Study On High-valued Conversion Of Biomass-derived Carbohydrates Into Sorbitol

With the gradual depletion of fossil feedstock,the production of biomass chemicals from carbohydrates has become a research hotspot.Cassava dregs are generated during the cassava-based bioethanol production,whose main compositions are cellulose and starch.Therefore,it is of great significance to convert cassava dregs into biomass chemicals.Sorbitol,an important chemical intermediate and new energy chemical,which has applied significantly in foods,medicines,spinning,and cosmetics as well as in chemical industry.In this work,a series of carbon-based catalysts were prepared using cassava dregs as raw material,and much work was focused on the development of various reaction systems for the catalytic conversion of biomass carbohydrate into sorbitol.In this thesis,carbonized cassava dregs supported ruthenium nanoparticles catalyst（Ru/CCD）were prepared using cassava dregs as raw material by carbonization and impregnation method for conversion of glucose into sorbitol.The structure of catalysts was analyzed by using various characterization methods.The effects of reaction conditions on performance of catalysts and properties of recycled catalysts were investigated.Characterization results showed that Ru particles were well dispersed throughout the CCD.The glucose conversion of 99.7%and sorbitol yield of 98.6%could be obtained under the conditions of carbonization temperature of 450°C,catalyst dosage of 1.0%,H₂ pressure of 3MPa,reaction temperature of 120°C,reaction time of 1.5 h.Properties of recycled catalysts were excellent.After using five times,the dispersity of Ru was declined,and the sorbitol yield was decreased slightlyThe catalysts were modified to catalyze conversion of cellulose into sorbitol.Sulfonic acid-functionalized carbonized cassava dregs supported ruthenium bifunctional catalyst（Ru/CCD-SO₃H）was prepared by sulfonation-impregnation method.The sulfonate groups（-SO₃H）were detected on catalyst by using FT-IR and EA.The existence of the interaction between sulfonic groups and Ru nanoparticles in the Ru/CCD-SO₃H catalyst was observed.The sulfonate groups and metal sites in the adjacent position were important for enhancing the yield of sorbitol.The effects of reaction conditions on performance of catalysts and properties of recycled catalysts were also investigated.The experimental results showed that the cellulose conversion of 100%and sorbitol yield of 63.8%could be obtained under the optimal conditions,and the catalysts exhibited great stability.In addition,the bifunctional catalysts were applied for conversion of cassava dregs and strach into sorbitol.The holocellulose and starch were detdcted with total content of 81.41%by analyzing composition of cassava dregs.The sorbitol yield of 81.7%could be obtained under the conditions of reaction temperature of 180°C,reaction time of 5.0 h.However,the catalysts were less active in the aspects of conversion of cassava dregs into sorbitol.The sorbitol yield was only 11.4%and a mass of by-products were generated.In conclusion,the biomass-based catalysts were prepared by using cassava dregs as raw material for conversion of glucose,cellulose,starch and cassava dregs into sorbitol.The cassava dregs were utilized efficiently in this work.In addition,this study has provided theoretical foundation and technical support about solving pollution problem that was caused by burning of cassava dregs,exploiting biomass energy chemicals,accomplishing efficient conversion and large-scale utilization of biomass waste.