Synthesis Of 5-hydroxymethylfurfural From Hexose Catalyzed By Polyoxometalate

The contents of this paper mainly research the use of polyoxometalate compounds, we control the system by changing the composition of elements, thus to design and synthesize the active catalyst for heterogeneous acid-catalyzed reaction. In this paper, we make hexose (glucose and fructose) dehydrate to produce 5-hydroxymethylfurfural (HMF) in water- methylisobutylketone (MIBK) biphasic systems, using the acid catalysts. The effect of the reaction time, reaction temperature, the amount of MIBK , the amount of catalyst, sugar concentration, reusability of the catalyst on the selectivity of HMF and the conversion of sugar are investigated. The experiment solves a lot of drawbacks, such as serious corrosion of equipments, generating more by-products and so on. In addition, the paper has a certain theoretical significance and economic value for the research and development of new and efficient catalysts. In this paper, the results are mainly as follows:1. Cesium ions partially replace the proton of 12 phosphotungstic acid to form a Br?nsted (B) Acid catalyst, Cs_2.5H_0.5PW₁₂O₄₀, which was characterized by using infrared spectra and elemental analysis. To the dehydration of hexose to HMF in the heterogeneous acid-catalyzed reaction using Cs_2.5H_0.5PW₁₂O₄₀ as a catalyst, the results showed that the conversion of fructose and selectivity of HMF are 78.2% and 94%, respectively, at 388 K for 60 min with volume ratio of water to MIBK 1:3 when 30wt% fructose as a reactant. After the reaction, the Cs_2.5H_0.5PW₁₂O₄₀ catalyst was collected by centrifuge, washing away the impurities with water, activated at 353 K for 3 h under the protaction of nitrogen, then made for reuse. All the results illustrated that Cs_2.5H_0.5PW₁₂O₄₀ is a water-tolerant type, recycled and environmentally benign B-acid catalyst for the dehydration of hexose toHMF.2. Silver ions completely replace the protons of 12 phosphotungstic acid to form a Lewis (L) Acid catalyst, Ag₃PW₁₂O₄₀, whose structure was characterized by using infrared spectra and elemental analysis and infrared spectra of pyridine adsorption and X-ray powder diffraction. To the dehydration of hexose to HMF in the heterogeneous acid-catalyzed reaction using Ag₃PW₁₂O₄₀ as a catalyst, the results showed that the conversion of frucose and selectivity of HMF are 80.1% and 89%, respectively, at 393 K for 90 min with volume ratio of water to MIBK 1:3 for 30wt% fructose. After the reaction, the Ag₃PW₁₂O₄₀ catalyst was collected by centrifuge, washing away the impurities with water, activated at 353 K for 3 h under the protaction of nitrogen, then made for reuse. All the results illustrate that Ag₃PW₁₂O₄₀ is a water-tolerant type, recycled and environmentally benign L-acid catalyst for the dehydration of hexose to HMF.