Study On Two-stage Pretreatments To Enhance Lignocellulose Saccharification

Lignocellulose is a large-scale renewable biomass resource with a wide range of sources.Biorefinery with biomass as raw material is a research hotspot in the field of clean and renewable energy.At present,steam explosion pretreatment is one of the promising pretreatment methods in biorefiny.However,in the process of steam explosion pretreatment under severe conditions,lignin is liable to be repolymerized,which hinders the enzymatic hydrolysis of cellulose to a greater extent.To solve this problem,this paper puts forward the strategy of adding basic modification(sulfonation or oxidation)steps of lignin before steam explosion,namely two-stage pretreatment,to reduce the repolymerization of lignin,such as to improve the enzymatic hydrolysis performance of cellulose,enhance the saccharification of lignocellulose,and realize the comprehensive utilization of lignocellulosic materials.After wet grinding and steam explosion pretreatment,it was found that wet grinding had little effect on the components of wood fiber;steam explosion pretreatment selectively removed hemicellulose from wood fiber;both of which improved the cellulose accessibility and enzymatic hysrolysis yield.Results showed that the higher the temperature was,the greater the degree of lignin repolymerization was.After sulfonation of wet ground pulp and steam exploded pulp,it was noted that there were more acid groups in wet ground slurry through sulfonation than that in steam explosion material.The results showed that the reactivity of lignin to subsequent chemical modification was reduced by the repolymerization reaction.After two-stage pretreatment of poplar by pre-alkaline sulfonation and post-steam explosion,it was clear that the alkali sulfonation(16 % sodium sulfite + 4 % sodium bicarbonate)-steam explosion gave rise to the highest pretreatment efficacy.The lignin removal rate was 73.23 %,and the degree of lignin repolymerization was significantly reduced to 3.04.The recovery of cellulose and hemicellulose were 96.93% and 81.32%,respectively.The content of acid group was increased to 120 mmol / kg,especially the sulfonic group to 93.3 mmol / kg,the water retention value was significantly increased,andthe hydrolysis efficiency of cellulase was significantly increased to 89.60%.At the same time,the amount of Pb(?)adsorbed to the lignin recovered from the spent liquor was significantly increased,and the maximum amount of Pb(?)adsorbed was 108.70mg/g.The minimum degree of lignin repolymerization was 11.81,the maximum rate of lignin removal was 58.30%,the content of acid group in substrate was 150.51mmol/kg,the degree of fiber swelling was obviously improved,so the yield of cellulose hydrolysis yield was increased to 89.18 %,and the adsorption capacity of lignin recovered after two-stage pretreatment of alkaline oxidation and steam explosion can reach 212.77mg/g,after pre-alkaline oxidation and post-steam explosion treatment.Results show that the two-stage pretreatment including alkali modification and steam explosion can significantly reduce the repolymerization of lignin by modifying and removing lignin while retaining cellulose and hemicellulose in the pretreated water-insoluble fraction.Therefor,the two-stage pretreatment can not only improve the hydrolysis performance of cellulose,but also promote the subsequent recycling of lignin,and prepare heavy metal ion adsorbent,which can facilitate the full utilization of lignocellulosic materials.