Thin-film composite membranes (TFC or TFM) are

semipermeable membrane Semipermeable membrane is a type of synthetic or biologic, polymeric membrane that allows certain molecules or ions to pass through it by osmosis. The rate of passage depends on the pressure, concentration, and temperature of the molecules o ...

s manufactured to provide selectivity with high permeability. Most TFC's are used in

water purification Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water that is fit for specific purposes. Most water is purified and disinfected for hu ...

water desalination Desalination is a process that removes mineral components from saline water. More generally, desalination is the removal of salts and minerals from a substance. One example is soil desalination. This is important for agriculture. It is possible ...

systems. They also have use in chemical applications such as

gas separation Gas separation can refer to any of a number of techniques used to separate gases, either to give multiple products or to purify a single product. Swing adsorption techniques Pressure swing adsorption Pressure swing adsorption (PSA) pressurizes ...

dehumidification A dehumidifier is an air conditioning device which reduces and maintains the level of humidity in the air. This is done usually for health or thermal comfort reasons or to eliminate musty odor and to prevent the growth of mildew by extracting wate ...

, batteries and

fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen fuel, hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most bat ...

s. A TFC membrane can be considered a

molecular sieve A molecular sieve is a material with pores of uniform size comparable to that of individual molecules, linking the interior of the solid to its exterior. These materials embody the molecular sieve effect, in which molecules larger than the pore ...

constructed in the form of a film from two or more layered materials. The additional layers provide structural strength and a low-defect surface to support a selective layer that is thin enough to be selective but not so thick that it causes low permeability. TFC membranes for water treatment are commonly classified as

nanofiltration Nanofiltration is a Membrane technology, membrane filtration process that uses nanometer sized pores through which particles smaller than about 1–10 nanometers pass through the membrane. Nanofiltration membranes have pore sizes of about 1–10 n ...

(NF) and

reverse osmosis Reverse osmosis (RO) is a water purification process that uses a partially permeable membrane, semi-permeable membrane to separate water molecules from other substances. RO applies pressure to overcome osmotic pressure that favors even distribu ...

(RO) membranes. Both types are typically made out of a thin

polyamide A polyamide is a polymer with repeating units linked by amide bonds. Polyamides occur both naturally and artificially. Examples of naturally occurring polyamides are proteins, such as wool and silk. Artificially made polyamides can be made throug ...

layer (<200 nm) deposited on top of a

polyethersulfone Polysulfones are a family of high performance thermoplastics. These polymers are known for their toughness and stability at high temperatures. Technically used polysulfones contain an aryl- SO2-aryl subunit. Due to the high cost of raw material ...

polysulfone Polysulfones are a family of high performance thermoplastics. These polymers are known for their toughness and stability at high temperatures. Technically used polysulfones contain an aryl- SO2-aryl subunit. Due to the high cost of raw material ...

porous layer (about 50 microns) on top of a

non-woven Nonwoven fabric or non-woven fabric is a fabric-like material made from staple fibre (short) and long fibres (continuous long), bonded together by chemical, mechanical, heat or solvent treatment. The term is used in the textile manufacturing ind ...

fabric support sheet. The three layer configuration gives the desired properties of high rejection of undesired materials (like salts), high filtration rate, and good mechanical strength. The polyamide top layer is responsible for the high rejection and is chosen primarily for its permeability to water and relative impermeability to various dissolved impurities including salt ions and other small, unfilterable

molecule A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...

s. Although not fully commercialized yet, TFC's are also used in other water treatment technologies, including

Forward osmosis Forward osmosis (FO) is an osmotic process that, like reverse osmosis (RO), uses a semi-permeable membrane to effect separation of water from dissolved solutes. The driving force for this separation is an osmotic pressure gradient, such that a " ...

membrane distillation Membrane distillation (MD) is a thermally driven separation process in which separation is driven by phase change. A hydrophobic membrane presents a barrier for the liquid phase, allowing the vapour phase (e.g. water vapour) to pass through the m ...

, and

electrodialysis Electrodialysis (ED) is used to transport salt ions from one solution through ion-exchange membranes to another solution under the influence of an applied electric potential difference. This is done in a configuration called an electrodialysis ...

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

UCLA The University of California, Los Angeles (UCLA) is a public land-grant research university in Los Angeles, California, United States. Its academic roots were established in 1881 as a normal school then known as the southern branch of the C ...

in 1959 and patented in 1960. In 1972, John Cadotte of North Star Technologies (later FilmTec Corporation) developed the first interfacial polyamide (IP) thin-film-composite (TFC) membrane. The current generation of reverse osmosis (RO) membrane materials are based on a composite material patented by FilmTec Corporation in 1970 (now part of

DuPont Dupont, DuPont, Du Pont, duPont, or du Pont may refer to: People * Dupont (surname) Dupont, also spelled as DuPont, duPont, Du Pont, or du Pont is a French surname meaning "of the bridge", historically indicating that the holder of the surname re ...

). Today, most such membranes for reverse osmosis and nanofiltration use a Polyamide active layer.

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

layered with

as a porous support layer. The active layers tend to be extremely thin and relatively nonporous. The chemistry of these layers often imparts selectivity. Meanwhile the support layers tend to need to be both extremely porous and robust to higher pressures. Other materials, usually

zeolites Zeolites are a group of several Microporous material, microporous, crystalline aluminosilicate minerals commonly used as commercial adsorption, adsorbents and Catalysis, catalysts. They mainly consist of silicon, aluminium, oxygen, and have the ge ...

, are also used in the manufacture of TFC membranes.

Applications

Thin film composite membranes are used in * Water purification * In RO Plant; * as a chemical reaction

buffer Buffer may refer to: Science * Buffer gas, an inert or nonflammable gas * Buffer solution, a solution used to prevent changes in pH * Lysis buffer, in cell biology * Metal ion buffer * Mineral redox buffer, in geology Technology and engineeri ...

(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 Biofouling or biological fouling is the accumulation of microorganisms, plants, algae, or small animals where it is not wanted on surfaces such as ship and submarine hulls, devices such as water inlets, pipework, grates, ponds, and rivers that ...

). 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 importance of throughput, 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 throughput against both selectivity and operational pressure. In applications other than filtration, parameters such as mechanical strength, temperature stability, and electrical conductivity may dominate.

Active research areas

Nano-composite membranes (TFN). Key points: multiple layers, multiple materials. Mitigation of membrane fouling New materials, synthetic zeolites, etc. to obtain higher performance. NanoH2O Inc. commercialized a membrane in which zeolite nanoparticles were synthesized and embedded within an RO membrane to form a thin-film nanocomposite, or TFN, which has proven to be more than 50-100% more permeable compared to conventional RO membranes while maintaining the same level of salt rejection. Seah MQ, Lau WJ, Goh PS, Tseng HH, Wahab RA, Ismail AF. “Progress of Interfacial Polymerization Techniques for Polyamide Thin Film (Nano)Composite Membrane Fabrication: A Comprehensive Review.” Polymers (Basel). 2020 Nov 27;12(12):2817. doi: 10.3390/polym12122817. PMID: 33261079; PMCID: PMC7760071. Fuel-cells. Batteries.

References

{{reflist Filters Membrane technology Water technology