Investigation On Effects Of Different Pretreatment Methods On Chemical Composition Of Wheat Straw And Enzymatic Hydrolysis

Wheat Straw was pretreated by different pretreatment methods.The effects of pretreatment on chemical composition and enzymatic hydrolysis were investigated.The lignin in pretreatment liquid was recycled and analyzed.Partial phenol was replaced by lignin for synthesising phenolic resin,with the purpose of promoting high value utilization of lignocellulosic biomass.Wheat Straw was pretreated by four kinds of pretreatment methods,namely,Liquid Hot Water,soaking aqueous ammonia(SAA),sodium hydroxide and sodium hydroxide combined with ethanol.The effects of pretreatment on chemical composition and enzymatic hydrolysis were investigated.Results showed that Liquid Hot Water pretreatment on hemicellulose was significant,the removal rate of hemicellulose were 74.32% at 188 ?reaction time 40 min,but the delignification is only 21.32%.Na OH has a good removal of lignin and ash,the removal rate of lignin and ash were 72.00% and 75.93% respectively by 1% Na OH at 140 ?reaction time 3h.Because of lignin has good solubility in the ethanol,pretreatment using Na OH with 50% ethanol,the removal rate of the lignin up to 84.11%.XRD result showed that the crystallization index of four pretreated Wheat Straw were greater than the raw material because of the removal of lignin and hemicellulose,the crystallization index of pretreated samples increased from 28.80% to 31.23%-33.61%.The objectives of pretreatment are to remove lignin or hemicellulose,increase biomass surface area to benefit lignocellulosic enzymes accessing the recalcitrant structure of cellulose.Under the conditions of cellulose enzyme 30 FPU/g(of cellulose)and ?-glucose glycosides enzyme 30 IU/g,enzymatic hydrolysis temperature 50 ?,and reaction time 72 h,cellulose enzymatic hydrolysis ratio increase obviously.Especially,cellulose enzymatic hydrolysis ratio of sodium hydroxide combined with ethanol treated Wheat Straw reached 92.58%,it improved 6 times of raw material.Based on Box-Behnken design,temperature,mass fraction of alkali and time were chosen as the three important factors with three levels.The process conditions of alkali ethanol solution pretreatment were optimized by response surface methodology,and a second order quadratic equation was established,and the applicability of the model and interaction involved factors on predicting the yield of cellulose enzymatic hydrolysis ratio was verified.The results indicated that the effects order of three factors on the cellulose enzymatic hydrolysis ratio were as follows: mass fraction of alkali,temperature and time.The optimal levels for achieving the highest total sugar conversion were obtained,including temperature of 150 ?,mass fraction of alkali of 1.05% and reaction time of 2.29 h.Thecellulose enzymatic hydrolysis ratio reached 91.40% under optimized conditions.Chemical composition and scanning electron microscopy analysis showed that 84.62% of lignin was removed through alkali alcohol pretreatment,The compact structure of fiber was damaged,and the pores and cracks formed on the fibril promote the accessibility of substrate and enzyme,and increases the efficiency of enzymatic hydrolysis.The effectiveness of hydrothermal pretreatment and sequentially alkaline ethanol process on chemical composition of Wheat Straw and enzymatic hydrolysis were investigated.It was found that hydrothermal pretreatment significantly removed partial hemicelluloses and acid-soluble lignin,the removal rate increased significantly with the increasing of hydrothermal temperature.The removal rate of hemicelluloses and acid-soluble lignin were 76.56% and 83.52%.respectively at the optimal temperature of 190 ?.Due to the massive removal of lignin,Cellulose-rich fractions(cellulose content of 89.71%)from Wheat Straw were prepared after the sequentially alkaline ethanol pretreatment.XRD result showed that the crystallization index(CI)of pretreated Wheat Straw were greater than the raw material because of the removal of lignin and hemicellulose,the CI of pretreated samples increased from 28.80% to 32.29%-33.59%.the cellulose enzymatic hydrolysis ratio increased obviously reached 94.97% after the sequecntial treatment by hydrothermal pretreatment and alkaline ethanol pretreatment.The characterize of FT-IR showed that the lignin functional groups remained intact except the partially rupture of the C=O bond and C-O-C bond.This study demonstrates that the combination of hydrothermal pretreatment and alkaline ethanol process could potentially be used as one of the component separation process for claiming lignin fraction from wheat straw for maufacturing value added products.