Commercially available non-woven MERV and HEPA filters are made of glass fibers which utilize traditional filtration mechanisms like inertial impaction, diffusion and interception, which involves sticking filtrates to the surface of the fiber. This has been explained by the single fiber filtration efficiency model. These surface filters clog up with filtrate after brief use, thus rendering it ineffective for long term applications. To address this problem, a novel depth filter media was synthesized in which flocks of Vapor Grown Carbon Nanofibers (VGCFs) were embedded in the microfibrous ACFs matrix. The single fiber efficiency model does not account for the role of internal porosity found in porous fibers like ACFs in filtration. Therefore, movement of filtrate into the pores has been contemplated for the first time. Similarly nanofibers were utilized because it enabled capture of NaCl aerosols via wall-slip phenomenon occurring over the nanofiber surfaces. Wall-slip causes increase in filtration efficiency without pressure drop penalty. Preliminary filtration experiments were conducted for NaCl aerosol filtration. The inherent wet pores of hydrophilic ACFs were expected to warehouse excess NaCl until saturation, potentially extending the dirt loading capacity. The results showed that the inclusion of nanofiber flocs improved the Quality Factor of the filter media, which was attributed to wall-slip. Additionally, chlorine mapping via EDS indicated the preferential loading of the VGCF flocks further indicating the wall-slip occurring over nanofibers. 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 loading capacity of the media was also found to be higher than MERV 16 and HEPA filter media at various RH conditions. Overall, this novel filter media shows promising results for long term and high dirt loading filtration applications due to wall-slip phenomenon occurring over nanofibers and due to the movement of NaCl into ACFs pores.

Novel depth filter media with carbon nanofibers and porous activated carbon fibers (ACFs) for enhanced filtration of aerosols

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