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

Tert‐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.     

Batch‐Rektifikation azeotroper Gemische in Verstärkungs‐ und Abtriebskolonnen

Batch distillation is an efficient unit operation which allows the separation of a multicomponent mixture into its pure constituents in a single column. However, the separation of azeotropic mixtures by distillation is quite difficult because at the azeotrope the liquid and the gas have the same composition and, in turn, the driving force for distillation disappears. A systematic presentation of batch distillation processes for the separation of binary azeotropic mixtures using an entrainer is given.     

THE RECOVERY OF ETHYL ACETATE BY EXTRACTIVE DISTILLATION

Ethyl acetate cannot be easily removed from either mixtures with ethanol and water because of the minimum ternary azeotrope or from methyl ethyl ketone because of the proximity of boiling points. Ethyl acetate can be readily recovered from mixtures with these two by using extractive distillation in which the extractive agent is a higher boiling oxygenated, nitrogenous or sulfur-containing organic compound or a mixture of these.     

Distillation of Nonideal Ternary Zeotropic Mixtures in Two-Feed Columns

The continuous distillation of ternary nonideal zeotropic mixtures in two-feed columns is modeled. The results obtained are compared with the results of continuous distillation in one-feed columns. The topography of the field of relative-volatility coefficients is considered for various types of zeotropic systems. Possible separation flow sheets are presented for various distillation processes.     

Hydrate dissociation pressure minima in multicomponent systems

Conditions for which gas hydrates have a minimum dissociation pressure are determined analytically. The development allows direct determination of the gas phase compositions which will result in such azeotropic conditions. Results show that the azeotrope is not a manifestation of non-idealities in the hydrate phase but rather a direct result of the hydrate structure. Minima will occur for some ternary mixtures (2 gases + water), but, surprisingly, not for more complex systems. Analysis shows that molecular size can be used as the basis for choosing ternary mixtures which will display dissociation pressure minima.     

Effect of thermodynamic parameters on prediction of phase behavior and process design of extractive distillation

Extractive distillation was investigated for separation of the minimum azeotrope of n-propanol/water,via the Aspen Plus simulation platform.Experimental data of n-propanol/water,which could pass the thermodynamic consistency test,were regressed to get suitable binary interaction parameters (BIPs) by the UNIQUAC thermodynamic model.The azeotrope system was heterogeneous in the simulation with built-in BIPs,which was contrary to the experimental data.The study focused on the effect of thermodynamic parameters on the prediction of phase behavior,and process design of extractive distillation.N-methyl-2-pyrrolidone (NMP) and ethylene glycol were used as solvents to implement the separation.Processes with built-in and regressed BIPs were explored,based on the minimum total annual cost (TAC).There were significant differences in the phase behavior simulation using different thermodynamic parameters,which showed the importance of BIPs in the design and optimization of extractive distillation.     

Feasible separations and entrainer selection rules for heteroazeotropic batch distillation

A feasibility analysis is presented for the separation of close-boiling and azeotropic (minimum- and maximum-boiling) binary mixtures into pure components by the addition of an entrainer introducing a heterogeneous azeotrope. The analysis is done for both the conventional batch rectifier and the multivessel batch column. The analysis is theoretical and based on the assumptions of total reflux/reboil ratios and infinite number of stages. Two feasibility conditions are formulated that make it possible to investigate feasibility based on information coming solely from the distillation line map along with the binodal curve of the ternary mixture. Serafimov's classification is used for classifying the azeotropic phase diagrams. The feasibility analysis provides the necessary background and information for formulating rules for entrainer selection for the process. Two simple rules are then proposed, which make it possible to “screen” entrainers for heteroazeotropic batch distillation with minimum efforts.     

Use of Columns with Coupled Heat and Material Flows in Separation of Multicomponent Zeotropic Mixtures

The possibility of bringing real distillation processes to thermodynamically reversible distillation is considered. Distillation systems involving partially or fully thermally coupled columns are suggested for the separation of ternary mixtures. The transformation of the optimal flowsheet in response to variation of feed composition is studied. Recommendations are provided as to the choice of an energy saving distillation design.__________Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 3, 2005, pp. 264–268.Original Russian Text Copyright © 2005 by Ivanova, Timoshenko.     

Advances on modeling and simulation of alcoholic distillation. Part 2: Process simulation

Several studies developed by the authors on the application of process simulators to the distillation processes of alcoholic mixtures are analyzed and discussed in this second part of the series on advances on modeling and simulation of alcoholic distillation. Three study cases are presented and discussed to show the usefulness of simulation packages, and in particular of ChemCAD: (i) production of whisky in a sequence of double batch distillation; (ii) production of brandy in a single continuous column; and (iii) production of neutral spirits in a sequence of multiple columns (concentrator, light component separator, and rectification column). In all cases the selection of the thermodynamic models considered previous studies as discussed in Part 1 of the series in which the NRTL model was recommended for phase equilibrium modeling. Applications of two industrial and pilot plant cases are presented, so the validity of the simulations and the appropriateness of the thermodynamic and process simulation studies presented in this series of papers. The main conclusion of the study is that simulators can play an important role in understanding alcoholic distillation processes, in optimizing resources and in making distillation of wine and musts a more efficient process.     

1,4-丁二醇分离乙酸甲酯-甲醇二元恒沸物的研究

利用1,4-丁二醇与乙酸甲酯-甲醇二元恒沸物形成三元恒沸物,研究了乙酸甲酯与甲醇恒沸物的分离工艺。实验采用精馏、常压蒸馏、减压蒸馏及冷冻的方法,主要研究了各种方法对甲醇分离的影响,并获得了较佳的工艺条件。研究得出常压蒸馏法可行,乙酸甲酯纯度达到99.7%,收率98.1%,甲醇纯度96.1%,收率95.2%。     

Separation of di-n-propyl ether and n-propyl alcohol by extractive distillation and pressure-swing distillation: Computer simulation and economic optimization

Azeotropic mixtures are impossible to separate by ordinary distillation. Two of the most common methods for separating a binary homogeneous azeotrope are pressure-swing distillation (PSD) and extractive distillation (ED). The PSD process is effective if the azeotropic composition changes significantly with pressure. The ED process is effective if a suitable solvent can be found.This paper compares these two alternatives to separate a mixture made up of 50 mol% of di-n-propyl ether and 50 mol% of n-propyl alcohol by means of a practical case of a plant to treat 12,000 Tm/year of this mixture.The simulation has been carried out satisfactorily by mean of a package of commercial software (Aspen Hysys^®) using the thermodynamic model UNIQUAC with binary parameters obtained experimentally by us in previous papers.The two processes evaluated have been optimized independently from each other and the best configurations have been evaluated economically. Results show that, for this particular case, the PSD is more attractive than the extractive distillation.     

用于描述三元水醇系统汽液平衡的活度系数模型

In this study, three semipredictive activity coefficient models: Wilson, non-random-two liquid model (NRTL), and universal quasi-chemical model (UNIQUAC), have been used for modeling vapor-liquid equilibrium properties of ternary mixtures that include substances found in alcoholic distillation processes of wine and musts. In particular, vapor-liquid equilibrium in ternary mixtures containing water + ethanol + congener has been modeled using parameters obtained from binary and ternary mixture data. The congeners are substances that although present in very low concentrations, of the order of part per million, are important enological parameters. The results given by these different models have been compared with literature data and conclusions about the accuracy of the models studied are drawn, recommending the best models for correlating and predicting phase equilibrium properties of this type of mixtures.     

Conceptual design of distillation processes for mixtures with distillation boundaries: I. Computational assessment of split feasibility

Geometric design methods for the conceptual design of azeotropic distillation processes are fast and efficient tools for the economic screening of different process alternatives. This two‐part series presents a fully automated conceptual design method for finding an optimal recycle policy for the separation of mixtures with distillation boundaries. It does not require visualization and graphical inspection of residue curve or pinch maps and is, hence, not limited to ternary mixtures. The first part introduces a fully computational geometric split feasibility test based on bifurcation analysis. This bifurcation‐based feasibility test can be used as a valuable stand‐alone tool for the assessment of different separation options. It is also one of the core elements of the recycle optimization discussed in the second part of this series. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Separating Some Crude Oil Products (azeotropic mixture) by Gas Extraction with Carbon Dioxide at Elevated Pressure

Abstract

The ethanol/octane system has an azeotrope at normal pressure. This renders separation by simple distillation impossible. The system was studied at elevated pressure to see whether it was possible to separate the azeotropic mixture by gas extraction with carbon dioxide. It was found that the ternary had isologous phases with a ratio not very different from that in the azeotrope.     

Thermodynamic modeling of HNO3‐H2SO4‐H2O ternary system with symmetric electrolyte NRTL model

The nitric acid concentration/sulfuric acid concentration (NAC/SAC) process has been widely used for concentrating dilute aqueous nitric acid and recovering spent sulfuric acid. Dilute nitric acid (65 to 80 wt %) is concentrated using sulfuric acid to bind water and break the nitric acid‐water azeotrope at approximately 68 wt % nitric acid. To support heat and mass balance calculations and process simulation for NAC/SAC processes, we develop a comprehensive thermodynamic model for nitric acid‐sulfuric acid‐water ternary system based on previously published thermodynamic models of nitric acid‐water and sulfuric acid‐water binary systems with eNRTL equation. The ternary system model correlates well the isobaric vapor‐liquid equilibrium data at one atmosphere and the water and nitric acid activities data at 273.15 K for the ternary. Contour plots of boiling points, vapor phase composition, and specific heat capacity of the ternary system, as well as a Merkel enthalpy‐concentration chart are generated for engineering use. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3110–3117, 2017     

Initial column profile with composition-dependent relative volatility

When solving the large scale, highly nonlinear, equation systems of steady state multistage distillation processes modelled with theoretical plates, convergence depends on the initial values. The conventionally applied linear initial profiles frequently give rise to divergence when azeotrope is present. The usual practice in such cases is initializing with engineering insight, i.e. anticipating the results. Composition-dependent relative volatility model is developed in the present work, and applied successfully to initialize the composition profiles of distillation columns. The model describes the implicit temperature dependence through composition dependence. Equlibrium plots computed with the new model well approximate the measured data of strongly non-ideal, and even azeotropic, mixtures. The initial column profiles computed with the new model are rather similar to the final solution, and thus accelerate the computation. Processes can be modelled with the new initial profile when the solution algorithms do not converge with the conventional initialization.     

Pressure relief of nonideal mixtures: Composition trajectories and residue curve maps

During the course of a pressure relief discharge from a vessel containing a multicomponent liquid mixture, composition changes occur that affect the properties of the vessel contents. In this work, a model of the dynamic relief process for ternary, nonideal, homogeneous mixtures is developed, under the assumption of vapor-only venting. Opening/reclosing of the relief valve introduces state-events, which require reinitialization of the model at each state transition. The relationship between the pressure relief model and the concept of residue curves, which describe simple-distillation processes, is demonstrated. It is known that the presence of azeotropes and distillation boundaries in mixtures restricts the composition trajectories of simple-distillation processes, as well as continuous distillation columns at total reflux. In this work, the residue-curve analogy is extended to vapor-only pressure-relief, where vapor composition changes directly affect the operation of the pressure-relief device. Examples of dynamic relief processes are developed for ternary mixtures with varying nonideality.     

A knowledge-based expert system for the prediction of ternary azeotrope formation in organic mixtures

New functions of AZEOPERT [Kim and Simmrock, 1997] were investigated to predict the occurrence of ternary azeotropes and their azeotropic compositions in an organic mixture. This study describes its new problem-solving strategy. The knowledge base of AZEOPERT for ternary azeotropes is hierarchically structured with the several levels of domain-specific knowledge on ternary azeotropy. First, an azeotropic data bank including ternary azeotropic experimental data was implemented in AZEOPERT as the lowest level. It may be used to determine whether or not ternary azeotropic experimental data for the consulted organic mixture are already available. Moreover, compiled heuristic knowledge as the second level and class-oriented model-based knowledge as the highest level were implemented in the knowlege base. The problem-solving strategy through the integration of model-based reasoning into compiled reasoning gives a very efficient, general way for the prediction of ternary azeotrope formation in a wide varitey of organic mixtures, and especially, in unknown mixture systems.     

DMC-甲醇-水三元混合物的萃取精馏分离工艺

运用Aspen Plus软件回归文献数据校正了碳酸二甲酯（DMC）-水（H₂O）混合物的UNIQUAC热力学模型参数,并以该模型为基础分析了水作为萃取剂萃取精馏分离DMC-甲醇（CH₃OH）-水三元混合物的分离原理,结合混合组分的三角相图和物料组成设计了反向萃取精馏工艺,发现选用水为萃取剂可以利用DMC-水的部分互溶特性,通过三塔精馏即可分离DMC-甲醇-水三元混合物,沸点较高的DMC和少量水由塔顶馏出,而沸点较低的甲醇和大部分水由塔底采出,避免了DMC-甲醇二元共沸物的形成。同时,在相同分离要求下设计了变压精馏工艺,通过对两个精馏工艺参数模拟优化,发现萃取精馏工艺的总冷凝负荷和总加热负荷分别为888.7kW和898.2kW,其总能耗较变压精馏工艺节约了47.2%,萃取精馏工艺的年总费用（TAC）比变压精馏工艺下降了48.8%。