Study On The Alcoholysis Of Carbohydrates To Ethyl Levulinate Catalyzed By Solid Acid Catalysts

Ethyl levulinate is used widely in numerous fields, such as perfume, additive, pharmaceutical, energy due to good reaction activity. In recent years, the application of solid acid catalysts in biomass chemical has attracted researchers’ attention due to their environment protection, mild reaction conditions, high selectivity, easy recovery and repeated use.In this paper, the conversion of carbohydrates to ethyl levulinate catalyzed by solid acid catalysts was investigated. Firstly, alcoholysis of fructose to ethyl levulinate was catalyzed by supported phosphotungstic acid, then, conversion of fructose to ethyl levulinate using phosphotungstates was studied; finally, ethyl levulinate from cellulose was prepared with cheap Al2(SO4)3. The conclusions are as follows:1. A series of supported phosphotungstic acid(H3PW12O40, HPW) catalysts were prepared with an impregnation method for alcoholysis of fructose to ethyl levulinate in ethanol. Among these catalysts, HPW/H-ZSM-5 showed the highest catalytic activity. The yield of ethyl levulinate reached 43.1% at 160 °C for 2 h over 20 wt.% HPW/H-ZSM-5, and the solid catalyst could be reused at least three times. Ethyl levulinate yields of 19.1 mol%, 27.3 mol%, 37.4 mol%, and 8.7 mol% could be obtained from glucose, sucrose, inulin, and cellulose, respectively. The catalysts were further characterized by XRD, FT-IR, BET and XPS, and the results showed catalytic activity decreased because of the loss of HPW.2. A series of metal-modified phosphotungstates were prepared and performed for direct synthesis of ethyl levulinate from fructose in ethanol. Considering the cost of catalysts, catalytic activity of catalysts, and easy separation of catalysts together, K1H2 PW was chosen as the most suitable catalyst for synthesis of ethyl levulinate from fructose. The highest ethyl levulinate yield of 64.6 mol% was obtained at 150 oC within 2 h in ethanol. The introduction of low polar toluene as a co-solvent improved the yield of ethyl levulinate to 68.7 mol%. Moreover, the generality of the catalyst was further demonstrated by glucose, sucrose, inulin, and cellulose with ethyl levulinate yield 14.5 mol%, 35.4 mol%, 52.3 mol%, and 14.8 mol%, respectively. The recovered catalyst remained high activity with the yield of ethyl levulinate converted from fructose above 50 mol% after being used five times. The catalysts were further characterized by XRD, FT-IR, and SEM, and the reused catalyst remained Keggin structure.3. Ethyl levulinate was prepared from cellulose as a raw material directly by cheap Al2(SO4)3. The highest yield of ethyl levulinate was obtained at 180 ℃ for 3 h in toluene-ethanol media with the content of 10%. Under the same condition, the yields of ethyl levulinate from fructose, glucose, sucrose, and inulin were 54.3 mol%, 47.3mol%, 51.4 mol% and 49.6 mol%, showing that Al2(SO4)3 has a good universal applicability.