Regulation And Control For Subcritical Hydrothermal Pretreatment Process Of Sweet Sorghum Bagasse Based On The C₅-C₆ Co-metabolism Technique

Sweet sorghum,as non grain materials,could be widely and economically used in the ethanol industry.The sweet sorghum residues as waste in the industry containing the cellulose and hemicellulose of 60%are an excellent biomass feedstock.Currently,they mainly used for producing feeds or drying as fuel and the components of hemicellulose and cellulose in the sweet sorghum residues could not be fully utilized,which restrict the development of sweet sorghum ethanol industry.In recent years,with the development of C₅-C₆ co-metabolism technology,the new requirements have been put forward for the treatment of cellulosic raw materials.In the study,the subcritical hydrothermal pretreatment and regulation technology of sweet sorghum residues were put forward to realize the high added value of sweet sorghum residues and alleviate the shortage of raw material for sweet sorghum ethanol production.The recycling regulation of the subcritical hydrothermal pretreatment process were firstly used to pretreat sweet sorghum residue.The severity factor?R₀?was introduced into the subcritical hydrothermal pretreatment process.Meanwhile,with the maximum concentration of xylose as the target,the optimal severity factor LogR₀=3.96,namely the reaction temperature of 180°C and the reaction time of 40min,was obtained.Based on the above study,the content of acetic acid,lactic acid and the mixed acids in the subcritical hydrothermal pretreatment were investigated,respectively.The results showed that the suitable concentration of acetic acid and lactic acid were respectively 0.8 wt%and 1.2 wt%.At the same time,when the mixed acids concentration was 1 wt%,the optimal ratio of lactic acid and acetic acid was60%.With the largest concentration of xylose as the optimal target,regulating the ratio of lactic acid and acetic acid of was 60%,the method of CCD was used to optimize the condition of the recycling regulation of subcritical hydrothermal pretreatments.The optimal conditions:reaction temperature of 178°C,reaction time of 43 min,mixed acid concentration of 1.12 wt%;the predicted xylose concentration could reach 9.06 g/L,experimental value was 8.79 g/L and the prediction accuracy was 97.02%,which indicated that the optimization model was reliable.Based on the investigation of the recycling regulation of the subcritical hydrothermal pretreatments,the kinetic model of hydrolysis of sweet sorghum residues was established.By the fitting of experimental results,the rate constant of xylose formation?k₂?under different conditions were obtained,as follow:the recycling regulation of organic acids as catalyst>lactic acid as catalyst>acetic acid as catalyst>subcritical water as catalyst;the rate constants of furfural?k₄?were displayed as:acetic acid as catalyst>lactic acid as catalyst>the recycling regulation of organic acids as catalyst>subcritical water as catalyst.Compared with the single acid,lactic acid/acetic acid,as catalyst,the recycling regulation of subcritical hydrothermal pretreatment of sweet sorghum residues could effectively promote the hydrolysis of hemicellulose and inhibit the formation of byproducts.According to the method of density functional theory?DFT?,the mechanism of hemicellulose hydrolysis catalyzed by acetic acid or lactic acid was investigated by using the DMol³ module of Materials and Studio.The result showed that the glycosidic bond breaking in the lactic acid environment was higher than that in the acetic acid environment.