Filtration of silica nanoparticles on conventional commercial filters

The increased use of silica nanoparticles in the workplace for the production of nanotech products raises concerns on the human exposure and environmental effects of nanoparticles. Filtration is a technology used for the removal of particles in industrial gas streams. However, particles approaching molecular sizes smaller than the gas mean free path could not follow diffusion filtration or Brownian motion and could pass through a filter without being removed from the gas stream. The purpose of my research is to determine the effect of nanoparticle size, gas surface velocity and filtration time on the removal efficiency of silica nanoparticles using commercially available filters.;A bench scale filtration systems was designed, set up and tested for the filtration efficiency of silica nanopowder using pleated and high-efficiency particulate air (HEPA) filters. The experimental apparatus consisted of a compressed air supply system, nanoparticle aerosol generator, filtration chamber, and nanoparticle detection system. Purified compressed air was used to generate aerosol streams of silica nanoparticles using an atomizer. The generated aerosol stream was then passed through the filtration chamber. The particle number concentration and size distribution of the silica nanoparticles were measured upstream and downstream of the filtration chamber through water-based condensation particle counters and a scanning mobility particle sizer instrument.;The filtration efficiency tests were conducted under gas surface velocities of 2.0 cm/s, 2.8 cm/s and 3.6 cm/s using MERV 11 fiber filters and a HEPA filter. Experimental results showed that 55-85% of total silica nanoparticles were removed using the fiber filter while 97.5-99.5% of the silica nanoparticles were removed using a HEPA filter. The filtration efficiency decreased 10-20% when gas surface velocity increased 30%. The filtration efficiency decreased 10-20% when silica nanoparticles increased from 14 to 290 nm in size. Experimental data was also modeled using single fiber theory. The single-fiber model predictions were in good agreement (total relative error, TRE = 11.4%, sum of the squared error, SSE = 111) with experimental results during the first filtration hour when the gas surface velocity was 2.8 cm/s. At the gas surface velocity of 2.0 cm/s, the single-fiber model predicted the experimental results the best (TRE = 12.6%, SSE = 110) at the fourth hour of filtration time.;HEPA filters are more efficient than MERV 11 filters to protect people when they have the potential of being exposed to engineered nanomaterials in the workplace.