Special Distillation Research Articles

A novel intermediate heat exchange intensified extractive pressure-swing distillation process for efficiently separating n-hexane-tetrahydrofuran-ethanol

The new intensified strategy can be used in special distillation processes to achieve energy savings. Through analyzing the influence of different extractants and pressure on the separation performance of n-hexane-tetrahydrofuran-ethanol. system, extractive pressure-swing distillation process (EPSD) using dimethyl sulfoxide as extractant was proposed. Multi-objective optimization was performed to definite the best operating parameters of EPSD. Based on the phenomenon that the temperature of high-temperature column top is lower than low-temperature column bottom, making it impossible to perform traditional thermal integration, an intermediate heat exchange intensified process (IHE-EPSD) was developed. The performance influencing factors and heat exchange network of IHE-EPSD were analyzed to obtained the optimal IHE-EPSD process. Three heat integration schemes of the IHE-EPSD were designed to further save energy consumption. Finally, the processes were assessed from economy, energy, environment and exergy. The results indicate that the IHE-EPSD process exhibits excellent separation performance, achieving the efficient separation of n-hexane-tetrahydrofuran-ethanol.

Recovery of biofuel additives isopropyl alcohol and diisopropyl ether using ionic liquids with intermolecular interactions and process design

Isopropyl alcohol (IPA) and diisopropyl ether (DIPE) are widely used as biofuel additives in fuel processing. When IPA is produced by propylene hydration, a by-product IPA and DIPE is made. Since the existence of azeotropic point formed between IPA and DIPE, the separation of the azeotrope is achieved using special distillation technologies in industry, which requires high energy consumption. Liquid-liquid extraction was used to separate the mixture due to its energy saving in this work. Three imidazolium-based ionic liquids (ILs) 1-butyl-3-methylimidazolium thiocyanate ([BMIM]SCN), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM]NTf2) and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) were synthesized as the extractants. The influence of extraction time, extraction temperature, mass ratio of mixture (IPA + DIPE) to ILs and the initial content of IPA in the mixture (IPA + DIPE) on the extraction performance of ILs were studied. The optimal extraction conditions were determined using the response surface method (RSM). The results showed that the IL [BMIM]SCN had better extraction capacity for separation of the mixture (IPA + DIPE). The interactions between molecules were investigated by quantum chemical calculations. Finally, a conceptual separation process is designed to separate the mixture, which can provide a helpful technology to purify the biofuel additives.

Flowsheets for hydroxyacetone–phenol binary mixture separation: The use of special distillation methods

Objectives. To study the possibility of hydroxyacetone–phenol binary mixture (a constituent of a mixture of phenol production by the cumene method) separation in flowsheets based on the use of distillation special methods. This is the addition of separating agents to increase the relative volatility of the components of the original mixture, and the variation of pressure in the columns.Methods. A computational simulation in Aspen Plus® was used as the research method. Mathematical modeling of the vapor–liquid equilibrium was carried out using a local compositions model Non-Random Two Liquid. The viability of the latter was confirmed by comparing experimental and calculated on phase equilibrium data, and azeotropic data. The average relative error does not exceed 3%.Results. The dependence of the composition and boiling point of the hydroxyacetone–phenol azeotrope on pressure was determined in a computational experiment (as the pressure increases, the azeotrope is enriched with phenol). The possibility of using a complex of columns operating under different pressures to separate the mixture was shown (the shift of the azeotrope is about 9%). The change in the relative volatility of components of the original mixture in the presence of a high(diethylene glycol) and a low-boiling (acetone) separating agent was investigated. Both solvents are selective agents used in extractive and re-extractive distillation processes. Three technological separation flowsheets containing two distillation columns were proposed.Conclusions. The study established the operation parameters of the columns (number of theoretical stages, feed stages of the original mixture and separating agent, and reflux ratio) and energy consumption (total heat supplied to the columns boiler) of three separation flowsheets ensuring the production of products of a given quality (not less than 0.99 mol fractions). The flowsheet with diethylene glycol is characterized by the lowest energy consumption. It is recommended that complexes of extractive and re-extractive distillation be further optimized. This enables the second product of cumulus production—acetone—to be involved in the technological cycle.

Research progress in reactive distillation

As a special distillation process, reactive distillation technology has been widely used in the petrochemical field due to its outstanding advantages such as high efficiency and energy saving. It has been paid more and more attention from researchers in the field of chemical process enhancement since the 1920s. With the progress of social development level, resource conservation and environmental friendliness have become the general trend. In order to pursue the maximization of energy utilization and higher economic benefits, scientific researchers have developed a variety of new reactive distillation processes suitable for various occasions considering the advantages and limitations of traditional reactive distillation technology. The biggest difference from traditional reactive distillation is that the new processes have the characteristics of saving equipment investment, low reaction energy consumption, improving mass transfer, heat transfer efficiency and energy utilization rate. In order to fully understand and apply the technology, this paper describes the process flow of traditional and new reactive distillation technologies in detail, and focuses on analyzing and summarizing the latest developments in the industrial application of reactive distillation technologies in various fields. Finally, it points out that reactive distillation technologies issues that need attention and future development directions.

Economic and entropy production evaluation of extractive distillation and solvent-assisted pressure-swing distillation by multi-objective optimization

Extractive distillation (ED) and solvent-assisted pressure-swing distillation (SA-PSD) are both special distillation processes that perform good at separating pressure-insensitive azeotropes. However, few reported studies have compared the performance of the two processes. In this paper, ED processes with N-methylpyrrolidone (NMP) and dimethlac-etamide (DMCA) as entrainer, SA-PSD process with isopropyl-alcohol (IPA) as solvent and SA-PSD process with partial heat integration (PHI-PSD) are proposed to achieve high purity separation of a mixture of cyclohexane/2-butanol system. The optimal operating conditions of the processes are obtained after optimizing with NSGA-II algorithm when total annual cost (TAC) and the entropy production of process are set as objectives. The optimal results show that the optimal PHI-PSD process has lower TAC by 28.7% and the lower entropy production by 39.5% than the optimal SA-PSD process while the ED process with NMP as entrainer has lower TAC by 50.9% and the lower entropy production by 56.1% than the optimal SA-PSD process. The optimal results show that the ED process with NMP as entrainer has the best economic and thermodynamic efficiency among the four proposed processes in this paper.

Better Lightweight Network for Free: Codeword Mimic Learning for Massive MIMO CSI Feedback

The channel state information (CSI) needs to be fed back from the user equipment (UE) to the base station (BS) in frequency division duplexing (FDD) multiple-input multiple-output (MIMO) system. Recently, neural networks are widely applied to CSI compressed feedback since the original overhead is too large for the massive MIMO system. Notably, lightweight feedback networks attract special attention due to their practicality of deployment. However, the feedback accuracy is likely to be harmed by the network compression. In this paper, a cost free distillation technique named codeword mimic (CM) is proposed to train better feedback networks with the practical lightweight encoder. A mimic-explore training strategy with a special distillation scheduler is designed to enhance the CM learning. Experiments show that the proposed CM learning outperforms the previous state-of-the-art feedback distillation method, boosting the performance of the lightweight feedback network without any extra inference cost.

Process intensification by integration of distillation and vapor permeation or pervaporation - An academic and industrial perspective

Since membrane separations, such as vapor permeation (VP) or pervaporation (PV), are not limited by vapor-liquid equilibrium, their coupling with distillation can exert a synergistic effect, overcome the thermodynamic limits of distillation, and improve energy efficiency, especially suitable for the separation of azeotropic mixtures that otherwise requires special distillation processes. Therefore, there is an increasing number of such studies, and it is of great significance to comprehensively explore the process integration of distillation with VP or PV. This review first introduces the mechanism model of membrane separation and membrane materials, then comprehensively summarizes the academic research in terms of hybrid configurations of distillation with VP or PV in the following aspects: separation of azeotropic or close-boiling mixtures, promoting reactions by selectively removing a product, and energy savings, providing guidelines for subsequent application and future research. Finally, this review gives typical industrial cases of distillation and membrane-coupled separation processes and highlights some deficiencies of current research in this area.

Comparison of Controllability Features of Extractive and Pressure Swing Distillations on the Example of Tetrahydrofuran Dewatering.

The controllability study is an integral part of chemical process design. In this work, the controllability of two special distillation techniques, extractive distillation and pressure swing distillation, designed for the separation of azeotropic mixtures is investigated with dynamic tools. The control design interface of Aspen Plus and Matlab are applied for the modeling and evaluation of the two systems. Dynamic controllability indices are determined and aggregated in a desirability function. The results are compared to obtain efficient help for process design activity. The pressure swing distillation shows significantly better controllability features than the extractive distillation. The reason can be the fact that in the case of the extractive distillation, a third compound, the extractive agent, is added to the system to carry out the separation, therefore making the system more complex. As far as the selection of manipulated variables is concerned, in the case of the extractive distillation, the reflux flows should be preferred to the reflux ratios but in the case of the pressure swing distillation, the reboiler heat loads are preferred to the reflux ratios since those are closer to the controlled compositions. Both separation systems show worse controllability features if the product purity requirement is approaching to the pure products, that is, close to 100%. Although the energy consumption of the pressure swing distillation is higher than that of the extractive distillation, it has the inherent feature that it can be automatically heat integrated due to a column operated at high pressure and, as a consequence, higher temperatures.

Intensified hybrid reactive-extractive distillation process for the separation of water-containing ternary mixtures

• Process intensification for separating water-containing ternary azeotropic mixtures. • Combine reactive distillation and extractive distillation into one column. • Systematic VLE analysis helps to screen for feasible ternary systems. • Three ternary systems including: TBA/EtOH/water, THF/EtOH/water, and ACN/IPA/water. • Significant reduction in total annual cost is achieved in all applications. Separation of ternary mixture is a challenging task if multiple azeotropes exist among the components, and special distillation techniques should be adopted. For water-containing ternary mixtures with multiple azeotropes, a dehydrating agent, ethylene oxide (EO), can be used to consume water with the production of ethylene glycol (EG) as the product, which can be utilized as entrainer for separating the remaining two components. In this work, systematic thermodynamic analysis was conducted to screen for the feasible ternary systems. After conducting suggested analysis without needing of rigorous process simulation, tert -butyl alcohol (TBA)/ethanol (EtOH)/water, tetrahydrofuran (THF)/EtOH/water and acetonitrile (ACN)/isopropyl alcohol (IPA)/water mixtures were chosen to be suitable for this application. Within the scope of using dehydrating agent, a process configuration of triple column reactive-extractive distillation (TCRED) is developed for three different ternary systems. Subsequently, an intensified process configuration - double column reactive-extractive distillation (DCRED), which combines both functions of reactive distillation and extractive distillation in a single unit, is constructed to significantly reduce capital cost and energy consumption. With the application of further energy-saving schemes in the systems, total annual cost and total operating cost of the final proposed design flowsheets can be considerably saved compared to respective separation systems recently published in open literature.

Process design and intensification for the clean separation of ternary multi-azeotropes system via special distillation coupled with reaction

A ternary mixture of diisopropyl ether, isopropanol and water exists in the production process of isopropanol. Ensuring the clean separation of this mixture is of great significance for the clean production of isopropanol from both economy and environment. However, there are three binary and one ternary minimum boiling point homogeneous azeotropes in this system, which complicate the clean production of isopropanol. In this study, with the aid of the hydration reaction of ethylene oxide, clean separation of a ternary mixture of diisopropyl ether–isopropanol–water was realized. Three separation processes—reaction–pressure swing distillation, reaction–extractive distillation and reaction–dividing wall extractive distillation—were proposed. These processes were optimized based on the sequential iterative algorithm, with the minimum total annual cost as the objective. Reaction-pressure swing distillation had the best economic performance, reaction-extractive distillation followed, and reaction-dividing wall extractive distillation performed the worst. The carbon dioxide, sulfur dioxide, and nitrogen oxide emissions of the three processes were calculated based on the optimization results. Reaction-pressure swing distillation had the lowest emissions, followed by reaction-dividing wall extractive distillation. However, reaction-extractive distillation had the highest emissions. The exergy analysis of distillation units and exchanger was performed, and the results showed that reaction-pressure swing distillation had the best exergy performance. Reaction-pressure swing distillation was better than reaction-extractive distillation and reaction-dividing wall extractive distillation in terms of economy, environment, and thermodynamic efficiency. This study provides an original idea for the clean separation of diisopropyl ether-isopropanol-water azeotropes.

Anhydrous tert-butanol production via extractive distillation using glycerol as an entrainer: technical performances simulation

tert-Butanol is widely used as a main solvent in the industries. The high purity of tert-butanol is required to fulfil the industrial standard for the solvent. Unfortunately, tert-butanol separation from water required a special distillation named extractive distillation due to the azeotropic point in the mixture. Thus, entrainer as a third component should be used to break the azeotropic point. Glycerol is one of the potential green entrainer used in the extractive distillation. The simulation of the extractive distillation using glycerol as entrainer for the separation of tert-butanol/water mixture was conducted in this study. The Aspen Plus Process Simulator V.10 was used to simulate the feasibility of the glycerol as an entrainer and determine the optimum operating condition of the extractive distillation and recovery column in the anhydrous tert-butanol production. The results show that the optimum configuration for the extractive distillation column design consists of the number of stages of 25, binary feed stage of 21, entrainer feed stage of 3, reflux ratio of 0.6, mixed feed temperature of 25°C, and an entrainer feed temperature of 45°C. The condenser and reboiler duties are -1171.04 kW and 1744.48 kW, respectively. Moreover, the tert-butanol purity with this configuration can be achieved up to 0.996 of mole fraction.

Research progress and optimization prospect of constant boiling distillation technology

Coboiling distillation is a special distillation method of separating the azeotropic system mixture, which is widely used in petroleum refining and chemical production. This paper reviewed the selection and characteristics of azeoliling agents, and introduced the research progress of home and abroad in detail. The system compares the advantages and disadvantages of the traditional constant boiling distillation and the new heat pump, compare the advantages, and presents the prospect of constant boiling distillation.

Comparison of alternative methods for methyl acetate + methanol + acetic acid + acetic anhydride mixture separation

Objectives. The paper is a comparative analysis of methyl acetate + methanol + acetic acid + acetic anhydride industrial mixture separation flowsheets based on the use of special distillation methods (extractive distillation and pressure-swing distillation). The results obtained illustrate the variability of the structure of the technological separation flowsheet.Methods. Mathematical modeling using the software package Aspen Plus V. 10.0 was chosen as the research method. The simulation was based on the local composition equation NRTL and the Hayden–O’Connell equation of state. The relative uncertainties of phase equilibrium description do not exceed 3%.Results. The vapor–liquid diagram of the quaternary mixture of methyl acetate + methanol + acetic acid + acetic anhydride was studied using thermodynamic topological analysis. It was shown that the system contains one binary azeotrope and is characterized by one distillation region. Although the structure is not complex, there is a possibility of using several methods for mixture separation: pressure-swing distillation, and extractive distillation with different entrainers. Twelve flowsheets with different structure were proposed, and 29 variants of separation were compared.Conclusions. It was shown that the most perspective structure for the separation of a methyl acetate + methanol + acetic acid + acetic anhydride mixture is a combination of distributed sequence separation and extractive distillation.

Research Progress on Azeotropic Distillation Technology

Azeotropic distillation is a special distillation method for separating liquid mixtures, which has better distillation effect and obvious advantages of energy saving and consumption reduction compared with traditional distillation. In this paper, the latest research progress of azeotropic distillation technology in separation, synthesis and energy saving at home and abroad is reviewed. The research progress in separation is reflected in product separation and product purification, and the research progress in energy saving is reflected in heat pump distillation and dividing wall column distillation respectively. Existing studies have shown that azeotropic distillation technology can produce higher purity target products than conventional distillation for the separation and purification of azeotropic or near-boiling compounds. Heat pump distillation and dividing wall column distillation are used in azeotropic distillation field, resulting in obvious energy-saving effect for distillation equipment. The follow-up research direction of new separation technology with the goal of reducing energy consumption and exploring new materials as entraining agents should be studied in detail, which provides certain guidance for the development of distillation technology in China’s chemical industry.

Refining Ancient Lead by Vacuum Distillation

A complex method for refining lead by distillation in vacuum has been described. A brief comparative description of different methods of lead refining was submitted. Analysis of different methods showed that to increase the efficiency of lead deep cleaning the development of complex refining processes is required. The computational studies of the behavior of impurity elements in the ancient lead are performed. The ideal coefficients of impurities separation αi are calculated at lead distillation temperatures. The range of volatile and nonvolatile impurities was detected by magnitude αi in lead. Performed computational studies of the impurity elements behavior in lead formed the basis for developing an integrated method of deep refining of ancient lead. To implement this approach the special distillation device was developed, and the procedure of deep purification of lead was described.The results of the study of the deep refining ancient lead have been demonstrated. The cleaning high efficiency of the proposed approach, combined with high performance and yield of the suitable product, was shown. A pilot batch of ancient lead containing base metal > 99.998 wt. % suitable for growing high quality scintillation crystals PbWO4 and PbMoO4 has been produced.

Separation of Process Wastewater with Extractive Heterogeneous-Azeotropic Distillation

Abstract The application of vapour-liquid equilibria-based separation alternatives can be extraordinarily complicated for the treatment of process wastewaters containing heterogeneous-azeotropic. Despite dissimilar successfully tested methods for separation, there is possibility to get better distillation method by enabling the separation of more and more specific process wastewater. Extractive heterogeneous-azeotropic distillation (EHAD) is a new advance in treatment of fine chemical wastewater showing special features to cope with the treatment of highly non-ideal mixtures. This method combines the worth of heterogeneous-azeotropic and extractive distillations in one apparatus without addition of any extra materials. The study of the separations of ternary component process wastewater from the fine chemical industry shows both in the modelled and experimental results that EHAD can be successfully applied. The measured and modelled compositions at extreme purities, that is, close to 0% or 100%, can be different because of the inaccuracies of the modelling. This highlights the paramount importance of the experiments if special extra-fine chemicals with almost no impurities, e.g. of pharmacopoeial quality are to be produced by special distillation technique. This study expands the application of EHAD technique, this new field is the separation of process wastewaters.

Evaluation and Comparison between Crude Oil Straight Run Fractions and Its Commercial Fractions (Gasoline, Kerosene and Gas Oil) at Dura Oil Refinery

Atmospheric distillation according to ASTM-D 2892 and ASTM-D 86 distillation methods was carried out to one selected crude oil at Dura oil refinery. Its straight run fractions (Gasoline, Kerosene and Gas Oil) were tested using the physical properties: Boiling point, Density, Pour point, Surface tension and Aniline point in addition to the calculated results: API gravity, Kw factor and Correlation index to make a comparison with commercial fractions (refinery final products): Gasoline, Kerosene and Gas Oil. A special distillation curves were obtained for crude oil to determine the straight run fractions and for the commercial fractions to establish their characteristics and support the preliminary results of the physical properties with valuable data which enhanced the comparison. Distillation of commercial gasoline shows that it is heavier than straight run ones, while there were matching in the characteristics for kerosene. Commercial gas oil was lighter than straight run due to the presence of kerosene.

Extractive distillation with ionic liquids: A review

Extractive distillation is commonly used for the separation of azeotropic or close‐boiling mixtures in the chemical industry. During the past decade, the use of ionic liquids (ILs) as entrainers has received considerable attention due to their unique advantages when applied in extractive distillation. This work is devoted to providing an easy‐to‐read and comprehensive review on the recent progress made by chemical engineers, focusing on the issues of predictive thermodynamic models, structure‐property relations, separation mechanisms, and process simulation and optimization. This review spans from the molecular level to the industrial scale, to provide a theoretical insight into the molecular interactions between ILs and the components to be separated. Moreover, a comprehensive database on the vapor–liquid equilibria and activity coefficients at infinite dilution concerning ILs is provided as Supporting Information. Concluding remarks are made on the unsolved scientific issues with respect to this promising special distillation technology. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3312–3329, 2014

Special distillation regime involving an infinite reflux ratio and an infinite number of separation stages

Distillation at an infinite reflux ratio in combination with an infinite number of trays has been investigated.

Experimental investigation, modeling and scale-up of hydrophilic vapor permeation membranes: Separation of azeotropic dimethyl carbonate/methanol mixtures

The separation of azeotropic mixtures is a challenging task that is currently performed by special distillation processes, such as heteroazeotropic, extractive or pressure-swing distillation. In recent years, membrane materials that are used to separate different combinations of chemical compounds have constituted an energy-efficient and competitive alternative to special distillation processes. Vapor permeation is a promising type of membrane separation processes which enables to overcome limitations caused by the thermodynamic phase equilibrium. This characteristic facilitates the separation of azeotropic mixtures. However, the membrane needs to be large to handle high throughputs or to achieve high purities. Thus, the use of membranes in combination with established unit operations in so-called membrane-assisted separation processes is advantageous. Nevertheless, in addition to the reliable selection of a suitable membrane polymer for a given design task, a model-based scale-up is still challenging and complicates the design of said membrane separations. These disadvantages limit the application of vapor permeation in the chemical industry. Therefore, the aim of this paper is to enable scale-up by systematically identifying the influence of vapor permeation operating parameters at two different experimental scales with a scale-up factor of 50. Based on these experiments, a rigorous model was developed using experimental data from lab-scale to predict the separation characteristics in pilot-scale. These findings were validated against experimental data from this scale. In this work, the separation of dimethyl carbonate and methanol showing a low-boiling azeotrope with high methanol content was used as a case study. The separation of these two compounds is of significant interest because valuable dimethyl carbonate is usually produced from methanol feedstocks, thus necessitating the separation of both components.