Abstract

FTIR PAS has been used to characterize the reaction products on and near the surface of particulate CaCO₃ and CaO during and after exposure to 1.5% SO₂ in He. The reaction has been studied as a function of temperature (up to 900°C), time of exposure, concentration of SO₂, presence of O₂, precalcining, and addition of promoters. The PAS results confirm the initial reaction to be the formation of ${\text{SO}}_3^{=}$. The production of ${\text{SO}}_4^{=}$ is found to occur via disproportionation and by further reaction of ${\text{SO}}_3^{=}$ with SO₂ (pseudodisproportionation). No evidence is found for gas phase oxidation, and the role of direct solid state oxidation in the formation of ${\text{SO}}_4^{=}$ is of minimal importance. The mechanism of action of various additives in promoting or inhibiting sintering, oxidation, and/or disproportionation has also been investigated by following the course of the reaction by PAS as a function of temperature and time. Use of mirror velocity (modulation frequency) variation indicates that the limiting factor for the reaction is the formation of an impervious product layer on the surface of the particles. Implications of these results for the application of limestone injection in the control of SO_x emission from fossil fuel plants are discussed.

© 1985 Optical Society of America