Investigation On Effects Of NaOH/AQ Pretreatment For Enhancing Enzymatic Digestibility Of Corn Stalk

The lignocellulose biomass is one of the most abundant nature resources in the global.It can be transformed into oligosaccharides or fermentable sugars by some suitable pretreatment processes,and further into the high-valued bio-chemicals products or fuel ethanol,which shall provide one available measures for the human kinds with the less dependment on fossil resource,thus slow down the climate changes because of global warming.It was investigated that the effects of the main factors,i.e.reaction temperature,reaction time and NaOH dosages,of the NaOH/AQ pretreatment,and was discussed the effects of the lignin removal rate on the enzymatic digestibility of the NaOH/AQ pretreated corn stalk in this paper.The conditions of the pretreatment process was optimized in term of the lignin removal and the polysaccharides conversion rate.The suitable conditions of the emzymatic hydrolysis was obtained by using the response surface method.The mass balance calculation of sugars components in the corn stalk,the pretreated solids and the emzymatic liqulids based on the HPLC analysis was completed.Four chemimechancal pretreatment methods,i.e.,the chemical impregnation plus mechanical treatment in the refiner,were carried out as well.The performance differences between the NaOH/AQ pretreatment and the four chemimechanical pretreatment were compared in the end of this paper.In this research,the delignification rate and polysaccharide conversion rate were selected as index,and the factors,i.e.,NaOH content,reaction time and reaction temperature,have been investigated in the process of NaOH/AQ pretreatment.NaOH dosages have an important impact on the delignification rate,and the rate of delignification could rearch to 65%-85%with a higher polysaccharide conversion.Furthermore,the effect of raw material enzymolysis is closely related to the lignin removal rate.Analyzed by single factor and orthogonal experiments,the optimal condition of NaOH/AQ pretreatment was 160?,2.8% w/w NaOH and 90 min,which obtains the optimum efficiency of pretreatment.Besides,the influence ofvarious factors on the hydrolysis conversion sequence is: the reaction time > NaOH dosage >reaction temperature within the scope of the orthogonal design of the experimentThe enzymolysis condition of NaOH + AQ pretreatment was investigated.According to response surface analysis(RSM),the optimal condition of enzymolysis is cellulase dosage of29.82FPU/g,71.48 h,50.73?,and other condition of enzymatic hydrolysis,i.e.,a dosage of?-glucosaccharase of 10 CBU/g and the substrate concentration of 2.5% were arbitrarily determined..The reducing sugar yield is 88.35% according to the calculation by the regression equation,and the actual reducing sugar yield is 89.76%.The carbohydrate composition of the hydrolysate were mainly glucose and xylose.Based on the HPLC analysis,the total sugar conversion rate was 78.09 % at the optimal condition in the NaOH/AQ pretreatment process.The performances of NaOH/AQ pretreatment and four kinds chemical pretreatment,with mild chemical processing conditions,combined with mechanical refining were compared in term of solids yield,lignin removal,reducing sugar yield and polysaccharides conversion rate.Only part of the lignin and hemicellulose were removed for the four chemical mechanical pretreatment for corn stalk.Because of a higher lignin content was removed,due to the strong chemical pretreament conditions in NaOH/AQ pretreatment,its polysaccharides conversion rate is 75.56%,the highest one among the five compared processes;The polysaccharide conversion rate for NH3·H2O chemimechanical pretreatment,about 70.49%,is the second one.The NaOH/AQ pretreatment and NH3·H2O chemimechanical pretreatment can both be used as a promising pretreatment process.