Directional Conversion Of Ethanol From Poplar Fiber Treated By Double-Enzyme Method

In recent years,the resources on the earth have been continuously consumed,and bioethanol has attracted wide researchers' attention around the world as a renewable and clean energy source.The conversion of low-cost,widely-sourced lignocellulose into bioethanol has good application prospects.The optimization and the pretreatment process of lignocellulose can effectively change the structure of the lignocellulosic raw material after which can promote the degradation of enzymes.Yeast,as an easily cultured,fast-growing microorganism,plays a vital role in the conversion of lignocellulosic bioethanol.In this study,poplar was used as the raw material,the pretreatment process of poplar was optimized,ethanol fermentation was used for fermentation of Saccharomyces cerevisiae,different fermentation methods were optimized and compared,and the influence of different stimulating factors on the fermentation process was explored.The main results obtained are as follows:(1)In order to improve the conversion rate of reducing sugar in poplar fiber,high-pressure steam blasting of poplar wood chips was impregnated by phosphoric acid,and then the enzymatic treatment was carried out by using a dual-enzyme method in which high-temperature pre-enzymolysis of xylanase followed by enzymatic hydrolysis.The seven factors of liquid to solid ratio,xylanase addition amount,xylanase pre-enzymatic time,xylanase pre-enzymatic temperature,cellulase addition amount,cellulase enzymatic time,and cellulase enzyme were used for single-factor experiments.Then after the Plackett-Burman design,three important factors were selected:liquid to solid ratio,xylanase pre-enzymatic temperature,and cellulase hydrolysis time.The above three factors were optimized with the Box-Behnken design and the best conditions are liquid to solid ratio of 5:1,the pre-enzymatic temperature of xylanase of 70?,and the hydrolysis time of cellulase of 53 h.At this time,the predicted value of reducing sugar conversion can reach 159.64 mg/g.(2)The poplar fiber hydrolyzed via a xylanase-aided two-stage pretreatment was compared with the poplar fiber hydrolyzed via only a cellulase pretreatment,using scanning electron microscopy.The xylanase-aided treatment revealed a surface with a more damaged structure,indicating that the utilization of xylanase could further improve the effects of hydrolysis on poplar fibers.(3)Using Saccharomyces cerevisiae CICC-1517RM for semi-synchronous saccharification fermentation and simultaneous saccharification fermentation for ethanol production,combined with single-factor test and Box-Behnken response surface optimization test,the optimal temperature,the rotation speed,and the inoculation amount conditions were respectively:30?,170 rpm,11%And 39?,170 rpm,10%.The predicted values of ethanol production were 15.67 mg/mL and 14.75 mg/mL,respectively,and the actual measured values in the experiment were similar to them.However,the ethanol content of optimized semi-synchronized saccharification fermentation is only 6.24%higher than that of optimized synchronous saccharification fermentation.Considering the time cost,it is more appropriate to choose synchronous saccharification fermentation to obtain ethanol production.(4)By investigating the effects of acetic acid and furfural on the fermentation of Saccharomyces cerevisiae CICC-1517RM,it was found that both acetic acid and furfural had an inhibitory effect on the strain.When the concentration of acetic acid and furfural reached 7 g/L and 2.5 g/L respectively,the growth of Saccharomyces cerevisiae CICC-1517RM was basically inhibited.