Semi-permeable membranes - Gas permeability membranes

A gas permeation membrane is a non-porous, organic, anisotropic (asymmetric) or composite artificial membrane.

In all cases, the active layer is a dense, glassy polymer or elastomer layer less than 0.1 µm thick. In the case of composite membranes, this active layer is supported by one or more more porous, mechanically stronger layers, the whole having a thickness of around 100 µm.

A gas permeability membrane is therefore similar to a pervaporation membrane, but is different from a porous gas diffusion (gas effusion) membrane, which also separates the constituents of a gas mixture, but based on the relative values of pore diameter and mean free path of the molecules.