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 [P?(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 P?(CO₂) > P?(O₂) > P?(N₂) > P?(CH₄). In poly(BTAC-EDA) composite membranes, the permeation of different gases decreases in the order of P?(CO₂) > P?(O₂) > P?(CH₄) > P?(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.