The Role of Charcoal Ash Content in the Performance of Air Purification Filters

A nutshell-based activated carbon was treated with hydrochloric acid to partially de-ash it. The de-ashed sample was then treated with bromine water and subsequently hydrogenated. The base sample was also treated with bromine water and then hydrogenated. The surface areas and pore volumes available to water vapour were unchanged by these treatments, although the polar surface area was considerably reduced in each case. The sample with the lowest surface polarity had the worst performance (shortest penetration time) when pre-humidified at 80% RH and tested with hexane. Examination of the humidity leaving the bed during the adsorption of hexane vapour suggested that the rate-determining step was the surface transport of displaced water and that removing the ash content hindered this transport considerably. Bromination followed by hydrogenation, although reducing the polarity, did not remove the ash content and may even have improved its ability to transport displaced water.