Prediction of Ternary Liquid Adsorption on Solids from Binary Data

Analysis of Binary Adsorption Excess Isotherms at the Liquid/Solid Interface

Adsorption excesses of binary liquid mixtures are the primary experimental quantity in liquid-phase adsorption onto porous or disperse solids. Binary liquid adsorption isotherms can be easily measured and allow statements to be made about the characteristics of solid and liquid mixtures, immersion behaviour at the liquid/solid interface, multi-component adsorption, etc. In this paper, a brief summary is given of different ways of interpreting and analysing binary isotherms over the whole concentration range. Experimental data and calculation examples show that thermodynamics provides a powerful tool for obtaining relevant information from such isotherms.

Further advancements in predicting adsorption equilibria using excess formalism: calculation of adsorption excesses at the liquid/solid interface

Prediction of adsorption equilibria for ternary liquid mixtures on solid surfaces by means of adsorption data for the corresponding three binary liquid mixtures can be improved by combining the thermodynamic excess formalism with geometrical models. This new strategy for the prediction of excess adsorption isotherms is examined for four ternary adsorption systems ranging from ideal to highly non-ideal ternary mixtures. The predicted isotherms are discussed and compared with experimental ones as well as with those obtained for a model based on the absolute quantities. The results confirm: (i) superiority of predicting adsorption in terms of excess quantities, and (ii) utility of geometrical models for constructing ternary molar compositions on the basis of binary ones to predict equilibria not only for liquid mixtures alone but also for adsorption of liquid mixtures on solid surfaces.

Calculation of immersion enthalpy data from adsorption isotherms

The thermodynamic equations for the calculation of binary and ternary immersion data in excess formalism are presented. Immersion enthalpies and entropies of the n-hexane/n-octane, n-octane/n-tetradecane and n-hexane/n-tetradecane binary mixtures as well as the n-hexane/n-octane/n-tetradecane ternary mixture on activated carbon are calculated from the temperature dependence of adsorption isotherms. In order to evaluate the quality of the calculations, the calculated immersion enthalpies of the binary mixtures on activated carbon are compared with those that were measured calorimetrically. It is shown that phenomenological thermodynamics can be used successfully to predict calorimetric data on the basis of adsorption excess isotherms.

Prediction of multicomponent liquid adsorption using excess quantities

The utilization of excess quantities as the basis for a thermodynamic approach can simplify the prediction of multicomponent liquid adsorption from binary data. A new method for predicting liquid adsorption on solids is suggested, which is different from the existing equations with respect to the theoretical background and formulation. The applicability of the new model is tested with three ternary adsorption systems. The predicted surface excesses are discussed and compared with experimental ones and with those of other prediction models in the literature. The accordance between measured and predicted ternary data is convincing.

Prediction of multicomponent liquid adsorption using excess quantities

The utilization of excess quantities as the basis of a thermodynamic approach can simplify the prediction of multicomponent liquid adsorption from binary data. From statistical thermodynamics, the fundamental equation is derived for the prediction of ternary or higher order data from adsorption data for the constituent binary mixtures. An additive expression is obtained for the double Gibbs free excess energies, valid for adsorption on liquid mixture/air interfaces as well as liquid mixture/solid interfaces.

Calculation and Prediction of Adsorption Excesses on the Ternary Liquid Mixture/Air Interface from Surface Tension Measurements

The surface tensions of the n-propanol/ethylene glycol/water ternary mixture and its binary mixtures are measured at 293 K and described by mathematical functions. The experimental data and their descriptions are shown in the three-dimensional space by means of coordinate transformation. A thermodynamic model to calculate and predict ternary adsorption excess data on the ternary liquid mixture/air interface from surface tensions is presented. The calculated adsorption excess data in the ternary triangle are discussed.