Adsorption of cyanogen chloride and hydrogen cyanide by activated and impregnated carbons

Equilibrium adsorption and desorption isotherm data at room temperature are reported for cyanogen chloride and hydrogen cyanide vapors on BPL grade activated carbon, ASC whetlerite and several ASB impregnated carbons. Isotherm data have been analyzed in terms of the Dubinin-Polanyi equation. The experimental affinity coefficients (β_ex) for the vapors, with respect to chloroform, were determined from the slope of the Dubinin-Polanyi plot. The relative adsorptive capabilities of the adsorbents were assessed by comparing the theoretical affinity coefficient (β_th) with β_ex · β_th was estimated assuming that physical adsorption is the dominant adsorption process. Cyanogen chloride shows about 20% higher adsorption than predicted on BPL activated carbon and about 30% higher than predicted on the ASB impregnated carbons. Hydrogen cyanide shows about 30% higher adsorption than predicted on BPL activated carbon and about 45% higher adsorption than predicted on the ASB impregnated carbons. In the case of ASC whetlerite, the adsorption of both vapors was much greater than predicted and the isotherms displayed a levelling-off trend in the low pressure region indicating strong retention through chemisorptive interactions. No unique β_ex could be determined from the original isotherms. An attempt was made to separate the chemisorption contribution from the total adsorption, and thus assess β_ex for the physical adsorption contribution.