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Catalytic effect of tin oxide nanoparticles on cellulose pyrolysis
Journal of Analytical and Applied Pyrolysis 119 (2016) 69–74
Contents lists available at ScienceDirect
Journal of Analytical and Applied Pyrolysis journal homepage: www.elsevier.com/locate/jaap
Catalytic effect of tin oxide nanoparticles on cellulose pyrolysis Yusuf Osman Donar, Ali Sına˘g ∗ Ankara University, Department of Chemistry, 06100, Bes¸evler, Ankara, Turkey
a r t i c l e
i n f o
Article history: Received 11 August 2015 Accepted 13 March 2016 Available online 30 March 2016 Keywords: Catalytic pyrolysis SnO2 Nanoparticle Catalyst Micro-GC Gaseous product
a b s t r a c t In this study, SnO2 nanoparticles were synthesized via hydrothermal method and used as a catalyst for cellulose (model biomass) pyrolysis. Effect of catalyst on the yields of pyrolysis products was discussed in details. Optimum catalyst to biomass ratio was found as %5 (w/w). The pyrolytic oil (tar) was characterized by Gas chromatography–Mass spectrometry (GC–MS) while the gaseous products were characterized with micro Gas Chromatography (GC) to understand the catalytic ability of SnO2 nanoparticles. The results indicate that gaseous product yields significantly increase while the char yield decreases. Although the tar yields don’t change significantly in the uncatalysed runs, the product distribution in tar decreases in the presence of catalyst. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Nowadays, biomass energy is the most promising alternative to fossil fuels and it is the third biggest primary energy source after coal and petroleum [1,2]. Theoretically, the amount of CO2 released during biomass conversion is equal to the amount of CO2 absorbed by plants during photosynthesis, for this reason biomass energy is a known CO2 neutral energy type [3]. Biomass conversion techniques can be separated into four basic categories: direct combustion processes, thermochemical processes, biochemical processes and agrochemical processes. One of the most preferred techniques is thermochemical conversion process. These processes can be subdivided into gasification, pyrolysis, supercritical fluid extraction and direct liquefaction [4]. Pyrolysis is the thermal decomposition of substance in oxygen-free environment and it has an extremely important place among thermochemical conversion technologies. Pyrolysis studies are gaining increasing importance, as it is not only an independent process, but it is also a first step in the gasification or combustion process [5]. The pyrolytic oil (tar) contains many valuable hydrocarbons, therefore it can be used as a source of chemical feedstock. Moreover, due to its high calorific value of [6,7], tar can also be used as a fuel after refining. From the perspective of energy, one of the most valuable products obtained is gaseous products, the composition of which includes H2 , CH4 , C2 H4 , C2 H6 , C4 H10 , C3 H8 , C2 H2 etc. Espe-
∗ Corresponding author. E-mail address: [email protected] (A. Sına˘g). http://dx.doi.org/10.1016/j.jaap.2016.03.016 0165-2370/© 2016 Elsevier B.V. All rights reserved.
cially hydrogen is green and efficient energy source but due to high production costs and storage problems, its use is limited. One of the critical point about future is decreasing of the production costs of gases, such as hydrogen and methane, and obtaining with high calorific value products from renewable sources. Features of pyrolytic products can be upgraded via catalytic pyrolysis [8–11]. For upgrading the pyrolytic products, different kinds of catalysts were used such as clays [12,13] (ZSM-5, MCM41), supported metals [14,15] (Pt, Ni, Pd etc.) and salts [16] (Na2 CO3 , K2 CO3 , ZnCl etc.). In recent years, nano size metal oxides have attracted extensive attention in various catalytic processes due to their unique properties such as high specific surface area, strong base strength, quantum size effect, nanocrystal shape and polar surface [17–19] but they are not widely used in catalytic pyrolysis of biomass [20]. So catalytic behavior of nano metal oxides on cellulose pyrolysis should be identified. In our previous study, nano SnO2 was used as catalyst for pyrolysis of hazelnut shell and confirmed to have some good catalytic activity. Obtained results show that nano SnO2 catalyst promoted char reduction and gaseous product formation when compared with bulk form. This behavior of nano SnO2 can be explained by accelerated primary and secondary decomposition reactions of hazelnut shell due to the nano size and large external surface area of the nanoparticles [21]. Nowadays, it has been seen an increase in papers about metal oxide catalyzed pyrolysis [17,20–32] in the literature and also some of them about bulk metal oxides [17,23,25–28,32]. The aim of this study is, using SnO2 nanoparticles as a catalyst in the conversion of cellulose which is the major component of biomass (40–60% (w/w)) [33] and
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areas of the particles were determined by a Sorptometer (Nova 2200, Quantachrome). 2.3. Experimental set-up of pyrolysis system
Fig. 1. Cellulose pyrolysis products yields without catalyst in three different temperatures (%).
Pyrolysis experiments were performed by the system given in our previous study [21]. The pyrolysis reactor is made of stainless steel and it has a 2 mm wall thickness, 240 mm length and 20 mm diameter. 3 g of cellulose was directly mixed with the specified amounts of catalyst (1, 5, 15% (w/w)). The mixture was loaded into the reactor. Before the heating, whole pyrolysis system was purged by nitrogen about 30 min with a flow rate of 30 mL/min. The tubular furnace was heated from room temperature to intended temperature with the heating rate of 50 ◦ C/min. Pyrolysis procedure was continued for 1 h. At the end of 1 h no further liquid or gaseous product was observed. The effluent stream from the reactor was connected to condenser system and condenser system was put into ethanol/ice bath (−8 ◦ C). The tar was collected in the condenser and recovered by washing with 50 mL dichloromethane and then extracted with 50 mL water. Dichloromethane phase was used for analysis. Gaseous product was accumulated in tedlar bag connected to the output of the system. All experiments were repeated twice. The amount of residual solid product was defined as the char while the mass of liquid product collected in the condenser was defined as the tar. The amounts of char and tar were divided by the mass of the initial mass of cellulose in order to obtain char and tar yields respectively. The yield of gas was calculated by difference. 2.4. Analysis of gaseous products The composition of the gaseous product was analyzed with SRA Instruments T-3000 model micro GC. GC consists of two modules with TCD detector. The first module (MS5A) was set at 90 ◦ C and use for determination of He, H2 , N2 , O2 , CO and CH4 and use Argon as the carrier gas. The second module (PPU) was set at 70 ◦ C for the separation of CO2 , H2 O (g) and C1-C4 hydrocarbon gases with using Helium as the carrier gas. Analysis results obtained from instrument (% mole) were converted to [mg gas/g biomass] as specified in Eqs. (1)–(3).
Fig. 2. Effect of different amount of catalyst on total conversion ratio at 700 ◦ C.
determining the effects of products distribution, with this respect, nano SnO2 was used as a catalyst for the pyrolysis of cellulose to test whether they had the capability to upgrade the properties of pyrolytic oil and gaseous fractions. Characterization of the tar and gaseous fractions was performed using GC/MS and micro-GC. The catalytic and non-catalytic products were compared to reveal the catalytic capabilities of these catalysts.
Total gas amount (g) = [initial mass of cellulose (g) × gas yield (%)] ÷ 100
(1)
A: Total mole amount of gaseous products (mole) A=
total gas amount (g) M of gaseous products
g.mol−1
(2)
2. Experimental
mg gas = g cellulose
2.1. Materials
2.5. Analysis of liquid products
Sn powder (J.T. Baker), H2 SO4 (Sigma Aldrich 98%) and H2 O2 (Merck 35%) were used for synthesis of SnO2 nanoparticles. Microcrystalline cellulose powder (Sigma Aldrich) was used for pyrolysis experiments as a model biomass. All chemicals were analytical grade and used without further purification.
GC–MS analysis of the liquid products (dichloromethane phase) was performed by Shimadzu GC–MS-QP2010 Plus with a HP-5MS (30 m × 0.25 mm × 0.25 m) capillary column. Helium was used as the carrier gas. The amount injected was 1 L and split ratio was 4:1. The oven temperature was set to 50 ◦ C for 5 min, then raised to 300 ◦ C with 5 ◦ C/min and stayed at 300 ◦ C for 15 min. Total run time was 70 min and flow rate was 0.8 mL/min. Mass spectra were recorded under 70 eV electron ionization and 50–750 m/z interval. The mass spectra obtained by GC–MS was interpreted based on an automatic library search (Wiley & NIST) and discussed with related literature data.
2.2. Catalyst preparation and characterization Hydrothermal synthesis of SnO2 nanoparticles as well as transmission electron micrographs (TEM) and X-ray diffraction patterns (XRD) were described in our previous study [21,34]. The surface
Ax mole% result of the gas 100
×
molar mass of the gas initial mass of cellulose
(3)
Y.O. Donar, A. Sına˘g / Journal of Analytical and Applied Pyrolysis 119 (2016) 69–74
71
Fig. 3. Gaseous product distribution at different temperatures with and without 5% nano SnO2 .
3. Results and discussion
Table 1 Effects of 5% SnO2 catalyst and the different temperatures on the yields (%).
3.1. Material characterization The XRD patterns and TEM images of SnO2 nano particles were given in our previous study [21]. Synthesized SnO2 nanoparticles have 30.42 m2 /g BET surface area. SnO2 nanoparticles have a relatively low surface area due to the huge agglomeration that can be seen in TEM images, however SnO2 nanoparticles show catalytic activity as seen in the results of this study. 3.2. The effect of the amount of catalyst on cellulose conversion efficiency Pyrolysis experiments were conducted in three different temperatures with and without catalyst. Since the main purpose of this study was to obtain gaseous and tar from cellulose, best reaction condition was determined according to highest tar + gas yield (%) and this tar + gas yield was labeled as a total conversion ratio. Total conversion ratios were examined to investigate the amount of catalyst on cellulose conversion efficiency. Fig. 1 shows the products yields in different temperatures without catalyst. The temperature at which the highest total conversion was taken (61.65%) is 700 ◦ C. Therefore, 700 ◦ C was selected to determine the effect of different amounts of catalyst. Fig. 2 shows the effect of different amount of catalyst (1, 5, 15%) on total conversion ratio at 700 ◦ C. Catalyst ratio of 5% by weight was selected as an optimum ratio due to two reasons; first one is the economical usage of relatively expensive nano sized catalysts and the second one is the decreasing of total conversion ratio by amount of catalyst. Therefore, further experiments were conducted using 5% catalyst ratio. 3.3. Product yields Effects of catalyst and the different temperatures on the yields were given in Table 1. With increasing temperature, gas yields and total conversion ratio also increased in uncatalyzed experiments as
Char Tar Gas
500 ◦ C
600 ◦ C
700 ◦ C
38.46 ± 1.54 36.51 ± 4.81 25.03 ± 0.37
34.66 ± 0.88 33.49 ± 3.54 31.85 ± 6.02
16.48 ± 3.67 42.72 ± 7.49 40.81 ± 3.81
expected but in the presence of nano SnO2 catalyst, gaseous product yield was increased significantly when compared to uncatalyzed experiments. Furthermore, nano SnO2 catalyst also promoted char reduction reactions and char yield substantially decreased with increasing temperature. At the 700 ◦ C, nano SnO2 catalyst showed maximum activity. At this temperature the quantity of solid product greatly reduced compared to uncatalyzed experiments in parallel with tar and gaseous product yields increased. Consequently, SnO2 nanoparticles were catalyzed the char elimination reaction [35,36]. With the elimination of char, especially gaseous product yields increased significantly. This situation shows that SnO2 nanoparticles decomposed the char to non-condensable gaseous products. 3.4. Gaseous product distribution Influence of catalyst (nano SnO2 5% by weight) and the different temperatures on the amount of gaseous products was given in Fig. 3. It can be concluded that H2 , CH4 , CO2 , CO, C2 H4 , C2 H6 and C3 H8 were the main products, and C2 H2 , C4 H10 and H2 O were inconspicuous. It can be clearly seen that SnO2 nanoparticles showed superior activity especially in the case of methane formation. With increasing temperature in the presence of nano SnO2 catalyst, the quantity of hydrogen and low molecule weight hydrocarbon (C1-C4) gases were increased in comparison with uncatalyzed reactions (Fig. 3). This species may have formed as a result of char cracking. Besides of the valuable gaseous species, CO and CO2 are also formed during the pyrolysis procedure (Fig. 3B). Gaseous product analysis of uncatalyzed pyrolysis reactions showed that CO and CO2 have a good correlation and both species were increased with increasing
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Fig. 4. GC–MS chromatograms obtained from nano SnO2 catalyzed and uncatalyzed pyrolysis experiments.
temperature. However using nano SnO2 catalyst promoted CO2 formation. But at lowest (500 ◦ C) and highest (700 ◦ C) temperatures, the quantity of CO2 extremely increased when the amount of CO decreased and this change is completely independent from the gaseous product yield.
3.5. Tar product distribution GC–MS chromatograms of the tars were presented in Fig. 4. The liquid phase is rich with regard to furan derivative compounds. Main compounds of the tars on the chromatograms in Fig. 4 were given in Table 2. At 500 ◦ C and in the presence of SnO2 catalyst,
maximum yield of 2-furanmethanol was obtained in the tar at this temperature. Levoglucosan is formed in the first step of the cellulose pyrolysis via depolymerization of cellulose, and then it can transform to other anhydrosugars as a result of dehydration and isomerization reactions. Furan derivatives such as furfural and hydroxymethylfurfural (HMF) formed from dehydration of these anhydrosugars [37]. Kato¯ reported that furfural and 5-methyl furfural were the degradation products of HMF above 400 ◦ C [38]. 2-furanmethanol was also formed with dehydration and decarbonylation reactions of LGA and DPG respectively [39]. The amount of 2-furanmethanol is significantly increased with using nano SnO2 catalyst. It is inferred that nano SnO2 catalyst can be promoted the decarbonylation reactions.
Y.O. Donar, A. Sına˘g / Journal of Analytical and Applied Pyrolysis 119 (2016) 69–74 Table 2 Main compounds of the tars on chromatograms presented in Fig. 4 (% peak area). 500 ◦ C Compound
RT
600 ◦ C
700 ◦ C
No Cat. %5 SnO2 No Cat. %5 SnO2 No Cat. %5 SnO2
Furfural 5.60 27.14 6.72 4.43 2-propylfuran 8.36 3.84 2-acetylfuran 5-methyl furfural 10.31 5.89 2-furanmethanol 15.71 32.81
25.81 4.74 3.29 5.42 41.67
39.88 0.76 4.58 6.64 4.90
25.23 3.98 3.39 5.49 35.06
41.05 5.19 4.58 7.82 11.3
27.14 4.43 3.84 5.89 32.81
This phenomenon is also confirmed by micro GC analysis results. It can be clearly seen that the quantities of CO and 2-furanmethanol substantially increase with increasing reaction temperature from 500 to 600 ◦ C, comparing with the uncatalyzed runs due to the decarbonylation reaction. Carbonyl compounds (aldehyde and ketones) are key compounds in terms of oil quality and stability [40]. Table 2 shows that the amounts of the aldehyde (furfural, 5-methyl furfural) and ketone (2-acetylfuran) decreased with increasing alcohol content in the tar (2-furanmethanol) in the presence of catalyst comparing to uncatalyzed experiments. It can be said that obtained tar is more stable due to the low carbonyl content in the presence of catalyst. From the comparison of the catalyzed and uncatalyzed runs, it can be said that the amount of furan derivatives significantly decreased (except 2-methylfurfural) when SnO2 was used as a catalyst. This results can be explained that the secondary tar decomposition reactions [41]. Formation of furan derivatives to gaseous species with secondary reactions has been reported [42] and it was also confirmed with increasing gaseous product yield in the presence of nano SnO2 . Tin has lower reactivity than carbon. Tin oxide is reduced to metallic tin, while carbon is oxidized to carbon dioxide during the pyrolysis procedure as seen in Fig. 3. Metallic tin acts as a reducing agent and this influence of tin results in transformation of aldehyde (furfural) to alcohol (2-furanmethanol). Increasing of carbon dioxide amount and char reduction in the presence of catalyst is evidence for this transformation (Fig. 3 and Table 1). Because of the complex nature of tar, fully characterization is impossible [7]. Literature data comparison is also inadequate due to the difference of pyrolysis procedures. Distribution of the obtained products can be different from each other because of the different types of reactor systems (micro, macro, fluidzed bed reactors or Py-GC/MS) [43,44]. In general, low molar mass furan derivatives were determined in tar. In a previous study, Lu et al. used sulfonated metal oxide catalysts on the pyrolysis of cellulose to obtain low molar mass furan derivatives [45]. In this study, usage of nano metal oxides without acidic surface modification of bulk metal oxides leads to formation of furan derivatives with low molar mass. The list of other compounds in the tar according to the GC–MS results is shown in Table S1 (Supplementary data). In the presence of nano metal oxide catalysts, a significant increase in the portion of aromatic compounds is observed at high temperatures (600 and 700 ◦ C). The amount of aliphatic hydrocarbons is significantly reduced when SnO2 catalyst is used. Although the presence of higher amounts of hydrocarbons in tar is desirable, higher molecular weight hydrocarbons are broken down with the lower molecular weight hydrocarbons and energy effective products. Increasing amount of valuable gases in the presence of nano catalysts supports this proposition. 4. Conclusion SnO2 nano particles were synthesized successfully and used as a catalyst on cellulose pyrolysis. The optimum ratio of catalyst was
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determined as 5% by weight. SnO2 nanoparticles lead to significant changes in terms of product yield, gaseous and liquid product distribution during the cellulose pyrolysis. We observed that SnO2 nanoparticles promoted the char cracking reactions. Besides the reduction of char yields, an increase in temperature in the presence of nano SnO2 leads to an increase in the yields of gaseous product. The liquid phase consists mainly of furan derivative compounds, which is formed by dehydration of the anhydrosugars. Effect of nano SnO2 on the promotion of decarbonylation reactions is remarkable and the composition of tar is affected by this influence. In view of tar stability, the tar obtained in the catalyzed run is more stable due to its low carbonyl content. Acknowledgements Authors greatefully acknowledge Prof. Dr. Abdülkadir AKAY (Ankara University, Department of Chemistry) and Res. Asst. Emine Kübra ÖZDI˙ L I˙ NAL (Ankara University, Department of Chemistry) for GC–MS analysis. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jaap.2016.03.016. References [1] J. Werther, M. Saenger, E.-U. Hartge, T. Ogada, Z. Siagi, Prog. Energy Combust. Sci. 26 (2000) 1. [2] A. Sına˘g, B. Uskan, S. Gülbay, J. Anal. Appl. Pyrolysis 90 (2011) 48. [3] D.A. Bulushev, J.R.H. Ross, Catal. Today 171 (2011) 1. [4] A. Demirbas¸, Energy Convers. Manage. 42 (2001) 1357. [5] B. Babu, A. Chaurasia, Energy Convers. Manage. 44 (2003) 2135. [6] R. Helleur, N. Popovic, M. Ikura, M. Stanciulescu, D. Liu, J. Anal. Appl. Pyrolysis 58 (2001) 813. [7] J. Yanik, R. Stahl, N. Troeger, A. Sinag, J. Anal. Appl. Pyrolysis 103 (2013) 134. [8] A. Aho, N. Kumar, A.V. Lashkul, K. Eränen, M. Ziolek, P. Decyk, T. Salmi, B. Holmbom, M. Hupa, D.Y. Murzin, Fuel 89 (2010) 1992. [9] T.R. Carlson, T.P. Vispute, G.W. Huber, ChemSusChem 1 (2008) 397. [10] R. French, S. Czernik, Fuel Process. Technol. 91 (2010) 25. [11] B. Matas Güell, G. Van Rossum, W. Van Swaaij, S. Kersten, L. Lefferts, K. Seshan, Appl. Catal. B: Environ. 101 (2011) 587. [12] J. Adam, M. Blazso, E. Meszaros, M. Stöcker, M.H. Nilsen, A. Bouzga, J.E. Hustad, M. Grønli, G. Øye, Fuel 84 (2005) 1494. [13] T. Liang, S.R. Wang, X.J. Guo, Y. Zhou, Y.L. Gu, Adv. Mater. Res. 347–353 (2011) 2459. [14] H. Kobayashi, T. Komanoya, S.K. Guha, K. Hara, A. Fukuoka, Appl. Cata. A: Gen. 409 (2011) 13. [15] D. Neves, H. Thunman, A. Matos, L. Tarelho, A. Gómez-Barea, Prog. Energy Combust. Sci. 37 (2011) 611. [16] A. Demirbas¸, Energy Convers. Manage. 43 (2002) 897. [17] Z. Demrew Yigezu, K. Muthukumar, J. Anal. Appl. Pyrolysis 114 (2015) 60. [18] Q. Li, L.-S. Wang, B.-Y. Hu, C. Yang, L. Zhou, L. Zhang, Mater. Lett. 61 (2007) 1615. [19] E. Lucas, S. Decker, A. Khaleel, A. Seitz, S. Fultz, A. Ponce, W. Li, C. Carnes, K.J. Klabunde, Chem. A Eur. J. 7 (2001) 2505. [20] Q. Lu, Z.-F. Zhang, C.-Q. Dong, X.-F. Zhu, Energies 3 (2010) 1805. [21] Z. Gökdai, A. Sına˘g, T. Yumak, Biomass Bioenergy 34 (2010) 402. [22] D. Fabbri, C. Torri, V. Baravelli, J. Anal. Appl. Pyrolysis 80 (2007) 24. [23] N.H. Florin, A.T. Harris, Chem. Eng. Sci. 63 (2008) 287. [24] J. Li, R. Yan, B. Xiao, D.T. Liang, D.H. Lee, Energy Fuels 22 (2007) 16. [25] M.I. Nokkosmäki, E.T. Kuoppala, E.A. Leppämäki, A.O.I. Krause, J. Anal. Appl. Pyrolysis 55 (2000) 119. [26] H.J. Park, H.S. Heo, Y.K. Park, J.H. Yim, J.K. Jeon, J. Park, C. Ryu, S.S. Kim, Bioresour. Technol. 101 (Suppl. 1) (2010) S83. [27] E. Pütün, Energy 35 (2010) 2761. [28] Q. Lu, Y. Zhang, Z. Tang, W.-z. Li, X.-f. Zhu, Fuel 89 (2010) 2096. [29] Z.D. Yigezu, K. Muthukumar, J. Anal. Appl. Pyrolysis (2016). [30] D. Fabbri, F. Fabbri, G. Falini, V. Baravelli, A. Magnani, C. Torri, H. Maskrot, Y. Leconte, J. Anal. Appl. Pyrolysis 82 (2008) 248. [31] D. Fabbri, V. Baravelli, G. Chiavari, S. Prati, E. Finessi, J. Anal. Appl. Pyrolysis 79 (2007) 2. [32] C. Torri, M. Reinikainen, C. Lindfors, D. Fabbri, A. Oasmaa, E. Kuoppala, J. Anal. Appl. Pyrolysis 88 (2010) 7. [33] H. Yang, R. Yan, H. Chen, D.H. Lee, C. Zheng, Fuel 86 (2007) 1781. [34] B. Esen, T. Yumak, A. Sına˘g, T. Yıldız, Photochem. Photobiol. 87 (2011) 267. [35] J. Li, R. Yan, B. Xiao, D.T. Liang, L. Du, Environ. Sci. Technol. 42 (2008) 6224.
74
Y.O. Donar, A. Sına˘g / Journal of Analytical and Applied Pyrolysis 119 (2016) 69–74
[36] C. Myrén, C. Hörnell, E. Björnbom, K. Sjöström, Biomass Bioenergy 23 (2002) 217. [37] Y.-C. Lin, J. Cho, G.A. Tompsett, P.R. Westmoreland, G.W. Huber, J. Phys. Chem. C 113 (2009) 20097. ¯ Agric. Biol. Chem. 31 (1967) 657. [38] K. Kato, [39] A. Aho, N. Kumar, K. Eränen, B. Holmbom, M. Hupa, T. Salmi, D.Y. Murzin, Int. J. Mol. Sci. 9 (2008) 1665. [40] N. Muhammad, W.N. Omar, Z. Man, M.A. Bustam, S. Rafiq, Y. Uemura, Ind. Eng. Chem. Res. 51 (2012) 2280.
[41] P.R. Patwardhan, D.L. Dalluge, B.H. Shanks, R.C. Brown, Bioresour. Technol. 102 (2011) 5265. [42] B. Girisuta, L.P.B.M. Janssen, H.J. Heeres, Green Chem. 8 (2006) 701. [43] P.R. Patwardhan, D.L. Dalluge, B.H. Shanks, R.C. Brown, Bioresour. Technol. 102 (2011) 5265. [44] M.-q. Chen, J. Wang, M.-x. Zhang, M.-g. Chen, X.-f. Zhu, F.-f. Min, Z.-c. Tan, J. Anal. Appl. Pyrolysis 82 (2008) 145. [45] Q. Lu, W.-M. Xiong, W.-Z. Li, Q.-X. Guo, X.-F. Zhu, Bioresour. Technol. 100 (2009) 4871.
Contents lists available at ScienceDirect
Journal of Analytical and Applied Pyrolysis journal homepage: www.elsevier.com/locate/jaap
Catalytic effect of tin oxide nanoparticles on cellulose pyrolysis Yusuf Osman Donar, Ali Sına˘g ∗ Ankara University, Department of Chemistry, 06100, Bes¸evler, Ankara, Turkey
a r t i c l e
i n f o
Article history: Received 11 August 2015 Accepted 13 March 2016 Available online 30 March 2016 Keywords: Catalytic pyrolysis SnO2 Nanoparticle Catalyst Micro-GC Gaseous product
a b s t r a c t In this study, SnO2 nanoparticles were synthesized via hydrothermal method and used as a catalyst for cellulose (model biomass) pyrolysis. Effect of catalyst on the yields of pyrolysis products was discussed in details. Optimum catalyst to biomass ratio was found as %5 (w/w). The pyrolytic oil (tar) was characterized by Gas chromatography–Mass spectrometry (GC–MS) while the gaseous products were characterized with micro Gas Chromatography (GC) to understand the catalytic ability of SnO2 nanoparticles. The results indicate that gaseous product yields significantly increase while the char yield decreases. Although the tar yields don’t change significantly in the uncatalysed runs, the product distribution in tar decreases in the presence of catalyst. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Nowadays, biomass energy is the most promising alternative to fossil fuels and it is the third biggest primary energy source after coal and petroleum [1,2]. Theoretically, the amount of CO2 released during biomass conversion is equal to the amount of CO2 absorbed by plants during photosynthesis, for this reason biomass energy is a known CO2 neutral energy type [3]. Biomass conversion techniques can be separated into four basic categories: direct combustion processes, thermochemical processes, biochemical processes and agrochemical processes. One of the most preferred techniques is thermochemical conversion process. These processes can be subdivided into gasification, pyrolysis, supercritical fluid extraction and direct liquefaction [4]. Pyrolysis is the thermal decomposition of substance in oxygen-free environment and it has an extremely important place among thermochemical conversion technologies. Pyrolysis studies are gaining increasing importance, as it is not only an independent process, but it is also a first step in the gasification or combustion process [5]. The pyrolytic oil (tar) contains many valuable hydrocarbons, therefore it can be used as a source of chemical feedstock. Moreover, due to its high calorific value of [6,7], tar can also be used as a fuel after refining. From the perspective of energy, one of the most valuable products obtained is gaseous products, the composition of which includes H2 , CH4 , C2 H4 , C2 H6 , C4 H10 , C3 H8 , C2 H2 etc. Espe-
∗ Corresponding author. E-mail address: [email protected] (A. Sına˘g). http://dx.doi.org/10.1016/j.jaap.2016.03.016 0165-2370/© 2016 Elsevier B.V. All rights reserved.
cially hydrogen is green and efficient energy source but due to high production costs and storage problems, its use is limited. One of the critical point about future is decreasing of the production costs of gases, such as hydrogen and methane, and obtaining with high calorific value products from renewable sources. Features of pyrolytic products can be upgraded via catalytic pyrolysis [8–11]. For upgrading the pyrolytic products, different kinds of catalysts were used such as clays [12,13] (ZSM-5, MCM41), supported metals [14,15] (Pt, Ni, Pd etc.) and salts [16] (Na2 CO3 , K2 CO3 , ZnCl etc.). In recent years, nano size metal oxides have attracted extensive attention in various catalytic processes due to their unique properties such as high specific surface area, strong base strength, quantum size effect, nanocrystal shape and polar surface [17–19] but they are not widely used in catalytic pyrolysis of biomass [20]. So catalytic behavior of nano metal oxides on cellulose pyrolysis should be identified. In our previous study, nano SnO2 was used as catalyst for pyrolysis of hazelnut shell and confirmed to have some good catalytic activity. Obtained results show that nano SnO2 catalyst promoted char reduction and gaseous product formation when compared with bulk form. This behavior of nano SnO2 can be explained by accelerated primary and secondary decomposition reactions of hazelnut shell due to the nano size and large external surface area of the nanoparticles [21]. Nowadays, it has been seen an increase in papers about metal oxide catalyzed pyrolysis [17,20–32] in the literature and also some of them about bulk metal oxides [17,23,25–28,32]. The aim of this study is, using SnO2 nanoparticles as a catalyst in the conversion of cellulose which is the major component of biomass (40–60% (w/w)) [33] and
70
Y.O. Donar, A. Sına˘g / Journal of Analytical and Applied Pyrolysis 119 (2016) 69–74
areas of the particles were determined by a Sorptometer (Nova 2200, Quantachrome). 2.3. Experimental set-up of pyrolysis system
Fig. 1. Cellulose pyrolysis products yields without catalyst in three different temperatures (%).
Pyrolysis experiments were performed by the system given in our previous study [21]. The pyrolysis reactor is made of stainless steel and it has a 2 mm wall thickness, 240 mm length and 20 mm diameter. 3 g of cellulose was directly mixed with the specified amounts of catalyst (1, 5, 15% (w/w)). The mixture was loaded into the reactor. Before the heating, whole pyrolysis system was purged by nitrogen about 30 min with a flow rate of 30 mL/min. The tubular furnace was heated from room temperature to intended temperature with the heating rate of 50 ◦ C/min. Pyrolysis procedure was continued for 1 h. At the end of 1 h no further liquid or gaseous product was observed. The effluent stream from the reactor was connected to condenser system and condenser system was put into ethanol/ice bath (−8 ◦ C). The tar was collected in the condenser and recovered by washing with 50 mL dichloromethane and then extracted with 50 mL water. Dichloromethane phase was used for analysis. Gaseous product was accumulated in tedlar bag connected to the output of the system. All experiments were repeated twice. The amount of residual solid product was defined as the char while the mass of liquid product collected in the condenser was defined as the tar. The amounts of char and tar were divided by the mass of the initial mass of cellulose in order to obtain char and tar yields respectively. The yield of gas was calculated by difference. 2.4. Analysis of gaseous products The composition of the gaseous product was analyzed with SRA Instruments T-3000 model micro GC. GC consists of two modules with TCD detector. The first module (MS5A) was set at 90 ◦ C and use for determination of He, H2 , N2 , O2 , CO and CH4 and use Argon as the carrier gas. The second module (PPU) was set at 70 ◦ C for the separation of CO2 , H2 O (g) and C1-C4 hydrocarbon gases with using Helium as the carrier gas. Analysis results obtained from instrument (% mole) were converted to [mg gas/g biomass] as specified in Eqs. (1)–(3).
Fig. 2. Effect of different amount of catalyst on total conversion ratio at 700 ◦ C.
determining the effects of products distribution, with this respect, nano SnO2 was used as a catalyst for the pyrolysis of cellulose to test whether they had the capability to upgrade the properties of pyrolytic oil and gaseous fractions. Characterization of the tar and gaseous fractions was performed using GC/MS and micro-GC. The catalytic and non-catalytic products were compared to reveal the catalytic capabilities of these catalysts.
Total gas amount (g) = [initial mass of cellulose (g) × gas yield (%)] ÷ 100
(1)
A: Total mole amount of gaseous products (mole) A=
total gas amount (g) M of gaseous products
g.mol−1
(2)
2. Experimental
mg gas = g cellulose
2.1. Materials
2.5. Analysis of liquid products
Sn powder (J.T. Baker), H2 SO4 (Sigma Aldrich 98%) and H2 O2 (Merck 35%) were used for synthesis of SnO2 nanoparticles. Microcrystalline cellulose powder (Sigma Aldrich) was used for pyrolysis experiments as a model biomass. All chemicals were analytical grade and used without further purification.
GC–MS analysis of the liquid products (dichloromethane phase) was performed by Shimadzu GC–MS-QP2010 Plus with a HP-5MS (30 m × 0.25 mm × 0.25 m) capillary column. Helium was used as the carrier gas. The amount injected was 1 L and split ratio was 4:1. The oven temperature was set to 50 ◦ C for 5 min, then raised to 300 ◦ C with 5 ◦ C/min and stayed at 300 ◦ C for 15 min. Total run time was 70 min and flow rate was 0.8 mL/min. Mass spectra were recorded under 70 eV electron ionization and 50–750 m/z interval. The mass spectra obtained by GC–MS was interpreted based on an automatic library search (Wiley & NIST) and discussed with related literature data.
2.2. Catalyst preparation and characterization Hydrothermal synthesis of SnO2 nanoparticles as well as transmission electron micrographs (TEM) and X-ray diffraction patterns (XRD) were described in our previous study [21,34]. The surface
Ax mole% result of the gas 100
×
molar mass of the gas initial mass of cellulose
(3)
Y.O. Donar, A. Sına˘g / Journal of Analytical and Applied Pyrolysis 119 (2016) 69–74
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Fig. 3. Gaseous product distribution at different temperatures with and without 5% nano SnO2 .
3. Results and discussion
Table 1 Effects of 5% SnO2 catalyst and the different temperatures on the yields (%).
3.1. Material characterization The XRD patterns and TEM images of SnO2 nano particles were given in our previous study [21]. Synthesized SnO2 nanoparticles have 30.42 m2 /g BET surface area. SnO2 nanoparticles have a relatively low surface area due to the huge agglomeration that can be seen in TEM images, however SnO2 nanoparticles show catalytic activity as seen in the results of this study. 3.2. The effect of the amount of catalyst on cellulose conversion efficiency Pyrolysis experiments were conducted in three different temperatures with and without catalyst. Since the main purpose of this study was to obtain gaseous and tar from cellulose, best reaction condition was determined according to highest tar + gas yield (%) and this tar + gas yield was labeled as a total conversion ratio. Total conversion ratios were examined to investigate the amount of catalyst on cellulose conversion efficiency. Fig. 1 shows the products yields in different temperatures without catalyst. The temperature at which the highest total conversion was taken (61.65%) is 700 ◦ C. Therefore, 700 ◦ C was selected to determine the effect of different amounts of catalyst. Fig. 2 shows the effect of different amount of catalyst (1, 5, 15%) on total conversion ratio at 700 ◦ C. Catalyst ratio of 5% by weight was selected as an optimum ratio due to two reasons; first one is the economical usage of relatively expensive nano sized catalysts and the second one is the decreasing of total conversion ratio by amount of catalyst. Therefore, further experiments were conducted using 5% catalyst ratio. 3.3. Product yields Effects of catalyst and the different temperatures on the yields were given in Table 1. With increasing temperature, gas yields and total conversion ratio also increased in uncatalyzed experiments as
Char Tar Gas
500 ◦ C
600 ◦ C
700 ◦ C
38.46 ± 1.54 36.51 ± 4.81 25.03 ± 0.37
34.66 ± 0.88 33.49 ± 3.54 31.85 ± 6.02
16.48 ± 3.67 42.72 ± 7.49 40.81 ± 3.81
expected but in the presence of nano SnO2 catalyst, gaseous product yield was increased significantly when compared to uncatalyzed experiments. Furthermore, nano SnO2 catalyst also promoted char reduction reactions and char yield substantially decreased with increasing temperature. At the 700 ◦ C, nano SnO2 catalyst showed maximum activity. At this temperature the quantity of solid product greatly reduced compared to uncatalyzed experiments in parallel with tar and gaseous product yields increased. Consequently, SnO2 nanoparticles were catalyzed the char elimination reaction [35,36]. With the elimination of char, especially gaseous product yields increased significantly. This situation shows that SnO2 nanoparticles decomposed the char to non-condensable gaseous products. 3.4. Gaseous product distribution Influence of catalyst (nano SnO2 5% by weight) and the different temperatures on the amount of gaseous products was given in Fig. 3. It can be concluded that H2 , CH4 , CO2 , CO, C2 H4 , C2 H6 and C3 H8 were the main products, and C2 H2 , C4 H10 and H2 O were inconspicuous. It can be clearly seen that SnO2 nanoparticles showed superior activity especially in the case of methane formation. With increasing temperature in the presence of nano SnO2 catalyst, the quantity of hydrogen and low molecule weight hydrocarbon (C1-C4) gases were increased in comparison with uncatalyzed reactions (Fig. 3). This species may have formed as a result of char cracking. Besides of the valuable gaseous species, CO and CO2 are also formed during the pyrolysis procedure (Fig. 3B). Gaseous product analysis of uncatalyzed pyrolysis reactions showed that CO and CO2 have a good correlation and both species were increased with increasing
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Fig. 4. GC–MS chromatograms obtained from nano SnO2 catalyzed and uncatalyzed pyrolysis experiments.
temperature. However using nano SnO2 catalyst promoted CO2 formation. But at lowest (500 ◦ C) and highest (700 ◦ C) temperatures, the quantity of CO2 extremely increased when the amount of CO decreased and this change is completely independent from the gaseous product yield.
3.5. Tar product distribution GC–MS chromatograms of the tars were presented in Fig. 4. The liquid phase is rich with regard to furan derivative compounds. Main compounds of the tars on the chromatograms in Fig. 4 were given in Table 2. At 500 ◦ C and in the presence of SnO2 catalyst,
maximum yield of 2-furanmethanol was obtained in the tar at this temperature. Levoglucosan is formed in the first step of the cellulose pyrolysis via depolymerization of cellulose, and then it can transform to other anhydrosugars as a result of dehydration and isomerization reactions. Furan derivatives such as furfural and hydroxymethylfurfural (HMF) formed from dehydration of these anhydrosugars [37]. Kato¯ reported that furfural and 5-methyl furfural were the degradation products of HMF above 400 ◦ C [38]. 2-furanmethanol was also formed with dehydration and decarbonylation reactions of LGA and DPG respectively [39]. The amount of 2-furanmethanol is significantly increased with using nano SnO2 catalyst. It is inferred that nano SnO2 catalyst can be promoted the decarbonylation reactions.
Y.O. Donar, A. Sına˘g / Journal of Analytical and Applied Pyrolysis 119 (2016) 69–74 Table 2 Main compounds of the tars on chromatograms presented in Fig. 4 (% peak area). 500 ◦ C Compound
RT
600 ◦ C
700 ◦ C
No Cat. %5 SnO2 No Cat. %5 SnO2 No Cat. %5 SnO2
Furfural 5.60 27.14 6.72 4.43 2-propylfuran 8.36 3.84 2-acetylfuran 5-methyl furfural 10.31 5.89 2-furanmethanol 15.71 32.81
25.81 4.74 3.29 5.42 41.67
39.88 0.76 4.58 6.64 4.90
25.23 3.98 3.39 5.49 35.06
41.05 5.19 4.58 7.82 11.3
27.14 4.43 3.84 5.89 32.81
This phenomenon is also confirmed by micro GC analysis results. It can be clearly seen that the quantities of CO and 2-furanmethanol substantially increase with increasing reaction temperature from 500 to 600 ◦ C, comparing with the uncatalyzed runs due to the decarbonylation reaction. Carbonyl compounds (aldehyde and ketones) are key compounds in terms of oil quality and stability [40]. Table 2 shows that the amounts of the aldehyde (furfural, 5-methyl furfural) and ketone (2-acetylfuran) decreased with increasing alcohol content in the tar (2-furanmethanol) in the presence of catalyst comparing to uncatalyzed experiments. It can be said that obtained tar is more stable due to the low carbonyl content in the presence of catalyst. From the comparison of the catalyzed and uncatalyzed runs, it can be said that the amount of furan derivatives significantly decreased (except 2-methylfurfural) when SnO2 was used as a catalyst. This results can be explained that the secondary tar decomposition reactions [41]. Formation of furan derivatives to gaseous species with secondary reactions has been reported [42] and it was also confirmed with increasing gaseous product yield in the presence of nano SnO2 . Tin has lower reactivity than carbon. Tin oxide is reduced to metallic tin, while carbon is oxidized to carbon dioxide during the pyrolysis procedure as seen in Fig. 3. Metallic tin acts as a reducing agent and this influence of tin results in transformation of aldehyde (furfural) to alcohol (2-furanmethanol). Increasing of carbon dioxide amount and char reduction in the presence of catalyst is evidence for this transformation (Fig. 3 and Table 1). Because of the complex nature of tar, fully characterization is impossible [7]. Literature data comparison is also inadequate due to the difference of pyrolysis procedures. Distribution of the obtained products can be different from each other because of the different types of reactor systems (micro, macro, fluidzed bed reactors or Py-GC/MS) [43,44]. In general, low molar mass furan derivatives were determined in tar. In a previous study, Lu et al. used sulfonated metal oxide catalysts on the pyrolysis of cellulose to obtain low molar mass furan derivatives [45]. In this study, usage of nano metal oxides without acidic surface modification of bulk metal oxides leads to formation of furan derivatives with low molar mass. The list of other compounds in the tar according to the GC–MS results is shown in Table S1 (Supplementary data). In the presence of nano metal oxide catalysts, a significant increase in the portion of aromatic compounds is observed at high temperatures (600 and 700 ◦ C). The amount of aliphatic hydrocarbons is significantly reduced when SnO2 catalyst is used. Although the presence of higher amounts of hydrocarbons in tar is desirable, higher molecular weight hydrocarbons are broken down with the lower molecular weight hydrocarbons and energy effective products. Increasing amount of valuable gases in the presence of nano catalysts supports this proposition. 4. Conclusion SnO2 nano particles were synthesized successfully and used as a catalyst on cellulose pyrolysis. The optimum ratio of catalyst was
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determined as 5% by weight. SnO2 nanoparticles lead to significant changes in terms of product yield, gaseous and liquid product distribution during the cellulose pyrolysis. We observed that SnO2 nanoparticles promoted the char cracking reactions. Besides the reduction of char yields, an increase in temperature in the presence of nano SnO2 leads to an increase in the yields of gaseous product. The liquid phase consists mainly of furan derivative compounds, which is formed by dehydration of the anhydrosugars. Effect of nano SnO2 on the promotion of decarbonylation reactions is remarkable and the composition of tar is affected by this influence. In view of tar stability, the tar obtained in the catalyzed run is more stable due to its low carbonyl content. Acknowledgements Authors greatefully acknowledge Prof. Dr. Abdülkadir AKAY (Ankara University, Department of Chemistry) and Res. Asst. Emine Kübra ÖZDI˙ L I˙ NAL (Ankara University, Department of Chemistry) for GC–MS analysis. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jaap.2016.03.016. References [1] J. Werther, M. Saenger, E.-U. Hartge, T. Ogada, Z. Siagi, Prog. Energy Combust. Sci. 26 (2000) 1. [2] A. Sına˘g, B. Uskan, S. Gülbay, J. Anal. Appl. Pyrolysis 90 (2011) 48. [3] D.A. Bulushev, J.R.H. Ross, Catal. Today 171 (2011) 1. [4] A. Demirbas¸, Energy Convers. Manage. 42 (2001) 1357. [5] B. Babu, A. Chaurasia, Energy Convers. Manage. 44 (2003) 2135. [6] R. Helleur, N. Popovic, M. Ikura, M. Stanciulescu, D. Liu, J. Anal. Appl. Pyrolysis 58 (2001) 813. [7] J. Yanik, R. Stahl, N. Troeger, A. Sinag, J. Anal. Appl. Pyrolysis 103 (2013) 134. [8] A. Aho, N. Kumar, A.V. Lashkul, K. Eränen, M. Ziolek, P. Decyk, T. Salmi, B. Holmbom, M. Hupa, D.Y. Murzin, Fuel 89 (2010) 1992. [9] T.R. Carlson, T.P. Vispute, G.W. Huber, ChemSusChem 1 (2008) 397. [10] R. French, S. Czernik, Fuel Process. Technol. 91 (2010) 25. [11] B. Matas Güell, G. Van Rossum, W. Van Swaaij, S. Kersten, L. Lefferts, K. Seshan, Appl. Catal. B: Environ. 101 (2011) 587. [12] J. Adam, M. Blazso, E. Meszaros, M. Stöcker, M.H. Nilsen, A. Bouzga, J.E. Hustad, M. Grønli, G. Øye, Fuel 84 (2005) 1494. [13] T. Liang, S.R. Wang, X.J. Guo, Y. Zhou, Y.L. Gu, Adv. Mater. Res. 347–353 (2011) 2459. [14] H. Kobayashi, T. Komanoya, S.K. Guha, K. Hara, A. Fukuoka, Appl. Cata. A: Gen. 409 (2011) 13. [15] D. Neves, H. Thunman, A. Matos, L. Tarelho, A. Gómez-Barea, Prog. Energy Combust. Sci. 37 (2011) 611. [16] A. Demirbas¸, Energy Convers. Manage. 43 (2002) 897. [17] Z. Demrew Yigezu, K. Muthukumar, J. Anal. Appl. Pyrolysis 114 (2015) 60. [18] Q. Li, L.-S. Wang, B.-Y. Hu, C. Yang, L. Zhou, L. Zhang, Mater. Lett. 61 (2007) 1615. [19] E. Lucas, S. Decker, A. Khaleel, A. Seitz, S. Fultz, A. Ponce, W. Li, C. Carnes, K.J. Klabunde, Chem. A Eur. J. 7 (2001) 2505. [20] Q. Lu, Z.-F. Zhang, C.-Q. Dong, X.-F. Zhu, Energies 3 (2010) 1805. [21] Z. Gökdai, A. Sına˘g, T. Yumak, Biomass Bioenergy 34 (2010) 402. [22] D. Fabbri, C. Torri, V. Baravelli, J. Anal. Appl. Pyrolysis 80 (2007) 24. [23] N.H. Florin, A.T. Harris, Chem. Eng. Sci. 63 (2008) 287. [24] J. Li, R. Yan, B. Xiao, D.T. Liang, D.H. Lee, Energy Fuels 22 (2007) 16. [25] M.I. Nokkosmäki, E.T. Kuoppala, E.A. Leppämäki, A.O.I. Krause, J. Anal. Appl. Pyrolysis 55 (2000) 119. [26] H.J. Park, H.S. Heo, Y.K. Park, J.H. Yim, J.K. Jeon, J. Park, C. Ryu, S.S. Kim, Bioresour. Technol. 101 (Suppl. 1) (2010) S83. [27] E. Pütün, Energy 35 (2010) 2761. [28] Q. Lu, Y. Zhang, Z. Tang, W.-z. Li, X.-f. Zhu, Fuel 89 (2010) 2096. [29] Z.D. Yigezu, K. Muthukumar, J. Anal. Appl. Pyrolysis (2016). [30] D. Fabbri, F. Fabbri, G. Falini, V. Baravelli, A. Magnani, C. Torri, H. Maskrot, Y. Leconte, J. Anal. Appl. Pyrolysis 82 (2008) 248. [31] D. Fabbri, V. Baravelli, G. Chiavari, S. Prati, E. Finessi, J. Anal. Appl. Pyrolysis 79 (2007) 2. [32] C. Torri, M. Reinikainen, C. Lindfors, D. Fabbri, A. Oasmaa, E. Kuoppala, J. Anal. Appl. Pyrolysis 88 (2010) 7. [33] H. Yang, R. Yan, H. Chen, D.H. Lee, C. Zheng, Fuel 86 (2007) 1781. [34] B. Esen, T. Yumak, A. Sına˘g, T. Yıldız, Photochem. Photobiol. 87 (2011) 267. [35] J. Li, R. Yan, B. Xiao, D.T. Liang, L. Du, Environ. Sci. Technol. 42 (2008) 6224.
74
Y.O. Donar, A. Sına˘g / Journal of Analytical and Applied Pyrolysis 119 (2016) 69–74
[36] C. Myrén, C. Hörnell, E. Björnbom, K. Sjöström, Biomass Bioenergy 23 (2002) 217. [37] Y.-C. Lin, J. Cho, G.A. Tompsett, P.R. Westmoreland, G.W. Huber, J. Phys. Chem. C 113 (2009) 20097. ¯ Agric. Biol. Chem. 31 (1967) 657. [38] K. Kato, [39] A. Aho, N. Kumar, K. Eränen, B. Holmbom, M. Hupa, T. Salmi, D.Y. Murzin, Int. J. Mol. Sci. 9 (2008) 1665. [40] N. Muhammad, W.N. Omar, Z. Man, M.A. Bustam, S. Rafiq, Y. Uemura, Ind. Eng. Chem. Res. 51 (2012) 2280.
[41] P.R. Patwardhan, D.L. Dalluge, B.H. Shanks, R.C. Brown, Bioresour. Technol. 102 (2011) 5265. [42] B. Girisuta, L.P.B.M. Janssen, H.J. Heeres, Green Chem. 8 (2006) 701. [43] P.R. Patwardhan, D.L. Dalluge, B.H. Shanks, R.C. Brown, Bioresour. Technol. 102 (2011) 5265. [44] M.-q. Chen, J. Wang, M.-x. Zhang, M.-g. Chen, X.-f. Zhu, F.-f. Min, Z.-c. Tan, J. Anal. Appl. Pyrolysis 82 (2008) 145. [45] Q. Lu, W.-M. Xiong, W.-Z. Li, Q.-X. Guo, X.-F. Zhu, Bioresour. Technol. 100 (2009) 4871.