Function of sulfur dioxide in the kinetic mechanism of oxidation of carbon

Retardation of the gasification reaction of carbon with oxygen by SO₂ was observed. Rates of oxidation were determined by thermal gravimetric analysis (TGA) of a nuclear graphite in the temperature range of 550–700°C, and of a coconut charcoal in the temperature range of 400–505°C. The oxidant gases were dry air containing 0–6% SO₂. Reduction of the rate by SO₂ varied with burn-off. Differential thermal analysis (DTA) was also applied to detect the retardation effect of SO₂. The technique of infrared internal reflection spectroscopy (IRS) was used to examine the surface species of reacted charcoal samples. Absorption bands were assigned to surface carbonyls, lactones, and a chemisorbed SO₂ in the form of sulfate. Chemisorption of SO₂ was attributed to cause the retardation of the oxidation reaction.