OVERVIEW

Membrane separations are an accepted means for separating non-condensable gases; that is, gases that ordinarily condense only under low-temperature or cryogenic conditions. The technology might be in wider use if (1) better and more selective membrane materials were available and (2) the necessary mathematical representations and calculations were better spelled-out for the separations attainable. In fact, the one sometimes depends on the other. Of particular interest are ways in which separations could be enhanced using relatively nonselective membranes.

A special case is pervaporation, in which the feed material is a liquid but the permeate is a gas. That is, the temperature and pressure of the permeate are such that the permeated components exist in the gaseous phase. Conceivably, however, the feedstream could be a gas but the permeate conditions and compositions are such that the components constitute a liquid phase. For the particular purposes here, however, all streams are in a gaseous state.

The general subject has been explored in a number of past reviews ^[1]- ^[8] and, for instance, is the main concern of the Journal of Membrane Science. The subject has also been of interest to the Gas Research Institute, which has held workshops on the subject. ^[3], ^[4] The Gas Research Institute, in fact, jointly sponsored a project with the Dow Corning Corporation and others aimed at correlating and predicting the permeability behavior of membranes from the chemical structure. ^[9], ^[10]

The American Institute of Chemical Engineers has maintained an...