Sorbitol Hydrogenolysis To Lower-Carbon Glycols Over Carbon Nanofibers Supported Ru Catalyst

Sugar-derived sorbitol can be conversed into ethylene glycol and propylene glycol via hydrogenolysis reaction, which is of great significance for the sustainable development of chemical industry and human society. Developing highly effective catalysts will make this conversion economically feasibile. In this dissertation, Ru catalysts for sorbitol hydrogenolysis, using carbon nanofibers (CNFs) as a support, have been developed and investigated. Furthermore, CNFs/Graphite-felt (GF) has been prepared by in-situ synthesizing CNFs on GF substrate and applied as a structured catalyst support. Ru/CNFs/GF structured catalyst was prepared and tested in sorbitol hydrogenolysis. The main work and results in this dissertation are as follows:(1) A high performance liquid chromatogram method was established to determine the concentrations of sorbitol, ethylene glycol, propylene glycol and glycerol in sorbitol hydrogenolysis product solution. This method was of good accuracy and precision, easy operation and economy. It was proved that base was a necessary catalyst for sorbitol hydrogenolysis. A combined anlysis of the main unknown byproduct by X-ray diffraction (XRD) and Fourier transfer infrared spectroscopy (FTIR) showed that the main unknown byproduct was a complex compound or an organic salt containing the metal element of base catalyst, probably derived from some base-catalyzed byreactions.(2) Ru/CNFs powdered catalyst was prepared using CNFs as a support and RuCl3 hydrate as a precursor and investigated in autoclave for sorbitol hydrogenolysis. The results showed that Ru/CNFs catalyst performed better than activated carbon supported Ru catalyst and other catalysts published in patents under a moderate operating condition. The good performance of Ru/CNFs was attributed to the novel properties of CNFs support. It was proposed that the metal cation in base catalyst participated in sorbitol hydrogenolysis in the form of sorbitol-metal cation complex compounds. In comparison with Na+,K+and Ba2+, Ca2+was more favorable for lower-carbon glycol's selectivity and yield. Because a series of dehydrogenation and hydrogenation reactions were involved in sorbitol hydrogenolysis, there was a preferable hydrogen pressure for sorbitol conversion, which was lower for Ru/CNFs catalyst than that for other reported catalysts. (3) The effect of calcination treatment before catalyst reduction on the properties of Ru/CNFs catalyst was investigated using thermal gravimetry analysis (TGA), temperatured-programmed reduction (TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and N2 physisorption. It was found that the calcination treatment significantly increased the amount of CNF surface oxygen-containing groups (SOCGs) and changed the catalytic performance of Ru/CNFs catalyst. The catalyst calcined at 240℃displayed the highest glycol selectivity and reasonable glycol yield. It was proved that the change in the distribution of SOCGs should be responsible for the catalytic performance of Ru/CNFs, and the increase in SOCGs was favorable for the selectivity to lower-carbon glycols. The small amount of residual Cl in the catalyst for use could slightly affect the catalytic performance of Ru/CNFs, so RuCl3 hydrate with low price and good stability was considered to be the most suitable Ru precursor for the preparation of Ru/CNFs catalyst.(4) CNFs/GF composite were synthesized by virtue of in-situ growth of CNFs on GF substrate, and the Ru/CNFs/GF structured catalyst was applied in sorbitol hydrogenolysis. Characterization showed that CNFs/GF composite possessed good abrasion resistance and the typical mesoporous structure of CNFs, promising as a catalyst support. When Ru/CNFs/GF structured catalyst was used as stirrer blades in autoclave, the problem of catalyst/product separation, which was encountered by Ru/CNFs powdered catalyst, was overcome and the selectivity to lower-carbon glycols could also be improved. In a trickle bed reactor, Ru/CNFs/GF structured catalyst displayed better catalytic performance and much lower pressure drop through catalyst bed in comparison with Ru/CNFs powdered catalyst. The catalytic performance of Ru/CNFs/GF catalyst in trickle bed reactor depended on the structure properties of Ru/CNFs/GF catalyst. Using Ru/CNFs/GF catalyst with less CNFs and increasing the catalyst loading in trickle bed reactor could be helpful to increase the yield of lower-carbon glycols.