Nano filtration is a separation process characterized by organic, thin-film composite membranes with a pore size range of 0.1 to 10nm. Unlike reverse osmosis (RO) membranes, which reject all solutes, NF membranes can operate at lower pressures and offer selective solute rejection based on both size and charge.
Wide range of Nano filtration membranes offer varying degrees of ion selectivity to aid in the development of customized process solutions. Nano filtration membranes allow water and some salts to pass through the membrane while retaining multivalent ions, low molecular weight molecules, sugars, proteins, and other organic compounds. Nano filtration membrane products have been proven to offer great resistance to fouling, a high degree of selectivity, and the physical durability needed for application in a wide range of industrial separation processes.
The membrane separation process known as Nano filtration is essentially a liquid phase one, because it separates a range of inorganic and organic substances from solution in a liquid – mainly, but by no means entirely, water. This is done by diffusion through a membrane, under pressure differentials that are considerable less than those for Reverse Osmosis, but still significantly greater than those for ultrafiltration. It was the development of a thin film composite membrane that gave the real impetus to Nano filtration as a recognized process, and its remarkable growth since then is largely because of its unique ability to separate and fractionate ionic and relatively low molecular weight organic species.
NF has greatly extended their capabilities in very high or low pH environments, and in their application to non-aqueous liquids. NF membranes tend to have a slightly charged surface, with a negative charge at neutral pH. This surface charge plays an important role in the transportation mechanism and separation properties of the membrane.
As with any other membrane process, Nano filtration is susceptible to fouling, and so Nano filtration systems must be designed to minimize its likelihood – with proper pretreatment, with the right membrane material, with adequate cross-flow velocities to scour the membrane surface clear of accumulated slime, and by use of rotating or vibrating membrane holders.