Aromatic Polyamide Membranes

Aromatic polyamide (aramid) membranes represent an important segment of the rapidly developing technology for the separation of components of aqueous solutions, gaseous mixtures and organic liquid mixtures. This paper highlights the historical aspects of polyamide membrane research in Du Pont from 1962 to 1984. Materials science aspects of this paper deal with the broad range of structures possible with aramid polymers and membranes. Structure-property relationships of aramid membranes are illustrated on four levels of structure: segmental composition of the polymer, steric relationships of the segmental structure, morphology of the asymmetric membranes and morphology of thin-film composites. Steric relationships for aromatic polyamides and polyimides for membranes intended for gas separations correlate well with flux/selectivity properties. The nature of asymmetry in aromatic polyamide membranes is discussed with reference to flux/selectivity properties of membranes for water desalination. Characteristics and performance of Du Pont's Permasep permeators which employ aramid membranes in the form of fine hollow fibers for desalination of brackish and sea water illustrate how the materials science studies of aromatic polyamide membranes have been applied to provide the basis of an important membrane business.