The main objective of this program is to develop a membrane process for the separation of hydrogen sulfide and other impurities (carbon dioxide and water vapor) from low-quality natural gas. The overall program involves development and parametric testing of appropriate membrane materials in the form of thin-film composite membranes. These membranes will then be made on a larger scale and incorporated into spiral-wound modules which will be tested first in the laboratory, and then at different field sites. A technical and economic analysis of the membrane process will then be performed and compared with existing processes. An extensive experimental study was performed to assess the properties of our membranes under various feed conditions. Composite membranes made from four polymers belonging to the family of polyether-polyamide copolymers were investigated to determine their hydrogen sulfide/methane and carbon dioxide /methane selectivity. Two membranes (designated MTR 701 and MTR 704) were then selected for a further parametric study. The parametric study showed that the membranes exhibit a hydrogen sulfide/methane selectivity in the range 40--70 and carbon dioxide /methane selectivity in the range 14--16. These selectivities are maintained at pressures as high as 1,000 psig and with water vapor present in the feed gas. The methane flux of our membranes is comparable to or higher than that of commercially available cellulose acetate membranes, whereas the hydrogen sulflde/methane selectivity of our membranes is two to three times higher.
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