Investigators at the University of California at Berkeley have studied all 14 possible sequences for separating the following mixture at a flow rate of \(200 \mathrm{lbmol} / \mathrm{hr}\) into its five components at about \(98 \%\) purity each (D.L. Heaven, M.S. thesis in Chemical Engineering, University of California, Berkeley, 1969).

For each sequence, they determined the annual operating cost including depreciation of the capital investment. Cost data for the best three sequences and the worst sequence are in Figure 9.53. Explain in detail, as best you can, why the best sequences are best and the worst sequence is worst using the heuristics. Which heuristics appear to be the most important?

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Species Symbol Feed Mole Fraction Approximate Volatility Relative to n-Pentane Propane Isobutane n-Butane Isopentane n-Pentane ABCDE 0.05 8.1 0.15 4.3 0.25 3.1 0.20 1.25 0.35 1.0 1.00