Direct Conversion Of Cellulose To Sorbitol Via An Enhanced Pretreatment With Ionic Liquids

Sorbitol is a large industrial commodity with a wide range of applications.The Department of Energy(DOE,USA)has screened it as one of the twelve most promising bio-based platform compounds.The production of sorbitol in industry is mainly through glucose hydrogenation.The production cost of sorbitol is extremely high because of the high cost of glucose.Therefore,it is very important to reduce the production cost of sorbitol.Cellulose is a widely distributed and cheap biomass resource.It is of great economic importance to use cellulose as raw material in sorbitol production.However,there are still difficulties in the direct conversion of cellulose to sorbitol.The main reason is that there is a complex hydrogen bond network structure in the cellulose structure,which makes the cellulose difficult to be degraded efficiently and resulting in the subsequent catalytic conversion of low yield and selectivity of sorbitol.This study focuses on the disruption of hydrogen bond network structure in cellulose molecules in order to promote the conversion of cellulose to sorbitol.The main research contents and achievements are as follows:(1)Pretreatment of cellulose by ball milling and ionic liquid dissolution.After 4 h ball milling,the crystallinity of cellulose decreased sharply from the initial 79.9%to 3.2%,indicating that the area of the crystalline region of cellulose decreased significantly,and the structure of the intramolecular hydrogen bond network was destroyed.The cellulose after ball milling is dissolved in[Amim]Cl,and the anions and cations in the ionic liquid are combined with hydrogen and oxygen atoms in the hydroxyl groups of dehydrated glucose in the cellulose molecule.The combination of ionic liquid and hydroxyl group further destroys the hydrogen bond structure network in the cellulose molecule.In addition,the dissolving of cellulose in the ionic liquid can transform the insoluble solid cellulose into a liquid form of ionic cellulose solution,which increase the contact area between the cellulose and the catalyst,and reduce the difficulty of the cellulose hydrolysis reaction.(2)Cellulose hydrolysis and glucose hydrogenation were studied respectively.In the reaction of cellulose hydrolysis,based on the strong acidity of solid acid Nafion NR50,it can effectively promote the hydrolysis of cellulose,and the yield of glucose can reach up to 55.2%.In the reaction of glucose hydrogenation,the large particle size distribution of Ru/AC can effectively promote the conversion of glucose to sorbitol.With the catalysis of Ru/AC,the glucose conversion can reach 100%,and the yield of sorbitol as high as 96.1%.(3)The study on the direct conversion of cellulose to sorbitol.With the catalysis of Nafion NR50 and Ru/AC,the ball-milled cellulose which is dissolved in the[Amim]Cl can be converted into sorbitol by hydrolytic hydrogenation.The yield of sorbitol can reach 34.3%after 1 h reaction under 150?.In this study,a new production process of sorbitol was proposed from microcrystalline cellulose,and this research also expanded the application of ionic liquids in biomass conversion to platform compounds.