A membrane is a selective layer that allows certain components to pass while rejecting others. Membrane technology uses these selective layers for efficient separation without the need for phase transitions. The actual membrane is typically a thin film manufactured from polymers, metals, or ceramics. Membranes can operate with liquid or gaseous feed streams and can be either dense or porous.
Membranes are manufactured in various geometries: flat sheets, spiral wound, capillary, and tubular. Separation by means of membranes requires concentration or pressure difference as the driving force. In pressure-driven water applications, membranes are categorized by pore size:
uses dense membranes without pores to desalinate seawater and produce potable water. In gas separation, membranes are used to separate oxygen from nitrogen or to improve natural gas quality by removing carbon dioxide.