Study On Alkaline Deep Eutectic Solvent Pretreatment Of Corn Stover And Subsequent Lipid Fermentation

In recent years,the technical route of preparing microbial oil by hydrolyzing lignocellulose into fermentable sugars has attracted extensive attention from researchers.However,lignocellulose is one of the main obstacles to the successful commercialisation of lignocellulosic biofuels due to its tight and stubborn structure which severely hampers the enzymatic accessibility of cellulose.Pretreatment can significantly disrupt the rigid structure of lignocellulose.However,the large amount of waste generated from pretreatment is not reasonably recycled for reuse.This is undoubtedly causing huge waste of resources and environmental pollution problems.Based on the above,this thesis developed a new lignocellulosic recycling pretreatment process,systematically studied its pretreatment performance and the feasibility of recycling.And according to the advantages of this process,the fed-batch saccharification of recycled straw was carried out with a ultra-high solid-to-liquid ratio,then using the prepared high concentration of sugar solution for fed-batch high density fermentation of Cutaneotrichosporon oleaginosum ATCC 20509.It provides an important support for the industrialisation of microbial lipid.The results of the study are as follows:1.In this study,a novel alkaline choline chloride-glycerol(ChCl:Gly)deep eutectic solvent(DES)was described very effective for disrupting the recalcitrant structure of corn stover facilitating high monomeric sugars yield for the first time.The pretreatment could significantly preserve glucan and xylan,while strongly remove lignin to enhance enzyme digestibility.A response surface optimization referring temperature,processing time,and Na OH content was conducted and the maximum monomeric sugars yields could reach 90.41% at 143℃ for 2.25 h containing 1.06wt%of NaOH.In addition,the corn stover was characterised by FITR,XRD and SEM,showing that the straw was pretreated indicating a significant increase in roughness and porosity,which resulted in high enzyme accessibility to cellulose.2.The alkaline Ch Cl:Gly DES described in this study exhibited good recoverability and cyclic pretreatment performance.The recovered pretreatment liquor in the 20 g small system could be pretreated in at least four cycles,with only a slight downward trend in the monomeric sugars yield with increasing cycle number,but no significant difference.Interestingly,when the reaction system was expanded by a factor of 70,the monomeric sugar yield instead increased slightly with the number of cycles.And the fed-batch saccharification of recycled stover prepared by cyclic pretreatment of the large system was carried out with 61% solid-to-liquid ratio,achieving the 355.07 g/L highly concentration sugar liquor.3.In order to make full use of the total sugar in the high solid-to-liquid ratio enzymatic hydrolysis system,this paper prepared the sugar solution with three levels of concentration which suitable for the fed-batch fermentation process in the fermenter.Compared with conventional one-step solid-liquid separation,36.12%more total sugar was recovered.A fed-batch fermentation in a 3-L fermenter yielded the biomass of 61.83 g/L and the lipid content of 65.42% in 120 h.