Study On The Separation And Conversion Of Lignocellulose And Ionic Liquid Recovery

With the growing energy demand and depletion of fossil fuels,biomass resources have gradually gained attention worldwide for their diversity and environmentally friendly features.Biomass resources utilization with the novelly green solvent-ionic liquids has become a hot spot in the field of high-value conversion of biomass.The outstanding characteristics and diverse types of ionic liquids make them effective solvents or media for research involved with high-value biomass conversion,including the dissolution and separation of biomass components and production of biomass fuels,chemicals,and materials.The high cost of ionic liquids and carcity of recycling techniques are major factors currently restricting the application of ionic liquids in biomass utilization and other industrial processes.To solve these problems,this study focused on the application and conversion of ionic liquids in the separation and conversion of lignocellulose,which is widely used as biomass resource.Industrialized and mature membrane treatment was adopted to recover ionic liquids.The effective recovery of ionic liquids was combined with the separation and conversion of biomass components to make the recovery process more suitable for practical industrial processes.Besides,the precipitation mechanism for the separation process of biomass components after ionic liquid-assisted dissolution was also studied.Furthermore,complete chemical conversion path was also explored with the cellulose fraction and the degradation products of hemicellulose obtained by the pretreatment.Firstly,methanol,dichloromethane,water and isopropanol were screened out from a series of potential low-boiling point precipitants to precipitate the dissolved lignin in the ionic liquid AmimCl solvent system.Kamlet-Taft parameters,polar empirical parameters and Hildebrand solubility parameters were used to analyze the separation behavior of potential precipitants during lignin fractionation process.The measurement results and analysis showed that functional groups of lignin samples isolated by different precipitants were basically the same and the molecular weight distribution range was approximate.The precipitated lignin displayed low-molecular weight,concentrated distribution,and significantly low-polydispersity(1.12-1.13),which could be the potential raw material for the production of high-value chemicals and fuels.Electrodialysis treatment was used to directly recover ionic liquid AmimCl after biomass pretreatment.The stability of electrodialysis treatment in AmimCl recovery process was verified by the differentiated pretreatment process with different AmimCl-alcohol-water systems.Characterization of recovered AmimCl sample showed that chemical structure of AmimCl was not destroyed after pretreatment and following recovery process.With intermittent recovery treatment,66%-71% of the ionic liquid in feed solution can get recovered and the energy consumption of AmimCl recovery process varied in the range of 429-467 g/kw?h,while semi-continuous recovery treatment would result in a much higher recovery ratio of 93% and the recovery energy consumption of 482 g/kw?h.Cost analysis showed that the recovery cost of AmimCl is less than 2.5% of its selling price.Based on the fractionation of biomass components,electrodialysis combined with ultrafiltration treatment was used to recover the ionic liquid BmimBr after pretreatment.Ultrafiltration treatment is used to remove residual lignin in the ionic liquid solution after pretreatment and reduce the interference for following electrodialysis-assisted recovery.Single-factor experiments were performed to determine the influence of molecular weight cut-off in ultrafiltration,BmimBr concentration in the feed solution of electrodialysis,voltage of electrodialysis membrane stack and flow rate in each zone in electrodialysis device on ionic liquid recovery with intermittent recovery treatment.The highest recovery ratio of BmimBr reached 75.2%,the highest current efficiency was close to 80% and the minimum recovery energy consumption was about 514 g/kw?h.The characterization results of the recovered BmimBr samples indicated that the stability of BmimBr chemical structure was not destroyed during the pretreatment and following recovery process.The cost of BmimBr recovery by the hybrid treatment of electrodialysis with ultrafiltration was less than 3% of its selling price,which is lower than the cost of BmimBr recovery using electrodialysis alone.The hybrid method of electrodialysis with ultrafiltration treatment was further applied for the recovery of choline-polyol type deep eutectic solvent(choline chloride-ethylene glycol).Two-step fractionation of eucalyptus wood was performed using hydrothermal and DES treatment.Ultrafiltration treatment can effectively filtrate DES solution obtained by the pretreatment.During electrodialysis treatment,the retention of ethylene glycol molecules and migration of chloride ions and choline ions by the ion exchange membrane enabled the separation of the two constituents of DES,which laid the foundation for the recovery of DES.The recovery ratios of choline chloride and ethylene glycol were up to 92% and 96% with the highest purity reached 98% and 99%.The purity of choline was closed by the two kinds of recovery treatment.The recovery ratio of choline chloride by semi-continuous treatment was higher than that of intermittent treatment by 7% to 8%.The recovery ratio and purity of ethylene glycol by semi-continuous treatment was slightly lower than that of intermittent treatment.The reconstituted DES after recovery can be used for subsequent pretreatment and its pretreatment efficiency is a little worse than that of the original DES but significantly better than that of the recovered DES without using the hybrid recovery treatment.Finally,a series of biomass-based carbon solid acid catalysts were prepared based on the separation of eucalyptus wood components with the hydrolysate obtained by hydrothermal treatment.The catalysts were used with BmimCl-methanol system to catalyze the conversion process of the fractionated cellulose component.When using methyl levulinate as the target product,optimal catalyst was screened out combining the conversion efficiency with the characterization of surface morphology of catalyst.Considering the energy consumption and other aspects,the optimized condition was determined as follows: deionized water content in the solvent is 3%,the amount of ionic liquid is 20 times the mass of cellulose,the amount of catalyst is 20%,reaction time is 75 minutes and the reaction temperature is 220?.Under the optimized condition,the cellulose conversion rate reached 100% and methyl levulinate yield was 38.7%.Besides,the catalytic effect of the recovered catalyst and ionic liquid is similar to that of first operation.Cellulose conversion ratio can be maintained at 100% while the yield of methyl levulinate was above 33% during the repeated experiments.