The chemical coupling between moist CO oxidation and gas-phase potassium sulfation

In the present work, the chemical coupling between moist CO oxidation and transformation of gaseous potassium salts (KCl or KOH) in the presence and absence of SO2 was investigated experimentally and through chemical kinetic modeling. The experiments were performed in a laminar flow quartz reactor at temperatures ranging from 873 to 1473 K.

The experimental results showed that both KCl and KOH inhibited CO oxidation, but addition of SO2 reduced the inhibiting effect by sulfating the potassium. The degree of sulfation of KCl and KOH by SO2 was evaluated by EDX analysis of the aerosols collected downstream in a filter. Also, the consumption of SO2 and, for KCl, the formation of HCl were indications of the level of sulfation.

The results indicated that KCl was only sulfated to a small degree, consistent with the observation that addition of SO2 had little effect on the inhibition of CO oxidation by KCl. Contrary to this, the captured KOH particles were fully sulfated according to the EDX results; however, most of the KOH was captured on the quartz reactor surface, forming potassium silicates.

The experimental results were interpreted in terms of a chemical kinetic model. Thermodynamic data for key potassium intermediates were re-evaluated by ab initio methods and the mechanism was updated according to recent results. The modeling predictions were in qualitative agreement with the experimental results for the effect of K/Cl/S on moist CO oxidation, but the degree of sulfation was strongly overpredicted for KCl.

Analysis of the calculations indicates that sulfation pathways in the model involving KOSO3 contribute to the overprediction, but both the thermodynamic properties and rate constants in the model involve significant uncertainties and more work is required to resolve the discrepancy.