Study On Alkaline Sulfite Pretreatment Process Of Corncob Residue

Using abundant and renewable lignocellulosic biomass to produce fuels as well as chemicals through biorefinery process to replace fossil fuels is considered as an effective way to mitigate the energy crisis.Agricultural and forestry waste is an inexpensive lignocellulosic resource.A large amount of hydrolysed residue?corncob residue?was produced during the production of furfural and xylose from the discarded corn cob.In order to improve the comprehensive utilization effect of corncob,the lignin in corncobs residue was extracted by alkaline treatment,following the enzymatic hydrolysis and fermentation to produce fuel ethanol.However,lignin solution need acidification to be purified,which not only increases the cost of the whole process,but also generates acidic waste,resulting in a substantial increase of alkali lignin prices.In addition,the cellulose will be partially degraded into disaccharides or monosaccharides,which were difficult to recover,leading to lower the utilization of cellulose.In this paper,alkaline sulfite pretreatment was used to replace alkaline pretreatment of corncob residues.It is of great significance to improve the utilization of corncob in this process,which could obtain high valued sodium lignosulfonate solution while maintaining the high enzymatic hydrolysis efficiency of pretreatment substrate.The conditions of alkaline sulfite pretreatment were optimized by control variable method.The optimum pretreatment conditions were as follows: pretreatment temperature was 160 ?,sodium sulfite dosage was 10%?w/w?,sodium hydroxide dosage was 5%?w/w?,and liquid-solid ratio was 6 m L/g.Under this condition,86.1% lignin in corncobs residue could be removed,and the retention rate of cellulose was 82.4%.The substrate enzymatic digestibility?pH=5.5,cellulase loading of 5 FPU/g-glucan?at 72 h after pretreatment was 85.1%.Meanwhile,the yield of sodium lignosulfonate in the spent liquor reached 31.5 g/100g-CCR,and its purity reached 75%.In the alkaline sulfite pretreatment of corn cob residue,the addition of sodium hydroxide enhanced the removal rate of lignin in the raw material,but it increased the loss of cellulose.The sodium sulfite was conducive to the retention of cellulose but was weak in removing lignin.The effect of sodium hydroxide on the enzymatic hydrolyse and the yield of lignosulfonate in pretreatment solution was greater than that of sodium sulfite.The predictive reaction model of alkaline sulfite pretreatment of corn cob residue was established.The Lignin Factor?LF?,which is a parameter for predicting the content of lignin in the corncob residue after pretreatment,was defined by the fitting by a large amount of experimental data.The lignin content in corncob residue predicted by LF after pretreatment was in good agreement with the experimental data.A sulfonated degree factor?SF?,which is related to the content of sulfonic acid groups in the substrate,was also defined.An overall hydrolysis factor?OF?was formed with LF and SF.By fitting a large amount of experimental data,the relationship between OF and the substrate enzymatic digestibility was built: SED=SED_Max-?SED_Max×e^-OF/?,OF=LF+?SF,where ? and ? are constants determining by characteristics of substrate.The substrate enzymatic digestibility of corncob residue could be predicted by using this function,and the deviation between predicted value and experiment value was less than ± 10%.The relationship between lignin factor and the yield of sodium lignosulfonate in the pretreatment liquid was also established,which would provide a reference for the selection of alkaline sulfite pretreatment conditions.