Enhancement Of The Production Of Light Aromatics From Biomass By Combined Approaches Of Wet Torrefaction Pretreatment And Catalytic Fast Pyrolysis

Light aromatics,mainly composed of xylene,toluene,and benzene,is extremely important building blocks to produce various industrial products,such as synthetic resin,plastics,solvents,and pharmaceuticals.Nowadays,light aromatics are usually produced by catalytic reforming of non-renewable petroleum fractions.However,with the rapid depletion of fossil fuels,the development of new technologies using renewable feedstocks is essential to establish a sustainable supply of light aromatics.Lignocellulosic biomass is considered to be the most promising alternative feedstock to fossil fuels due to its renewability,low environmental impact and abundance.In addition,catalytic fast pyrolysis of biomass(CFP)is a promising technology for the production of light aromatics.However,the yield of light aromatics derived from catalytic pyrolysis of biomass is often limited by the shortcomings of high oxygen content and ash content of biomass.High oxygen content in biomass(35-45%)leads to low effective hydrogen-carbon ratio(H/Ceff).Bio-oil produced by fast pyrolysis of biomass consists of high concentration of oxygen compounds and low content of valuable aromatics.The wet torrefaction pretreatment of biomass can realize synchronous deoxidation and demineralization of biomass,so as to improve the quality of biomass s and further improve the yield of aromatics.(1)Light aromatics are important organic building blocks in the chemical industry which can be produced by catalytic fast pyrolysis(CFP)of biomass.In this work,wet torrefaction pretreatment(WTP)was employed to improve the quality of bamboo by synergistic effect of deoxygenation and demineralization.Then,CFP was employed to produce bio-aromatics by using zeolite(e.g.HZSM-5,HY,Al-MCM-41,and USY)as catalyst.Results showed that WTP temperature(180–260℃)had more significant influence on the mass yields of torrefied products compared to WTP duration(30–150 min).The maximum deoxygenation rate was 49.36%at WTP conditions of 260℃and 150 min,and the maximum demineralization rate followed the order of 96.29%(K)>94.54%(Na)>90.33%(Mg)>89.22%(Ca).Among the five types of zeolite catalyst tested,HZSM-5(25)was the best catalyst to obtain bio-aromatics due to its unique pore size and reasonable acidity.The maximum yield of aromatics(25.46×10~7 a.u./mg)was obtained at the WTP temperature of 220℃,biomass-to-catalyst ratio of 3:1,and CFP temperature of 850℃.Toluene was the more favored monocyclic aromatic hydrocarbon formed during CFP compared to xylene and benzene.(2)Wet torrefaction pretreatment(WTP)can upgrade the property of biomass by synergistic effect of deoxygenation and deminerization(e.g.K,Ca,Na,Mg).In this work,valorisation of cotton stalk(CS)was performed by using combined approaches of WTP and catalytic fast pyrolysis(CFP)to produce bio-aromatics.First,the maximum deoxygenation and deminerization rates were 53.84%and over 90%,respectively,at the WTP temperature of 260℃.Second,the bifunctional catalyst of Ga modified hierarchical HZSM-5 with micro-mesopore structure allowed more oxygenates diffusing into the channel of catalyst and increased the reaction rates of deoxygenation and aromatization reactions which highly improved the yield of bio-aromatics.Third,higher CFP temperature was favored for the formation of aromatics.The yield of aromatics increased first with the raise of catalyst-to-biomass(C/B)ratio from 1:1 to 1:3,then decreased slightly at the highest C/B of 1:5.At last,the operation parameter of WTP and SS-CFP was optimized which the maximum yield of light aromatics was 1.08×10~8 a.u./mg at WTP temperature of 220℃,biomass-to-catalyst ratio of 3:1,and CFP temperature of 850℃.(3)Light aromatics are extremely important building blocks in the chemical industry which can be produced from the catalytic fast pyrolysis(CFP)of biomass.In this work,wet torrefaction pretreatment(WTP)was employed to improve the quality of poplar wood(PW)in terms of the synergetic deoxygenation and demineralization.Then,metal-modified hierarchical HZSM-5 was prepared by the combined approach of Na OH desilication pretreatment and metal(Zn、Ga,and Fe)modification.At last,the CFPof torrefied PW was carried out by using the metal-modified hierarchical HZSM-5 as catalyst toproduce light aromatics.Results showed that the deoxygenation and demineralization rates gradually increased with the increase of WTP temperature from 180 to 260℃,the maximum removal rates of oxygen,K,Mg,Ca,and Na were 47.96%,90.99%,86.65%,66.09%,and 36.29%,respectively.Na OH desilication pretreatment and metal modification on HZSM-5 promoted the formation of light aromatics.The Zn-modified hierarchical HZSM-5 presented the highest yield of light aromatics.The yield of aromatics increased first with the raise of catalyst-to-torrefied PW ratio from 1:1 to 1:3,then decreased slightly at the highest catalyst-to-torrefied PW ratio of 1:5.At last,the operation parameter of WTP and CFP was optimized which the maximum yield of light aromatics was 7.83×10~7a.u./mg at WTP temperature of 220℃,catalyst-to-biomass ratio of 1:3,and CFP temperature of 850℃.