| Straw waste is a kind of most abundant regenerated cellulose in the world,and it has great potential to produce 2,3-butanediol or ethanol after being pretreatment,fermentation and hydrolysis.This project may be very useful in enhancing the efficient usage of cellulosic biomass and relieving the energy problem in the future.Due to the utilization ratio of raw material and product yield rate are low,the conversion technology of straw waste is limited.In this dissertation,we have mainly studied the bioconversion from liquefied straw to 2,3-butanediol on the basis of liquefaction and enzymatic hydrolysis technology in the lab.Through the process of liquefaction and enzymolysis,2,3-butanediol is prepared by fermentation of Klebsiella pneumoniae CICC 10011.The total sugar concentration of liquefied straw can be increased by using double-membrane technology.2,3-butanediol is separated by aqueous two-phase extraction systems.Through the comparison of Saccharomyces cerevisiae and Candida shehatae on the effect of the bioconversion from straw to ethanol,we also obtain the best fermentation conditions of ethanol producting by hydrolyzate glucose.The results are as follows:Fristly,after double-membrane concentration of hydrolysate,the total sugar concentration of liquefied straw could be controlled between 85mg/mL and 95mg/mL.It not only provided enough carbon sources,but also realized the automation of process control.It was also beneficial to increase product concentration and reduce the cost of separation.The optimum fermentation conditions were as follows:initial total sugar concentration was 94.3mg/mL,temperature was 37℃,pH was 5.5,scale of inoculum was 10%(v/v),rotation speed was 170 r/min,fermentation time was 72h,the conversion of 2,3-butanediol was 36.47mg/mL,the yield of the total sugar converted to 2,3-butanediol was 42.5%,the efficiency was 0.51g/(L·h),and the highest yield of liquefied products converted to 2,3-butanediol was 33.4%.Secondly,the effect of different aqueous two-phase extraction systems on the extraction of 2,3-butanediol was studied,consequently the ethanol/ammonium sulphate aqueous two-phase system was chosen.The optimum phase composition for the extraction of 2,3-butanediol by ethanol/ammonium sulphate system was decided as 28%(w/w)of ethanol,22%(w/w)of ammonium sulphate for fermentation broth.In this condition,the partition coefficient and yield of 2,3-butanediol were 6.3 and 86.4%,respectively.After the broth concentration multiple was 50%(v/v),aqueous two-phase extraction system was used,the concentration of 2,3-butanediol in top phase could reach to 127.5mg/mL.Finally,through the comparison of double strains,ethanol was prepared by fermentation of Saccharomyces cerevisiae.The optimum fermentation conditions were as follows:initial glucose concentration was 60-65mg/mL,temperature was 30℃,pH was 6.0,volumes of medium was 80mL,inoculation amount was 10%,fermentation time was 36h,the yield of ethanol from the sugar was 49.3%,and the highest yield of ethanol from liquefied products was 27.3%. |
