Impact of moisture on the thermal behavior of K2CO3-impregnated respirator carbons Original Research Article

The effect of moisture on the kinetics of the reaction of K2CO3-impregnated carbons with air at elevated temperature has been studied. Differential scanning calorimetry (DSC) measurements, isothermal DSC measurements and oven exposure tests all show that the reaction of the impregnated carbons with air is accelerated by the presence of moisture adsorbed by the impregnated carbon. Reaction kinetics extracted from isothermal DSC measurements show that this acceleration is caused by an increase in the frequency factor (γ2) while the activation energy (Ea2) remains unchanged. For example, for an impregnated carbon containing 22.4% by weight moisture, the frequency factor was found to increase by about 65% compared to that of the dry precursor. X-ray diffraction experiments show that the increase in frequency factor is caused by a decrease in the particle size of the impregnant through a series of steps initiated by the adsorbed water. First, the deliquescent K2CO3 impregnant dissolves in sufficient adsorbed water; then this solution dries during heating to initially form KHCO3, which subsequently decomposes to form small nano-particles of K2CO3 that apparently have a larger specific surface area and hence more catalytic activity. We suspect that the adsorbed moisture will cause such impregnant redistribution, and hence accelerated reaction kinetics with air, whenever deliquescent impregnants on hydrophilic surfaces are used.