Effects Of H₂O₂/HCl Pretreatment On Lignin Removal And Enzymatic Hydrolysis Of Wheat Straw

The methods of improving of the removal efficiency of lignin of straw and enzymatic hydrolysis properties were discussed in this paper,against to the main problems inefficiency,high-energy consumption and easy to produce by-products at high temperature of straw pretreatment technology of straw-to-ethanol conversion.Under medium and low temperature conditions,the solid to liquid ratio?S/L?of 1:8,the pretreatment of wheat straw with H₂O₂ without secondary pollution was carried out,the effects of H₂O₂ concentration,pretreatment time and temperature on lignin removal and enzymatic hydrolysis of wheat straw were studied.Firstly,wheat straw was pretreated with 2%to 8%H₂O₂ at 121?for60 min;followed by 6%H₂O₂,temperature was 60,80,121?,respectively,pretreatment for60 min;then,pretreated for 10-180 min at 4%,6%,8%H₂O₂,at 121?;finally,all pretreated wheat straws were enzymatically hydrolyzed under the following conditions:concentration of substrate was 3%,added cellulose 15 mg with activity of enzyme was200000/U to the acetic acid-sodium acetate buffer solution,with pH 4.8.The results of lignin analysis and enzyme hydrolysis showed that the yield of reducing sugar reached the maximum 28.05 g/100 g DM,when the concentration of H₂O₂ was 6%,temperature was121?pretreat for 80 min,enzymatic hydrolysis after 48h,simultaneously,the removal rate of lignin was 78.35%and the recovery rate of dry matter rate was 54.11%.To further enhance reducing sugar field,the two-step pretreatment method consist of H₂O₂ pretreatment in the first step and HCl pretreatment in the second step was discussed in this paper.At the S/L of 1:8,the parameters in H₂O₂ pretreatment were as followed:6%H₂O₂;T:121?;t:80 min.Then,at 121?,the wheat straw treated with H₂O₂ was retreated by HCl,the processing conditions as followed,respectively:one was at concentration of HCl ranging from 0.2%-1.5%for 40 min,the other was at concentration of HCl in 0.4%,0.6%,0.8%for 5-50 min.Enzymatic hydrolysis conditions were listed below:concentration of substrate was 3%,added cellulose 15 mg with activity of enzyme was200000/U to the acetic acid-sodium acetate buffer solution with pH 4.8.Results suggests that wheat straw was pretreated with 0.6%HCl at 121?for 30 min,the maximum reducing sugar yield was obtained,which can reach 35.83g/100g DM.In order to further analyze the mechanism of H₂O₂ and HCl pretreatment on wheat straw,SEM analysis was conducted before and after pretreatment.The results indicated that H₂O₂ pretreatment had a certain degree of damage to the wheat straw structure,and compared with situations at 60?and 80?,the damage at 121?increased significantly.After two-step H2O2/HCl pretreatment,the structural damage of wheat straw was strengthened,with the cellulose chain structure fractured and the debris and holes increased.