Development and Application of Hollow Fiber Membranes Specialized in Direct Contact Membrane Distillation

Abstract

As a thermally driven process, membrane distillation (MD), has been investigated in application of the new technology for desalination process. Development in membrane market since 1980’s, improvement and better understanding toward membrane have started to obtain the desired properties in membrane separation process. MD process obtains pure water from evaporation of feed volatile components through porous hydrophobic membrane. Furthermore, MD process shows the similar evaporation law compared to evaporation process, but benefits operation process in low temperature and high separation efficiency. For these reasons, membrane distillation (MD) process is considered as new technology in desalination. However, the MD process is not commercially implemented yet due to its relatively very low permeability compared RO process. MD process has started to gain its interest recently because of availability in water treatment for high salt concentration. Especially, integrated MD with RO hybrid process for water desalination show the possibility to treat a high concentration of RO brine for enhancing the efficiency and water recovery. For the successful performance of MD, development of hydrophobic porous membrane should be investigated in future. In this study, PVC was chosen for the main polymer materials because commercial hydrophobic polymers are still relatively expensive in spite of the decreasing trend of membrane costs. The PVC, then, chloride on the PVC backbones were replaced with hydrophobic monomers via atomic transfer radical polymerization (ATRP) method to improve the hydrophobic characteristics for MD. The grafted PVC-g-octene polymers showed higher contact angle (114 °) and tensile strength than PVC (82 °). The grafted PVC-g-octene polymers were fabricated with both methods thermally induced phase separation (TIPS) and non-solvent phase separation (NIPS) as hollow fiber membranes with changing the concentration of dope solution, additives and bore solutions. The fabricated membranes were applied in the direct contact membrane distillation (DCMD) with various conditions for its performance stability without wetting phenomenon. These membranes exhibited pure water flux with 7.8Kg/㎡•h and high salt rejection with 99.99%. Form this result, the grafted PVC-g-octene porous hydrophobic hollow fiber membranes gave promising potential in DCMD for water desalination.