An Experimental and Chemical Kinetic Modeling Study of the Role of Potassium in the Moist Oxidation of CO

Arphaphon Chanpirak, Hao Wu, Peter Glarborg, Paul Marshall

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Abstract

The effect of KCl on moist CO oxidation in a laminar flow quartz reactor was investigated. Experiments were conducted in the absence of O2 (gasification), as well as under reducing and fuel-lean conditions, in the temperature range 873–1573 K, and the results were interpreted in terms of a chemical kinetic model. The impact of reactions on the quartz surface of the reactor was carefully examined. Under the conditions of interest, KCl reacts with SiO2 to form potassium silicates, releasing HCl to the gas phase. This reaction alters the condition of the quartz surface, making it more active in catalyzing radical recombination, even in the presence of water vapor. Under gasification and reducing conditions, loss of hydrogen atoms on the wall, enhanced by the exposure to KCl, strongly inhibits CO oxidation, with gas-phase inhibition playing a minor role. Under fuel-lean conditions, the state of the surface does not affect the CO oxidation and the observed inhibition can be attributed to gas-phase reactions. The most important reaction for the inhibition is the chain terminating step KO2 + OH ⇆ KOH + O2. Assuming that this reaction proceeds without a barrier, the rate constant is controlled by a long-range dipole–dipole interaction. We calculate a capture rate constant of 2.5E15 T−0.163 cm3 mol−1 s−1. This value, which is significantly higher than earlier estimates used in modeling, allows a satisfactory prediction of the inhibiting effect of KCl on CO oxidation under oxidizing conditions.
Original languageEnglish
Article number127075
JournalFuel
Volume335
ISSN0016-2361
DOIs
Publication statusPublished - 2023

Keywords

  • CO oxidation
  • Potassium chloride (KCl)
  • Inhibition
  • Surface reaction, kinetic modeling

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