Process And Mechanism On The Transformation And Co-production Of Functional Products From Polysaccharide Feedstocks By High-effective Pretreatments

Industrial solid residues,such as sugarcane bagasse?SCB?and Camellia oleifera shell?COS?are rich in cellulose and hemicellulose polysaccharides.They are perfect feedstocks for the transformation of energy and the co-production of functional products.Many polysaccharide feedstocks cannot be used in high value on an industrial scale due to the existence of lignin.In this study,the effect of various pretreatments on the structural components and transformation of polysaccharide feedstocks were compared.On the one hand,the effect of pretreatment methods on the enzymatic hydrolysis and fermentation processes to ethanol of cellulose and hemicellulose from SCB were deeply investigated by biological transformation method,thus achieving the fermentation at high-solids loading;on the other hand,the hemicelluloses from SCB and COS were used for the production of xylooligosaccharides?XOS?with main degree of polymerization?DP?of 2-5 by pretreatments.The mechanism of catalytic degradation of hemicellulose was described,and the pretreated solid residues were directly used for the first time to co-produce activated carbon?AC?,thus realizing the high-value utilization of COS.The main conclusions were as follows:Steam explosion?SE?pretreatment can significantly improve the degradation rate of hemicelluloses and destroy the dense structure of lignin,thus improving substrate accessibility,and increasing the efficiency of enzymatic hydrolysis.Glucose yields of SE pretreated SCB increased with the increase in the dosage of enzyme during 72 h of enzymatic hydrolysis.The highest glucose yield of SE pretreated SCB reached to 74.99%,which was increased by 57.86%with the same enzyme loadings of 30 FPU/g-cellulose compared with raw SCB.Sapindus peel?SP?containing natural surfactant can evidently reduce the surface tension of hydrolysate and stable the activity of enzyme at an economic concentration of 1.2g/L.The highest glucose yield was of 80.99%with the cellulase loading of 10 FPU/g-cellulose and the addition of 1.2 g/L SP,which was 2.22 times higher than that detected in the hydrolysis process without the addition of SP.The effects of steam explosion pretreatment with dilute acid impregnation?SE-DAI,210? for 5 min?,low-pressure steam explosion pretreatment with dilute acid impregnation?LP-SE-DAI,190? for 10 min?,Soda green liquors?Soda GL?combined with ethanol?Soda GL-ethanol?and hydrogen peroxide?GL-H₂O₂?pretreatments on the transformation of ethanol from SCB were compared via simultaneous saccharification and fermentation?SSF?process.100%and 88.25%of hemicelluloses were solubilized after pretreatments,which greatly improving the ethanol yields?of the theoretical?of 93.19%and 92.20%by SE-DAI and LP-SE-DAI,respectively.81.59%and 33.01%of lignin were removed through Soda GL-ethanol and Soda GL-H₂O₂pretreatments,respectively.In addition,the ethanol yield reached to 72.58%after Soda GL-ethanol pretreatment,and some active lignin produced from pretreatment process could lower the reduction potential of the system,thus producing more glycerol.The mortality of high content yeast?>60%?of Soda GL-H₂O₂pretreated SCB resulted in the highest content of lactic acid,thus leading to the maximum ethanol yield of only 20.92%,which was equal to the raw material??20%?.Higher ethanol concentration can be obtained by cofermentation process using mixed strains and increasing substrate loading.Soda GL-ethanol pretreatment is a promising pretreatment method for delignification while improving both glucan and xylan conversion efficiencies of SCB.The effects of different yeast cell mass ratio of common S.cerevisiae?CSC?to thermophilic S.cerevisiae?TSC?on the bioethanol production of Soda GL-ethanol pretreated SCB were investigated via simultaneous saccharification and cofermentation?SSCF?process.Compared to the fermentation process only using the CSC with the ethanol yield of 70.15%,the synergistic effect between CSC and TSC could significantly improve the utilization rate of total sugars and achieve fermentation process at high-solids loading.The higher ethanol concentration of 23.22 g/L was obtained from Soda GL-ethanol pretreated SCB with 1.5 m L Soda GL/g-dry substrate?DS?at 5%?w/v?-solids loading and a CSC-to-TSC yeast cell mass ratio of 1:2?w/w?;using 10%-solids loading under the same conditions,the ethanol concentration increased to 42.53 g/L.The ethanol concentration dramatically went up to 68.24 g/L with increasing the solids loading to 15%?w/v?using a CSC-to-TSC yeast cell mass ratio of 1:3?w/w?,thus effectively reducing the ethanol distillation cost.The effect of the amount of lignin from SCB on the transformation of ethanol were studied and compared in different fermentation systems.The solid-to-liquid ratios and pretreatment temperatures of peroxide-HAc pretreatment were optimized,and the pretreated SCB after optimization was used for the bioethanol production via SSCF using TSC in deionized water?DW?and sodium citrate buffer solution?SCS?systems,respectively.Compared with DW system,SCS system can decrease the residual sugars content of pretreated SCB during SSCF process.100? pretreated SCB obtained the lowest residual lignin content of 2.88%,thus resulting in the highest ethanol yield of 92.10%in DW system.The addition of Tween 80 can significantly improve the fermentation performances of 80? pretreated SCB that had a relatively high residual lignin content of 16.44%.Besides,the concentration of glycerol and acetic acid byproducts from 80? pretreated SCB can be decreased by DW and SCS systems,respectively.Peroxide-HAc pretreatment could increase the XOS yields of xylan that was extracted from peroxide-HAc pretreated SCB by 20%?w/v?Na OH.The highest XOS yields of 80? pretreated SCB was 41.38%using 4 mg/m L xylanase after 2 h by enzymatic hydrolysis,of which the yields of X₂and X₃were 17.68%and 4.45%,respectively.Zn Cl₂ can not only be used for the catalytic pretreatment of COS,but also used as an activator for the preparation of AC.Zn Cl₂as one inorganic salt exhibited excellent catalysis on the removal of xylan and the release of XOS from COS owing to its Lewis acid and Br?nsted acid characters as well as the effect of the hydronium of water molecules?H₃O⁺?from water autoionization in aqueous solution.The effect of pretreatment temperature,reaction time and Zn Cl₂ concentration on the contents and DP distributions of XOS were optimized.The maximum value 61.38%of XOS yields including 16.94%X₂ and 18.42%X₃,peaked at 170? for 30 min using 0.5%?w/w?Zn Cl₂.The solid residues derived from the production process of XOS are rich in cellulose and lignin?up to 75%carbon?,which were directly used as the precursor for the first time in the co-production of AC.It has been observed that the maximum iodine value and BET surface area of the prepared AC were5623.94 mg/g and 1244.46 m²/g,respectively,using 2.20 M Zn Cl₂ as the activating agent.The high surface area of the obtained AC is comparable to the surface areas of commercially available AC.