Preliminary Research On Butanol Production From Hydrolyzation Corncob Residue

As the consumption of fossil fuels,the energy problem has become the focus and attracted much more attention these years.Fossil fuels are the lifeblood of industrial civilization but are non-renewable.New energies are necessary to substitute fossil fuels. Cellulose,the most abundant biopolymer in the world,is considered to be a promising resource for energy production.The highly-efficient conversion of cellulose to fuels might relieve or even solve the energy problem in the future.Cellulosic ethanol has been accepted widely by more people and brought some hope recently.Cellulose could be hydrolyzed to fermentable sugars and transformed to other products in the next step.We have isolated a Penicillium decumbens 114-2 with a complete cellulolytic enzyme system from soil.A catabolite-repression-resistant mutant JU-A10 was also obtained using physical and chemical mutagenesis from 114-2. JU-A10 could produce higher amounts of cellulase and has been used to cellulase and cellulosic ethanol production.Butanol is not only an important industrial material but also an excellent alternative fuel.Butanol is a four carbon alcohol with a higher energy content,which made it a better biofuel than ethanol.In this paper,cellulase produced by P.decumbens JU-A10 was used to degrade corncob residues,a waste of xylo-oligosaccharide production in Shandong Longlive Bio-technology Company,and then butanol was produced from fermentable sugars by Clostridium acetobutylicum.The main results of the thesis are as follows:1.Saccharification of corncob residues using cellulase produced by P. decumbens JU-A10.P.decumbens JU-A10 was cultured to produce cellulase and the broth was applied to the saccharification of corncob residues.As the optimum temperature of cellulase produced by P.decumbens JU-A10 was between 40℃and 50℃,we usually performed the saccharification experiment at 50℃in the previous work.Considering the the optimum growth temperature of the Clostridium used in this study was 37℃,both 37℃and 50℃were used and the results were compared.When saccharification was performed at 50℃,more reducing sugars were released in the prior period but less in the latter period than that at 37℃.After a 3 days' saccharification,37.1 g / L and 37.7 g / L reducing sugars were produced at 37℃from corncob residues and corncob powder respectively,which were 9.7 g/L and 7.6 g/L more than that at 50℃.So we choose 37℃as the temperature of simultaneous saccharification and fermentation.We also pretreated corncob residues with dilute sulfuric acid,dilute NaOH solution or tap water at 121℃.Corncob residues pretreated with dilute sulfuric acid released the most,while that pretreated with dilute NaOH solution released the least reducing sugars after saccharification.So we used dilute sulfuric acid or tap water to pretreat corncob residues.2.Fermentation characteristics of Clostridium acetobutylicum CICC8016 and ATCC55025Clostridium acetobutylicum CICC8016 was purchased from China Center of Industrial Culture Collection;Clostridium acetobutylicum ATCC55025 was kindly provided by Dr.Li Fuli(Qingdao Institute of Biomass Energy and Bioprocess Technology,CAS).C.acetobutylicum was cultured for butanol production for 3 to 4 days.Based on the medium P2 which was suitable for the growth of CICC8016,glucose or yeast extract of different concentration were compared for their effects on butanol production. When the medium contained 25 g / L glucose and 0.63 g / L yeast extract,a high volume production was obtained,including 2.54 g / L acetone and 7.21 g / L butanol.C. acetobutylicum ATCC55025 could also grow well and produce butanol when cultured with P2 medium.When 30 g / L glucose,8-15 g / L yeast extract or 8 g / L ammonium sulfate was in the medium,4 g / L acetone and 14 g / L butanol were detected.By comparing the two strains,C.acetobutylicum ATCC55025 consumed more sugars and produced more butanol than C.acetobutylicum CICC8016.When the initial pH was controlled at a low level,C.acetobutylicum could produce more acetone and butanol in the prior period,but the effect was not obvious.3.Cellulosic butanol production via simultaneous saccharification and fermentation(SSF)As C.acetobutylicum exhibited a high protease activity,cellulase might be hydrolyzed to support the growth of bacteria.When cellulase was added to the culture of C.acetobutylicum CICC8016 and ATCC55025,86%and 69%filter paper activities were assayed after 93 h respectively,indicating butanol production via simultaneous saccharification and fermentation was feasible.C.acetobutylicum ATCC55025 could produce butanol from cellobiose detected in the saccharification slurry of corncob residues.At the same time,xylose could also be used.A high butyric acid concentration was detected after 3 days' SSF of corncob residues using C.acetobutylicum CICC8016.Addition of glucose in the fermentation process caused an increase of butanol,while butyric acid showed no decrease. Glucose-limited fed batch culture might be helpful for butanol production.When C. acetobutylicum ATCC55025 was used,butanol production of corncob residues SSF was higher than that of pre-saccharification for 12 h.Butanol production was higher for filter paper SSF than corncob residues SSF.Use of pretreated corncob residues(50% ethanol,200℃for 20 min) brought about a higher butanol production than untreated corncob residues.