Research On Biomass Pretreatment And Enzymatic Hydrolysis Characteristics Based On Organic Acid System

Nowadays,the rapid development of economy and society has intensified the consumption of fossil energy,and the increasing exhaustion of resources restricts the sustainable development of human society,and the search for new and renewable energy has become a top priority.Biomass energy,as one of the new green energy sources,has great potential in replacing traditional fossil energy.The pretreatment of biomass is the basis and key of the biorefinery and conversion process,which also face many challenges.This article mainly studies the use of organic acid(p-TsOH,p-toluenesulfonic acid)system to pretreat biomass.The separation of the components of lignocellulose raw materials,the enzymatic saccharification and fermentation of cellulose,and the extraction of high value-added lignin are studied and discussed.(C,T,t stand for acid concentration,treatment temperature and time,respectively.)The specific research of this article is as follows:In the first part,a physicochemical method using p-TsOH as a pretreatment solvent combined with ultrasonic treatment was proposed,and the effects of ultrasonic-assisted treatment on cellulose enzymatic hydrolysis characteristics and ethanol conversion were studied.This study integrates the characteristics of the two pretreatment processes,which is economical and efficient.The enzymatic hydrolysis efficiency of cellulose obtained by high-intensity pretreatment(C80T80t30)was as high as 93.61±3%,and the enzymatic hydrolysis effect of cellulose after 10 s ultrasonic treatment was more significant.Therefore,under milder conditions(C80T80t15),the enzymatic hydrolysis effect of cellulose after ultrasonic treatment was similar to that of C80T80t30,and the final enzymatic hydrolysis efficiency reached 93.36±2%,and the removal rates of lignin and hemicellulose were 59.00% and 83.30%,respectively,ensuring excellent pretreatment effects.The characterization results of lignin showed that milder pretreatment conditions can reduce structural damage during the lignin extraction process,and the resulting lignin products are more valuable.Therefore,the best pretreatment conditions: ultrasound assisted after C80T80t15,the ethanol conversion rate of the obtained fiber material after fermentation can reach 81.87±3.91%.The second part proposed the cooperative pretreatment of p-TsOH/formaldehyde mixed solvent,and explored the pretreatment effect,cellulose enzymatic hydrolysis characteristics and lignin structure changes under this system.The purpose was to ensure efficient pretreatment while reducing the malignant condensation in the lignin separation process,and to promote the extraction of high value-added lignin.On the one hand,formaldehyde acts as a stabilizer to protect lignin and reduce the condensation reaction of lignin during the pretreatment process.The characterization results of lignin confirm the protective mechanism of formaldehyde.On the other hand,during the pretreatment process,formaldehyde not only reacts with lignin but also reacts with monosaccharides,which can affect the enzymatic hydrolysis effect of cellulose,so the amount of formaldehyde was controlled at 1.5% to reduce the adverse effect of formaldehyde on the enzymatic hydrolysis efficiency.Under the pretreatment conditions of C80T80t30 and1.5% formaldehyde content,the removal rates of lignin and hemicellulose were about67.10% and 83.80%,respectively,and the final cellulose enzymatic hydrolysis efficiency reached 85.5%.The ethanol conversion rate obtained by subsequent fermentation was as high as 82.9±2.2%.This pretreatment strategy was basically feasible and promotes the effective conversion and comprehensive utilization of biomass.In the third part,p-TsOH/chlorate pretreatment system was proposed.The pretreatment effect of the system,the enzymatic hydrolysis characteristics of cellulose,the properties of the obtained lignin,and the apparent changes of cellulose and lignin were also discussed.During pretreatment,the addition of a small amount of sodium hypochlorite and sodium chlorite can promote the dissolution of hemicellulose,especially lignin.Under the optimal conditions(T80t45),the removal rates of lignin and hemicellulose were about 84.33% and 76.79%,respectively.In addition,this method can achieve bleaching of cellulose under the conditions of low temperature,normal pressure,and short time,and the whiteness reached 60.1.The final enzymatic hydrolysis efficiency of cellulose under the optimal conditions was 89.6±1.9%,and the maximum ethanol conversion rate was 82.31±1.1%.Through the characterization of lignin,the structural changes were discussed.The benzene ring structure might be destroyed by oxidation and new groups were formed.Compared with the single organic acid pretreatment,this method reduced the acid concentration,and compared with the traditional pulp bleaching process,this system avoided the high temperature and complex process.The advantage of this strategy was that the bleaching of cellulose and the extraction of lignin are carried out at the same time during the pretreatment process,and the conversion of sugar and ethanol was effectively promoted.