Affinity coefficients of the Polanyi/Dubinin adsorption isotherm equations: A review with compilations and correlations

Abstract A historical review presents the assumptions and approximations made in the Polanyi and Dubinin adsorption theories, which have defined the affinity coefficient β and proposed parameters to calculate it. A previous compilation of experimental β [Wood GO. Activated carbon adsorption capacities for vapors. Carbon 1992;30:593–599] for gases and vapors on activated carbons has been supplemented to more than double the available database. Experimental affinity coefficients reported and calculated for water vapor have also been compiled. For water vapor at relative humidity >50% on normal industrial (unacidified) activated carbons, 0.1 is a good average value of the affinity coefficient relative to that of benzene. Direct correlations of experimental affinity coefficients (other than for water) with molecular parachor, molar polarizability, and molar volume were successful ( β standard deviations of 0.09, 0.12, and 0.12, respectively). Power functions with exponents less than unity (0.9, 0.75, and 0.9, respectively) provided slightly better fits of predictions to experimental values (standard deviations of 0.08, 0.10, and 0.11, respectively). Any of these correlations can be used. Listed advantages of using molar polarization make it the correlation parameter of preference. Correlation of β with critical temperature was largely unsuccessful. No obvious effects of adsorbate polarity, adsorbent molecular sieve properties, or form of the Dubinin equations were detected for β and its correlations.