ABSTRACT
This chapter begins with an analysis of the notion of "what is a membrane?" It argues that polymeric gas separation membranes are only a particular case of a much wider field of membranes used in different processes and based on various principles of operation. Physicochemical phenomena that form the foundations of some membrane and traditional processes are often the same. The history of research on the permeation properties of polymers and membrane gas separation reveals an interesting evolution of the materials being investigated. Simultaneously, since the 1960s interest in nontraditional types of membrane materials, such as media providing coupled or facilitated transport by means of free or fixed carriers, emerged. Much effort has been devoted to the development of efficient hollow fiber membranes and modules based on them. The chapter also presents an overview of the key concepts discussed in this book.
