AEROSOL FILTRATION BY SORBENT BEDS

Fixed beds of sorbent media are used for the evaluation of polynuclear aromatic hydrocarbons (PAH) present in air. Two-stage sampling and se parate extraction and analyses of PAH associated with aerosol particle s and those present in the vapor state are usually performed. The abil ity of commonly used sorbents to retain particulate matter introduces a potential for reducing the time and cost of PAH evaluation procedure s. The filtration efficiency of three sorbent media, Florisil, XAD-2, and polyurethane foam (PUF), for particles in 0.1 to 1 mum size range was studied using air flow rates from 4 to 250 L/min through a PS-1 so rbent cartridge. Theoretical considerations were used to identify the principal filtration mechanisms and to assess the predictability of th e aerosol filtration performance of sorbent filters. The results of th is study indicate XAD-2 to be an efficient filtration medium owing to the electrostatic enhancement of capturing and retaining aerosol parti cles. As a result of theoretical considerations, Brownian diffusion an d inertial deposition were found to be major filtration mechanisms acc ompanied by electrostatic effects. While the efficiency of the diffusi onal deposition mechanism was reasonably well predicted with available theories, modeling of submicron particle impaction at higher fluid ve locities appeared to be inadequate. Further developments are suggested to improve our understanding of filtration phenomena in sorbent beds under high flow rate conditions.