Nanofiltration is a membrane separation process whose cut-off lies between that of reverse osmosis and ultrafiltration. Diluted solutions of monovalent ions can mostly pass through a nanofiltration membrane unhindered while most of the multi-valent ions (such as sulfate and carbonate) are retained.
Nanofiltration membranes have a nominal pore size of approximately 0.001 microns and an MWCO of 180 to 2000 daltons. Hence the components possessing this molecular weight can be easily separated from the components possessing higher molecular weight. The commonly used operating pressure is in the range of 3 – 40 Bar. The surface of the NF membranes is slightly charged. Charge interaction plays major role because the dimensions of the pores are less than one order of magnitude larger than the size of ions. This property also helps in separating ions of different valencies
The selectivity of a nanofiltration membrane is determined by two different parameters. Firstly, retention depends on the compound size i.e. from molecular weight. As far as nanofiltration membranes are concerned, retention and permeability are also a function of electric charge and the valence of the salts and compounds in the solution.
The rejection rate of divalent and multivalent cations especially calcium and magnesium is higher in nanofiltration due to this, it is used extensively in industrial water softening applications as well as pre-treatment for reverse osmosis.
More salt is allowed to pass in nanofiltration as compared to reverse osmosis. NF can operate at higher recoveries as compared to reverse osmosis, which enables the conservation of water usage because of lower concentrate stream flow rate.
The other main difference between reverse osmosis and the NF lies in the removal of monovalent ions such as chlorides. The monovalent ion level removed by the RO is 98-99% level at 200 psi. But in case of NF membrane’s removal of monovalent ions ranges between 50% to 90%. The removal of monovalent ion by NF depends on the material and manufacture of the membrane due to this, there is a variety of Nanofiltration membranes available. Nanofiltration uses less fine membrane hence the feed pressure required in the system is lower as compared to RO systems. The fouling rate in NF system as compared to RO system is also lower.
AMFOR® NF membrane elements are designed for process applications where a separation of solutes is desired. NF membrane is a durable membrane designed to reject organics with a molecular weight above 200 while passing monovalent salts, we also can produce sanitary NF membranes.
Membrane type : Poliamide thin-film composite
Molecular weight cut-off: 200-300 Da
Appliance with FDA regulations.
Industrial membranes