| The decrease of fossil fuel reserves and deterioration of the social environment drive people to seek sustainable resources. As an abundantly available, cheap, renewable and low sulfur content resource, biomass stand out from the background of a low-carbon economy. In the conversion of biomass, the study of the dehydration of C6-sugars into 5-hydroxymethylfurfural(5-HMF) has received considerable attention.In this work, we prepared a series of solid acid catalysts, including the zirconia-based solid acid catalysts(Zr O2, WOx/Zr O2, Mo Ox/Zr O2, SO42-/WOx-Zr O2 and SO42-/Mo Ox-Zr O2) and carbon-based solid acid catalysts(C-SO3 H, AC-SO3 H, BC and BC-SO3H). These catalysts were characterized via certain methods, such as X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FTIR), nitrogen adsorption–desorption measurement(BET), transmission electron microscopy(TEM), X-ray photoelectron spectroscopy(XPS), and ammonia-temperature programmed desorption(NH3-TPD), and the surface acid amount was obtained by combining pyridine adsorption and UV spectrometry.As a new technology, microwave has a unique heating mode which could make organic reaction speeds faster than traditional heating methods and reaction yields are high as there are fewer by-products,in addition,the product is easily separated.In this work, we investigated the dehydration of fructose into 5-HMF under microwave assistance in dimethyl sulfoxide(DMSO). The effects of different catalysts, catalyst concentration, fructose concentration, reaction time and reaction temperature were investigated, in addition, the reaction kinetics of fructose decomposition under microwave irradiation was elementarily discussed.The zirconia-based solid acid catalysts were applied to the dehydration of fructose to 5-HMF, the catalyst SO42-/WOx-Zr O2 showed the best catalytic performance. The optimal reaction conditions were obtained as follows: fructose concentration 5wt%, catalyst concentration 10%, reaction time 5min and reaction temperature 150 °C, a fructose conversion of 95.80% with a 83.90% 5-HMF yield under this optimal condition. Furthermore the reaction kinetics of fructose decomposition under microwave irradiation was investigated, the results indicated that fructose decomposition reaction in DMSO was first-order reaction, while the SO42-/WOx-Zr O2 was catalyst, the reaction activation energy of fructose decomposition was 68.31 k J·mol-1 and the apparent frequency factor was 1.45×108 min-1. In addition, the characterization of catalysts indicated that the addition of the WOx and Mo Ox doping could effectively improve the specific surface area and the amount of acid catalysts and the impregnation with H2SO4 could improve the specific surface area and the amount of acid catalysts as well.The carbon-based solid acid catalysts were applied to the dehydration of fructose to 5-HMF, in this study, the surface acid amounts of the catalyst was the main factor influencing the fructose conversion and 5-HMF yield, the catalyst C-SO3 H showed the best catalytic performance, which was simply prepared via thermal treatment of p-toluenesulfonic acid with D-fructose. The optimal reaction conditions were obtained as follows: When the fructose concentration was 5wt% and the temperature increased up to 170 °C, a fructose conversion of 99.4% with a 88.5% 5-HMF yield in a 3 min reaction time, microwave power was almost did not affect the fructose conversion and 5-HMF yield. In addition, the catalyst C-SO3 H kept a high catalytic activity after it was used for three times, which indicates that it has a good reusability.In addition, comparing the conventional heating with microwave heating, it revealed the latter had a remarkable accelerating effect on the fructose conversion and 5-HMF yield. |
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