A kinetic study of the selective production of difluoromethoxymethane from chlorodifluoromethane.

The reaction of chlorodifluoromethane (R-22) with sodium methoxide produces difluoromethoxymethane, an alternative refrigerant with low ozone depleting potential. In this study a kinetic model of the dehydrochlorination process was identified, based on rate data obtained from a semi-batch gas–liquid reactor. The reaction was studied at a reaction temperature of 283–303 K, R-22 inlet partial pressures of 40.5–60.8 kPa and initial sodium methoxide concentrations between 1.5 and 2.5 mol·dm −3 . The products obtained were difluoromethoxymethane and trimethyl orthoformate as well as sodium chloride and fluoride salts. The reaction proceeds via a three step mechanism, initiated by an α -elimination and involving a difluoromethylene intermediate. The elimination step has an identified pre-exponential factor of 1.18 × 10 4 dm 3 ·mol −1 ·min −1 and activation energy of 15.54 kJ·mol −1 . The reaction yielding the target compound has a pre-exponential factor of 1.15 × 10 8 dm 3 ·mol −1 ·min −1 and activation energy of 47.67 kJ·mol −1 . The byproduct formation reaction has a pre-exponential factor of 8.25 × 10 1 (dm 3 ·mol −1 ) 2 ·min −1 and activation energy of 12.75 kJ·mol −1 . In a semi-batch system the reaction is strongly inhibited by the formation and accumulation of precipitated sodium salts. This feature was incorporated into the reaction model using an inhibition term. [ABSTRACT FROM AUTHOR]