Multisolute equilibria

The overall mass transfer coefficients are also likely to vary with concentration, owing to the complex multisolute equilibria, such that ... 

The procedure of Beutier and Renon as well as the later on described method of Edwards, Maurer, Newman and Prausnitz ( 3) is an extension of an earlier work by Edwards, Newman and Prausnitz ( ). Beutier and Renon restrict their procedure to ternary systems NH3-CO2-H2O, NH3-H2S-H2O and NH3-S02 H20 but it may be expected that it is also useful for the complete multisolute system built up with these substances. The concentration range should be limited to mole fractions of water xw 0.7 a temperature range from 0 to 100 °C is recommended. Equilibrium constants for chemical reactions 1 to 9 are taken from literature (cf. Appendix II). Henry s constants are assumed to be independent of pressure numerical values were determined from solubility data of pure gaseous electrolytes in water (cf. Appendix II). The vapor phase is considered to behave like an ideal gas. The fugacity of pure water is replaced by the vapor pressure. For any molecular or ionic species i, except for water, the activity is expressed on the scale of molality m ... 

This method is applicable to the complete multisolute aqueous solution described before. It is estimated that total solute concentrations up to 10 or 20 molal may be handled. The limitation on temperature results mainly from the limited temperature range for which experimental results for equilibrium constants and Henry s constants are available (cf. Appendix II and tables I and II). Although for some constants this range only extends up to 60 °C, it is expected that by an appropriate extrapolation the method may be used also at temperatures up to 170 oc. 

Quinones et al. [17] measured by frontal analysis multisolute adsorption equilibrium data for the system benzyl alcohol, 2-phenylethanol and 2-methyl benzyl alcohol in a reversed-phase system. Data were acquired for the pure compoimds, for nine binary mixtures (1 3,1 1, and 3 1) and four ternary mixtures (1 1 3,1 3 1, 3 1 1, and 1 1 1). These data exhibited very good thermod5mamic consistency. The thermodynamic functions of adsorption were derived from the single-solute ad-... 

In order to obtain a single equilibrium curve, we have to specify enough variables that only one degree of freedom remains. For binary distillation this can be done by specifying constant pressure. For absorption, stripping, and extraction we specified that pressure and tenperature were constant, and if there were several solutes we assumed that they were independent. In general, we will specify that pressure and/or temperature are constant, and for multisolute systems we will assume that the solutes are independent. 

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