Adsorptive retention of volatile vapors for nondestructive filter leak testing

Experimental equilibrium and breakthrough data are reported for the adsorption of 14 vapors on activated and impregnated carbons to demonstrate their effectiveness as tracers in filter leak measurements. Particular attention is given to the effect of adsorbed water and vapor solubility on breakthrough time. Measured adsorption isotherms are shown to approximate the order of retention in the dynamic mode, indicating that breakthrough is equilibrium-controlled. Breakthrough time is significantly affected by the amount of adsorbed water, limiting the use of higher vapor pressure tracers to adsorbents with low water loadings. On adsorbents with less than 0.025 g/g of water, the order of retention of the higher vapor pressure tracers is HFC-236fa > HFC-227ea > HFC-245cb > C-318 > CFC-12 > HFC-134a. With water loadings up to 0.38 g/g, the retention is improved significantly with lower vapor pressure tracers. The order of retention is 2-propanol > ethanol > methyl acetate > methyl nonafluorobutyl ether > HFC-4310mee > perfluorodimethylcyclobutane > CFC-11 > ammonia. Although adsorbed water reduces the breakthrough time, it is shown that the relative retention is improved by an increase in the vapor's solubility. The increase in retention correlates with the number of hydrogen atoms and inversely with the number of fluorine atoms on the adsorbate.