Bifurcation Phenomena in the Azeotropic Distillation Process for Dehydration of Acetic Acid with Impurity

摘要

In the production of terephthalic acid, tiny amounts of p-xylene may remain in the unreacted aqueous acetic acid. A dehydration column is thus design for the recovery of the acetic acid from this aqueous solution. Isobutyl acetate as an entrainer is used so that the dehaydration column involves heterogenous azeotropic distillation[1]. It was found that the remaining p-xylene impurty has essential effects on the design of this dehydration process. Under some given specifications, bifurcation with output multiplicity is found when feed has p-xylene impurity. Two operating variables are identified to be related to these bifurcation phenomena. One is the aqueous reflux flow and the other is the reboiler duty. This bifurcation does not exist in case of clean feed. It implies that the bifurcation is mainly due to the p-xylene impurity. The two steady states in these bifurcation phenomena, one is on a stable branch and the other on an unstable branch. It is further found that the open-loop unstable steady-state can be made stable by increasing the reboiler duty on a cost of more energy expense.