Synergistic Effect Of Mechanical Activation And Alkali On Pretreatment Of Sugarcane Bagsse And Its Enzymatic Hydrolysis

With the rapid development of economy,social demand for energy is higher and higher,leading to the depletion of non-renewable resource,global warming,environmental pollution,and so on.Therefore,fuel ethanol,a new type of renewable energy,has already attracted the attention of many countries.The cellulosic biomass becomes the most promising raw material for bioethanol production because of its abundant,low cost,environment friendly and widely available source.However,lignocellulose is characterized by high degree of crystallinity and low accessibility,making it hard to be hydrolyzed by enzyme.Therefore,pretreatment becomes the key process for the conversion of biomass into fuel ethanol.In this paper,on the basis of the study of synergistic interaction of mechanical activation(MA)/metal salt on cellulose,the synergistic pretreatment of MA-alkali for sugarcane bagasse(SCB)was investigated,aiming to destroy its stable internal structure,remove lignin,decrease the crystallinity index(CrI)of cellulose and improve its enzymatic hydrolysis efficiency.The main research contents and results are as follows:A comparative study of the effects of different pretreatments(MA,alkali,MA before alkali,and MA-alkali)on the removal ratio of lignin was carried out with SCB as raw material to investigate the difference of these four pretreatment methods for removing lignin from SCB.The results showed that the synergetic pretreatment of MA-alkali was the best method.Under MA-alkali pretreatment,the effects of alkali dosage,MA temperature,MA time,extraction temperature,extraction time and milling speed were investigated respectively by using the removal ratio of lignin as evaluating index.The results indicated that under the optimum conditions of alkali dosage 20.0%,MA temperature 80?,MA time 120 min,extraction temperature 90?,extraction time 120 min,and milling speed 500 rpm,removal ratio of lignin from SCB reached 85.92%.The influence of synergistic effect of MA-alkali on the structures of SCB was characterized by SEM,FTIR and XRD,investigating the changes of particle morphology,molecular groups and crystalline structure of SCB with different process conditions.SEM examination indicated that compared with alkali pretreatment,the size of SCB particles obviously decreased for the destruction of SCB by MA pretreatment.The SCB particles became smaller and its surface became looser as the increase of alkali dosage,milling speed and MA time in MA-alkali pretreatment.FTIR analysis showed that in the spectra of untreated and MA-pretreated SCB,there was an absorption peak at 1732 cm-1,but this peak disappeared in the samples with alkaline pretreatments,indicating that the ester bonds between lignin and hemicellulose were cleaved in alkaline pretreatments.XRD analysis showed that the alkali dosage,MA time and milling speed had impact on the crystal structure of SCB,contributing to the change of CrI.When the milling speed reached a certain intensity,the crystalline region of cellulose had been seriously disrupted.This meant that MA intensity had significant effect on the crystal structure of SCB.Enzymatic hydrolysis experiments of untreated and different pretreated SCB samples were performed with enzymatic hydrolysis rate as evaluation index.A comparative study of the effects of four different pretreatments on the enzymatic hydrolysis of SCB was carried out.The results showed that the synergetic pretreatment of MA-alkali was the best method.Under MA-alkali pretreatment,the effects of alkali dosage,MA temperature,MA time,extraction temperature,extraction time and milling speed on the enzymatic hydrolysis of SCB were investigated respectively.The results indicated that under the optimum conditions of alkali dosage 20.0%,MA temperature 80 ?,MA time 120 min,extraction temperature 80?,extraction time 120 min,and milling speed 500 rpm,enzymatic hydrolysis rate of SCB reached 91.74%.From the above study,it was found that milling speed had the most significant effect in the lignin removal and enzymatic hydrolysis of SCB.In order to explore the influence of the intensity of MA,the effects of MA time on the removal ratio of lignin,CrI and enzymatic hydrolysis rate of SCB pretreated by MA and MA-alkali were investigated at high milling speed(500 rpm).The results showed that after MA-alkali pretreatment of SCB,the removal rate of lignin was 85.92%with MA time of 120 min.XRD analysis showed that the CrI of MA pretreated SCB decreased from 61.2%to 15.4%and CrI decreased from 50.7%to 14.1%under the MA-alkali pretreatment with MA time of 120 min.The enzymatic hydrolysis rate of MA pretreated SCB was 71.49%with MA time of 120 min,while that of MA-alkali pretreated SCB reached 91.74%with the same MA time.