Study On Cellulose And Biomass Conversion Based On DMSO-assisted Ionic Liquid Pretreatment

In this thesis,biomass and its components,cellulose,hemicellulose and lignin,were investigated.The pretreatment,saccharification and fermentation of biomass based on ionic liquids,and the potential application of lignin were studied.In the first part,the effects of dimethyl sulfoxide(DMSO)as a co-solvent on the pretreatment of several biomasses by ionic liquids were studied.The purpose was to find an economically viable pretreatment method for mixed solvents that could replace the pure ionic liquid pretreatment.In this study,we fixed the mass ratio of biomass or cellulose to ionic liquid while adding a series of different proportions of DMSO(0-100 wt.%)for biomass pretreatment.The pretreatment effect was evaluated by component analysis,XRD detection and enzymatic hydrolysis efficiency measurement.It was found that the samples pretreated with 58 wt.%DMSO and 42 wt.%1-ethyl-3-methylimidazolium acetate(EmimAc)had the highest sugar conversion rate,indicating a synergistic effect of pretreatment with DMSO and EmimAc on enzyme digestibility.This synergistic effect is because addition of an appropriate amount of DMSO reduced the viscosity of the ionic liquid,thereby improving the mass transfer and heat transfer of the system and improving the pretreatment efficiency.Another reason is that DMSO can dissolve part of lignin and hemicellulose,and it can increase the specific surface area of biomass.This enhances our understanding of the pretreatment of biomass with IL/organic solvent mixtures and facilitates the development of an effective biomass pretreatment process.The second part studied the preparation of isoprenol by fermentation from switchgrass pretreated by DMSO/EmimAc,and the recovery and reuse of pretreatment solvent.We studied the use of a 58 wt.%DMSO solution for pretreatment and the corresponding enzymatic hydrolysis.The hydrolysates were easily converted to isoprene using Separate Hydrolysis and Fermentation(SHF)or SHF in a one-pot configuration,reaching a titer of 1.23 and 0.72 g/L,respectively.A comparative study of dry and wet SG samples by SANS revealed disintegration of biomass particulates upon hydration which is enhanced by pretreatment with IL solutions.Pure DMSO causes minimal deconstruction of the biomass;however,it may enhance the interaction between IL and biomass by increasing the porosity of the biomass sample and possibly increasing cellulose solubility.The interaction between porosity and cellulose crystallinity determines the amount of total sugar released,where an increase in porosity does not always lead to an increase in the sugar conversion.The recycling and reuse of pretreatment fluids is a major challenge that has yet to be optimized.In this experiment,58 wt.%of DMSO solution was selected as pretreatment solvent.The experiments were conducted for switchgrass,poplar and pine at 130 °C for 3 hours(5 hours for poplar and pine),and the recycle was carried out four times.Finally effect of recycled pretreatment solvent on biomass samples was evaluated by the rate of saccharification.The results showed that with the increase of recycling times,the saccharification rate of switchgrass decreased.The recovery effect of switchgrass was the best,and it was the worst for pine.The results of this study provide a foundation for developing a potential economically viable IL based pretreatment technology.The third part studied the dissolution mechanism of lignin in DMSO and the feasibility of preparing nanoparticles.Lignin nanoparticle has been proposed as a method for high-value utilization of lignin.In order to fabricate lignin nanoparticles with controllable structure,we first investigated and summarized the lignin solution structure and the existing methods for preparing lignin nanoparticles.We used SANS,HQSC-NMR and 31P N-MR to study the dissolution of three lignin in DMSO and alkali solution.The intermolecular hydrogen bonds and ?-? interactions together determine the solubility of the elements.Lignin with less aliphatic hydroxyl groups is more easily dissolved,while softwood lignin is more difficult to dissolve than hardwood lignin in organic solvents such as DMSO;in alkaline solutions,aggregation is strongly influenced by the degree of ionization and S-containing wood is included.The interaction between the elements is stronger.These results will help guide the lignin conversion and value-added technologies.