Catalytic Conversion of Biomass Derivates over Acid Dealuminated

Article pubs.acs.org/IECR

Catalytic Conversion of Biomass Derivates over Acid Dealuminated ZSM‑5 Shanshan Shao, Huiyan Zhang, Lijun Heng, Mengmeng Luo, Rui Xiao,* and Dekui Shen Key Laboratory of Energy Thermal Conversion and Control, Ministry of Education, School of Energy and Environment, Southeast University, Nanjing 210096, People’s Republic of China ABSTRACT: The present study describes the catalytic performance of acid treated HZSM-5 catalyst for the conversion of biomass derivates to olefins and aromatics. The ZSM-5 catalysts were prepared by changing several modifying parameters, such as the leaching agent, H+ concentration, processing temperature, and time. Fresh and modified catalysts were characterized by X-ray diffraction, scanning electron microscopy, surface area analysis, and NH3 temperature programmed desorption. The results show that modified ZSM-5 (leaching agent of H3PO4, H+ concentration of 2 mol/L, temperature of 20 °C, and time of 4 h) produced the maximum yield of chemicals (13.9% olefins and 31.8% aromatics), which are much higher than that obtained with the original ZSM-5 catalyst (9.8% olefins and 24.5% aromatics). The coke yield decreased from 44.1% with original ZSM-5 to 27.4% with modified ZSM-5. At the optimized dealumination condition, the selectivities of ethylene, propylene, and toluene increased, while those of butylene, C5, and benzene decreased compared with the original ZSM-5 catalyst.

1. INTRODUCTION Greenhouse gas emission associated with fossil energy disappearance is of great concern around the world. In the context of a petroleum-deprived age, it is imperative to look for sustainable carbon sources in conjunction with more efficient pathways for high energy density liquid fuels.1,2 Therefore, the conversion of biomass into fuel and energy has attracted increasing attention in recent years. Biomass fast pyrolysis is regarded as a promising way to produce liquid fuel which is called bio-oil.3−7 Bio-oil can be directly used as a fuel in boilers; nevertheless, it has many disadvantages such as high oxygen content, high instability, and low heat values, which hinder its further industrial application. To obtain desired low-oxygen chemicals, many researchers have focused on adding catalyst to the pyrolysis process. Catalytic fast pyrolysis (CFP) involving heating biomass with catalysts in the 400−650 °C temperature range can realize biomass pyrolysis and vapor upgrading in one reactor.7 Oxygenates (furans, acids, etc.) are first formed from the initial decomposition of biomass and then are catalytically converted within the catalysts to valuable hydrocarbons via a series of reaction steps.8,9 Most reports paid attention to catalytic pyrolysis involving the use of many solid acid catalysts such as zeolites to promote cracking reactions. Many studies used ZSM-5 for conversion of different types of biomass and biomass derivatives.10−12 ZSM-5, which is one type of zeolite, has been proved to be suitable for biomass conversion for olefins and aromatic hydrocarbons.13−16 However, the addition of catalysts also leads to coke formation which will reduce the yields of targeted olefin and aromatic hydrocarbons. A 23.7% carbon yield of chemicals was obtained from pine wood catalytic pyrolysis in a fluidized bed reactor, but it is much lower than the theoretical yield (more than 60%).17 It can be attributed to the rapid catalyst deactivation for coke deposition, which is one of the biggest barriers to CFP commercialization.18 © 2014 American Chemical Society

In zeolite-catalyzed hydrocarbon formation reactions, loss of catalyst activity is due to coke formation. Some high-molecularweight oxygenates cannot enter the pores of microporous catalysts and would polymerize and form coke on the surfaces.19−24 Actually, carbonaceous species formed at the active sites (Al atoms) act as the real active centers in ZSM-5 to produce olefins and aromatics. It is the carbonaceous species of the internal acid sites that have catalytic characteristics, whereas those of the external acid sites usually produce coke instead of the targeted products.24 Thanks to some developed effective methods, they can be used to improve the internal acid site characteristics and reduce the external acid sites which will inhibit coke formation.25,26 One method in a previous study is related to acid site coverage which presents good catalytic activity. The other commonly used method for reducing external acid sites is the selective removal of aluminum in the zeolite framework.27 The framework Al is responsible for the acidity of the zeolite, and the dealumination treatment would reduce many acid sites. Thus, the formation of coke would be inhibited. Under specific dealumination conditions, this leads to both activity and selectivity improvements for particular reactions. Such an effect was ascribed to the presence of fewer Brønsted acid sites.28 Some zeolite dealumination techniques have been under consideration.29 Cesteros and co-workers used HCl medium to partially dealuminate commercial mordenite, beta, and ZSM-5 zeolites.27 They reported that the extent of dealumination can be well controlled by the dealumination conditions. Pant and co-workers modified Zn/Cu/ZSM-5 by dealumination with oxalic acid to prepare catalysts for the transformation of methanol.31 The results showed that catalyst performance was Received: Revised: Accepted: Published: 15871

June 18, 2014 September 13, 2014 September 18, 2014 September 18, 2014 dx.doi.org/10.1021/ie5024657 | Ind. Eng. Chem. Res. 2014, 53, 15871−15878

Industrial & Engineering Chemistry Research

Article

Table 1. Catalyst Propertiesa H+ concn (mol/L)

SBET (m2/g)

pore vol (cm3/g)

av pore diam (nm)

Si/Al ratio

0 2 8

319.59 299.73 294.86

73.43 68.87 67.74

2.02 2.19 3.09

20.38 (A) 22.72 (B) 27.969 (C)

Al P (wt %) (wt ‰) 1.57 1.55 1.54

0.103 0.195 0.225

a

Deposited conditions are shown as follows: dealuminated agent of PA, processing temperature of 20 °C, and time of 2 h.

Figure 1. XRD patterns of fresh and modified ZSM-5 catalysts: (a) fresh catalysts; (b) dealuminated catalysts of 2 mol/L H+ concentration; (c) dealuminated catalysts of 8 mol/L H+ concentration.

improved due to the elimination of external surface sites, which results in an easier access of feedstocks to the internal surface sites. In this work, catalytic conversion of biomass pyrolysis derived compounds (furan) over ZSM-5 by acid treatment was conducted in a fixed bed reactor. The effects of dealumination treatment conditions (leaching agent, H+ concentration, processing temperature, and time) on the product yield and distribution, especially on the olefin, aromatic, and coke yields, were investigated.

Figure 3. NH3-TPD analysis of original and modified ZSM-5: (a) fresh catalysts; (b) dealuminated catalysts of 2 mol/L H + concentration; (c) dealuminated catalysts of 8 mol/L H+ concentration.

leaching agent, dealumination temperatures, and times were prepared. 2.2. Characterization of Catalysts. The parent and dealuminated samples were characterized by several techniques. The structure of the ZSM-5 samples was determined through X-ray powder diffraction (Thermo Fisher Scientific). Elemental analysis was performed by inductively coupled plasma (ICP) in which zeolites were first dissolved in hydrofluoric acid. The amount of silicon cannot be determined because SiF4 gas released after acid addition. Scanning electron microscopy− energy dispersive X-ray (SEM−EDX) experiments were performed to obtain the morphology and elemental analysis on the surface of the fresh and modified catalysts. The nitrogen adsorption characteristics were measured using a BELSORPMAX gas adsorption analyzer (BEL, Japan). The micropore volume (pore diameter < 2 μm; Vmicro) and the specific surface area were both estimated by the t-method using the Harkins and Jura equation.32 Each sample was outgassed at 200 °C for 5 h before measurement. The acidity of the catalysts was

2. EXPERIMENTAL SECTION 2.1. Catalyst Preparation. The ZSM-5 catalysts were modified following the procedure described in ref 27. A certain concentration (0.1, 0.5, 1, 2, 4, and 8 mol/L) of leaching agent (HNO3, HCl, H3PO4, 5-sulfosalicylic acid dehydrate, oxalic acid, and tartaric acid) was prepared using deionized water as solvent in a volumetric flask. ZSM-5 zeolite (10 g) and leaching agent (200 mL) were placed in a conical flask, heated with stirring in oil bath, and maintained at the tested temperatures (20, 40, 60, 90, and 120 °C). Leaching agent was then removed by suction filtration in a Büchner funnel. The samples were diverted into the conical flask, infusing 200 mL of deionized water into the conical flask to wash the sample. The used deionized water was separated by suction filtration, and the sample was washed three times. The samples were dried at 80 °C in a drying oven for 2 h, and then dried at 110 °C for 2 h. After drying, the samples were then calcined at 600 °C in a muffle furnace for 6 h. Samples at different concentrations of

Figure 2. SEM photograph of fresh and modified ZSM-5 catalysts: (a) fresh catalysts; (b) dealuminated catalysts of 2 mol/L H+ concentration; (c) dealuminated catalysts of 8 mol/L H+ concentration. 15872

dx.doi.org/10.1021/ie5024657 | Ind. Eng. Chem. Res. 2014, 53, 15871−15878


Article

conversion of furan in a fixed bed reactor which was reported elsewhere.30 The reactor was made of a quartz tube with an inside diameter of 17.4 mm. Pure nitrogen was used as carrier gas and controlled by a mass flow controller. The reaction temperature was tested by a K-type thermocouple inserted from the top of the reactor. Before each experiment, the ZSM-5 catalyst (90 mg) was placed on the grid plate of the reactor and activated at 600 °C for 1 h in a 100 mL/min O2 stream. After activation, the carrier gas was switched to N2 and furan was injected into the reactor by a spring pump from the top of the reactor. A condenser filled with ethanol in an ice−water container was used to obtain condensable products. The liquid compounds were identified and quantified by gas chromatography− mass spectrometry (GC−MS) and GC-FID/TCD (FID, flame ionization detector). The noncondensable gases were collected using gas sampling bags and analyzed by GC-FID/TCD. All the experiments were operated at the temperature of 600 °C, carrier gas flow rate of 200 mL/min, and weight-hourly space velocity (WHSV) of 1.5 h−1. After reaction, the carrier gas was switched to O2 at 100 mL/min to combust the coke and to determine its carbon yield. During the coke combustion process, CO was further converted into CO2 by use of a CO converter (copper oxide). The combustion gas was introduced to a water adsorption unit (allochroic silica gel) and then to a CO2 adsorption unit (ascarite). All the experiments were repeated three times, and the reported data were the average values. The yield in this paper means the product quality divided by the converted furan quality (not its feeding quality). The selectivity of one product means one product percentages in the total products of olefins or aromatics.

estimated by the NH3 temperature programmed desorption (TPD) technique. The sample was pretreated at 600 °C in flowing He for 0.5 h. After the pretreatment, the sample was cooled to 150 °C and saturated with NH3 gas. Then, NH3-TPD was carried out under a constant flow of He (20 mL/min). The temperature was raised from 50 to 700 °C at a heating rate of 18 °C/min. The concentration of ammonia in the exit gas was determined continuously by a gas chromatograph equipped with a thermal conductivity detector (TCD). 2.3. Catalytic Conversion of Furan. The performances of modified ZSM-5 catalysts were evaluated through catalytic

Figure 4. Comparison of NH3-IR spectra for three samples: (a) original ZSM-5 and (b and c) dealuminated ZSM-5 with H+ concentrations of 2 and 8 mol/L.

Figure 5. Effects of different leaching agents on carbon yields and selectivities of catalytic conversion of furan with modified ZSM-5: (a) carbon yields of aromatics, olefins, and petrochemicals; (b) carbon yields of CO, CO2, and coke; (c) carbon selectivities of ethylene, propylene, butylene, and C5; (d) carbon selectivities of benzene, toluene, xylene, naphthalene, and indene. 15873



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0.5 h. The spectra were finally determined by subtracting from the background at 400 °C.

Brønsted acid sites and Lewis acid sites were also characterized by a Nicolet 5700 IR analyzer using a PerkinElmer Spectrum 100 spectrometer equipped with an MCT-A detector and a high temperature chamber (Harrick) with CaF2 windows. Spectra were acquired at a resolution of 4 cm−1 and 32 scans. The zeolite was pretreated under N2 flow (10 mL/min) from room temperature to 500 °C at a heating rate of 5 °C/min. Then the chamber was cooled to room temperature, and 10 mL/min of NH3 was introduced and absorbed on the zeolites. The gas was then switched to nitrogen and desorption happened from room temperature to 400 °C and kept for

3. RESULTS AND DISCUSSION 3.1. Physicochemical Properties of Samples. The X-ray diffraction (XRD) patterns in Figure 1 show that, whatever the operating conditions, the acid treatment does not change the crystalline structure. In Figure 2, scanning electron microscopic (SEM) images demonstrated that more irregular clumps appeared with the increasing H+ concentration of dealumination agent for the treatment of acid. The main physicochemical parameters are given in Table 1. As expected, elemental analysis of a particular region (A, B, C) in Figure 2 shows that the Si/Al ratio increased, which indicated that dealumination actually happened after treatment. After dealumination treatment, the specific surface area and pore volume decreased slightly, while the average pore diameter increased dramatically when the H+ concentration was 8 mol/L. In Figure 3, it can be seen that the dealumination process brings great reduction of strength and amount of strong acid sites, while its effect on weak acid sites is small. The influence of residual phosphorus on catalytic activity can be eliminated, because the amount of phosphorus was at the level of parts per million (ppm) according to Table 1. The Brønsted acid sites (B) and Lewis acid sites (L) and B/L ratios of three samples are shown in Figure 4. Bands at 1355 and 1361 cm−1 for the original ZSM-5 are due to protonation of the NH3 molecule by Brønsted acid sites and NH3 adsorbed on Lewis acid sites, respectively. The relative concentration of Brønsted and Lewis acid sites in zeolites is determined using

Table 2. Furan Conversion over Modified ZSM-5 Catalysts furan conva concn (mol/L) furan convb temp (°C) furan convc time (h) furan convd

untreated 69.2 0

NA 58.8 0.1

HA 66.8 0.5

PA 69.7 1

SA 58.4 2

OA 70.7 4

TA 63.9 8

69.2 untreated 69.2 0 69.2

65.9 20 72.8 0.5 63.4

67.0 40 66.4 1 67.9

69.7 60 69.6 2 71.0

71.0 90 74.8 4 72.8

65.7 120 75.8 8 70.4

61.4

12 64.5

a

Reaction conditions: H+ concentration, 1 mol/L; dealumination temperature, 20 °C; dealumination processing time, 2 h. bReaction conditions: leaching agent, PA; processing temperature, 20 °C; processing time, 2 h. cReaction conditions: leaching medium, PA; H+ concentration, 2 mol/L; processing time, 4 h. dReaction conditions: leaching agent, PA; H+ concentration, 2 mol/L; processing temperature, 20 °C.

Figure 6. Effects of H+ concentrations on carbon yields and selectivities of catalytic conversion of furan with modified ZSM-5: (a) carbon yields of aromatics, olefins, and petrochemicals; (b) carbon yields of CO, methane, CO2, and coke; (c) carbon selectivities of ethylene, propylene, butylene, and C5; (d) carbon selectivities of benzene, toluene, xylene, naphthalene, and indene. 15874



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Figure 7. Effects of dealumination processing temperature on carbon yields and selectivities of catalytic conversion of furan with modified ZSM-5: (a) carbon yields of aromatics, olefins, and petrochemicals; (b) carbon yields of CO, methane, CO2, and coke; (c) carbon selectivities of ethylene, propylene, butylene, and C5; (d) carbon selectivities of benzene, toluene, xylene, naphthalene, and indene.

the relation B/L = (AB/AL)(QL/QB), where AB/AL is the absorbance ratio and QL/QB is the extinction coefficient ratio. With the increase of H+ concentration, both Brønsted acid sites and Lewis acid sites show slightly weaker strength and shift to higher wavenumbers, which presents their weaker strongelectron-withdrawing property. The B/L ratios of three samples are also shown in Figure 4. The B/L ratio of modified catalyst with H+ concentration of 2 mol/L is relatively higher than those of the other two samples. 3.2. Effect of Leaching Agent on the Product Distribution of Furan Catalytic Conversion over Modified ZSM-5 Catalyst. The product yields of catalytic conversion of furan over modified ZSM-5 catalysts with different leaching agents are shown in Figure 5. ZSM-5 catalysts were dealuminated using different leaching agents with H+ concentration of 1 mol/L, dealumination temperature of 20 °C, and processing time of 2 h. The leaching agents in this study included HNO3 (NA), HCl (HA), H3PO4 (PA), 5-sulfosalicylic acid dehydrate (SA), oxalic acid (OA), and tartaric acid (TA). Table 2 gives furan conversions under several processing conditions. Furan conversions as shown in Table 2 over ZSM-5 dealuminated with PA and OA were similar to that over original ZSM-5, while furan conversion over ZSM-5 dealuminated with NA and SA were lower compared with the original catalysts. The overall yield, olefin selectivity, and aromatic selectivity were also clearly given as seen in Figure 5. As shown in Figure 5a,b, dealumination brought about an obvious effect on the increase of total chemical yield and decrease of coke yield. The chemical yield over PA modified ZSM-5 showed the highest value, while

the coke yield showed the lowest value compared with the original ZSM-5. It can be attributed to the high yield of aromatics. Furan conversion over ZSM-5 dealuminated with SA gave the lowest yield of chemicals. It is found that the detailed product selectivities of olefins and aromatics in Figure 5c,d are similar. Namely, the leaching agents used in the catalyst modification have no great influence on the product selectivity. Generally, it seems that PA shows better performance in the furan catalytic conversion over modified ZSM-5. 3.3. Effect of H+ Concentration on the Product Distribution of Furan Catalytic Conversion over Modified ZSM-5 catalyst. ZSM-5 catalysts were dealuminated using PA, a processing temperature of 20 °C, and a time of 2 h. H+ concentrations included 0.1, 0.5, 1, 2, 4, and 8 mol/L. As shown in Table 2, the furan conversion percentages at different H+ concentrations are similar. The furan conversion was mainly between 65 and 71%. If the H+ concentration is high enough, destructive dealumination may happen, which leads to complete destruction of acid sites. The influences of H+ concentration on the overall yield, olefin selectivity, and aromatic selectivity were also given as seen clearly in Figure 6. With the increasing H+ concentration, the total yield of chemicals increased and then decreased with a maximum value of 46.2% at the H+ concentration of 1 mol/L. The olefin and aromatic yields at the acid concentration of 2 mol/L were just a little smaller than that at 1 mol/L. It can be found that the coke yield decreased dramatically from 44.1% of the original ZSM-5 catalyst to 27.4% at the H+ concentration of 2 mol/L. Therefore, 2 mol/L acid concentration is believed to be good 15875



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Figure 8. Effects of dealumination processing time on carbon yields and selectivities of catalytic conversion of furan with modified ZSM-5: (a) carbon yields of aromatics, olefins, and petrochemicals; (b) carbon yields of CO, methane, CO2, and coke; (c) carbon selectivities of ethylene, propylene, butylene, and C5; (d) carbon selectivities of benzene, toluene, xylene, naphthalene, and indene.

In Table 2, furan conversion decreased from 72.8% to a minimum of 66.4% at the processing temperature of 40 °C and then increased. As seen from Figure 7a, the highest chemical yield of 45.8% could be obtained when the processing temperature was 20 °C, which enhanced the chemical yield of 60.7%. At the same time, coke yield could be reduced effectively from 44.1 to 27.4%. It can be concluded that oxygen in the furan was deleted mainly as CO + CO2 as shown in Figure 7b. Actually, oxygen would better be deleted as CO2 because one C molecule can be removed with two O molecules. Figure 7c,d presents the selectivities of olefins and aromatics. Compared with original ZSM-5, the selectivities of ethylene, propylene, and toluene increased and the selectivities of butylene, C5, and benzene decreased. 3.5. Effect of Dealumination Time on the Product Distribution of Furan Catalytic Conversion over Modified ZSM-5 Catalyst. ZSM-5 catalysts were modified using PA as leaching agent at the H+ concentration of 2 mol/L and processing temperature of 20 °C. As seen from Table 2, furan conversion increased at the processing time of 4 h and then decreased. It is not favorable if the dealumination time is higher than 4 h, because some necessary acid sites may be removed, which will reduce furan catalytic conversion. As shown in Figure 8a, the chemical yield can reach a maximum value of 48.4% at the processing time of 4 h. Both olefin and aromatic yields increased and then decreased with the increasing processing time. In Figure 8b, little methane can

for enhancing olefin and aromatic yields and inhibiting coke formation, which is in good agreement with the idea of catalyst characterization of NH3-IR. The treatment of ZSM-5 does not modify their porosities but decreases the concentration of aluminum atoms on the outer surface of their crystallites, which is related to active sites.33 Excess acid sites could be removed, meanwhile, which could also ensure furan catalytic conversion when the H+ concentration was less than 2 mol/L. Conversely, if the H+ concentration was higher than 2 mol/L, the residual acid sites were insufficient for furan catalytic conversion. As shown in Figure 6b, the yields of CO and CO2 decreased and then almost remained constant after the H+ concentration of 2 mol/L. Figure 6c,d gives the selectivities of olefins and aromatics as a function of H+ concentration. We can see that the selectivities of ethylene and propylene show similar trends between the original and modified catalysts, and those of butylene and C5 are also similar. As for aromatics, the selectivity of benzene decreased and then increased with the minimum of 51.8% when the H+ concentration was 2 mol/L, while that of toluene increased and then remained almost constant. 3.4. Effect of Dealumination Processing Temperature on the Product Distribution of Furan Catalytic Conversion over Modified ZSM-5 catalyst. The tested temperatures included 20, 40, 60, 90, and 120 °C. The catalyst modification conditions were as follows: leaching medium of PA, H+ concentration of 2 mol/L, and processing time of 4 h. 15876



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(6) Huber, G. W.; Iborra, S.; Corma, A. Synthesis of transportation fuels from biomass: Chemistry, catalysts, and engineering. Chem. Rev. 2006, 106, 4044−4098. (7) Carlson, T. R.; Vispute, T. P.; Huber, G. W. Green gasoline by catalytic fast pyrolysis of solid biomass derived compounds. ChemSusChem 2008, 1, 397−400. (8) Mullen, C. A.; Boateng, A. A.; Goldberg, N. M. Production of deoxygenated biomass fast pyrolysis oils via product gas recycling. Energy Fuels 2013, 27, 3867−3874. (9) Aho, A.; Kumar, N.; Eränen, K.; Salmi, T.; Hupa, M.; Murzin, D. Y. Catalytic pyrolysis of woody biomass in a fluidized bed reactor: influence of the zeolite structure. Fuel 2008, 87, 2493−2501. (10) Zheng, A. Q.; Zhao, Z. L.; Chang, S.; Huang, Z.; Wu, H. X.; Wang, X. B.; He, F.; Li, H. B. Effect of crystal size of ZSM-5 on the aromatic yield and selectivity from catalytic fast pyrolysis of biomass. J. Mol. Catal. A: Chem. 2014, 383, 23−30. (11) Jae, J.; Coolman, R.; Mountziaris, T. J.; Huber, G. W. Catalytic fast pyrolysis of lignocellulosic biomass in a process development unit with continual catalyst addition and removal. Chem. Eng. Sci. 2014, 108, 33−46. (12) Kantarelis, E.; Yang, W.; Blasiak, W. Effect of zeolite to binder ratio on product yields and composition during catalytic steam pyrolysis of biomass over transition metal modified HZSM-5. Fuel 2014, 122, 119−125. (13) Zhang, H. Y.; Nie, J. L.; Xiao, R.; Jin, B. S.; Dong, C. Q.; Xiao, G. M. Catalytic co-pyrolysis of biomass and different plastics (PE, PP, PS) to improve hydrocarbon yield in a fluidized bed reactor. Energy Fuels 2014, 28, 1940−1947. (14) Mihalcik, D. J.; Mullen, C. A.; Boateng, A. A. Screening acidic zeolites for catalytic fast pyrolysis of biomass and its components. J. Anal. Appl. Pyrolysis 2011, 92, 224−232. (15) Guisnet, M.; Magnoux, E. Coking and deactivation of zeolites: Influence of the pore structure. Appl. Catal. 1989, 54, 1−27. (16) Zaidi, H. A.; Pant, K. Combined experimental and kinetic modeling studies for the conversion of gasoline range hydrocarbons from methanol over modified HZSM-5 catalyst. Korean J. Chem. Eng. 2010, 27, 1404−1410. (17) Zhang, H. Y.; Calson, T. R.; Xiao, R.; Huber, G. W. Catalytic fast pyrolysis of wood and alcohol mixtures in a fluidized bed. Green Chem. 2012, 14, 98−110. (18) Luque, R.; Herrero-Davila, L.; Campelo, J. M.; Clark, J. H.; Hidalgo, J. M.; Luna, D.; Marinas, J. M.; Romero, A. A. Biofuels: a technological perspective. Energy Environ. Sci. 2008, 1, 542−564. (19) Valle, B.; Castaño, P.; Olazar, M.; Bilbao, J.; Gayubo, A. G. Deactivating species in the transformation of crude bio-oil with methanol into hydrocarbons on a HZSM-5 catalyst. J. Catal. 2012, 285, 304−314. (20) Du, S. C.; Valla, J.; Bollas, G. Characteristics and origin of char and coke from fast and slow, catalytic and thermal pyrolysis of biomass and relevant model compounds. Green Chem. 2013, 15, 3214−3229. (21) Fogassy, G.; Thegarid, N.; Schuurman, Y.; Mirodatos, C. From biomass to bio-gasoline by FCC co-processing: effect of feed composition and catalyst structure on product quality. Energy Environ. Sci. 2011, 4, 5068−5076. (22) Li, J. Z.; Wei, Y. X.; Qi, Y.; Tian, P.; Li, B.; He, Y. L.; Chang, F. X.; Sun, X. D.; Liu, Z. M. Conversion of methanol over H-ZSM-22: The reaction mechanism and deactivation. Catal. Today 2011, 164, 288−292. (23) Li, J. Z.; Wei, Y. X.; Liu, G. Y.; Qi, Y.; Tian, P.; Li, B.; He, Y.; Liu, Z. M. Comparative study of MTO conversion over SAPO-34, HZSM-5 and H-ZSM-22: Correlating catalytic performance and reaction mechanism to zeolite topology. Catal. Today 2011, 171, 221−228. (24) Guisnet, M.; Costa, L. F.; Ribeiro, R. Prevention of zeolite deactivation by coking. J. Mol. Catal. A: Chem. 2009, 305, 69−83. (25) Zhang, H. Y.; Zheng, J.; Xiao, R. Catalytic pyrolysis of willow wood with Me_ZSM-5 (Me= Mg, K, Fe, Ga, Ni) to produce aromatics and olefins. Bioresources 2013, 8, 5612−5621.

be found in the gas product. There was a minimum coke yield of 26.8% at the dealumination time of 4 h, which was consistent with furan conversion. As seen from Figure 8c, the variation trends of olefin selectivities as a function of dealumination processing time were similar to that as a function of H+ concentration, which were both related to the contact time between aluminum and H+. The selectivities of aromatic compounds are shown in Figure 8d. When the processing time was higher than 4 h, the selectivity of benzene increased, while the selectivity of toluene decreased along with the increase of coke selectivity. This means that high processing time favors the production of benzene and toluene catalytic conversion to large molecules.

4. CONCLUSION The acid leaching under several conditions has significant effects on the physicochemical and catalytic performances in furan pyrolysis. Performances of dealuminated catalysts were found to be better under carefully controlled conditions depending on variables such as leaching agent, H+ concentration, processing temperature, and time. The carbon yields of chemicals (olefin and aromatic) were improved significantly, while the coke yield was reduced efficiently. The favorable processing conditions of acid dealumination with H3PO4 over ZSM-5 were obtained (H+ concentration of 2 mol/L, processing temperature of 20 °C, and time of 4 h) with the highest chemical yields (13.9% olefins and 31.8% aromatics). This study demonstrates that a selective deactivation of the outer surface of ZSM-5 zeolite through simple acid leaching will promote catalytic conversion of biomass derivates into olefins and aromatics along with reducing coke yield.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +86-25-83795726-803. Fax: +86-25-83795508. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors acknowledge the financial support of the National Natural Science Foundation of China (Grant 51476035 and 51306036), the Major Research Plan of National Natural Science Foundation of China (Grant 91334205), and the National Basic Research Program of China (973 Program) (Grant 2012CB215306).

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REFERENCES

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Catalytic Conversion of Biomass Derivates over Acid Dealuminated

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