Improving the understanding of reaction kinetics Of CS2 formation in the Claus plant front-end reaction furnace (RF) is a key step in developing strategies to reduce CS2 formation and, consequently, the environmental impact of Claus plants. Specifically, experiments were carried out in a high-temperature flow reactor with pressures of 101-150 kPa, temperatures of 8001250 degreesC, and residence times of 90-1400 ms to study the kinetics of CH4-S-2 and CH4-H2S reactions; these conditions are typical of those encountered in the Claus RF. The reaction between methane and sulfur was found to be very rapid, resulting in complete consumption of sulfur in less than 100 ms at 1100 degreesC with formation Of CS2 and H2S as the primary sulfur-containing products. At higher temperature (> 1000 degreesC), the produced H2S decomposes with a proportional increase in CS2 formation. A simple rate expression for CS2 formation was obtained, and a kinetic model was developed to describe H2S formation/consumption in the CH4-S-2 system. In the CH4- H2S reacting system, H2S thermal decomposition appears to be the rate-limiting step for CS2 formation. The consumption of H2S in the CH4-H2S system proceeds at a rate characteristic of thermal decomposition of H2S, i.e., at a rate independent of any reaction of H2S with methane.