Study On Enzymatic Hydrolysis Of Corn Straw And Butanol Fermentation

Environment pollution due to the use of fossil fuels as well as their shortfall makes it necessary to find alternative energy source that are environmentally friendly and renewable. Butanol is not only an excellent feedstock chemical(in the plastics industry),a food-grade extractant(in the food and flavor industry),but also a replacement for gasoline as a fuel,a superior fuel to ethanol for higher energy content and safety.Agricultural straw is an important renewable resource.In recent years,the problem of environment pollution caused by agricultural straw has been paid increasing attention.Thus utilizing the agricultural straw for butanol fermentaion can achieve the two purposes:biofuel production from biomass and protection of environment.In the current study,corn straw was adopted as a potential substrate to investigate the optimal conditions of pretreatment,solid-state fermentation and butanol fermentation.In the pretreatment of corn straw,two chemical,namely ammonia solution and diluted sodium hydroxide solution,were used to study their effect on the corn straw's pretreatment. The results showed that the content of cellulose in NaOH-pretreated corn straw was increased by 38.9%,but lignin decreased by 7.25%and the content of cellulose and hemicellulose in NH3-pretreated corn straw was increased by 7.7%and 3.05%,respectively.Furthermore,the NaOH-pretreated corn straw was in favor of butanol fermentation and NH₃-pretreated corn straw was in favor of solid-state fermentation.In order to produce the cellulase,the NH3-pretreated corn straw was solid-state fermented by Trichoderma koningii.The results of single factor experiment showed that the optimal substrate concentration(mass of corn straw/volume of solution) was 1/3.The optimal initial pH was 4.The best inorganic nitrogen source was(NH₄)₂SO₄ and there was no obvious effect on fermentation when(NH₄)₂SO₄ concentration was between 2%～6%.The optimal inoculum size was 8%.The condition of enzymatic hydrolysis of NaOH-pretreated corn straw was studied.The experimental results showed that the optimum enzymatic hydrolysis conditions were:pH 4.5～5.0,temperature 50℃,substrate concentration 3.33%,and enzyme dosage 950 FPU/g(corn stalk),tween-80 1.5g/L.The ortho-experiment of enzymatic hydrolysis demonstrated that the best combination condition of enzymatic hydrolysis was the reaction time 60h,temperature 50℃,the amount of enzyme 750u/g,substrate concentration of 3.33%.In order to investigate the effect of single factors on butanol fermentation process,glucose was fermented by Clostridium acetobutylicum CICC 8008.The optimal conditions of butanol fermentation were:CaCO₃ concentration 0.8%,inoculum size 8%,temperature 37℃.The best norganic nitrogen was(NH₄)₂SO₄ and its optimum concentration was 1%.Enzymatic hydrolysis of corn stalk was utilized in this study to produce butanol by Clostridium acetobutylicum CICC 8008.Plackett-Burman(P-B) design and Central Composite Design(CCD) were adopted to screen crucial factors during fermentation as well as the optimization of experimental conditions.The results demonstrated that among the seven factors,namely,yeast extract,(NH₄)₂SO₄,NH₄Cl,KH₂PO₄,Na₂HPO₄,MgSO₄,FeSO₄, MnSO₄,ZnSO₄,CuSO₄,p-aminobenzoic acid,Vitamin B,Vitamin H,tween 80and CaCO₃, only CaCO₃ was selected as the most critical factor.The optimization experiment results for CaCO₃ usage,temperature and reaction time by CCD were determined to be 5.04g/L,35℃and 70h,respectively.Corresponding mathematical model was established to predict the fermentation experiment and maximum butanol yield of 6.57g/L was acquired.The result of verification experiment under the optimum conditions showed that 6.20g/L was the maximum butanol yield.This demonstrated that statistical method was a powerful tool for the optimization of butanol production from enzymatic hydrolysis of corn stalk.