Study On The Pretreatment Of Lignocellulose By Deep Eutectic Solvents

Lignocellulose is the most abundant renewable resource.For its inherently complex constitutes and structure,the first step of lignocellulose's transformation is the pretreatment.Ionic liquids(ILs)have been used as the solvents in the pretreatment of lignocellulose.They could increase the accessibility of polysaccharides by the effective deconstruction of the spatial structure of lignocellulose.However,the high price and toxicity of ionic liquids have largely restricted its industrial application.Deep eutectic solvents(DESs),also called ionic liquids alternative,is a kind of emerging green solvent with the similar physicochemical properties with ILs.Moreover,it has many advantages such as low price,easy to prepare,biodegradable and biocompatible,leading its wide applications in the fields of electrochemistry,biotransformation and nanotechnology.In this study,firstly three classes of deep eutectic solvents were synthesized just by simply heating and mixing the components,including monocarboxylic acid/ choline chloride,dicarboxylic acid/ choline chloride and alcohol/ choline chloride.Besides,the structures and constitutes of deep eutectic solvents were determined by the 1HNMR and FT-IR.The dissolving ability of lignin and cellulose in the deep eutectic solvents was studied.The results showed that the lignin could be dissolved well in the deep eutectic solvents,yet cellulose was scarcely soluble.Besides,the effects of deep eutectic solvents on the treatment of lignin and cellulose were investigated.The results of SEM,FT-IR,TGA and XRD indicated that the deep eutectic solvents broke the intramolecular hydrogen bond in cellulose to some extent,reduced the degree of crystallinity and roughened the surface of cellulose in the process of treatment.On the other hand,the framework structure of lignin has not altered,but its thermal stability was reduced.Lastly,these three classes of deep eutectic solvents were used to pretreat the corncob.The effects on extracting lignin in the corncob and enhancing the efficiency of enzymatic hydrolysis were systematically discussed.In addition,the pretreatment mechanisms were investigated by combining the SEM,FT-IR and XRD results.They showed that increasing the amount of acid in the deep eutectic solvents is beneficial to extract the lignin in the corncob and raise the prime saccharification rate.Compared to carboxylic acid/ choline chloride,alcohol/ choline chloride had an exceptional ability to extract the lignin in the corncob and recover the treated lignocellulose.Besides,they had relatively high glucose yields.In conclusion,alcohol/ choline chloride turned to be an eminent solvent to pretreat the lignocellulose.These could be ascribed to the theory that the deep eutectic solvents broke the intramolecular hydrogen bond in cellulose to some extent,cut off the ester bond between lignin and carbohydrates,or remove acetyl groups to extract the lignin partly.At the same time,the effects of pretreatment temperature and pretreatment time were investigated and the optimum pretreatment condition was 90 ?,24 h.