Fuel Processing Technology 91 (2010) 25–32

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Fuel Processing Technology

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Catalytic pyrolysis of biomass for biofuels production

Richard French, Stefan Czernik ⁎National Bioenergy Center, National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401, United States

⁎ Corresponding author. Tel.: +1 303 384 7703; fax:E-mail address: Stefan_Czernik@nrel.go (S. Czernik)

0378-3820/$ – see front matter © 2009 Elsevier B.V. Aldoi:10.1016/j.fuproc.2009.08.011

a b s t r a c t

a r t i c l e i n f o

Article history:Received 3 February 2009Received in revised form 10 July 2009Accepted 17 August 2009

Keywords:BiomassPyrolysisCatalytic crackingZeolitesMass spectroscopy

Fast pyrolysis bio-oils currently produced in demonstration and semi-commercial plants have potential as afuel for stationary power production using boilers or turbines but they require significant modification tobecome an acceptable transportation fuel. Catalytic upgrading of pyrolysis vapors using zeolites is apotentially promising method for removing oxygen from organic compounds and converting them tohydrocarbons. This work evaluated a set of commercial and laboratory-synthesized catalysts for theirhydrocarbon production performance via the pyrolysis/catalytic cracking route. Three types of biomassfeedstocks; cellulose, lignin, and wood were pyrolyzed (batch experiments) in quartz boats in physicalcontact with the catalysts at temperature ranging from 400°C to 600°C and catalyst-to-biomass ratios of 5–10 by weight. Molecular-beam mass spectrometry (MBMS) was used to analyze the product vapor and gascomposition. The highest yield of hydrocarbons (approximately 16 wt.%, including 3.5 wt.% of toluene) wasachieved using nickel, cobalt, iron, and gallium-substituted ZSM-5. Tests performed using a semi-continuousflow reactor allowed us to observe the change in the composition of the volatiles produced by the pyrolysis/catalytic vapor cracking reactions as a function of the catalyst time-on-stream. The deoxygenation activitydecreased with time because of coke deposits formed on the catalyst.

© 2009 Elsevier B.V. All rights reserved.

1. Introduction

In recent years biofuels have attracted considerable attentionmainly because of high crude oil prices, national security concerns,and potential climate change consequences. In addition to thecommercial production of biodiesel and corn-based ethanol, researchis increasingly being focused on developing processes for producingliquid fuels from lignocellulosic biomass. One of the emergingtechnologies is fast pyrolysis that produces high yields of a liquidproduct, called bio-oil, which contains up to 70% of the energy of thebiomass feed [1]. However, certain bio-oil properties such as its lowheating value, incomplete volatility, acidity, instability, and incom-patibility with standard petroleum fuels significantly restrict itsapplication [2]. The undesirable properties of pyrolysis oil resultfrom the chemical composition of bio-oil that mostly consists ofdifferent classes of oxygenated organic compounds. The eliminationof oxygen is thus necessary to transform bio-oil into a liquid fuel thatwould be broadly accepted and economically attractive. Two types ofprocesses that have been used to reject oxygen from organicmolecules are hydrotreating and catalytic cracking. The former useshydrogen to remove oxygen in the form of water while the latteraccomplishes the removal of oxygen in the form of water and carbonoxides using shape-selective catalysts like zeolites. Recent reviews on

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hydrotreating [3] and on catalytic cracking [4] describe the principlesof these processes and provide numerous references to originalstudies in those areas. The research described in this paper focuses oncatalytic reforming using zeolite catalysts. This approach offersseveral potential advantages over hydrotreating such as no or lowneed for hydrogen, atmospheric pressure processing, and a possibilityof close coupling with pyrolysis that could make the processlogistically and economically attractive.

2. Catalytic cracking of oxygenated organic compounds

Catalytic cracking accomplishes deoxygenation through simulta-neous dehydration, decarboxylation, and decarbonylation reactionsoccurring in the presence of zeolite catalysts. In the late 1970s,synthetic zeolites such as ZSM-5 were successfully used to convertoxygenated organic compounds into hydrocarbons [5,6]. ZSM-5proved to be particularly effective for the conversion of methanol togasoline range hydrocarbons [7], which led to the commercializationof the methanol-to-gasoline process by Mobil. This discovery alsostimulated research focused on the production of hydrocarbons frombiomass-derived pyrolysis oil and pyrolysis vapors [8–10]. Because ofthe complexity of bio-oil, most of the research was conducted usingmodel compounds representing different chemical classes of bio-oilcomponents. Extensive research in this area has been conducted inseveral centers, especially at Laval University [9–11], University ofSaskatchewan [12–15], University of The Basque Country [16,17] andmost recently at University of Massachusetts [18]. In the temperature

Table 1Feedstock composition.

Elemental analysis, wt.% (m.f.) Avicel Lignin Aspen

C 44.3 62.7 49.5H 6.2 6.0 6.1O 49.5 28.6 43.8N b0.01 1.1 0.1Ash b0.01 1.4 0.5

26 R. French, S. Czernik / Fuel Processing Technology 91 (2010) 25–32

range of 350–450°C oxygenated organic compounds in contact withzeolite catalysts have been found to undergo a suite of chemicalreactions including dehydration, decarboxylation, cracking, aromati-zation, alkylation, condensation, and polymerization. The product wasalways a two-phase liquid (aqueous and organic) and gas, while cokedeposits formed on the catalyst surface. The conversion and theproduct composition varied depending on the class of compoundstested. Using a fixed bed of ZSM-5 catalyst, high conversions (N90%)were obtained for alcohols, aldehydes, ketones, acids, and esters whilephenols and ethers remained mostly unchanged. Alcohols andketones reacted to produce high yields of aromatic hydrocarbonswhile acids and esters were mostly converted to gas, water, and cokewith low yield of hydrocarbons. For example, initially complete aceticacid conversion declined to 60% after 3 h on stream with the totalhydrocarbon yield below 10%. The high production of coke resulting ina rapid catalyst deactivation was observed especially for thecompounds having low (b1) effective hydrogen index defined byChen [10] as:

ðH=CÞeff = ðH−2OÞ= C

where H, C, and O represent the number of moles of hydrogen,carbon, and oxygen in the feedstock. This coke is mostly produced bydehydration of oxygenated organic compounds containing highamount of oxygen; dehydration of low-oxygen-content compoundsproduces mostly hydrocarbons. Chen [10] demonstrated that asignificant improvement in the production of hydrocarbons fromlow effective-hydrogen-index compounds such as acetic acid can beobtained by co-processing with methanol, which has a hydrogenindex equal to 2. When zeolites were applied for deoxygenation ofbiomass pyrolysis oils and its fractions [9,12,19] hydrocarbon yields of12–15% were reported but also high coke production and rapidcatalyst deactivation were observed due to hydrogen deficiency(effective hydrogen index b0.3) of biomass pyrolysis oils.

Diebold and Scahill of the National Renewable Energy Laboratory[20,21] proposed an integrated fast pyrolysis/catalytic crackingprocess concept in which vapors from the pyrolyzer were notcondensed and collected as bio-oil but directly fed to a catalyticreactor and converted to aromatic and olefin hydrocarbons. Using apilot plant vortex reactor followed by a fixed-bed catalytic cracker(450 °C, commercial Mobil MCSG-2 catalyst), they achieved 12.7% oftotal hydrocarbon yield based on wood feedstock. The IEA BiomassLiquefaction Task technoeconomic evaluation [22] of the processbased on this data estimated the production cost of gasoline at $0.97/gal (1992 dollars) for a biomass cost of $30/ton, which was notattractive at that time. Comparable yields of hydrocarbons were alsoreported by Evans and Milne [23] who used a packed-bed micro-reactor coupled with a molecular-beam mass-spectrometer (MBMS)and obtained 11% total hydrocarbons, with 3–6% single-ring aromaticsand similar amounts of alkenes and heavier aromatics. This was only athird of the theoretical yield estimated based on the assumption thatoxygen would be rejected mostly as carbon oxides with the excess aswater [20]. In the experiments of Evans and Milne, excessive cokingwas also noted and was hypothesized to be due to the high acidity ofthe HZSM-5 catalyst that enhanced dehydration reactions. In an effortto improve the process performance a series of modified ZSM-5catalysts was produced at the University of Utah and at NREL withvarying silica-to-alumina ratio and metal substitutions. We hopedthat the presence of transition metals would affect the mode ofoxygen rejection by producing more carbon oxides and less watermaking that way more hydrogen available for incorporation intohydrocarbons. The present work is an attempt to verify that modifiedzeolite catalysts of reduced acidity can produce higher yields ofhydrocarbons and less coke than commercial ZSM-5 catalysts testedbefore.

3. Experimental

The catalytic pyrolysis tests were performed using a tubular quartzmicro-reactor coupled with the MBMS. About 10 mg of biomasssample contained in a quartz boat was covered with a layer of catalyst(50–100 mg) then inserted into flowing, preheated carrier gas. Such ahigh catalyst-to-biomass ratio in those exploratory tests was chosenarbitrarily only to show the potential for producing hydrocarbonsfrom biomass; it will have to be optimized in later stages of theprocess development. The carrier gases (helium) at a flow rate of 10 L/min and 10 cm3/min of argon (used as a tracer gas) were introducedthrough the end of the reactor that consisted of a 22 mm innerdiameter quartz tube. The reactor was electrically heated to thedesired temperature (400–600 °C) and coupled to the MBMS forproduct detection. The experimental sequence consisted of: 1)biomass pyrolysis in the bottom of the boat, 2) pyrolysis vaporreaction in the catalyst bed, and 3) movement of the catalyticallyupgraded vapors through the sampling orifice of the MBMS to form amolecular beam, which provided rapid sample quenching andinhibited condensation and aerosol formation. Using an ionizationenergy of 22.5 eV, the MBMS detected volatile products within a massrange of 15–350 amu. A detailed description of the experimental unitand the MBMS techniques is provided elsewhere [24].

The three biomass feedstocks used in the pyrolysis/catalyticcracking tests were ground aspen wood, Avicel® PH-105 cellulose,and straw lignin (provided by a biotechnology company Granit). Theelemental composition of these materials is shown in Table 1.

Forty catalysts were tested representing four groups: 10 commer-cial zeolites (including ZSM-5, Y, and SAPO types), 22 laboratory-prepared ZSM-5 catalysts modified by substituting Al or hydrogenwith different metals (Co, Fe, Ni, Ce, Ga, Cu, Na), four laboratory X andY zeolites, and four different silica and alumina materials. The list ofcatalysts is provided in Table 2. The laboratory catalysts wereprepared using gel precipitation method followed by drying andcalcinations similar to that described in the Mobil patent [7].Laboratory ZSM-5 catalysts had silica-to-alumina ratio of 75, whichvaried for the transition metal-substituted catalysts. The catalystswere not fully characterized yet and the degree of substitution is notknown at this time. For each catalyst two samples were tested usuallyat varying catalyst-to-wood ratios. At least one sample of aspen woodwas pyrolyzed without catalyst each day when the experiments wereconducted to measure the pyrolysis products for comparison withprevious data to assess variability, which was on the order ofexperimental error. Initial pyrolysis/catalytic cracking tests werecarried out for all three feeds at 400 °C and catalyst-to-feed ratios ofapproximately 5 and 10. Following the results of the preliminary tests,the nine best-performing catalysts were used to evaluate hydrocarbonyields produced from aspen wood at temperatures of 400, 500, and600 °C. These yields were determined based on the intensity ofrespective spectrum lines compared to the calibration using toluene.

In addition to the batch experiments, semi-continuous tests wereinitiated to observe the catalyst performance (product gas composi-tion) as a function of the time-on-stream for three selected catalysts.In these experiments 2 g of the catalyst was placed between quartzwool plugs in the bottom of a 10 mm internal diameter tube heated byan electric furnace as shown in Fig. 1. 3–4 mm long, 1 mm diameter

Table 2List of catalysts used in biomass pyrolysis tests.

Catalyst numbera Catalyst name Producer Coke yieldb, wt.%

1 BiZSM-5 NREL2 CeZSM-5 NREL 28.03 H/[Co,Fe]ZSM-5 U Utah4 Co/Al2O3 NREL5 H/[Co]ZSM-5 NREL 29.26 CoZSM-5 U Utah 22.87 H/[Cu,Fe]ZSM-5 U Utah8 H/[Al,Fe]ZSM-5 U Utah 22.99 H/[Fe]ZSM-5 U Utah10 H/FeZSM-5 U Utah11 GaZSM-5 NREL 31.212 H/ZSM-5 NREL13 H/ZSM-5 U Utah 26.414 H/ZSM-5/Al NREL15 MC-50 Mobil16 MC-508 Mobil17 Mn/Al2O3 NREL18 Na/ZSM-5 NREL19 ZSM-5/Al NREL20 ZSM-5/B NREL21 HZSM-5/B NREL22 NiZSM-5 NREL 22.023 BaX zeolite NREL24 CaX zeolite NREL25 BaY zeolite NREL26 CaY zeolite UOP27 NaY zeolite WR Grace28 LZY-8 Union Carbide29 Z-1000 Engelhardt30 ZSM-5 U Utah31 γAl2O3 Johnson Matthey32 H/alumina U Utah33 Kaolin NBS34 Silica gel Merk35 CBV 760 (Y zeolite) Zeolyst36 CBV 720 (Y zeolite) Zeolyst37 CBV 520 (Y zeolite) Zeolyst38 SAPO-11 U Utah39 CBV 5524G Zeolyst 24.640 CBV 8014 Zeolyst 26.0

a Catalyst number in Fig. 5.b Catalytic pyrolysis of aspen wood at 600 °C.

Fig. 1. Semi-continuous flow pyrolysis/catalytic cracking reactor.

Table 3Yields of char (wt.%) produced by pyrolysis of biomass feedstocks.

Temperature, °C Avicel Lignin Aspen wood

400 1 46 16500 b1 39 13600 b1 29 10

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hardwood dowels were dropped onto the catalyst at 20 s intervals(8 g/h, space velocity 4 h−1) and the product gases were swept to theMBMS in a 10 L/min flow of helium. Amounts of char and coke weredetermined by the gain in mass of the inner reactor piece measured atthe end of the test. The product gas composition was measured byMBMS.

4. Results and discussion

Pyrolysis of biomass resulted in the formation of volatiles (gas andvapors) that were analyzed by mass spectrometry and solids (charand coke) whose amount was measured by weighing. The yields ofthe solids are shown in Table 3. As expected, Avicel cellulosevolatilized almost completely (b1% residue) while lignin producedsignificant amounts of solid residue (char). The temperature increaseenhanced volatilization of biomass polymers, especially lignin. Thesechar yields are comparable to those reported in the literature for fastpyrolysis of similar feedstocks [25].

Typical analyses of the volatiles produced by pyrolysis of biomassfeedstocks in quartz boats are shown in Fig. 2. The prominent peaks inthe spectra correspond to water (18) and carbon oxides (28 and 44)that were produced from all studied feedstocks. The yields of H2O,CO2, and CO from aspen wood were respectively 10 wt.%, 6 wt.%, and5 wt.% accounting together for about 33% of biomass oxygen. Theother peaks represent different organic molecules that were formedfrom cellulose and lignin resulting from the breakdown of their

polymeric structure. For aspen pyrolysis, they account for about60 wt.% of feed and 50% of biomass oxygen. The top spectrumobtained from pyrolysis of cellulose shows the typical carbohydratebreakdown products such as hydroxyacetaldehyde and acetic acid(60) (in this case, this spectrum line also represents a fragment ion oflevoglucosan (162) which is the major product of cellulose depoly-merization), and furfuryl alcohol (98). The middle spectrum includeslignin-derived aromatic monomers syringol (154), isoeugenol (164),coniferyl alcohol (180), sinapyl alcohol (210), and heavier fragmentions corresponding to dimers and trimers. The aspen wood pyrolysisspectrum includes both cellulose and lignin-derived compounds. Thetemperature effect on the volatile pyrolysis product in the range of400–600°C was not very significant. Almost all pyrolysis productswere oxygenated compounds and only insignificant amountsof hydrocarbons could be produced directly by simple thermaldecomposition of biomass at this temperature range (Fig. 2 andTable 4, row 4).

In the presence of catalysts, the volatiles released by pyrolysisunderwent various reactions including deoxygenation (dehydration,decarboxylation, decarbonylation) that resulted in the production ofhydrocarbons but also in additional carbonaceous solids— coke. In ourtests we measured the combined amounts of solid residues then thecoke yields were determined by subtracting from total solids theyields of char produced in non-catalytic experiments for respectivefeedstocks assuming that the presence of the catalyst did not affectthe production of char, which is a primary non-volatile pyrolysisproduct. The amount of coke varied depending on the feedstock, thecatalyst and the process temperature. For Avicel cellulose the amountof coke left on the catalyst ranged from 30% to 50%, for aspen woodfrom 10% to 30%, and for lignin from 5% to 15%. The yields of cokeproduced by catalytic pyrolysis of aspenwood at 600 °C using selectednine catalysts is shown in Table 2. This data confirms the earlierobservation [10] that the coke production increases with a decrease of

Fig. 2. Mass spectra of the volatile product from pyrolysis of Avicel cellulose (top), lignin (middle), and aspen wood (bottom) at 500°C; Y axis corresponds to the spectral lineintensity expressed in arbitrary units.

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the effective hydrogen index, which equals 0 for cellulose, 0.16 foraspen wood, and 0.47 for lignin. In general, higher coke productionwas observed for the catalysts that also favored greater yields ofhydrocarbons, which is related to their dehydration activity. Thoughlignin-derived vapors produced less coke than those from celluloseand wood pyrolysis the total amount of solids (char and coke) couldreach 30–60% of the feedstock. Lower amount of solids formed at

Table 4Total hydrocarbon yields from catalytic pyrolysis of aspen wood.

Catalyst Hydrocarbon yield, wt.%

400°C 500°C 600°C

NiZSM-5 10 12 16Zeolyst 5524-G 9 14 16Y zeolite 1.5γAl2O3 b1

600°C than at 400°C, which was mostly due to the reduced charproduction at higher temperature, especially from lignin.

The catalytic pyrolysis spectra are very much different from thosefor simple thermal process. Fig. 3 shows catalytic pyrolysis spectraobtained from three biomass feedstocks using one of the bestcatalysts, nickel-substituted ZSM-5. All the primary pyrolysis productsexcept water and carbon oxides appear to have converted mostly tohydrocarbons of molecular mass less than 156 and to coke. The newspectrum lines correspond to alkenes (27, 41, 42, 55, 56, 69, 70),single-ring aromatics (78, 91, 92, 105, 106, 120), naphthalenes (128,142, 156, 170), and methyl anthracene (192).

The spectra obtained using less active catalysts (silica, alumina or Yzeolites) still showed some of the primary pyrolysis components(mostly lignin-derived) as well as partially dehydrated oxygenates —furan (68), methyl furan (82), furfural (96), andmethyl furfural (110).Fig. 4 illustrates the difference of the product spectra obtained usingpoor, medium, and good catalysts. No qualitative differences were

Fig. 3. Mass spectra of the volatile product from pyrolysis of Avicel cellulose (top), lignin (middle), and aspen wood (bottom) at 500°C, in the presence of NiZSM-5 catalyst; Y axiscorresponds to the spectrum line intensity expressed in arbitrary units.

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observed in the spectra obtained for the same catalyst at differenttemperatures though inmost cases, the temperature increase resultedin higher amounts of hydrocarbons. These spectra did not vary withthe catalyst loading because all the tests were performed using a largecatalyst excess. Interestingly, despite important differences inchemical composition of primary pyrolysis products from celluloseand lignin, the composition of volatiles from catalytic pyrolysis of allthree feedstocks was similar, at least for the best catalysts showingmostly the same hydrocarbons with more alkenes obtained fromlignin than from cellulose and wood, most likely resulting fromsplitting off propene side chains from aromatic lignin units.

The mass spectrometric data was evaluated using principal com-ponent analysis (PCA). The PCA application to biomass pyrolysis/mass spectroscopy data has been described in detail by Evans andMilne [24]. This multivariate pattern recognition technique reducesthe data complexity by finding correlated spectral intensities andexpressing them as new variables, the principle components. Usuallya few components account for the bulk of the variance in the databecause underlying chemical and physical relationships cause mass

intensities associated with a particular compound or family ofcompounds to vary together as catalysts, conditions or feedstockschange even when that is not obvious in the raw spectrum. Using theCamo Unscrambler software we identified six principal componentsthat describe over 98% of the variance of the whole data set. The mostimportant principal components were associated with water (PC1),hydrocarbons (PC2), and aromatic and furanoic oxygenates (PC3) andaccounted for 81% of the variance in the whole data set. Fig. 5 shows amass spectrum representing PC2 and its scores for all the catalyststested (only positive values of the scores are shown in Fig. 5b). Thecatalysts for which the PC2 was high are considered to be the mostpromising for the production of hydrocarbons from biomass pyrolysisvapors. This group included laboratory-prepared catalysts: CeZSM-5,CoZSM-5, CoHZSM-5, H[AlFe]ZSM-5, GaZSM-5, HZSM-5, and NiZSM-5as well as the commercial Zeolysts 5524G and 8014. The preliminaryexperiments confirmed that ZSM-5 type catalysts perform the best inthe process for converting oxygenated biomass pyrolysis vapors tohydrocarbons. Contrary to some observations [26], larger-porezeolites proved less efficient in the deoxygenation of pyrolysis vapors

Fig. 4. Mass spectra from catalytic wood pyrolysis using alumina (top), Z100 (middle), and Ga/ZSM-5 (bottom) at 500 °C.

30 R. French, S. Czernik / Fuel Processing Technology 91 (2010) 25–32

produced from all three types of feedstocks. Table 4 shows theyields of hydrocarbons obtained by catalytic pyrolysis of wood in thepresence of selected best and less effective catalysts.

Semi-quantitative catalytic pyrolysis of aspen wood using ninebest catalysts showed only small performance difference between theselected ZSM-5 zeolites. The yields of hydrocarbons were in the rangeof 10–16 wt.% and increased with temperature. This could be due toboth higher catalytic activity but also to more volatile pyrolysisproduct (less char formed at higher temperature) available for thesecondary catalytic conversion. The highest yields of the desiredhydrocarbon product from wood, 16 wt.% including 3.5wt.% oftoluene were obtained at 600°C using NiZSM-5 though the yieldsproduced by several other catalysts (gallium, cobalt, and iron-substituted ZSM-5 zeolites as well as the commercial Zeolyst 8014)were within the experimental error estimated at ±3%. These yieldsare comparable to those reported by Evans and Milne [23] for similar

zeolites. At this stage, we did not observe significant differences inthe performance between laboratory-prepared HZSM-5 and metal-substituted zeolites that were expected to have lower dehydration,and consequently lower coking activity.

Tests performed using the semi-continuous flow reactor allowedus to observe the change in the composition of the volatiles producedby the pyrolysis/catalytic vapor cracking reactions as a function of thecatalyst time-on-stream. An example presented in Fig. 6 shows thechanges in the product slate represented by the intensity for selectedions:m/z=92 (toluene),m/z=94 (phenol), andm/z=60 (combinedacetic acid, hydroxyacetaldehyde, and levoglucosan) occurring duringthe pyrolysis/catalytic cracking of hardwood at 500°C, using a HZSM-5 catalyst. Despite the oscillation of the curves resulting from the non-uniform feeding rate of biomass to the reactor (especially between the9th and 13th minute) a clear trend can be observed in the productcomposition as a function of time. Initially, oxygenated compounds

Fig. 5. Mass spectrum (a) and scores of PC2 (b), the principal component representing hydrocarbons in aspen catalytic pyrolysis product at 400 °C.

Fig. 6. Intensity of selected ions vs. time during hardwood pyrolysis/catalytic vaporcracking at 500 °C. Wood feed rate 0.13 g/min, 2 g of Mobil HZSM-5 catalyst.

31R. French, S. Czernik / Fuel Processing Technology 91 (2010) 25–32

were not present in the toluene-rich product gas. In the first minutethe product spectrum was very similar to that from Fig. 3. With time,in addition to hydrocarbons, oxygenates such as phenol and cresolshowed up in the product. Finally, primary pyrolysis products becamedominant though the presence of hydrocarbons indicates that thecatalyst still retained some deoxygenation activity.

The semi-continuous tests, even of a relatively short duration(30 min) showed that ZSM-5 catalysts could operate with highdeoxygenation activity for a short time after which they requireregeneration. Potentially, a circulating fluidized bed system similar tothat used in fluidized catalytic cracking of heavy oils could be appliedfor the catalytic biomass pyrolysis to produce hydrocarbons.

5. Summary and conclusions

We performed a preliminary study of biomass catalytic pyrolysisto assess the efficiency of selected catalysts for producing hydro-carbons that could be used as fuels or fuel blends. Batch mode testsusing three biomass feedstocks were conducted at the process

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temperature that ranged from 400°C to 600°C to identify the mostpromising catalysts from a set of 40 selected for this study.

The molecular-beam mass-spectrometer was used to analyze theproduct gas composition. The mass spectra were analyzed usingprincipal component analysis. The best-performing catalysts belongedto the ZSM-5 group while larger-pore zeolites showed less deoxy-genation activity. The highest yields of hydrocarbons from wood,16wt.% including 3.5wt.% of toluenewere obtained for the laboratory-prepared nickel-substituted ZSM-5 zeolite though a few otherlaboratory-prepared ZSM-5 zeolites and a commercial Zeolyst 8014performed almost as well.

Semi-continuous operation of the pyrolysis/vapor cracking pro-cess using a fixed bed of a ZSM-5 catalyst at 500°C and a WHSV of 4showed good deoxygenation performance for up to 4 min. At the endof this time period the catalyst was partly deactivated and requiredregeneration to maintain high activity.

Future tests will be conducted using a continuous flow system thatwill allow us to collect the product and calculate mass balances fordifferent process conditions.

Acknowledgment

Financial support for this work was provided by the U.S.Department of Energy Office of Biomass Programs.

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