Abstract

While granular activated carbon (GAC) filters have been used extensively for removal of contaminants from industrial gas streams, little research has been done on their adsorption capacity for indoor environmental purposes where ventilation systems are used to remove volatile organic compounds (VOC) contaminants and may allow higher air recirculation. This research investigates the performance of GAC filters for indoor environments by challenging them with various VOCs and subsequently measuring their removal efficiencies and breakthrough times. A small environmental, closed-loop, dynamic test chamber was designed, constructed and used to measure the performance of eight different GAC filter samples when they were exposed to cyclohexane, ethyl acetate and toluene at different humidity levels. Three of the filters were composed of virgin activated carbon with granules of different sizes and/or shapes. The remainder filters were impregnated with either phosphoric acid or potassium hydroxide. The breakthrough times and removal efficiencies of the filters were analyzed. Within the concentration range examined and at 50% relative humidity (RH), toluene exhibited the highest adsorption capacity on the filters, followed by ethyl acetate and cyclohexane. At 50% RH, the virgin filters were 25% more efficient in adsorbing the VOCs than the impregnated ones. For toluene, the 50% breakthrough times of filters 1A, 1B and 1C were 4, 0.13 and 0.03 hours, respectively, and the 80% breakthrough times were 5.60, 1.03 and 0.50 hours. respectively. The effects of RH on adsorption of soluble (ethyl acetate) and insoluble (cyclohexane and toluene) VOCs on the performance of GAC filters were also investigated. The presence of water vapor in the chamber had little effect on the adsorption capacity of the toluene until about 50% RH. At 50% RH and above, an increase of 16.5% in adsorption capacity of ethyl acetate occurred, while the adsorption capacity of cyclohexane and toluene rapidly decreased. The 80% breakthrough times of filters IA, 2A and 3A for toluene decreased on average, up to 33%. 38% and 25%, respectively, when the RH increased from 30% to 70%. Therefore, competitive adsorption of VOCs with water vapor molecules shortened the breakthrough times of the filters for toluene and cyclohexane as the RH level increased.