Combined Alkali Pretreatment Of Sugarcane Leaves And Ethanol Production

Our group had found that metal alcoholates were very strong pretreatment agents in lignocellulose pretreatment.In this research,the weak base reagent calcium hydroxide was combined with the strong base reagent sodium ethoxide as combined alkali to pretreat the sugarcane leaves（SCL）.The enzymatic hydrolysis was carried out under the optimal pretreatment conditions.Then the fermentation using Saccharomyces cerevisiae strain was carried out to convert the sugarcane leaves into bioethanol.The experiment using strong alkali reagent sodium ethoxide alone to pretreat sugarcane leaves showed that 3%sodium ethoxide had the best results in both pretreatment and enzymatic hydrolysis.Under these conditions,the lignin removal rate,the content of glucan and xylan was 90.14%,55.16%and 28.00%,respectively.The total fermentable sugar concentration and total enzymatic efficiency could reach15.82 g/L and 84.90%respectively.The pretreatment conditions of combined alkali were optimized using orthogonal array.The optimized conditions obtained were pretreating sugarcane leaves with C₂H₅ONa:Ca（OH）₂ volume ratio of 4:1 at 121℃for 30 min.Under these conditions,the lignin removal rate,the content of glucan and xylan was 86.26%,52.00%and30.63%,respectively.The total fermentable sugar concentration and total enzymatic efficiency could reach 14.82 g/L and 80.02%respectively.These pretreatment results were similar to those of using strong base alone.Under the optimal combined alkali pretreatment conditions,the enzyme loading was optimized in enzymatic hydrolysis.The 30 FPU/g substrate group had the best hydrolysis effects,while the total fermentable sugar concentration and total enzymatic efficiency could reach 16.99 g/L and 91.69%,respectively.Fermentation of sugarcane leaves to produce ethanol was performed using S.cerevisiae.In the separate hydrolysis and fermentation（SHF）,the highest ethanol concentration could reach 4.26 g/L,while the theoretical ethanol yield was 72.31%and the sugar alcohol conversion rate was 76.59%.In the simultaneous saccharification and fermentation（SSF）,the highest ethanol concentration could reach3.08 g/L and the theoretical ethanol yield was 52.36%.The SHF demonstrated better results compared with SSF.This research showed that using combined alkali in pretreatment,20%of the dosage of strong alkali could be saved and the reaction time could be shorten compared with using strong base alone.Thus both costs and environmental pollution could be reduced using this method.These advantages made the combined alkali pretreatment suitable for large-scale production.