Abstract
Insufficient mechanical strength and wide pore size distribution of nanofibrous membranes are the key hindrances for their concrete applications in membrane distillation. In this work, various post-treatment methods such as dilute solvent welding, vapor welding, and cold-/hot-pressing processes were used to enhance the physical properties of styrene–acrylonitrile (SAN) nanofiber membranes fabricated by the modified electrospinning process. The effects of injection rate of welding solution and a working distance during the welding process with air-assisted spraying on characteristics of SAN nanofiber membranes were investigated. The welding process was made less time-consuming by optimizing system parameters of the electroblowing process to simultaneously exploit residual solvents of fibers and hot solvent vapor to reduce exposure time. As a result, the welded SAN membranes showed considerable enhancement in mechanical robustness and membrane integrity with a negligible reduction in surface hydrophobicity. The hot-pressed SAN membranes obtained the highest mechanical strength and smallest mean pore size. The modified SAN membranes were used for the desalination of synthetic seawater in a direct contact membrane distillation (DCMD). As a result, it was found that the modified SAN membranes performed well (>99.9% removal of salts) for desalination of synthetic seawater (35 g/L NaCl) during 30 h operation without membrane wetting. The cold-/hot-pressing processes were able to improve mechanical strength and boost liquid entry pressure (LEP) of water. In contrast, the welding processes were preferred to increase membrane flexibility and permeation.
Highlights
As a consequence of rapid population growth, climate change, and destructive human activities, the accessibility of potable water has become a global issue
Cetyltrimethylammonium bromide (CTAB) salt was bought from Merck (Darmstadt, Germany) and used in the polymer spinning solution preparation
SAN nanofiber membranes were fabricated by the electroblowing process as described in our previous work [39]
Summary
As a consequence of rapid population growth, climate change, and destructive human activities, the accessibility of potable water has become a global issue. Membrane-based desalination technologies have been introduced as a viable solution to produce potable from various water sources, including seawater. Reverse osmosis (RO) is a well-known membrane process for seawater desalination due to its good performance (>99% removal of monovalent and multivalent ions). Membrane distillation (MD) is a promising method for producing pure water from saline water sources. In MD, the water vapors in the feed side pass through the pores of a hydrophobic membrane and turn into liquid on the permeate side. The required driving force for water vapor transportation is supplied by the temperature difference between feed and permeate sides, and the liquid evaporation occurs on the membrane surface [7,8,9,10,11,12,13]
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