TABLE OF CONTENTS The subject of membrane separations can be broadly extended to include not only the separation of gaseous mixtures, but the two-phase separation of liquid-phase components into a gaseous phase, a process called pervaporation, and the separation of liquid phases as such, plus the separation of solutions, or solid-rich concentrates apart from liquids or lean solutions. Variously included are the processes called reverse osmosis, hyperfiltration, and ultrafiltration. What is called the permeate phase may be the desired product, or what is called the reject or raffinate phase may instead be the desired product. At the same time, we may speak of single-stage separations, multistage separations, and differential permeations and of concurrent and countercurrent flow-all with or without recycle. Concomitantly, we may make the usually necessary simplification of perfect mixing within a phase.
The methods and literature are briefly reviewed for solid-suspension separations, solution-phase separations, liquid-phase separations, and gas-phase separations. In the terminology used, the objective is to separate a feed stream (or streams) into a permeate phase and a reject phase, either of which may contain the components) of more interest. For a single membrane, say, the permeate phase remains on the feed side or high-pressure side of the membrane, and is subsequently discharged, whereas the reject or raffinate phase builds up on the opposite or low-pressure side of the membrane, and is then discharged.
For the most part, the membrane is regarded as a solid, albeit liquid membranes may serve if sufficiently immiscible with the feed, reject, and...
