Filtration characteristics of a fibrous filter pretreated with anionic surfactants for monodisperse solid aerosols

Abstract

This study elucidates the effects of using an anionic surfactant-pretreated filter as an electret filter on the aerosol penetration. Anionic surfactants (sodium oleate, SO; sodium dodecyl sulfate, SDS) were used to pretreat polypropylene fibrous filters to make them negatively charged. Various factors, including the particle size (0.05– 0.5 μ m ), the aerosol charge state (Boltzmann-equilibrium charge, neutral and singly charge), the face velocity (0.1, 0.3, 0.5 and 1.0 m / s ), the species of aerosol (sodium chloride, NaCl and aluminum oxide, Al 2 O 3 ), the relative humidity (RH 30% and 70%) and the concentration of surfactant (0.01, 0.05 and 0.08 M) were considered to evaluate their effects on the aerosol collection characteristics. Experimental results from our study demonstrate that the aerosol penetrations through anionic surfactant-pretreated filters (ASPFs) were lower than through the untreated filter. The 0.3 μ m -aerosol penetrations through an untreated, 0.01, 0.05 and 0.08 M SO-pretreated filters with Boltzmann-equilibrium charged aerosol were about 78%, 53%, 45% and 40%. The penetration of 0.3- μ m aerosol of 0.01, 0.05 and 0.08 M SDS-pretreated filters with Boltzmann-equilibrium charged aerosol were, 62%, 58% and 51%. Pretreating the filter with anionic surfactant did not change the structure of the filter and the mechanical capture force. The electric field measured by an electrofieldmeter of the ASPFs was larger than that of untreated filter obviously. These findings imply that pretreatment with anionic surfactant made the filters charged. The surface charge of the ASPFs increased with the anionic-surfactant concentration. The increase of the collection efficiency of the ASPFs is in the range of 5–30%, and that depends on the aerosol size and surfactant concentration. Comparing between the aerosol penetration through the ASPFs with singly charged aerosol and that through the untreated filter with neutral aerosol indicates that the penetration through the ASPFs with singly charged aerosol decreases by a factor of 1.3–12.5. In contrast with the penetration through the ASPFs to that through the untreated filter with neutral aerosol, the penetration reduction factor of the ASPFs is in the range of 1.1–1.9. As the results shown, the Coulombic capture force is dominant for the smaller aerosol ( < 0.1 μ m ) and the dielectrophoretic capture mechanism works at larger aerosol size ( > 0.2 μ m ) . Additionally, the penetrations through the ASPFs increased with the face velocity. ASPFs performed better when the tested aerosol had a larger dielectric constant ( k ) such as the penetration through 0.05 M SO-pretreated filter with 0.3 μ m Al 2 O 3 aerosol ( k = 9.6 ) was 47% and that with NaCl aerosol ( k = 5.9 ) was about 53%. RH has no effect on the aerosol penetration through the ASPFs.