Study On The Catalytic Preparation Of Diethyl Carbonate From Diethyl Oxalate Via Gaseous Decarbonylation

Diethyl carbonate (DEC) is a versatile compound that represents an attractive eco-friendly alternative to both ethyl halides and phosgene for ethylation and carbonylation processes, respectively. The alkali catalytic preparation of diethyl carbonate (DEC) from gaseous diethyl oxalate (DEO) via decarbonylation was investigated in the paper.The thermodynamics analysis results showed that the change of reaction enthalpy was 20.88kJ/mol and the equilibrium constant was 3.12×109(533K)which indicated that the direct decarbonylation of DEO to DEC was feasible thermodynamically. Moreover, the blank experiment results indicated that the decarbonylation could occur without catalyst, but the temperature control was the necessary and key point for this reaction.The products in DEC preparation from DEO via gas phase decarbonylation were analyzed by gas chromatography-mass spectrometry. DEC, ethanol, ethyl chloroformate, ethyl acetate, 1,1-diethoxyethane were separated and qualitatively analyzed respectively, and the reasons for the formation of the by-products was explained. It can be deduced that the existence of H2O was the main reason for the formation of by-products.In this paper, the detailed preparation of DEC from gaseous phase DEO via decarbonylation under the alkali catalyst was investigated. Evaluation results showed that 6wt % (based on K) K2CO3/AC (activated carbon) catalyst exhibited a relative high catalytic activity when the reaction temperature was 513K and the gas hourly space velocity lied in 800-1000h-1. 54.3% conversion of DEO, 27.8% selectivity to DEC and 300.0 g/L·h space time yield of DEC were obtained under the optimum reaction condition.By means of XRD analysis, it can be concluded that the K2CO3 with high dispersion on the catalyst surface is favorable for the production of DEC, while the formation of crystalline K2CO3 results in the decrease of the catalytic activity. Moreover, the crystalline KHCO3 results from the reaction of K2CO3, CO2 and H2O appeared after reaction on the catalyst surface and it enhances with the increase of the amount of K-loading. Furthermore, possible reasons for the decrease of catalytic activity of catalysts were discussed by the measurement of the specific surface area and the characterization of XPS, ICP-OES, TGA, FT-IR. Test results indicated that H2O existed in the reaction system was not benefit for the DEC production. Drastic reduction of the specific surface area and the decrease of K content and so on are the important aspects with regards to the decreasing catalytic activity.