Effects of Adsorbed Water Vapor on the Adsorption Rate Constant and the Kinetic Adsorption Capacity of the Wheeler Kinetic Model

A recent trend in occupational safety and health has focused on the use of respiratory protective equipment to supplant engineering controls as the primary means of protecting workers from toxic substances. Respirator adsorbent cartridges have been demonstrated to have a finite capacity to adsorb toxic vapors. The knowledge of when this limit is approached or has been exceeded is crucial to the user. The Wheeler kinetic breakthrough model has been shown to describe accurately organic vapor penetration through beds of activated carbon. The model, however, does not account for competitive adsorption of water vapor or other organic vapors. The investigations reported here demonstrate the effect of adsorbed water vapor on the kinetic adsorption parameters (kinetic rate constant and kinetic saturation capacity) of the Wheeler equation. Adsorbent beds were equilibrated at varying concentrations of water vapor and then challenged with carbon tetrachloride vapor-laden air. Dry carbon had an initial rate constant of 62.5 s-¹¹ and a kinetic adsorption capacity of 0.36 g of adsorbed CCh/gram (g/g) of adsorbent. These parameters decreased in proportion to the amount of water vapor adsorbed, with the minimum predicted values occurring at 100% relative humidity. The minimum experimental value for the kinetic rate constant was 17.6 s -1, a decrease of 73% from the dry carbon values. The minimum predicted value for the kinetic adsorption capacity was 0.16 g/g, a decrease of 45%.