Abstract
A non-destructive method has been developed to measure the residual adsorption capacity (RAC) of charcoal filter beds while in use. A small sample of a weakly adsorbed gas is pulsed as a square wave into the gas stream that passes through the adsorption filter. The effluent pulse is detected by means of an appropriate detector. The RAC of the carbon bed is proportional to the retantion time of the gas. The filter is an adsorption bed that behaves as a gas-solid Chromatograph, and only bare sites, not covered by heavy adsorbate, are available to the pulsed gas. The system chosen was M-11 gas mask canisters containing 2.8 cm × 87 cm 2 ASC Whetlerite charcoal beds loaded to various degrees with highly polar dimethyl methyl phosphonate (DMMP), which simulated a strongly adsorbed pollutant. 10 cm 3 aliquots of non-polar test gases methane and ethane were pulsed into a stream of dry air, at flow velocities of 5.47 l./min (1.05 cm/sec) and bed temperature of 25°C. The retention times of CH 4 dropped from 0.9 min over bare ASC Whetlerite to 0.5 min over carbon 50% saturated with DMMP. Ethane times fell from 24 to 7 min. The accuracy of RAC determination using methane was ± 1.0%. The time required for the test was < l min for methane, < 30 min for ethane.
Published Version
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