Heterogeneous Catalytic H2S Oxidation within Supercritical CO2 for a New Sulfur Recovery Process
Many natural gas sources can have small amounts of acid gases (H2S and CO2). These acid gases are removed from the natural gas for the consumers due to toxicity and low heating value. Conventionally, acid gas is removed by absorption into aqueous amine solutions. This separated acid gas can then be injected into reservoirs for sequestration or can be further processed to convert the H2S to S8 by sulfur recovery. For low-quality acid gases (< 1% H2S in CO2), available methods to remove H2S results in waste rather than marketable sulfur. The remaining CO2 is at near atmospheric pressure, often being released to the environment due to high recompression costs. In this thesis, an alternative sulfur recovery process is investigated to produce marketable sulfur and high-pressure CO2 using post cryogenic separation of low-quality acid gases. Cryogenic distillation for acid gas separation is beneficial, resulting in a high-pressure liquid form of acid gas that does not require recompression. However, currently available low-pressure methods to convert H2S to S8 do not take the advantage of this high-pressure. Heterogeneous catalysis was utilized to convert H2S to S8 within the high-pressure CO2 in this thesis. For the high-pressure sulfur recovery process to be viable, several studies were completed in order to provide the best conditions to carry out the heterogeneous catalysis in high-pressure CO2. Sulfur solubility within high-pressure CO2 was initially studied to define the process conditions to maintain a single-phase product and subsequent separation of produced sulfur and CO2. The sulfur solubility study also allowed for the modelling of the sulfur fugacity coefficient within high-pressure CO2, which was utilized in a high-pressure Gibbs Free Energy Minimization routine to calculate the theoretical equilibrium conversion limit of H2S to S8. Heterogeneous H2S oxidation catalyses were experimentally carried out to verify calculated high-pressure thermodynamic conversion limits by the Gibbs Free Energy Minimization routine. Kinetic limitations were found at lower temperatures and higher pressures in pursuit of improving the thermodynamic conversion limit. The kinetics of the high-pressure heterogeneous H2S oxidation catalysis were studied to model the kinetic limitations of the reaction within the high-pressure CO2. The three models developed allow for high-pressure calculations of S8/CO2 solubility conditions, thermodynamic H2S equilibrium conversion limits, and minimum residence times required for the equilibrium conversion limits to establish. These models therefore enable practical industrial condition optimization to carry out the heterogeneous catalytic oxidation of H2S within high-pressure CO2.
Lee, S. (2021). Heterogeneous Catalytic H2S Oxidation within Supercritical CO2 for a New Sulfur Recovery Process (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.