Cellulose Solvent-based Lignocellulose Pretreatments And Its Enzymatic Saccharification

Lignocellulose is the largest renewable resource on Earth,and the use of lignocellulose to produce bioethanol is an important way to solve the problems of environment and energy.In the long-term natural evolution process,the plant cell wall formed a complex structure against external microbial and enzymatic degradation.However,due to the complexity of substrate structure and the enzymatic process,the traditional pretreatment method has the disadvantages of low efficiency and high energy consumption.Compared with the traditional pretreatment method,cellulose solvent based pretreatment method has unparalleled advantages in the pretreatment condition and pretreatment effect of lignocellulosic biomass and has wide application prospect.In this paper,corn stover were pretreated by alkali and acidic cellulose solvent,and the performances of pretreatment methods were compared.Lignin was extracted from pretreated corn stover.The effect of pretreatment on the physical and chemical structure of lignin was studied.The applicability of the cellulose solvent was further expanded to study on wheat straw,and the effect of solid loading was analyzed.The method of preparing fermentable sugar by pretreatment and enzymatic hydrolysis “one-pot”was proposed.The feasibility of the method was studied and compared with the traditional method to analyze its superiority.Some main results are summarized as follows:(1)After acid and alkaline cellulose solvent pretreatment,corn stover enzyme hydrolysis conversion rate was greatly improved.The enhancement of enzymatic saccharification by cellulose solvent pretreatments was attributed to the decrystallization of cellulose and partial removal of lignin and hemicellulose.Compared with 85% concentrated phosphoric acid,low temperature NaOH/urea solution had better effect on corn stover.The cellulose-rich substrate achieved nearly complete enzymatic hydrolysis within 24 h with an enzyme loading of 15FPU/g substrate.(2)The appreciable changes in cellulose structure with the phosphoric acid pretreatment did not lead to an enhancement in enzymatic hydrolysis.The reason for this low efficacy might be the high amount of lignin remaining.Lignin had a great effect on the enzymatic hydrolysis of corn stover compared with the crystallinity of cellulose.After low temperature NaOH/urea pretreatment,the lignin “core structure” was not destroyed and contained more chemically active groups,which might have good chemical activity.(3)Low temperature NaOH/urea solution also had a good pretreatment effect on wheat straw.The conversion of glucan was 95% and the conversion of xylan was 84% within 48 h with an enzyme loading of 15 FPU/g substrate.The different pretreatment solid loading had effect on the crystallinity of cellulose,but had no significant effect on the chemical composition and enzymolysis performance of wheat straw,which provided a reference for the further study in large scale.(4)NaOH/urea pretreatment and saccharification could be combined into a single-unit or one-pot process.Under the optimum pretreatment and enzymatic hydrolysis,the enzymolysis conversion rate of glucan and xylan could reach more than 90%.The “one-pot” produced more fermentable sugars than the traditional method,which produced 90.24% of the total sugar in the wheat straw higher than the traditional step method of 73.17%.Low temperature NaOH/urea pretreatment solution did not contain fermentation inhibitor such as furfural and 5-hydroxymethyl furfural,the method had broad application prospects.