Study On The Technology Of Low Carbon Cascade Utilization Of Corn Stover Based On Steam Explosion Combined With Urea Pretreatment

Corn stover is an important biomass resource in in my country,the utilization of corn stover with high value has become a hot research topic.Co-production of ethanol and methane from corn stover is an efficient way to realize low-carbon utilization of crop stover,however,the difficulty of lignocellulose degradation,the difficulty of regulating the fermentation process and the low yield of ethanol restrict the development of cellulosic ethanol from corn stover.In this paper,the characteristics of co-production of ethanol and biogas from corn stover by urea combined with steam explosion pretreatment were studied,and the effect of steam explosion pretreatment combined with urea on enzymatic saccharification of corn stover was studied,the effect of steam explosion pretreatment combined with urea on ethanol fermentation of corn stover was studied,and the effect of anaerobic fermentation of ethanol distillate on biogas production was also studied.The purpose of this study is to improve the utilization of corn stover,and improve the high added value of products,and provide a theoretical basis for the realization of“double carbon”.The main findings and conclusions of this study are as follows:(1)The experiment of enzymatic hydrolysis and saccharification of corn stover showed that the effect of different pretreatment conditions(urea concentration of 3%,5%,7%and steam explosion pressure of 0.9 MPa,1.2 MPa,1.5 MPa)on enzymatic hydrolysis of corn stover were analyzed,the components of lignocellulose got to different degrees of degradation.The degradation rate was:hemicellulose(9.81%-16.23%),cellulose(23.92%-28.61%)and lignin(4.46%-6.32%),and the reducing sugar content was between 10.03-11.58 mg/m L,and the p H was between 6.36-6.82.,and the recovery rate of reducing sugar was between 28.9%and 40.2%and the initial absorption rate of cellulose was between 26.7%and 40.3%after enzymatic hydrolysis.When the pressure of steam explosion is 1.2 MPa and the concentration of urea is 5%,the recovery rate of reducing sugar is40.2%and the initial absorption rate of cellulase is 40.3%.(2)The experiment on ethanol fermentation of corn stover showed that:After fermentation,the reducing sugar content in the pretreatment group ranged from 5.56 mg/m L to 6.98 mg/m L,when the pretreatment conditions were urea concentration of 5%and steam explosion pressure of 1.2 MPa,the reducing sugar content decreased fastest and the utilization ratio of reducing sugar was the highest.After distillation,the conversion of sugar-alcohol and ethanol yield remained the same conversion of sugar alcohol was 21%-40%,the alcohol content was 4%-6%,and the ethanol yield was 17%-35%.Response Surface Methodology(RSM)was used to study the optimum conditions of ethanol fermentation,which were urea concentration of 4.87%,and steam explosion pressure was1.22 MPa.At this time,the cellulose degradation rate is 34.29%,sugar alcohol conversion rate is39.25%,and ethanol yield is 34.05%.The experimental results show that the cellulose degradation rate is 34.89%,the sugar-alcohol conversion rate is 39.87%,the ethanol yield is 34.56%,and the relative error is 1.72%,1.56%,1.48%respectively.The results of SEM showed that the microstructure of corn stover was destroyed under the optimum pretreatment conditions,which was more helpful to ethanol fermentation than that without pretreatment.(3)Ethanol waste liquid anaerobic fermentation test showed that:anaerobic fermentation was carried out in anaerobic fermentation of ethanol waste liquid under optimum pretreatment conditions,and the reduction glycol content in the fermentation process exhibited a small fluctuation.The volatile fatty acid content gradually decreased,and p H was between 6.84-7.20,in anaerobic fermentation 4d,getting the maximum amount of methane production per day,which is 6.48 m L/g VS·d.The modified Gompertz model(R~2=0.9987)shows that the actual cumulative methane production(Y_a)is 46.03 m L/g VS.The composition of ethanol waste liquid before and after anaerobic fermentation was compared.Compared with that before anaerobic fermentation,the content of Chemical oxygen demand(COD)in ethanol waste liquid after anaerobic fermentation was reduced by 76.18%,and total organic carbon(TOC)in ethanol waste liquid was reduced by 67.17%.