| Currently, the emergences of environmental pollution issues and energy crises caused by the massive consumption of the traditional fossil energy is increasingly serious. Production of fine chemicals and liquid fuels from the renewable and sustainable lignocellulosic biomass resources for the alternative to petroleum-based resources has gained widespread attention all over the world. Furfural and 5-hydroxymethylfurfural (HMF) play crucial roles in the process of lignocellulosic biomass conversion, which can be used to produce biomass-derived liquid fuels and high value-added chemicals, such as succinic acid, furfuryl alcohol,1,5-pentanediol, 2,5-furandicarboxylic acid, levulinic acid,1,6-hexanediol. Various polymer materials can be synthesized from these chemicals via polymerization reactions. Furfural and HMF have built a bridge between lignocellulosic biomass and liquid fuels, chemicals or materials. Therefore, highly efficient production of furfural and HMF from biomass resources is the most fundamental and important point for the realization of replacing conventional fossil resources-derived fuels and chemicals with biomass. Based on the background, this work is aimed to develop an efficient and eco-friendly method to convert various biomass-derived carbohydrates into furfural and HMF.In this study, a novel solid acid catalyst PTSA-POM was prepared simply by the copolymerization of p-toluenesulfonic acid (PTSA) and paraformaldehyde (POM). The influence of calcination temperature and POM content on the catalyst was investigated detailedly and then characterized by FT-IR, TG/DTG, TEM, N2-BET. Test results display that the catalyst exhibits good water resistance, high thermal stability, excellent reusability. In order to overcome many defects of conventional solvents, GVL, as a new generation of green renewable solvent, was selected as a reaction medium for the carbohydrates transformation into furfural and HMF. GVL is considered as a sustainable liquid and can be prepared from lignocellulosic biomass. It occurs naturally in fruits and has been used by the food industry.Firstly, this paper focused on acid-catalyzed conversion of xylose, xylan and corn stalk into furfural in GVL/H2O reaction medium with PTSA-POM. The effects of various reaction conditions including solvent, acid catalyst, temperature, residence time, water concentration, xylose and catalyst dosage on the dehydration of xylose to furfural were studied. When the reaction was carried out at 170 "C for 10 min, furfural yield was as high as 80.4%, and PTSA-POM can be recycled at least 5 times with out significant loss of activity under this reaction conditions. Furthermore,86.3% furfural yield could be obtained from raw corn stalk at 190℃ for 40 min.In order to further extend the catalytic application of PTSA-POM for biomass conversion, the catalyst was selected for the production of HMF from fructose, and the influences of main reaction parameters on HMF yield were investigated. Experiment results indicated that the reaction system also exhibited good catalytic activity for the production of HMF from fructose. High HMF yields of 78.1% was obtained at 130 "C for 30 min, and PTSA-POM could be reused at least for seven cycles. One-step conversion of glucose and microcrystalline cellulose to HMF was also examined using the efficient catalytic system, but the result was far from satisfying.Finally, Al-free Sn-Beta zeolite as a Lewis acid was synthesized directly in fluoride system by common hydrothermal method, and then combined with the Bronsted acid PTSA-POM for the one-step conversion of glucose into HMF. Interestingly, HMF yield of 57.2% was achieved at 140℃ for 30 min, and Sn-Beta made the reaction conditions much milder, lower temperature or shorter reaction time was required to achieve good yields. Then, we also explored one-step conversion of microcrystalline cellulose and raw com stalk into HMF using the catalytic system, and HMF yield increased significantly, reaching 20%. |
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