Cellulose Pretreatment With Ionic Liquid For Enzymatic Hydrolysis

The rapid consumption of fossil fuel resources has motivated research for the biofuels and biochemicals. Cellulose is the most abundant carbohydrate component of biomass, and it is of particular interest as a kind of renewable and sustainable material of providing monomeric sugars for fermentation into fuels and biochemicals. However, owing to the extensive network of inter- and intra- molecular hydrogen bonding between its fibrils, cellulose is difficult to dissolve in either water or most organic solvents. It is, thus, recalcitrant to hydrolyze into individual glucose subunits. Therefore, in this study, cellulose pretreated with ionic liquid for enzymatic hydrolysis.In this work, we used response surface methodology (RSM) for optimizing the synthesis process of N-methyl-N-methylimidazolium dimethylphosphate ([MMIM]DMP), three independent variables including reaction temperature, reaction time and the molar ration of trimethyl phosphate and N-methylimidazole were selected as impact factors. The experiments with three factors and three levels, which were designed according to Box-Benhnken with the yield of [MMIM]DMP as the response value, investigated by response surface methodology. Optimum process parameters were obtained by optimizing and verifying. The results were as follows: reaction temperature 100℃, reaction time 9h, the molar ration of trimethyl phosphate and N-methylimidazole 1.2:1, the yield of [MMIM] DMP was 99.58%.In the pretreatment process, the cellulose pretreatment process is indispensable for the [MMIM]DMP-treated cellulose TRS yield by hydrolysis is 96.4%, while the the yield is 46.8% without [MMIM]DMP pretreatment. FT-IR, X-ray diffraction and specific surface instrument determined that cellulose crystallinity decreased, cellulose crystalline transformation from cellulose I to cellulose II and cellulose specific surface increased after [MMIM]DMP pretreatment. Additionally, the crystallinity index (CI) was characterized by FT-IR spectroscopy. The CI values including CI(IR), CI(IR-CI) and CI(IR-CII) were calculated. When correlated with these values, the concentrations of TRS released after the pretreatment of microcrystalline cellulose (MC) were found to show a distinct relationship with the [CI(MC-CI)– CI(IR-CI)] values.RSM was used for studying on [MMIM]DMP-pretreated cellulose hydrolysis kinetics. Three independent variables including reaction temperature, the amount of cellulase and the concentration of substrate were selected as impact factors. The results were as follows: reaction time 8.17h, the amount of cellulase 0.05g, the concentration of substrate 20g/L for the maximum TRS yield 99.58%, and the reaction time 9h, the amount of cellulase 0.02g, the concentration of substrate 20g/L for the maximum glucose yield 47.4%.