The fractional extraction system shown in Figure 13-5 is separating abietic acid from other acids. Solvent 1, heptane, enters at = 1000 kg/h and is pure. Solvent 2, methylcellosolve + 10% water, is pure and has a flow rate of R = 2500 kg/h. Feed is 5 wt % abietic acid in solvent 2 and flows at 1 kg/h. There are only traces of other acids in the feed. We desire to recover 95% of the abietic acid in the bottom raffinate stream. Feed is on stage 6. Assume that the solvents are completely immiscible and that the system can be considered to be very dilute. Equilibrium data are given in Table 13-3. Find N.

Figure 13-5. Fractional extraction Solvent 2 ) (R,XAO XBO Feed (A+B+Solvent I or 2) B + Solvent 2 (R) ) *80 I 14--11 XjVj NF N A+ Solvent I (E. YA, YB) Solvent I (E.YAN. ON+1)