Effect Of Nonionic Surfactant On Enzymatic Saccharification Of Cellulose

With the aggravation of energy crisis and environmental pollution, more and moreattention is paid to lignocellulosic bioethanol conversion. Enzymatic saccharification oflignocellulose is one of the key steps and makes up of its prime cost. The present study aimsdirectly to the mechanism of the positive effect of non-ionic surfactant/polymer on thesaccharrification of cellulose with the view point of reaction kinetics. The results are usefulfor the application of surfactant/polymer in the bioethanol production.A fractal kinetic model, including the rate constant and fractal exponent, had been usedto describe the complex kinetics of enzymatic saccharification of cellulose. Dilute acidpretreated corn stover was used as substrate of the enzymatic saccharrification oflignocellulose. The effect of triblock copolymer L64on the reducing sugar production wasanalysized under various conditions. The fractal kinetic analysis shows that the positive effectof L64can be obviously observed under every condition. Also, the results indicate thatglucose inhibition as well as the high lignocellulose loading is indexed by decreasing rateconstant while lignin inhibition along with high operation temperature is indexed byincreasing fractal exponent. The effect of a nonionic surfactant on the enzymaticsaccharification of lignocellulose mainly contributed to the elimination of lignin inhibition bydecreasing the corresponding fractal exponent. However, the effect of the nonionic surfactanton cellulase activity and stability was very limited.PEG10000was screened as one of the most effective surfactant/polymer during theenzymatic saccharification of cellulose Avicel PH101. The results show that the positive effectof PEG10000is very remarkable under low enzyme and low substrate loading, and anadditional β-glucosidase enhances this effect. However, the positive effect is very limitedunder high enzyme loading or high substrate loading. The profile of cellobiose concentrationover the course of enzymatic saccharification of cellulose indicates that the enzymaticsaccharification is limited by the enzymatic hydrolysis of cellobiose into glucose catalyzed byβ-glucosidase. PEG10000maily works on the conversion of cellulose to cellobiose and hasnearly no effect on on β-glucosidase activity during the enzymatic saccharification of AvicelPH101. The activation effect of the polymer PEG10000on the increase of reducing sugarconcentration may be counterbalanced to an undetectable extent. Thus, the effect of PEG10000on the increase of reducing sugar concentration in the enzymatic saccharification ofcellulose depends on reaction condition.There are different effects of L64and PEG10000on enzymatic saccharification of cellulose and lignocellulose. L64can eliminate the inhibition effect of lignin on β-glucosidaseactivity. Thus, the effect of Pluronic L64on increasing reducing sugar concentration in theenzymatic saccharification of lignocellulose is observed under various conditions. While theeffect of PEG10000on enzyamric saccharification of cellulose mainly works on theenzymatic hydrolyis of cellulose into cellobiose, which depends on the reactive conditions.Also, the results show that ethanol and butanol have nearly no inhibiton effect onβ-glucosidase, which suggests that simultaneous saccharification and fermentation (SSF) in anonionic surfactant aqueous solution is potential for the application of biomass to bioethanolproduction.