Direct Synthesis Of Dimethyl Carbonate From Methanol and Carbon Dioxide Using Supported Calcined Hydrotalcite As Catalyst With Ionic Liquid As Promoter Under Supercritical Condition

A sustainable process was developed using supported calcined hydrotalcite catalyst and by avoiding use of harmful organic solvents in the presence of ionic liquid and supercritical CO₂. Present work focuses on direct synthesis of dimethyl carbonate from carbon dioxide and methanol, using supported calcined hydrotalcite as catalyst with phosphonium based ionic liquids as promoter. Different modified Keggin type heteropoly acids supported on hexagonal mesoporous silica were also compared. Ionic liquids are good solvents for many substances and shown good results as promoter for the catalyst. The conversion, selectivity and yields were measured as a function of the amount of reactants, reaction time, temperature, pressure and amount of catalyst. The trihexyl (tetradecyl) phosphonium chloride ionic liquid was found to be good alkali promoter. Lower concentration of methanol, lower temperature and higher pressure favors good conversion and selectivity of desired product DMC. At higher concentrations of methanol there was decrease in conversion as well as selectivity. Higher temperature and lower pressure favors undesired reaction and forms dimethyl ether. The reaction was found to be first order with respect to methanol and the activation energy was calculated as 10.09 Kcal/mol. The catalyst is reusable and can be separated easily. Thus it is a green and environmental benign process.