Alcohol fuels production by fermentation from chemical pretreatment and enzymatic saccharification of corncob

Abstract

This study was aiming for produce biobutanol from corncob to substitute fossil fuel, which approach the shortage in the near future. The first work focused in the optimization of biobutanol production using 2 bacterial strains, Clostridium beijerinckii TISTR1461 and Clostridium acetobutylicum TISTR1462, provided by Thailand Institute of Scientific and Technological Research (TISTR). They were chosen as they have a potential in the excretion of solventogenic products. The fermentation was performed via the ABE (Acetone-Butanol-Ethanol) fermentation or Weizmann process under the anaerobic condition. The comparison between 2 strains were studied in the typical condition and further investigated in the regulation of ammonium acetate and D-xylose consumption which was expected to increase the biobutanol production. The studied condition was applied to corncob hydrolysate obtained from dilute sulfuric acid pretreatment instead of synthetic medium to monitor the possibility of carbon source substitution (mainly glucose and xylose). The positive result of acid pretreated corncob substitution led to the second work of base pretreatment (Sodium hydroxide). The base pretreatment and enzymatic hydrolysis of corncob was studied using microwave irradiation as a heating source which was expected to hydrolyse better than conventional heating source. The characterization of corncob after base pretreatment was evaluated along with the result of total monomeric sugar after enzymatic hydrolysis using Celluclast 1.5L. Obtained sugars were used as a substrate for ethanol production using Saccharomyces cerevisiae instead of C. beijerinckii since it was inhibited by salt from base pretreatment. Then, acid pretreatment of corncob was promised to be the better route than base pretreatment. The third part of this work then involved with the optimization condition of acid pretreatment by sulfuric acid using Response Surface Methodology (RSM). The characterization of corncob before and after pretreatment under the optimum condition was carried out to observe surface morphology of corncob and its relation to enzymatic hydrolysis. Sugars obtained from sulfuric pretreatment combined with enzymatic hydrolysis were subjected to use as a substrate for ABE fermentation. However, due to the inhibitors from sulfuric pretreatment, sulfuric hydrolysed corncob cannot be applied as a substrate for ABE fermentation without the detoxification process which consume cost and time. The alternate type of acid, nitric and phosphoric acid, were studied in the fourth work. Since it was found that phosphoric pretreated corncob could be used as a substrate for ABE fermentation, the condition of enzymatic saccharification was optimized using RSM and confirmed by non-commercial enzyme from Siam Victory Company. The effect of cellobiase loading was studied to enhance the released sugars of cellulase at the optimum condition. Then the hydrolysate was used as a substrate for ABE fermentation under different conditions to define its limitation for bacterial growth and biobutanol production.