The hydrolysis of halocarbon refrigerants in freeze desalination processes part II. Theoretical prediction of hydrolysis rates and comparison with experimental data

Abstract

A theoretical model has been developed for the calculation of the hydrolysis rate constant of freon refrigerants. The model is based on the assumption that the rate determining step in the hydrolysis of a halocarbon is the primary ionization of the neutral molecule to a carbonium ion and a halide ion. The theory includes the effects of hydration of ions as well as the effects of the dielectric constant and ionic strength of the solution. Comparison of the theory with experimental hydrolysis rate constants for Freon 21 (CHCl 2F), Freon 31 (CH 2ClF) and Freon 114 (CClF 2CClF 2) gives excellent agreement with three adjustable parameters, the Arrhenius collision frequency, the hydration energy of the carbonium ion and the ionic distance of closest approach. The hydration energy is the controlling value in the model and the best fit to the data is obtained for a value of 115 kcal per mole. This value is the electrostatic equivalent of five water molecules of hydration at a separation distance of 2.2 angstroms. The model can be used to predict the hydrolysis rate constants of other refrigerants which are of interest to freeze or hydrate desalination processes since convenient semi-empirical methods for predicting the required thermodynamic and molecular parameters for the model can be utilized in the absence of tabulated data.