Conversion Carbohydrates Into 5-hydroxymethylfurfural Catalyzed By Schiff Base Complex And Ionic Liquid Immobilized On Mesoporous Silica

In recent year, the rapid development of economy and increase of population have brought the risis of energy emerges and environment pollution, and the development of new technical route to produce clean and renewable energy has become imperative. Lignocellulosic biomass is a highly abundant and renewable green resource, being an ideal alternative option for the production of important platform compound and fine chemicals using effectively catalytic technologies from conventional biomass. Moreover, 5-Hydroxymethylfurfural(HMF) is a versatile biomass-derived platform compound that can be used to synthesize a broad range of chemicals currently derived from petroleum. Therefore, the research how to improving the preparation of HMF from biomass efficiently is quiet important and significant. Base on this, a series of novel catalysts had been prepared and the catalytic activity was investigated for the conversion of carbohydrates. The main research results are achieved as follows:(1) N, N-Bis(salicylidene)ethylenediamine complexes[Cr(Salen-X)] were prepared and studied the effects on the isomerization of glucose to fructose in DMSO. The homogeneous complexes Cr(Salen) showed the higher catalytic performance in the conversion of glucose. Conversion of glucose for 3 h at 120 °C with Cr(Salen) gave a 27.8% yield of fructose in the presence of DMSO. The mechanism of glucose isomerization to fructose catalyzed by chromium complexes were investigated by DFT calculations. Comparing to Cr(Salen-Cl) and Cr(Salen-Br), the high catalytic performance of Cr(Salen) towards glucose transformation is due to the lower barrier for the hydride shift step resulting from the presence of a relatively strong acidic bridging silanol group cooperating with the Lewis acidic Cr site. The simulation computed barrier is in agreement with experiments.(2) A series of novel catalysts were prepared by immobilizing chromium(III) Schiff base complexes and acidic ionic liquid(AIL) onto the surface of MCM-41. The catalytic activity of the prepared solid catalysts was investigated for the conversion of carbohydrates(including glucose, fructose and inulin). The dependencies of catalytic activity on the reaction parameter such as catalyst type and amount, reaction solvent, reaction temperature and time were investigated and the reaction conditions were optimized. A HMF yield of 43.5% with a 99.2% glucose conversion was achieved from glucose using Cr(Salen)-IM-HSO4-MCM-41 as the catalyst in DMSO at 140 °C for 4 h. Furthermore,the catalyst also demonstrated good activity, and as high as 83.5% HMF was directly obtained from fructose, and the HMF yield reached 80.2% when inulin was selected as the substrate. The immobilized catalyst has been efficiently and easily recycled at least five times without loss of activity.(3) We synthesized bifunctional catalysts via the anchoring of salicylidene-ο-aminophenol complexes and SO3H-functionalized ionic liquids(AIL) on the surface of mesoporous silica, MCM-41. The catalyst Cr(SAP-Br)-IM-HSO4-MCM-41 has been demonstrated to be the most active, exhibiting a high frucose conversion(99.8%) and a high HMF yield(89.5%) at 120 °C for 3 h in DMSO. The catalyst Cr(SAP-Br)-IM-HSO4-MCM-41 has been demonstrated to be the most active, exhibiting a high frucose conversion(99.8%) and a high HMF yield(89.5%) at 120 °C for 3 h in DMSO. The Cr(SAP-Br)-IM-HSO4-MCM-41 catalyst also shows good catalytic activity for the dehydration of biomass-derived glucose, inulin and sucrose to HMF, resulting in maximum yield of 38.9%、81.6% and 41.9%, respectively. Notably, the catalyst can be recovered and reused with good activity even after five runs.