Thin film composite membrane 5563726 180660986 2007-12-28T19:45:32Z 164.107.78.100 /* Structure and Materials */ [[Thin film]] [[composite material|composite]] [[artificial membrane|membranes]] (TFC or TFM) are [[semipermeable membrane]]s manufactured principally for use in [[water purification]] or [[desalination]] systems. They also have use in chemical applications such as [[battery (electricity)|batteries]] and [[fuel cell|fuel cells]]. Essentially, a TFC material is a [[molecular sieve]] constructed in the form of a film from two or more layered materials. Membranes used in [[reverse osmosis]] are typically made out of [[polyimide]], chosen primarily for its permeability to water and relative impermeability to various dissolved impurities including [[salt (chemistry)|salt ions]] and other small, unfilterable [[molecule|molecules]]. == History == The first viable reverse osmosis membrane was made from cellulose acetate as an integrally skinned asymmetric semi-permeable membrane. This membrane was made by Loeb and Sourirajan at [[University of California, Los Angeles|UCLA]] in 1959 and patented in 1960. The current generation of reverse osmosis (RO) membrane materials are based on a composite material patented by [[FilmTec|FilmTec Corporation]] in 1970. FilmTec's FT30 membrane is known as a [[polyamide]] thin film composite membrane. == Structure and Materials == As is suggested by the name, TFC membranes are composed of multiple layers. Membranes designed for desalination use an active thin-film layer of polyimide layered with [[polysulfone]] as a porous support layer. Other materials, usually [[zeolites]], are also used in the manufacture of TFC membranes. == Applications == Thin film composite membranes are used in * Water purification; * as a chemical reaction [[buffer solution|buffer]] (batteries and fuel cells); * in industrial gas separations. == Limitations == Thin film composites membranes typically suffer from compaction effects under pressure. As the water pressure increases, the polymers are slightly reorganized into a tighter fitting structure that results in a lower porosity, ultimately limiting the efficiency of the system designed to use them. In general, the higher the pressure, the greater the compaction. Surface fouling: Colloidal particulates, bacteria infestation (biofouling). Chemical decomposition and oxidation. == Performance == A filtration membrane's performance is rated by selectivity, chemical resistance, operational pressure differential and the pure water flow rate per unit area. Due to the emphasis on flow rate, a membrane is manufactured as thinly as possible. These thin layers introduce defects that may affect selectivity, so system design usually trades off the desired flow rate against both selectivity and operational pressure. In applications other than filtration, parameters such as mechanical strength, temperature stability, and electrical conductivity may dominate. Saturation. == Active Research Areas == Nano-composite membranes (TFN). Key points: multiple layers, multiple materials. New materials, sythetic zeolites, etc. to obtain higher performance. Fuel-cells. Batteries. == See also == [[Langmuir adsorption]] [[Maxwell-Stefan diffusion]] Fighting Fouling with Cross linked Polyamide-Urea Membranes http://www.trisep.com/x20_sub4.htm [[Category:Filters]]