Study on Validity of Maxwell-Stefan Theory and Fick Law to Model a Extractive Distillation Column

摘要

Because of high relative volatility and existence of azeotropic point, it is not efficient to regain butene from the mixture of butene and n-butane (C4) using simple distillation column. To overcome the difficulties, extractive distillation column was engaged in industry. However, the operation of an existing extractive distillation column indicated that the HETP value of the real plant was more than twice as much as ideal test system. One essential information source to estimate HETP-value and thereof the overall height of column is measured value by manufacturer using ideal material system. Therefore, it exists a information gap between theoretical stage number, which was calculated on the base of Fick law concept, and the overall height of real column. It raises a question now, if there is a methodological error in designing of extractive distillation column and if the Maxwell-Stefan Theory (MST) is able t°Close this gap. With the help of simulation program ASPEN three different extractive distillation columns were modeled and implemented on the base of MST (non-equilibrium model) and Fick Law ( equilibrium model) to study the validity of models and the plausibility of results. The investigation in this paper focuses on the analysis of heat transfer coefficient and effective interfacial area for heat transfer. As the result shows that non-equilibrium model provides more realistic and more plausible performance than equilibrium model, such performance mainly attribute to the sound physical principles of Maxwell-Stefan theory.