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

Law concentrations (e.g. < 3 %) of H2S 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 H2S catalytic oxidation process, the process was conducted in the temperature range 125 - 200 degrees C, at pressures 230 - 3200 kPa, with the O/H2S 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 degrees C for high H2S conversion and low SO2 production with an O/H2S 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 H2S 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 H2S conversion and an increase in SO2 product-ion 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% H2S and with "acid gas" containing both H2S and CO2. It gives somewhat higher H2S conversion and low SO2 production with feed gas containing low concentrations of CO2. PI kinetics study to determine the rate-controlling step for the H2S catalytic oxidation reaction over "granular Hydrodarco" activated carbon has been conducted. It was concluded that either adsorption of O-2 or H2S from the bulk phase onto the catalyst surface is the rate-controlling step of the H2S catalytic oxidation reaction.