Study On The Catalysts For The Synthesis Of Diethyl Carbonate By The Vapor Phase Oxidative Carbonylation Of Ethanol

Oxidative carbonylation of ethanol for preparation of diethyl carbonate (DEC) offers prospects for a "green chemistry" replacement of phosgene used for polymer production and other processes. In recent years, diethyl carbonate is found to substitute for methyl tert-butyl ether (MTBE), which is used as an oxygen-containing fuel additive. The synthesis of diethyl carbonate over the CuCl2-PdCl2-NaOH/AC catalyst from oxidative carbonylation of ethanol was evaluated. The influence of potassium promoter on the catalytic performance was mainly studied.The synthesized products from the oxidative carbonylation of ethanol were analyzed by combined means of programmed temperature-capillary gas chromatography-mass spectrometry. Diethyl carbonate, ethanol, ethyl acetate, acetic acid, acetaldehyde, 1,1-diethoxyethane were separated and qualitatively analyzed, respectively. The reaction mechanism was concluded and the thermodynamic analysis was carried out.The effect of various potassium promoters on the CuCl2-PdCl2-NaOH/AC catalyst for diethyl carbonate synthesis was investigated. The evaluation results showed that there was a significant variety on the catalyst activity when KCl was used as a promoter. The conversion of ethanol reached above 30% without any decrease of the selectivity to DEC. For CuCl2-PdCl2-KCl-NaOH/AC catalyst, the influence of flow rate of oxygen and carbon monoxide on the conversion of ethanol and selectivity of DEC was also investigated. The optimal molar ratio of the reactant (CO:O2:C2H5OH) was around 10:1:4, giving ethanol conversion 31.2% and the selectivity to DEC 96%. The morphological analysis by X-ray diffraction and XPS showed that the deactivation of catalyst was attributed to the leaching of chloride ion. The improved performance of CuCl2-PdCl2-KCl-NaOH/AC catalysts was closely related with the existence of copper chloride hydroxides (Cu(OH)Cl). CO-TPD analysis also indicated that the adsorbed capacity of CO was improved and the desorption temperature was shifted higher on the CuCl2-PdCl2-KCl-NaOH/AC catalyst. The obvious improvement in the catalytic performance for preparation of DEC was attributed to the efficiency of electronic transform between PdCl2 and Cu(OH)Cl crystal by reaction mechanism analysis.