Ethanol Production From Sweet Sorghum Residue

Fuel ethanol prodution from lignincellulose is one of the effective ways to alleviate the energy crisis. Large amount of sweet sorghum residue was difficult to process.The problem can be solved by transforming this lignincellulose resources to ethanol.Ethanol production from sweet sorghum residue was studied. Sweet sorghum residue was hydrolyzed with katalysts,such as H2SO4,H3PO4,HC1, under mild conditions. Orthogonal experiments were carried out to investigate the effect of main factors,namely, reaction temperature, acid concentration,time, solid and liquid ratio. Sugar concentration was measured, results showed that the optimal condition should be120℃,80g·L-1,80min and1:10, respectively. Under these conditions,0.3024g sugar/g dry material was obtained.During the phosphoric acid pretreatment of sweet sorghum residue sweet sorghum residue, hemicellulose is hydrolyzed to monosaccharides, and meanwhile, by-products which may influence ethanol fermentation are generated. In this study, five by-products, acetic acid, formic acid, vanillin, furfural and5-hydroxymethylfurfural, were identified by HPLC in the phosphoric acid hydrolysate of local sweet sorghum residue. The concentrations of acetic acid and vanillin were higher. Overliming might remove some of the by-products, but no significant influence on the concentrations of carboxylic acids was observed.The work indicated that ethanol production was inhibited by formic acid and acetic acid to a lesser extent than that to the growth of yeast cells, formic acid was shown to be more toxic than acetic acid, and severe inhibition was observed at the concentration of1g·L-1half of the concentration for acetic acid which showed remarkably inhibition effect. Vanillin caused a longer lag-phase for the growth of yeast cells when its concentration was2g·L-1,while the lag-phase was not obvious at lower concentrations, and complete inhibition on the ethanol fermentation was observed at the concentration of6g·L-1.5-Hydroxymethylfurfural was showed to remarkably inhibit ethanol production, but the biomass yield was a little bit higher than that of the control experiment. Furfural at0.5-1.5g·L-1inhibited the growth of yeast cells, but the ethanol yield was higher. It was found that vanillin, furfural and5-hydroxymethylfurfural could be assimilated and metabolized by Pachysolen tannophilus.The synergetic impact of the toxic components on the ethanol fermentation was observed. It was observed that these fermentation inhibitors stimulated the consumption of xylose, improving the ethanol production when their concentrations were low.Conditions of Simultaneous Saccharifieation and Fermentation of sweet sorghum residue was studied.The optimum technical parameters as follow:temperature was37℃, fermentation time was72h, the dosage of cellulase was60U/g, inoculation rate was10%.Under this conditions, the transform rate was0.314g/g substrate.The technics of ethanol production from sweet sorghum residue was finalized.firstly,sweet sorghum residue was pretreated by diluted phosphoric acid,then hydrolysate was detoxified by Ca(OH)2,and fermented with Pachysolen tannophilus, mean while, simultaneous saccharification and fermentation was performed on hydrolysis residue with cellulase and Saccharomyces cerevisiae. The ethanol yield was0.22g/g sweet sorghum residue. The results showed that ethanol production from sweet sorghum residue is feasible and has a good prospect.