Synthesis of Cum ene from Lignin by Catalytic Transform ation

Feng JinM ing-hui FnQi-fng JiQun-xin Li

a.Department ofChem ical Physics,Key Laboratory ofUrban Polxlutant Conversion,Chinese Academy of Sciences,Anhui Key Laboratory of Biomass Clean Energy,University of Science and Technology of China,Hefei230026,China

b.Anhui Key Laboratory of Tobacco Chem istry,China Tobacco Anhui Industrial.Co.,LTD,Hefei 230088,China

Synthesis of Cum ene from Lignin by Catalytic Transform ation

Feng Jina,M ing-hui Fanb,Qi-fang Jiaa,Quan-xin Lia?

a.Department ofChem ical Physics,Key Laboratory ofUrban Polxlutant Conversion,Chinese Academy of Sciences,Anhui Key Laboratory of Biomass Clean Energy,University of Science and Technology of China,Hefei230026,China

b.Anhui Key Laboratory of Tobacco Chem istry,China Tobacco Anhui Industrial.Co.,LTD,Hefei 230088,China

Cumene is an im portant intermediate and chem ical in chem ical industry.In this work, directional preparation of cumene using lignin was achieved by a three-step cascade process. The m ixture arom atics were fi rst produced by the catalytic pyrolysis of lignin at 450?C over 1%Zn/HZSM-5 catalyst,monocyclic arom atics w ith the selectivity of 85.7 w t%were obtained.Then,the catalytic dealkylation ofheavier aromatics resulted in benzene-rich aromatics w ith 93.6 w t%benzene at 600?C over Hβcatalyst.Finally,the cumene synthesis was performed by the arom atic alkylation,giving cum ene selectivity of 91.6 C-m ol%using the[bm im]Cl-2A lCl3ionic liquid at room tem perature for 15 m in.Besides,adding a sm all amount ofmethanol to the feed can effi ciently suppress the coke yield and enhance the aromatics yield.The proposed transformation potentially providesa useful route for production of cumene using renewable lignin.

Lignin,Cumene,Catalytic pyrolysis,Dealkylation,A lkylation

I.INTRODUCTION

Over the past decade,the development of alternative bio-fuels or bio-chem icals from renewable biomass has stimulated significant interest,main ly because of its potential environm ental benefi ts and the continual decrease in fossil sources[1–3].Lignin,a natural polymer consisting of phenylpropane type unitsbonded through several diff erent C?O and C?C linkages,is a main constituent of lignocellulosic biomass.Considering its aromatic structure characteristics,lignin can be used potentially as a p lentiful and renewable starting m aterial for the production of green aromatics[1–6]. So far,there has been considerable work involved in the lignin chem istry aswell as its utilization by means of lignin hydrogenation reduction,oxidation,pyrolysis, catalytic pyrolysis,aqueous phase reform ing,or enzymatic conversion[2,7–10].Catalytic pyrolysis of lignin over zeolites,for instance,hasbeen w idely investigated, m ainly producing a variety of the m ixture arom atics such as benzene,alkylbenzenes,naphthalenes and indenes[5,7,10–13].Another typical conversion route for lignin use is the hydrogenation of lignin,which involves lignin depolymerization followed by the rem oval of the functionality of the lignin subunits to form simp ler monomeric com pounds.The products,depending on catalysts and reaction conditions,generally con-tain a w ide range of compounds such as phenols,aromatics,alkanes,and low oligom ers[8,14–16].And the directional transform ation of lignin into the desired chem icals is still a challenging task.

Cumene is an im portant basic organic chem ical raw material that ism ainly used for the production of phenol and acetone,and more than 90%of the worldw ide phenol production is based on the cumene process[17–19].Besides,cum ene is also in demand for the manufacture of bisphenol-A,α-m ethylstyrene,cymene,the synthesis of perfume and the additive for high octane number of fueloiland so on[17].Currently,the capacity of cumene production throughout the world,which is only 9.5 m illion m t/yr by the end of 1998 and up to 550.0m t/yr in 2014,has increased significantly[20,21]. Traditionally,cumene is prepared by the isopropylation of benzene w ith propylene or isopropanol(namely the Friedel-Craft alkylation reactions)[21–23].For examp le,UOP’s Cumox process and Monsanto-Lummus cumene process are the two typical technique w idely used on industrial scale.Cum ox process is conducted in the m ixture reaction system of p ropylene w ith excess benzene using solid phosphoric acid catalyst,offering a high propylene conversion and high selectivity of cum ene[22].For the M onsanto-Lummus p rocess,dry benzene and propylene are reacted through the alkylation reaction under low benzene recycle ratio using the A lCl3-HCl catalyst,and this process p roduces the lowest cost[22].However,the traditional technique of the cumene productionmay suffer from someproblem ssuch as equipment corrosion and pollutant discharge due totheuseofstrong acid catalysts.A lternatively,theuseof zeolite catalystsoffersan environmentally friend ly route to produce cumene,which can achieve a high selectivity of the desired product through pore size and acidity control[17,24–27].The ZSM-5 catalyst is one of the most prom ising candidates for the selective conversion of benzene into cum ene.Other zeolites w ith diff erent structures and acidities have also been investigated in alkylation of benzene,such as beta,mordenite,TNU-9 and SSZ-33[27].The remaining challenges for the production of cum ene by the benzene alkylation using zeolite catalysts include im proving the selectivity and yield of the target product,especially enhancing the benzene conversion.

As far aswe know,there isno report regarding directional p roduction of cum ene from lignin.In this work, wedemonstrated that lignin wasdirectionally converted into cumene by a three-step process.This process included the catalytic pyrolysis of lignin into them ixture aromatics,followed by the dealkylation of arom atics to benzene-rich aromatics and the alkylation of benzenerich aromatics to cumene by room-tem perature liquid phase reactions using the ionic liquid catalysts.Potentially,the proposed cum ene synthesis route p rovides a usefulway for the production of the basic petrochemicalmaterial and of the high-value chem ical using the abundant natural arom atic resource of lignin.

II.EXPERIM ENTS

A.M aterials

The lignin was purchased from Lanxu Biotechnology Co.Ltd.(Hefei,China).It was a brown and sulfurfree lignin powder manufactured from wheat straw. And the lignin contained carbon of 63.18 w t%,hyd rogen of 5.72 w t%,oxygen of 29.45 w t%and nitrogen of 1.65 w t%,which was carried out by the elementalanalysisw ith an elemental analyzer(Vario EL-III,Elementar,Germ any).A ll analytical reagents used were purchased from Sinopharm Chem ical Reagent Com pany Ltd.(Shanghai,China).

B.Catalysts preparation and characterization

The zeolite catalysts including HZSM-5,Hβ,and Re/HY were supplied by Nankai University catalyst Co.,Ltd.(Tianjin,China).Prior to use,the zeolite catalystswere calcined at 550?C for 4 h at nitrogen atm osphere.The catalyst of1%Zn/HZSM-5wasprepared by the impregnation method.The HZSM-5 zeolitewas im pregnated in the corresponding zinc nitrate solution over night,followed by rotary-evaporation at 60?C,and drying at 110?C for 6 h.Finally,the dried sam p lewas calcined at 550?C for 5 h,and crushed to 40?60mesh. The[bm im]Cl-xA lCl3(x=1?2)(bm im refers to 1-butyl-3-methylim idazolium chloroalum inate)ionic liquid was prepared by the samemethod described in our previouswork[28].Briefl y,[bm im]Cl was fi rst prepared by the reactions of N-methylim idazolium w ith 1-chlorobutane at the tem perature of80?85?C for 24 h.Then them ixturewascooled to room tem perature,and theunreacted reactantswere removed using a rotary evaporator.The resulting im idazolium saltwaswashed using acetonitrile as solvent,and dried in a vacuum drying box to remove the residual solvent and water.Finally,the ionic liquid of[bm im]Cl-xA lCl3(x=1?2)was prepared by slow ly adding the dried alum inum chloride to the im idazolium salt w ith a given m olar ratio of 1.0?2.0 between A lCl3and[bm im]Cl and stirring overnight.The ionic liquid, once prepared,wasstored in a dry nitrogen atmosphere.

TABLE I M ain propertiesof the catalysts.Si/A l is the ratio of silicon to alum inum in the zeolites,SBETis Brunauer-Emm ett-Teller surface area in m2/g andVpis pore volume in cm3/g.The acid density was estimated by the Gaussian fi tting of NH3-TPD profi les.Total acidity is in μmol NH3/gcat.

The metallic element contents in the catalysts were determ ined by inductively coup led p lasm a and atom ic em ission spectroscopy(ICP/AES,Atomscan Advantage,Thermo Jarrell Ash Corporation,USA). The zeolite catalysts were also characterized by N2adsorp tion/desorption and amm onia tem peratureprogrammed desorption(NH3-TPD)analyses[29]. Typically,the N2adsorption/desorption isotherms of the catalysts were performed at 77 K using the M icrom eritics ASAP 2020 V 3.00 analyzer.The acidity of the catalystswasmeasured by NH3-TPD from 100?C to 800?C w ith a heating rate of 10?C/m in.M ain properties of the catalystswere summ arized in Table I. M oreover,acidity characterizations of the ionic liquid were carried out by infrared spectroscopy(Bruker Tensor 27FT-IR spectrometer)using pyridineas theprober molecule of Lew is and Bronsted acid at room tem perature.The sam p les were prepared by m ixing pyridine and the ionic liquid in a volume ratio of 5:1,and then smeared into liquid fi lms on KBr w indows.A ll spectra were acquired at a 1 cm?1resolution w ith a total of 16 scans.The1H NMR and27A lNMRmeasurementswere carried on a high-resolution liquid nuclearmagnetic resonance spectrometer(Bruker Avance 300 MHz).

C.Procedures for production of cumene using lignin

The lignin was directionally converted into cumene by a three-step process under atmospheric pressure,including the catalytic pyrolysis of lignin into them ixed aromatics(fi rst step),the dealkylation of the alkylaro-matic com pounds to benzene(second step),and the alkylation of the benzene-rich aromatics to cumene by the low-tem perature liquid phase reactions(third step).

In the fi rst step,the production of aromatics by the catalytic pyrolysis of lignin was performed in the continuous flow pyrolysis reactor using the 1%Zn/HZSM-5 catalyst[30,31].The system wasm ainly com posed of a tube reactor,a feeder for solid reactants,two condensers and a gas analyzer.Before each run,the reactor was flushed w ith nitrogen(300 m L/m in)for 2 h,and was externally heated to a given tem perature by the carborundum heater.To reduce the coke deposition and the deactivation of the catalysts,co-feeding lignin w ith m ethanol was conducted in this step.Generally,the catalytic pyrolysis experim ents were carried out under the follow ing reaction conditions:400?550?C,N2gas flow rate of 200m L/m in,and themethanol content of 0?50w t%in the lignin/methanolm ixture.The organic liquid products(nam ed as catalytic pyrolysis oil,CPO) were collected by two condensers,weighed and analyzed by a GC-MSmass spectrometer.

In the second step,the catalytic dealkylation of alkylaromatic com pounds(namely CPO)to benzene was conducted over the zeolite catalysts(HZSM-5,Hβ,and Re/HY).The dealkylation reactionswere run in a fixedbed reactor,sim ilar to the procedures described in the fi rst step.Typical reaction condition for the catalytic dealkylation process was as follows:temperature of 560?C,space velocity of 0.5 h?1,and the methanol content of 30 w t%in the CPO/methanolm ixture.The resulting organic liquid products(named as catalytic dealkylation aromatics,CDA)were collected by two condensers,weighed,and analyzed by a GC-MSm ass spectrometer.

In the third step,the alkylation of rich-benzene aromatics of CDA to cumene was conducted by the lowtem perature liquid phase reactions using the catalysts of ionic liquid,in which propylenewas used as an alkylating agent.The alkylation reactions were run in batch mode in a 20-m L reactor equipped w ith a gasin let,a reflux cooler,sam p ling exit and a m agnetic stirrer under the follow ing reaction conditions:mass ratio of CDA/catalyst of 4:1,propylene flow rate(f) of 30 m L/m in,tem perature of 20?80?C and time of 5?90m in.At the end of the reactions,the products on the upper layer were separated from the ionic liquid catalyst at the bottom of the flask by decantation, weighted and analyzed.

D.Products analysis and evaluation

The gas products obtained in each run were analyzed using a gas chrom atograph(GC-SP6890,Shandong Lunan Co.,Ltd.,China).The gas chromatograph equipped w ith two detectors:a TCD for analysis of H2, CO,CH4,and CO2separated on TDX-01 column and a FID for gas hydrocarbons separated on Porapak Q column.Themoles of the gas products were determ ined by the normalization method w ith standard gases.The com positions of the liquid products were analyzed by GC-MS(Thermo Trace GC/ISQ MS,USA;FID detector w ith a TR-5 capillary colum n).Them oles ofm ain organic liquid productswere determ ined by thenormalizationmethod w ith standard samp lesand a known concentration.The conversion,yield,selectivity and distribution of the products were calculated as described in our previouswork[30,31].

whereYi,Yj,Yk,Yl,andSiare overall weight yields, liquid products distribution,distribution of gas products,conversion,and selectivity of products.A ll the tests were repeated three tim es and the reported data are themean values of three trials.

III.RESULTS AND DISCUSSION

A.Transform ation of lignin into aromatics

To produce cumene from the lignin,fi rst of all,the transform ation of lignin into aromatics is required.This conversion was conducted through the catalytic depolymerization and deoxygenation of lignin over theselected 1%Zn/HZSM-5 catalyst.As shown in FIG.1(a),cofeeding lignin w ith methanol significantly decreased the formation of coke and tar,as a result,enhanced the yield of the resulting organic liquid products(namely CPO)as well as the gas products.For exam p le,the yield of cokeand tar derived from the catalytic pyrolysis of lignin was 40.2 w t%,and reduced to 27.2 w t%when co-feeding lignin and methanol w ith themass ratio of 1:1.Addingm ethanol into lignin also changed the aromatic distribution in the aromatics(FIG.1(b)).W ithout addingmethanol,the com position of CPO obtained from the lignin essentially consisted of 17.3 w t%benzene,27.9 w t%toluene,26.2 w t%xylenesand 15.5 w t% naphthalenes.For co-feeding lignin w ith m ethanol, however,the content of benzene was obviously decreased accom panied by the increase in contents of toluene and xylenes,indicating that part of benzene was converted into toluene and xylenes by themethylation process.Besides,adding methanol into the lignin also suppressed the form ation of polycyclic arom atics caused by the polym erization of arom atics.Considering that methanol itself also formed aromatics by thearomatization of methanol,as a result,the CPO distribution for co-feeding m ethanol w ith lignin was determ ined by the competitive reaction pathways,mainly including the catalytic pyrolysis of lignin,aromatization of methanol,methylation of arom atics and polym erization ofaromatics[13,32,33].In addition,adding methanol increased the gas products of H2,alkenesand alkanes,along w ith the decline of carbon oxides and m ethane.So m ethanol also influenced the distribution of gas.

FIG.1 The eff ect of co-feeding methanol(M eOH)on the production of aromatics by the catalytic pyrolysis of lignin(LN) over 1%Zn/HZSM-5.Reaction conditions:the weight ratio of catalyst to lignin of 2 at 450?C.CPO:catalytic pyrolysis oil. (a)Yield,(b)distribution of CPO,(c)distribution of gas.

FIG.2 Eff ect of tem perature on the p roduction of arom atics by the catalytic pyrolysis of lignin/m ethanol m ixture over 1%Zn/HZSM-5.Reaction conditions:the weight ratio of catalyst to lignin=2,lignin/methanol=1:1,T=400?550?C.(a) Y ield,(b)distribution of CPO,(c)distribution of gas.

FIG.2 shows the eff ect of tem perature on the production of aromatics by the catalytic pyrolysis of lignin/methanolm ixture over 1%Zn/HZSM-5 catalyst. Increasing the reaction tem peratures resulted in the decrease in the yields of CPO and coke/tar,accom panied by the increase in the gas yield(FIG.2(a)).This indicates that high tem peratures enhance the catalytic depolym erization and gasification of lignin,and reduce the polymerization ofaromatics.For the distribution of organic liquid products(FIG.2(b)),the CPO consisted primarily of C6?C8m onocyclic aromatics and a small amount of polycyclic aromatics.For exam p le,the typicalCPO obtained at450?C contained 8.4w t%benzene, 30.2 w t%toluene and 47.1 w t%xylenes.Thesem ixed aromaticsm ainly originated from the C?C and C?O bonds cleavage of lignin together w ith the decarboxylation,decarbonylation,dehydration,aromatization and polym erization over the zeolite catalyst[34–36].Notably,the form ation of benzene and toluene increased w ith increasing tem perature along w ith a decrease in the heavier aromatics(like xylenes and other C8+aromatics),attributed to the rem oval of the alkyl groups in the heavier arom atics at higher tem peratures.In addition,oxygen in the lignin was removed mainly by the decarbonylation,decarboxylation,and dehydration, considering that CO,CO2and H2O were the dom inant oxygen-containing products observed.Gaseous olefins and alkanes that come from the catalytic pyrolysisof the lignin/methanolm ixture exhibited a descending trend w ith increasing the tem perature(FIG.2(c)),because of the enhanced decom position and/or aromatization of light olefinsand alkanesat higher tem peratures[34–36].

B.Reform ing of arom aticsm ixture into benzene

FIG.3 Transform ation of CPO into benzene over the diff erent catalysts.Reaction conditions:T=560?C, CPO:M eOH=0.7:0.3.CPO was obtained by the catalytic pyrolysis of lignin atT=450?C,lignin/m ethanol=1:1,and the weight ratio of catalyst to lignin=2.CDA:catalytic dealky lation aromatics.(a)Yield,(b)distribution of CDA,(c) distribution of gas.

FIG.4 Infl uence of methanol on the production of benzene by the catalytic dealkylation of CPO over Hβ.Reaction conditions:T=560?C.CPO was the sam e sam p le as described in FIG.3.(a)Y ield,(b)distribution of CDA;(c)distribution of gas.

Since CPO derived from the direct catalytic pyrolysis of lignin was comp lex aromatic com pounds,the transformation of these aromatics into the key intermediate of benzene was further conducted by the catalytic dealkylation process.As can be seen from FIG.3(a), w ithin the tested catalysts,the HZSM-5 catalyst produced m ore organic liquid products(CDA)along w ith lower yields of coke/tar and gas.The CDA,after the catalytic dealkylation reactions at 560?C over HZSM-5,consisted of 67.9 w t%benzene together w ith toluene (21.7 w t%),xylenes(8.6 w t%)and other heavier aromatics(1.8 w t%).The Re/HY catalyst that had a strong acidity(Table I),present the highest dealkylation effi ciency for the C6+arom atics,leading to the highest content of benzene(95.9 w t%)in the liquid products(FIG.3(b)).However,the catalytic dealkylation using this catalyst produced m ore coke/tar by the oligom erizationsof arom aticsand m ore gas productsby gasification of aromatics(FIG.3(a)and(c)).Another catalyst Hβw ith a medium acidity exhibited the high activity for the transform ation of them ixture arom atics into benzenew ith a high liquid yield(FIG.3(a)and (b)),which was selected in the catalytic dealkylation process.

FIG.4 shows the influence of m ethanol on the catalytic dealkylation ofalkylaromatic com poundsover the Hβcatalyst.Adding methanol into CPO was able to eff ectively inhibit the formation of coke/tar.For exam p le,the yield of coke/tar w ithout adding methanol was 32.8 w t%,but in the cases of 30 w t%and 50 w t% methanoladded,was significantly reduced to 21.2 w t% and 15.1 w t%respectively.W hat’s m ore,co-feeding methanol also apparently changed the arom atic distribution in the CDA.W hen 30 w t%methanol was co-fed w ith CPO,the content of benzene slightly decreased to 82.7 w t%along w ith the increase in the contents of toluene and xylenes.In view of thatmethanol also formed aromaticsby thearomatization ofmethanol (FIG.4(b)),the content of benzene in CDA should be aff ected by the dealkylation of arom atics,the oligomerizationsofaromaticsand thearomatization ofmethanol in the presence of methanol.Besides,the temperature also influenced the transform ation of alkylaromatic com pounds into benzene during the dealkylation of aromatics(FIG.5).Increasing the reaction temperature decreased the CDA yield mainly due to theincrease in the gas yield by the decom position of aromatics.Notably,the content of benzene increased from 41.8 w t%to 93.6 w t%w ith increasing the temperature from 520?C to 600?C(FIG.5(b)),accom panied by the decrease in toluene,xylenes and other C8+heavier aromatics.This suggested that high temperatures enhanced the removal of the alkyl groups in the alkylarom atic com pounds such as toluene and xylenes.In addition,the gas productsmainly consisted of H2,and CH4(FIG.5(c)),which come from the catalytic cracking of arom atics and methanol.

FIG.5 Eff ect of tem perature on the production of benzene by the catalytic dealkylation of CPO over Hβ.Reaction conditions:T=520?600?C,CPO:MeOH=0.7:0.3.CPO was the same sam p le described in FIG.3.(a)Yield,(b)distribution of CD,(c)distribution of gas.

FIG.6 Production of cumene by the alkylation of CDA over diff erent ionic liquid catalysts.Reaction conditions:mass ratio of CDA/catalyst=4:1,f(propylene)=30m L/m in,T=20?C,t=15m in.CDA contained 93.6 w t%benzene,5.1 w t%toluene, 0.5 w t%xylenes and other aromatics of 0.8 w t%.(a)Conversion,(b)selection,(c)distribution.

C.Synthesis of cum ene by the alkylation of lignin derived arom atics

In the follow ing step,we demonstrated that directional p roduction of cumene was able to be realized by the room-tem prature liquid-phase alkylation of the benzene-rich aromatics(CDA)using the ionic liquids.Three ionic liquid catalysts,[bm im]Cl-2A lCl3, [bm im]Cl-1.5A lCl3,[bm im]Cl-A lCl3,have been tested for thealkylation ofCDA to cumene via propyleneasan alkylating agent(FIG.6).The[bm im]Cl-2A lCl3ionic liquid,even at the room tem prature(20?C),showed excellent catalytic activity for the CDA alkylation w ith a propylene conversion of 97.3 m ol%(FIG.6(a)).Especially,the products obtained using[bm im]Cl-2A lCl3were dom inated by the desired cumene with a selectivity of 91.6 C-mol%(FIG.6(b)),together w ith small amount ofp,m,o-diisopropylbenzene(p,m,o-DIPB) andp,m,o-isopropyltoluene(p,m,o-cymene).

FIG.7 Influence of the reaction tim e on the production of cum ene by the alky lation of CDA using[bm im]C l-2A lC l3ionic liquid catalyst.Reaction conditions:mass ratio of CDA/catalyst=4:1,f(propylene)=30 m L/m in,T=20?C.CDA was the sam e sam p le as described in FIG.6.(a)Conversion,(b)selection,(c)distribution.

It was found that the m olar ratio between the 1-butyl-3-methylim idazolium chloride([bm im]Cl)and alum inum chloride(A lCl3)in the ionic liquids greatly aff ected the alkylation activity of CDA and the product selectivity.W hen the[bm im]Cl-A lCl3catalyst was used,for exam p le,the conversion of propylenewasonly 4.6 mol%(FIG.6(a))and the main products becamep,m,o-cym ene(FIG.6(b)),which was clearly diff erent from the behavior of the[bm im]Cl-2A lCl3ionic liquid. Chem ically,the[bm im]Cl-2A lCl3ionic liquid consists of the cations of 1,3-two alkyl substituted im idazolium together w ith the anions of A l2Cl7?,as dem onstrated by the27A l NMR analysis(FIG.S1 in the supp lementary materials)and1H NMR analysis(FIG.S2 in the supp lementary materials).In addition,the acidic characteristicsof the ionic liquid were also conducted by infrared spectroscopy using pyridine as a probemolecule of Lew is and Bronsted acid(FIG.S3 in the supp lem entary m aterials).The bands at 1454 and 1540 cm?1for pyridine/[bm im]Cl-2A lCl3ionic liquid were observed, corresponding to the characteristic peaks of Lew is acid (pyridinebonded at a Lew isacid site)and Bronsted acid (pyridine bonded at a Bronsted acid site),respectively (Table S1 in the supplementarymaterials).In addition, the increase in the molar ratio of A lCl3to[bm im]Cl obviously increased the Lew is acid of the ionic liquids (FIG.S4 in the supplementary materials).The above characterization results supported that the ionic liquid [bm im]Cl-2A lCl3had the properties of both Lew is acid and Bronsted acid.The ionic liquid could enhance the olefinic protonation and the formation of active electrophilic species(positive ions of olefins or carbenium ions),leading to the enhancem ent of the alkylation reactions of arom atics[37].

FIG.7 presents the influence of the reaction time on the alkylation of CDA at room temprature(20?C). As increasing reaction tim e from 5 m in to 90 m in,the propylene conversion slightly reduced from 97.6%to 86.4%.Notably,the selectivity and distribution of the productswere shifted towards the heavier arom atics by prolonging reaction tim e.The cumene selectivity decreased from 91.6C-mol%to 25.3C-mol%w ith increasing reaction time from 5 m in to 90 m in,accompanied w ith an increase ofp,m,o-DIPB from 2.2 C-m ol%to 59.3 C-m ol%.The alkylation of aromatics in CDA is a consecutive reaction process,and the primary products (like the benzene alkylation to cumene)can generally undergo the second alkylation reactions(like the alkylation of cumene top,m,o-DIPB).Asa result,increasing the reaction time enhanced the cascade reaction,leading to the rise in the by-products for longer reaction time.

Moreover,the influences of tem perature on the alkylation of CDA using the[bm im]Cl-2A lCl3ionic liquid was investigated(Table II).The conversions of propylenewere slightly increased w ith the increasing temperature in the range of 20?50?C,and then,showed a reduction trend over 50?C.Considering that the aromatic alkylation is an exotherm ic reaction[38],increasing temperature results in the decrease of equilibrium constants and is not beneficial to the aromatic alkylation.But increasing tem perature is conducive to overcom e the activation energy required to the alkylation reactions.Meanwhile,the collision probability between ionic liquid and reactants could be enhanced at higher tem peratures,leading to the increase in the reaction ratesof thearomatic alkylation.Accordingly,the directional products of cumene were able to be expediently tuned via the reaction tim e and/or the the tem prature during the alkylation of lignin derived aromatics using the[bm im]Cl-2A lCl3ionic liquid catalyst.

IV.CONCLUSION

Thiswork demonstrated that lignin can be directionally converted into cum ene by the catalytic pyrolysis of lignin into the m ixture arom atics,followed by the dealkylation of alkylaromatic com pounds to benzenerich aromatics and the alkylation of benzene-rich aromatics to cumene under the moderate reactions.The liquid products consisted primarily of C6?C8monocyclic aromatics and a small amount of polycyclic aromatics for the catalytic depolymerization and deoxygenation of lignin over the 1%Zn/HZSM-5 catalyst. Then,the key intermediate of benzene was produced w ith a high content of93.6w t%by dealkylation process at 600?C over the Hβcatalyst.The[bm im]Cl-2A lCl3ionic liquid,even at the room tem prature(20?C), showed excellent catalytic activity for the aromatic alkylation in the third step.The desired production of cum ene was obtained through the alkylation of the benzene-rich aromatics w ith a selectivity of 91.6 C-mol%at 20?C,and can be tunablevia the reaction timeand/or the the tem prature.Moreover,a small amount ofmethanol into the feed is benefi tial for suppressing the coke yield and enhancing the yield of aromatics. Potentially,the proposed cumene synthesis route providesa usefulway for the production of the basic petrochem icalmaterialusing the abundant naturalaromatic resource of lignin.

TABLE II Eff ect of tem perature on the production of cumeneby thealkylation of lignin-derived CDA using[bm im]Cl-2A lCl3ionic liquid catalysta.

Supp lem entary m aterials:The results of the ionic liquid characterization are shown.The[bm im]Cl-2A lCl3ionic liquid consists of the cations of 1,3-two alkyl substituted im idazolium together w ith the anions of A l2Cl7?,as demonstrated by the27A lNMR analysis w ith the peak around 103 ppm(see FIG.S1).Based on the com parison of1H NMR spectra before and after being titrated w ith KOH solution(FIG.S2),the absence of H in the star site after titrated w ith KOH solution suggests that the ionic liquid can provide protons from the ionic liquid.Furthermore,the acidic characteristics of the ionic liquid were conducted by infrared spectroscopy using pyridine as a probemolecule of Lew is and Bronsted acid.The bands at 1454 and 1540 cm?1for pyridine/[bm im]Cl-2A lCl3ionic liquid were observed(FIG.S3).These bandswere attributed to the characteristic peaks of Lew is acid(pyridine bonded at a Lew is acid site)and Br?nsted acid(pyridine bonded at a Br?nsted acid site)respectively(see Table S1 in the Supporting Information).W ith increasing the content of A lCl3in the ionic liquid,the peak intensity at 1454 cm?1increased(FIG.S4),indicating Br?nsted acid was enenhaned at higher content of A lCl3.In conclusion,the above observations supported that the ionic liquid had thepropertiesofboth Br?nsted acid and Lew is acid.

V.ACKNOW LEDGM ENTS

Thiswork was supported by the National Key Basic Program ofChina(No.2013CB228105),the Program for Changjiang Scholars and Innovative Research Team in University and the FundamentalResearch Funds for the Central Universities(No.wk2060190040).

[1]C.Xu,R.A.D.A rancon,J.Labidi,and R.Luque, Chem.Soc.Rev.43,7485(2014).

[2]Q.Yao,Z.Tang,J.H.Guo,Y.Zhang,and Q.X.Guo, Chin.J Chem.Phys.28,209(2015).

[3]L.Zhang,R.Liu,R.Y in,and Y.M ei,Renew.Sustain. Energy Rev.24,66(2013).

[4]Q.Y.Wu,L.L.M a,J.X.Long,R.Y.Shu,Q.Zhang, T.J.Wang,and Y.Xu,Chin.J.Chem.Phys.29,474 (2016).

[5]P.Huang and L.F.Yan,Chin.J.Chem.Phys.29,742 (2016).

[6]Y.Zhao,L.Deng,B.Liao,Y.Fu,and Q.X.Guo, Energy Fuels 24,5735(2010).

[7]J.Chen,C.Liu,and S.B.Wu,BioResources 11,663 (2015).

[8]W.W ei,S.W u,and S.Xu,J.Chem.Technol.Biotechnol.92,580(2017).

[9]L.P.Xiao,Z.J.Shi,F.Xu,and R.C.Sun,Bioresour. Technol.118,619(2012).

[10]L.Xu,Y.Zhang,and Y.Fu,Energy Technol.4,1 (2016).

[11]B.Zhang,Z.P Zhong,X.B.Wang,K.Ding,and Z.W. Song,Fuel Process Technol.138,430(2015).

[12]C.Li,X.Zhao,A.W ang,G.W.Huber,and T.Zhang, Chem.Rev.115,11559(2015).

[13]S.Adhikari,V.Srinivasan,and O.Fasina,Energy Fuels 28,4532(2014).

[14]S.Kang,X.Li,J.Fan,and J.Chang,Renew.Sus. Energy Rev.27,546(2013).

[15]W.Y.Xu,S.J.M iller,P.K.Agrawal,and C.W.Jones, Chem SusChem 5,667(2012).

[16]C.Rutten,A.Ram′?rez,and J.Posada Duque,J.Chem. Technol.Biotechnol.92,257(2016).

[17]Y.Zou,H.Jiang,Y.Liu,H.Gao,W.Xing,and R. Chen,Sep.Purif.Technol.170,49(2016).

[18]J.Zhai,Y.Liu,L.Li,Y.Zhu,W.Zhong,and L.Sun, Chem.Eng.Res.Des.102,138(2015).

[19]R.Navarro,S.Lopez-Pedrajas,D.Luna,J.M.Marinas, and F.M.Bautista,App l.Catal.A 474,272(2014).

[20]T.F.Degnan,C.M.Sm ith,and C.R.Venkat,App l. Catal.A 221,283(2001).

[21]M.P.Bailey,Chem.Eng.121,79(2014).

[22]V.V.Bokade and U.K.Kharu l,Chem.Eng.J.147, 97(2009).

[23]O.V.Shutkina,O.A.Ponomareva,and II.Ivanova, Catal.Ind.7,282(2015).

[24]H.R.Norouzi,M.A.Hasani,B.Haddadi-Sisakht,and N.M ostou fi,Chem.Eng.Commun.201,1270(2014).

[25]C.Perego and P.Ingallina,Catal.Today 73,3(2002).

[26]C.Dai,Z.Lei,J.Zhang,Y.Li,and B.Chen,Chem. Eng.Sci.100,342(2013).

[27]T.Odedairo and S.A l-Khattaf,Catal.Today 204,73 (2013).

[28]P.W.Jiang,X.P.Wu,L.J.Zhu,F.Jin,J.X.Liu, T.Y.X ia,T.J.Wang,and Q.X.Li,Energ.Convers. M anage.120,338(2016).

[29]F.Gong,Z.Yang,C.Hong,W.Huang,S.Ning,Z. Zhang,and Q.Li,Bioresour.Technol.102,9247(2011).

[30]M.H.Fan,S.M.Deng,T.J.Wang,and Q.X.Li,Chin. J.Chem i.Phys.27,221(2014).

[31]J.C.Wang,P.Y.Bi,Y.J.Zhang,H.Xue,P.W.Jiang, X.P.Wu,J.X.Liu,T.J.W ang,and Q.X.Li,Energy 86,488(2015).

[32]P.S.Rezaei,H.Shafaghat,and W.M.A.W.Daud, App l.Catal.A 469,490(2014).

[33]G.Q.Zhang,T.Bai,T.F.Chen,W.T.Fan,and X. Zhang,Ind.Eng.Chem.Res.53,14932(2014).

[34]G.Caeiro,R.H.Carvalho,X.W ang,M.A.N.D.A. Lemos,F.Lemos,M.Guisnet,and F.R.Ribeiro,J. M ol.Catal.A 255,131(2006).

[35]Y.Ono,Catal.Rev.34,179(1992).

[36]N.Rahim i and R.Karim zadeh,J.Anal.App l.Pyrolysiss 115,242(2015).

[37]Z.Zhao,W.Qiao,X.Wang,G.Wang,Z.Li,and L. Cheng,App l.Catal.A 290,133(2005).

[38]T.F.Degnan,C.M.Sm ith,and C.R.Venkat,App l. Catal.A 221,283(2001).

ceived on March 17,2017;Accepted on April 10,2017)

?Author to whom correspondence shou ld be addressed.E-m ail: liqx@ustc.edu.cn