Long term stability of PTFE and PVDF membrane contactors in the application of propylene/propane separation using AgNO3 solution

This study reports the long term stability of highly hydrophobic polymeric membranes such as PTFE and PVDF in the application of membrane contactors for propylene/propane separation using silver nitrate as carrier. Initial comparisons revealed that the PTFE membrane module was able to operate under non-wetting conditions where the separation performance was the highest. Conversely, the PVDF membrane module showed a much lower performance under the same operating conditions due to partial wetting of the pores. Moreover, a long-term stability analysis was also carried out for a period of 2 months to check whether any additional deterioration in the performance of these membranes was possible. Interestingly, the performance of PTFE did not change with time, whereas the PVDF membranes exhibited a linear decrease in the overall mass transfer coefficient along the investigation period, owing to an increase in the wetted pore fraction of the membrane. Characterization of these hollow fibres after 2 months contact with the solvent revealed that PVDF have undergone some considerable accumulation of silver deposits that induced the formation of voids and defects on the membrane surface. The tendency for PVDF to wet with the solvent and its incompatibility with Ag degrees particles resulted in significant variations to the membrane properties which makes PVDF a non-suitable membrane material for this application. On the other hand, although silver deposition still occurred on the PTFE membranes, its impact was not as severe as that of PVDF to further cause any structural damage. PTFE membranes seem to be a better option for the application of olefin/paraffin separation using silver carriers as no deterioration in the long term performance was observed, at least for an operating period of 2 months as demonstrated in this article. (c) 2013 Elsevier Ltd. All rights reserved.