Bioresource Technology 155 (2014) 57–62

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Bioresource Technology

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Catalytic conversion of biomass pyrolysis-derived compoundswith chemical liquid deposition (CLD) modified ZSM-5

0960-8524/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.biortech.2013.12.085

⇑ Corresponding author. Tel.: +86 25 83795726.E-mail address: ruixiao@seu.edu.cn (R. Xiao).

Huiyan Zhang a, Mengmeng Luo a, Rui Xiao a,⇑, Shanshan Shao a, Baosheng Jin a, Guomin Xiao b,Ming Zhao c, Junyu Liang c

a Key Laboratory of Energy Thermal Conversion and Control, Ministry of Education, School of Energy and Environment, Southeast University, Nanjing 210096, PR Chinab School of Chemistry and Chemical Engineering, Southeast University, Nanjing 210096, PR Chinac Electric Power Research Institute, Yunnan Electric Power Test and Research Institute (Group), Kunming 650217, PR China

h i g h l i g h t s

� ZSM-5 was modified using chemical liquid deposition (CLD) for biomass conversion.� The maximum hydrocarbon yield was obtained with KH550 modified ZSM-5.� The hydrocarbon yield was boosted by 50% compared to that obtained with pure ZSM-5.� The coke yield decreased from 44.1% with pure ZSM-5 to 26.7% with modified one.

a r t i c l e i n f o

Article history:Received 2 October 2013Received in revised form 16 December 2013Accepted 19 December 2013Available online 27 December 2013

Keywords:BiomassModified ZSM-5Chemical liquid depositionFuran catalytic pyrolysis

a b s t r a c t

Chemical liquid deposition (CLD) with KH550, TEOS and methyl silicone oil as the modifiers was used tomodify ZSM-5 and deposit its external acid sites. The characteristics of modified catalysts were tested bycatalytic conversion of biomass pyrolysis-derived compounds. The effects of different modifyingconditions (deposited amount, temperature, and time) on the product yields and selectivities were inves-tigated. The results show KH550 modified ZSM-5 (deposited amount of 4%, temperature of 20 �C and timeof 6 h) produced the maximum yields of aromatics (24.5%) and olefins (16.5%), which are much higherthan that obtained with original ZSM-5 catalyst (18.8% aromatics and 9.8% olefins). The coke yielddecreased from 44.1% with original ZSM-5 to 26.7% with KH550 modified ZSM-5. The selectivitiesof low-molecule-weight hydrocarbons (ethylene and benzene) decreased, while that of highermolecule-weight hydrocarbons (propylene, butylene, toluene, and naphthalene) increased comparingwith original ZSM-5.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Lignocellulosic biomass, as the only carbon neutral renewablesource, is one of the most important substitutes for petroleum-based energy by converting to liquid fuels and chemicals (Huberet al., 2006). The development and application of biomass energytechnology is a vital approach for solving environmental issuesand the security of energy supplies. Biomass fast pyrolysis canproduce considerable liquid fuels named as bio-oils. However,the obtained bio-oils have some disadvantages, such as high oxy-gen content, high instability, and low heat values. They must beupgraded before used as transportation fuels or chemicals.

Catalytic fast pyrolysis (CFP) of biomass is a promising methodto upgrade biomass pyrolysis vapors to high-quality liquid fuels

and chemicals (Stefanidis et al., 2013; Thilakaratne et al., 2014;Wang et al., 2013). In CFP process, biomass pyrolysis with catalystsis proceeded in a single reactor, which has much higher energyconversion efficiency compared to bio-oil upgrading because ofthe elimination of the costly condensation and re-evaporation pro-cesses (Lappas et al., 2002). However, there are still some problemsto restrict the development of biomass catalytic pyrolysis, such aslower petrochemical yield and higher coke yield. We have obtained23.7% carbon yield of olefins and aromatics from pine woodcatalytic pyrolysis in a fluidized bed reactor, but this yield is muchlower than the theoretical yield (more than 60%) (Zhang et al.,2012). One of the most important reasons for lower targeted prod-uct yield and higher coke yield is the structure, active sites, andtheir distribution of the catalysts.

Dozens of acid catalysts are used in the biomass catalytic pyro-lysis process (Adam et al., 2005; Zabeti et al., 2012; Zhang et al.,2013b). ZSM-5 catalyst has been proved to be one of the best cat-alysts for producing olefins and aromatics because of its special

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Fig. 1. NH3-TPD analysis of original and modified (TEOS, KH550, and methylsilicone oil modifiers) ZSM-5 (Deposited conditions are shown as follows: silicadeposited amount of 4%, deposited temperature of 20 �C and deposited time of 6 h).

58 H. Zhang et al. / Bioresource Technology 155 (2014) 57–62

pore structure and activity (Du et al., 2013; French and Czernik,2010). ZSM-5 catalyst has a 3-dimensional pore structure withpore size of 5.5–5.6 Å which is suitable for aromatics and olefinsformation. The shape selectivity of ZSM-5 makes it hard to formcoke in the pores because the molecule diameter of coke is muchlarger than that of the pores. However, there are the growingspaces on the outside surface of the catalysts for coke formation.On one hand, the large-molecule oxygenates from biomass

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Fig. 2. The carbon yields and selectivities of catalytic conversion of furan with modified Zaromatics, olefins, and petrochemicals; (b) carbon yields of CO, CO2, methane, and cselectivities of benzene, toluene, xylene, naphthalene, and indene.

pyrolysis can not enter the pores of microporous catalysts andwould polymerize and form coke on the surfaces. This can be re-lieved by using mesoporous and macroporous bond-broken cata-lysts to crack the large-molecule oxygenates into small-moleculeoxygenates (Zhang et al., 2013a). On the other hand, some small-molecule oxygenates with high activity can also polymerize andform coke in the presence of outside acid sites of the catalysts.For example, furan and its derivates are the major intermediatesfrom CFP of biomass. They show high activity when they undergocatalytic conversion and form significantly amount of coke (Chengand Huber, 2011; Shao et al., 2013). Furan can polymerize at thesurface of ZSM-5 catalyst at room temperature and lead to the col-or of the catalyst changing from white to red (Cheng and Huber,2011). It causes by the outside acid sites of ZSM-5. In CFP process,it is the internal acid sites in the pores having the catalytic charac-teristics to produce olefins and aromatics, whereas the externalacid sites of catalyst particles produce coke instead of the targetedproducts (Foster et al., 2012). Therefore, a method that keeps theinternal acid sites and reduces or deposits the external acid sitescan be used to modify ZSM-5 in order to improve the hydrocarbonyield and decrease the coke yield.

Chemical liquid deposition (CLD) is a common surface modifica-tion technology used for external surface modification of catalysts.CLD could change the pore-opening size and reduce the amount ofacid sites on the surface of catalyst (Teng et al., 2011). CLD technol-ogy have many advantages, such as simple equipment, low cost,and easy operation, thus it used widely to modify catalysts in thefield of petrochemical engineering. In CLD process, modifier with

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SM-5 as the function of silica deposited amount on the catalysts: (a) carbon yields ofoke; (c) carbon selectivities of ethylene, propylene, butylene, and C5; (d) carbon

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Fig. 3. Effects of silica deposited temperature on the 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, methane, and coke; (c) carbon selectivities of ethylene, propylene, butylene, and C5; (d) carbon selectivities ofbenzene, toluene, xylene, naphthalene, and indene.

H. Zhang et al. / Bioresource Technology 155 (2014) 57–62 59

molecular diameter which is greater than pore diameter of catalystdeposits on the external surface to modify acid sites of the catalyst,so as to achieve high selectivity of the products and preferableresistance to coking properties. Zheng and his co-workers used tet-raethyl orthosilicate (TEOS) as the modifier to modify the HZSM-5catalyst (Zheng et al., 2003). The results showed that hydroxy onthe surface decreased from 28% to 13%. Disproportionation reac-tion of xylene was conducted with the modified catalyst. The resultshowed the selectivity of p-xylene increased from 22.5% to 44.3%.Cheng and his co-workers also modified ZSM-5 using CLD methodwith TEOS to prepare catalysts for catalytic pyrolysis of biomass(Cheng et al., 2012). The results showed the aromatic yieldsincreased obviously in catalytic pyrolysis of biomass with themodified ZSM-5. Besides, the p-xylene (having higher value thanother mono-aromatics) selectivity increased from 51% withgallium spray-dried ZSM-5 to 72% with the CLD modified catalystin the pyrolysis of pine wood.

In this work, catalytic conversion of biomass pyrolysis-derivedcompounds (furan) with CLD modified ZSM-5 was conducted in afixed bed reactor. The effects of CLD conditions (deposit quantity,deposit temperature, and reaction time) on the product distribu-tion, especially on the olefins, aromatics, and coke yields wereinvestigated. The performances of different modifiers (KH550,TEOS, and methyl silicone oil) were also compared at the sameconditions.

2. Methods

2.1. Materials

Furan (>99.9%, analytical grade) which was bought from Alad-din Company, PR China was used as feedstock (typical representa-tive of biomass pyrolysis-derived compounds). The original ZSM-5with SiO2/Al2O3 of 50 was provided by Nankai University in China.Three modifiers including 3-triethoxysilylpropylamine (KH550),tetraethyl orthosilicate (TEOS), and methyl silicone oil, and n-hex-ane (>99.9%, analytical grade) were bought from Aladdin Company,PR China.

2.2. Experimental

2.2.1. Chemical liquid depositionZSM-5 zeolite (15 g) and n-hexane (150 mL) were placed in a

conical flask, heated with stirring in water bath and maintainedat the tested temperatures. The modifier (KH550, TEOS or methylsilicone oil) was added into the conical flask. After reaction, n-hex-ane was removed by evaporation in a rotary evaporation appara-tus. The sample was diverted into a corundum boat and dried at80 �C using drying oven for 2 h, and then dried at 110 �C for 2 h.After drying, the sample was calcined at 600 �C using muffle

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Fig. 4. The carbon yields and selectivities of catalytic conversion of furan with modified ZSM-5 as the function of silica deposited time on the catalysts: (a) carbon yields ofaromatics, olefins, and petrochemicals; (b) carbon yields of CO, CO2, methane, and coke; (c) carbon selectivities of ethylene, propylene, butylene, and C5; (d) carbonselectivities of benzene, toluene, xylene, naphthalene, and indene.

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furnace for 6 h. The samples at different deposited amount, depos-ited temperature, deposited time were also prepared. NH3-TPDanalysis for acidity of the original and modified ZSM-5 has beenshown in Fig. 1. As can be seen from the figure, the modifiedcatalysts have lower acid amount and strength.

2.2.2. Catalytic conversion of furanThe performances of the modified ZSM-5 catalyst were evalu-

ated through catalytic conversion of furan in a fixed bed reactorwhich was described elsewhere (Shao et al., 2013; Zhang et al.,2014). The reactor was made by quartz tubular with the insidediameter of 17.4 mm. Pure nitrogen (99.999%) was used as carriergas and controlled by a mass flow controller. The reaction temper-ature was tested by a K-type thermocouple inserted from the top ofthe reactor. Before experiments, the ZSM-5 catalyst (90 mg) wasplaced on grid plate of the reactor and activated at 600 �C for 1 hin 100 mL/min O2 stream. After activation, the carrier gas wasswitched to N2 and furan was injected into the reactor by a springpump from the top of the reactor. A condenser with ethanol wasused to obtain condensable products. The condenser was put inan ice-water bath to keep low temperature. The compounds ofthe obtained liquid were identified and quantified by GC–MSinstrument with external standard. The non-condensable gaseswere collected using gas sampling bags and analyzed by GC-FID/TCD. All the experiments were operated at the temperature of600 �C, carrier gas flow rate of 200 mL/min and weight hourly

space velocity (WHSV) of 1.5 h�1. The reaction was conductedabout 20 min. The total mass of feeding furan in each run was45 mg. After reaction, the carrier gas was switched to O2 at100 mL/min to obtain coke yield. During the coke combustion pro-cess, the produced CO was further converted into CO2 by using aCO converter (copper oxide). The gas was introduced to a wateradsorption unit (allochroic silica gel) and then to a CO2 adsorptionunit (ascarite).

3. Results and discussion

3.1. Effect of the deposited amount on the product distribution of furancatalytic conversion over KH550 modified ZSM-5 catalyst

The product yields and selectivities of catalytic conversion offuran over modified ZSM-5 catalysts with different silica depositedamounts are shown in Fig. 2. ZSM-5 catalysts were modified usingKH550 at deposited temperature of 20 �C and deposited time of6 h. The deposited amounts included 1%, 2%, 4%, 8%, and 16%. Asshown in Fig. 2(a), the aromatic yield increases with increasingdeposited amount, while that of C2–C4 olefins first increases thendecreases with the maximum value of 17.2% at 8% silica depositedamount. The total yield of petrochemicals (aromatics plus olefins)increases from 28.6% with pure ZSM-5 to the maximum value of42.8% with 8% silica deposited ZSM-5 catalyst. It can be seen fromFig. 2(b), the coke yield decreases significantly from 44.1% with

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

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pure ZSM-5 to the lowest yield of 26.7% at 4% silica depositedamount. As the NH3-TPD analysis shown in Fig. 1, silica depositedon the surface of catalyst made acid concentration and acid sitesdecreasing largely, it restrained the generation of coke, and re-duced the chances of secondary reaction on the surface of catalyst.The similar results were obtained by Niwa and his co-researchers(Niwa et al., 1984). Therefore, petrochemical yield increases andcoke yield decreases with the increasing deposited amount. How-ever, large silica deposit amount led to the blocking of ZSM-5 poresand reduced petrochemical yield. The carbon selectivities of olefinsand aromatics are shown in Fig. 2(c) and (d). Olefins mainly includeethylene, propylene, and butylene, while aromatics mainly includebenzene, toluene, and naphthalene. The selectivities of ethyleneand benzene are reduced, whereas that of propylene, butylene,toluene, and naphthalene are enhanced with the silica depositedZSM-5 catalysts. It seems that the silica deposition of ZSM-5produced more high-carbon content compounds.

3.2. Effect of the deposited temperature on the product distribution offuran catalytic conversion over KH550 modified ZSM-5 catalyst

Fig. 3 shows the effect of deposited temperature of modifiedZSM-5 catalysts on product yields and selectivities in furan cata-lytic conversion process. ZSM-5 catalysts were modified usingKH550 at silica deposited amount of 4% and deposited time of6 h. The deposited temperature included 20, 50, and 90 �C. As

shown in Fig. 3(a), both the aromatic and olefin yields increase firstand then decrease with a maximum value of 27.3% and 18.8% at thedeposited temperature of 50 �C, respectively. The highestpetrochemical yield of 46.1% was reached with the deposited tem-perature of 50 �C. High temperature made the deposition moreuniform and more external active sites were covered by silica.However, much higher temperature may result in hard deposition.The coke yield slightly increases with increasing deposited temper-ature. The CO2 yield increases dramatically from 6.4% with pureZSM-5 to 11.8% with modified one at the deposited temperatureof 90 �C, whereas CO yield decreases from 8.1% to 5.4%. It can beseen from Fig. 3(c), the selectivity of propylene decreases, whilethat of butylene increases with increasing deposited temperature.In aromatic products, toluene selectivity slightly decreases, whilenaphthalene selectivity increases with the increase of temperature.

3.3. Effect of the deposited time on the product distribution of furancatalytic conversion over KH550 modified ZSM-5 catalyst

The product yields and selectivities of catalytic conversion offuran over modified ZSM-5 catalysts with different silica depositedtime are shown in Fig. 4. ZSM-5 catalysts were modified usingKH550 at silica deposited amount of 4% and deposited temperatureof 20 �C. Both of olefin and aromatic yields increase with increasingdeposited time. Furthermore, there is an inflection point at thedeposited time of 6 h. The aromatic and olefin yields increase

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dramatically when the deposited time is less than 6 h. Coke yielddecreases and shows the opposite trend with aromatic and olefinyields. However, they share the same inflection point of 6 h. Theiryields have almost no change after 6 h. The increase of depositedtime made silica deposition on the external surface of catalystmore uniform, which led to its higher performance. CO2 yield in-creases, whereas CO yield decreases with increasing depositedtime. This means more oxygen in the feedstock was removed byCO2. Oxygen can be removed via water, CO and CO2. CO2 is the bestway because one carbon atom can remove two oxygen atomwithout hydrogen consumption. As shown in Fig. 4(c) and (d),the selectivities of propylene, butylene, toluene, and naphthaleneincrease, whereas that of ethylene and benzene decrease withincreasing deposited time.

3.4. Effect of the different modifiers on the product distribution offuran catalytic conversion over modified ZSM-5 catalysts

The carbon yields and selectivities of furan catalytic conversionwith different modifiers modified ZSM-5 are shown in Fig. 5. Thetested modifiers included KH550, TEOS, and methyl silicone oil.The catalyst deposited conditions are shown as follows: silicadeposited amount of 4%, deposited temperature of 20 �C anddeposited time of 6 h. KH550 modifier produced the maximumyield of petrochemicals. The petrochemical yield decreases in thefollowing order: KH550 > methyl silicone oil > TEOS > originalZSM-5, while the coke yield shows the opposite trend. KH550 pro-duced the maximum yield of CO2 and TEOS produced the lowestone. The CO yield decreases in the following order: methyl siliconeoil > TEOS > original ZSM-5 > KH550. Ethylene, propylene, andbutylene are the three main olefins in furan catalytic conversionruns with original and modified ZSM-5. The sum of ethylene, pro-pylene, and butylenes selectivities is more than 95% in all catalyticruns. The propylene selectivity of KH550 is much higher than thatof ethylene, whereas the selectivities of propylene and ethylene arealmost the same value. KH550 produced the highest selectivities ofpropylene and butylene. Benzene, toluene, and naphthalene arethe three main aromatics in furan catalytic conversion runs withoriginal and modified ZSM-5. The selectivities of toluene and naph-thalene increase with modified ZSM-5. TEOS shows the highestselectivity of toluene and the lowest selectivity of benzene.

4. Conclusion

Catalytic conversion of furan was conducted in a fixed bed reac-tor with CLD modified ZSM-5 catalysts. The carbon yields of olefinsand aromatics were enhanced significantly, while coke yield wasreduced dramatically with KH550, TEOS, and methyl silicone oilmodified catalysts. KH550 is the best modifier for catalytic conver-sion of furan. The best modifying conditions for KH550 wereobtained (silica deposited amount of 8%, deposited temperatureof 50 �C and deposited time of 6 h). This paper offers a simpleand useful way to modify catalyst for catalytic conversion ofbiomass pyrolysis vapors into aromatics and olefins with reducingcoke yield.

Acknowledgements

The authors acknowledge the financial support of the NationalNatural Science Foundation of China (Grant No. 51306036), theMajor Research plan of National Natural Science Foundation ofChina (Grant No. 91334205), the National Basic Research Programof China (973 Program) (Grant No. 2010CB732206) and the JiangsuNatural Science Foundation (Grant No. BK20130615).

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