Abstract
A series of KF/γ-Al2O3 solid base catalysts were prepared by a wet impregnation method and applied to the synthesis of glycerol carbonate (GC) from glycerol and dimethyl carbonate. The influences of KF loading and calcination temperature of catalyst on the synthesis were investigated. The results showed that KF/γ-Al2O3 catalysts could promote glycerol conversion to GC efficiently. The structure and properties of the catalysts were studied by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), N2-adsorption, CO2-temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and Hammett indicator method. It was found that several types of basic centers such as KF, KAlO2, KOH and possibly coordinately unsaturated F- ion existed on the catalysts. The strong basic centers could not only accelerate the conversion of glycerol, but also enhance the formation of glycidol from the decomposition of GC. The recycling of KF/γ-Al2O3 revealed that deactivation of catalyst was strengthened with the reuse times, which was mainly caused by the partial leaching of active potassium species. High calcination temperature favored the transformation of KF to KAlO2 and alleviated the deactivation of the catalyst. Based on the product distribution and obtained results, a possible reaction mechanism on reaction of glycerol with dimethyl carbonate was proposed.
Highlights
Biodiesel has attracted considerable attention as an alternative to the fossil fuel resources
To find out the actual active phases, X-ray diffraction (XRD) was used to learn the structure of KF/γ-Al2O3 catalysts with various KF loading
When 5 wt.% of KF was loaded on γ-Al2O3, the catalyst displayed similar XRD patterns (Figure 1b) to that of γ-Al2O3, indicating that KF or its derivatives were highly dispersed on the surface of the support, or their amounts was smaller than those detectable via the XRD technique
Summary
Biodiesel has attracted considerable attention as an alternative to the fossil fuel resources. European Union and U.S government have promulgated mandatory regulations for the use of biodiesel in transportation fuel and on-road diesel.[1] production of biodiesel by plant oil methanolysis generates large amount of glycerol (about 10 wt.%) as an unavoidable by-product, which has to be valorized to improve the economic competitiveness of biodiesel.[2] transformation of glycerol into value-added products is of great significance. Among the various downstream products of glycerol, glycerol carbonate (4-hydroxymethyl-2-oxo-1,3-dioxolane, GC) represents an important and potential glycerol derivative that shows low toxicity and volatility, biodegradability, high boiling point, etc.[5] GC has been widely used as a solvent in the cosmetics industry, as a membrane component for gas separation, as a component of coatings and detergents, as a precursor of glycidol, and as a monomer in preparing polycarbonate and polyurethane.[6,7,8]
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