热集成变压精馏分离甲苯-异丙醇的模拟

甲苯-异丙醇混合物的共沸组成对压力较为敏感,为此提出了热集成变压精馏工艺分离该共沸物.利用ASPEN PLUS化工模拟软件,以修正的WILSON活度系数方程作为物性计算模型,以甲苯和异丙醇的纯度作为约束变量,以分离过程能耗最低为目标函数,对主要工艺参数进行了模拟优化,得到了热集成变压精馏分离甲苯-异丙醇体系的最佳工艺操...     

Heat Integrated Ethanol Dehydration Flowsheets

Abstract

A theoretical evaluation of heat-integrated heterogeneous-azeotropic ethanol-water distillation flowsheets is presented. Simulations of two column flowsheets using several different hydrocarbon entrainers reveal a region of potential heat integration and substantial reduction in operating energy. In this paper, methods for comparing hydrocarbon entrainers are shown.

Two aspects of entrainers are related to operating and capital costs. The binary azeotropic composition of the entrainer-ethanol mixture is related to the energy requirements of the flowsheet. A temperature difference in the azeotropic column is related to the size of the column and overall process staging requirements. Although the hydrophobicity of an entrainer is essential for specification of staging in the dehydration column, no substantial increase in operating energy results from an entrainer that has a higher water content. Likewise, liquid-liquid equilibria between several entrainer-ethanol-water mixtures have no substantial effect on either staging or operation. Rather, increasing the alcohol content of the entrainer-ethanol azeotrope limits its recovery in the dehydration column, and increases the recycle and reflux streams. These effects both contribute to increasing the separation energy requirements and reducing the region of potential heat integration.

A cost comparison with a multieffect extractive distillation flowsheet reveals that the costs are comparable; however, the extractive distillation flowsheet is more cost effective as operating costs increase.

The destruction of organic model substances by indirect electrooxidation was investigated. The oxidation agent Co(III) was used because of the high redox potential of the Co(III)/Co(II) redox couple (E₀ = 1.808 V).

Several supercritical fluid extraction (SCFE) processes have been proposed for removing toxic and intractable organic compounds from a range of contaminated solids. These include soil remediation and the regeneration of adsorbents used to treat wastewater streams such as granular activated carbon (GAC). As a separation technique for environmental control, SCFE has several distinct advantages over conventional liquid extraction methods and incineration. Most notably, the contaminant is removed from the solvent in a concentrated form via a change in pressure or temperature and can be completely separated upon expansion to atmospheric pressure.

The viability of SCFE hinges on process conditions such as solvent-feed ratio and solvent recycle ratio. The necessity of recycling solvent complicates the contaminant separation step since a complete reduction to atmospheric pressure would create large recompression costs. Because of this, the pressure and temperature dependence of contaminant solubility must be understood so that operating conditions for the separation step can be defined. Fortunately, this is the most developed aspect of SCF technology. However, the mass transfer limitations to removing contaminants from solids change with solvent flow rate.

This paper discusses the use of SCFE for environmental control and presents results for the removal of DDT and 2-chlorophenol from GAC. 2-chlorophenol is almost completely removed with pure CO₂ at 40°C and 101 bar while only 55% of the DDT is removed at 40°C and 200 bar. These differences in regeneration efficiency cannot be understood solely in terms of solubility but point to a need for detailed studies of adsorption equilibrium and mass transfer resistances in supercritical fluid systems.     

Simulation and optimization of extractive distillation sequence with pre-separator for the ethanol dehydration using n-butyl propionate

Extractive distillation is the most promising alternative for the ethanol-water separation than azeotropic and pressure swing distillation using suitable solvent n-Butyl propionate. We have studied, simulated, optimized and economically evaluated the separation of a mixture of 50 mole% ethanol and 50 mole% water to treat the 16 Kmol/hr (512.67 kg/hr) of the original mixture. Rigorous simulation and optimization has been carried out by means of a software CHEMCAD version 6.5 using thermodynamic model UNIQUAC with binary interaction parameters. The simulations allow us to conclude that extractive distillation is more economical and trustworthy than pressure swing distillation due to the relative pressure insensitive nature of the ethanol-water mixture after the azeotropic composition. The separation of 99.7% of ethanol from ethanol water mixture claim by Mulia-Soto, Flores-Tlacuahuac, 2011 is contradictory as the feasibility for the operating pressure of 10 atm with or without heat integration.     

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.     

Diffusion distillation — a new separation process for azeotropic mixtures part II: Dehydration of isopropanol by diffusion distillation

A design is submitted for a diffusion distillation apparatus in the form of a tube bundle, which represents a new means for separating azeotropic mixtures. It is combined with two rectification columns for separating binary mixtures. The results thus obtained in separating isopropanol—water mixtures are compared with those for an established extractive distillation process. It is shown how the energy consumption in the entire plant can be minimized.     

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.     

How to Improve the Energy Savings in Distillation and Hybrid Distillation‐Pervaporation Systems

Abstract

As the worldwide demand for energy is growing, engineers are facing a challenge to design plants with minimum energy requirements. Distillation is an energy intensive process regardless of the products being separated. Using as an example the separation of alcohol–aqueous mixture, this article describes some options applicable to both revamp and new installations where the reduction of energy consumption is achieved. The “Hybrid” application is represented by the Water‐Tetrahydrofurane (THF) separation comparing a conventional two column Pressure Swing Distillation(PSD) system with a pressure distillation using a membrane unit. The main focus is on energy savings for a given separation problem trough the introduction of membrane unit.     

Separation of 2-Propanol–Water Mixture with Capillary Porous Plates

ABSTRACT

Distillation of the 2-propanol–water mixture of different compositions was experimentally studied in a continuous distillation column equipped with polar and nonpolar porous plates as well as normal sieve plates. The results showed that while no separation was achieved in a distillation column with porous carbon plates or with conventional stages, the azeotropic. point of this system was broken in a distillation column with polar sintered stainless steel porous plates. A distillate of about 80.0 mol% 2-propanol was obtained for a feed of azeotropic composition, i.e., 68.0 mol% 2-propanol. These results showed that the main factors affecting the separation efficiency in a given porous plate are the polarization of the pure liquids and porous plates as well as the polarization difference between the mixture components.     

Energy saving in acetic acid process using an azeotropic distillation column with a side stripper

Dilute acetic acid is obtained primarily from fermentation and synthesis processes and cannot be produced by simple distillation due to relatively low volatility of acetic acid compared to water. Instead, an azeotropic distillation is applied to increase the concentration of dilute acetic acid. When acetic acid is extracted from a dilute aqueous solution using a solvent mixture of ester and alcohol, its recovery requires an energy-intensive azeotropic distillation. In the water stripping process that follows azeotropic distillation, two distillation columns handle the acetic acid and water mixture in similar composition. Therefore, the two columns can be combined as a side stripper connected to the azeotropic distillation column. The energy-saving effect is examined with the HYSYS (Aspentech Corporation) evaluation of the process. Compared to the conventional process, the modified process suggests 39% reduction in heating duty and 24% coolant savings. The economic analysis shows 32% decrease in investment and 36% utility savings. Based on heat utilization analysis, the thermodynamic efficiency is enhanced by 11%.     

合成氨工艺正丙醇废液精馏处理的工艺技术

采用共沸精馏技术处理合成氨工艺流程中脱碳工段产生的含大量正丙醇混醇废液。本文采用共沸精馏的方法,选用合理可行的共沸剂,在间歇精馏塔内进行正丙醇-水共沸物系的分离实验,优化了该共沸精馏技术处理工业混醇废液的最佳操作条件。结果表明：采用共沸精馏方法,以环己烷为共沸剂,可使原料液中20%～40%的正丙醇含量提纯至质量分数≥95%,塔顶回收的共沸剂质量分数≥97%。该工艺流程较大地减小了设备投资和能耗。实验表明采用共沸精馏技术用于正丙醇-水共沸物系的分离具有可靠性和实用性。     

醋酸甲酯和甲醇热集成变压精馏分离工艺模拟与优化

基于对醋酸甲酯与甲醇二元共沸特性的分析,提出热集成变压精馏分离醋酸甲酯和甲醇的工艺. 利用Aspen Plus软件对该分离过程进行模拟,以NRTL活度系数方程为物性计算方法,其二元相互作用参数由气液相平衡数据回归,分析了加压塔和常压塔的理论板数、进料位置及回流比对分离效果的影响,并进行了能耗比较. 结果表明,该工艺能很好地分离醋酸甲酯和甲醇,较佳的工艺条件为：加压塔操作压力909 kPa,理论板数32,第21块板进料,回流比4.2,塔釜醋酸甲酯纯度99.8%;常压塔操作压力101 kPa,理论板数30,第20块板进料,回流比4.6,塔釜甲醇纯度99.0%. 与常规变压精馏相比,热集成变压精馏可节能达45.8%;与以水为萃取剂的萃取精馏分离工艺相比,热集成变压精馏分离工艺更适合醋酸甲酯与甲醇体系的分离.     

Production of Motor Fuel Grade Alcohol by Concentration Swing Adsorption

Abstract

A new cyclic process concept called “concentration swing adsorption” for separation of bulk binary liquid mixtures is described. The process carries out the primary separation by selective liquid-phase adsorption of one of the components of the feed mixture on an adsorbent. The adsorbed component is then desorbed by a desorbent liquid which is equally or more strongly adsorbed than the slectively adsorbed component of the feed mixture. The desorbent liquid is removed from the adsorbent by displacing it with the less strongly adsorbed component of the feed mixture so that the adsorbent can be resused. The process also includes a complementary step where the adsorbent is rinsed with the more strongly adsorbed component of the feed mixture so that two essentially pure products are produced from the feed mixture with high recoveries of both components. At least one simple distillation is also required by the process which separates the desorbent liquid from the less strongly adsorbed component of the feed mixture. The process can be used to separate liquid mixtures with close boiling components or azeotropic mixtures which require energy intensive distillation. A very efficient separation can be achieved in these cases by spending only a fraction of the distillation energy. An example of such an application, viz., separation of a bulk ethanol–water mixture for motor fuel grade alcohol production, is described. A local equilibrium model of the process is used to evaluate the performance of the process for that separation using an activated carbon as the adsorbent and acetone as the desorbent liquid. Experimentally measured equilibrium adsorption characteristics for ethanol–water, acetone–water, and acetone–ethanol binary liquid mixtures on the carbon as well as adsorption column dynamics for the steps of the process are reported.     

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.     

隔壁共沸精馏塔分离异丙醇水溶液的模拟

提出一种单塔共沸精馏生产无水异丙醇的新工艺流程,即采用隔壁塔替代常规共沸精馏流程中的脱水塔及提浓塔。应用Aspen Plus模拟软件,对隔壁共沸精馏塔流程及常规共沸精馏流程进行了模拟,比较了两种流程的液相组成、温度、汽液相流量及能耗,结果显示新工艺流程可以节省能耗14.6%,并能降低设备投资费用和操作费用。其模拟结果还需试验进一步验证。     

Reducing Energy Consumption and CO2 Emissions in Thermally Coupled Azeotropic Distillation

The design and optimization procedures of a heterogeneous thermally coupled azeotropic distillation sequence with a side stripper (TCADS‐SS) for the purification of isopropanol has been investigated. The proposed procedures can detect the optimal values of the design variables and thereby guarantee the minimum energy consumption, which is related to the minimum CO₂ emissions and the lowest total annual cost (TAC). The procedures are applied to the study of the separation of azeotropic mixtures using the two distillation sequences. In the TCADS‐SS, the top end of the side stripper has both liquid and vapor exchange with the main column, which eliminates a condenser in contrast with the conventional heterogeneous azeotropic distillation sequence (CHADS). The results show that not only reductions in energy consumption and CO₂ emissions but also higher thermodynamic efficiency can be obtained for the TCADS‐SS.     

共沸剂对碳酸二甲酯-甲醇共沸物分离效率的影响

采用正庚烷、正己烷、环己烷、1,2-二氯乙烷、四氯化碳和苯等共沸剂，较系统地考察了共沸剂及回流比对碳酸二甲酯（DMC）-甲醇（CH3OH）共沸物共沸精馏分离效果的影响。结果表明，采用共沸精馏法可以高效分离DMC-CH3OH共沸物，通过调控回流比以及共沸剂可以有效改变分离后釜液中组分的组成。采用相同共沸剂下，当回流比为7∶1和8∶1时DMC-CH3OH共沸物的分离效果较好。相同回流比7∶1下，采用不同共沸剂共沸精馏DMC-CH3OH混合物得到DMC的质量分数和收率顺序为：1,2-二氯乙烷＞四氯化碳＞环己烷＞苯＞正己烷＞正庚烷。     

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.     

内部热耦合精馏塔基于非理想物系的最优评价

Internal thermally coupled distillation column(ITCDIC) is a frontier in energy saving distillation research. In this paper, the optimal assessment on the energy saving and the operating cost for ITCDIC of nonideal mixture is explored. An evaluating method is proposed, and the pertinent optimization model is then derived. The ethanol-water system is studied as an illustrative example. The optimization results show that the maximum energy saving in ITCDIC process is about 35% and the maximum operating cost saving in ITCDIC process is about 30%,as compared with a conventional distillation column(CDIC) under the minimum reflux ratio operating; the optimal operating pressure of the rectifying section is found to be around 0.25 MPa; the effects of the feed composition,operating pressure and the heat transfer rate on operation are also found and analyzed. It is revealed that ITCDIC process possesses high energy saving potential and promising economical prospect.     

Energy-saving technologies of autoextractive distillation of an acetone-chloroform-n-butanol-dimethylformamide mixture

The autoextractive distillation of an azeotropic solvent mixture of acetone, chloroform, n-butanol, and dimethylformamide is considered. A set of flowsheets belonging to different structural classes is synthesized (flowsheets containing two-withdrawal columns and flowsheets involving complex columns with a single side section). The flowsheet that is optimal in energy consumption is revealed, and it is shown that flowsheets with coupled heat and material flows are more efficient than conventional ones.     

Energy Evaluation of Ethanol Dehydration with Glycol Mixture as Entrainer

Extractive distillation of ethanol dehydration using glycols as entrainers is proposed. Specifically, ethanol dehydration of an azeotropic mixture in the presence of ethylene glycol + glycerol mixture is evaluated. Simulation is performed and the vapor‐liquid equilibrium of ethanol + water + ethylene glycol + glycerol is predicted with the NRTL model. Minimization of energy consumption in both extractive and regeneration columns is attempted. Optimal operating parameters of the process including glycol concentration in the solvent mixture, main feed, and entrainer feed trays, total number of theoretical trays, and heat supplied to the reboiler are determined in order to achieve a specified distillate purity of 99.9 mol % ethanol.