ABSTRACT
In recent years membranes and membrane processes have become industrial products of substantial technical and commercial importance. The worldwide sales of synthetic membranes in 1990 were in excess of US $2.0 x 109. Taking into consideration that in most industrial applications membranes account for about 40% of the total investment costs for a complete membrane plant, the total annual sales of the membrane based industry is close to US $5 x 109 [1]. Membranes and membrane processes have found a very broad range of applications. They are used today to produce potable water from seawater, to treat industrial effluents, to recover hydrogen from off-gases, or to fractionate, concentrate, and purify molecular solutions in the chemical and pharmaceutical industry. Membranes are also key elements in artificial kidneys and controlled drug delivery systems. The growing significance of membranes and membrane processes as efficient tools for laboratory and industrial scale mass separations is based on the several properties, characteristic of all membrane separation processes, which make them superior to many conventional mass separation methods. The mass separation by means of membranes is a physical procedure carried out at ambient temperature; thus the constituents to be separated are not exposed to thermal stress or chemical alteration. This is of particular importance for biochemical or microbiological application where often mixtures of sensitive biological materials have to be separated. Furthermore membrane processes are energy-efficient and rather sim-
pie to operate in a continuous mode. Up-or downscaling is easy and process costs depend only marginally on the plant size.
