In Example 14-2 and Figure 14-5, we plotted solute mole fractions on the ordinate and solvent mole fractions on the abscissa (x-axis). Instead, we could have plotted solid mole fractions \(\mathrm{x}_{\mathrm{D}}\) or \(\mathrm{y}_{\mathrm{D}}\) on the abscissa. Why is plotting solvent mole fractions on the abscissa the better choice? To answer this question, you will probably need to plot the graph with solid mole fractions on the abscissa so that you can compare with Figure 14-5.

Example 14-2

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We wish to treat 1000.0 kg/h (wet basis) of insoluble meal (D) that contains 20.0 wt% oil (A) and no solvent (S). Inlet solvent is pure solvent and flows at 662 kg/h. We desire an underflow product that is 4.0 wt% oil. Temperature and pressure are constant, and equilibrium data are given in Table 14-2. Find the outlet extract concentration and the number of equilibrium stages needed in a countercurrent leaching system. TABLE 14-2. Test data for extraction of oil from meal with solvent Mass Fraction Oil (Solute) in Solution Mass Fraction Underflow (Raffinate) XD XS 0.0 0.0 0.670 0.333 0.1 0.0336 0.664 0.302 0.2 0.0682 0.660 0.272 0.3 0.1039 0.6541 0.242 0.4 0.1419 0.6451 0.213 0.5 0.1817 0.6366 0.1817 0.6 0.224 0.6268 0.1492 0.7 0.268 0.6172 0.1148 Source: Prabhudesai (1997) .5 .4 EN 3 Conjugate Line -Saturated Raffinate F=RN+I R3 Saturated Extract R2 or XOXY .3 .2 E2 E E- R E-S .2 .4 .6 .8 1.0 yoor xp