Oxidation of low concentrations of hydrogen sulphide: Process optimization and kinetic studies

Abstract

AbstractLow concentrations (e.g. < 3) of H2 S in natural gas can be selectively oxidized over an “granular Hydrodarco” activated carbon catalyst to elemental sulphur, water and a small fraction of by‐product sulphur dioxide, SO2. To optimize the H2 S catalytic oxidation process, the process was conducted in the temperature range 125—200 °C, at pressures 230—3200 kPa, with the O/H2 S ratio being varied from 1.05 to 1.20 and using different types of sour and acid gases as feed. The optimum temperature was determined to be approximately 175 °C for high H2 S conversion and low SO2 production with an O/H2 S ratio 1.05 times the stoichiometric ratio. The life of the activated carbon catalyst has been extended by removing heavy hydrocarbons from the feed gas. The process has been performed at elevated pressures to increase H2 S conversion, to maintain it for a longer period and to minimize SO2 production. The process is not impeded by water vapour up to 10 mol% in the feed gas containing low concentrations of CO2 (< 1.0). A decrease in H2 S conversion and an increase in SO2 production were obtained with an increase in water vapour in the feed gas containing a high percentage of CO2. The process works well with “sour natural gas” containing approximately 1% H2 S and with “acid gas” containing both H2 S and CO2. It gives somewhat higher H2 S conversion and low SO2 production with feed gas containing low concentrations of CO2. A kinetics study to determine the rate‐controlling step for the H2 S catalytic oxidation reaction over “granular Hydrodarco” activated carbon has been conducted. It was concluded that either adsorption of O2 or H2 S from the bulk phase onto the catalyst surface is the rate‐controlling step of the H2 S catalytic oxidation reaction.