Production of 5-methylfurfual or furfural via thermal-catalytic conversion of fructose with pyrolytic solid residue-derived catalysts

Abstract

5-Methylfurfural (5-MF), is a useful chemical intermediate which has been widely used in the synthesis of various chemicals for agriculture, pharmaceuticals, flavouring agents, perfumes, renewable fuels, and so on. Furfural (FF) also deserves attention as a potential platform chemical for the bio-fuels, biochemical and biopolymer industries. However, long reaction time, high pressure, noble metal catalysts, and large qualities of organic solvent and surfactants were required in current 5-MF and FF production processes, and some of them were environmentally harsh. In this study, we demonstrate an efficient and environmentally friendly process to selectively produce 5-MF or FF via thermal-catalytic conversion of fructose with activated sulfonated carbon (A-SC) and sulfonated carbon (SC) catalysts. In order to realize the comprehensive utilization of biomass, the A-SC and SC catalysts were prepared from the fructose pyrolytic solid residues through two different methods. They were characterized by scanning electron microscope (SEM), N2 physisorption, elemental analysis, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). Compared with A-SC, SC possessed more -SO3H groups and thus displayed stronger acidity. The effects of catalysts, temperature and the mass ratio of catalyst to fructose on the production of the target products were examined systematically. All these factors played important roles on the yield and selectivity of 5-MF and FF. Highly concentrated target products could be obtained selectively by adjusting these factors. In the presence of A-SC catalyst, both 5-MF and FF were formed. The optimal condition for the production of 5-MF from fructose was using A-SC as catalyst and conversion at about 325℃ with mass ratio of catalyst to fructose as 0.8:1. Whereas in the presence of SC catalyst, FF was the main product. The maximal yield up to 24.6 mol% was achieved at 325℃ with the catalyst to fructose as about 1:1. Accordingly, the possible pathways for the formation of 5-MF and FF from fructose were also proposed based on both the experimental and quantum calculation studies. The possible conversion mechanism of fructose to 5-MF and FF via thermal-catalytic conversion was related to the strength of the internal bond energy of intermediate 5-hydroxymethylfurfural and 5-MF molecules, and the acidity or acid concentration of the catalyst.