Studies On The Pretreatment And Fermentation Process With High Solid Loading Of Lignocellulose

The main problems induce the inefficiency of cellulosic ethanol production are large amount of water consumption in pretreatment process resulting in increased energy consumption and high solid loading fermentation leading to a decrease in substrate utilization.In this paper,the research has been carried out on high solid loading pretreatment technology and high solid loading fermentation process.The main research contents and results are as follows:1.High solid loading pretreatment can reduce the amount of water consumption,thereby reducing the energy consumption and improving pretreatment efficiency.This paper examined the effect of solid to liquid ratio on different pretreatment processes.The results reavealed that increasing the pretreatment solid to liquid ratio was beneficial to improving the lignin removal of EDA pretreatment,but it also leaded to a decrease in lignin removal of NaOH pretreatment.Although the extremely high solid to liquid ratio pretreatment condition is conducive to the removal of hemicellulose by H₂SO₄pretreatment,the formation of a large number of pseudo-lignin seriously affected the enzymatic conversion rate.To conclude,EDA pretreatment is a pretreatment technique well suited for high solid to liquid ratio conditions.2.The high solid to liquid ratio EDA pretreatment economizes water and energy,and causes high-efficient pretreatment.However,the mechanism of action of EDA and lignin is still unclear.In this thesis,the chemical structure changes and characteristics of lignin pretreated with EDA were studied by virtue of various of methods,including2D heteronuclear single quantum coherence?HSQC?NMR,³¹P NMR,Fourier transform infrared?FTIR?,gel permeation chromatography?GPC?,elemental analysis and thermogravimetric analysis?TGA?.The results showed that EDA depolymerized lignin by attacking the ether bonds and ester bonds,which reduced the molecular weight and thermal stability of lignin.The solubility of lignin is closely related to the pH.The acid solubility of lignin is significantly increased by EDA pretreatment,which lays a foundation for further efficient depolymerization and catalytic degradation of lignin.3.Although most EDA can be recovered in the pretreatment process,there is still a small amount of residue in the substrate.The effect of residual EDA on the enzymatic hydrolysis of lignocellulose is still unclear.In this paper,the main reason for the decrease of xylose yield caused by EDA was the Maillard reaction between EDA and reducing sugar.By adding Maillard reaction inhibitor,the formation of macromolecular browning products was significantly inhibited,but the loss of reducing sugar is still significant.By means of reducing the enzymatic hydrolysis temperature,the loss of reducing sugar could be effectively avoided.4.In view of the problem of the decrease in the utilization of hexose in the high solid loading fermentation process,this study effectively improved the substrate utilization and ethanol yield through two-step fermentation process and the adaptive evolution strain.In the optimal two-step fermentation process,the final concentration of xylose decreased by 55.6%and the ethanol yield increased by 32.2%,which was significantly higher than that in traditional simultaneous saccharification and co-fermentation process.The strain obtained by adaptive evolution has significantly enhanced furfural conversion and antioxidant stress resistance.Under high concentration of complex inhibitors,the reactive oxygen species?ROS?of the adapted strain was 67.7%of the parental strain,the final concentration of xylose was 16.5%lower than that of the parental strain,and the ethanol yield was increased by 22.9%.