Thermal decomposition of lignocellulosic biomass in the presence of acid catalysts

Thermal decomposition of lignocellulosic biomass in the presence of acid

catalysts

Cherif Larabi a ,b ,Walid al Maksoud a ,b ,Kai C.Szeto a ,Anne Roubaud c ,Pierre Castelli c ,Catherine C.Santini a ,?,Jean J.Walter b

Universitéde Lyon,ICL,C2P2,UMR 5265CNRS-ESCPE Lyon-UCBL,43bd du 11Novembre 1918,69616Villeurbanne Cedex,France b

Synthopetrol,37Rue des Mathurins,75008Paris 8,France c

CEA,LITEN,LTB,F 38054Grenoble,France

h i g h l i g h t s

The decomposition of lignocellulose is studied by in situ and ex situ techniques. Three fractions,solid,liquid and gas are quanti?ed and characterized.

The degradation temperature is lowered by 100°C in the presence of H 3PW 12O 40. At 300°C with H 3PW 12O 40,the amount of liquid collected reaches 30wt.%.

Traces of furfural was observed from pure wood,with H 3PW 12O 40it reaches 2wt.%.

a r t i c l e i n f o Article history:

Received 17July 2013

Received in revised form 8August 2013Accepted 10August 2013

Available online 23August 2013Keywords:Thermolysis Pine wood Acidic support Heteropolyacid

Thermal pretreatment

a b s t r a c t

Transformation of lignocellulosic biomass to biofuels involves multiple processes,in which thermal decomposition,hydrotreatment are the most central steps.Current work focuses on the impact of several solid acids and Keggin-type heteropolyacids on the decomposition temperature (T d )of pine wood and the characterization of the resulted products.It has been observed that a mechanical mixture of solid acids with pine wood has no in?uence on T d ,while the use of heteropolyacids lower the T d by 100°C.Moreover,the treatment of biomass with a catalytic amount of H 3PW 12O 40leads to formation of three fractions:solid,liquid and gas,which have been investigated by elemental analysis,TGA,FTIR,GC–MS and NMR.The use of heteropolyacid leads,at 300°C,to a selective transformation of more than 50wt.%of the holo-cellulose part of the lignocellulosic biomass.Moreover,60wt.%of the catalyst H 3PW 12O 40are recovered.

1.Introduction

The steady depletion of fossil fuels resources throughout the world as well as ecological and sustainable development issues have turned current research interest for alternative fuel sources (Menon and Rao,2012).Biomass is considered as renewable en-ergy source.Its contribution to the global warming is negligible compared to fossil fuels,because of its ability to ?x CO 2from the atmosphere.Moreover,employing biofuels is reported to give a positive effect with respect to current greenhouse gas emission (Menetrez,2012;Pires et al.,2012).Biofuels can be divided into ?rst,second and third generation.First generation comprises liquid biofuels originated from corn,sugarcane,soybean,oil palm,etc.The most common ?rst generation biofuels is bio-ethanol.However these sources are considered as unsustainable,mainly due to their use of food feed (Poganietz,2012).Second-generation biofuels originates from non-edible biomass sources,such as lig-nocellulosic materials,forest residues and wastes.The synthesis of second generation biofuels is indeed independent on the use of crops for food consumption (Poganietz,2012).However,exten-sive research efforts are required to make this process economical (Macrelli et al.,2012).The third generation biofuel is known also as Oilgae.It is believed that the cost of their production is low.Moreover,the energy produced as biofuel per acre is higher compared to the land required by other conventional feedstock (Nigam and Singh,2011).Nevertheless,the production of fuels from microalgae is still at its early stage of development (Fiorese et al.,2013).On the other hand,biore?neries for second genera-tion biofuel production can easily be implemented and size adapted just near the lignocellulosic material,this is not the case for the algae resources.

Corresponding author.Tel.:+33(0)472431810;fax:+33(0)472431795.

E-mail address:catherine.santini@univ-lyon1.fr (C.C.Santini).

The transformation of lignocellulosic materials to biofuel as well as chemical feedstocks,requires thermal or thermocatalytic treatment.The challenge lies in depolymerizing the complex struc-ture of the cellulose,hemicellulose and lignin and ideally further upgrade without decomposition into CO,CO2and H2O.A possibil-ity to circumvent this is to perform the thermolysis at lower tem-perature.It is reported that during the thermal decomposition process of lignocellulosic biomass,the holocellulose is decomposed ?rst followed by lignin at higher temperatures(Gronli et al.,2002). In the case of the pine wood,it was found that the decomposition of the holocellulose starts at275°C and the lignin decomposes at ca.350°C(Larabi et al.,2013).Furanic compounds including furfu-ral were released during the decomposition process(Larabi et al., 2013;Sagehashi et al.,2006).Upon hydrotreatment,furfural can be converted to methylfuran(Sitthisa et al.,2011),which is re-ported to have a high octane number and can be used as additive for conventional fuels(Roman-Leshkov et al.,2007).Some of the thermal reactions such as dehydration,depolymerization and even decarboxylation can be catalyzed by solid acidic catalyst(Chheda and Dumesic,2007;Wan et al.,2009).Solid acids under oxidative conditions are largely used in the transformation of the wood into paper pulp(Gaspar et al.,2007),and cellulose into chemicals(Deng et al.,2012;Guo et al.,2012;Tian et al.,2010).Herein,we focus on the transformation of pine wood,in the presence of acid catalysts under reductive condition in order to lower the temperature of the thermolysis,to produce valuable chemicals,reduce the forma-tion of CO and CO2and the potential cost.

For this purpose,the thermal decomposition of pine wood was performed in batch and dynamic reactors,under hydrogen,at tem-perature lower than300°C in the presence of Keggin heteropolyacid (H3PW12O40).Keggin type heteropolyacid was chosen for its stability and strong acidity,which is more pronounced that of typically used strong mineral acids(Cui et al.,2011).Moreover,heteropolyacid maintains its property in the liquid phase as well as a solid by precip-itation or grafting on supports(Marme et al.,1998;Rao et al.,2005; Shimizu et al.,2009).During this investigation,three main fractions were collected,quanti?ed and characterized,by various techniques including FTIR,GC–MS,elemental analysis and solid state NMR.

2.Experimental

2.1.Materials

The lignocellulosic biomass used is originated from pine wood. It was grounded in a Retcsh type RM100mortar mill,and then sieved to give particle size less than0.5mm.In order to distinguish between the water formed during the decomposition process and the physisorbed,the wood dust was pretreated and dried at 110°C,then stored in the glove box.

c-Al2O3(Puralox TM50/150,Sasol),SiO2–Al2O3(Azko Nobel), ZSM-5(Sasol),SiO2(Evonik aerosil-200),H3PW12O40á24H2O (HPW,Phosphotungstic acid hydrate),H3PMo12O40á24H2O(HPMo, Phosphomolybdic acid hydrate),H4SiW12O40á24H2O(HSiW, Silicotungstic acid hydrate),H4SiMo12O40á24H2O(HSiMo, Silicomolybdic acid hydrate),(Aldrich)were used as received.11-Molybdo-1-vanadophos-phoric,H4SiMo11VO40á24H2O(HSiMoV), and10-Molybdo-2-vanadophosphoric H4SiMo10V2O40á24H2O (HSiMoV2),acids were synthesized according to the literature (Tsigdino and Hallada,1968;Berndt et al.,1998).Their purity was checked by31P and29Si liquid-NMR.

2.2.Characterization of product

2.2.1.In-operando DRIFTS-GC/MS

The experiments were carried out in an integrated system comprising mass?ow controllers(Brooks),FT-IR adapted high temperature reaction chamber(Harrick Scienti?c)and online GC/MS(Agilent GC6850MS5975C).The reaction chamber was equipped with ZnSe windows and?tted into the Praying Mantis optical unit also provided by Harrick.In the glove box,about 15mg of pine wood were placed onto a porous stainless steel frit in the reaction chamber.A selected gas(argon or hydrogen)was continuously?owing through the pine wood bed.FT-IR spectra were recorded in a Nicolet6700spectrophotometer with a MCT detector and4cmà1resolution.The formed compounds were separated by a MS compatible25m PORA BOND Q column and analyzed in the online GC–MS.

2.2.2.Nuclear magnetic resonance(NMR)characterization

Solution NMR spectra were recorded on BRUKER AVANCE300 spectrometer(1H:300.1MHz,13C:75.4MHz;31P:121.5MHz; 29Si:59.6MHz).Chemical shifts were measured relative to85% H3PO4aqueous solution for31P.29Si chemical shifts are referenced to Me4Si in DMSO-d6using the substitution method.

Solid state NMR spectra were collected on BRUKER AVANCE III 500spectrometer operating at202.5MHz for31P,125MHz for 13C.The zirconia impeller of4mm is?lled with the desired product and sealed with a kel-f stopper.It was then transferred into the probe Bruker CP4mm spectrometer allowing rotation of the rotor at a speed of10kHz.The time between two acquisitions was always optimized to allow complete relaxation of the protons. 2.2.3.Elemental analyses(C,H,and N)

Microanalyses were performed at the Welience–P?le Chimie Moléculaire Facultédes Sciences Mirande(Dijon,France),using CHNS/O thermo electron?ash1112Series elemental analyzer. 2.2.4.Ex situ IR analysis

Diffuse re?ectance Fourier-transformed infrared(DRIFT)spec-tra were recorded on a Nicolet6700-FT spectrometer using a cell equipped with CaF2window.Typically,64scans were accumulated for each spectrum(resolution4cmà1).

2.2.5.IR quanti?cation of the CO and CO2analysis

The quanti?cation of evolved CO and CO2was performed by transmission FT-IR spectroscopy using a Nicolet5700-FT spec-trometer and infrared cell equipped with CaF2windows.Typically, 64scans were accumulated for each spectrum(resolution1cmà1). To estimate the amount of gases(CO,CO2)in the reactor during the pyrolysis by FTIR technique,the IR detector was calibrated toward CO and CO2.A calibration curve was obtained by reporting for a gi-ven gas pressure the corresponding area related to their asymmet-ric stretching frequency integrated between2220–2140cmà1for CO and2400–2250cmà1for CO2.The calibration curve is provided in Fig.S.1.

2.3.Design of experiments

A mixture of grounded wood and a desired amount of hetero-polyacids(HPA)was stirred in water at25°C for1h.After evapo-ration of water at60°C,the impregnated wood was dried2h at 80°C under vacuum(10à5mbar),then stored in glove box.A mix-ture of grounded wood and10wt.%of solid acid(SA)was mechan-ically mixed,dried2h at80°C under vacuum(10à5mbar),then stored in glove box.

2.3.1.Thermogravimetric analysis

Approximately10mg of the sample was placed in an Al2O3cru-cible and heated under30mL minà1of nitrogen.Three indepen-dent decomposition studies were performed,(i)the weight loss from room temperature to700°C in the presence of10%in weight of solid acid(SA)or heteropolyacids(HPA)with a heating rate of

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5°C minà1.(ii)The weight loss from room temperature to700°C in the presence of different amount of H3PW12O40á24H2O(2,10,20, 30,40,50wt.%).(iii)The weight loss pro?les with time under iso-thermal conditions(150,200,250°C)with a heating rate of 5°C minà1with or without H3PW12O40á24H2O.

2.3.2.In-operando DRIFT/GC–MS

The crucible in the DRIFT cell was?lled with dried wood (15mg)or with the dried wood impregnated with10wt.%of H3PW12O40á24H2O,HPW,in the glove box under argon atmo-sphere.Once the cell was inserted into the spectrophotometer,a controlled mass?ow of argon or hydrogen(6ml minà1)was intro-duced into the reaction chamber at1bar.Heating was pro-grammed from20°C to a desired temperature,using heating rate of5°C minà1.The?nal temperature was then kept for5h.A DRIFT spectrum of64scans was recorded every minute.A continuous analysis by GC–MS of the released volatiles was also carried out.

2.3.3.Scale up wood thermolysis

In this part,experiments were performed either in a continuous ?ow reactor or batch stainless autoclave under1bar of hydrogen.

2.3.3.1.Dynamic reactor.In a glove box,1g of dried wood,or1.1g of wood impregnated with10wt.%of H3PW12O40á24H2O were introduced in the reactor,then placed in the oven and connected to a gas line of hydrogen.The wood thermolysis was carried out in a temperature range between150and300°C under pressure of1bar and a?ow of5mL minà1.This allowed the analysis of light hydrocarbons by an online GC(Varian CP3800).

2.3.3.2.Batch reactor.1g of dried wood or1.1g in the case of the impregnated wood with10wt.%of HPA,were introduced into the batch reactor and heated at different temperatures.The reactor was connected and?ashed under vacuum to remove the water that could be adsorbed while transferring the biomass sample and dur-ing the?xation of the autoclave,in order to distinguish between the adsorbed water and the one produced from the degradation process.Afterwards1bar of hydrogen was introduced and the autoclave was heated at different temperature ranging from150 to300°C and kept for two hours with a heating rate of5°C minà1. The liquid phase collected after distillation under vacuum(10à2 mbar)was characterized by GC–MS,and the amount of furfural produced was evaluated.The residual solid was weighed,and ana-lyzed by elemental analyses(C,H),and13C CP MAS solid state NMR.

2.3.4.FTIR characterization and evaluation of gas phase

Under argon,250mg of wood or275mg in the case of the impregnated wood with H3PW12O40á24H2O were placed in the reactor.The cell was closed and the argon was removed under vac-uum(10à5mbar).The sample was then heated with a rate of 5°C minà1until the target temperature(150,200,250,275, 300°C)and kept at that temperature for2h.The gases obtained were analyzed by mean of transmission FT-IR spectroscopy using a NICOLET5700FT-IR spectrometer.

CO calibration:The peaks were integrated between2220and 2140cmà1and the variation of the amount(mmol)was propor-tional to the surface with a coef?cient of2.684(Fig.S.1a and b).

CO2calibration:The peaks were integrated between2400and 2250cmà1and the variation of the quantity(mmol)was propor-tional to the surface with a coef?cient of0.022(Fig.S.1c and d).

2.3.5.Ex situ DRIFT

The samples of wood and wood impregnated with10%of HPA are thermally treated at different temperatures(150,200,250,275,300°C)in a reactor under hydrogen?ux.The solid obtain in each experience was analyzed by ex situ DRIFT.

3.Results and discussion

The thermal treatment of the pine wood in the presence of acid catalysts has been performed mainly under hydrogen atmosphere. First,the impact of the solid acids(SA=Al2O3,SiO2–Al2O3,ZSM-5 and SiO2)compared to the water soluble heteropolyacids (HPA=H3PW12O40,H3PMo12O40,H4SiW12O40,H4SiMo12O40, H4PVMo11O40,H5PV2Mo10O40)has been investigated.

The DRIFT spectra of dried wood(Larabi et al.,2013),and of the wood sample impregnated with10wt.%H3PW12O40are repre-sented in(Fig.S.2).In Fig.S.2,besides the absorption bands of pine wood,supplementary peaks at1089,989,896and818cmà1are observed,attributed to m(P–O a),m(W=O t),m(W–O c–W)and m (W–O e–W),respectively where a,t,c and e correspond to different oxygen position atoms in Keggin structure(internal,terminal, corner and edge-shared)(Caliman et al.,2010).

The31P solid state NMR of a wood sample impregnated with 10wt.%H3PW12O40(Fig.S.3b),shows one peak atà15.5ppm in agreement with the chemical shift observed in31P liquid NMR for H3PW12O40(Fig.S.3a),suggesting that the Kegging structure of the HPA is preserved after impregnation.

3.1.Thermo-gravimetric studies of wood and wood/solid acid or wood/ heteropolyacid under argon

Mixtures of wood/SA and wood/HPA from40°C to700°C with heating rate of5°C minà1have been investigated by TGA.The evo-lution of the weight loss with the temperature in the presence of various SA(SA=Al2O3,SiO2–Al2O3,ZSM-5and SiO2)is depicted in Fig.1a.The decomposition temperature(T d)of the wood in the presence of the selected SA shows no change(275°C).The evo-lution of the weight loss with the temperature for wood/HPA, (HPA=H3PW12O40,H3PMo12O40,H4SiW12O40,H4SiMo12O40, H4PVMo11O40,H5PV2Mo10O40),(Fig.1b)shows that the(T d)is low-ered with ca.100°C.However,(T d)is not affected by the acidity strength of HPA(H3PW12O40>H3PMO12O40>H4SiW12O40> H4SiMo12O40>H4PVMo11O40>H5PV2Mo10O40).

The in?uence of the amount of H3PW12O40on(T d)is re-ported in Fig.1c.The(T d)decreases from280°C to250°C when 2wt.%of HPW are added,and in the presence of quantities higher than10wt.%the decomposition occurs at180°C.The in-crease of the?nal weight with the loading of HPW can be ex-plained by the fact that the residue comprises charcoal originated from the biomass itself and tungsten oxide formed after thermal treatment at high temperature(higher than 400°C)of HPW.

These experiments show that(T d)is independent on the pres-ence of solid acids,while HPA have a signi?cant impact on(T d) with an optimum for the weight ratio wood/HPA equal to90/10. Therefore,further studies are dedicated to the thermolysis of the pine wood in the presence of mainly phosphotungstic heteropoly-acid H3PW12O40,hereafter noted as HPW.

The isothermal TGA experiments,at150,200and250°C car-ried out on wood and wood/HPW(90/10)show a rapid weight loss of ca.6%,related to the removal of physisorbed water (Fig.S.4).At150°C,only the weight of wood/HPW sample de-creases continuously(Fig.S.4).At200and250°C,the weight of both samples decreases but more deeply and earlier for the wood/HPW sample.Clearly,the kinetic of the decomposition of the wood is faster and occurs at lower temperature in the pres-ence of HPW.

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3.2.Thermolysis of the wood and of the wood/HPW under hydrogen

Determination of the formed products after the decomposition of pine wood in the presence of HPW is of high interest.Therefore,during the thermal treatment of each sample(wood/HPW(90/10) and wood)at a selected temperature(200,250,275and300 gas phase,the liquids and the solid residue have been isolated, quanti?ed and characterized by elemental analyses,GC,GC–MS, solid state and solution NMR https://www.360docs.net/doc/b413983943.html,stly,the possibility recover the HPW is essential in order to make the system more sustainable.For this,the HPW structure has been determined different steps of the treatment and its recovering has been realized.

3.2.1.In situ monitoring by DRIFT-GC–MS coupled system

The samples wood and wood/HPW have been treated,in three independent experiments,at200,250,and300°C in the high tem-perature IR cell.The volatiles produced were analyzed by online GC–MS,Fig.S.5.In the absence of HPW,no products were detect-able at300°C or below.With wood/HPW,furfural was observed 200°C and,at250°C,other compounds including acetic acid and methanol were also detected,mainly originated from decomposition of holocellulose part of the lignocellulosic biomass already described(Larabi et al.,2013;Tian et al.,2010).It is ported as well that the acid hydrolysis of cellulose leads to the mation of glucose(de Vasconcelos et al.,2013;Ni et al.,2013;Tian et al.,2010),further degradation affords furfural derivates(Hu et al.,2013;Li et al.,2012).

To allow the identi?cation of the chemicals obtained during the thermolysis,250mg of wood/HPW were treated in the same experimental conditions.The volatiles analyzed by GC–MS

Fig.1.Thermogravimetric analyses of pine wood from40°C to700°C with heating rate of5°C minà1under argon.(a)In the presence of different solid catalyst(Al2O SiO2,SiO2–Al2O3,ZSM-5);(b)in the presence of different HPA(H3PW12O

PMo12O40,H4SiW12O40,H4SiMo12O40,H4PVMo11O40,H5PV2Mo10-O40),(c)in the presence of different loading of HPW(H3PW12O40)2wt.%,10wt.%,20wt.%,30wt.%, 40wt.%and50wt.%.

2.The amount of the CO(a)and CO2(b)produced during the thermal treatment of the biomass black and biomass in the presence of10wt.%of HPW gray.

(Fig.S.6)con?rms that only the holocellulose moieties have been transformed.

3.2.2.Scale up wood thermolysis in a continuous ?ow and batch reactors

The quanti?cation of the different fractions was reproduced higher quantities in a continuous ?ow reactor.The thermolysis wood and wood/HPW samples,at 200,250,275and 300°C under 1bar of hydrogen were run in a batch stainless autoclave reactor.For each experiment,three fractions (gas,liquid and solid)have been obtained and analyzed by GC,GC–MS,FTIR,elemental analy-ses and solid state NMR.Their proportions (wt.%)are mainly dependent on the reaction temperature.

Gas phase:With both samples the gas phase contained alkanes and mainly CO 2and CO.With the pure wood,the light alkanes were identi?ed and quanti?ed by GC.The methane was the major component followed by ethane and traces of other light alkanes (C n (n =1–5)%1wt.%of the initial mass),(Fig.S.7).With wood/HPW sample,the amount of the same light alkanes reaches about 2wt.%of the initial wood mass (Fig.S.7).

The evolution of the quantities of CO and of CO 2with the tem-perature has been followed by FTIR,(Fig.istic stretching bands.Their integration the calibration curves reported in Fig.evolved CO 2and CO at different Fig.2.The amount s of CO and CO 2as already observed by Sagehashi et al.Japanese cedar from 150°C to 400°C (presence of HPW,the amounts of CO and up to 260°C are higher compared to above 270°C,it is lower,suggesting that oxygenated volatiles than CO and CO 2.wood/HPW produced 45mg of CO and wood while the wood affords 70mg of the presence of HPW,the quantity of light alkanes is doubled (Fig.S.7).The amount of CO and CO 2is higher for temperatures lower than 260°C indicating that the reaction takes place faster due to presence of HPW.The tendency is inversed for temperatures higher than 260°C,suggesting that the presence of HPW leads to the formation of other oxygenated chemical including furan derivatives.

Liquid phase:The liquid phase collected for each experiment run at 200,250,275and 300°C for both samples was weighed and ana-lyzed by GC–MS.The weights of the liquid phase obtained for each experiment are represented in Fig.3.The formation of liquids oc-curred at 275°C for the wood and at 200°C for the sample wood/HPW.Its amount increases with the temperature.It is ob-served as well that the yield of the liquids for each temperature was superior in the presence of HPW.

In the liquid phase,furfural has been observed.Its amount,still higher in the presence of HPW,increases with temperature and reaches a peak at 275°C (%30%of the liquid phase,i.e.2%of the ini-tial wood mass),Fig.4.As already reported,the formation of furfu-ral from the holocelluloses is favored by acid catalyst (Deng et al.,2012).It is believed that the furfural is mainly obtained from the decomposition of hemicelluloses (Sahu and Dhepe,2012).The amount of the hemicelluloses in the pine wood is ca.15wt.%as determined by Van Soest method (Vansoest et al.,1991),which also limits the maximum yield of furfural.The observed amount of furfural is decreasing with temperature due to the polymeriza-tion of the furfural favored at higher temperature (Guerbuez et al.,2013).

Solid residue:The solid residues collected at the end of the ther-mal treatments were weighed (Fig.3)and characterized by ele-mental analysis,13C and 31P solid state NMR.The amount of the Fig.5.13C CPMAS solid state NMR of the solid residue recovered after thermolysis 200,250,275,300°C;(A)without HPA,(B)in the presence of 10wt.%of HPW.

4.Evolution of the furfural amount produced during the thermal treatment samples wood (black)and wood/HPW (gray).

3.Evolution with the temperature of the weight (in %from isolated liquid,gas and solid phases during the thermal samples wood (a)and wood/HPW (90/10)(b).

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slightly affected at275°C and decrease sharply at300°C.At this temperature,three broad signals,between10and60ppm(satu-rated carbon bonds,O–C@CH–carbons composing the furanic ring),100–165ppm(C@C carbon of aromatic rings)and 200–220ppm(attributed to carbonyl functionalities)are observed. Additionally,the intensity of the peaks at55and147ppm assigned to O–CH3and C@C of aromatic rings of lignin increase indicating a higher relative amount of lignin in the sample since the holocellu-loses have been converted into liquids.The evolution the spectra of the wood/HPW samples are similar except that as early as 200°C the holocelluloses are affected as evidenced by the decrease in the intensity of the peaks at64and74ppm,and that at300°C,the amount of the holocellulose present in the residue is lower(Bardet et al.,1997,2002,2004).

During the thermal treatment of wood/HPW(90/10)samples at different temperature,the31P solid state NMR were performed on the residue.All spectra presente a well resolved peak atà15.5ppm characteristic H3PW12O40(Fig.S.9),suggesting that the HPW struc-ture is preserved after thermolysis even at300°C.

After extraction of the residue by water the31P solid state NMR (Fig.S.10)the intensity of the peak atà15.5ppm has drastically decreased and c.a.60%of the initial amount H3PW12O40is recov-ered and reused.

This observation is supported by the comparison of the results of elemental analyses of all solids residues,Fig.S.11.Elemental analyses have been obtained after Soxhlet extraction of the HPW with water.The carbon content in the residue of the wood varies from49.71wt.%at150°C to53.72wt.%at300°C i.e.an increase of4%with a concomitant decrease of3.5%of the oxygen content. For the wood/HPW(90/10)sample,after HPW extraction,the car-bon content in the residue varies from49.57wt.%at150°C to 58.05wt.%at300°C i.e.an increase of8.48%with a concomitant decrease of6.8wt.%of the oxygen content.

4.Conclusion

This work shows that the decomposition temperature of pine wood impregnated with10wt.%Keggin-type heteropolyacid is lowered by100°C compare to pure wood or wood mixed with so-lid acids.At300°C,a catalytic amount of H3PW12O40transforms more than50%of the holocellulose into solid,liquid and gas phases which have been characterized by various techniques including elemental analysis,FTIR,GC–MS and NMR.The yield of liquid is higher in the presence of H3PW12O40(30wt.%,$2wt.%furfural versus17wt.%and trace of furfural for the wood).Finally,60%of H3PW12O40is recovered.

Appendix A.Supplementary data

Supplementary data associated with this article can be found,in the online version,at https://www.360docs.net/doc/b413983943.html,/10.1016/j.biortech.2013.

08.070.

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