Solutions for Separations


           Membrane separation processes are based on the ability of semipermeable membranes of the appropriate physical and chemical nature to discriminate between molecules primarily on the basis of size, and to a lesser extent, on shape and chemical composition.  A membrane's role is to act as  a selective barrier, enriching certain components in a feed stream, and depleting it of others. In this regard, the phenomena is very similar to "osmosis", which has been observed and studied for more than 265 years, beginning with the efforts of the French scientist Abbe Nollet in 1748.  However, there was little interest in the osmosis process as an industrial tool until the early 1950s, mostly because membranes capable of withstanding the high pressures necessary (600 psi, 40 bar) and giving high flux and high rejections were not available.  Serious study of reverse osmosis (RO) as a practical tool for the production of potable water from brackish or saline water began in 1953 when the U.S. Department of the Interior, Office of Saline Water, began supporting research projects aimed at developing RO technology for desalination.  The first breakthrough was made by Reid and Breton (1959) who, while screening membrane materials for desalination, discovered that cellulose acetate membranes gave high rejections and reasonable fluxes (dewatering rates).  Shortly thereafter, Loeb and Sourirajan (1960, 1962) developed the casting procedure for asymmetric cellulose acetate membranes and demonstrated that flux could be greatly improved by making asymmetric rather than homogeneous membranes.

            This landmark event is generally considered the birth of modern membrane separations technology. Originally termed the "surface skimming" of sea water or brackish water for the production of pure water by a non-thermal energy-efficient method, it led to a vast array of applications unmatched by any other processing technique in its variety and versatility.  Desalination and water treatment by reverse osmosis is probably the earliest and best known application. The decade of the 1970s saw increasing usage in the chemical process industries (paint, textiles, oil recovery, pulp and paper) and in the 1980s, it was the food and biotechnology industries that benefited most from membrane technology, particularly ultrafiltration (UF). With the development and maturation of sister processes microfiltration (MF) and nanofiltration (NF), the applicability of membrane technology widened considerably in the 1990s, especially for water treatment (for potable, industrial, semiconductor and biotechnology uses) and in waste treatment in the form of membrane bioreactors. Today, it is difficult to imagine a liquid phase process that would not benefit from one or more of the many membrane technologies. 


Cheryan, M. 1998. Ultrafiltration and Microfiltration Handbook. CRC Press/Taylor & Francis, Boca Raton, FL.

Reid, C.E. and Breton, E.J. 1959. Water and ion flow across cellulose acetate membranes. J.Appl. Polymer Sci. 1 (2): 133-143.

Loeb, S. and Sourirajan, S. 1960. Sea water demineralization by means of semi-permeable membranes. UCLA Engineering Report No. 60.

Loeb, S. and Sourirajan, S. 1962. Sea water demineralization by means of an osmotic membrane.  Advan. Chem. Ser. 38: 117-132.