Improved multisite langmuir model for mixture adsorption using multiregion adsorption theory

Prediction of mixed gas adsorption by the multisite Langmuir (MSL) theory is significantly improved by incorporating the multiregion adsorption (MRA) theory. The new model, called the multiregion multisite Langmuir (MR-MSL) model, is thermodynamically consistent. MR-MSL uses the same pure-component isotherm parameters as MSL does, and no new parameters are introduced. Eight binary systems and one ternary system are used to test the MR-MSL model. For systems containing like components (such as mixtures of hydrocarbons and that of O₂ + N₂), MR-MSL yielded only minor improvements over MSL. This is true regardless of the magnitude of the differences in the pure-component MSL parameters among different components. For highly nonideal mixtures, MR-MSL results in very substantial improvements. It is also capable of predicting the azeotropic behavior of the adsorption of CO₂ + C₃H₈ on H-mordenite and the correct azeotropic compositions. For such systems, it is also shown that surface heterogeneity needs to be considered.