EFFECT OF DESIGN ON THE OPERATION OF HOMOGENEOUS AZEOTROPIC DISTILLATION

In homogeneous azeotropic distillation, the entrainer feed flowrate re presents a design degree of freedom which does not exist in simple dis tillation. This degree of freedom has a significant impact on the cont rol properties. For high ratios of entrainer feed to azeotrope feed an d low internal flows, the stripping and rectifying sections dominate t he extractive section, and the control properties we obtain are simila r to those of simple distillation. In particular, internal flows have a positive impact on separation. When the ratio of entrainer to azeotr ope feed is low and the internal flows are high, the extractive sectio n dominates and we obtain control properties which have no equivalent in simple distillation. In this case, the internal flows have a negati ve impact on separation. Furthermore, it is shown that economical stea dy-state optimization of the column design and operation may lead to r elatively complex control problems. However, a simpler control situati on can be obtained by increasing the entrainer feed flow above its eco nomically optimum value. Thus, integrating design and control is essen tial in the case of homogeneous azeotropic distillation. These propert ies are completely general and will be observed for any homogeneous se paration of a minimum boiling azeotrope with a high boiling entrainer which does not introduce any new azeotrope in the mixture.