Equilibrium data for extraction of methylcyclohexane (A) from nheptane (D) into aniline (S) are given in Table 13-8. Compare batch extractions of \(20 \mathrm{~kg}\) of \(40 \mathrm{wt} \%\) methylcyclohexane and \(60 \mathrm{wt} \% \mathrm{n}-\) heptane feed. Solvent added is first presaturated with diluent n-heptane so that, according to data in Table \(13-8\), it is \(93.8 \%\) aniline and \(6.2 \% \mathrm{n}\) heptane.

Table 13-8

a. Do a normal batch extraction adding \(20 \mathrm{~kg}\) of presaturated solvent. Find flow rates and compositions of extract and raffinate products.

b. Process same feed with presaturated solvent in a continuous solvent addition batch extraction. First, presaturated solvent is added with no removal of extract until a two-phase mixture is obtained. How much presaturated solvent is added to obtain two phases? Second, continuous solvent addition batch extraction is conducted until raffinate has a methylcyclohexane weight fraction of 0.292 . How much solvent is added during this step? What is final raffinate composition? How much extract is collected, and what is its average composition? Assume \(\mathrm{R}_{\mathrm{t}}\) is constant, and Eq. (13-29a) is valid.

Equation (13-29a)

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TABLE 13-8. Equilibrium data for methylcyclohexane, n-heptane-aniline Hydrocarbon Phase, wt% Aniline-Rich Phase, wt% Methylcyclohexane XA n-Heptane xD Methylcyclohexane YA n-Heptane YD 0.0 92.6 0.0 6.2 9.2 83.1 0.8 6.0 18.6 73.4 2.7 5.3 22.0 69.8 3.0 5.1 33.8 57.6 4.6 4.5 40.9 50.4 6.0 4.0 46.0 45.0 7.4 3.6 59.0 30.7 9.2 2.8 67.2 22.8 11.3 2.1 71.6 18.2 12.7 1.6 73.6 16.0 13.1 1.4 3.3 5.4 15.6 0.6 88.1 0.0 16.9 0.0