Aerosol Filtration by Sorbent Beds

Fixed beds of sorbent media are used for the evaluation of poiynuclear aromatic hydrocarbons (PAH) present in air. Twostage sampling and separate extraction and analyses of PAH associated with aerosol particles and those present in the vapor state are usually performed. The ability of commonly used sorbents to retain particulate matter introduces a potential for reducing the time and cost of PAH evaluation procedures.

The filtration efficiency of three sorbent media, Florisil, XAD-2, and polyurethanefoam (PUF), for particles in 0.1 to 1 µm size range was studied using airflow rates from 4 to 2501 /mm through a PS 1 sorbent cartridge. Theoretical considerations were used to identify the principal filtration mechanisms and to assess the predictability of the aerosol filtration performance of sorbent filters. The results of this study indicate XAD-2 to be an efficient filtration medium owing to the electrostatic enhancement of capturing and retaining aerosol particles.

As a result of theoretical considerations, Brownian diffusion and inertial deposition were found to be major filtration mechanisms accompanied by electrostatic effects. While the efficiency of the diffusional deposition mechanism was reasonably well predicted with available theories, modeling of submicron particle impaction at higher fluid velocities appeared to be inadequate. Further developments are suggested to improve our understanding of filtration phenomena in sorbent beds under high flow rate conditions.