THE RATES OF ADSORPTION AND DESORPTION OF WATER-VAPOR FROM AIR-FLOWS THROUGH ACTIVATED CARBONS

The rates of water vapor adsorption from humidified air flows have been determined from weight changes at 22 to 25-degrees-C for a number of commercial adsorbent carbons and whetlerites. The rates were exponential with time at constant humidity from 40 to 95% relative humidity (RH). The rates of drying into an equivalent flow of ultradry air were determined. The two rates were nearly equal for new materials, indicating that the time dependence of desorption and adsorption follows equivalent tortuous paths through the porous structures. The rate of adsorption for weathered carbons was less in magnitude than for the subsequent desorption. The difference is attributed to the displacement of volatile impurities by adsorbed water vapor. Measurements were also made after ozone and/or hydrazine pretreatments at ambient temperature. The steady-state values calculated from the rate data were close to independent isotherm measurements.