Adsorption of C-1-C-7 normal alkanes on BAX-activated carbon. 2. Statistically optimized approach for deriving thermodynamic properties from the adsorption isotherm

A new stepwise (SW) statistically optimized model and also a virial-type (V T) model were correlated successfully with adsorption equilibria for the n- alkane series C-1-C-7 On Westvaco BAX-1100 activated carbon over a wide ran ge of temperatures and pressures. Both models predicted reasonable temperat ure-dependent isosteric heats of adsorption, and from these slight dependen cies, sensible deviations between the adsorbed- and gas-phase heat capaciti es were indicated. However, the SW model was more reliable under extreme co nditions. The SW model also showed that the observed linear dependence of l n(P) on 1/T at constant loading, according to the Clausius-Clapeyron equati on, only occasionally contributed to the overall description; statistically , more complicated temperature dependencies of ln(P) were revealed, indicat ing that the temperature dependence of the isosteric heat of adsorption can be easily overlooked. The ideal-gag assumption, inherent in the Clausius-C lapeyron equation, was also relaxed. The resulting real-gas isosteric heats of adsorption were reduced compared to the ideal-gas values, especially at high loadings and high temperatures. Finally, the temperature-independent isosteric heats of adsorption predicted from the potential theory correlati on developed in Part 1 of this series fell almost in the exact middle of th e range predicted by the temperature-dependent SW and VT models for the lig htly to moderately adsorbed alkanes, but severely underpredicted those for the heavily adsorbed alkanes (i.e., heavier than n-propane).