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

摘要

In the production of terephthalic acid, tiny amounts of p-xylene may remain in the unreacted aqueousacetic 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 azeotropicdistillation[1]. It was found that the remaining p-xylene impurty has essential effects on the design of thisdehydration process. Under some given specifications, bifurcation with output multiplicity is found when feed hasp-xylene impurity. Two operating variables are identified to be related to these bifurcation phenomena. One is theaqueous reflux flow and the other is the reboiler duty. This bifurcation does not exist in case of clean feed. Itimplies that the bifurcation is mainly due to the p-xylene impurity. The two steady states in these bifurcationphenomena, one is on a stable branch and the other on an unstable branch. It is further found that the open-loopunstable steady-state can be made stable by increasing the reboiler duty on a cost of more energy expense.