Heterogeneous Distillation Column Research Articles

Conceptual analysis of single-feed heterogeneous distillation columns

<p class="Abstractandkeywordscontent">Separation in heterogeneous distillation columns is attained by interaction of two liquid and one vapor phases, interaction of three phases involves complexities due to the determination of vapor-liquid-liquid equilibrium and hence, in the design of separation units. Nevertheless, the liquid-liquid equilibrium allows developing separations that may be unfeasible by vapor-liquid equilibrium. In this way, heterogeneous azeotropic distillation is a useful operation for the separation of azeotropic and close-boiling mixtures. In this work, a new methodology for evaluating the feasibility of this process is developed. This methodology is an extension of that proposed by Castillo <em>et al</em>. (1998) for homogeneous systems. Operation leaves for heterogeneous systems are calculated using the concept of pinch point curves in order to establish the process feasibility. Heterogeneous columns with external decanter are considered as the only heterogeneous stage (OHED: only heterogeneous external decanter). The initialization process for the column calculation requires the selection of the distillate composition using thermodynamic criteria in order to guarantee homogeneous phases within the column. A system with industrial and academic relevance was considered as case study: water-acetic acid-amyl acetate. Results show that the developed shortcut method allows evaluating process feasibility and estimating design parameters, without the use of trial and error procedures implemented, with the aid of simulation tools.</p><div> </div>

Column configurations of continuous heterogeneous extractive distillation

AbstractIncreasing regulations and constraints have renewed interest for more efficient distillation process in separating azeotropic mixtures and close boiling components. We investigate the feasibility of heterogeneous extractive distillation process in a continuous column considering several feed point strategies for the entrainer recycle stream and for the main azeotropic feed. Depending on these choices, the heterogeneous distillation column is composed of one, two, or three column sections. A differential mass balance model enables to compute continuous liquid composition profiles of the rectifying, extractive, and stripping sections. Unlike homogeneous extractive distillation, reflux policy composed by a single or both decanted liquid phases is considered as well as the external feeding influence on the composition of the top column liquid stream. Limiting operating conditions of key parameters like the entrainer/feed flowrate ratio and reflux ratio required to obtain a target top and bottom product compositions are obtained. For illustration, separation of acetonitrile–water mixture using butyl acetate as a heavy heterogeneous entrainer is selected. In this case, withdrawal of a saddle binary heteroazeotrope is the main difference of this process compared with the well‐known heterogeneous azeotropic distillation process where the top vapor product is the lower boiling point of the ternary system. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Robust Dynamic Simulation of Three-Phase Reactive Batch Distillation Columns

The dynamic simulation of heterogeneous distillation columns is a demanding task because the number of liquid phases can vary over time on each tray. The success of the simulation depends on the rapid, reliable, and robust assessment of the number of phases and the correct initialization of the compositions of the liquid phases. In this work, a flexible simulation strategy is presented that decouples the phase split and flash algorithms from the process model. Therefore, no discontinuous model switching occurs in the process model, and the column can easily be simulated using standard tools employing a simultaneous equation-oriented simulation strategy. The phase state is assessed with a rapid and reliable homotopy−continuation algorithm that is well-suited for dynamic simulation because it decomposes the phase stability problem into two steps to minimize the necessary computational effort. The simulation strategy is applied to the production of butyl acetate from butanol and acetic acid in a three-phase ...

Influence of Impurities on the Control of Heterogeneous Azeotropic Distillation Columns

A concept is presented for the design of heterogeneous distillation columns under aspects of operability. The column behavior is analyzed using residue curve maps and a theoretical finite reflux/infinite length column. In particular, the influence of impurities on the operation of the column is discussed. Depending on the impurities, different control schemes with different designs of the process have to be used to guarantee robust performance. In this paper, robustness is not against modeling errors but against typical nonlinear phenomena such as the disappearance of the phase split in the decanter. The theoretical findings are illustrated by steady-state and dynamic simulations of an industrial column where a heavy-boiling organic substance is dewatered using methyl tert-butyl ether as a light entrainer.

Design of heterogeneous distillation columns for separation of azeotropic non-reactive and reactive mixtures

An algorithm for computation of simultaneous chemical and phase equilibrium in homogeneous as well as in heterogeneous liquid mixtures has been developed. It is based on the rigorous tangent plane stability test performed in transformed coordinates. The coordinates make it possible to represent phase equilibrium in reactive systems in a similar way as for non-reactive mixtures. Therefore, the reactive phase diagrams look similar to the non-reactive ones and geometric design procedures for non-reactive heterogeneous distillation columns can be extend to reactive systems. A detailed algorithm for design of a reactive distillation column with top decanter is presented.

Design and synthesis of heterogeneous azeotropic distillations—II. Residue curve maps

A residue curve map analysis for ternary heterogeneous mixtures is developed to aid in the sequencing of heterogeneous distillation columns. In the analysis, distillation boundaries and the projected liquid boiling envelope are superimposed to divide the triangular composition diagram into distinct distillation regions. This provides a starting point for column sequencing In Part III.

Design and minimum reflux for heterogeneous azeotropic distillation columns

AbstractA simple design technique for heterogeneous distillation columns has been developed. The underlying geometric conditions which govern minimum reflux are shown to share certain common features with homogeneous distillations, but differ in some important respects. It is shown that heterogeneous columns display some unusual sensitivities to the design parameters. The most notable being the drastic swings in the composition and temperature profiles with very small changes in the level of trace impurities in the product stream.