Azeotropic Batch Distillation Research Articles

Separation of ethyl acetate–isooctane mixture by heteroazeotropic batch distillation

This paper studies the separation of an ethyl acetate–isooctane mixture by heterogeneous azeotropic distillation in a batch rectifying column. An initial list of 60 candidates was studied but only methanol and acetonitrile were obtained as potential heterogeneous entrainers. These entrainers form a low boiling heterogeneous azeotrope with isooctane. Experimental verification of the miscibility gap with isooctane was performed at 25°C for each entrainer giving a smaller region for methanol than for acetonitrile. Feasibility of the heterogeneous azeotropic batch distillation was carried out experimentally in a laboratory batch distillation column having 44 theoretical equilibrium stages and using a high reflux ratio. Several distillate fractions were taken as a function of the temperature at the top of the column. For both methanol and acetonitrile, the main fraction was defined by the condensed vapor providing a liquid–liquid split of the isooctane/entrainer heteroazeotrope into the decanter. Ethyl acetate impurity was detected in both decanted phases, but in much lower amount when using acetonitrile as entrainer. The process with acetonitrile also resulted in a shorter operating time and higher purity and recovery yield of isooctane as the main distillate product. Pure ethyl acetate remained into the boiler at the end of each process.

A New Algorithm for the Determination of Product Sequences in Azeotropic Batch Distillation

A New Algorithm for the Determination of Product Sequences in Azeotropic Batch Distillation

Separation of tert‐Butyl Alcohol‐Water Mixtures by a Heterogeneous Azeotropic Batch Distillation Process

AbstractTert‐butyl alcohol and water form an azeotrope at normal pressure. Simple distillation cannot be used to separate these two components. In this article, a systematic study of the separation of tert‐butyl alcohol–water mixtures with an entrainer by heterogeneous azeotropic batch distillation was performed. Based upon the thermodynamic behavior of the ternary mixtures, cyclohexane was chosen as the entrainer. It formed ternary and binary heterogeneous azeotropes with the original components. The process feasibility analysis was validated by using rigorous simulation with chemical process simulation software – HYSYS Plant 2.2 and DISTIL 4.1. Simulation results were then corroborated in a batch experimental column for the selected entrainer.

Optimal design of azeotropic batch distillation

AbstractThis study explores integrating models with different degrees of detail for optimizing azeotropic batch distillation systems. A detailed dynamic model is used from outside the optimization program both to verify feasibility of the design and to update the parameters needed by the optimization model. The updated parameters are the constant relative volatilities between pseudo‐components, used in a binary Fenske–Underwood–Gilliland‐type model. The approach was used to optimize the design of a batch process for the recovery of spent isopropyl alcohol, which works cyclically to separate the excess water, satisfying an environmentally acceptable specification, and using cyclohexane as entrainer, which in turn is recovered in the same process and recycled. The approach permitted optimizing the batch sizes, number of separation stages, the reflux ratios of a piecewise constant multilevel reflux policy, the extent of each separation, and the size of the intermediate cuts to be recycled, with affordable computation and problem setup times. © 2005 American Institute of Chemical Engineers AIChE J, 2006

Analysis and control of heteroazeotropic batch distillation

AbstractThe separation of close‐boiling and azeotropic mixtures by heterogeneous azeotropic distillation is addressed in batch columns. Both a common rectifier and a multivessel batch column are considered. Theoretical and graphical analyses of the process are presented for both column configurations and different separation strategies are presented. A simple control scheme is proposed for the practical operation of the columns, the implementation of different separation strategies and the realization of the final results. Dynamic simulations for mixtures classified under Serafimov's topological classes 2.0‐2b and 3.1‐2 verify the theoretical findings. The results show that heteroazeotropic batch distillation exhibits substantial flexibility. The column profile can be totally restored during the process and lie in regions different from those of the initial feed. The still path can cross distillation boundaries and the still product does not have to be the stable node of the feed region. Such results cannot be obtained by homogeneous azeotropic batch distillation. © 2005 American Institute of Chemical Engineers AIChE J, 2005

Separation of n-hexane–ethyl acetate mixtures by azeotropic batch distillation with heterogeneous entrainers

In this article, a systematic study of the separation of the n-hexane–ethyl acetate mixture with an entrainer by heterogeneous azeotropic batch distillation is performed. Based upon the thermodynamic behaviour of the ternary mixtures, potential entrainers partially miscible with one or two original azeotropic components are chosen. In all cases, the entrainer adds a heterogeneous binary or ternary azeotrope that is the lowest boiling point in the ternary diagram. Therefore, it leaves the column by the overhead stream which is subcooled to get two liquid phases in the decanter. The phase with the highest amount of the original component is removed as distillate product whereas the entrainer-rich phase is continuously refluxed to the column. Considering methanol, acetonitrile, water and nitromethane as heterogeneous entrainers, screening was performed based on the composition of the unstable heteroazeotropic mixture, the ratio of both liquid phases in the condensed top vapour and the purity of the distillate product determined by the liquid–liquid envelope at the decanter temperature. The process feasibility analysis is validated by using rigorous simulation with the batch process simulator ProSimBatch. Simulation results are then corroborated in a bench experimental column for the selected entrainer, showing several advantages of heterogeneous batch distillation (HBD) compared to homogeneous systems.

Optimization and Control of Heterogeneous Azeotropic Batch Distillation

Optimization and Control of Heterogeneous Azeotropic Batch Distillation

Optimization and Control of Heterogeneous Azeotropic Batch Distillation

Optimization and Control of Heterogeneous Azeotropic Batch Distillation

Product sequences in azeotropic batch distillation

AbstractThe formation of multicomponent azeotropes in waste‐solvent streams often complicates separation and recovery of solvents. The implications of applying batch distillation to such a mixture can be studied in a residue curve map. Ahmad and Barton (1996) extend and generalize the theory for ternary residue curve maps applied to batch distillation to homogeneous systems with an arbitrary number of components. These theoretical results are used to develop an algorithm for elucidating the structure of the batch distillation composition simplex for a system with an arbitrary number of components. The batch distillation regions are identified by completing unstable boundary limit sets. The completed boundary limit sets accurately represent the topological structure of the composition simplex and make it possible to extract all product sequences achievable when applying batch distillation. The algorithm is demonstrated on the five‐component system acetone, chloroform, methanol, ethanol, and benzene, which exhibits nine azeotropes. Furthermore, the set of batch distillation product sequences predicted is validated using a commercial dynamic batch distillation column model. Although the problem does not closely approach the limiting conditions of the theory, the predictions agree excellently with the simulations.

Synthesis of Azeotropic Batch Distillation Separation Systems

The sequencing of batch distillation systems, in particular batch distillation columns, can be complicated by the existence of azeotropes in the mixture. These azeotropes can form batch distillation regions where, depending on the initial feed to the batch column, the types of feasible products and separations are limited. It is very important that these distillation regions are known while attempting to synthesize sequences of batch columns so infeasible designs can be eliminated early on in the design phase. The distillation regions also give information regarding the feasible products that can be obtained when the mixture is separated by using a variety of batch column configurations. The authors will show how a tool for finding the batch distillation regions of a particular mixture can be used in the synthesis of batch distillation column sequences. These sequences are determined by the initial feed composition to the separation network. The network of all possible sequences will be generated by using state-task networks when batch rectifying, stripping, middle vessel, and extractive middle vessel columns are allowed. The authors do not determine which sequence is the best, as the best sequence will depend on the particular application to which one is applying the algorithms. Theymore » show an example problem for illustration of this technique.« less

Azeotropic batch distillation New Problems and Some Solutions

Azeotropic batch distillation New Problems and Some Solutions

Azeotropic batch distillation new problems and some solutions

Two methods of separating a complex quaternary industrial mixture of methanol, cyclohexane, ethanol and water using batch distillation are presented. The first method is an extractive batch distillation and the second method is a cyclic operation. Both methods are based on a thermodynamic analysis of the system (which contains four binary azeotropes and a ternary azeotrope, three of which are heterogeneous) and predictions of the product sequences. The effectiveness of these predictions is demonstrated by comparison with detailed simulations.It is found that quantities of products are important in the separation scheme as well as their relative sequence. The column hold-up seems to directly influence the period during which a given product may be obtained at the distillate. Therefore both thermodynamic and dynamic aspects must be considered in the design of optimal operations.

An application of qualitative analysis of ordinary differential equations to azeotropic batch distillation

Recently, a new approach to automate the qualitative analysis of dynamic systems has emerged in the AI literature. This approach has been successful in automatically constructing the phase portraits of explicitly specified second-order nonlinear dynamic systems, using the mathematics of nonlinear dynamics. In this paper, we extend the capability of the existing techniques to implicitly defined equations and apply it to the batch distillation of ternary azeotropic systems. Rigorous models for the batch distillation of azeotropic systems are computationally complex, and the derivation of properties such as feasible regions of operation does not seem possible. In this paper, we develop abstract models (short-cut models) for ternary azeotropic batch distillation based on simplifying assumptions to rigorous models. These abstract models are computationally simpler to analyze without compromising fidelity and would allow the derivation of a feasible region of operation. A knowledge of distillation boundaries and azeotropic points is essential for the proposed process of abstraction. The derivation of the distillation boundaries requires a qualitative analysis of ordinary differential equations describing the simple distillation operation.

Patterns of composition change in multicomponent batch distillation

A simple dynamic model has been developed to study the behavior of multicomponent batch distillation. The distillate compositions obtained for ideal mixtures behave in accord with intuition since the fractions contain the individual pure components in order of increasing boiling point. Azeotropic mixtures are more complex and counter-intuitive, in some cases displaying non-adjacent distillate fractions which have the same composition. The general behavior of ternary azeotropic batch distillation is described in simple terms based on the nature of the distillate and still composition changes in the phase plane. At large reflux ratio and number of stages, the sequence of distillate fractions generated from any initial composition in the still can be found with little or no computational effort.

Distillates Composition Change in Ternary Azeotropic Batch Distillation

Distillates Composition Change in Ternary Azeotropic Batch Distillation