Adsorption of Pollutants on Charcoal Cloth in Simulated Guard Filters

Abstract

The removal of toluene, tetrachloroethylene, heptane and o-xylene from air by adsorption on activated charcoal cloth and the subsequent regeneration of the cloth in a stream of hot air was investigated. The above four solvents were chosen as typical organics, due to their less hazardous properties. They are all in reasonably common use and relevant detailed information is readily available about them. The potential of charcoal cloth for use as a filter was studied. The experimental results could be represented by the Langmuir isotherm for the macropore region of the cloth. The micropore region is highly dependent on the manufacturing process due to variations in the quality of the cloth. This variation obstructs close correlation. The adsorbate-adsorbent mass ratio was obtained at breakthrough. The theoretical adsorbate-adsorbent mass ratio was calculated and gave a good approximation to experimental values. Equations were developed to calculate the theoretical time required to reach an effluent concentration 10% of the inlet solvent vapour concentration. Experiments at various values showed reasonable correlation. The residual activity of the charcoal cloth remained fairly constant even after repeated regeneration. The apparatus constructed for this study consisted of a solvent vaporiser, an air-solvent mixing section, a filter canister holding the cloth and a ventilated oven for regeneration. Four different designs of canister were tried and it has been found that perpendicular flow shows higher adsorption capacity than parallel flow, even though the former shows higher pressure drop. A 0.2286 m (9") diameter canister was used to conform to typical fume cupboard dimensions. The results were compared with the 0.1524 m (6") diameter canister, and it was concluded that the smaller canister would be advantageous provided that the physical parameters, especially the volumetric flow rate were similar to the conditions used in the present research.