Nanofiltration (NF)

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Dupont

Wisconsin, USA

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Description
Product Reviews

Reverse osmosis (RO) and nanofiltration (NF), a membrane liquid separation technique, have many similarities. NF offers low rejection of monovalent ions like chloride and strong rejection of multivalent ions like calcium, in contrast to RO, which has high rejection of almost all dissolved solutes. With our experience, knowledge, and portfolio of reverse osmosis and nanofiltration membrane technology, we assist clients from a variety of markets and industries in resolving their most difficult water treatment problems. We are a worldwide acknowledged pioneer in liquid-separation innovations and solutions.
Crossflow and pressure
The flow of a solvent across a semipermeable membrane is reversed from an area of higher solute concentration to an area of lower concentration using nanofiltration membranes, which work similarly to reverse osmosis membranes in separation systems that use applied pressure to successfully overcome the system's osmotic pressure. Because of this "reversed" flow and the nanofiltration membrane's level of permeability, solutes that are too big to fit through the membrane stay on the side with the higher concentration, while purer water with acceptable or desired solutes passes through.
Another similarity between RO membranes and nanofiltration membranes is their application in crossflow arrangements. Fouling, or the buildup of solutes that are unable to flow through the semipermeable membrane, is lessened by crossflow. To put it simply, in crossflow, a pressurized feedwater flow pushes lower-concentration water through the NF membrane, while the higher-concentration water flow, which has been isolated, passes across the membrane's surface and removes the rejected salts and other contaminants. The higher-concentration water is referred to as the concentrate or reject, while the cleansed water is known as the permeate.
Factors that influence
Permeate flux and salt rejection are the two main performance factors of a nanofiltration membrane separation process. Rejection and flux (the rate of permeate transmitted per unit of membrane area) are known, inherent characteristics of membrane performance under particular reference conditions. The following variable parameters primarily affect a membrane system's flow and rejection:
Pressure: The permeate flux will rise and the permeate TDS will fall as the effective feed pressure rises.
Temperature: The permeate flow and the salt passage will increase as the temperature rises while maintaining constant pressure, recovery, and feedwater salt concentration.
The ratio of permeate flow to feed flow is known as recovery.
If the salt concentration rises to a point where the concentrate's osmotic pressure equals the supplied feed pressure, the permeate flux will drop and cease to increase recovery. As healing increases, the salt rejection will decrease.
Concentration of salt in the feedwater: As the concentration of salt in the feedwater rises, the permeate flow will fall and the salt passage will rise.
Additional elements that could impact an NF system's performance include:

Upkeep and functioning of the plant.
Design of pretreatment.

Our strategy for nanofiltration
Our industry-leading and internationally renowned FilmTecTM portfolio includes our nanofiltration membranes. Three layers make up FilmTecTM thin film composite membranes, each of which is made to meet certain specifications.

The layers consist of:

A support web made of polyester.
An interlayer of microporous polysulfone.
A barrier layer of ultrathin polyamide on the upper surface.

For a wide range of applications, FilmTecTM NF membranes provide exceptional performance in terms of flux, fouling resistance, and rejection of organics and salt. FilmTecTM elements are resistant to compaction, work well at temperatures up to 45 °C, and can function throughout a pH range of 2 to 11. Depending on the temperature, they can be cleaned efficiently at pH 1 and pH 13. (For the pH limits for certain NF membranes, please refer to the product data sheets.)
They work steadily over a number of years, even in challenging operating conditions, and are long-lasting and simple to clean.
When other salts like calcium and magnesium need to be decreased but the high level of sodium rejection that reverse osmosis (RO) membranes can provide is not required, FilmTecTM NF elements can be employed to filter public drinking water. Nanofiltration membrane softening is less expensive than sodium chloride (NaCL) zeolite softening and lime softening technologies. For instance, the FilmTecTM NF270 nanofiltration membrane provides steady performance following repeated cleaning, low energy usage, and reduced salt rejection. It is an excellent option for contaminated surface waters because of these characteristics.