NER: Fractal Nanoagglomerates: A New Filter Media For HEPA Filters

This project seeks to determine whether a medium made of fractal agglomerates of nanoparticles will act as an efficient and cost-effective filter for removing ultra-fine aerosol particles from gas streams and to evaluate whether such a filter medium can perform as well or better than fiber-based HEPA filters with respect to providing low pressure drop, high filtration efficiency, and high capacity before clogging. The work also will develop models to predict filtration efficiency, pressure drop, and capacity of the nano-agglomerate filter medium. Nanoparticles in the dry state have been found to consist of porous agglomerates with a hierarchical fractal structure and a high porosity (> 0.99). This structure results in a multi-modal pore size distribution within the agglomerates, which is very different from the unimodal pore-size distribution found in widely used fiber-based HEPA filters. Preliminary evidence has shown that such nano-agglomerate filters act as a depth filters and thus have significantly greater capacity (up to two orders of magnitude) than traditional fiber-based HEPA filters. HEPA filters are widely used in many industrial processes and even in homes, and if successful, this work could have significant economic benefits.