(652c) Developing Hollow Fiber Air Filters for Filtration of Ultrafine Particles

Air pollution is an important issue in recent decades. Among various air pollutants, particulate matters (PM) are of particular concerns due to their adverse health effects to human being. To remove these airborne particles, researchers have developed a variety of filters, such as high efficiency particulate air (HEPA) and electrospun air filters. However, most filtrations show a limited filtration efficiency for removing ultrafine particles (particles <0.3 mm).

Rather than normal flat sheet filters, the hollow fiber is another mature technique which has been applied to nanofiltration and gas separation. The particles separated by hollow fibers are within nanometer or even angstrom sizes. Moreover, hollow fibers are self-supported and have a large volume to area ratio. Therefore, we believe hollow fibers would be a great candidate as air filters to remove PMs, especially for ultrafine particles. The objectives of this study are to (1) fabricate suitable hollow fiber air filters by studying their membrane formation mechanisms; (2) investigate the effects of dope additives to fabricate fibers with high gas flux and filtration efficiency; (3) examine the operation mode of air filtration using hollow fiber filters to obtain the best separation performance.

In this study, we have developed various hollow fiber air filters from different polymer materials, such as polyvinylidene difluoride (PVDF), polyacrylonitrile (PAN), and polyethersulfone (PES). The experimental results showed that our hollow fibers were able to remove > 99.999% particles down to 30-50 nm. To further enhance the gas permeance and lower the pressure drop of hollow fibers, we introduced high molecular weight polyethylene glycol (PEG) and Pluronic F127 in polymer dopes. Moreover, the dope concentrations were decreased. As a result, the N₂ permeance of hollow fiber was increased by 5 time. In addition, we also developed another approach to increase the hollow fiber gas permeance by adding silica particles in dopes and washing out from the resultant hollow fiber subsequently. Finally, to ease the module fabrication process, the mechanical properties of hollow fibers were also considered. Comparing to PVDF and PES hollow fibers, PAN hollow fiber possessed the most balanced filtration performance in terms of N₂ permeance, mechanical properties, and filtration efficiency. In summary, hollow fiber air filters demonstrate an excellent filtration efficiency of ultrafine particles which show a great potential to be a new generational air filter.