The effects of temperature and humidity on the ageing of TEDA impregnated charcoals

Samples of triethylene diamine (TEDA) impregnated 207B carbon have been aged for up to 1000 hours at temperatures in the range 40 deg. to 70 deg. and relative humidities of 50% and 90%. The rate of ageing (in terms of methyl iodide-131 trapping efficiency) increases progressively as the temperature is raised above 50 deg. C and also as the relative humidity is increased; below 50 deg. C however the ageing rate is relatively low, even at 90% RH. A parallel examination by temperature programmed desorption of the growth of surface oxygen groups with ageing indicates that, unlike KI impregnated carbons, the groups formed on the TEDA carbons are not linked to the decline in performance. Also, the presence of an amine, which, as a group, are generally regarded as anti-oxidants, does not reduce the rate of surface oxidation. Since the rate of ageing of TEDA carbons has been shown to follow the increase in the partial pressure of water above the sample it is proposed that TEDA carbon ageing could be caused by loss of TEDA either by a process akin to steam distillation, or by reaction with or catalysis by water, to form a less efficient impregnant. (author). 6 refs, 8 figs, 2 tabs