An experimental and chemical kinetic modeling study of the role of potassium in the moist oxidation of CO. (1st March 2023)

• Record Type: Journal Article
• Authors: Chanpirak, Arphaphon; Wu, Hao; Glarborg, Peter; Marshall, Paul
• Is Part Of: Fuel. Volume 335(2023)
• Publication Date: 2023-03-01
• Subjects: Potassium chloride (KCl) -- CO oxidation -- Inhibition -- Surface reaction -- Kinetic modeling; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2022.127075
• Languages: English
• ISSNs: 0016-2361

Abstract

Highlights: The he first reported study of the influence KCl on CO oxidation under gasification, reducing and oxidizing conditions in a flow reactor. Under fuel-lean conditions, inhibition by KCl is dominated the terminating reaction KO2 + OH = KOH + O2, estimated to be very fast. A chemical kinetic model is established that provides a satisfactory prediction of the experimental results under fuel-lean conditions. 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 cm 3 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.