An investigation of temperature effects on the properties and CO2 absorption performance of porous PVDF/montmorillonite mixed matrix membranes

Abstract

Although alterations of polyvinylidene fluoride (PVDF) membrane performance and properties in contactor applications are more severe at high temperature, to date, detailed information on the relationship between performance and properties with temperature is available. Hence, this study was undertaken to improve thermal stability of PVDF membranes by montmorillonite (MMT) incorporation. The fabricated membranes were operated in a closed contactor loop with water temperature of either 27 °C or 80 °C, followed by measuring CO2 absorption flux before and after 2 days exposure. Higher partial pore wetting at elevated temperature resulted in performance reduction of 31% and 13% for plain PVDF and 5 wt% MMT-filled PVDF membrane (MMM hollow fiber), respectively. To determine the reasons, the membranes were immersed in water of 80 °C for 7 days and analyzed by analytical characterization methods after drying. It was revealed from FESEM images that large pores on the membrane surfaces became larger while the small pores became smaller, leading porous membrane surfaces to deform to semi-dense layers with small number of large pores. Furthermore, strong reductions in membrane gas permeance, porosity, contact angle and wetting resistance were detected after 7-day immersion. Therefore, changes in the absorbent-induced membrane properties were found to be the reasons of the flux reduction at high operation temperatures. The alterations were, however, less pronounced for PVDF-filled MMT membrane than the original PVDF indicating thermal stability enhancement effect of the embedded clay particles. The results suggest that the impregnation of polymeric membranes by hydrophobic inorganic particles can be an effective method to stabilize the performance and properties of PVDF hollow fibers at harsh contactor operating conditions.