Selective Components Fractionation Of Lignocellulose And Conversion By Carboxylic Acid-fuctionalized Ionic Liquids

Currently, the diminishing fossil resource together with the ongoing climate changehas led to an intensified search for renewable resources. Lignocellulose biomass is anabundant and renewable resource for the production of biofuels and valuable chemicals.Lignocellulose maintly composes by cellulose, hemicellulose and lignin. Cellulose andhemicellulose are potential sources of monomeric sugars, which can be used as carbonsource for the production of biofuels by fermentation and converted into chemicals bychemical transformation. However, lignocellulose has tough and complex threedimensional structure remarkably resistant against chemical and microbial attack.Therefore, pretreatment is regarded as a keypoint for utilization of lignocellulose.ILs are designable for a specific application by the variation of anions and cations.Herein, we synthesized a carboxylic acid functionalized ionic liquids (1-carboxymethyl-3-methylimidazolium chloride, IL-COOH) and used its aqueous solution to pretreat cornstraw. The effect of pretreatment time, pretreatment temperature and ionic liquidsconcentration on composition and enzymatic hydrolysis results of corn stover wasinverstigated. The pretreatment of corn straw by IL-COOH aqueous solution under mildconditions can remove hemicellulose selectively and enhance enzymatic hydrolysisefficiency of the residuals. For example, when the corn stover was pretreated with40wt%IL-COOH aqueous solution at120℃for4h, the content of cellulose and lignin inthe corn stover-based biomass increased from37.9%, and21.1%to55.6%and26.5%,respectively, and the content of hemicelluloses decreased from24.4%to9.34%; furtherenzymatic hydrolysis of the pretreated corn stover results in0.32g.g-1,0.45g.g-1ofglucose and total reducing sugars yields, respectively. IL-COOH was stable in thepretreatment process and can be recycled by recrystallization.In addition, we investigated the potentials in the fractionation of cellulose,hemicellulose and lignin from corn straw and spruce TMP (Themomechanical pulp) byintegrating the IL-COOH aqueous solution pretreatment process and extraction process ofNaOH aqueous solution. It was found that although the40wt%IL-COOH aqueoussolution pretreatment process at120℃for12h can significantly remove hemicellulosein these two materials, the following extraction of the pretreated materials by NaOHaqueous solution can not remove a large amount of lignin. Even prolonging pretreatmenttime to24h, there is no significant effect on composition fractionation of corn stover andspruce TMP.To achieve a facile recycling and reuse processing of IL-COOH after thepretreatment, we primary investigated the in situ conversion of xylose into furfural using IL-COOH as a catalyst. The effect of heating methods (microwave and oil bath),reaction temperature, reaction time and substrate concentration were studied. The resultsshowed that the yield of furfural was only14.1%under typical reaction conditions so far.Hence, the yield of furfural has space of very big promotion by addition of inorganicstrong acid as catalyst.