Multisolute batch extraction

Two solutes distribute themselves between the two phases as concentrations Xa and Ya, and Xb and Yb and with rates Qa and Qb, respectively as shown in Fig. 3.32. The corresponding equilibrium concentrations Xa and Xb are functions of both the interacting solute concentrations, Ya and Yb, and can be expressed by functional relationships of the form 

Typical representations of the way that the two differing equilibrium relationships can interact are shown in Fig. 3.33, and it is assumed that the equilibria can be correlated by appropriate, explicit equation forms. 

For multi-component systems, it is necessary to write the dynamic equation for each phase and for each solute, in turn. Thus for phase volume Vl, the balances for solute A and for solute B are 

Vl = - KtBaCXB - Xb ) Vl For phase volume Vq the balances for both solutes are 

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

these functional relationships should ideally be available in an explicit form in order to ease the numerical method of solution. Two-solute batch extraction is covered in the simulation example TWOEX. 

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Wang CC and Bunge AL. Multisolute extraction of organic acids by emulsion liquid membranes. I. Batch experiments and models. J Membr Sci 1990 53 71-103. 

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