Characterization of Macroporous Hydrophobic Membranes Used in Membrane Distillation Process
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FILTECH 2015 Conference
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The field of membrane distillation is currently enjoying a great deal of interest and its field of application is expanding rapidly. However, many commercial macroporous hydrophobic membranes used in membrane distillation (MD) experiments have been developed for microfiltration (MF) applications and the specification of the manufacturer data are characteristics for MF. Since, the membrane structural characteristics are directly associated with the MD separation performance, the successful application of MD (to ensure MD efficiency and to avoid pore wetting) is aided by knowing the membrane morphological parameters (e.g., mean pore size, pore size distribution and porosity). In this paper a number of techniques which are used for the characterization of various porous MD membranes were tailored. Gas permeation experiment and liquid displacement method are used to determine membranes? effective porosity, mean pore sizes and their distributions. A penetration pressure determination method was also developed to determine the minimum required pressure for the aqueous solution to go into dry membrane pores. The gas permeation test was conducted using nitrogen as the standard gas, while the liquid displacement and penetration pressure determination methods were performed using isopropanol alcohol as a standard medium. The comparison between the membrane pore sizes obtained from different characterization techniques showed the gas permeation test actually measures the diameter of the large pores of the membrane, while liquid displacement method takes into account the smaller pores. Therefore, these techniques are complementary rather than completive for characterization of the MD membranes. Additionally, liquid entry pressure (LEP) measurements showed a strong dependency of pore wetting in the pore sizes, the presence of organic solutes in aqueous solution and on the type of organic solutes.