1-Butyl-3-Methyl Imidazolium Chloride Pretreatment And Enzymatic Hydrolysis Of Cotton Stalk

The rapid depletion of fossil fuels and the threat of global warming have driven the world to utilize renewable energy sources in order to reduce the total dependency on nonrenewable energy sources.Biomass-based renewable fuels such as lignocellulosic ethanol are generally counted as a potential solution to the energy crisis and global warming.Cotton stalk is a renewable,cheap and widely available biomass resource.It is one of the most effective ways for biological conversion to fuels and chemicals after hydrolyzed to fermentable sugars.However,its dense and complex cell walls make it hard to downstream steps,such as enzymatic hydrolysis of sugar polymers.Therefore,pretreatment is absolutely required to increase the yield of fermentable sugars.Ionic liquids(ILs)are a new class of non-volatile solvents that exhibit unique solvating properties.They can be tuned to dissolve a wide variety of compounds including cellulose.ILs pretreatment has been used in wheat straw and rice straw.The pretreatments of ionic liquids for conversion of cotton stalk to ethanol were investigated in the study.Cotton stalk cellulose was dissolved in the ionic liquids,then the influence of the process was investigated by studying the influence factors(the ratio of liquid-solid,temperature and dissolving time),and the experimental indicators contain weightlessness rate,reducing sugar yield.Then the most appropriate parameters of solution were obtained.On the basis of this,the regeneration of the straw was enzymatic hydrolysis,and the optimum conditions were discussed.The microstructure of before and after processing were investigated through the Scanning Electronic Microscopy and Fourier Transform Infrared spectrum.The main research results as follow:The reaction temperature showed significant influence on reducing sugars yield and weight loss in the [Bmim]Cl treated cotton straw,while liquid solid ratio and time don't have significant influence.Under the optimum conditions of liquid solid ratio 10:1,reaction temperature 120? and time 5 h,the reducing sugar yield was 29.72%,being higher than the original value(17.4%).Through the observation of SEM images of before and after processing,ionic liquids pretreatment can destroy the original straw and expose more cellulose.FT-IR spectra shows that cotton straw directly dissolved in ionic liquids,and no derivatizationreaction occurred.The hydrogen bondings between cellulose molecules were broken,lignin and hemicellulose is partially removed.The damage for lignocellulosic will be weakened with recycle times of ionic iquids increasing,so the reducing sugar yield decreased.During the enzymatic hydrolysis of regenerated cotton straw,the cellulase concentration had the greatest influence on the reducing sugar yield following the order of cellulase concentration>pH>substrate concentration.The optimum enzymatic conditions were obtained.When the the substrate concentration was 40 g/L,the cellulase concentration was 90 FPU/g,pH 5.0,enzymatic hydrolysi was carried out at 50? for 72 h,and the reducing sugar yield was66.24%.SEM images indicated that after enzymatic hydrolysis,cellulase destroyed the crystal structures of the original straw,and this process is conducived to the enzymatic hydrolysis reaction.FT-IR spectra showed that the structure of cellulose was changed and the glycosidic bonds of cellulose was destroyed in the process.In this study,ionic liquid pretreatment technology was applied in cotton straw,and then enzymatic hydrolysis technology was preliminary studied,hoping to provide theoretical supports and reference for the comprehensive utilization of cotton straw.