The primary role of the ultrafiltration membrane is to allow the passage of water and low molecular weight solutes, but retain macromolecules whose size is larger than the pore size of the membrane. The ultrafiltration membrane enables concentration, purification and fractionation of macromolecules in solution to be carried out at temperatures close to ambient temperature and without a phase change or addition of solvents. Ultrafiltration utilizes permeable membranes to separate macromolecules and suspended solids from solution on the basis of size, separation compounds with molecular weights from 10,000 to 500,000. The application of high pressure to the feed side of the membranes enables the passage of water through the membrane. Nanofiltration and Reverse Osmosis Membranes Reverse Osmosis is a separation technique involving the passage of water molecules through a semipermeable membrane due to the application of pressure and involves no change in either phase or temperature.
Reverse osmosis follows the well-known phenomenon of osmosis.
Osmosis is the flow of water from an area of low concentration to an area of high concentration of dissolved solids. For example, in figure 5, the beaker is full of pure water and the tube is full of a solution with a high concentration of salt water. Separating the two solutions is a semipermeable membrane. The water will continue to transfer from the dilute solution to the more concentrated until the pressure difference from the volume changes or the two sides are equal to the osmotic pressure. Osmotic pressure is a property particular to the solution and is independent of the membrane.