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 fibres. Membranes are built in membrane systems like plate and frame, spiral-wound module, hollow fibre 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.
Such membranes are employed in a wide range of membrane operations, such as microfiltration, ultrafiltration, reverse osmosis, pervaporation, gas separation, dialysis or chromatography. The applications depend on the type of functionality incorporated in the membrane, which can be based on size-exclusion, chemical affinity or electrostatics.
Typical applications in which membranes have been used are water purification, removal of microorganisms in dairy products, water desalination, dehydrogenation of natural gas, hemodialysis or as components of fuel cells.