Butanol Production From Lignocellulosic Biomasse Hydrolysates By Clostridium Tyrobutyricum △Ack-adhE2

At present,sugar and starch are the main substrates in acetone-butanol-ethanol(ABE)fermentation.The use of these substrates has led to the increasing cost and affected the final large-scale and industrialized progress of butanol fermentation.In addition,As an important food resource,the utilization of starch fermentation substrate will lead to a series of social problems,such as the increase of food price.Therefore,how to solve the related problems such as substrate cost has become an important issue in butanol fermentation.Lignocellulose is the most abundant biomass resource on earth.Cellulose and hemicellulose in lignocellulose raw materials can be converted into carbohydrate used by microbial fermentation after acid hydrolysis or enzymatic hydrolysis.Therefore,butanol fermentation was investigated by the engineering Clostridium tyrobutyricum Δack-adhE2 using lignocellulose as raw materials in this thesis,in order to solve the high cost of substrates in traditional fermentation.The principal results was as follows:(1)Optimization of fermentation medium by response surface methodology,with focus on the effects of ferrous iron sulfate,dipotassium phosphate and ammonium sulfate concentrations.The Box–Behnken design results indicated that the maximum butanol concentration of 15.21 g/L was obtained when ferrous iron sulfate,dipotassium phosphate and ammonium sulfate concentrations were 0.02 g/L,2.75 g/L and 5.71 g/L,respectively.(2)Engineered Clostridium tyrobutyricum Δack-adhE2 immobilized in a fibrous-bed bioreactor was used for butanol production from glucose and xylose present in the hydrolysates of low-cost lignocellulosic materials including corn fiber,cotton stalk,soybean hull,and sugarcane bagasse.The biomass hydrolysates obtained after acid pretreatment and enzymatic hydrolysis were supplemented with corn steep liquor and used in repeated-batch fermentations.Butanol production with a high titer(15 g/L),yield(0.30 g/g),and productivity(0.30 g/L?h)were obtained from cotton stalk,soybean hull,and sugarcane bagasse hydrolysates,while corn fiber hydrolysate with higher inhibitor contents gave inferior results.(3)Simulation with Software SuperPro Designer was performed for the butanol production of butanol fermentation process.Results indicated that,for a plant with an annual production capacity of 50,000 t,the production cost of biobutanol is 0.95$ /kg or $2.85 / gal.