An experimental, theoretical, and kinetic modeling study of gas-phase sulfation of KCl

The effect of a radical pool on KCl sulfation by SO₂ is investigated through flow reactor experiments on KCl sulfation with and without the presence of CO. These experiments, together with results reported in literature, are interpreted in terms of an updated chemical kinetic model for sulfation. In the absence of combustibles, the rate limiting step in the sulfation of KCl is the oxidation of potassium sulfite to potassium sulfate through the reaction KHSO₃ + O₂ → KHSO₄ + O (R17b). Based on chemical kinetic modeling of a range of sulfation experiments, the rate constant for the reverse, exothermic step KHSO₄ + O is estimated to be k₁₇ ∼ 2·10¹² cm³ mol⁻¹ s⁻¹. Oxidation of combustibles such as CO facilitates establishment of a radical pool that strongly promotes sulfation. In this case, the sulfation rate is controlled by the oxidation of SO2 to SO3, mostly through SO₂ + O (+M) →SO₃ (+M). An alternative sulfation pathway involving KSO₄ as an intermediate is discarded, because the formation through either KO₂ + SO₂ or KSO₂ + O₂ involves significant barriers to reaction.