Effective Hydrolysis Of Wheat Straw Polysaccharides Based On Organic Acid Pretreatment

Based on the integration of bioengineering and chemical engineering technology,wheat straw was used as the main research object,the mild and safe organic acids（acetic acid and xylonic acid）and cellulase were selected as the main catalysts.According to the thermodynamics and kinetic of the hydrolysis reaction of two cell wall polysaccharides of hemicellulose and cellulose,as well as the analysis of the difference in migration and conversion performance during bioprocessing,the green cascade utilization and poly-generation technology idea was proposed,which realized the‘one-step method’integration effect of directional hydrolysis of xylan and pretreatment of raw materials,that is high-efficiency co-production of xylo-oligosaccharides（XOS）and fermentable monosaccharides.This provided the theoretical basis and key technical support for the totalization and high-value industrial transformation of wheat straw polysaccharides.The main research results are as follows:（1）Based on the double-effect target of hydrolysis of hemicellulose xylan and cellulose polysaccharide,the preparation method and technical process of poly-generation of XOS and enzymatic hydrolysis glucose with feed-adapted and recyclable acetic acid as catalyst were developed.The thermodynamic differences of cellulose and hemicellulose in the raw materials during the acetic acid heating catalytic reaction process were compared through multi-scale analysis,and the reaction kinetic model was studied and established.The optimum technological conditions for the preparation of XOS were established:at a reaction temperature of 170℃,the highest XOS yield of 38.2%could be obtained by pretreating wheat straw with only 5%acetic acid for 20 min,and the corresponding glucose yield is 85.6%.（2）Aiming at the utilization of acetic acid component in XOS product solution,based on the technical ideas of simplifying the process,operation and significantly reducing the energy consumption,the method and technology for in-situ chemical neutralization and fixation of acetic acid were innovatively proposed and established,which provided a theoretical basis for the creation of new products of XOS-acetate composite feed additive.The study found that the yields of in-situ chemical neutralization and fixation of acetic acid by CaCO₃,CaO,Na₂CO₃,and NaOH were 92.6%,94.9%,95.1%,and 95.6%,respectively.And the production efficiency and application performance of two types of compounds XOS products,calcium salt,and sodium salt,were compared and analyzed.（3）Given the obstacle of the waxy component on the wheat straw epidermis to the catalysis of organic acids,the effects of organic solvent extraction on the chemical process of XOS preparation and the biological process of enzymatic hydrolysis were studied,and the results showed that there were differences in the effects of different lipid extraction methods on the yield of XOS and enzymatic hydrolysis of glucose from different agricultural and forestry wastes.The removal of benzene-ethanol extractives increased the yields of XOS catalyzed by acetic acid from wheat straw,corn cob,and bagasse by 16.7%,14.8%,and 21.1%,respectively.Removal of the ethanol extractive could increase the yield of XOS from wheat straw,corn cob,and bagasse by1.3%,11.9%,and 17.4%,respectively.（4）To further improve the yield of XOS prepared from wheat straw catalyzed by the‘one-step acetic acid method’,a new method of‘two-step acetic acid method’was studied and proposed.The uniform design optimization method found that temperature was the primary factor affecting the yield of XOS and the degradation of xylan by the two-step acetic acid method.Using the two-step acetic acid method,the yield of XOS from wheat straw was significantly increased from 38.2%to 61.4%,the yield of enzymatic hydrolysis of residual cellulose was increased from85.6%to 98.2%,and the yield of XOS of corncob and the yield of enzymatic hydrolysis of cellulose from corn cob were increased to 63.4%and 100%,respectively.（5）Based on the enlightenment of the acetic acid catalytic method,the method of preparing XOS by using self-supplied xylonic acid instead of adding exogenous acetic acid catalyst was further explored.The yield of XOS was 39.2%by uniform design optimization of wheat straw xylonic acid pretreatment parameters.The whole-cell catalytic technology could efficiently convert the monosaccharide simultaneously generated in the acid catalytic process into sugar and acid compounds including xylonic acid,which was then completely separated by electrodialysis,thereby providing a new idea for the preparation of green XOS.