gas (N2) flow rate of 100 cm3 min1 at 500 C pyrolysis temperature and heating rate of 25 C min1 using particle size upto 0.4 mm. Bio-oil fraction was characterized by FT-IR, GC/MS and 1H NMR. The analysis shows that bio-oil obtained from the babool seed pyrolysis contain mixture of different functional groups. The characterization of bio-oil indicates that their further upgradation for removing of oxygen can make them suitable to be used to produce renewable fuel. Acknowledgements The authors would like to thank Chemical Engineering Department, Indian Institute of Technology, Delhi for FT-IR and 1H NMR analysis and AIRF (Jawaharlal Nehru University), Delhi for GC/MS analysis. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.renene.2016.04.059. References [1] Exxonmobil, The Outlook for Energy: a View to 2040, 2013. http://www.esso. com/Thailand-English/PA/Files/2013_eo_eng.PDF (accessed on 31.08.14). [2] T. Bhaskar, A. Pandey, Advances in thermochemical conversion of biomasseintroduction, in: Recent Advances in Thermo-chemical Conversion of Biomass, 2015, pp. 3e30.
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[3] J. Akhtar, S.K. Kuang, N.A.S. Amin, Liquefaction of empty palm fruit bunch (EPFB) in alkaline hot compressed water, Renew. Energy 35 (2010) 1220e1227. [4] J. Akhtar, N.A.S. Amin, A review on operating parameters for optimum liquid oil yield in biomass pyrolysis, Renew. Sustain. Energy Rev. 16 (2012) 5101e5109. [5] A.V. Bridgewater, Principles and practice of biomass fast pyrolysis processes for liquids, J. Anal. Appl. Pyrolysis 51 (1993) 3e22. [6] H.B. Goyal, D. Seal, R.C. Saxena, Bio-fuels from thermochemical conversion of renewable resources: a review, Renew. Sustain Energy Rev. 12 (2008) 504e517. [7] P. McKendry, Energy production from biomass (part 2): conversion technologies, Bioresour. Technol. 83 (2002) 47e54. [8] S. Czernik, A.V. Bridgwater, Overview of applications of biomass fast pyrolysis oil, Energy Fuels 18 (2004) 590e598. [9] E. Karimi, C. Briens, F. Berruti, S. Moloodi, T. Tzanetakis, M.J. Thomson, Mud as a catalyst for the upgrading of hemp-seed pyrolysis bio-oil energy, Fuels 24 (2010) 6586e6600. [10] S.H. Beis, O. Onay, O.M. Kockar, Fixed-bed pyrolysis of safflower seed: influence of pyrolysis parameters on product yields and compositions, Renew. Energy 26 (2002) 21e32. [11] R.K. Singh, K.P. Shadangi, Liquid fuel from castor seeds by pyrolysis, Fuel 90 (2011) 2538e2544. [12] M.A. Kader, M.R. Islam, M. Parveen, H. Haniu, K. Takai, Pyrolysis decomposition of tamarind seed for alternative fuel, Bioresour. Technol. 149 (2013) 1e7. [13] O. Onay, Fast and catalytic pyrolysis of pistacia khinjuk seed in a well-swept fixed bed reactor, Fuel 86 (2007) 1452e1460. [14] A. Kumar, S. Sharma, An evaluation of multipurpose oil seed crop for industrial uses (Jatropha curcas L.): a review, Ind. Crops Prod. 28 (2008) 1e10. [15] K. Barman, S.N. Rai, In vitro nutrient digestibility, gas production and tannin metabolites of Acacia nilotica pods in goats, Asian Aust. J. Anim. Sci. 21 (1) (2008) 59e65. [16] S.T. Bhaskar, A. Mutoa, Y. Sakata, T. Oshiki, T. Kishimoto, Low-temperature catalytic hydrothermal treatment of wood biomass:analysis of liquid products, Chem. Eng. J. 108 (2005) 127e137. [17] S. Ucar, A.R. Ozkan, Characterization of products from the pyrolysis of rapeseed oil cake, Bioresour. Technol. 99 (2008) 8771e8776. [18] S. Naik, V.V. Goud, P.K. Rout, K. Jacobson, A.K. Dalai, Characterization of Canadian biomass for alternative renewable biofuel, Renew. Energy 35 (2010) 1624e1631. [19] T 222 om-06, T 236 cm-85, T 203 cm-99, T 204 cm-97. Standard procedure for the estimation of lignin, cellulose and extractives, http://www.tappi. org;(accessed on August 2011). [20] N. Sen, Y. Kar, Pyrolysis of black cumin seed cake in a fixed-bed reactor, Biomass Bioenergy 35 (2011) 4297e4304. [21] S. Sensoz, D. Angın, Pyrolysis of safflower (Charthamus tinctorius L.)seed press cake: part 1. The effects of pyrolysis parameters on the product yields, Bioresour. Technol. 99 (2008) 5492e5497. [22] I. Demiral, S.C. Kul, Pyrolysis of apricot kernel shell in a fixed-bed reactor: characterization of bio-oil and char, J. Anal. Appl. Pyrolysis 107 (2014) 17e24. [23] C.A. Zaror, I.S. Hut Chings, D.L. Pyle, H.N. Stiles, R. Kandiyoti, Secondary char formation in the catalytic pyrolysis of biomass, Fuel 64 (1985) 990e994. [24] M. Ertas, M. Alma, Pyrolysis of laurel (Laurus nobilis L.) extraction residues in a fixed-bed reactor: characterization of bio-oil and bio-char, J. Anal. Appl. Pyrolysis 88 (2010) 22e29. [25] P. Mohanty, S. Nanda, K.K. Pant, S. Naik, J.A. Kozinski, A.K. Dalai, Evaluation of the physiochemical development of biochars obtained from pyrolysis of wheat straw, timothy grass and pinewood: effects of heating rate, J. Anal. Appl. Pyrolysis 104 (2013) 485e493. [26] A.M. Charles, G.D. Strahan, A.A. Boateng, Characterization of various fastpyrolysis bio-oils by NMR spectroscopy, Energy Fuels 23 (2009) 2707e2718.
Contents lists available at ScienceDirect
Renewable Energy journal homepage: www.elsevier.com/locate/renene
Pyrolysis of babool seeds (Acacia nilotica) in a fixed bed reactor and bio-oil characterization Rahul Garg, Neeru Anand*, Dinesh Kumar University School of Chemical Technology, GGS IP University, Delhi, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 August 2015 Received in revised form 17 March 2016 Accepted 19 April 2016
With the growing awareness of environmental issues, production of biofuel has a potential to provide an alternative source of renewable energy sources. In the present work, the effect of pyrolysis temperature, particle size and sweep gas flow rate (N2) was investigated for production of bio-oil from pyrolysis of babool seeds (Acacia nilotica). Optimum conditions obtained for the maximum liquid and bio-oil yield (~49% & 38.3%, respectively) were 500 C, 100 cm3/min sweep gas flow rate (N2) and particle size range upto 0.4 mm. Bio-oil with a calorific value of 36.45 MJ/kg was characterized by FT-IR, 1H NMR, GC/MS. The characterization of bio-oil indicates that it can be an alternative fuel for transportation sector. © 2016 Elsevier Ltd. All rights reserved.
Keywords: Babool seed Pyrolysis Bio-oil FT-IR 1 H NMR GC/MS
1. Introduction The demand for energy is increasing at an exponential rate due to population growth in developing countries like India, Brazil and Africa [1]. To overcome this problem clean, domestic and renewable energy is commonly accepted as the key for the future worldwide. Biomass has various environmental and social benefits but these renewable energy technologies are not easily commercialized because of various associated costs. Biomass containing cellulose, hemicellulose and lignin can be converted into many useful products like oil, gas, solid and/or valuable feedstock for chemical industry. Various thermochemical processes like gasification, hydrolysis, pyrolysis and liquefaction are used to convert forest crop, agricultural waste into desired product [2]. Among these processes, pyrolysis has attracted more attention for the conversion of biomass into liquid products as the process conditions are easy to maintain and have low installation/operating cost with respect to liquefaction [3]. The yield of different products and their physiochemical properties depend on process conditions like biomass type, temperature, particle size and inert gas flow rate [4]. In addition to the process conditions, technology type is also another
* Corresponding author. E-mail address: [email protected] (N. Anand). http://dx.doi.org/10.1016/j.renene.2016.04.059 0960-1481/© 2016 Elsevier Ltd. All rights reserved.
important factor, and big efforts are being made to develop new reactors for maximizing bio oil yield. Various reactors that have been used for pyrolysis of biomass includes ablative, entrained, free fall, rotating cone, vacuum, fluidized bed, auger, spouted based on mode of heat transfer and acceptability of feedstock in various sizes [5]. Each reactor has its advantages and limitations. Bio-oil obtained from the pyrolysis has stability, corrosion issues and low calorific value due to high oxygen content. GC/MS analyses by various authors have confirmed that bio-oil contains various organic compounds such as oxygenated hydrocarbons, ketones, alcohols, aldehydes and phenol [6]. The advantage of liquid fuel is that it can be stored until required or readily transported to places where it can be most effectively utilized [7,8]. In the recent, literature study shows that different biomass feedstock like oily seeds can be converted into various useful products using pyrolysis for example hemp seed (liquid yield 40% at 350 C) [9], safflower seed (liquid yield 44% at 500 C) [10], castor seed (liquid yield 64.4% at 550 C) [11], tamarind seed(liquid yield 45% at 400 C) [12], pistacia khinjuk seed (liquid yield 51% at 600 C) [13], Jatropha curcas L. (liquid yield 55% at 550 C) [14]. Above studies show that high liquid yield can be obtained at temperature between 450 and 600 C and short vapor residence time. Babool seed obtained from Babool tree grown in the wasteland of India is a forestry waste. Babool (Acacia nilotica) is a tree of
168
R. Garg et al. / Renewable Energy 96 (2016) 167e171
5e20 m height with a dense spherical crown, stems and branches. The number of seeds produced by Babool plant is approximately 8000/kg. Seeds contain 35e45% oil. Annually, 6 lakhs tones babool pods and 60,000 tones babool seeds are available in India [15]. Hence, it may be feasible to use babool seeds as a raw material for fuel production besides being used for medicinal application. In this work Babool seeds were pyrolized to produce transportation grade liquid fuel. The effect of important parameters e.g. temperature, sweep gas flow rate and particle size were investigated for obtaining high yield of bio-oil. Further the bio-oil was analyzed using spectroscopic and chromatographic techniques for their candidacy as transportation grade fuel. 2. Materials and methods 2.1. Materials The babool seeds (Acacia nilotica) investigated in this study were acquired from waste land on the banks of Najafgarh drain, Delhi. Physical impurities were removed from seeds by washing, and drying at 100 C to remove the moisture. Further the seeds were crushed in ball mill and sieved into fractions of different particle diameter as (i) upto 0.4 mm (ii) 0.4e0.6 mm (iii) 0.6e0.8 mm, and (iv) 0.8e1.0 mm. Other chemicals for analysis and characterization like KBr, CS2, acetone, CdCl3 etc were purchased from Fischer Scientific, Agfa Acer and CDH with 99% purity. 2.2. Experimental procedure
of temperature from 400 to 700 C in an interval of 100 C at a heating rate of 25 C/min, particle size upto 1 mm (upto 0.4 mm, 0.4e0.6 mm, 0.6e0.8 mm and 0.8e1.0 mm) and sweep gas (N2) flow rate of 100e400 cm3 min1. For every experiment 20 g of seeds were introduced in the reactor. Vapors produced after pyrolysis were condensed using water cooled condenser with the help of chiller maintained at 4 C. The condensed liquid phase was collected from the bottom of a separator. The liquid product comprised of bio-oil (organic) as well as aqueous fraction. To separate the bio-oil from aqueous fraction, the liquid product was mixed with equal quantity of diethyl ether. The obtained bio-oil fraction was dried over anhydrous sodium sulfate, and then filtered and evaporated in a rotary evaporator at 25 C in order to remove diethyl ether [16,17]. Then the organic fraction was weighed, bottled and denoted as bio-oil in the present study. Acetone was added to solid products to separate any heavy hydrocarbons, if any. The product yield was calculated using the following equations
Liquid Yieldð%Þ ¼ YLiquid ¼
Liquid ðgÞ 100 Biomass fed to reactor ðgÞ (1)
Char Yield ð%Þ ¼ YChar ¼
Char ðgÞ 100 Biomass fed to reactor ðgÞ (2)
Gas Yield ð%Þ ¼ YGas ¼ 1 YLiquid YChar
The pyrolysis studies were performed in a SS316 fixed bed reactor with the following dimensions i.d. of 1.8 cm and total length of 18.5 cm (Fig. 1). The experimental setup consists of electrical heated furnace, PID controller and double condenser. K type (Cr: Al) thermocouple (L-2001E) was used for temperature measurement inside the reactor. Experiments were conducted to study the effect
(3)
Bio oil Yield ð%Þ ¼ YBiooil ¼
Bio oil ðgÞ 100 Biomass fed to reactor ðgÞ
Fig. 1. Schematic diagram of experimental setup for bio-oil generation.
(4)
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2.3. Characterization of feed and bio-oil The raw material i.e. babool seeds was characterized by proximate and ultimate analysis. Percent Moisture, ash, volatile and fixed carbon content was determined according to ASTM standards D 2016 74, D1102 84, D3174 89 [18]. Ultimate analysis was carried out in Elemental CHNO analyzer to determine the carbon, hydrogen, nitrogen and oxygen content. Lignocellulosic content with extractives of the seeds was obtained using TAPPI standards [19]. Bio-oil was characterized for their functional group compositional analyses by using a Nicolet 6700 Fourier transform infrared (FT-IR) spectrophotometer using KBr pellets of 1 mm thickness. The analysis of the organic compounds in the bio-oil was performed on GC/MS-QP 2010 SHIMADZU, Omega Wax TM 250 (column: 30 mm 0.25 mm, 0.25 mm film thickness). The 1H NMR of bio-oil was obtained at a frequency of 300 MHz, High Resolution NMR spectrometer (BRUKER) instrument by dissolving sample in CdCl3.
3. Result and discussion
Fig. 2. Yield of pyrolysis products at different temperatures (heating rate of 25 C min1, sweep gas flow rate of 100 cm3 min1 and particle size upto 0.4 mm).
3.2. Effect of particle size
The crushed seeds were characterized for ultimate, proximate and lignocellulosic fractions as discussed earlier. As shown in Table 1 it was observed that seed contains 41% of extractives and 20% proteins. High content of oxygen as well as ash was observed which makes it less suitable to be used as fuel.
3.1. Effect of pyrolysis temperature The yield of pyrolysis products at different temperatures with particle size upto 0.4 mm using sweep gas (N2) flow rate of 100 cm3 min1 is shown in Fig. 2. With the increase in temperature from 400 C to 700 C, Char yield was observed to decrease from 21% to 12% whereas an increase in the gas yield was noticed from 32% to 48%. With the increase in temperature char yield decreased because the char materials decompose at higher temperature [4]. Liquid yield was observed to increase initially from 47% at 400 C to 49% upto500 C and thereafter decreased. The decrease in liquid yield can be due to increase of secondary volatile decomposition of intermediate hydrocarbons [20]. Maximum liquid (~49%) as well as bio-oil yield (~38.7%) were obtained at 500 C and hence it was considered as the optimum temperature for further studies. Similar liquid yields 45% and 44% were obtained for the pyrolysis of safflower seed at 500 C [10] and tamarind seed at 400 C [12], respectively. It can be said that the liquid yield is comparable and can be promising for the production of alternative fuel.
The effect of particle size in the range from 0 to 1 mm on the product yield with pyrolysis temperature of 500 C using the sweep gas (N2) flow rate of 100 cm3 min1 was performed and results are shown in Fig. 3. An increase in the char yield from 18% to 25.8% was obtained with the increase of particle size whereas gas yield decreased from 37% to 29%. A reduction in the liquid yield was observed with increase in particle size indicating that large particle do not enhance the heat transfer and mass transfer associated with the cracking mechanism [21,22]. Liquid yield decreased from 42.7% to 41.8% with the increase of particle diameter due to non-uniform heating of particles. Maximum bio-oil yield (~32%) was obtained with particle diameter 0e0.4 mm. This indicates that small particles (below 0.4 mm) are suitable for obtaining a high bio-oil yield. 3.3. Effect of sweep gas (N2) flow rate Fig. 4 shows the yield of pyrolysis products using different sweep gas (N2) flow rate with particle size upto 0.4 mm at pyrolysis
Table 1 Babool seeds characterization. Characteristics
Percentage composition
Extractive (wt %) Hemi-cellulose (wt %) Lignin (wt %) Protein (wt %) Proximate Analysis (wt %) Moisture content Volatile matter Ash content Fixed carbon Ultimate Analysis (%) C H N O
41 24 15 20 12.5 69.1 7.3 11.0 54.1 6.12 5.23 34.53
Fig. 3. Yield of pyrolysis products using different particle size (heating rate of 25 C min1, pyrolysis temperature of 500 C and sweep gas flow rate of 100 cm3 min1).
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Fig. 4. Yield of pyrolysis products using different sweep gas flow rates (heating rate of 25 C min1, pyrolysis temperature of 500 C, particle size upto 0.4 mm).
temperature of 500 C. It can be observed that both liquid and biooil yield were maximum (~44 and 33.5% wt %) at nitrogen flow rate 100 cm3 min1. Liquid yield was observed to decrease continuously from 44% to 30% with the increase in the sweep gas flow rate from 100 to 400 cm3 min1. The decrease may be due to the following reasons: at high sweep rate, low residence time is available for cracking of long polymeric chains of lignin, cellulose and hemicellulose to small hydrocarbons and thus higher char yield was obtained at higher sweep gas rates. The insufficient condensation of the hot vapors by the cooling can also be responsible for higher gas yield [23,24]. The Char yield first decreased from 20% to 19% and then increased to 22% whereas gas yield increased from 36% to 48% as sweep gas flow rate is increased from 100 to 400 cm3 min1. 3.4. Chemical composition of bio-oil Bio-oil used for the analysis was obtained at the following process conditions T ¼ 500 C, Particle size ¼ upto 0.4 mm and Sweep gas flow rate ¼ 100 cm3 min1. HHV analysis indicates a high calorific value of bio-oil ~36.45 MJkg1 which is close to that of transportation grade fuel. Elemental analysis shows a decrease in the oxygen content from 34.5% for Babool seeds to 27.4% for the biooil. The functional groups present in the bio-oil were identified and spectra by FT-IR are shown in Fig. 5. Table 2 shows the peak identification for the different functional groups as reported in literature. The presence of eOH, eNH, water impurities were detected at 3400 cm1 with eCH stretching in CH3 and CH2 at 30002800 cm1. The peak in the range of 1750e1600 cm1 shows the presence of >C]O group in ketones, ester and aldehydes eCH deformation vibration was found at 1500e1400 cm1. CO vibration in alcohols was detected at 1300e1000 cm1. Aromatics and Phenols vibration were observed at 850e650 cm1 [25]. The pyrolytic oil obtained from babool seed was characterized using GC/MS diluted with CS2. More than 100 peaks were observed in the spectra and the compounds were identified from NIST library. Different compounds such as alkanes, alkenes, saturated fatty acids and their derivatives such as esters, amides and nitriles were identified. Nitrogenous compounds were observed due to the presence of proteins within the seeds. The major peaks were identified as Heptadecane (7.3%), Hexadecene (35.4%), 2-Tetradecene (4.2%),
Fig. 5. FT-IR spectra of the bio-oil. Table 2 FT-IR analysis of bio-oil obtained from Babool seeds pyrolysis. Wave number (cm1)
Functional group
3400 3000e2800 1750e1600 1500e1400 1300e1000 850e650
OH, NH, water impurities CH stretching of CH3, CH2 C]O…ketones, esters, aldehydes CH CO…alcohols aromatics, phenols
Trans-7-Pentadecene (1.8%), Tetradecane, 1-Iodo (3.8%), Trans-7Pentadecene (3.9%), Phenol (2%), Tridecene, (Z) (2.4%), 9,10Anthracenediol (9.76%) and 1-Tridecanol (14.17%) as shown in Table 3. Presence of straight chain hydrocarbon could be due to Table 3 GC/MS analysis of bio-oil. Peak
Retention time
% Area
Name
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
4.21 4.54 4.91 5.1 5.27 5.38 5.79 6.19 6.71 7.15 7.79 8.85 10.05 12.18 12.42 13.9 14.8 16.14 17.33 19.4 20.9 22.29 24.92 25.41 25.91 26.67 27.2 29.22 34.18
7.3 0.7 35.4 4.2 0.5 1.8 3.8 3.9 1.2 0.4 0.6 0.18 0.82 2.0 0.4 1.47 1.34 0.23 0.24 0.48 0.59 1.0 1.23 1.37 2.44 0.8 1.2 9.76 14.17
Heptadecane Tetradecanol Hexadecene 2-Tetradecene Ethanone, 1-Phenyl Trans-7-Pentadecene Tetradecane, 1-Iodo Trans-7-Pentadecene 1-Dodecanol 3z)-3-Hexenyl 2-Oxopropanoate Dodecane, 1,1-Difluoro Isoxazole, 3-(3-Butenyl)-5-MethylDodecane, 1,1-Difluoro Phenol 1-Methylbutyl Nitrite Methane, Bis(4-Methylphenoxysulfonyl) Dodecane, 1,1-Difluoro 6-Oxabicyclo[3.2.1]Oct-2-Ene-7-Ethanol Nonanoic Acid, Methyl Ester Octane, 1-Iodo-N-Octyl Iodide Pentadecanal Methyl 2-Hydroxydodecanoate Nonadecanol Pentadecanenitrile Tridecene, (Z) Phthalic Acid, 4-Cyanophenyl Nonyl Ester 1,2-Benzenedicarboxylic Acid, Dibutyl Ester 9,10-Anthracenediol 1-Tridecanol
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cracking of various acids e.g. palmitic, stearic or oleic acid in seed. 1 H NMR was performed for the bio-oil and various components were identified as Paraffinic, olefinic, aromatics and oxygenated compounds. High presence of aliphatic protons attached to carbon atoms removed from C]C or heteroatom was observed in the region 0.5e1.5 ppm. Similarly high concentration of aromatic/olefinic was noticed in the region of 1.5e3.0 ppm. Presence of lignin derived methoxy phenol was confirmed by the peaks between 4.4 and 6.0 ppm. Also peaks between 6.0 and 8.5 ppm confirm the presence of oxygen and nitrogen attached with aromatic compounds. The peaks after 8.5e10 ppm were due to the presence of aldehydes and carboxylic acids [26]. 4. Conclusions Babool seeds, a forestry waste in northern India, can be a suitable candidate for the production of transportation grade fuel for reducing the dependency on fossil fuel in transportation sector. Maximum liquid as well as bio-oil yield (~49% & 38.3%, respectively) of Babool seed pyrolysis were obtained at sweep gas (N2) flow rate of 100 cm3 min1 at 500 C pyrolysis temperature and heating rate of 25 C min1 using particle size upto 0.4 mm. Bio-oil fraction was characterized by FT-IR, GC/MS and 1H NMR. The analysis shows that bio-oil obtained from the babool seed pyrolysis contain mixture of different functional groups. The characterization of bio-oil indicates that their further upgradation for removing of oxygen can make them suitable to be used to produce renewable fuel. Acknowledgements The authors would like to thank Chemical Engineering Department, Indian Institute of Technology, Delhi for FT-IR and 1H NMR analysis and AIRF (Jawaharlal Nehru University), Delhi for GC/MS analysis. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.renene.2016.04.059. References [1] Exxonmobil, The Outlook for Energy: a View to 2040, 2013. http://www.esso. com/Thailand-English/PA/Files/2013_eo_eng.PDF (accessed on 31.08.14). [2] T. Bhaskar, A. Pandey, Advances in thermochemical conversion of biomasseintroduction, in: Recent Advances in Thermo-chemical Conversion of Biomass, 2015, pp. 3e30.
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