Study On The Separation And Activation Mechanism Of Lignocellulose Components In Ionic Liquid

To solve the environmental problems caused by the excessive use of fossil fuels,and to alleviate the contradiction between the increasing shortage of fossil resources and the growing demand for energy due to economic growth,it is imperative to find new alternative energy sources for fossil resources.Biomass,as an abundant renewable resource with large storage and easy availability,has been widely studied as a biological platform chemical.However,biomass is difficult to process and use due to its rigid structure,so it is necessary to pretreatment biomass to destroy its special structure to enhance the reactivity and convert it into a wide range of biological platform compounds.Many pretreatment techniques based on previous studies have been used to destroy the structural rigidity of lignocellulose.But simultaneously,many difficulties and challenges are found pretreatment techniques,such as high cost,environmental hazards,low pretreatment efficiency,and difficulty in solvent recovery.Therefore,it is meaningful to develop new lignocellulose pretreatment technologies to face the environmental problems arising from the overuse of fossil fuels.In this paper,the pretreatment of corn stover with bio-based acid protic ionic liquid and enzymatic hydrolysis and saccharification was studied to achieve a high yield of sugars.It was also found that lignocellulose has the potential to determine lignin content after dissolving in ionic liquid.（1）Economically competitive and sustainable dissolution pretreatment technology is in high demand due to the remarkable achievement in the pretreatment of lignocellulose using ionic liquids（ILs）for enhanced enzymatic hydrolysis.Herein,levulinic acid（Lev）,a well-known bio-based platform chemical derived from carbohydrates,in conjunction with a series of organic superbases,was used as a raw chemical to prepare a new class of protic ILs（PILs）.The findings indicated that the obtained PILs exhibited a good solubility of up to 10 wt%toward corn stover-based lignocellulose at 140°C in 40 mins,based on which a facile and efficient dissolution pretreatment technology was developed for enhanced enzymatic hydrolysis of corn stover.The facile dissolution and regeneration of corn stover resulted in significant changes in the composition and physical-chemical structures.These changes led to significantly enhanced enzymatic hydrolysis behavior of the pretreated sample with total reducing sugar and glucose yields of 0.8 and 0.49 g/g within 48 h under optimal conditions,respectively.The Kamlet-Taft solvent parameters of the PILs were systematically evaluated,and the interaction between the lignocellulose and PILs was studied by ¹³C NMR,indicating that the satisfactory performance of PILs was benefited from the higherβparameter value and the stronger interactions,particularly the existence of the extra hydrogen-bond interaction from the potential keto-enol tautomerism of the ketone groups in levulinate anions.The compositional and physicochemical changes in the lignocellulose were systematically evaluated to achieve an in-depth understanding of the dissolution activation mechanism using various characterization techniques.The findings also showed that 44.3%of lignin could be fractionated during the facile dissolution and regeneration process,together with a transformation of the crystalline structure of cellulose I to cellulose II and of the packed morphology to a porous one.The structure of the fractionated lignin was also characterized for a better understanding of the fractionation process.The study demonstrated a new sustainable dissolution pretreatment technology for enhanced enzymatic hydrolysis,which can provide significant insights into the design of new solvents for biomass dissolution and processing.（2）The lignin quantification of biomass is crucial for both the transformation and utilization of lignocellulose.In this study,a simple and fast method was developed to quantify lignin in lignocellulosic biomass,a novel lignin test for direct measurement of lignin content using[Emim][OAc]ionic liquid to completely dissolve lignocellulosic biomass method（IL method）.The biomass samples were completely dissolved in the[Emim][OAc]ionic liquid within 60 minutes,resulting in a completely dissolved lignocellulose-IL solution.The lignin content in the solution can then be determined by UV spectrophotometry,and treated with different types of biomass in the same way to establish the applicability of this method（IL method）,including herbs（rice husks,corn stover and bamboo flour）,hardwoods（poplar）and softwoods（pine）,The results quantified using the IL method were compared with the lignin content tested using the Klason method,and a satisfactory correlation was observed.The IL method only needs a small amount of sample（10 mg）to achieve an accurate determination of lignin content;and has the characteristics of high efficiency,green reagents,and wide applicability.