KINETICS OF THE HIGH-TEMPERATURE REACTION OF SO2 WITH CAO PARTICLES USING GAS-PHASE FOURIER-TRANSFORM INFRARED-SPECTROSCOPY

The reaction of SO2 with CaO particles (size ~4 μm), at temperatures between 100 and 1000 °C, in both the presence and absence of O2, has been investigated by using gas-phase FTIR spectroscopy of SO2. By analyzing the time dependence of the fractional capture of SO2 up to 1 min at each temperature, it is concluded that diffusion through the product layer is the controlling step for this reaction at all temperatures investigated. However, the nature of diffusing species for the low-temperature (T ≤ 500 °C) and the high-temperature (T ≥ 700 °C) regions are different, as evidenced by different activation energies in the two regions. For T ≤ 500 °C, E ≃ 5 kcal/mol, both with and without O2 whereas for T ≥ 700 °C, E = 26.3 (34.7) kcal/mol in the absence (presence) of oxygen. It is argued that, for the lower temperatures, the diffusion of SO2 gas through the sulfite product layer is the controlling step, whereas for T ≥ 700 °C, ionic diffusion controls the kinetics in agreement with the recent conclusion of Borgwardt and Bruce. However, the question of the nature of the diffusing species for the latter case is not fully resolved. © 1990, American Chemical Society. All rights reserved.