Gasmembranen

Gasmembranen are selective barriers that separate gas mixtures by allowing some molecules to pass more readily than others. They are used to reduce or separate components within gas streams, such as oxygen, nitrogen, carbon dioxide, methane, or hydrogen, by maintaining a driving force such as a partial pressure difference across the membrane.

Most polymer membranes operate by the solution-diffusion mechanism: gas molecules first dissolve into the membrane material and then diffuse through it at rates governed by solubility and mobility. Porous inorganic membranes can rely on different transport regimes, including Knudsen diffusion and molecular sieving, depending on pore size. The performance of a gas membrane is commonly described by two metrics: permeability, P, which measures the rate of gas transport through the membrane, and selectivity, α, which quantifies the membrane’s ability to distinguish between gas pairs. Permeability is often reported in Barrer, and selectivity is the ratio of the permeabilities of two gases. A well-known constraint in membrane design is the trade-off between permeability and selectivity, sometimes summarized by the Robeson upper bound curve.

Materials used for gas membranes include polymeric types (such as polyimides, polysulfones, and polyether ether ketones), inorganic membranes (alumina, silica, zeolites), and mixed-matrix membranes that combine polymers with inorganic fillers. Applications span air separation (producing oxygen-enriched or nitrogen-enriched streams), natural gas sweetening (CO2/CH4 removal), hydrogen recovery, and carbon dioxide capture.

Manufacturing approaches include phase inversion and hollow-fiber fabrication for polymers, as well as thin-film deposition and templated growth for inorganic membranes. Challenges in the field include physical aging and plasticization of polymers, fouling and aging of membranes, thermal and chemical stability, and achieving scalable, cost-effective performance.