An asymmetric membrane of polyimide 6FDA-BDAF and its pervaporation desulfurization for n-heptane/thiophene mixtures

Polyimide (PI) is a type of important membrane material. A soluble polymer was synthesized from 4,4 ''-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 2,2-bis[4-(4-anninophenoxy) phenyl] hexafluoropropane (BDAF) by the two-step polymerization method. The polymer was proved to be polyimide 6FDA-BDAF by the Fourier transform infrared (FT-IR), the 1H-NMR and 19F-NMR spectra. An asymmetric membrane was prepared with the synthesized polyimide 6FDA-BDAF, it was porous in the 50 pm height bulk and dense in a 3-5 pm height surface. The membrane was used to separate n-heptane/thiophene mixtures by pervaporation with sulfur (S) contents from 50 to 900 pg g(-1). The total flux was enlarged from 7.96 to 37.61 kg m(-2) h(-1) with temperature increasing from 50 to 90 C. The membrane's enrichments factor for thiophene were about 3.13 and dependent on the experimental conditions. The experimental results demonstrated that polyinnide 6FDA-BDAF would be a potential membrane material for desulfurization and controlled release of the S-containing fertilizer.