Optimization Of Dilute Acid Hydrolysis And Enzymatic Saccharification Of Cotton Stalks For Sugars Production By Using Artificial Neural Network Model

The main bottleneck of the efficiency saccharification of cotton stalkis the high cost and low efficiency of pretreatment and enzymatic hydrolysis.Xinjiang is rich in cotton stalk.In order to improve its utilization efficiency from dilute acid pretreatment and enzymatic hydrolysis in cellulase and xylanase solution,using response surface method(RSM)and artificial neural network(ANN)coupled with genetic algorithms(GA)as a tool,the influence factors of each process were investigated,and the reaction conditions were optimized so as to improve the efficiency of pretreatment and enzymatic hydrolysis,and provide a theoretical basis for the efficient utilization of cotton stalk resources in Xinjiang.The main research contents are as follows:(1)Artificial neural network(ANN)coupled with genetic algorithms(GA)was used to predict and optimize the xylose and glucose production of cotton stalk in dilute acid.ANN is suitable to model nonlinear process,GA can act as an optimization algorithm.At the same hydrogen cations concentration,diprotic acid H2SO4 was compared with monoprotic HCl in the ability of releasing sugars from cotton stalk.42.98% of xylose and 2.46 g·g-1 of xylose selectivity could be obtained in H2SO4 system,which were a little higher than that in HCl system(35.05% of xylose and 2.41 g·g-1 of xylose selectivity,respectively),indicating a slight better hydrolysis of cotton stalk in H2SO4 than in HCl solution.H+ concentration was the significant factor influencing hydrolysis of cotton stalk in the presence of H2SO4,while in HCl solution,temperature was the major influence factor.(2)RSM and ANN model wereused to optimize the reaction conditions of enzymatic hydrolysis(temperature,enzyme dosage,p H and time).The optimum reaction conditions were obtained by cellulase enzyme solution after dilute sulfuric acid and dilute hydrochloric acid pretreatment for sugars production: 45?,425 FPU of cellulase enzyme dosage and 4.98 of p H value,70 hof reaction time,the sugar yield was 72.58% and 64.78%,respectively.Dilute sulfuric acid pretreatment of cotton stalk in cellulase enzymatic saccharification significantly influence the sequence of number of factors: the most obvious effect is enzymatic time,then is enzyme dosage,the not significant effect is p H.After dilute hydrochloric acid pretreatment,the influence factors of enzymatic hydrolysis of reducing sugar yield strength in order of cellulase enzyme dosage,temperature,time and p H.The effect of interaction between each two factorsof cotton stalk for sugar production by cellulose showedthat both temperature and enzyme dosage play a decisive roleafter sulfuric acid/hydrochloric acid pretreatment.(3)RSM was used to optimize the conditions of enzymatic hydrolysis in xylanase.When the temperature?xylanase dosage?pH and reaction time was 46??203 IU?5and 48 h,respectively,the 33.85% of sugar yield was obtained after H2SO4 pretreatment.However,after HCl pretreatment,the sugar yield was 35.36%,slightly higher than the former.The enzymatic process combined xylanase with cellulose is an effective method to improve the sugar yield.The results showed that xylanase could enhance the enzymatic hydrolysis efficiency of cellulase,not only improve the efficiency of enzymatic hydrolysis,short the reaction time and reduce the cost of enzymatic hydrolysis.(4)Cotton stalk materials before and after acids pretreatment and enzymatic saccharification were characterized by SEM,XRD,FT-IR.The results showed that dilute acid pretreatment can greatly removes external fibers by destroying the cellulose–hemicellulose–lignin network.The fragments were separated from the initial connected structure and fully exposed,hence increasing the external surface area and porosity of the cotton stalks,improving the efficiency of enzymatic hydrolysis.Most of the cellulose is hydrolyzed by enzymes into sugars after enzymatic saccharification,confirming disintegration of the lignocellulosic structure as a result of enzymatic conversion of cellulose to constituent sugars.Xylanase can degrade hemicellulose in the pretreatment stage,which play a synergistic action for cellulase hydrolysis.