Application of Extractive Distillation for the Separation of Benzene and Cyclohexane Mixtures

Foo Chwan Yee, Lee Lean Eng, Zainuddin bin Abd. Manan
Chemical Engineering Department
Faculty of Chemical and Natural Resources Engineering
Universiti Teknologi Malaysia,
81310 Skudai, Johor.

Keywords: azeotrope; distillation boundary; homogeneous azeotropic distillation, residue curve; Robbins Chart.


Distillation is the most widely used separation technique in the chemical process industries. Not all liquid mixtures can be separated by ordinary fractional distillation, however. When the components to be separated of system have relative volatilities of close to 1.00 (i.e. close boiling mixture), separation becomes difficult and expensive because a large number of trays and a high reflux ratio are necessary. Both the equipment and utility will costs increase markedly and the separation by ordinary distillation can become uneconomical. If the mixture forms azeotropes, a different problem arises - the azeotropic composition can limit the separation. In such a case, the azeotrope must be "broken" to enable separation.

This paper discusses the procedure for separating two close boiling components; i.e. benzene (C6H6) and cyclohexane (C2H12) by extractive distillation technique to overcome the "azeotrope barrier". A computer simulation has been performed to enable performance comparison among a few candidate solvents which include phenol, aniline and 1,2-propanediol to achieve cyclo-hexane purity specification in excess of 99%.

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