Aromatic Polyamide Hydrazide Membranes for Reverse Osmosis Separations

Abstract

Wholly aromatic polyamide hydrazide (PAH) polymers were synthesized by low temperature polycondensation from freshly prepared m-amino benzhydrazide, p-amino benzhydrazide, isophthaloyl chloride, and terephthaloyl chlorides in dimethyl acetamide solvent. A series of film-forming polymers prepared by altering the molar ratios of the reacting monomers was characterized in terms of % moisture regain, η_inh, and x-rays. Asymmetric membranes prepared from selected polymer samples were tested in reverse osmosis test cells, and the pure water permeability and the membrane constant were determined. An optimum meta: para molar ratio of the reacting monomers has been identified for the best performance under reverse osmosis which gave solute separation close to 98% for a feed concentration in the range of seawater. The PAH membranes appear to be potential barrier candidates for treatment of effluents containing ammonium, nitrates, etc. and radioisotopes. Separation data for a few other solute systems were also evaluated and compared with those obtained from cellulose acetate membranes.