New double column system for heteroazeotropic batch distillation

A new double column system (DCS) operated in closed mode is suggested for heterogeneous batch distillation. This configuration is investigated by feasibility studies based on the assumption of maximal separation and is compared with the traditional batch rectifier (BR). We study the configurations also by dynamic simulation based on a detailed model using a professional simulator. For the new configuration the minimal duration of the process is determined. The influence of the most important operational parameters is studied. The calculations and the simulations are performed for a binary (n-butanol–water) and for a ternary heteroazeotropic mixture (isopropanol–water + benzene as entrainer). One of the advantages of the DCS is that distillation of binary and ternary systems is performed in only one step. Furthermore the recovery of components is usually higher and the amount of byproducts is lower.     

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.     

反置式间歇蒸馏塔的设计程序(Ⅰ)多组分理想物系

Inverted batch distillation column(stripper) is opposed to a conventional batch distillation column(rectifier). It has a storage vessel at the top and products leave the column at the bottom. The batch stripper is favourable to separate mixtures with a small amount of light components by removing the heavy components as bottom products. In this paper, we are presenting a shortcut procedure based on our earlier work for design and simulation of the inverted batch distillation column, which is equivalent to the Fenske-Underwood-Gilliland procedure for continuous distillation. Given a separation task, we propose to compute the minimum number of stages(Nbmin) and the minimum reboil ratio(Rbmin) required in a batch stripper,which are the stages and reboil ratio required in a hypothetical inverted batch distillation column operating in total reboil ratio or having an infinite number of stages,respectively. Then, it is shown that the performance of inverted batch columns with a finite number of stages and reboil ratios could be correlated in Gilliland coordinates with the minimum stages Nbmln and the minimum reboil ratio Rbmin.     

Generalised method for the determination of heterogeneous batch distillation regions

A new, general method for the calculation of residue curves and for the determination of batch distillation regions of heteroazeotropic distillation is suggested. The method proposed, which means the extension of the method of Pham and Doherty, takes into consideration the possibility of the withdrawal of any fraction of either liquid phase from the decanter as distillate. The simplified and rigorous simulation calculations were carried out for the mixtures dichloromethane-acetone (low α) + water (heavy, selective, heterogeneous entrainer), water-ethylenediamine (maximum azeotrope) + benzene (light, selective, heterogeneous entrainer) and isopropanol-water (minimum azeotrope) + benzene (light, non-selective, heterogeneous entrainer). The new method gives the right sequence of the cuts for all operation modes and strategies of heterogeneous batch 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.     

Shortcut Procedure for Inverted Batch Distillation Column (Ⅰ) Multicomponent Ideal System

Inverted batch distillation colunm(stripper) is opposed to a conventional batch distillation column(rectifier). It has a storage vessel at the top and products leave the column at the bottom. The batch stripper is favourable to separate mixtures with a small amount of light components by removing the heavy components as bottom products. In this paper, we are presenting a shortcut procedure based on our earlier work for design and simulation of the inverted batch distillation column, which is equivalent to the Fenske-Underwood-Gilliland procedure for continuous distillation. Given a separation task, we propose to compute the minimum number of stages(Nbmin)and the minimum reboil ratio(Rbmin) required in a batch stripper,which are the stages and reboil ratio required in a hypothetical inverted batch distillation colnmn operating in total reboil ratio or having an infinite number of stages,respectively. Then, it is shown that the performance of inverted batch columns with a finite number of stages and reboil ratios could be correlated in Gilliland coordinates with the minimum stages Nbmin and the minimum reboil ratio Rbmin.     

Operation and control of batch extractive distillation for the separation of mixtures with minimum-boiling azeotrope

Batch distillation is commonly used in the fine chemicals, specialty polymer, biochemical, pharmaceutical, and food industries. For separating mixtures with minimum-boiling azeotrope, a heavy entrainer is frequently added to the top section of the batch column to aid in the separation. This process is called batch extractive distillation. Most of the papers in open literature have only studied the first operating step of the batch extractive distillation which is the recovery of the light component without mentioning the later steps for the recovery of the other component and entrainer. In this paper, two real chemical systems, one separating acetone and methanol using water as entrainer and the other separating isopropyl alcohol (IPA) and water using dimethyl sulfoxide (DMSO) as entrainer, are studied for the feasible operation of the complete batch distillation sequence. The operating variables, including the pre-load amount with the mixture, continuous feed rate of the entrainer, and reflux ratio at each operating step are determined in the operating sequence. The constant reflux ratio and constant entrainer feed rate operating policy and another policy to allow these two operating variables to be varied will be compared in order to further improve the batch operation. All dynamic simulations that are performed directly mimic industrial situations from an empty column using a rigorous dynamic simulator, Aspen Dynamics™.     

Batch extractive distillation as a hybrid process: separation of minimum boiling azeotropes

The batch extractive distillation is compared with the hybrid process (absorption+distillation) by feasibility studies and rigorous simulation. A new method is presented for the assessment of feasibility of the hybrid batch extractive distillation. The limiting values of the operational parameters are determined. Calculations are presented for the separation of the minimum boiling azeotropic mixtures of acetone-methanol and ethanol-water by the application of water and ethylene glycol as heavy solvents, respectively.     

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.     

非均相间歇共沸精馏研究进展

非均相间歇共沸精馏广泛地应用于共沸物系的分离。本文在三元相图上,结合残余曲线、塔釜路径和塔的浓度轮廓线,对该过程中的关键问题,如回流比策略、可行性分析、操作模式等进行了定性讨论,对该过程的设计和操作有很大帮助。     

Feasibility of separation of ternary mixtures by pressure swing batch distillation

Feasibility of the pressure swing batch distillation separation of ternary homoazeotropic mixtures in different single and double column configurations is investigated by assuming maximal separation. Feasibility regions where the ternary mixture can be separated into its pure components (by applying in at least one step pressure swing) and the separation steps for the recommended configurations are determined. The method is presented in details for the most frequent types of ternary mixtures with minimum azeotrope(s).     

Separation process of butanol-butyl acetate-methyl isobutyl ketone system by the analysis to residual curve and the double effect pressure-swing distillation

The separation of ternary mixture of butanol,butyl acetate,and methyl isobutyl ketone (MIBK) was initially analyzed by the residual curve.In this process,MIBK was chosen as the azeotropic agent during the first step of separation.The optimum mass ratio of extra MIBK was 1.6 in the modified feed stream according to the residual curve.Thus on this condition the top product was butanol-MIBK azeotrope while the bottom product was butyl acetate in the preliminary separation of the mixture.Then the butanol and MIBK azeotrope was separated by the double effect pressureswing distillation with the low pressure column performing at 30 kPa and the atmosphetic pressure column at 101 kPa.The optimal operating conditions were then obtained by using Aspen Plus to simulate and optimize the process.The results showed that the mass purities of butanol,butyl acetate,and MIBK were all more than 99％ and reached the design requirements.Additionally,compared with the traditional distillation with outside heating,the double effect pressure swing distillation saved the reboiler duty by 48.6％ and the condenser duty by 44.6％.     

双溶剂进口的双釜间歇萃取精馏

提出了带有塔底回收釜及双溶剂进口的间歇萃取精馏操作方式。在新操作方式中,塔内回流液不流回塔釜,而是流入塔底回收釜,再经简单蒸馏气相返回塔釜,回收后的溶剂返回精馏塔中。以乙二醇作溶剂分离乙醇-水物系的实验结果表明,当间歇操作次数为2时,产品采出率最大,单位产品消耗的新鲜溶剂量最少。新操作方式具有塔釜温度变化平稳,新鲜溶剂用量相对较少等优点。     

单乙醇胺(MEA)间歇萃取精馏甲醇-丙酮研究

用常规的间歇萃取精馏实验装置,研究了以单乙醇胺(MEA)为萃取剂间歇萃取精馏分离甲醇—丙酮恒沸物的过程。考察了萃取剂、全回流时间、共沸物组成、溶剂与混合物的体积比、回流比等因素对萃取精馏分离甲醇—丙酮共沸体系的影响,从而得出最优的萃取条件。     

The energy consumption in a batch stripper and a batch rectifier

The energy consumption in a batch rectifier and a batch stripper was investigated with a shortcut mathematical model. The minimum energy consumption of a batch stripper was compared to that of a batch rectifier under “general constant reflux” and “general constant distillate composition” with the ratio of minimum energy consumption E_S/E_R. When the feed contains a large amount of light component, the product purity specification is low and the relative volatility is small, the minimum energy consumption of a batch stripper is less than that of a batch rectifier under “general constant reflux” and “general constant distillate composition”. When the feed contains a small amount of light component, the product purity specification is very high and the relative volatility is low, a batch stripper can also consume less energy only in the “general constant distillate composition” operation mode. In other cases, a batch rectifier can consume less energy.     

Integrating product and process design with optimal control: A case study of solvent recycling

This paper proposes the simultaneous integration of environmentally benign solvent selection (product design), solvent recycling (process design) and optimal control for the separation of azeotropic systems using batch distillation. The previous work performed by Kim et al. (2004. Entrainer selection and solvent recycling in complex batch distillation. Chemical Engineering Communications 191(12), 1606-1633) combines the chemical synthesis and process synthesis under uncertainty. For batch distillation, optimal operation is also important due to the unsteady state nature of the process and high operating costs. Optimal control allows us to optimize the column operating policy by selecting a trajectory for the reflux ratio. However, there are time-dependent uncertainties in thermodynamic models of batch distillation due to the assumption of constant relative volatility. In this paper, the uncertainties in relative volatility were modeled using Ito processes and the stochastic optimal control problem was solved by combined maximum principle and non-linear programming (NLP) techniques. Then the previous work of optimal solvent selection and recycling was coupled with optimal control. As a real world example for this integrated approach, a waste stream containing acetonitrile-water was studied. The optimal design parameters obtained by Kim et al. (2004. Entrainer selection and solvent recycling in complex batch distillation. Chemical Engineering Communications 191(12), 1606-1633), for this separation were used and the optimal control policy is computed first without considering uncertainties by variable transformation technique. The deterministic optimal control policy improves the product yield by 4.0% as compared to the base case, verified using a rigorous simulator for batch distillation. When the stochastic optimal control policy was computed representing the relative volatility as an Ito process, a similar recovery rate was obtained from simulations, but the batch time was reduced significantly, producing the most profitable operation.     

The energy consumption in a batch stripper and a batch rectifier

The energy consumption in a batch rectifier and a batch stripper was investigated with a shortcut mathematical model. The minimum energy consumption of a batch stripper was compared to that of a batch rectifier under “general constant reflux” and “general constant distillate composition” with the ratio of minimum energy consumption E _S /E _R . When the feed contains a large amount of light component, the product purity specification is low and the relative volatility is small, the minimum energy consumption of a batch stripper is less than that of a batch rectifier under “general constant reflux” and “general constant distillate composition”. When the feed contains a small amount of light component, the product purity specification is very high and the relative volatility is low, a batch stripper can also consume less energy only in the “general constant distillate composition” operation mode. In other cases, a batch rectifier can consume less energy.     

乙醇-乙酸乙酯体系的间歇萃取精馏研究

在常规的间歇萃取精馏实验装置中,研究了以N,N-二甲基酰胺(DMF)和二甲亚砜(DMSO)作萃取剂;在间歇萃取精馏塔中分离乙醇-乙酸乙酯体系的过程。对全回流时间、不同萃取剂、恒沸物组成、溶剂和混合物的体积比、加盐及加碱等因素考察,分析萃取精馏分离乙醇-乙酸乙酯共沸体系的影响,从而得出最佳的萃取条件。     

Design and Control Comparison of Alternative Separation Methods for n‐Heptane/Isobutanol

The binary mixture of n‐heptane and isobutanol forms an azeotrope at atmospheric pressure, with a composition of 66.9 mol % n‐heptane and a temperature of 364 K. Several methods of separation are possible. This study compares the steady‐state economics and the dynamic controllability of three alternative separation techniques: a two‐column extractive distillation process, a two‐column pressure‐swing distillation process, and a single column with a refrigerated condenser.     

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.