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Aromatic polyamide–hydrazides for water desalination. I. Syntheses and RO membrane performance



Wholly aromatic polyamide–hydrazides (PAH) were synthesized by low-temperature solution polycondensation of m-amino benzhydrazide (MABH)/p-amino benzhydrazide (PABH) with isophthaloyl chloride (ICL)/terephthaloylchloride (TCl) in N,N-dimethyl acetamide (DMAC)/N-methyl-2-pyrrolidone (NMP). The polymers were characterized for their properties. Membranes were prepared from these (PAH) polymers under different casting conditions by varying the casting solution composition, evaporation time, post-annealing treatment, etc. The reverse osmosis (RO) tests for these membranes were performed with 5000 ppm aqueous sodium chloride feeds at 40 and 70 kg/cm2 operating pressures. Addition of lithium chloride to casting solutions and annealing in hot water conferred optimum selectivity to RO membranes. Membranes showed rejections up to 98.5% at flux > 20 cm/day.

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