Azeotropic Distillation in a Middle Vessel Batch Column. 2. Nonlinear Separation Boundaries

TitleAzeotropic Distillation in a Middle Vessel Batch Column. 2. Nonlinear Separation Boundaries
Publication TypeJournal Article
Year of Publication1999
AuthorsCheong W, Barton PI
JournalIndustrial & Engineering Chemistry Research

On the basis of the analytical tools developed for the middle vessel column ({MVC}) operated under limiting conditions, analysis of the qualitative dynamics of the {MVC} in separating an azeotropic mixture is extended to the more realistic case in which the separation boundaries are nonlinear. The differences between batch stripper pot composition boundaries and batch rectifier pot composition boundaries in the presence of curved separatrices results in the {MVC} still pot composition being able to cross these pot composition boundaries. On the basis of these insights, operating procedures are developed in which ternary azeotropic mixtures of acetone, benzene, and chloroform can be separated into their constituent pure components, a separation not achievable with either the batch stripper or the batch rectifier. The operating procedures suggested for separating the ternary azeotropic mixture of acetone, benzene, and chloroform in the {MVC} are then shown to be the time analogues of sequences of continuous distillation columns that achieve the same separation. On the basis of this space-time analogy, further analogies are developed between the {MVC} and a continuous column, and it is postulated that many complex separations currently achieved with sequences of continuous columns can also be achieved with a single {MVC}. Thus, the {MVC} represents the ultimate multipurpose solvent recovery technology, as it can handle, in a batch multipurpose mode, separations that will otherwise require a dedicated continuous distillation sequence. Finally, the characteristics of perfect {MVC} batch entrainers, which allow the complete separation of any azeotrope into its constituent pure components in a single {MVC}, are discussed.