(287g) Sweetening Natural Gas with High Hydrogen Sulfide Concentrations: Hydrogen Sulfide and Hydrocarbon Separations with Cellulose Triacetate Hollow Fiber Membranes

Natural gas typically contains methane (CH₄), C₂ and C₃ hydrocarbons, carbon dioxide (CO₂), hydrogen sulfide (H₂S), and other trace gases. The acid gases, CO₂ and H₂S, must be largely removed from the natural gas mixture to meet pipeline specifications. Although some natural gas reserves produce gas with H₂S concentrations in excess of 20%, measurements of H₂S separation are not commonly reported. H₂S permeation and hydrocarbon separations were investigated using commercial asymmetric cellulose triacetate (CTA) hollow fiber membranes with realistic mixtures of hydrocarbons containing H₂S. The gas mixture used in this study was 5% CO₂, 21% H₂S, 15% C₂H₆, and 10% C₃H₈, balanced with CH₄. The mixed-gas permeation tests were carried out at three temperatures, 15 ^â—¦C, 25 ^â—¦C, and 35 ^â—¦C, and four pressures, 15 bar, 29 bar, 39 bar, and 46 bar. The permeate header pressure was 1.013 bar (atmospheric pressure). H₂S permeation increased with increasing feed pressure. At feed pressures between 15 bar and 30 bar, the H₂S/hydrocarbon selectivities were stable. However, selectivities decreased dramatically at feed pressures in excess of 30 bar, likely due to penetrant-induced plasticization of the hollow fibers by H₂S and CO₂. Modulation of process temperature was found to be an effective tool by which plasticization could be managed, making bulk H₂S removal from realistic hydrocarbon mixtures using cellulose acetate economically feasible. We will discuss how temperature and pressure can be considered for controlling and optimizing the H₂S removal in field applications.