The development and application of nanofiltration (NF) membranes(做超链NF膜) is about 20 years later than that of reverse osmosis membranes. In the 1970s, J·E·Cadotte's research on NS-300 membrane was the beginning of research on NF membrane. At that time, Israel Desalination Company used "hybrid filtration" to represent the membrane separation process between reverse osmosis and ultrafiltration, called loose RO membrane. Later, Filmtec Company in the United States called this membrane technology nanofiltration, which has been used until now. After that, nanofiltration technology developed rapidly, and membrane modules were commercialized in the mid-1980s. At present, nanofiltration technology has become one of the research hotspots in the field of membrane separation in the world.
So far, the understanding of the precise definition, mechanism, characteristics, etc. of nanofiltration membranes is far from sufficient.
A relatively unified interpretation of the definition of nanofiltration membrane in the academic community includes the following seven aspects:
①Nanofiltration membrane is between reverse osmosis and ultrafiltration membrane, and the separation skin layer on the membrane surface may have a nano-scale microporous structure.
② Compared with the reverse osmosis membrane, the NaCI removal rate is above 95%. Generally, a membrane with a NaCI removal rate below 90% can be called a nanofiltration membrane.
③ The reverse osmosis membrane has a high removal rate for almost all solutes, while the nanofiltration membrane only has a removal rate for specific solutes.
④ The pore size of the nanofiltration membrane is more than 1nm, generally 1-2nm.
⑤ Mainly remove solute particles of about one nanometer, and the molecular weight cut-off is 200-1000 Dalt
⑥ Almost all reverse osmosis membranes are made of polyamide, while nanofiltration membrane materials can be made of various materials, such as cellulose acetate, cellulose acetate-triacetate, sulfonated polysulfone, sulfonated polyethersulfone, and aromatic polyamide composite materials and inorganic materials.
⑦ Generally, the surface of the nanofiltration membrane forms a polymer electrolyte, so it often has a strong negative charge.
