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

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 H 2 O concentration were continuously monitored in a Fourier transform infrared (FTIR) cell with ZnSe windows. The HCl and H 2 O 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.