Study On Enzymatic Hydrolysis Of Wheat Straw For Lignin Separation

The chemical properties and structure of lignin molecules are closely related to their use value,and different structure of lignin have different uses.For example,alkali lignin produced in the pulp industry is generally chemically modified for industrial use,and sulfonated alkali lignin to lignosulfonate is used as a surfactant.The lignin is obtained by cooking under strong alkali,high temperature and high pressure,and its molecular weight is small,and it is difficult to separate from the black liquor of papermaking,and its application range is also greatly limited.Some new technologies have gained greater value in obtaining large molecular weight lignin.In recent years,with the rapid development of biological enzyme technology,some biological enzymes of higher activity have been applied in industrial production.For example,xylanase,pectinase,cellulase and other biological enzymes are used in cellulosic ethanol,biological pulping and other processes.The enzymes have the function of directional cut?hydrolysis?.Therefore,the lignin products with complete biological morphology can be obtained by directional cut according to the linkage sites of each component of wheat straw by enzyme.In this paper,various alkaline enzymes were used to extract lignin from wheat straw by enzymatic hydrolysis and the process was optimized.In addition,the lignin separated from wheat straw was studied by enzymatic hydrolysis and compared with the lignin from traditional alkali cooking method.The lignin separation and extraction by two methods was characterized and analyzed by GPC,2D-HSQC and FT-IR.The reaction liquids?enzymatic hydrolysate and alkali black liquor?were studied by the two processes and the flocculation experiments were investigated.Firstly,the free radical scavenging of 1,1-diphenyl-2-trinitrophenylhydrazine?DPPH?was carried out for two lignins.Secondly,the adsorption behavior and kinetics of lignin on hexavalent chromium ions were systematically studied.The difference between the two lignins could be distinguished by characterization and experiment.The main results were as follows:The AL yield was 86.21%higher than that of the EHL?78.62%?.The flocculation effect of the reaction solution?enzymatic hydrolysate and alkali black liquor?produced by the two processes was completely different.Enzymatic liquid was floating,and alkali liquid was sediment after flocculation.Because carbonate could be formed during enzymatic hydrolysis and CO₂gas was produced under flocculation conditions,which caused the flocs to float;The results of FT-IR and 2D-HSQC indicated that the S and G units in the EHL were not severely damaged compared with the AL.The three units composition of the two lignin was different.The G/S/H of alkali lignin was36.44/60.61/2.95.However,enzymatic lignin was 62.42/36.23/1.35;The molecular weight of the enzymatic lignin?3348 g/mol?was higher than that of the alkali lignin?3047 g/mol?,and its free radical scavenging ability was stronger than that of alkali lignin;The adsorption capacity of the two lignin to Cr???was studied.The effects of p H value of solution,dose of the two lignin,temperature and time for Cr???removal efficiency was studied.The results showed that the adsorption of alkali lignin and enzymatic lignin to Cr???was fitted to pseudo-second order kinetic model and the Langmuir isothermal adsorption model.The maximum adsorption capacities of alkali lignin and enzymatic lignin were calculated by the Langmuir isothermal model as271.7 mg/g and 135.1 mg/g,respectively.The results showed that the adsorption effect of the two lignins on Cr???was different,which indicated that there were differences in the structure of the two lignins.