An evaluation of multicomponent absorption equilibria models

Abstract

An investigation into the modelling of competitive adsorption equilibria data using the ideal adsorbed solution theory (IAST), the modified simplified competitive adsorption models (MSCAM), and the equivalent background compound (EBC) method is presented. The models were evaluated with the only competitive isotherms available which quantified both natural organic matter (NOM) and synthetic organic chemical (SOC) adsorption. The data used a mixture of 1,1,2-trichloroethane (TCEA) and NOM from river water measured as dissolved organic carbon (DOC). The IAST method was applied by representing the NOM in the river water as pseudocomponents. It was observed that the laborious and time-consuming regressions of only the TCEA isotherm data yield different sets of parameters, many of which do not describe the NOM data well. Simultaneous regression of TCEA and NOM isotherm data, like TCEA isotherm data regression, is highly dependent on the initial guesses of the parameters. MSCAM simulated the NOM adsorption very well but TCEA less so. TCEA simulation with the EBC method provided good results, but unrealistic EBC characteristics led to poor predictions. Model predictions of the experiment showed that the MSCAM model described the data better than the IAST method, but not perfectly. DOC-based MSCAM simulation does not offer any significant improvements over molar-based simulation.