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Porous membranes as gas-liquid contactors are widely used in carbon dioxide (CO2) absorption systems. It provides larger mass transfer area and excellent operational flexibility. Membrane contactors have been considered as alternative to conventional approaches in removing CO2. In spite of its advantages over conventional technologies, membrane wetting is a major problem which reduces performance of CO2 absorption. This paper explains the concept of membrane wetting phenomenon and its influence on the CO2 mass transfer through the membrane and absorption performance. The factors that cause membrane wetting were presented including hydrophobicity of membranes surfaces, membrane pore size, liquid entry pressure and properties of absorbent liquid. Current proposed methods to alleviate the membrane wetting were reviewed and discussed. Development of mathematical model was presented for all types of membrane wetting modes, as well as its validity for CO2 physical and chemical absorption.

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The hydrophobic membranes have been widely explored to meet the membrane characteristics for the membrane distillation (MD) process. Inorganic metal oxide nanoparticles have been used to improve the membrane hydrophobicity, but limited studies have used nano clay particles. This study introduces halloysite nanotube (HNT) as an alternative material to synthesis a hydrophobic poly(vinylidene fluoride) (PVDF)-HNT membrane. The PVDF membranes were fabricated using functionalized HNTs (e.g., carnauba wax and 1H,1H,2H,2H-perfluorooctyl-trichlorosilane (FOTS)). The results were determined by Fourier transform infrared-attenuated total reflection, scanning electron microscope, goniometer and porometer to determine the desired hydrophobic membrane for direct contact membrane distillation (DCMD). The addition of FOTS-HNT (fs-HNT) and carnauba wax-HNT (fw-HNT) in the PVDF membrane enhanced the water contact angle (CA) to 127° and 137°, respectively. The presence of fw-HNT in the PVDF membrane exhibited higher liquid entry pressure (LEP) (2.64 bar) compared to fs-HNT in the membrane matrix (1.44 bar). The PVDF/fw-HNT membrane (Pfw-HNT) obtained the highest flux of 7.24 L/m2h with 99.9% salt removal. A stable permeability in the Pfw-HNT membrane was obtained throughout 16 h of DCMD. The incorporation of fw-HNT in the PVDF membrane had improved the anti-wetting properties and the membrane performance with the anti-fouling effect.