Fabrication and Investigation of Polyamine Thin Film Composite Membrane based on Poly(2,5-benzimidazole) with High Chemical Stability

Hypothesis: Despite the wide application of nanofiltration (NF) membranes in aqueous solutions, their potential usage in the treatment of organic solution has been considered. However, it is still a challenge to develop polymeric solvent resistant nanofiltration membranes (SRNF) that can be applied in a broad range of organic solvents. There are many polymers with high resistance to solvents such as polyimide (PI) and polybenzimidazole (PBI) which used for making ultrafiltration membrane for SRNF. Poly(2,5-benzimidazole) (ABPBI) is a sort of polymer with similar or even better chemical structure than PBI. At first, a high-purity poly(2,5-benzimidazole) (ABPBI) polymer was synthesized. In the next step, ABPBI and polyvinylidene fluoride (PVDF) membranes were synthesized. TFC polyamine membranes were prepared by the interfacial polymerization (IP) of polyethylenimine and cyanuric chloride. Finally, the physical and chemical structure as well as chemical stability and membrane performance of UF and TFC membranes obtained by ABPBI polymer were evaluated and compared with those of PVDF membrane. Chemical stability tests including solubility, gel content and swelling degree indicated much higher stability of ABPBI membrane. The swelling degree in ethanol, methanol and n-hexane for ABPBI and PVDF membranes were 0.0132, 0.175, 0.01 and 0.9, 0.808, 0.34, respectively. The water fluxes for ABPBI-PA and PVDF-PA membranes were 20 and 26 kg/m2.h and the rejection for 10 ppm aqueous solution of crystal violet (CV, 408 g/mol) was 85 and 81, respectively.