Polymeric Membranes

An artificial membrane, also called a synthetic membrane, is a membrane prepared for separation tasks in laboratory and industry. Its active part, which permits selective transport of material, usually consists of polymers or ceramics, seldom glass or metals. A membrane may contain auxiliary parts for mechanical support, drainage, patch etc. The driving force of the material transport is given by concentration, pressure, electrical or chemical gradient across the membrane. Membranes can be prepared in the form of flat sheets, tubes, capillaries and hollow fibers. Membranes are built in membrane systems like plate and frame, spiral-wound module, hollow fiber module, tube-in-shell module.

Some of the most common artificial membranes are polymeric membranes. Under some conditions ceramic membranes can be utilized with advantage. Polymeric membranes are membranes that take the form of polymeric interfaces, which can selectively transfer certain chemical species over others. There are several mechanisms that could be deployed in their functioning. Knudsen diffusion and solution diffusion are prominent mechanisms. Polymeric membranes are of particular importance in gas separation applications. Key industrial applications include: oxygen-nitrogen separation, removal of organics and natural gas enrichment. Gas mixtures can be effectively separated synthetic membranes.

Polymeric membranes are employed in separation of hydrogen from gases like nitrogen and methane, recovery of hydrogen from product streams of ammonia plants, separation of methane from biogas and others. Usually nonporous polymeric membranes are utilized. There, vapors and gases are separated due to their different solubility and diffusivity in polymers. Polymers in glassy state, generally more effective for separation, predominantly differentiate in diffusivity. Small molecules of penetrants move among polymer chains according to the formation of local gaps by thermal motion of polymer segments. Free volume of the polymer, its distribution and local changes of distribution are of the utmost importance. Then diffusivity of a penetrant depends mainly on the size of its molecule.

« Back