Effect Of Pretreatment On Biomass Cell Wall And Enzymatic Hydrolysis Efficiency

With the increasing energy problem,seeking the renewable and clean energy has attracted more and more atentions.Transformation of agricultural and forestry waste into new materials,calorific value of energy,and chemical materials is becoming an important new tendency.However,lignocellulosic biomass is difficult to be effectively used due to its complex chemical composition and structure.In this study,wheat straw and poplar,taken as the starting materials,were subjected to the different pretreatment processes(hydrothermal,microwave-assisted alkaline and acidic)and the variation in physicochemical structure and enzymatic hydrolysis efficiency were evaluated.It provides a theoretical basis for the comprehensive utilization of lignocellulosic biomass.Taking wheat straw as the starting materials,hydrothermal pretreatment was performed at different temperature range of 120-180? with the maintaining time 0 h or 3 h.As the results,the bioconversion efficiency exhibited the appreciable differences among the chosen conditions.The optimal condition was chosen based on the sugar releasement after enzymatic hydrolysis,loss of pentose sugars,formation of sugar degradation products such as 5-HMF and furfural.Finally,the optimal hydrothermal operation for wheat straw(1:20 w/v%)was 180? and the incubation time was 0 h..Although treatment at more severe conditions with longer incubation time could lead to almost 100%conversion of cellulose,the weight losses(mainly sugars)and inhibitors in the process liquid were not adequate for an industrial scale.After alkaline petreatment with microwave-assistant irradiationthe component of the raw and treated poplar were analyzed and the changes of cell wall were correspondingly observed.The experimental results showed that in the high temperature and high alkali concentration conditions,more hemicellulose and lignin was dissolved,and the cell wall was obviously damaged.After emzymatic hydrolys,the highest glucose conversion rate(100%)was achieved at a pretreatment condition of 120? 200 mmol,as well as the bioconversion efficiency of xylose.According to the data,the conversion of glucose and xylose become higher at lower pretreatment intensity after the microwave-assistant alkali pretreatment.For the acidic pretreatment,both reaction temperature and acid concentration significantly influenced the components and physical charateristics of poplar.It is can be observed that the cell wall became broken,with the increase of temperature and acid concentration,It is also can be seen some spherical particle from lignin on the cell wall.After pretreatment,hemicellulose was degraded in great quantities and part ofdespite lignin was also changed.However,the lignin condensed in the surface of cell wall thus hindered the reaction between cellulose and enzyme,and the highest conversion rate of cellulose was only 10.5%.Microcrystalline cellulose was used as cellulose I to prepare cellulose ?,?? and ??,and cellulose crystal variants were studied by thermochemical analysis and nuclear magnetic resonance techniques.The endothermic reaction is related to the destruction of the energy consumption of the crystalline regions of the cellulose,and cellulose II has unique thermal properties.The chemical shifts of C1 and C4 in the solid and liquid NMR spectra were significantly different,indicating that the conformation of the cellulose chains changed during the dissolution process.