Enhancing cellulose saccharification with alcohols-assisted acidic deep eutectic solvents
Lignocellulosic biomass is one of the most abundant and renewable resources in nature,being considered as an ideal source for the preparation of petroleum-based chemicals and materials.The main components of lignocellulosic biomass are cellulose,hemicellulose and lignin,in which hemicellulose and lignin are covalently cross-linked with each other and interact with cellulose by hydrogen bonds and van der Waals forces.Recently,deep eutectic solvent(DES)has been considered as an ideal solvent for biomass pretreatment,due to its advantages of simple preparation,good biocompatibility and recyclability.The acidic DES system(ADES)can efficiently remove lignin and hemicellulose while retaining most of cellulose and has gradually become a hot spot in the research field of biomass fractionation.In this study,compared with untreated corn cobs and binary DES treated residues(choline chloride/p-toluene sulfonic acid and ChCl/p-TsOH),the agricultural waste corn cob was fractionated and saccharified efficiently using ethanol/ethylene glycol(EG)/1,4-butanediol(BDO)assisted acidic deep eutectic solvents(ChCl/p-TsOH).The effect of different temperatures of alcohols-assisted ADES pretreatment on the xylan/lignin removal and cellulose enzymatic hydrolysis was investigated by the X-ray diffraction(XRD),scanning electron microscope(SEM),Fourier transform infrared(FT-IR),and Brunauer-Emmett-Teller surface area(BET).The results demonstrated that the high removal of hemicellulose(＞90％)could be attained in all systems,up to 98.24％(EG).The lignin removal reached up to 94.53％in the ethanol-ADES system,as well as the maximum cellulose recovery in ethylene glycol(BDO)assisted ADES system(81.69％).The SEM images revealed that the quantities of curled,folded and porous structures emerged in pretreated residues,with a significant increase in fragmentation and specific surface area as the temperature rose.The relative crystallinity of pretreated residues was promoted,with natural Type-I cellulose crystalline structure using XRD.The FT-IR spectra verified that the intensity of related signals decreased with hemicellulose/lignin removal.The BET examination results showed that,compared with the untreated material(0.004 557 cm3/g and 1.12 m2/g),the pore volume and specific surface area of the pretreated material increased(up to 0.008 346 cm3/g and 2.94 m2/g).The specific surface area was strongly correlated with the hydrolysis efficiency of cellulose,and the coefficient of determination R2 reached 0.99,which was consistent with SEM results.The near complete enzymatic hydrolysis of cellulose(99.40％)was achieved in the EG-ADES system.In conclusion,the effective fractionation of corn cob and near-complete enzymatic hydrolysis could be achieved using alcohol-assisted ADES systems under mild condition,indicating its potential in the development of agricultural waste valorization processes.
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