Energy Fuels 2010, 24, 5735–5740 Published on Web 09/29/2010
: DOI:10.1021/ef100896q
Aromatics Production via Catalytic Pyrolysis of Pyrolytic Lignins from Bio-Oil Yan Zhao,† Li Deng,† Bin Liao,‡ Yao Fu,*,† and Qing-Xiang Guo*,†,‡ † Anhui Province Key Laboratory of Biomass Clean Energy, Department of Chemistry, University of Science and Technology of China, Hefei 230026, China, and, and ‡Key Laboratory of Cellulose and Lignocellulosics Chemistry, Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, China
Received July 14, 2010. Revised Manuscript Received August 28, 2010
Herein we reported a promising method for the production of aromatics from pyrolytic lignin (PL). Compared to the lignins derived from pulping process, the PLs obtained from bio-oil give more aromatics (40% in carbon yield) and do not generate eff luvial gas containing sulfur. More importantly, phenols are the main products with selectivity over 90% at 600 °C without catalyst. In the presence of ZSM-5, the coke deposition was not obvious and the selectivity for aromatic hydrocarbons is more than 87%, indicating robustness of ZSM-5 for deoxygenating and high tolerance to PLs. Therefore we have demonstrated the catalytic pyrolysis of PLs is an alternative way to produce fuel additives and useful chemicals.
low heating value, low thermal stability, high viscosity, and poor volatility, which limited its usage in internal combustion engines.4 To upgrade the bio-oil, researchers developed several methods including esterification,5-7 catalytic reforming,8-11 hydrogenation,12,13 and ketonization.14,15 Because of the different reactivity and interactions of more than 300 components in the oil, it is rather difficult to improve its qualities to meet the requirement of transportation fuels by a single treatment. Hence the combination of different methods and tools is necessary. Herein, we propose a strategy containing separation and catalytic conversion steps for bio-oil upgrading (Scheme 1). As we have previously shown, bio-oil can be separated effectively into two fractions: the distillate and the nonvolatile PL by the distillation in glycerol.16 Moreover, in a recent publication by Huber et al., alkanes, hydrogen, and polyols can be obtained from the water-soluble bio-oil via aqueous phase reforming (APR).17 Considering the similarity of the organic composition of the distillate and the water-soluble bio-oil, it is believed that the distillate can also be converted to alkanes by the APR technique. With the aim of converting the other fraction of biooil and finishing the upgrading strategy for the whole bio-oil, the pyrolysis of PL has been carried out in this work. It is well-known that lignin is the second most abundant component of biomass, which accounts for about 30% of plant biomass. Indeed lignin can be regarded as the major aromatic source of a biobased economy. The selective transformation of lignin to aromatics with high yield and less coke
1. Introduction Traditional chemical industry has been dependent on petroleum for more than a half century, which results in rapid depletion of fossil resource and the problem of greenhouse gas emissions. It requires strategies for alternative fuels and chemicals production from biomass especially from nonedible biomass.1-3 In this respects, fast pyrolysis is a promising technology for biomass utilization and has many advantages. The product of this technology, known as bio-oil, has lower cost than other biofuels, a wide range of feedstock, and more than 60% energy of the feedstock.2 However, it is of poor qualities: *To whom correspondence should be addressed. Fax: þ86-5513606689. E-mail:
[email protected] (Y.F.);
[email protected] (Q.X.G.). (1) Huber, G. W.; Iborra, S.; Corma, A. Synthesis of transportation fuels from biomass: Chemistry, catalysts, and engineering. Chem. Rev. 2006, 106 (9), 4044–4098. (2) Corma, A.; Iborra, S.; Velty, A. Chemical routes for the transformation of biomass into chemicals. Chem. Rev. 2007, 107 (6), 2411–2502. (3) Zakzeski, J.; Bruijnincx, P. C. A.; Jongerius, A. L.; Weckhuysen, B. M. The catalytic valorization of lignin for the production of renewable chemicals. Chem. Rev. 2010, 110 (6), 3552–3599. (4) Czernik, S.; Bridgwater, A. V. Overview of applications of biomass fast pyrolysis oil. Energy Fuels 2004, 18 (2), 590–598. (5) Zhang, Q.; Chang, J.; Wang, T. J.; Xu, Y. Upgrading bio-oil over different solid catalysts. Energy Fuels 2006, 20 (6), 2717–2720. (6) Peng, J.; Chen, P.; Lou, H.; Zheng, X. M. Upgrading of bio-oil over aluminum silicate in supercritical ethanol. Energy Fuels 2008, 22 (5), 3489–3492. (7) Xiong, W. M.; Zhu, M. Z.; Deng, L.; Fu, Y.; Guo, Q. X. Esterification of Organic Acid in Bio-Oil using Acidic Ionic Liquid Catalysts. Energy Fuels 2009, 23, 2278–2283. (8) Sharma, R. K.; Bakhshi, N. N. Catalytic Upgrading of Pyrolysis Oil. Energy Fuels 1993, 7 (2), 306–314. (9) Gayubo, A. G.; Aguayo, A. T.; Atutxa, A.; Aguado, R.; Olazar, M.; Bilbao, J. Transformation of oxygenate components of biomass pyrolysis oil on a HZSM-5 zeolite. H. Aldehydes, ketones, and acids. Ind. Eng. Chem. Res. 2004, 43 (11), 2619–2626. (10) Gayubo, A. G.; Aguayo, A. T.; Atutxa, A.; Aguado, R.; Bilbao, J. Transformation of oxygenate components of biomass pyrolysis oil on a HZSM-5 zeolite. I. Alcohols and phenols. Ind. Eng. Chem. Res. 2004, 43 (11), 2610–2618. (11) Nilsen, M. H.; Antonakou, E.; Bouzga, A.; Lappas, A.; Mathisen, K.; Stocker, M. Investigation of the effect of metal sites in Me-Al-MCM-41 (Me = Fe, Cu or Zn) on the catalytic behavior during the pyrolysis of wooden based biomass. Microporous Mesoporous Mater. 2007, 105 (1-2), 189–203. r 2010 American Chemical Society
(12) Elliott, D. C. Historical developments in hydroprocessing biooils. Energy Fuels 2007, 21 (3), 1792–1815. (13) Tang, Z.; Lu, Q.; Zhang, Y.; Zhu, X. F.; Guo, Q. X. One Step Bio-Oil Upgrading through Hydrotreatment, Esterification, and Cracking. Ind. Eng. Chem. Res. 2009, 48 (15), 6923–6929. (14) Gartner, C. A.; Serrano-Ruiz, J. C.; Braden, D. J.; Dumesic, J. A. Catalytic Upgrading of Bio-Oils by Ketonization. Chemsuschem 2009, 2 (12), 1121–1124. (15) Deng, L.; Fu, Y.; Guo, Q. X. Upgraded Acidic Components of Bio-oil through Catalytic Ketonic Condensation. Energy Fuels 2009, 23 (1), 564–568. (16) Deng, L.; Yan, Z.; Fu, Y.; Guo, Q. X. Green Solvent for Flash Pyrolysis Oil Separation. Energy Fuels 2009, 23, 3337–3338. (17) Vispute, T. P.; Huber, G. W. Production of hydrogen, alkanes and polyols by aqueous phase processing of wood-derived pyrolysis oils. Green Chem. 2009, 11 (9), 1433–1445.
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Energy Fuels 2010, 24, 5735–5740
: DOI:10.1021/ef100896q
Zhao et al.
Scheme 1. Strategy for Bio-Oil Upgrading with Combined Treatments
formation was described as “new technology” by Zakzeski et al.3 In terms of heating value and elemental composition, it is more adaptable to produce fuels than cellulose and hemicellulose and drawing more and more attention. Kou et al. carried out a two step hydroprocess over noble-metal catalysts converting it to gasoline and diesel selectively.18,19 The Acell lignin obtained from organosolv pulping process was catalytic pyrolyzed with acetone for the production of gasoline range hydrocarbons.20 Under pyrolysis conditions, natural lignin is broken down into volatile aromatics and nonvolatile oligomers, the so-called PL, which will polymerize with aldehydes and phenols forming coke in bio-oil causing poor stability of the oil. Nevertheless the PL contributes a large part of the heating value of bio-oil for its low oxygen content. Zhang et al. transformed it to stable organics by employing ruthenium catalysts combining the supercritical ethanol technique.21 Bakhshi et al upgraded PL over HZSM-5 using tetralin as hydrogen-donating dilute.8 Regarding the economic feasibility of the fuels and chemicals, zeolite catalysts are superior for industrial scale process because they do not need noble metals and external hydrogen for catalytic cracking. They play important roles not only in the petroleum industry but also in biomass conversion. For instance, carbohydrates, more than a half of which is oxygen, can be converted to aromatics over zeolites with a maximum carbon yield of 30%.22,23 In this study, employing the powerful tools, an initial approach to the abovementioned “new technology” has been carried out. The PLs produce near 40% aromatics under pyrolysis condition.
Table 1. Typical Properties of the Catalysts entry 1 2 3 4 5 a
catalysts ZSM-5 HZSM-5 β-zeolite MCM-41 SBA-15
BET surface area/m2/g 420 350 63 1000a 807
average pore diameter/nm a
0.5 0.5a 0.7a 3.8a 6.9
Si/Al ratio 50a 50a 50a 50a pure silica
Provided by the manufacturers.
Figure 1. Schematic diagram of experimental apparatus for catalytic pyrolysis of PLs.
according to the method of Scholze,24,25 and the PL separated from the mixture of glycerol and bio-oil (GPL) was obtained as described elsewhere.16 The other two lignins: alkali lignin (AL) and kraft lignin (KL) were purchased from Sigma-Aldrich Co. Ltd. The catalysts ZSM-5, HZSM-5, and β-zeolite were provided by the catalyst plant of Nankai University, and MCM-41 was obtained from Fuxu Zeolite Co. Ltd. SBA-15 was synthesized according to the method described elsewhere.26 The typical properties of them are listed in Table 1. 2.2. Experimental Procedure. The pyrolysis of PLs was carried out in a tubular reactor (1 cm i.d.) made of quartz glass. As described in Figure 1, before the reaction, 0.5 g of lignin and 0.5 g of zeolite were loaded in the branched tube and the heating zone with quartz wool, respectively. During the pyrolysis, lignin was fed into the heating zone by a piston continuously within 3 min, and the temperature was kept for another 2 min with nitrogen at the rate of 50 mL/min. Then liquid product was condensed and collected in a liquid nitrogen trap. For catalyst regeneration, air (50 mL/min) was employed to remove the coke at 600 °C.
2. Experimental Section 2.1. Materials. The bio-oil used in this work was produced through the fast pyrolysis of rice husk in the fluidized reactor at about 550 °C. The PLs were obtained from bio-oil by two methods. The PL precipitated from water (WPL) was prepared (18) Yan, N.; Zhao, C.; Dyson, P. J.; Wang, C.; Liu, L. T.; Kou, Y. Selective Degradation of Wood Lignin over Noble-Metal Catalysts in a Two-Step Process. Chemsuschem 2008, 1 (7), 626–629. (19) Zhao, C.; Kou, Y.; Lemonidou, A. A.; Li, X. B.; Lercher, J. A. Highly Selective Catalytic Conversion of Phenolic Bio-Oil to Alkanes. Angew. Chem., Int. Ed. 2009, 48 (22), 3987–3990. (20) Thring, R. W.; Katikaneni, S. P. R.; Bakhshi, N. N. The production of gasoline range hydrocarbons from Alcell lignin using HZSM-5 catalyst. Fuel Process. Technol. 2000, 62 (1), 17–30. (21) Tang, Z.; Zhang, Y.; Guo, Q. X. Catalytic Hydrocracking of Pyrolytic Lignin to Liquid Fuel in Supercritical Ethanol. Ind. Eng. Chem. Res. 2010, 49 (5), 2040–2046. (22) Carlson, T. R.; Vispute, T. R.; Huber, G. W. Green gasoline by catalytic fast pyrolysis of solid biomass derived compounds. Chemsuschem 2008, 1 (5), 397–400. (23) Carlson, T. R.; Tompsett, G. A.; Conner, W. C.; Huber, G. W. Aromatic Production from Catalytic Fast Pyrolysis of Biomass-Derived Feedstocks. Top. Catal. 2009, 52 (3), 241–252. (24) Scholze, B.; Meier, D. Characterization of the water-insoluble fraction from pyrolysis oil (pyrolytic lignin). Part I. PY-GC/MS, FTIR, and functional groups. J. Anal. Appl. Pyrol. 2001, 60 (1), 41–54.
(25) Scholze, B.; Hanser, C.; Meier, D. Characterization of the waterinsoluble fraction from fast pyrolysis liquids (pyrolytic lignin) Part II. GPC, carbonyl goups, and C-13-NMR. J. Anal. Appl. Pyrol. 2001, 58, 387–400. (26) Zhao, D. Y.; Feng, J. L.; Huo, Q. S.; Melosh, N.; Fredrickson, G. H.; Chmelka, B. F.; Stucky, G. D. Triblock copolymer syntheses of mesoporous silica with periodic 50 to 300 angstrom pores. Science 1998, 279 (5350), 548–552.
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Table 2. Elemental Composition of the Lignins a
entry lignin C/wt% H/wt% O/wt% 1 2 3 4
WPL GPL AL KL
63.7 62.54 49.01 41.68
6.26 6.12 5.15 5.08
28.86 30.04 38.77 33.97
Table 3. Molecular Weight and TGA of the Lignins c
N/wt% S/wt% Na/wt% 1.18 1.30 0.19 0.14
trace trace 4.00b 11.13b
trace trace 2.88 8.00
a The oxygen content was estimated by difference. b The sulfur content was provided by the Aldrich Co., Ltd. c The sodium content was estimated according to the sulfur content.
Mn
Mw
DPb
weight loss/wt%
DTG peak temperature/°C
1 2 3 4
WPL GPL AL KL
644a 757a 10 000c 7 000c
1 047a 1 331a 60 000c 52 000c
6-7 8-9 ∼400 ∼350
66.31 62.57 42.72 54.69
313 357 341 293
Figure 2. Pyrolysis product distributions of the lignins without catalyst: aromatics (green), gas (cyan), and coke (gray).
The molecular weight and the degree of polymerization of the lignins are given in Table 3. It is clear that the two PLs are oligomers with a degree of polymerization (DP) less than 8 while the other two are polymers with the weight average molecular weight more than 50 000. The results of TGA clearly show that WPL leaves only 34 wt % of coke (dry basis), and GPL leaves 37 wt % coke at 800 °C. For differential thermal gravimetry (DTG), the weight loss peak of GPL appears at higher temperature, which is probably caused by the polymerization when heated in glycerol. Although the peak temperature of AL is close to WPL, the coke yields of it are much higher (see the Supporting Information for TGA and DTG curves). It seems that high degree of polymerization and salt composition increase the coke yield. 3.2. Pyrolysis of Lignin without Catalyst. The lignins are the solid oligomers and polymers which cannot contact the internal surface of the zeolites directly. When heated in the presence of catalysts, they are broken down forming pyrolytic vapors first and then the vapors enter the pores of zeolites and undergo catalytic reactions. In order to find the product distributions of the vapors formed in the first step, the lignins were pyrolyzed without catalyst. As shown in Figure 2, the distribution was examined at different temperature. Generally, at 600 °C, lignins yield the most organic liquid products and moderate coke and gas. PLs exhibit higher selectivity for the aromatics and the carbon yield are 40% and 37% for WPL and GPL. Regarding the structural properties of GPL and WPL, the difference in yield of aromatics may be attributed to the molecular weight and condensation with some aldehydes.16 Higher temperature will increase the yield of gas while reduce the liquids and coke formation.
3. Results and Discussion 3.1. Lignins Properties. To compare the difference in pyrolysis behavior of PLs and other lignin compounds, four kinds of lignins, WPL, GPL, AL, and KL, were used as feed. The later two lignins are the byproduct of paper industry. Because of the different treatments, the four lignins have different properties. According to elemental analysis (Table 2), the chemical formulas of WPL, GPL, AL, and KL are CO0.34H1.17N0.02, CO0.36H1.17N0.02, CO0.59H1.25S0.03Na0.03, and CO0.29H1.45S0.10Na0.10, respectively. The C, O, and H contents of lignins are similar to coal. Assuming the products of the cracking reaction are toluene, CO, and H2O, the theoretical molar carbon yield of toluene from PLs is about 79% (eq 1) while the value for glucose is 63%.23 It suggests PLs will produce more aromatics than carbohydrates. The hydrogen-to-carbon effective ratio defined as eq 2 is another important factor to compare the relative amount of hydrogen and predict the hydrocarbons yield. For example, the value of glucose, PLs, benzene, and alkene are 0, 0.5, 1.0, and 2, respectively. It means the feed with the higher ratio may produce more hydrocarbons using less hydrogen. C100 O35 H117 f 247=22C7 H8 ð79% carbon yieldÞ
Heff =C ¼ ðH - 2OÞ=C
lignin
a Adapted from ref 16. b Estimated according to ref 25. c The values are provided by Aldrich Co. Ltd.
2.3. Analytical Determination. Nitrogen adsorption/desorption isotherms was measured by a Micromeritics ASAP 2020 analyzer. The surface area was determined using the BarrettEmmet-Taller (BET) method, and the average pore size of SBA-15 was determined by the Barret-Joyner-Halenda (BJH) method. Liquid samples were analyzed by a gas chromatograph-mass spectrometer (GC-MS; Thermal Trace GC Ultra with a PolarisQ ion trap mass spectrometer) equipped with a TR-35MS capillary column (30 m 0.25 mm 25 μm). Split injection was performed at a split ratio of 50 using helium (99.999%) as the carrier gas. The water content in the liquid samples was determined by Karl Fischer titration. The gas was collected by a gasbag and sampled for analysis using a GC with thermal conductivity detector (TCD). The yield of gaseous products were measure by weight difference (weight of gas = weight of feed - weight of liquid - weight of coke). The components were determined by the external standard method using calibration gas (a mixture of H2, CO, CO2, CH4, C2H6, C2H4, C3H8, and C3H6). The elemental analysis of lignins and coke was performed employing a Vario EL III analyzer. The thermal gravity analysis (TGA) of lignins was carried out using a Shimazu DTG-60H thermogravimetric analyzer. The measurements were carried out at a rate 30 °C/min to 1000 °C under nitrogen atmosphere.
þ 471=22CO þ 523=22 H2 O
entry
ð1Þ ð2Þ
For PLs, the sulfur contents of PLs are trace ( or < 1 atm), together with robust catalysts. We believe that further optimization will eventually make the process
viable for the industrial production of fuel additives and chemicals. Acknowledgment. This work was supported by National Basic Research Program of China (Grant 2007CB210205), Knowledge Innovation Program of Chinese Academy of Science (Grant KGCX2-YW-3306), the NSFC-Guangdong Province Joint Fund (Grant U0834005), and NCET (Grant 080519). Supporting Information Available: Thermal gravity analysis (TGA) curves of the lignins, comparison of aromatic selectivity with and without ZSM-5 using GPL as feed, and gas selectivity of the PLs with zeolites. This material is available free of charge via the Internet at http://pubs.acs.org.
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