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Analysis of Gaseous and Liquid Products from Pressurized Pyrolysis of Flax Straw in a Fixed Bed Reactor Mohammad Shahed Hasan Khan Tushar,† Nader Mahinpey,*,‡ Pulikesi Murugan,‡ and Thilakavathi Mani‡ EnVironmental Systems Engineering, Faculty of Engineering and Applied Science, UniVersity of Regina, 3737 Wascana Parkway, Regina, SK, Canada, S4S 0A2 and Department of Chemical and Petroleum Engineering, Schulich School of Engineering, The UniVersity of Calgary, Calgary, AB, Canada, T2N 1N4
Pyrolysis of flax straw was investigated under a nitrogen atmosphere using a tubular reactor at different pressures, ranging from 10 to 40 psi. The effects of pressure on the pyrolysis yields and the products obtained (gas, liquid, char) have been analyzed. The gaseous products were analyzed by online GC, and the bio-oils were characterized by gas chromatography/mass spectrometry (GC/MS). Scanning electron microscopy (SEM) was used to view the char surfaces in order to characterize the char and validate the presence of porosity. As the pyrolysis pressure increased, the yield of char and liquid decreased while the gas products increased. The gas products were mainly CO, H2, CO2, CH4, and C3’s. The bio-oils were mostly composed of phenolic compounds, carboxylic acids, and furfural. The pH and the density of the bio-oil revealed a moderate increase with increasing pressure. The SEM study confirms the porous nature of the char. Overall, bio-oil production was maximized at 10 psi; however, char and hydrogen production was maximized at 20 psi. 1. Introduction The oil embargo and consequent increased oil costs around the world during the mid 1970s, the rapid depletion of fossil fuel, and the ensuing “energy crisis” gave rise to the development of an alternative energy program. Domestic and indigenous biomass feedstocks can be an important source for alternative fuels, which in turn will reduce the need for foreign oil. Being carbon neutral and low in sulfur, nitrogen, and metal content make biomass a promising source for alternative fuels. The use of biomass means the recycling of mobile carbon rather than mobilization of fixed carbon in combustion of fossil fuel.1 Today, biomass is considered as a renewable resource with a high potential for energy production. Biomass can be converted to various forms of energy through numerous thermochemical conversion processes, depending upon the type of energy desired. Among the thermochemical processes, pyrolysis is a promising tool for providing bio-oil that can be used as fuel or chemical feedstock. The pyrolysis of biomass is a very old energy technology that is becoming popular again for the energetic utilization of biomass.2 Agricultural residues have been estimated to represent significant potential for the development of bioenergy industries in numerous countries. The potential of agricultural residues for energy production has been investigated by many researchers.3–6 Flax is a commercially important crop grown for fiber and oilseed worldwide. In North America, Canada is the largest producer and exporter of flax seed.7 Depending on the acreage planted and the rainfall, the potential salvageable oilseed flax straw on the prairies is 500 000 to 1 000 000 tonnes annually.8,9 Growing flax can present “the straw problem.” Oilseed flax has a significant percentage of long tough stem fibers that decay slowly over time. This makes it difficult to incorporate flax straw into the soil after harvest since the fibers wrap themselves around * To whom correspondence should be addressed. Phone: (403) 2106503. Fax: (403) 284-4852. E-mail:
[email protected]. † University of Regina. ‡ The University of Calgary.
or plug disks, wheels, and shovels. In the past, the only way to cope with flax straw was to drop it in windrows after the combine and then burn it directly or harrow or rake it into piles and then burn it. More recently, straw choppers on the largest new combines have been used to effectively chop and spread flax straw, if the straw was relatively short. The straw has also been used as animal bedding, duck nesting sites, lining for drainage ditches, horticultural mulch, or as a fuel source in “bale burners”.8 Concern against global warming and greenhouse gas emission has fostered a need to find an alternate way to use this abundant flax straw. As a biomass, flax straw can be used as a renewable energy source due to the rapid depletion of fossil fuel and price rise of fossil fuel. The objective of the present work is to study the influence of process conditions on the characteristics and yield of products obtained from flax straw pyrolysis. A thorough analysis of the various products was carried out with the help of various analytical techniques like GC, GC/MS, elemental analyzers, etc. The surface morphology and porosity of the chars produced at different pyrolysis pressures were investigated by means of SEM analysis. 2. Materials and Methods 2.1. Flax Straw. Flax straw, investigated in this study, has been supplied by Biolin Research Inc., Saskatoon, Saskatchewan, Canada. This straw was chopped and subsequently sieved to obtain an average particle size of 1 mm. The sieved flax straw was dried at 150 °C for 4 h and stored in desiccators. 2.2. Pyrolysis Experiment. The pyrolysis experiments were performed in a stainless steel (316 SS) fixed-bed tubular reactor (60.5 × 1.91 cm o.d., 0.165 cm wall thickness). The experimental schematic diagram is shown in Figure 1. The reactor was heated in a cylindrical furnace, and the temperature was measured using thermocouples placed at three different locations (upstream, downstream, and center (as shown in Figure 1)) in the reactor. The biomass was secured in place with glass wool
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after which it was raised to 260 °C, at a ramp of 5 °C/min. A split injection was used with a split ratio of 25:1. The ion source and transfer line temperatures were 230 and 280 °C, respectively. Data were acquired in the full-scan mode between m/z 10 and 550. Chromatographic peaks were identified by means of NIST mass spectral data library and from their retention times using standard compounds. The percentages of the peaks were calculated from the TIC (total ion chromatogram) peak area. Basic bio-oil properties such as pH and density were measured using a digital pH meter (Fisher Scientific Accumet AB15+ Basic and BioBasic pH/mV/°C Meters) and density meter (DE40 Density Meter). Three consecutive measurements of pH and density were performed for the reproducibility of results, which are presented in Table 3. 2.5. SEM Analysis. Scanning electron microscopy (SEM) analysis was performed on a JEOL JSM-5600 model scanning electron microscope. Gold coating (with a 10-20 nm thickness) was performed using Polaron SC7620 Sputter Coater (Quorum Technologies) in order to increase the surface conductivity of the sample, to prevent surface charging, and also to improve the image quality. During coating, an 18 mA current was applied on the sample for a duration of 150s. The distance between the source and sample was 3 cm. 2.6. Calorific Value Determination. The theoretical calorific value (CV) was calculated using the equation given by Friedl et al.13 These calculations are mainly based on the carbon, hydrogen, and nitrogen content; an ordinary least-squares regression (OLS; eq 1); and a partial least-squares regression (PLS) method (eq 2). These equations were calibrated using 122 different biomass samples and provide the energy content of fuels on an as-received basis.14
Figure 1. Schematic diagram of the tubular reactor.
plugs, which were placed on both ends of the reactor. The gas flows were regulated using a digital mass flow controller. A back pressure regulator was employed to regulate the pressure in the tubular reactor. Nitrogen was used as the inert gas with a constant flow rate of 50 cm3/min throughout the process. During the experiments, the sample was heated at the rate of 25 °C/min, up to 500 °C, at which the maximum oil yield was obtained.10–12 The temperature ramping was controlled by NI LabVIEW software (20th Anniversary Ed.). About 40 g of flax straw was loaded into the reactor and pyrolyzed under different pressures from 10 to 40 psi. The volatile products were passed through a cold trap to collect the liquid condensate (bio-oil), and subsequently the gases were analyzed by an online GC. The pyrolysis reaction was stopped once the outlet nitrogen percentage exceeded around 98%. This implies that, once the reaction completed, only the nitrogen gas is exiting the reactor. After the completion of the reaction, the reactor was cooled by passing air over the reactor for several minutes. Finally, the solid product, biochar, was collected after cooling the reactor to the ambient temperature. 2.3. Experimental Analysis. Online gas analysis was performed on an Agilent 6890N GC, equipped with two columns (porapak, molecular sieve). Argon gas was used as a carrier gas for the TCD. Ultimate analysis was carried out using an automatic elemental analyzer (Perkin-Elmer 2400 Series, CHNS-O analyzer). 2.4. Bio-Oil Characterization. The chemical composition of the bio-oils was obtained from the GC/MS analysis. A Hewlett-Packard HP 6890 gas chromatograph coupled to a quadrupole mass spectrometer HP 5973 equipped with mass selective detector (MSD) was used for this purpose. A 30 m × 0.25 mm capillary column (Agilent 19091N-133) coated with a 0.25 µm thick film of 5% polyethylene glycol (HP-INNOWax) was used to separate the various components of bio-oil. Helium was used as a carrier gas at a constant flow rate of 1 mL/min. Initially, the oven temperature was held at 45 °C for 1 min,
Higher Heating Value (OLS) ) 1.87C2 - 144C - 2802H + 63.8C × H + 129N + 20 147 (1) Higher Heating Value (PLS) ) 5.22C2 - 319C - 1647H + 38.6C × H + 133N + 21 028 (2) 3. Results and Discussion 3.1. Ultimate and CV Analysis. The results obtained from elemental analysis and the corresponding HHV calculated for the flax straw and its char obtained at different pressures are given in Table 1. Considerable differences were observed in the carbon and hydrogen content of the raw flax straw and its char. The measured carbon content and hydrogen content of the raw flax straw were 45.24% and 6.25%, respectively. According to an ordinary least-squares regression (OLS), the heating value of the flax straw was 18 116 kJ/kg, while in the partial least-squares regression (PLS) method, the heating value was 18 034 kJ/kg. A similar calorific value (18 000 kJ/kg) was reported for flax straw by another study.15 Further, flax straw has a per tonne heating value similar to soft coal and yet cheaper than conventional fuels.15 For char particles, maximum carbon content was obtained at 30 psi, which is the best operating pressure for gas production during flax straw pyrolysis. The maximum calorific value (29 401 kJ/kg (OLS); 36 366 kJ/kg (PLS)) was obtained at 30 psi compared to other pressures. The
Table 1. Ultimate Analyses of Flax Straw and Its Chars sample flax straw char @ 10 char @ 20 char @ 30 char @ 40
psi psi psi psi
N (wt %)
C (wt %)
S (wt %)
H (wt %)
HHV (OLS) (kJ/kg)
HHV (PLS) (kJ/kg)
1.01 0.85 0.99 0.91 0.86
45.24 80.38 81.97 84.37 81.83
1.18 0.56 0.54 0.48 0.48
6.25 3.16 3.12 3.09 2.89
18 116.92 28 114.82 28 610.09 29 401.01 27 986.41
18 034.72 33 825.87 34 818.01 36 366.42 34 361.14
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Table 3. Basic Properties of the Bio-oil
Figure 2. Pyrolysis product yields at different pressures.
heating value of biochar varies with different pressures. The product yields were analyzed for the effect of pyrolysis pressure. As shown in Figure 2, the char and liquid yield decreases as the pressure increases from 10 to 40 psi. The char yield varies from 32 to 43 wt %, with the lowest occurring at 40 psi, while the highest occurs at 20 psi. At longer residence times (such as 5-30 min), the char yield decreases as the pressure increases. Generally, the pyrolysis includes two processes: (i) the removal of moisture and the breakage of weak bonds and (ii) the secondary pyrolysis of the condensed carbon matrix. The trends observed suggest that there is a competition between these two steps with increasing pressure. As a result, the increased rate of the secondary reaction at higher pressures becomes dominant.16 This implies that, at longer residence times, the higher pressures increase the density of material trapped within the particles. It also increases the heat-transfer rate, which leads to an increased rate of cracking of the large organic groups. The higher pressure promotes cracking, which leads to more gas being released and, therefore, resulting in a lower char yields.17 3.2. Bio-Oil Characterization. Optimum operational parameters were established for the pressurized pyrolysis of flax
pyrolysis pressure (psi)
pH
density (lb/ft3)
10 20 30 40
3.34 3.38 3.73 3.89
62.64 64.00 64.84 65.26
straw. The bio-oil yield was 27.4% at the pyrolysis pressure of 10 psi, and it appeared to go through a minimum of 21.5% at 40 psi (Figure 2). The bio-oils were subjected to GC/MS analysis, in which the chromatographic separation was done in the GC, while the identification was done by the mass spectrometer. Results obtained thereof are presented in Table 2. As noted from Table 2, more than 28 compounds were detected and identified by their specific m/z values, and the corresponding retention times are also shown. The perfect separation of all the peaks was not possible due to the complex composition of the pyrolysis condensate. It is a well established fact that biomass derived pyrolysis oils contain a very wide range of complex organic compounds.18–21 Similarly, numerous types of compounds were detected in the present study, as listed in Table 2. The major components present in the bio-oil were carboxylic acids, phenolic compounds, cyclopentenes, and furfural. Among the various carboxylic acids, formic acid, acetic acid, and propanoic acid were found to be prominent, explaining the acidic nature (pH < 4) of the bio-oil. According to Ates¸ and Is¸ıkdag˘10 and Ates¸ et al.,22 the pyrolysis conditions govern the bio-oil composition, irrespective of the biomass used. However, the comparison between the pyrolysis of wheat straw18 and flax straw (present study) showed that, under exactly similar experimental conditions, different compositions of bio-oils were produced. Phenolic compounds were found in flax straw as well as wheat straw. However, the total content of phenolic compounds is higher in wheat straw than flax straw, which is similar to the results obtained by other researchers.23 The pH and density measurement values are presented in Table 3. The pH
Table 2. Tentative GC-MS Characterization of Pyrolysis Liquid Products area (%)
a
compound
retention time (min)
10 psi
20 psi
30 psi
40 psi
1-hydroxy-2-butanone 2,3-butanedione 2,3-pentanedione 2-cyclopenten-1-one 2-cyclopenten-1-one, 2-hydroxy-3-methyl2-cyclopenten-1-one, 2-methyl2-cyclopenten-1-one, 3-methyl2-furanol, tetrahydro-2-methyl2-methoxy-4-vinylphenol 2-propanone, 1-(acetyloxy)2-propanone, 1-hydroxy3-furanmethanol 3-pyridinol acetaldehyde acetic acid acetic acid, methyl ester acetone butyrolactone cyclopropyl carbinol formic acid, ethyl ester furan, tetrahydro-2-(methoxymethyl)furfural phenol phenol, 2,6-dimethoxyphenol, 2-methoxyphenol, 2-methoxy-4-methylphenol, 4-ethyl-2-methoxypropanoic acid
6.47 1.859 2.517 6.107 11.703 6.23 8.167 18.706 19.339 7.528 5.603 9.87 32.755 0.967 6.95 1.182 1.152 9.483 16.08 1.44 8.02 7.466 14.353 22.297 12.047 13.375 14.697 8.382
1.93 1.34 0.51 0.57 1.25 0.57 0.74 3.29 0.73 0.85 4.07 1.87 0.86 1.00 20.87 1.63 1.06 1.07 1.62 5.41 2.01 1.42 nd 1.25 2.71 1.17 0.73 1.97
1.90 0.92 nd nd 1.29 0.50 0.94 nd nd 0.95 2.97 2.35 0.92 0.75 21.71 2.18 nd 1.35 1.75 nd nd 1.09 0.84 1.49 2.92 0.96 0.7 2.08
1.47 0.93 nd 0.52 1.18 0.50 nd 2.12 nd 0.89 2.62 2.07 0.88 0.75 21.99 1.37 1.06 1.32 1.69 5.14 nd 0.99 0.98 1.42 2.87 1.01 0.67 2.23
1.33 nda 0.52 0.53 1.07 0.54 nd 2.46 nd 0.85 2.40 1.97 0.96 0.80 21.28 1.88 1.55 1.40 1.69 6.31 nd 0.75 0.88 1.34 3.16 1.18 0.84 2.18
nd: not detected.
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Figure 3. The variations in the percentage of (a) CO, (b) H2, (c) CO2, (d) CH4, (e) C3 gases due to increases in pressure.
and the density of the bio-oil revealed a modest increase with increasing pressure. 3.3. Gas Analysis. The gaseous products were mainly composed of H2, CO, CO2, CH4, and C3 fractions. A pressure of 20 psi was found to be optimum to produce H2, while 30 psi yielded more CO. The gas produced during the pressurized pyrolysis of flax straw was analyzed by an online GC and was found to be composed of CO, H2, CO2, CH4, and C3’s. Figure 3 shows the variation in the percentage composition of the gases evolved during pyrolysis as a function of pressure. Although chars and bio-oils are the main products of pyrolysis, the gases evolved also have significant commercial value. More specifically, if the evolved gases have CO and H2 in a stoichiometric ratio, then it can be utilized in oxo-synthesis or hydroformylation processes. As per Figure 3, the rate of CO and CH4 production is high at 30 psi. A pyrolysis pressure of 20 psi was found to yield fractions rich in H2 and C3’s. The pyrolysis gas yields declined with time, which was due to the loss of volatile components in the biomass. Increasing the pyrolysis pressure decreases the composition of syngas.24 3.4. Char Characterization. SEM micrographs of the raw flax straw and chars are given in Figure 4. From the image of
the raw flax straw, it is evident that the raw sample is amorphous and heterogeneous in nature. It can be concluded from the micrographs that the surface morphology of the flax straw changed after pyrolysis. The application of pressure along with temperature caused the formation of cracks on the surface of the sample. These cracks become larger as the pyrolysis pressure increased. The chars exhibit a more open porous structure, as a result of devolatilization of the biomass matter. Destruction of cell contents may be also observed, even though the highly directional structure is preserved. The chars were also observed to have embedded particles. These particles have been attributed to the deposition of pyrolytic carbon as a result of the cracking of the hydrocarbons during pyrolysis.25,26 During a typical pyrolysis process, flax straw almost rapidly experiences a 65% weight loss due to the phenomenon of devolatilization. The volatiles formed get trapped in the surfaces, causing distorted surfaces. Also, the pressure and temperature cause the chemical bonds to be decomposed thermally, which in turn broke the fibers of original biomass. According to the SEM images, larger cavities with thinner cell walls were seen for chars produced at high pressures (30 and 40 psi). Due to the thermal decomposition
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Figure 4. SEM images of the (a) flax straw, (b) char at 10 psi, (c) char at 20 psi, (d) char at 30 psi, and (e) char at 40 psi.
of chemical bonds and melting, as the pressure increased, the cracks formed in chars increased and the cell did not retain its structure. 4. Conclusions The present study revealed that the process conditions are critical for the efficient utilization of biomass and production of suitable biorenewable fuels. Results obtained from this study can be used to determine the optimal conditions for the secondary combustion processes. The present work provides the results on the pyrolysis of flax straw for the production of
biorenewable fuels like char, bio-oil, and gas at different pressures of 10, 20, 30, and 40 psi. Pyrolysis of flax straw was carried out in a tubular reactor under a N2 flow (50 cc/min). All three fractions (gas, liquid, and solid) that evolved during the process were analyzed thoroughly. The produced gas was mainly composed of H2, CO, CO2, CH4, and C3 fractions. On the basis of the results of this study, 20 psi was found to be favorable for producing H2, while 30 psi yielded more CO. The bio-oil yield was a maximum (27.4%) at a pyrolysis pressure of 10 psi, and it appeared to be a minimum (21.5%) at 40 psi. The bio-oils were mostly composed of carboxylic acids, phenolic
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compounds, and furfural, and bio-oil contains a maximum amount of acetic acid than other compounds. The pH and the density of the bio-oil revealed a moderate increase with increasing pressure. The char yield varied from 32 to 43% with the lowest occurring at 40 psi, while the highest was at 20 psi. Maximum heating values (29 401 kJ/kg (OLS) and 36 366 kJ/ kg (PLS)) of biochar were obtained for 30 psi. The char structure and surface morphology were investigated using SEM analysis, and it was found that chars are porous in nature. Results obtained from this study can be used to determine the optimal conditions for the secondary combustion processes. Acknowledgment The authors wish to thank the Natural Science and Engineering Research Council (NSERC) for providing funding for this study. We would also like to acknowledge Saskatchewan Research Council, Regina for providing experimental setup and the NSERC-RTI for support used to acquire instrumentation for chemical analysis in these studies. Literature Cited (1) Sharma, R. K.; Bakhshi, N. N. Catalytic Upgrading of Biomassderived Bio-oils to Transportation Fuels and Chemicals. Can. J. Chem. Eng. 1991, 69, 1071–1081. (2) Yanik, J.; Kornmayer, C.; Saglam, M.; Yu¨ksel, M. Fast Pyrolysis of Agricultural Wastes: Characterization of Pyrolysis Products. Fuel Process. Technol. 2007, 88, 942–947. (3) Brossard Perez, L. E.; Cortez, L. A. B. Potential for the use of Pyrolytic Tar from Bagasse in Industry. Biomass Bioenergy. 1997, 12 (5), 363–366. (4) Natarajan, E.; Öhman, M.; Gabra, M.; Nordin, A.; Liliedahl, T.; Rao, A. N. Experimental Determination of Bed Agglomeration Tendencies of some common Agricultural Residues in Fluidized Bed Combustion and Gasification. Biomass Bioenergy 1998, 15, 163–169. (5) Di Blasi, C.; Signorelli, G.; Di Russo, C.; Rea, G. Product Distribution from Pyrolysis of Wood and Agricultural Residues. Ind. Eng. Chem. Res. 1999, 38, 2216–2224. ¨ zc¸imen, D.; (6) S¸enso¨z, S.; Yorgun, S.; Angın, D.; C¸ulcuog˘lu, E.; O Karaosmanog˘lu, F. Fixed Bed Pyrolysis of Rapeseed Cake. Energy Source. 2001, 23, 873–877. (7) Agricultural statistics. Information from the Government of Saskatchewan Web site. (8) Fridfinnson, E.; Hale, C. Flax Council of Canada, 4th ed.; Saskatchewan Flax Development Commission: Saskatoon, SK, Canada, 2002; ISBN 0-9696073-4-2. (9) Comeau, G. Options to the practice of burning of flax straw on the Canadian prairies. Petition: No. 186, Office of the Auditor General of Canada: Ottawa, Ontario, 2006.
(10) Ates¸, F.; Is¸ıkdag˘, M. A. Evaluation of the Role of the Pyrolysis Temperature in Straw Biomass Samples and Characterization of the oils by GC/MS. Energy Fuels 2008, 22, 1936–1943. (11) Pu¨tu¨n, A. E.; Özcan, A.; Pu¨tu¨n, E. Pyrolysis of hazelnut shells in a fixed-bed tubular reactor: Yields and structural analysis of bio-oil. J. Anal. Appl. Pyrolysis 1999, 52 (1), 33–49. ¨ zbay, N.; Pu¨tu¨n, A. E. (12) Uzun, B. B.; Apaydin Varul, E.; Ates¸, F.; O Synthetic fuel production from tea waste: Characterisation of bio-oil and bio-char. Fuel 2010, 89 (1), 176–184. (13) Friedl, A.; Padouvas, E.; Rotter, H.; Varmuza, K. Prediction of Heating Values of Biomass Fuel from Elemental Composition. Anal. Chim. Acta 2005, 554, 191–198. (14) Bridgeman, T. G.; Darvell, L. I.; Jones, J. M.; Williams, P. T.; Fahmi, R.; Bridgwater, A. V.; Barraclough, T.; Shield, I.; Yates, N.; Thain, S. C.; Donnison, I. S. Influence of Particle Size on the Analytical and Chemical Properties of two Energy Crops. Fuel 2007, 86, 60–72. (15) Naik, S.; Goud, V. V.; Rout, P. K.; Jacobson, K.; Dalai, A. K. Characterization of Canadian biomass for alternative renewable biofuel. Renew. Energy 2010, 35, 1624–1631. (16) Solomon, P. R.; Serio, M. A.; Carangelo, R. M.; Markham, J. R. Very rapid coal pyrolysis. Fuel 1986, 65, 182–194. (17) Li, C.; Zhao, J.; Fang, Y.; Wang, Y. Pressurized fast-pyrolysis characteristics of typical Chinese coals with different ranks. Energy Fuels 2009, 23, 5099–5105. (18) Mahinpey, N.; Murugan, P.; Mani, T.; Raina, R. Analysis of BioOil, Biogas, and Biochar from Pressurized Pyrolysis of Wheat Straw Using a Tubular Reactor. Energy Fuels 2009, 23, 2736–2742. (19) S¸enso¨z, S.; Demiral, ˙I.; Gerc¸el, H. F. Olive Bagasse (Olea europea L.) Pyrolysis. Bioresour. Technol. 2006, 97, 429–436. (20) Onay, O. Fast and Catalytic Pyrolysis of Pistacia Khinjuk seed in a well-swept Fixed Bed Reactor. Fuel. 2007, 86, 1452–1460. (21) Vitolo, S.; Seggiani, M.; Frediani, P.; Ambrosini, G.; Politi, L. Catalytic Upgrading of Pyrolytic Oils to Fuel over Different Zeolites. Fuel. 1999, 78, 1147–1159. (22) Ates¸, F.; Pu¨tu¨n, A. E.; Pu¨tu¨n, E. Fixed Bed Pyrolysis of Euphorbia Rigida with Different Catalysts. Energy ConVers. Manage. 2005, 46, 421– 432. (23) Buranov, A. U.; Mazza, G. Lignin in straw of herbaceous crops. Ind. Crops Prod. 2008, 28, 237–259. (24) Okumura, Y.; Hanaoka, T.; Sakanishi, K. Effect of pyrolysis conditions on gasification reactivity of woody biomass-derived char. Proc. Combust. Inst. 2009, 32, 2013–2020. (25) Kumar, M.; Gupta, R. Scanning electron microscopic study of Acacia and Eucalyptus wood chars. J. Mater. Sci. 1995, 30, 544–551. (26) Della Rocca, P. A.; Cerrella, E. G.; Bonelli, P. R.; Cukierman, A. L. Pyrolysis of hardwoods residues: on kinetics and chars characterization. Biomass Bioenergy 1999, 16, 79–88.
ReceiVed for reView January 1, 2010 ReVised manuscript receiVed March 5, 2010 Accepted April 13, 2010 IE902036V
