Preparation of composite membranes via interfacial polyfunctional condensation for gas separation applications

Composite membranes were prepared by interfacial polycondensation of a water‐soluble diamine (4,4′;‐methylene dianiline [MDA] or ethylene diamine [EDA]) with an organic solvent (hexane)‐soluble 1,2,4,5‐benzenetetra acyl chloride (BTAC) on top of a porous polysulfone (PSF) support. For both the poly(BTAC‐MDA) and poly(BTAC‐EDA) composite film systems, the permselectivity of these films increases only slightly with an increasing number of coatings. The poly(BTAC‐MDA) composite membranes are treated at 135°C in a nitrogen atmosphere for 4 h, and they have a high selectivity [α*(CO2/CH4) = 20.51] and permeability [P̄(CO2) = 44.12 Barrer]. This is due mainly to the great chain stiffness of the formed polyimide, which has high selectivity. The high permeability is due to a porous polysulfone support. The trend of the permeability for this composite film is P̄(CO2) > P̄(O2) > P̄(N2) > P̄(CH4). In poly(BTAC‐EDA) composite membranes, the permeation of different gases decreases in the order of P̄(CO2) > P̄(O2) > P̄(CH4) > P̄(N2). As to the composite films being more permeable to CH4 than to N2, this is probably due to the presence of a considerable quantity of aliphatic chains (–CH2–CH2–) in the poly(BTAC‐EDA) composite film caused by its particularly excellent solubility for methane.