The Conversion Of Bioethanol And Biobutanol From Bagasse

Becuase of the shortage of fossil fuels researchers worldwide are eager to developbiofuels as substitution of fossil energy. Bioethanol and biobutanol from naturallignocellulose are considered as promising substituents because they are excellent ingeographical suitability, clean, environmentally friendly and renewable. Currently, most partsof bagasse are burned as boiler fuel directly except some parts used for papermaking. Thissituation not only wastes the resources, but also pollutes the environment. In this study,sugarcane bagasse was used as feedstock for ethanol and butanol production to increase theutilization of resources.The influences of several inhibitors on butanol and ethanol fermentation wereinvestigated. The toxicity on ethanol fermentation from highest to lowest are: phenoliccompounds, formic acids, and furan derivatives. The inhibition of formic acid was from thechange of the pH. The furfural caused a lag-phase in ethanol fermentation, but did notinfluence the final ethanol yield. The synergistic inhibitory effects of phenolic compounds,furan derivatives and formic acids was even stronger. The ethanol yield was decreased by88%in the presence of furfural (1g/L), HMF (1g/L), formic acid (1g/L), vanillin (1g/L),and guaiacol (1g/L). The influences of inhibitors on butanol were similar to ethanol exceptfurfural. When the furfural reached2g/L, the growth of the bacteria and the butanolfermentation was inhibited by90%.1g/L of lignin caused a15%decrease in ethanol yield.The addition of0.01mol/L MgSO4was able to shield the lignin inhibition on the ethanolfermentation. However, the low concentration of lignin (less than2g/L), did not inhibitbutanol fermentation, and less than0.5g/L lignin could promote fermentation weakly. Whenthe lignin concentration reached4g/L,20%butanol yield was inhibited.Secondly，the pretreatment of bagasse with acetic acid, the cellulase hydrolysis andsaccharification of pretreated bagasse residues(PBR) were studied. In the single-stageenzymatic hydrolysis process, the substrate enzymatic digestibility increased sharply at first30h and then increased gradually. The increase of the concentration of HAc in preatment hada positive effect on the substrate enzymatic digestibility. The enzymatic hydrolysis glucose yield(EHGY)(82%) of pretreated bagasse was achieved when the HAc concentration andsubstrate concentration were0.5%and5%, respectively. In this condition, the SED couldreach89%. In batches feeding multi-stage enzymatic process, the inhibition from inhibitoraccumulation could be effectively reduced and the SED decreased with the increase of initialsubstrate concentration.When treated with enough activated carbon(AC), nearly all the sugars (total8.4g/L) inpretreated liquor of bagasse were consumed by the strain,1.6g/L butanol and2.3g/L totalABE（acetone,butanol and ethanol） were produced compared with0g/L by the untreatedliquor. The evaporation could remove more than95%furfural in the liquors. The butanol andABE production from concentrated liquor treated by AC could reach6.6g/L and9.6g/L,respectively. The ABE production of5%and10%substrate concentration were increasedafter adding cellulase and β-glucosidase to the medium, which indicated that the supplementof cellulase and β-glucosidase with actively growing culture in the low substrateconcentration (lower than15%) could increase the butanol and ABE production and take fulladvantage of the glucan in the substrate.The furfural adsorption were followed more closely the pseudo-second order model. Theequilibrium adsorption capacity decreased with the increase of AC dosage and decrease of thefurfural. Equilibrium data measured agreed extremely well with the Freundlich isothermmodel. The equilibrium adsorption of furfural in the pretreated liquor was first increased andthen decreased with the increase of the dosage of activated carbon, which was resulted fromthe presence of lignin degradation products in the pretreated liquor and selective adsorption ofactivated carbon on lignin degradation products was stronger than furfural.