Membrane Separation:

Two types of classifications for different separation methods were proposed-one based on the property leading to separation and the other on equilibrium and rate processes. The membrane separations figure under the category of molecular geometry in one and in the rate processes under first. Inclusion of membrane separations in these two classifications extremely aptly describes the principles behind the membrane separations. It processes utilize semipermeable/ permselective membranes to achieve separations of several chemical substances that could be either in solid, liquid or in gaseous forms. Membrane processes could be used to separate chemical substances in several sizes from microscopic to molecular stages. For instance, membranes could be used to separate suspended particles from a turbid solution, separation of dissolved solutes from saline waters, separation of toxic metabolic products from blood, separation of a gas from a mixture of gases and so on.

The membrane separations are variants from several of the other separation processes like solvent extraction, chromatographic methods involving partition, adsorption, ion exchange etc. which involve equilibrium among the substances getting separated and the separating phases. The onset of equilibrium in this process restricts the extent of separation achievable and the equilibrium is shifted suitably to achieve the desired level of purity. In addition, in some of these processes, a reversal of equilibrium is often necessary to regenerate the separating medium so that it can be reused. Within these processes that are equilibrium governed, we always talk of how much separation is accomplished within terms of partition coefficients or distribution ratios.