Feasibility of heterogeneous batch distillation processes

Synthesis of heterogeneous batch distillation is discussed, which aims at splitting azeotropic mixtures by adding an entrainer partially miscible with one of the initial binary mixture components. Key operational parameters are identified such as the amount of entrainer added in the ternary feed, the reflux policy, and the vapor line position by examples. Synthesis and operation are less straightforward for heterogeneous batch distillation than those for the homogeneous case, but offer many advantages: more design alternatives, simplified distillation sequences, a lower consumption of entrainer, and a crossing of distillation boundaries by the still path. Feasibility is assessed using simplified modeling and confirmed using a commercial batch process simulator package. Synthesis expectations and simulated results are verified throughout bench-plant experiments for the separation of the acetonitrile—water mixture using acrylonitrile as a light heterogeneous entrainer.     

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.     

Systematic design of an extractive distillation for maximum‐boiling azeotropes with heavy entrainers

Extractive distillation is one of the most attractive approaches for separating azeotropic mixtures. Few contributions have been reported to design an extractive distillation for separating maximum‐boiling azeotropes and no systematic approaches for entrainer screening have been presented. A systematic approach to design of two‐column extractive distillation for separating azeotropes with heavy entrainers has been proposed. A thermodynamic feasibility analysis for azeotropes with potential heavy entrainers was first conducted. Then, five important properties are selected for entrainer evaluation. Fuzzy logic and develop membership functions to calculate attribute values of selected properties have been used. An overall indicator for entrainer evaluation is proposed and a ranking list is generated. Finally, the top five entrainers from the ranking list have been selected and use process optimization techniques to further evaluate selected entrainers and generate an optimal design. The capability of the proposed method is illustrated using the separation of acetone–chloroform azeotropes with five potential entrainers. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3898–3910, 2015     

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.     

结合图论和基团贡献法的非均相共沸精馏挟带剂设计

非均相共沸精馏挟带剂的计算机辅助分子设计(CAMD)由分子合成、分子筛选及分子确认3个环节递进构成。在分子合成环节,预选基团,限定合成分子的基团总数及类型,基于图论原理实现由基团到分子的自动合成。在分子筛选环节,依据基础物性筛选指标形成基础分子库,输入待分离物系,采用非均相共沸物形成判据筛选出若干候选分子。在分子确认环节,由非均相共沸温度及组成、挟带剂的汽化热等参数组成模糊综合评判函数,实现分子排序,从而输出一组较优挟带剂。以乙酸-水物系、乙腈-乙酸乙酯物系为例,得到了相应设计结果,与文献结果进行了对比。研究表明该方法及所编程序具备可靠实用性,可为近沸程及共沸混合物分离过程的开发与设计提供先导性支持。     

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.     

Separation of ethylene glycol, 1,2-butanediol and 1,2-propanediol with azeotropic distillation

1,2-butanediol (1,2-BDO) and 1,2-propanediol (1,2-PDO) are inevitably side produced in the ethylene glycol (EG) production processes from non-petroleum routes, but are very difficult to separate by the ordinary distillation method because of the closeness of their boiling temperatures to EG, thus compromise the economy of these processes. The azeotropic distillation process using 1-octanol (CPO) as an entrainer to separate EG and 1,2-BDO mixture with or without 1,2-PDO was studied in this paper. Four binary vapour–liquid equilibrium data of EG-1,2-BDO, EG-CPO, 1,2-BDO-CPO, and 1,2-PDO-CPO were measured using an Ellis equilibrium kettle and regressed with the thermodynamic model of non-random two liquid to obtain the corresponding binary interaction parameters. On this basis, azeotropic distillations with CPO as an entrainer were designed to separate EG and 1,2-BDO with or without 1,2-PDO. The complete separation processes, including the azeotropic distillation and CPO recovery process consisting of extraction with H₂O and subsequent distillation, were simulated and optimized with Aspen Plus for both the EG-1,2-BDO binary mixture and the EG-1,2-BDO-1,2-PDO ternary mixture. The simulation results show that the azeotropic distillation method with CPO as an entrainer can effectively separate the mixture of EG-1,2-BDO and EG-1,2-BDO-1,2-PDO, achieving EG of 99.90% purity with 99.98% recovery and 1,2-BDO of 99.30% purity with 99.45% recovery for the binary mixture, and achieving EG of 99.90% purity with 99.80% recovery, 1,2-BDO of 99.35% purity with 99.35% recovery, and 1,2-PDO of 90.59% purity with 94.38% recovery for the ternary mixture. These processes are promising for industrial application and can significantly improve the economy of non-petroleum EG production.     

间歇共沸精馏分离乙醇一水体系的改进研究

间歇共沸精馏是分离共沸物的一种方法,适用于化工、制药、溶剂回收、天然产物提取等产量小、品种多的行业,因此间歇共沸精馏近年来已成为非常活跃的研究和开发热点.对已有的常规间歇共沸精馏的操作方式作了改进,即共沸剂改为在塔釜回流,以正己烷为共沸剂,对分离乙醇-水共沸体系进行了改进研究,并与常规间歇共沸精馏的实验结果进行比较.结...     

MINLP optimization of a heterogeneous azeotropic distillation process: Separation of ethanol and water with cyclohexane as an entrainer

Heterogeneous distillation processes are widely used in industry for the separation of azeotropic and close-boiling mixtures. This paper addresses the optimization of a heterogeneous distillation process for the separation of an azeotropic ethanol/water mixture using cyclohexane as an entrainer. Starting from a given process superstructure a MINLP problem is set up to consider continuous as well as discrete decision variables such as the feed locations and the number of stages of the distillation columns. A modified Generalized Benders Decomposition algorithm to account for non-convexities of the model equations solves the MINLP problem. The algorithm can be attached via Visual Basic for Applications (VBA) to any commercial process simulator with NLP and VBA capabilities. Various optimization runs show that the algorithm is easily applicable and returns solutions independent of the initial values.     

共沸精馏分离乙醇-异丙醇

为了分离乙醇-异丙醇混合物,研究了共沸精馏在乙醇-异丙醇物系中的应用。根据共沸剂的选取原则选定出1-己烯作为共沸精馏分离乙醇-异丙醇混合物的共沸剂,使用ASPEN模拟软件模拟连续和间歇共沸精馏分离乙醇-异丙醇工艺流程,并通过间歇共沸精馏实验考察了所选共沸剂的分离效果。结果表明：使用1-己烯作为共沸剂能成功的分离乙醇-异丙醇混合物;采用有30块理论板的填料塔,回流比为25,共沸剂1-己烯与乙醇的质量比为4∶1,塔釜异丙醇的质量分数达到99.77%。     

甲醇-丙酮共沸物分离的研究进展

主要介绍了甲醇-丙酮共沸物系变压精馏和萃取精馏两种分离方法的研究进展。经过比较,萃取精馏方法在经济成本方面更具有显著优势。关于萃取精馏,首先阐述了萃取剂的选取以及近些年来萃取剂的研究,主要集中在3个方面:传统单一溶剂、各种盐类和离子液体。其次还介绍了各种萃取剂所对应的气液平衡模型的应用情况和操作条件的优化等方面,并对萃取精馏及其萃取剂的应用提出了展望。     

Feasibility studies for batch extractive distillation with a light entrainer

Our former method for the assessment of the feasibility of batch extractive distillation (usually performed in a rectifier with a heavy entrainer) was extended to the case where a light entrainer is fed continuously into a rectifier or a stripper. The method is based on the calculation of the vessel path and possible composition profiles of the column sections. The method is demonstrated for both configurations on the examples of separation of minimum boiling point azeotropic mixtures. For the rectifier the most important conclusions were also experimentally verified.     

Extractive distillation: Advances in conceptual design,solvent selection,and separation strategies

Extractive distillation(ED) is one of the most promising approaches for the separation of the azeotropic or closeboiling mixtures in the chemical industry. The purpose of this paper is to provide a broad overview of the recent development of key aspects in the ED process involving conceptual design, solvent selection, and separation strategies. To obtain the minimum entrainer feed flow rate and reflux ratio for the ED process, the conceptual design of azeotropic mixture separation based on a topological analysis via thermodynamic feasibility insights involving residue curve maps, univolatility lines, and unidistribution curves is presented. The method is applicable to arbitrary multicomponent mixtures and allows direct screening of design alternatives. The determination of a suitable solvent is one of the key steps to ensure an effective and economical ED process. Candidate entrainers can be obtained from heuristics or literature studies while computer aided molecular design(CAMD) has superiority in efficiency and reliability. To achieve optimized extractive distillation systems, a brief review of evaluation method for both entrainer design and selection through CAMD is presented. Extractive distillation can be operated either in continuous extractive distillation(CED) or batch extractive distillation(BED), and both modes have been well-studied depending on the advantages in flexibility and low capital costs. To improve the energy efficiency, several configurations and technological alternatives can be used for both CED and BED depending on strategies and main azeotropic feeds. The challenge and chance of the further ED development involving screening the best potential solvents and exploring the energy-intensive separation strategies are discussed aiming at promoting the industrial application of this environmentally friendly separation technique.     

间歇共沸精馏分离乙二醇单甲醚-水物系

通过绘制乙二醇单甲醚-水-共沸剂的简捷剩余曲线,提出了以乙酸异丙酯作为间歇共沸精馏法分离乙二醇单甲醚-水物系的共沸剂。然后完成剩余曲线数据的测定实验,根据实验数据绘制乙二醇单甲醚-水-乙酸异丙酯三元物系的剩余曲线图,确定了乙二醇单甲醚-水共沸物系的分离工艺。并通过实验研究了共沸剂加入量对乙二醇单甲醚回收率的影响,从而确定了适宜的共沸剂配比：当共沸剂与原料中水的质量比为2～2.5时,乙二醇单甲醚的一次性收率在90%以上。     

Heterogeneous extractive batch distillation of chloroform-methanol-water: Feasibility and experiments

A novel heterogeneous extractive distillation process is considered for separating the azeotropic mixture chloroform-methanol in a batch rectifying column, including for the first time an experimental validation of the process. Heterogeneous heavy entrainer water is selected inducing an unstable ternary heteroazeotrope and a saddle binary heteroazeotrope with chloroform (ternary diagram class 2.1-2b). Unlike the well-known heterogeneous azeotropic distillation process and thanks to continuous water feeding at the column top, the saddle binary heteroazeotrope chloroform-water is obtained at the column top, condensed and further split into the liquid-liquid decanter where the chloroform-rich phase is drawn as distillate. First, feasibility analysis is carried out by using a simplified differential model in the extractive section for determining the proper range of the entrainer flowrate and the reflux ratio. The operating conditions and reflux policy are validated by rigorous simulation with ProSim Batch Column^® where technical features of a bench scale distillation column have been described. Six reproducible experiments are run in the bench scale column matching the simulated operating conditions with two sequentially increasing reflux ratio values. Simulation and experiments agree well. With an average molar purity higher than 99%, more than 85% of recovery yield was obtained for chloroform and methanol.     

Choice of suitable entrainer in heteroazeotropic batch distillation system for acetic acid dehydration

Mixture containing acetic acid and water does not form azeotrope. However, because of tangent pinch on the pure water end, it is customary in industry to add an entrainer into this mixture to aid the separation via heterogeneous azeotropic distillation. When the production scale is relatively small, it is more beneficial to run the acetic acid dehydration in batch mode. In Chien et al. [Chien, I. L., K. L. Zeng, H. Y. Chao, and J. H. Liu, “Design and Control of Acetic Acid Dehydration System via Heterogeneous Azeotropic Distillation,” Chemical Engineering Science, 59, 4547 (2004)], a suitable entrainer for acetic acid dehydration operating in continuous mode was found to be iso-butyl acetate. This paper demonstrates that although iso-butyl acetate is a good entrainer for continuous heterogeneous azeotropic distillation system, it is not suitable in heteroazeotropic batch system for acetic acid dehydration. Instead, the performances of two other acetates are compared for the suggestion of better entrainer in batch operation. An extremely simple batch operating sequence for acetic acid dehydration will be demonstrated via dynamic simulation. The proposed batch operation is very robust in terms of the particular values chosen for the operating variables. This proposed batch operation gives very similar separation performance comparing to a multivessel operation and requires less process, instrumentation, and control equipments.     

Computing Homogeneous Azeotropes Using Interval Analysis

Determining the existence of homogeneous azeotropes, together with their composition and temperature, is important from both theoretical and practical standpoints in the analysis of phase behavior and in the synthesis and design of separation systems employing distillation. We describe here a new method that reliably locates any and all homogeneous azeotropes for multicomponent mixtures, and also verifies the nonexistence of homogeneous azeotropes if none are present. The method is based on interval analysis, and provides a mathematical and computational guarantee that all azeotropes are located. The technique is general purpose and can be applied in connection with any thermodynamic model describing vapor-liquid equilibrium. An example using a five-component mixture modeled with the NRTL equation is presented.     

乙二胺直接环化产物的分离与模拟

提出以甲苯为共沸剂去除混合溶液中的乙二胺和结晶水的间歇共沸精馏法,最后得到质量分数为96.79%的哌嗪及98.26%三乙烯二胺产品,并以水为萃取剂,实现共沸剂的回收利用。采用Aspen Plus化工模拟软件对精馏分离过程进行模拟计算,设计了4塔精馏分离及共沸剂回收的工业化实验装置,利用灵敏度分析模块对精馏塔各操作参数进行优化,从而获得质量分数分别为98.60%和99.20%的哌嗪和三乙烯二胺产品。