In the present work, consolidated agglomerates and granules of nanoparticles are introduced as a filter media to remove submicron size particles (0.1 to 1 µm, solid and liquid) which are the most difficult to filter, and are commonly known as the most penetrating particle size (MPPS). Recent research conducted by our group revealed that granular beds of nanoparticle agglomerates/granules have collection efficiency comparable to HEPA fiber based filters but with filtration capacities larger than HEPA.

The nanoparticles used as a filter media are fumed silica, hydrophilic or hydrophobic, and carbon black. These powders can be treated or processed, i.e., granulated or consolidated by vibration during sieving, to form granules ranging from 150 µm to 800 µm in size that can be customized into a granular bed. In this case, filtration occurs due to the deep bed filtration mechanism. It was found that the granulated bed provides a larger capacity than HEPA fiber based filters.

The customized filters were challenged against aerosol with solid PSLS particles or liquid oil droplets. In both cases, an atomizer was used to nebulize a water solution containing the solid PSLS particles or a solution of oil-ethanol. The experimental setup allowed challenging a customized filter and a HEPA filter simultaneously. The number of particles before and after both filters was measured with a Condensation Particle Counter (CPC). In addition, the particle size distribution of the challenging aerosol and the cleaned air was found by using a Scanning Mobility Particle Sizer (SMPS). Both data were used in the calculation of the collection efficiency at different gas velocities passing through the filters. The customized filters were characterized during operation by their pressure drop and their collection efficiency. The pressure drop across the filters was simultaneously monitored to determine its change with respect to time in order to compare filter's capacity against HEPA. Collection efficiencies similar to HEPA filters have been achieved with our granular filters made of agglomerates/granules of nanoparticles with the advantage of a higher capacity which is given by a slower rate in the increase of bed pressure drop when compared against the pressure drop increasing rate of HEPA filters.