Batch‐Rektifikation mit Mittelbehälter

Batch Distillation in Middle Vessel Columns Batch distillation in a middle vessel column is a promising alternative to conventional batch distillation as disadvantages such as high temperatures in the feed vessel or a high energy and time demand of the process can be avoided. The article describes the basics of the synthesis of processes for the separation of zeotropic and azeotropic mixtures using this type of column. Furthermore, experimental results are presented and the advantages of batch distillation in a middle vessel column are explained.     

Einfluß der Diffusion auf die Selektivität der Schleppmittel-Destillation

Influence of diffusion on the selectivity of entrainer distillation . The selectivity of azeotropic distillation generally depends not only on the relative volatility but also upon the rate of diffusion of the participating components in the liquid and the gaseous phase. If the less volatile material diffuses faster in the gas phase than the more volatile material, then the former can also accumulate in the gas phase. In such a case the azeotropic points do not necessarily represent separation limits. This effect might also be utilized in the separation of azeotropic mixtures in specific cases. On the other hand, a large diffusion resistance in the liquid phase can override any selectivity. An estimate shows that selective drying of porous materials containing binary solvent mixtures is therefore practically impossible. Azeotropic distillation is also suitable for investigating column plates and packings with the aim of isolating the hydraulic and kinetic reasons for the imperfect equilibration always observed. These questions, overcoming azeotropic points, non-selective drying, and the reasons for imperfect equilibration in separation columns, are discussed in the light of theoretical results and experimental data obtained for practical azeotropic distillations.     

Synthesis,experiments and simulation of heterogeneous batch distillation processes

The presence of azeotropes in multicomponent mixtures complicates the design of batch distillation separation processes widely used in pharmaceutical and speciality chemical industries. Most of those processes include the use of a homogeneous entrainer to ease the separation. We describe novel methods to break azeotropes using an entrainer that is partially miscible with one of the initial binary mixture components. We depict some of the advantages of heterogeneous batch distillation processes: more design alternatives for the separation of an azeotropic binary mixture than with homogeneous batch distillation, batch distillation boundary crossing thanks to a controlled reflux of the entrainer-rich phase, simplified distillation sequences as a consequence of less distillation tasks. Three examples based on the separation of non-ideal azeotropic or close boiling point binary mixtures through heterogeneous batch distillation are simulated using a commercial batch distillation package. Experiments validate the simulated separation of a minimum boiling azeotropic mixture.     

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.     

A simulation study on selection of optimized process for azeotropic separation of methanol and benzene: Internal heat integration and economic analysis

This work provides an insight into the separation of azeotropic mixtures by using two different techniques: pressure swing distillation and extractive distillation. Both methods are used to separate an azeotropic mixture of methanol and benzene. This mixture exhibits a minimum boiling azeotrope at temperature 57.97 °C and pressure 1 bar with mole fractions of 0.61 and 0.39 for methanol and benzene, respectively. However, the azeotropic point in methanol and benzene mixture is pressure sensitive, which can be shifted by changing pressure with a process called pressure swing distillation. Extractive distillation with suitable solvent is another method to separate such kind of mixture. Both methods are rigorously simulated and optimized for minimum heat duties. Internal heat integration is applied too for increasing energy efficiency. New optimization techniques are carried out with process simulator Aspen HYSYS V8.4 and results reveal the best method for separation of methanol and benzene azeotropic mixture.     

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...     

异丙醇-水分离技术进展

主要介绍了分离异丙醇-水共浦物的几种方法,其中不仅包括传统的苯共沸精馏工艺,而且还包含：吸附蒸馏、萃取精馏、渗透汽化法、加盐萃取共沸精馏等几种新工艺．并对这几种方法进行了比较。     

Concentration-Thermal Swing Adsorption Process for Separation of Bulk Liquid Mixtures

Abstract

A novel concentration-thermal swing adsorption process is described for separation of bulk binary liquid mixtures. The process is designed to produce essentially two pure products with high recoveries of both components. It is particularly suited for separation of azeotropic or close-boiling liquid mixtures which are difficult to separate by distillation. An example of the performance of the new process for separation of an azeotropic water-methyl acetate mixture is given. Experimental binary surface excess equilibrium isotherms, adsorptive mass transfer coefficients, and column dynamics for adsorption of water-methyl acetate mixtures on NaX zeolite are reported.     

Experimental Investigations of Three‐Phase Distillation in a Packed Column

An experimental study with three different heterogeneous azeotropic mixtures (acetone/toluene/water, 1‐propanol/1‐butanol/water and ethanol/cyclohexane/water) has been carried out with the object to analyze the separation efficiency of three‐phase distillation in a packed column. The experiments were made under total reflux in a 70 mm column packed with Sulzer Optiflow C.36. The results show the influence of the second liquid phase on the mass transfer and with that on the separation efficiency in a packed column.     

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.     

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.     

Thermodynamic efficiency of membrane-assisted distillation processes

Membrane processes are considered as comparably mild separation processes offering the potential for significant energy savings compared with azeotropic distillation processes. Despite higher investment and material costs, they are of particular interest for improving the energy efficiency in the chemical industry. However, energy savings of more than 20%–30% are rarely reported and even a general superiority can be disputed. To further elucidate this controversial, the current study pursues a quantitative assessment of the thermodynamic efficiency of pervaporation and vapor permeation processes with stand-alone distillation and hybrid membrane-assisted distillation processes for the separation of azeotropic mixtures. The results confirm the case-dependent potential of distillation processes to outperform membrane-assisted separations in terms of energy efficiency, considering proper heat integration. Although energy efficiency is becoming significantly important, it should be considered in the context of economic performance to determine an optimal trade-off and to select the best process alternative during conceptual process design.     

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     

Optimal design of extractive distillation columns—A systematic procedure using a process simulator

The separation of binary mixtures which form azeotropes is not possible through conventional distillation and they are usually separated by extractive or azeotropic distillation. The optimization of extractive distillation columns is usually performed using a process simulator; however, normally, the result is only obtained after several simulations and the simultaneous analysis of several graphs. This paper sets out to present a systematic procedure, using a process simulator (Aspen Plus^®), in order to obtain the optimum condition for extractive distillation columns. The optimization achieved is characterized by the fact that it is not necessary to perform various simulations, and it also avoids the simultaneous analysis of dozens of curves. The dehydration of aqueous mixtures of ethanol using ethylene glycol as solvent was the system chosen as a case study.     

Extractive Distillation Systems Involving Complex Columns with Partially Coupled Heat and Material Flows

A method based on the representation of flowsheets as graphs is proposed to synthesize flowsheets of extractive distillation of multicomponent azeotropic mixtures in complex columns with partially coupled heat and material flows. It is shown that the flowsheets constructed can provide a significant decrease in the energy consumption for separation because the process becomes structurally closer to thermodynamically reversible distillation.     

特殊精馏热耦合强化技术研究进展

在石油、医药、化工等行业生产和分离过程中,常伴随着共沸或沸点相近混合物的产生,其高效节能分离是工业清洁生产和可持续发展的前提。作为一种分离共沸或近沸等难分离混合物的重要手段,特殊精馏引起了广泛关注。然而,特殊精馏对能源的消耗量非常大,开发低成本、性能可靠的特殊精馏强化技术对实现经济和能源的可持续发展具有重要意义。基于对特殊精馏塔内外传质传热规律的研究,本文从强化原理和工艺改进技术两方面,重点介绍了热耦精馏、隔壁塔、侧线精馏、有机朗肯循环、热泵精馏、差压热耦合等内外热耦合强化技术在特殊精馏节能增效等方面的研究进展,并展望了其未来发展的挑战和机遇,以期为特殊精馏在热耦合强化方面的理论研究与应用提供参考。     

Research advances in thermally coupled intensification technology for special distillation

In the production and separation process of petroleum, medicine, chemical industry and other industries, it is often accompanied by the production of azeotropic or similar boiling point mixtures. Its high-efficiency and energy-saving separation is a prerequisite for industrial clean production and sustainable development. Special distillation as an effective separation method attracts substantial attention from researchers. However, special distillation is a process with high-energy consumption. Therefore, the development of intensification technology for special distillation with low costs and reliable performance is of great significance for the economy and energy sustainable development. According to the heat and mass transfer laws of special distillation, this work introduces the research advances of thermally coupled distillation, dividing wall column, side-stream distillation, organic Rankine cycle, heat pump and different pressure thermally coupled technologies in energy saving special distillation process from the intensification principles and retrofitting technologies. In addition, this work outlines the challenge and opportunity of intensification technology to provide references of the theoretical research and application to special distillation.     

Separation of Liquid Mixtures by Pervaporation

Separation of various mixtures, especially liquid mixtures, is a very necessary unit operation in industry. A large number of such techniques are available, such as distillation, adsorption, liquid-liquid extraction, and fractional crystalization [l]. The development of this type of technology became necessary to effect separation of azeotropic liquid mixtures. For liquid mixtures having components with similar boiling ranges, however, such conventional separation techniques are energy intensive and add considerably to the cost of the final product. With the advent of the necessity of reducing the energy requirements of Unit options, membrane separation has been recognized as an alternative to the conventional methods.