Study On Pretreatment Process And Enzymatic Hydrolysis Of Corncob For Glucose Preparation

Nowadays,we are faced with the increasingly serious global energy shortage and environmental pollution.Corncob,as an excellent lignocellulosic material,has been paid more attention due to its advantages of regeneration,biodegradability and abundance.Glucose,a promising raw material for bioethanol application,can be prepared from corncob via proper pretreatment and enzymatic hydrolysis process.Based on this background,in the present paper,different kinds of pretreatment methods and the process of glucose preparation by enzymatic hydrolysis from corncob were explored,which provided valuable information for the high value utilization of corncob.Firstly,the corncob was pretreated with dilute H2SO4 solution with the objective of removing the hemicellulose.The effects of solid-liquid ratio,acid concentration,reaction temperature and time on the hemicellulose removal rate were investigated by single factor test and orthogonal test.The optimal pretreatment conditions were obtained as follows:solid-liquid ratio of 1:10(g/ml),1.2%H2SO4,120? and 90 mins,under which the removal rate of hemicellulose reached 86.36%,and the content of cellulose increased from 33.98%to 61.52%.In addition,FT-IR,XRD and SEM analysis results showed that more holes were found on the surface of corncob fiber after acid treatment.Meanwhile,the applied pretreatment led to the increased specific surface area and the improved accessibility of the corncob fiber,which could greatly facilitate the subsequent enzymatic hydrolysis process.Subsequently,KOH treatment and enzymatic hydrolysis were conducted for glucose preparation.In detail,the influence of alkali addition,treatment temperature and time on the lignin removal rate,cellulose retention rate and digestibility efficiency were systematically investigated.The optimal pretreatment conditions were ultimately obtained as follows:KOH loading of 16%,70?,and 90 mins,under which the cellulose component and lignin removal rate increased to 86.74%and 80%,respectively.Besides,FT-IR,XRD and SEM analysis results showed that,with the increase of porosity on the micro surface of corncob,the fiber specific surface area increased.Under the optimum enzymatic hydrolysis conditions(the substrate concentration of 10%,the cellulase content of 6%,50?,and 72 h),85.22 g/L glucose was obtained in the ultimate cellulase system,thereby achieving 88.42%of glucose yield,which provided evidence that the digestion efficiency was quite excellent.In comparison,MgO was utilized as a catalyst in the pretreatment to remove lignin from corncob.Similarly,the effect of MgO addition,reaction temperature and time on the lignin removal rate,cellulose retention rate and digestibility efficiency were highlighted.The optimal pretreatment conditions were obtained as follows:MgO loading of 0.10 mol/L,190?,and 50 mins,under which the content of cellulose and the removal rate of lignin increased to 43.05%and 19.18%,respectively.According to FT-IR,XRD and SEM analysis,it could be found that the crystallinity of corncob was reduced.Furthermore,the porosity on the micro surface of corncob increased so as to promote the accessibility of corncob fiber,which supported the conclusion that MgO pretreatment could greatly facilitate the subsequent enzymatic hydrolysis for glucose preparation.Under the optimum enzymatic hydrolysis conditions,27.52 g/L glucose was allowed in the final digestion system,thus the yield of glucose reached up to 68.13%,The results of the two pretreatment methods demonstrated the increased porosity and purity of cellulose in corncob via pretreatment.It could be concluded that the yield of glucose via acid-alkali pretreatment and enzymatic hydrolysis process was higher.However,after MgO pretreatment,there were less inhibitor produced,and the pH value of the system was relatively mild,thus the process of detoxification and neutralization was not necessary,while the amount of MgO was small and costs were lower.It follows that two pretreatment methods provided theoretical basis and technical support for the preparation of high value-added product glucose.