Reaction Kinetics of Hydrogen Chloride with Calcium Oxide by Fourier Transform Infrared Spectroscopy

Abstract

The chemical kinetics of the HCl reaction with CaO was investigated over the temperature range of 148−400 °C. A thin film averaging 0.1 ± 0.05 μm CaO was deposited on quartz wool in order to minimize the effects of pore diffusion for this heterogeneous reaction. The decrease in HCl and increase in H2O concentration were continuously monitored in a Fourier transform infrared (FTIR) cell with ZnSe windows. The HCl and H2O spectra were collected automatically at 1.2 s intervals using gas chromatography software. The gaseous reactants and products were circulated continuously between the reactor and FTIR cell using a pump in order to minimize bulk mass-transfer effects on the CaO surface. In this way, rapid data collection at constant temperature could be achieved without sampling problems. The results were in excellent agreement with first-order reaction kinetics with respect to the HCl concentration. The Arrhenius activation energy of 31.1 ± 3.0 kJ/mol is slightly larger than that reported in the literature due to minimization of pore diffusion by study of a very thin layer of CaO and circulation of the reactants at a high rate to minimize mass-transfer effects.