(205h) Filtration of NaCl Aerosols Using Porous Versus Non-Porous Filter Media

Commercial filter media such as MERV rated filters and HEPA are typically made of glass fibers which are non-porous. These filters use traditional filtration mechanisms such as interception, inertial impaction and diffusion, which involve sticking filtrates to the surface of the fibers. This has been explained by the single fiber efficiency model. These surface filters have a relatively short useful life because they clog with filtrates after brief use and go to a high pressure drop state rendering it useless. To overcome this problem, a novel three dimensional filter media with nanofiber flocks embedded within the microfibrous ACFs matrix was designed. This media is hereinafter referred to as “AU filter media”.

The single fiber filtration efficiency model does not account for the role of internal porosity in filtration. The movement of filtrate into the pores of the fibers have not been contemplated before. We hypothesized that the inherent wet pores of hydrophilic ACFs can potentially wick particulates such as NaCl until saturation, thus increasing the dirt holding capacity and therefore prolonging the life of the filter media. In addition, highly porous nanofiber flocks made of Vapor Grown Carbon Fibers (VGCF) were utilized because of the potential of the nanofibers to capture filtrates via wall slip phenomenon. Wall-slip occurs when the diameter of the fiber approaches the mean free path of air. This causes an increase in filtration efficiency without the anticipated pressure drop penalty.

Preliminary filtration experiments were conducted for NaCl aerosol filtration. The results showed that the initial filtration efficiency and quality factor improved with nanofiber flock inclusion. The EDS spectrum verified the preferential loading of NaCl into VGCF flocks. This was attributed to the wall-slip occurring over nanofiber flocks. The decrease in BET surface area and total pore volume of ACFs, after loading it with NaCl, indicated the transfer of NaCl into the wet pores of ACFs. More importantly, the dirt holding capacity of the AU media was found to be higher than MERV 16 and HEPA at both low and high RH conditions. In conclusion, this novel filter media shows promising results for long term and high dirt loading filtration applications due to the dual effect of wall-slip occurring over nanofiber flocks and intra-fiber NaCl storage in ACFs.