A kinetic study of the selective production of difluoromethoxymethane from chlorodifluoromethane

作者：Prithipal Rasmika; Lokhat David^*; Govender Neelan; Starzak Maciej; Ramjugernath Deresh

来源：Journal of the Taiwan Institute of Chemical Engineers, 2016, 66: 70-79.

DOI：10.1016/j.jtice.2016.06.039

• Kinetics
• Difluoromethoxymethane
• Dehydrohalogenation
• Chlorodifluoromethane
• Refrigerant

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 alpha-elimination and involving a difluoromethylene intermediate. The elimination step has an identified pre-exponential factor of 1.18 x 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 x 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 x 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.

• 出版日期2016-9