Preparation and characterization of very thin polymer inclusion membranes (PIMs) and their application to the transport of thiocyanate

The possibility of reproducible fabrication of functioning polymer inclusion membranes (PIMs) thinner than 10 μm, referred to as very thin PIMs (VT-PIMs), was demonstrated with four membrane compositions used successfully in previous studies for the extraction of thiocyanate. These compositions included Aliquat 336 as extractant (carrier) and 70 wt% of one of the following base polymers: poly(vinyl chloride) (PVC), cellulose triacetate (CTA) or poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP). One PVC- and one CTA-based PIMs contained 10 wt% 1-tetradecanol as modifier and 20 wt% Aliquat 336, while another CTA-based PIM and the PVDF-HFP-based PIM contained only 30 wt% Aliquat 336. The PVDF-HFP-based membrane (effective thickness 7.4 μm) exhibited the highest rate of transport of thiocyanate between a feed and a receiving solution among the newly developed VT-PIMs. Its initial flux was found to be more than twice that of a conventional thickness PIM (50 μm) of the same composition while the long-term stability of these two PIMs, studied in consecutive transport experiments, was virtually identical. The results obtained indicated that VT-PIMs offered a promising way of significantly improving the transport performance of PIMs, thus making them attractive to separation applications in industry. The paper also reports on the development of a reliable method for determining the effective thickness of PIMs using their density, which is particularly useful for VT-PIMs where thickness measurements using optical microscopy are difficult to perform.