Structure Elucidation Of Lignin And Hydrolysis Of Carbohydrate During Supercritical CO₂ Pretreatment Process

Corn cob,as agricultural waste,has the characteristics of low price,renewable and rich in content.It is considered to be an excellent biomass resource for alternative fossil energy.Corn cob contains hemicellulose,cellulose,lignin and other components.where the abundant content of hemicellulose can be used to prepare polysaccharides.At the same time,the isolated cellulose and lignin also have great added value.However,because of the complex structure of the three major components in the corn cob,the better separation of hemicellulose,cellulose and lignin becomes difficult.Therefore,breaking through the natural barrier of raw materials,efficient separation becomes very important.in this study,corn cob was used as raw material,and three different solvent systems were used to cooperate with supercritical co₂ to achieve the effect of high efficiency separation.while preserving the natural structure of lignin.The effect of different reaction conditions on the separation of three major components in supercritical co₂ water system is discussed.By setting water consumption,carbon dioxide concentration and pretreatment temperature,the effects of different pretreatment conditions on material yield,lignin removal rate and sugar retention rate were investigated.with the increase of the pretreatment strength,the removal rate of hemicellulose lignin increased,but the cellulose content in the remaining solids decreased.when the temperature is 160?,the pretreatment time is 1 h,and the solid-liquid ratio is 1:10,the recovery of cellulose in the residue reaches 92.4%,which has high utilization value.meanwhile,the xylose content in the solid liquid product is 8.9%,and the furfural content is 8.3%.Secondly,this paper further discusses the effect of different temperatures,different co₂concentrations and different solvent ratios on the separation of the three major components under supercritical co₂ glycol water system.with the temperature,the concentration of co₂,the content of solvent ethanol increased,and the removal rate of hemicellulose and lignin all increased.when the concentration of co₂ is 36%,the temperature is 160%,and the solvent ratio is 1:1,13.2%furfural is obtained in the liquid product,while the cellulose content in the residual solid reaches 85.5%.In the end,the effect of different temperatures,different co₂ concentrations,and different reaction times on the pretreatment results under the supercritical co₂ lithium bromide water system was investigated.the dissolution of each component increased with increasing temperature,reaction time and co₂concentration.at 100?,reaction 4 h,co₂ concentration18%,the removal rate and recovery rate of each component reached a better level.the recovery rate of cellulose was 67.7%and the removal rate of hemicellulose was 98.8%.in liquid components,xylose content was 20.9%and furfural content was 8.7%.In addition,it is found that the enhancement of pretreatment reaction conditions is beneficial to enhance the thermal stability of lignin,and the molecular weight of lignin decreases with the enhancement of pretreatment conditions.co₂ concentration in the pretreatment environment increased,the signal of lignin aromatic group region increased,and the side chain region still had sugar signal,which had more natural structure.Analysis of the structural characteristics of the fiber solid after pretreatment,it is found that the fiber solid with different treatment conditions has different crystallinity.at the same time,after supercritical co₂ treatment,the surface of the fiber solid presents holes and folds,which is convenient for future reuse.