Performance of aromatic polyamide RO membranes synthesized by interfacial polycondensation process in a water–tetrahydrofuran system

In the present study, an attempt is made to synthesize thin film reverse osmosis membranes based aromatic polyamide polymer. Poly(m-phenylene isophthalamide), an aromatic polyamide, is synthesized in the laboratory by high-speed stirring interfacial polycondensation of m-phenylene diamine and isophthaloyl chloride in water and tetrahydrofuran solvents, respectively. FTIR results confirm the polymer synthesis. The yield of the polymer obtained is ∼100% of the theoretical value with an inherent viscosity of 1.99 dL/g. Different RO membranes were synthesized from this aromatic polyamide (PA) under different casting conditions by varying the casting solution composition and casting thickness using N,N-dimethylacetamide (DMAC) as solvent. As a result, five different membranes were obtained containing PA concentration ranged from 10 to 20% in three membrane casting thicknesses 0.1, 0.2 and 0.3 mm. The membranes were characterized by their physico-chemical properties. Mechanical characteristics showed that the increase in the polymer concentration from 10 to 20% in the membrane matrix as well as the increase in the membrane casting thickness from 0.1 to 0.3 mm resulted in increasing membrane strength and Young's modulus. On the other hand, this increase in the polymer concentration and membrane casting thickness resulted in membranes with poor elongation and toughness. SEM approved the anisotropic structure of the synthesized membranes. The reverse osmosis tests for the synthesized membranes were performed with 4000 ppm aqueous sodium chloride at operating pressures varied from 30 to 50 kg/cm2. All the membranes were characterized for their salt rejection (%), water flux (L/h m2) and permeability (L/h m2 bar). The data obtained for the RO performance showed that the increase in polymer concentration in the membrane content as well as the increase in the membrane casting thickness result in increasing salt rejection and decrease in both water flux and permeability. In 0.2 mm casting thickness membranes, the increase in polymer concentration from 10 to 20% results in an increase in salt rejection from 25.5 to 79.7%. Meanwhile, decrease in water flux and permeability ranged 34–12 L/m2 h and 0.9–0.3 L/m2 h bar, respectively also occurred in the membranes having polymer concentrations from 10 to 20% with the same 0.2 mm casting thickness.