A distillation column for the separation of n-butane from n-pent

A distillation column for the separation of n-butane from n-pentane was recently put into operation in a petroleum refinery. Apparently, an error was made in the design because the column fails to make the desired separation as shown in the following table

Actual Design Specification Operation Mol% nCs in distillate Mol% nC4 in bottoms 13.49 0.26 0.16 4.28

In order to correct the situation, it is proposed to add an intercondenser in the rectifying section to generate more reflux and an interreboiler in the stripping section to produce additional boilup. Show by use of a McCabe-Thiele diagram how such a proposed change can improve theoperation.



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Actual Design Specification Operation Mol% nCs in distillate Mol% nC4 in bottoms 13.49 0.26 0.16 4.28