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Biomass catalytic pyrolysis to produce olefins and aromatics with a physically mixed catalyst
Bioresource Technology 140 (2013) 256–262
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Biomass catalytic pyrolysis to produce olefins and aromatics with a physically mixed catalyst Huiyan Zhang a, Rui Xiao a,⇑, Baosheng Jin a, Guomin Xiao b, Ran Chen a a b
Ministry of Education of Key Laboratory of Energy Thermal Conversion and Control, School of Energy and Environment, Southeast University, Nanjing 210096, PR China School of Chemistry and Chemical Engineering, Southeast University, Nanjing 210096, PR China
h i g h l i g h t s Catalytic pyrolysis of rice stalk was conducted in a new fluidized bed reactor. Mesoporous or macroporous catalysts mixed with microporous catalyst were used. The maximum hydrocarbon yield was obtained with 10% Gamma-Al2O3/90% LOSA-1. The yield was boosted by 39.8% compared to that obtained with pure LOSA-1 catalyst.
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Article history: Received 1 February 2013 Received in revised form 23 April 2013 Accepted 25 April 2013 Available online 2 May 2013 Keywords: Biomass Catalytic pyrolysis Mixed catalysts Hydrocarbons Internally interconnected fluidized bed
a b s t r a c t Zeolite catalysts with micropores present good catalytic characteristics in biomass catalytic pyrolysis process. However, large-molecule oxygenates produced from pyrolysis cannot enter their pores and would form coke on their surfaces, which decreases hydrocarbon yield and deactivates catalyst rapidly. This paper proposed adding some mesoporous and macroporous catalysts (Gamma-Al2O3, CaO and MCM41) in the microporous catalyst (LOSA-1) for biomass catalytic pyrolysis. The added catalysts were used to crack the large-molecule oxygenates into small-molecule oxygenates, while LOSA-1 was used to convert these small-molecule oxygenates into olefins and aromatics. The results show that all the additives in LOSA-1 enhanced hydrocarbon yield obviously. The maximum aromatic + olefin yield of 25.3% obtained with 10% Gamma-Al2O3/90% LOSA-1, which was boosted by 39.8% compared to that obtained with pure LOSA-1. Besides, all the additives in LOSA-1 improved the selectivities of low-carbon components in olefins and aromatics significantly. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Dwindling petroleum resources combined with environmental concerns about fossil fuels are making it imperative to find renewable and sustainable liquid fuel sources (Saxena et al., 2009; Vispute et al., 2010). Lignocellulosic biomass is currently abundant and inexpensive renewable alternative energy resources. More importantly, biomass is the only sustainable carbon source which can be converted into olefins and aromatics in the world (Klass, 1998; Vispute et al., 2010). Catalytic fast pyrolysis (CFP) is a promising technology for the direct conversion of biomass into olefins and aromatics in one reactor (Carlson et al., 2011; French and Czernik, 2010; Zhang et al., 2012). CFP of biomass has much higher energy conversion efficiency compared to bio-oil upgrading methods because of the elimination of the costly condensation/re-evaporation processes (Lappas et al., 2002).
⇑ Corresponding author. Tel.: +86 25 83795726. E-mail address: [email protected] (R. Xiao). 0960-8524/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2013.04.094
Dozens of catalysts have been synthesized and evaluated for upgrading of bio-oil and pyrolysis vapors, including microporous catalysts (ZSM-5, USY, etc.) (Ma and van Bokhoven, 2012; Thangalazhy-Gopakumar et al., 2011), mesoporous catalysts (MCM-41, FCC, MSU, SBA-15, Gamma-Al2O3, etc.) (Adam et al., 2006, 2005; Antonakou et al., 2006; Ates and Isikdag, 2009; Bertero and Sedran, 2013) and macroporous catalysts (CaO, MgO, etc.) (Lu et al., 2010; Wang et al., 2010). The comparison of catalytic characteristics between these catalysts has been well reviewed by some researchers (Aho et al., 2010; Lappas et al., 2012; Park et al., 2011; Stöcker, 2008). ZSM-5 has a 3-dimensional pore structure with pore size of 5.5–5.6 Å which is suitable for aromatics and olefins formation (Jae et al., 2011). Actually, it has been proved that ZSM-5 is one of the best catalysts for producing hydrocarbons due to its special pore structure and activity (Cheng and Huber, 2012; Stefanidis et al., 2011; Thangalazhy-Gopakumar et al., 2012; Wang and Brown, 2013; Zhang et al., 2012; Zhao et al., 2012). The mesoporous catalysts used for biomass CFP, like FCC (Fluid Catalytic Cracking) catalyst, have strong cracking effect for biomass pyrolysis
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vapors. The most likely polymerization precursors (2-methoxyphenol, 2-methoxy-4-methyl-phenol, 4-ethyl-2-methoxy-phenol, 2-methoxy-4-vinylphenol, 2,6-dimethoxyphenol, etc.) decreased, while mono-functional phenols, ketones, and furans increased with FCC catalyst in biomass pyrolysis process according to our previous study (Zhang et al., 2009). Lin and co-workers (Lin et al., 2010) carried out catalytic fast pyrolysis of biomass with CaO in a fluidized-bed reactor. The results indicated that the relative abundances of small-molecule compounds (furfural, furfuryl alcohol, etc.) increased with CaO as the catalyst by dehydration reactions. Li et al. conducted catalytic fast pyrolysis of biomass in a spout-fluid bed with CaO and MgO to produce water-soluble organics (Li et al., 2012). The results showed these catalysts enhanced the ring opening reactions of cellulose into furans and carbonyl compounds. They displayed high ability to crack heavy compounds into smaller oxygenates. Biomass catalytic pyrolysis contains two steps: biomass fast pyrolysis and pyrolysis vapors catalytic conversion. Biomass is firstly fast heated and converted into pyrolysis vapors, non-condensable gas (mainly CO and CO2) and char. And then the pyrolysis vapors attain the surface of the catalysts, the small-molecule oxygenates can enter microporous catalysts (ZSM-5) and be converted into aromatics and olefins. However, large-molecule oxygenates from pyrolysis cannot enter the pores of microporous catalysts and would polymerize and form coke on their surfaces, which decreases hydrocarbon yield and deactivates catalyst rapidly. On the other hand, mesoporous and macroporous catalysts can crack heave compounds but cannot convert them into aromatics and olefins. These problems limit the development of CFP technology. In this paper, we proposed a new and simple method to enhance hydrocarbon yield in biomass CFP process by adding mesoporous and macroporous catalysts in microporous catalyst. Fig. 1 shows biomass CFP process with a physically mixed catalyst. Gamma-Al2O3, CaO and MCM-41 catalysts were used to crack the largemolecule oxygenates into small-molecule oxygenates using their strong cracking characteristics, while LOSA-1 was used to convert these small-molecule oxygenates into olefins and aromatics using their catalytic activation and structure selectivity. The experiments were conducted in an internally interconnected fluidized bed which is specially designed for catalytic pyrolysis. The effects of Gamma-Al2O3 percentage in the mixed catalysts on product yields and selectivities were studied. The catalytic characteristics of 10% Gamma-Al2O3, CaO and MCM-41 in mixed catalysts were compared with each other. 2. Methods 2.1. Materials Rice stalk was used as the biomass feedstock. It was grounded to 0.1–0.3 mm by a high-speed rotary cutting mil. The ultimate
Biomass
Pyrolysis
Large-molecule oxygenates
Mesoporous or macroporous catalysts Catalytic cracking
analysis of the rice stalk (air-dry basis) was 35.4 wt.% carbon, 4.8 wt.% hydrogen, 1.0 wt.% nitrogen, and 44.4 wt.% oxygen (by difference). The proximate analysis of the corncob (air-dry basis) was 3.0 wt.% moisture, 66.3 wt.% volatile, 16.3 wt.% fixed carbon and 14.5 wt.% ash. Rice stalk contains more ash than wood, thus rice stalk usually produces less liquid fuels than wood (Jung et al., 2008). If the conversion of rice stalk into hydrocarbons can be improved, that of wood would be easily enhanced, thus rice stalk was chose in this work. LOSA-1 mixed with Gamma-Al2O3, CaO and MCM-41 catalysts were used for catalytic fast pyrolysis of rice stalk in this work. LOSA-1 catalyst was provided by Sinopec Yangzi Petrochemical Company Ltd. LOSA-1 catalyst, mainly composed of ZSM-5, is usually used as an additive for increasing olefin yield in FCC process. Its Si/Al ratio is 40. Gamma-Al2O3 was bought from Shanghai Yuejiang Titanium Chemical Manufacture Co., Ltd. CaO was prepared by calcination of the reagent grade CaCO3 at 800 °C for 1 h in muffle furnace. MCM-41 was supplied by Jiangsu Oil-Chem Technology Co., Ltd. The physico-chemical properties of all the catalysts are shown in Table S1 . The particle sizes of all the catalysts distributed between 0.063 and 0.154 mm. All the catalysts were dried at 120 °C for 2 h to remove moisture and kept in a desiccator for experiments. Prior to reactions, the catalyst was calcined in a fluidized bed reactor for 2 h at 600 °C in 0.5 L/min flowing O2. All the experiments were conducted in duplicate/ triplicate. 2.2. Experimental Catalytic fast pyrolysis of rice stalk was performed in an Internally Interconnected Fluidized Bed (IIFB) which was specially designed for these reactions. Fig. S1 shows the experimental system which was described elsewhere (Zhang et al., 2013a,b). The diameter of outer bed is 60 mm and it was divided by two flanges into three parts: windbox (height is 320 mm), annulus region where combustion bed was located (480 mm) and fountain region where pyrolysis bed existed (400 mm). The draft tube with slots at the bottom is 470 mm in height and 19 mm in diameter. Biomass is fed into the reactor by a stainless steel auger from a sealed feed hopper. There are three lines of carrier gas, including 2.4 L/min N2 for biomass entrainment in horizontal tube, 1 L/min N2 in vertical tube and 0.5 L/min N2 for fluidizing gas. All carrier gases are controlled by a mass flow controller. Both the reactor and the inlet gas stream are heated to reaction temperature (550 °C) before reaction. For a typical run, rice stalk is fed to the reactor with the feeding rate of 44 g/h for 30 min the vapors were condensed in two groups of condensers which are 0 °C ice bath and 55 °C dry ice/ethanol bath. The liquids were analyzed by GC/MS, while the non-condensable gas was analyzed by GC/FID and GC/TCD. Restek Rtx-VMS capillary column (Catalog No. 19915) was used in GC/FID to quantify olefins, while HAYSEP
Small-molecule oxygenates
Acid micropore catalysts Catalytic conversion structure selectivity
Olefins Aromatics
Coke, CO, CO2, methane, water Fig. 1. Catalytic fast pyrolysis over mixed catalysts with mesoporous or macroporous for cracking large-molecule oxygenates into small-molecule oxygenates.
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D packed column in GC/TCD was used to analyze CH4, CO and CO2. Both FID and TCD detectors were maintained at 240 °C. Ultra helium was used as carrier gas. The following temperature ramp was used in this study: hold at 35 °C for 5 min, ramp to 140 °C at 5 °C/min, ramp to 230 °C at 50 °C/min and hold at 230 °C for 8.2 min. 3. Results and discussion 3.1. Product yields of rice stalk catalytic pyrolysis over Gamma-Al2O3 mixed with LOSA-1 LOSA-1 and its mixtures with 5%, 10%, 20% and 50% of GammaAl2O3 were used as the bed materials for catalytic fast pyrolysis of rice stalk. Fig. 2 shows product carbon yields as the function of Gamma-Al2O3 percentages in the mixed catalysts. Both aromatic and olefin yields first increased then decreased as the percentage of Gamma-Al2O3 increasing from 0% to 50% with a maximum value of 14.1% and 11.2% at 10% Gamma-Al2O3, respectively. The maximum total carbon yield of aromatic + olefin of 25.3% occurred at 10% Gamma-Al2O3, which was boosted by 39.8% compared to that obtained using pure LOSA-1 as the catalyst. The coke yield decreased from 30.3% with pure LOSA-1 to 23.5% with 50% GammaAl2O3 as the catalyst. CO and CO2 yields first increased from 17.6% to 11.9% with pure LOSA-1 to 24.8% and 14.0% with 10% Gamma-Al2O3, and then decreased to 12.2% and 2.4% with 50% Gamma-Al2O3, respectively. The unidentified compounds first decreased from 19.4% with pure LOSA-1 to the minimum value of 7.5% with 10% Gamma-Al2O3, and then increased to 41.9% with 50% Gamma-Al2O3 as the catalyst. According to our previous experiments, rice stalk pyrolysis produces a lot of large-molecule oxygenates. These oxygenates are unable to enter the micropores of zeolite catalysts. Furthermore, they would form coke on the surface of the catalyst and then block the entrances of these pores resulting in their deactivation. GammaAl2O3 has strong cracking characteristic and can convert the large-molecule oxygenates into small-molecule oxygenates. Fig. S2 shows the NH3-TPD analysis of LOSA-1 and GammaAl2O3. The strong acid peak of Gamma-Al2O3 is at higher temperature comparing with that of LOSA-1. Gamma-Al2O3, as the mesoporous catalyst, usually used as a tar removal additive in gasification process, has high cracking function for large-molecule compounds which usually form coke on the surface of acid catalysts (Li et al., 2008). The main components of the compounds obtained with Gamma-Al2O3 were some small-molecule oxygenates which can be converted into aromatics and olefins over a proper
(a)
3.2. Product selectivities of rice stalk catalytic pyrolysis over GammaAl2O3 mixed with LOSA-1 Fig. 3 shows the effect of Gamma-Al2O3 percentage in the mixed catalysts on the product selectivities. The selectivities of ethylene and toluene increased, whereas that of propylene, butylenes, xylenes and naphthalene decreased with increasing Gamma-Al2O3 percentage. The addition of Gamma-Al2O3 produced more olefins with shorter carbon chain and aromatics with smaller carbons. These can be attributed to the cracking effect of Gamma-Al2O3 on the feedstocks for LOSA-1 conversion. Furthermore, there is an inflection point at 10% Gamma-Al2O3/90% LOSA-1, where the product selectivity does not change as rapidly as it does before. The different chemical groups including benzene, indene and naphthalene and their derivatives are shown in Fig. 3c. The carbon selectivity of benzene and its derivatives is about 95% when the Gamma-Al2O3 percentage is higher than 10%. The reactions of monocyclic aromatics (benzene, toluene and xylenes) with oxygenated fragments produce naphthalene, indene and their derivatives (Carlson et al., 2009). The selectivities of indene and naphthalene decreased with increasing Gamma-Al2O3 percentage. Detailed selectivities of all products are shown in Table 1.
(b) 30
45 Aromatics Olefins Char and coke Unidentified compounds
40
25
Carbon yield (%)
35
Carbon yield (%)
catalyst. The experimental results show LOSA-1 is the type of the catalyst which can convert small-molecule oxygenates into aromatics and olefins. These small-molecule oxygenates can enter the 3-dimensional pores of LOSA-1 catalyst and be converted into hydrocarbons with CO, CO2 and water as by-products using its catalytic activation and structure selectivity. Therefore, the yields of olefins, aromatic, CO and CO2 increased with increasing LOSA-1 percentage from 50% to 90%. However, the hydrocarbon yield decreased when the Gamma-Al2O3 was lower than 10%. This is because there is no enough Gamma-Al2O3 for cracking largemolecule oxygenates. Thus coke yield increased quickly with the decreasing percentage of Gamma-Al2O3 from 10% to 0%. Fig. S3 shows the SEM analysis of the Gamma-Al2O3 mixed with LOSA-1 catalyst before and after reaction. Both the particles of GammaAl2O3 and LOSA-1 are spherical in shape. However, LOSA-1 is smoother and Gamma-Al2O3 has many edges and corners. Compared to the fresh catalyst, more broken pieces can be seen in the used catalyst. The fresh catalyst has surface irregularity characteristic, which is beneficial to catalytic reactions. However, the surface of the used LOSA-1 catalyst shows smoother than the fresh one because of coke formation.
30 25 20 15
CO CO2
20
CH4
15 10 5
10 5 0
10 20 30 40 Gamma-Al2O3 in the mixed catalysts (%)
50
0 0
10 20 30 40 50 Gamma -Al2O3 in the mixed catalysts (%)
Fig. 2. Product carbon yields as the function of Gamma-Al2O3 percentage in the mixed catalysts: (a) aromatics, olefins, unidentified compounds, char and coke; (b) CO, CO2 and CH4.
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(a)
80 Ethylene
Propylene
(a)
Butylenes
70
60 Benzene Naphthalene
50
Toluene
Xylenes
Carbon selectivity (%)
Carbon selectivity (%)
60 50 40 30 4
40 30 20 10
2 0
0
0 10 20 30 40 50 Gamma-Al 2O3 percentage in the mixed catalysts (%)
0
10 20 30 40 50 Gamma-Al 2O3 in the mixed catalysts (%)
(c) 100 95
Carbon selectivity (%)
90 Benzene and its derivatives Indene and its derivatives Naphthalene and its derivatives
85 80 10 5 0
0
10
20
30
40
50
Gamma-Al 2O3 percentage in the mixed catalysts (%) Fig. 3. Product carbon selectivities as the function of Gamma-Al2O3 percentage in the mixed catalysts: (a) ethylene, propylene and butylenes in olefins; (b) benzene, toluene, xylenes and naphthalene in aromatics; (c) different chemical groups in aromatics.
Table 1 Detailed product yields and selectivities of catalytic conversion of rice stalk with a physically mixed catalyst. Compound
Different percentage of catalyst in the mixed catalysts 100% LOSA-1
5% Al2O3
10% Al2O3
20% Al2O3
50% Al2O3
10% CaO
10% MCM-41
Overall yields Aromatics C2–C4 olefins Petrochemicals Methane CO2 CO Coke Total balance Unidentified
9.6 8.5 18.1 2.7 11.9 17.6 30.3 80.6 19.4
11.6 9.8 21.4 3.0 12.4 22.5 26.1 85.3 14.7
14.1 11.2 25.4 3.6 14.0 24.8 24.8 92.5 7.5
9.8 9.7 19.5 4.8 11.8 18.0 23.8 78.1 21.9
7.4 7.5 14.9 5.1 2.4 12.2 23.5 58.1 41.9
13.6 9.6 23.2 1.1 12.8 22.6 26.6 86.3 13.7
12.8 9.8 22.6 1.3 14.8 26.1 24.7 89.4 10.6
Aromatic selectivity Benzene Toluene Ethyl benzene p-Xylene and m-xylene Styrene o-Xylene 1-Ethyl-2-methyl benzene 1,2,3-Trimethyl benzene Indene 5-Methyl-1H-indene 2-Methyl naphthalene Naphthalene 4,7-Dimethyl-1H-indene 1-Methyl naphthalene
20.7 29.4 2.0 20.7 2.5 2.5 1.3 2.1 5.0 0 0 9.2 0.9 3.5
26.3 41.8 2.0 18.1 0 3.6 0 0 2.8 0 1.7 3.4 0 0
29.3 43.6 1.9 16.3 0 4.5 0 1.1 1.7 0.8 0.9 0 0 0
29.7 44.5 2.5 15.9 0 3.7 0 0 1.9 1.4 0.4 0 0 0
25.1 47.2 2.3 17.0 0 4.0 0 1.2 2.0 0.8 0.4 0 0 0
29.6 34.9 2.4 17.1 3.0 1.5 0.6 0 2.1 0.7 0.5 5.6 0 1.9
31.2 36.6 2.5 20.1 0 6.2 0 0 1.5 0 0 1.9 0 0
Olefin selectivity Ethylene Propylene Butenes
47.1 48.5 4.4
53.3 44.6 2.1
59.1 39.9 1.1
62.1 36.9 1.1
68.9 30.1 1.0
63.6 35.7 0.7
57.3 36.0 6.7
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(a)
40 35
Aromatics Char and coke
C2-C4 Olefins Unidentified compounds
(b)
30 CO CO2
25
CH4
20
Carbon yield (%)
Carbon yield (%)
30 25 20 15
15 10
10 5
5 0
0
100% LOSA-1 10% Al2O3
10% CaO 10% MCM-41
100% LOSA-1 10% Al2O3 10% CaO 10% MCM-41
Fig. 4. Product carbon yields of rice stalk catalytic pyrolysis with pure LOSA-1, 10% Gamma-Al2O3/90% LOSA-1, 10% CaO/90% LOSA-1 and 10% MCM-41/90% LOSA-1: (a) aromatics, olefins, unidentified compounds, char and coke; (b) CO, CO2 and CH4.
3.3. Product yields of rice stalk catalytic pyrolysis over different catalysts mixed with LOSA-1 The product yields of rice stalk catalytic pyrolysis over pure LOSA-1, 10% Gamma-Al2O3/90% LOSA-1, 10% CaO/90% LOSA-1
(a)
80 70
and 10% MCM-41/90% LOSA-1 are shown in Fig. 4. All the three additives in LOSA-1 catalyst increased the aromatic and olefin yields, and boosted olefin + aromatic yield by 24.9–39.8% compared to that obtained using pure LOSA-1. Gamma-Al2O3 shows the best characteristics in the three additives. Both the aromatic
(b) Ethylene
Propylene
50 Benzene Xylenes
Butylenes
Toluene Naphthalene
40 Carbon selectivity (%)
Carbon selectivity (%)
60 50 40 30 20
30
20
10 10 0
100% LOSA-1 10% Al2O3
10% CaO 10% MCM-41
0 100% LOSA-1 10% Al2O3
10% CaO 10% MCM-41
(c) 100 95
Carbon selectivity (%)
90 85 80 15 10 5 0
LOSA-1 10% Al2O3
10% CaO
Benzene and its derivatives
10% MCM-41
Indene and its derivatives
Naphthalene and its derivatives Fig. 5. Product carbon selectivities of rice stalk catalytic pyrolysis with pure LOSA-1, 10% Gamma-Al2O3/90% LOSA-1, 10% CaO/90% LOSA-1 and 10% MCM-41/90% LOSA-1: (a) ethylene, propylene and butylenes in olefins; (b) benzene, toluene, xylenes and naphthalene in aromatics; (c) different chemical groups in aromatics.
H. Zhang et al. / Bioresource Technology 140 (2013) 256–262
and olefin yields attained maximum value with 10% Gamma-Al2O3 as the additive, while the unidentified oxygenates yield attained the minimum value. The char and coke yields decreased with all the three additives. This is because these additives depolymerized large-molecular compounds which would form coke over pure LOSA-1 catalyst. The additions of Gamma-Al2O3, CaO and MCM41 produced more CO. This can be explained by two reasons: (1) the addition of these additives cracked some large-molecular and this process produced CO; (2) more small-molecular oxygenates entered the micropores of LOSA-1 catalyst and be converted to hydrocarbons and CO. 3.4. Product selectivities of rice stalk catalytic pyrolysis over different catalysts mixed with LOSA-1 Fig. 5 shows the product carbon selectivities of rice stalk catalytic pyrolysis over 10% different additives mixed with LOSA-1. Detailed selectivities of all products are shown in Table 1. Ethylene and propylene are the two main olefins in all experiments and their summation is up to 95%. The selectivity of ethylene is almost equal to that of propylene with pure LOSA-1 as the catalyst. Ethylene selectivity is much higher than propylene selectivity when Gamma-Al2O3, MCM-41 and CaO were added. The selectivities of benzene and toluene increased in all the experiments with the three additives, whereas that of naphthalene decreased significantly. LOSA-1 and Gamma-Al2O3 mixture resulted in highest toluene selectivity (43.6%) and no naphthalene selectivity, while LOSA-1 and CaO mixture resulted in the lowest toluene selectivity (34.9%). These results are related to the characteristics of GammaAl2O3 and CaO. Gamma-Al2O3 belongs to acid and mesoporous catalyst, while CaO belongs to strong base and macroporous catalyst. Different chemical groups in aromatics show that benzene and its derivatives accounted for 81.4% with pure LOSA-1 as the catalyst, and it increased to 89.2–96.6% with additives. CaO as the additive produced more naphthalene and its derivatives compared to other two additives. 4. Conclusion Catalytic fast pyrolysis of rice stalk over mesoporous and macroporous catalysts (Gamma-Al2O3, CaO and MCM-41) mixed with microporous LOSA-1 were conducted in an internally interconnected fluidized bed. The maximum yield of aromatic + olefin (25.3%) was obtained with 10% Gamma-Al2O3/90% LOSA-1, which was boosted by 39.8% compared to that obtained with pure LOSA-1. The addition of these catalysts improved the selectivities of low-carbon components significantly. This paper proposed a new and simple way to enhance hydrocarbon yield in biomass catalytic pyrolysis process. The synergistic effects and mechanisms of the physically mixed catalyst need to be further studied in future. Acknowledgements This work is financially supported by the National Natural Science Foundation of China (Grant No. 51076031), the National Basic Research Program of China (973 Program) (Grant Nos. 2010CB732206; 2012CB215306) and the China Postdoctoral Science Foundation. 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.biortech.2013. 04.094.
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Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Biomass catalytic pyrolysis to produce olefins and aromatics with a physically mixed catalyst Huiyan Zhang a, Rui Xiao a,⇑, Baosheng Jin a, Guomin Xiao b, Ran Chen a a b
Ministry of Education of Key Laboratory of Energy Thermal Conversion and Control, School of Energy and Environment, Southeast University, Nanjing 210096, PR China School of Chemistry and Chemical Engineering, Southeast University, Nanjing 210096, PR China
h i g h l i g h t s Catalytic pyrolysis of rice stalk was conducted in a new fluidized bed reactor. Mesoporous or macroporous catalysts mixed with microporous catalyst were used. The maximum hydrocarbon yield was obtained with 10% Gamma-Al2O3/90% LOSA-1. The yield was boosted by 39.8% compared to that obtained with pure LOSA-1 catalyst.
a r t i c l e
i n f o
Article history: Received 1 February 2013 Received in revised form 23 April 2013 Accepted 25 April 2013 Available online 2 May 2013 Keywords: Biomass Catalytic pyrolysis Mixed catalysts Hydrocarbons Internally interconnected fluidized bed
a b s t r a c t Zeolite catalysts with micropores present good catalytic characteristics in biomass catalytic pyrolysis process. However, large-molecule oxygenates produced from pyrolysis cannot enter their pores and would form coke on their surfaces, which decreases hydrocarbon yield and deactivates catalyst rapidly. This paper proposed adding some mesoporous and macroporous catalysts (Gamma-Al2O3, CaO and MCM41) in the microporous catalyst (LOSA-1) for biomass catalytic pyrolysis. The added catalysts were used to crack the large-molecule oxygenates into small-molecule oxygenates, while LOSA-1 was used to convert these small-molecule oxygenates into olefins and aromatics. The results show that all the additives in LOSA-1 enhanced hydrocarbon yield obviously. The maximum aromatic + olefin yield of 25.3% obtained with 10% Gamma-Al2O3/90% LOSA-1, which was boosted by 39.8% compared to that obtained with pure LOSA-1. Besides, all the additives in LOSA-1 improved the selectivities of low-carbon components in olefins and aromatics significantly. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Dwindling petroleum resources combined with environmental concerns about fossil fuels are making it imperative to find renewable and sustainable liquid fuel sources (Saxena et al., 2009; Vispute et al., 2010). Lignocellulosic biomass is currently abundant and inexpensive renewable alternative energy resources. More importantly, biomass is the only sustainable carbon source which can be converted into olefins and aromatics in the world (Klass, 1998; Vispute et al., 2010). Catalytic fast pyrolysis (CFP) is a promising technology for the direct conversion of biomass into olefins and aromatics in one reactor (Carlson et al., 2011; French and Czernik, 2010; Zhang et al., 2012). CFP of biomass has much higher energy conversion efficiency compared to bio-oil upgrading methods because of the elimination of the costly condensation/re-evaporation processes (Lappas et al., 2002).
⇑ Corresponding author. Tel.: +86 25 83795726. E-mail address: [email protected] (R. Xiao). 0960-8524/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2013.04.094
Dozens of catalysts have been synthesized and evaluated for upgrading of bio-oil and pyrolysis vapors, including microporous catalysts (ZSM-5, USY, etc.) (Ma and van Bokhoven, 2012; Thangalazhy-Gopakumar et al., 2011), mesoporous catalysts (MCM-41, FCC, MSU, SBA-15, Gamma-Al2O3, etc.) (Adam et al., 2006, 2005; Antonakou et al., 2006; Ates and Isikdag, 2009; Bertero and Sedran, 2013) and macroporous catalysts (CaO, MgO, etc.) (Lu et al., 2010; Wang et al., 2010). The comparison of catalytic characteristics between these catalysts has been well reviewed by some researchers (Aho et al., 2010; Lappas et al., 2012; Park et al., 2011; Stöcker, 2008). ZSM-5 has a 3-dimensional pore structure with pore size of 5.5–5.6 Å which is suitable for aromatics and olefins formation (Jae et al., 2011). Actually, it has been proved that ZSM-5 is one of the best catalysts for producing hydrocarbons due to its special pore structure and activity (Cheng and Huber, 2012; Stefanidis et al., 2011; Thangalazhy-Gopakumar et al., 2012; Wang and Brown, 2013; Zhang et al., 2012; Zhao et al., 2012). The mesoporous catalysts used for biomass CFP, like FCC (Fluid Catalytic Cracking) catalyst, have strong cracking effect for biomass pyrolysis
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vapors. The most likely polymerization precursors (2-methoxyphenol, 2-methoxy-4-methyl-phenol, 4-ethyl-2-methoxy-phenol, 2-methoxy-4-vinylphenol, 2,6-dimethoxyphenol, etc.) decreased, while mono-functional phenols, ketones, and furans increased with FCC catalyst in biomass pyrolysis process according to our previous study (Zhang et al., 2009). Lin and co-workers (Lin et al., 2010) carried out catalytic fast pyrolysis of biomass with CaO in a fluidized-bed reactor. The results indicated that the relative abundances of small-molecule compounds (furfural, furfuryl alcohol, etc.) increased with CaO as the catalyst by dehydration reactions. Li et al. conducted catalytic fast pyrolysis of biomass in a spout-fluid bed with CaO and MgO to produce water-soluble organics (Li et al., 2012). The results showed these catalysts enhanced the ring opening reactions of cellulose into furans and carbonyl compounds. They displayed high ability to crack heavy compounds into smaller oxygenates. Biomass catalytic pyrolysis contains two steps: biomass fast pyrolysis and pyrolysis vapors catalytic conversion. Biomass is firstly fast heated and converted into pyrolysis vapors, non-condensable gas (mainly CO and CO2) and char. And then the pyrolysis vapors attain the surface of the catalysts, the small-molecule oxygenates can enter microporous catalysts (ZSM-5) and be converted into aromatics and olefins. However, large-molecule oxygenates from pyrolysis cannot enter the pores of microporous catalysts and would polymerize and form coke on their surfaces, which decreases hydrocarbon yield and deactivates catalyst rapidly. On the other hand, mesoporous and macroporous catalysts can crack heave compounds but cannot convert them into aromatics and olefins. These problems limit the development of CFP technology. In this paper, we proposed a new and simple method to enhance hydrocarbon yield in biomass CFP process by adding mesoporous and macroporous catalysts in microporous catalyst. Fig. 1 shows biomass CFP process with a physically mixed catalyst. Gamma-Al2O3, CaO and MCM-41 catalysts were used to crack the largemolecule oxygenates into small-molecule oxygenates using their strong cracking characteristics, while LOSA-1 was used to convert these small-molecule oxygenates into olefins and aromatics using their catalytic activation and structure selectivity. The experiments were conducted in an internally interconnected fluidized bed which is specially designed for catalytic pyrolysis. The effects of Gamma-Al2O3 percentage in the mixed catalysts on product yields and selectivities were studied. The catalytic characteristics of 10% Gamma-Al2O3, CaO and MCM-41 in mixed catalysts were compared with each other. 2. Methods 2.1. Materials Rice stalk was used as the biomass feedstock. It was grounded to 0.1–0.3 mm by a high-speed rotary cutting mil. The ultimate
Biomass
Pyrolysis
Large-molecule oxygenates
Mesoporous or macroporous catalysts Catalytic cracking
analysis of the rice stalk (air-dry basis) was 35.4 wt.% carbon, 4.8 wt.% hydrogen, 1.0 wt.% nitrogen, and 44.4 wt.% oxygen (by difference). The proximate analysis of the corncob (air-dry basis) was 3.0 wt.% moisture, 66.3 wt.% volatile, 16.3 wt.% fixed carbon and 14.5 wt.% ash. Rice stalk contains more ash than wood, thus rice stalk usually produces less liquid fuels than wood (Jung et al., 2008). If the conversion of rice stalk into hydrocarbons can be improved, that of wood would be easily enhanced, thus rice stalk was chose in this work. LOSA-1 mixed with Gamma-Al2O3, CaO and MCM-41 catalysts were used for catalytic fast pyrolysis of rice stalk in this work. LOSA-1 catalyst was provided by Sinopec Yangzi Petrochemical Company Ltd. LOSA-1 catalyst, mainly composed of ZSM-5, is usually used as an additive for increasing olefin yield in FCC process. Its Si/Al ratio is 40. Gamma-Al2O3 was bought from Shanghai Yuejiang Titanium Chemical Manufacture Co., Ltd. CaO was prepared by calcination of the reagent grade CaCO3 at 800 °C for 1 h in muffle furnace. MCM-41 was supplied by Jiangsu Oil-Chem Technology Co., Ltd. The physico-chemical properties of all the catalysts are shown in Table S1 . The particle sizes of all the catalysts distributed between 0.063 and 0.154 mm. All the catalysts were dried at 120 °C for 2 h to remove moisture and kept in a desiccator for experiments. Prior to reactions, the catalyst was calcined in a fluidized bed reactor for 2 h at 600 °C in 0.5 L/min flowing O2. All the experiments were conducted in duplicate/ triplicate. 2.2. Experimental Catalytic fast pyrolysis of rice stalk was performed in an Internally Interconnected Fluidized Bed (IIFB) which was specially designed for these reactions. Fig. S1 shows the experimental system which was described elsewhere (Zhang et al., 2013a,b). The diameter of outer bed is 60 mm and it was divided by two flanges into three parts: windbox (height is 320 mm), annulus region where combustion bed was located (480 mm) and fountain region where pyrolysis bed existed (400 mm). The draft tube with slots at the bottom is 470 mm in height and 19 mm in diameter. Biomass is fed into the reactor by a stainless steel auger from a sealed feed hopper. There are three lines of carrier gas, including 2.4 L/min N2 for biomass entrainment in horizontal tube, 1 L/min N2 in vertical tube and 0.5 L/min N2 for fluidizing gas. All carrier gases are controlled by a mass flow controller. Both the reactor and the inlet gas stream are heated to reaction temperature (550 °C) before reaction. For a typical run, rice stalk is fed to the reactor with the feeding rate of 44 g/h for 30 min the vapors were condensed in two groups of condensers which are 0 °C ice bath and 55 °C dry ice/ethanol bath. The liquids were analyzed by GC/MS, while the non-condensable gas was analyzed by GC/FID and GC/TCD. Restek Rtx-VMS capillary column (Catalog No. 19915) was used in GC/FID to quantify olefins, while HAYSEP
Small-molecule oxygenates
Acid micropore catalysts Catalytic conversion structure selectivity
Olefins Aromatics
Coke, CO, CO2, methane, water Fig. 1. Catalytic fast pyrolysis over mixed catalysts with mesoporous or macroporous for cracking large-molecule oxygenates into small-molecule oxygenates.
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D packed column in GC/TCD was used to analyze CH4, CO and CO2. Both FID and TCD detectors were maintained at 240 °C. Ultra helium was used as carrier gas. The following temperature ramp was used in this study: hold at 35 °C for 5 min, ramp to 140 °C at 5 °C/min, ramp to 230 °C at 50 °C/min and hold at 230 °C for 8.2 min. 3. Results and discussion 3.1. Product yields of rice stalk catalytic pyrolysis over Gamma-Al2O3 mixed with LOSA-1 LOSA-1 and its mixtures with 5%, 10%, 20% and 50% of GammaAl2O3 were used as the bed materials for catalytic fast pyrolysis of rice stalk. Fig. 2 shows product carbon yields as the function of Gamma-Al2O3 percentages in the mixed catalysts. Both aromatic and olefin yields first increased then decreased as the percentage of Gamma-Al2O3 increasing from 0% to 50% with a maximum value of 14.1% and 11.2% at 10% Gamma-Al2O3, respectively. The maximum total carbon yield of aromatic + olefin of 25.3% occurred at 10% Gamma-Al2O3, which was boosted by 39.8% compared to that obtained using pure LOSA-1 as the catalyst. The coke yield decreased from 30.3% with pure LOSA-1 to 23.5% with 50% GammaAl2O3 as the catalyst. CO and CO2 yields first increased from 17.6% to 11.9% with pure LOSA-1 to 24.8% and 14.0% with 10% Gamma-Al2O3, and then decreased to 12.2% and 2.4% with 50% Gamma-Al2O3, respectively. The unidentified compounds first decreased from 19.4% with pure LOSA-1 to the minimum value of 7.5% with 10% Gamma-Al2O3, and then increased to 41.9% with 50% Gamma-Al2O3 as the catalyst. According to our previous experiments, rice stalk pyrolysis produces a lot of large-molecule oxygenates. These oxygenates are unable to enter the micropores of zeolite catalysts. Furthermore, they would form coke on the surface of the catalyst and then block the entrances of these pores resulting in their deactivation. GammaAl2O3 has strong cracking characteristic and can convert the large-molecule oxygenates into small-molecule oxygenates. Fig. S2 shows the NH3-TPD analysis of LOSA-1 and GammaAl2O3. The strong acid peak of Gamma-Al2O3 is at higher temperature comparing with that of LOSA-1. Gamma-Al2O3, as the mesoporous catalyst, usually used as a tar removal additive in gasification process, has high cracking function for large-molecule compounds which usually form coke on the surface of acid catalysts (Li et al., 2008). The main components of the compounds obtained with Gamma-Al2O3 were some small-molecule oxygenates which can be converted into aromatics and olefins over a proper
(a)
3.2. Product selectivities of rice stalk catalytic pyrolysis over GammaAl2O3 mixed with LOSA-1 Fig. 3 shows the effect of Gamma-Al2O3 percentage in the mixed catalysts on the product selectivities. The selectivities of ethylene and toluene increased, whereas that of propylene, butylenes, xylenes and naphthalene decreased with increasing Gamma-Al2O3 percentage. The addition of Gamma-Al2O3 produced more olefins with shorter carbon chain and aromatics with smaller carbons. These can be attributed to the cracking effect of Gamma-Al2O3 on the feedstocks for LOSA-1 conversion. Furthermore, there is an inflection point at 10% Gamma-Al2O3/90% LOSA-1, where the product selectivity does not change as rapidly as it does before. The different chemical groups including benzene, indene and naphthalene and their derivatives are shown in Fig. 3c. The carbon selectivity of benzene and its derivatives is about 95% when the Gamma-Al2O3 percentage is higher than 10%. The reactions of monocyclic aromatics (benzene, toluene and xylenes) with oxygenated fragments produce naphthalene, indene and their derivatives (Carlson et al., 2009). The selectivities of indene and naphthalene decreased with increasing Gamma-Al2O3 percentage. Detailed selectivities of all products are shown in Table 1.
(b) 30
45 Aromatics Olefins Char and coke Unidentified compounds
40
25
Carbon yield (%)
35
Carbon yield (%)
catalyst. The experimental results show LOSA-1 is the type of the catalyst which can convert small-molecule oxygenates into aromatics and olefins. These small-molecule oxygenates can enter the 3-dimensional pores of LOSA-1 catalyst and be converted into hydrocarbons with CO, CO2 and water as by-products using its catalytic activation and structure selectivity. Therefore, the yields of olefins, aromatic, CO and CO2 increased with increasing LOSA-1 percentage from 50% to 90%. However, the hydrocarbon yield decreased when the Gamma-Al2O3 was lower than 10%. This is because there is no enough Gamma-Al2O3 for cracking largemolecule oxygenates. Thus coke yield increased quickly with the decreasing percentage of Gamma-Al2O3 from 10% to 0%. Fig. S3 shows the SEM analysis of the Gamma-Al2O3 mixed with LOSA-1 catalyst before and after reaction. Both the particles of GammaAl2O3 and LOSA-1 are spherical in shape. However, LOSA-1 is smoother and Gamma-Al2O3 has many edges and corners. Compared to the fresh catalyst, more broken pieces can be seen in the used catalyst. The fresh catalyst has surface irregularity characteristic, which is beneficial to catalytic reactions. However, the surface of the used LOSA-1 catalyst shows smoother than the fresh one because of coke formation.
30 25 20 15
CO CO2
20
CH4
15 10 5
10 5 0
10 20 30 40 Gamma-Al2O3 in the mixed catalysts (%)
50
0 0
10 20 30 40 50 Gamma -Al2O3 in the mixed catalysts (%)
Fig. 2. Product carbon yields as the function of Gamma-Al2O3 percentage in the mixed catalysts: (a) aromatics, olefins, unidentified compounds, char and coke; (b) CO, CO2 and CH4.
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(a)
80 Ethylene
Propylene
(a)
Butylenes
70
60 Benzene Naphthalene
50
Toluene
Xylenes
Carbon selectivity (%)
Carbon selectivity (%)
60 50 40 30 4
40 30 20 10
2 0
0
0 10 20 30 40 50 Gamma-Al 2O3 percentage in the mixed catalysts (%)
0
10 20 30 40 50 Gamma-Al 2O3 in the mixed catalysts (%)
(c) 100 95
Carbon selectivity (%)
90 Benzene and its derivatives Indene and its derivatives Naphthalene and its derivatives
85 80 10 5 0
0
10
20
30
40
50
Gamma-Al 2O3 percentage in the mixed catalysts (%) Fig. 3. Product carbon selectivities as the function of Gamma-Al2O3 percentage in the mixed catalysts: (a) ethylene, propylene and butylenes in olefins; (b) benzene, toluene, xylenes and naphthalene in aromatics; (c) different chemical groups in aromatics.
Table 1 Detailed product yields and selectivities of catalytic conversion of rice stalk with a physically mixed catalyst. Compound
Different percentage of catalyst in the mixed catalysts 100% LOSA-1
5% Al2O3
10% Al2O3
20% Al2O3
50% Al2O3
10% CaO
10% MCM-41
Overall yields Aromatics C2–C4 olefins Petrochemicals Methane CO2 CO Coke Total balance Unidentified
9.6 8.5 18.1 2.7 11.9 17.6 30.3 80.6 19.4
11.6 9.8 21.4 3.0 12.4 22.5 26.1 85.3 14.7
14.1 11.2 25.4 3.6 14.0 24.8 24.8 92.5 7.5
9.8 9.7 19.5 4.8 11.8 18.0 23.8 78.1 21.9
7.4 7.5 14.9 5.1 2.4 12.2 23.5 58.1 41.9
13.6 9.6 23.2 1.1 12.8 22.6 26.6 86.3 13.7
12.8 9.8 22.6 1.3 14.8 26.1 24.7 89.4 10.6
Aromatic selectivity Benzene Toluene Ethyl benzene p-Xylene and m-xylene Styrene o-Xylene 1-Ethyl-2-methyl benzene 1,2,3-Trimethyl benzene Indene 5-Methyl-1H-indene 2-Methyl naphthalene Naphthalene 4,7-Dimethyl-1H-indene 1-Methyl naphthalene
20.7 29.4 2.0 20.7 2.5 2.5 1.3 2.1 5.0 0 0 9.2 0.9 3.5
26.3 41.8 2.0 18.1 0 3.6 0 0 2.8 0 1.7 3.4 0 0
29.3 43.6 1.9 16.3 0 4.5 0 1.1 1.7 0.8 0.9 0 0 0
29.7 44.5 2.5 15.9 0 3.7 0 0 1.9 1.4 0.4 0 0 0
25.1 47.2 2.3 17.0 0 4.0 0 1.2 2.0 0.8 0.4 0 0 0
29.6 34.9 2.4 17.1 3.0 1.5 0.6 0 2.1 0.7 0.5 5.6 0 1.9
31.2 36.6 2.5 20.1 0 6.2 0 0 1.5 0 0 1.9 0 0
Olefin selectivity Ethylene Propylene Butenes
47.1 48.5 4.4
53.3 44.6 2.1
59.1 39.9 1.1
62.1 36.9 1.1
68.9 30.1 1.0
63.6 35.7 0.7
57.3 36.0 6.7
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(a)
40 35
Aromatics Char and coke
C2-C4 Olefins Unidentified compounds
(b)
30 CO CO2
25
CH4
20
Carbon yield (%)
Carbon yield (%)
30 25 20 15
15 10
10 5
5 0
0
100% LOSA-1 10% Al2O3
10% CaO 10% MCM-41
100% LOSA-1 10% Al2O3 10% CaO 10% MCM-41
Fig. 4. Product carbon yields of rice stalk catalytic pyrolysis with pure LOSA-1, 10% Gamma-Al2O3/90% LOSA-1, 10% CaO/90% LOSA-1 and 10% MCM-41/90% LOSA-1: (a) aromatics, olefins, unidentified compounds, char and coke; (b) CO, CO2 and CH4.
3.3. Product yields of rice stalk catalytic pyrolysis over different catalysts mixed with LOSA-1 The product yields of rice stalk catalytic pyrolysis over pure LOSA-1, 10% Gamma-Al2O3/90% LOSA-1, 10% CaO/90% LOSA-1
(a)
80 70
and 10% MCM-41/90% LOSA-1 are shown in Fig. 4. All the three additives in LOSA-1 catalyst increased the aromatic and olefin yields, and boosted olefin + aromatic yield by 24.9–39.8% compared to that obtained using pure LOSA-1. Gamma-Al2O3 shows the best characteristics in the three additives. Both the aromatic
(b) Ethylene
Propylene
50 Benzene Xylenes
Butylenes
Toluene Naphthalene
40 Carbon selectivity (%)
Carbon selectivity (%)
60 50 40 30 20
30
20
10 10 0
100% LOSA-1 10% Al2O3
10% CaO 10% MCM-41
0 100% LOSA-1 10% Al2O3
10% CaO 10% MCM-41
(c) 100 95
Carbon selectivity (%)
90 85 80 15 10 5 0
LOSA-1 10% Al2O3
10% CaO
Benzene and its derivatives
10% MCM-41
Indene and its derivatives
Naphthalene and its derivatives Fig. 5. Product carbon selectivities of rice stalk catalytic pyrolysis with pure LOSA-1, 10% Gamma-Al2O3/90% LOSA-1, 10% CaO/90% LOSA-1 and 10% MCM-41/90% LOSA-1: (a) ethylene, propylene and butylenes in olefins; (b) benzene, toluene, xylenes and naphthalene in aromatics; (c) different chemical groups in aromatics.
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and olefin yields attained maximum value with 10% Gamma-Al2O3 as the additive, while the unidentified oxygenates yield attained the minimum value. The char and coke yields decreased with all the three additives. This is because these additives depolymerized large-molecular compounds which would form coke over pure LOSA-1 catalyst. The additions of Gamma-Al2O3, CaO and MCM41 produced more CO. This can be explained by two reasons: (1) the addition of these additives cracked some large-molecular and this process produced CO; (2) more small-molecular oxygenates entered the micropores of LOSA-1 catalyst and be converted to hydrocarbons and CO. 3.4. Product selectivities of rice stalk catalytic pyrolysis over different catalysts mixed with LOSA-1 Fig. 5 shows the product carbon selectivities of rice stalk catalytic pyrolysis over 10% different additives mixed with LOSA-1. Detailed selectivities of all products are shown in Table 1. Ethylene and propylene are the two main olefins in all experiments and their summation is up to 95%. The selectivity of ethylene is almost equal to that of propylene with pure LOSA-1 as the catalyst. Ethylene selectivity is much higher than propylene selectivity when Gamma-Al2O3, MCM-41 and CaO were added. The selectivities of benzene and toluene increased in all the experiments with the three additives, whereas that of naphthalene decreased significantly. LOSA-1 and Gamma-Al2O3 mixture resulted in highest toluene selectivity (43.6%) and no naphthalene selectivity, while LOSA-1 and CaO mixture resulted in the lowest toluene selectivity (34.9%). These results are related to the characteristics of GammaAl2O3 and CaO. Gamma-Al2O3 belongs to acid and mesoporous catalyst, while CaO belongs to strong base and macroporous catalyst. Different chemical groups in aromatics show that benzene and its derivatives accounted for 81.4% with pure LOSA-1 as the catalyst, and it increased to 89.2–96.6% with additives. CaO as the additive produced more naphthalene and its derivatives compared to other two additives. 4. Conclusion Catalytic fast pyrolysis of rice stalk over mesoporous and macroporous catalysts (Gamma-Al2O3, CaO and MCM-41) mixed with microporous LOSA-1 were conducted in an internally interconnected fluidized bed. The maximum yield of aromatic + olefin (25.3%) was obtained with 10% Gamma-Al2O3/90% LOSA-1, which was boosted by 39.8% compared to that obtained with pure LOSA-1. The addition of these catalysts improved the selectivities of low-carbon components significantly. This paper proposed a new and simple way to enhance hydrocarbon yield in biomass catalytic pyrolysis process. The synergistic effects and mechanisms of the physically mixed catalyst need to be further studied in future. Acknowledgements This work is financially supported by the National Natural Science Foundation of China (Grant No. 51076031), the National Basic Research Program of China (973 Program) (Grant Nos. 2010CB732206; 2012CB215306) and the China Postdoctoral Science Foundation. 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.biortech.2013. 04.094.
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