A novel type of equipment for reactive distillation: Model development,simulation, sensitivity and error analysis

A simulation study of heterogeneously catalyzed reactive distillation experiments carried out with the D + R tray, a novel type of laboratory equipment, is presented. One advantage of the D + R tray is that reaction and distillation are alternating stage‐wise, in a well‐defined way that can be modeled straightforwardly. An equilibrium stage model is used to describe the distillation and a plug flow reactor model to describe the catalyst bed reactors. The model parameters are derived from a systematic experimental characterization of the D + R tray both as a reactor and as a distillation unit. A validated physicochemical fluid property model is used. The primary experimental data are reconciled. Results from the predictive simulations are in good agreement with the experimental results. The influence of errors in the input parameters on the simulation results is investigated by means of a sensitivity and error analysis. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1533–1543, 2013     

催化精馏合成乙酸乙酯的工业试验

以固体酸为催化剂,在中试催化精馏塔中进行了乙酸与乙醇反应制备乙酸乙酯的工业试验,试验塔的精馏段塔径为600 mm,内装陶瓷规整填料,反应精馏段塔径为1 000mm,内装7层立体催化精馏塔板.采用连续操作,考察了不同的回流比、釜酸质量分数、进料流量对反应和分离过程的影响,同时测定了塔板上气液相质量分数的分布.通过试验得到...     

侧反应器反应精馏方法生产醋酸甲酯的模拟

采用强酸性阳离子交换树脂催化醋酸与甲醇反应精馏生成醋酸甲酯,可避免硫酸作为催化剂的不足。但该非均相催化反应受平衡限制,且达到平衡时间较长,采用传统反应精馏塔难以提供足够反应空间。文中设计侧反应器与精馏塔耦合新工艺,采用Aspen Plus软件模拟研究了侧反应器数量、位置,原料进料位置,回流比,醇酸比等对反应精馏过程的影响。结果表明,当装置具有7个侧反应器,反应器间隔4块板,在优化的操作条件下,醋酸甲酯质量分数可达99.1%。     

19万t/a醋酸乙烯精馏装置的技术改造

应用计算机模拟了进料热状况对醋酸乙烯精馏系统的影响,并计算了不同回流比下的塔板数、能耗、冷却负荷等参数值,通过改变进料热状况消除塔内恒浓区,优选出最佳精馏方案,即进料气化率20％、同流比为2、理论板数为63。应用复合斜孔塔板代替筛板塔板,对醋酸乙烯精馏塔进行了技术改造。改造后装置生产能力提高至19万t／a,节能20％,产品质量稳定,醋酸乙烯精馏塔运行周期延长至4年。     

反应精馏技术的关键问题分析

反应精馏是为增强反应与精馏效果而将两种单元操作进行耦合的多功能新技术。因既有化学反应又有精馏过程,反应精馏过程需考虑气液相平衡、气液质量传递、催化剂内扩散(非均相反应精馏)以及动力学等因素的相互作用,导致该过程存在定态多重性、动力学复杂性。文章系统地综述了近年来国内外科研工作者对反应精馏实验和理论的研究进展,分析了反应精馏技术工业应用中存在的关键问题,并对未来的发展方向进行了展望。     

Investigation on catalytic distillation for ethyl acetate production with different catalytic packing structures

The catalytic packing is the core component of the catalytic distillation, and how the catalyst exists in the packing has significant influence on the process. To investigate the effect of catalyst packings on the catalytic distillation process, the classical ethyl acetate reactive distillation system was utilized, and a supported catalytic packing(SCP) was prepared in comparison with the conventional tea-bag catalytic packing(TBP). Laboratory scale experiments showed that the ethyl acetate conv...     

Esterification of acetic acid with ethanol: Reaction kinetics and operation in a packed bed reactive distillation column

The reaction kinetics of the esterification of acetic acid with ethanol, catalyzed both homogeneously by the acetic acid, and heterogeneously by Amberlyst 15, have been investigated. The reactions were carried out at several temperatures between 303.15 and 353.15 K and at various starting reactant compositions. Homogeneous and heterogeneous reactions have been described using the models proposed by Pöpken et al. [T. Pöpken, L. Götze, J. Gmehling, Reaction kinetics and chemical equilibrium of homogenously and heterogeneously catalyzed acetic acid esterification with methanol and methyl acetate hydrolysis, Ind. Eng. Chem. Res. 39 (2000) 2601–2611]. These models use activities instead of mole fractions. Activity coefficients have been calculated using ASOG [K. Kojima, K. Tochigi, Prediction of Vapor–liquid Equilibria by the ASOG Method, Elsevier, Tokyo, 1979] and UNIFAC (Aa. Fredenslund, J. Gmehling, P. Rasmussen, Vapor–liquid Equilibria Using UNIFAC. A Group Contribution Method, Elsevier, Amsterdam, 1977] methods.

A packed bed reactive distillation column filled with Amberlyst 15 has been employed to obtain ethyl acetate. The influence of feed composition and reflux ratio have been analyzed.     

考虑水力学可行性的反应精馏塔板持液量设计及优化

以筛板塔为塔板基础构型,以原料转化率最大为目标,以塔径和出口堰高为主要调节参数,以塔板水力学可行性为约束条件,建立了一种可优化塔板液相持液量的塔板结构设计方法. 塔模拟计算在Aspen Plus平台上进行,化学反应采用动力学方程表达,塔板水力学计算采用Cup-Tower软件. 结果表明,本设计方法应用于DPC反应精馏过程,在满足流体力学可行性条件下,塔板上液相持液量比基础设计提高了1.39倍,苯酚转化率提高了33.6%.     

Design and control of reactive distillation for ethyl and isopropyl acetates production with azeotropic feeds

Reactive distillations for the production of ethyl acetate (EtAc) and isopropyl acetate (IPAc) are classified as the type-II process where the first column consists of a reactive zone and a rectifying section followed by a stripper [Tang et al., 2005. Design of reactive distillations for acetic acid esterification with different alcohols. A.I.Ch.E. Journal 51, 1683-1699]. Instead of using pure alcohols and acetic acid as reactants, this paper studies the effects of reactant purity on the design and control of reactive distillation. This offers significant economical incentives (by reducing raw materials costs), because ethanol forms an azeotrope with water at 90 mol% and isopropanol/water has an azeotrope at 68%. The purities of the acid is set to 95% for acetic acid (industrial grade), 87% for ethanol, and 65% for isopropanol. The results show that the total annual costs (TAC) increase by a factor of 5% for EtAc and 8% for IPAc production using reactive distillation. Next, the operability of the reactive distillations with azeotrope feeds is explored. Three disturbances, feed flow, acid feed purity, and alcohol feed composition, are introduced to assess control performance using dual-temperature control and one-temperature-one-composition control. Simulation results indicate good control performance can be achieved for reactive distillation with azeotropic feeds.     

离子液体催化反应精馏合成乙酸乙酯工艺模拟

为研究离子液体在反应精馏中的作用,采用离子液体1-丁基-3-甲基咪唑硫酸氢盐（[BMIM]HSO₄）作为催化剂,对乙酸和乙醇合成乙酸乙酯的反应精馏流程进行了计算模拟。在确定了参数的酯化反应动力学的基础上,用Aspen Plus软件建立了反应精馏流程,研究了催化剂用量、精馏段理论板数、反应段理论板数、乙醇进料位置、进料摩尔比、持液量及回流比等参数对反应精馏过程的影响。研究结果表明,塔顶乙酸乙酯的质量分数随催化剂用量、精馏段理论板数、反应段理论板数和持液量增大而增大,工艺流程存在最佳回流比以及最佳进料酸醇摩尔比。得到的优化条件如下：离子液体与乙酸摩尔比为1：2.5,进料酸醇摩尔比为4：1,理论塔板数为21块,乙酸和催化剂在第7块理论塔板进料,乙醇在第19块理论塔板进料,塔板持液量0.1L,回流比为4,塔顶乙酸乙酯的质量分数可以达到98.73%。     

Pilot plant synthesis of n-propyl propionate via reactive distillation with decanter separator for reactant recovery. Experimental model validation and simulation studies

Successful process intensification (PI) stories applied broadly are the reactive distillation (RD) processes used in esterification syntheses. One application is developed here with the heterogeneously catalyzed synthesis of n  -propyl propionate (ProPro) from 1-propanol (ProOH) and propionic acid (ProAc). In this investigation, conventional RD of ProPro was further improved. With the objective to recover product and reactant, an experimental column set-up was equipped with a decanter on top enabling to separate the distillate product into two main streams. The aqueous phase was discharged and part of the organic phase was refluxed back to the column. Experimental results comprising temperature and composition column profiles were obtained in a pilot-scale column (DN-50), equipped with structured packings (Sulzer BX and Katapak-SP 11 with Amberlyst 46™ for the reactive part). For simulation studies a non-equilibrium stage model (NEQ model) was applied which shows satisfactory agreement with the performed experiments. Further theoretical investigations of relevant operating parameters (total feed, molar feed ratio, reflux ratio and heat duty) and their effect on the overall process performance were realized. Studies with the given column configuration showed that product purity in the bottom stream could be increased to wProPro,bottom=91.0%$w_{\text{ProPro,bottom}}=91.0\%$ and maximum ProAc conversions to X_ProAc = 94.5%.     

Comparative control study of ideal and methyl acetate reactive distillation

The control of an ideal reactive distillation column is compared with that of a similar, but somewhat different, real chemical system, the production of methyl acetate. Similarities and differences are observed. Three control structures are evaluated for both systems. A control structure with one internal composition controller and one temperature controller provides effective control of both systems for both high and moderate conversion designs. A two-temperature control structure is effective when the system is overdesigned in terms of number of reactive trays, holdup and/or catalyst load. Direct control of product purity for the high-conversion/high-purity design is difficult because of system nonlinearity and interaction. Tray temperature control avoids the nonlinearity problem.     

Experimental study and process simulation of n-butyl acetate produced by transesterification in a catalytic distillation column

The production of n-butyl acetate by transesterification of methyl acetate with n-butanol, catalyzed by acidic ion-exchange resin NKC-9, was experimentally investigated in a homemade catalytic distillation column with a diameter of 80 mm. A non-equilibrium stage model for describing the catalytic distillation process was established and solved with Newton-Homotopy method. The effect of feeding mode, reflux ratio, material molar ratio and number of reactive sections on the conversion of methyl acetate was investigated. The experimental results agree well with those obtained by the theoretical simulation calculations, indicating the accuracy and reliability of the non-equilibrium model. It can be concluded that the non-equilibrium model established in this paper can provide theoretical guidance for the further process design and optimization.     

Evaluation of a two-temperature control structure for a two-reactant/two-product type of reactive distillation column

Several different control structures have been proposed for reactive distillation columns. The appropriate control structure depends on the flowsheet and on the type of reactions occurring in the column. If two reactants are involved and if it is desirable to operate the process without any excess of reactant, it is necessary to manage the fresh feed streams so that the stoichiometry is exactly balanced. A composition analyzer that measures an internal composition in the column is often required. However, if two products are produced, it is possible to avoid the use of an analyzer by using two temperatures in the column to adjust the two feed streams. This type of structure was proposed by Roat et al. [Roat, S., Downs. J., Vogel, E., Doss, J., 1986. Integration of rigorous dynamic modeling and control system synthesis for distillation columns. In: Chemical Process Control—CPC III. Elsevier, Amsterdam.] for the ideal reaction A+B↔C+D in one of the earliest papers dealing with reactive distillation control.The purpose of this paper is to explore the effectiveness of this two-temperature control structure for various column designs (number of reactive stages) to quantify the impact of design on controllability. We also discuss the issues of the selection of the trays whose temperatures are to be controlled and the tuning of the two interacting temperature controllers. Disturbances in production rate and fresh feed compositions are made to examine the rangeability of this control structure. Both an ideal reaction system and the methyl acetate system are studied. One of the main conclusions is that the locations of the temperature control trays should be made such that the two temperature controllers both have direct action (an increase in temperature increases feed), which requires negative openloop process gains for both loops.     

侧反应器反应精馏过程合成醋酸甲酯的模拟

采用Aspen Plus模拟了合成醋酸甲酯的侧反应器反应精馏过程,研究进料位置、回流比、酸醇比、侧反应器数量等对反应精馏过程的影响,得到优化的工艺条件。该研究结果与传统反应精馏装置对比表明,2种精馏装置性能接近,侧反应器反应精馏技术具有工艺流程环保、塔结构简单等优点。模拟研究结果可为合成醋酸甲酯侧反应器精馏塔提供基础理论和设计数据,为在类似反应精馏体系应用该装置提供技术支持。     

醋酸甲酯水解反应及产物分离工艺的改进研究

针对现有的醋酸甲酯水解反应及产物分离工艺提出一种反应与精馏结合的改造方案。使用工厂提供的进口阳离子交换树脂作为催化剂在间歇反应器中对醋酸甲酯水解反应动力学进行了研究,结果表明,反应平衡常数随着温度的升高而增大,温度对反应速率的影响符合Arrhenius公式,反应速率与催化剂用量呈线性关系。在消除外扩散的影响下得到了醋酸甲酯非均相水解的反应速率方程为:dcMeAc-r=-1dt=k(cMeAccH2O-cMeOHcHAc/K)Mk=4.95954×105exp(-69682.7/RT)m6·kmol-1·min-1·kg-1K=exp(1.44707-1114.9/T)在此基础上通过模拟计算对改进工艺进行研究并确定,理论塔板数为20块的精馏塔和第二水解塔结合后进料位置为第10块塔板,侧线采出位置为第2～9块塔板,适宜回流比为1 2603。经比较表明,新工艺比原工艺节约能耗8 33%。     

A disjunctive programming approach for the optimal design of reactive distillation columns

A generalized disjunctive programming formulation is presented for the optimal design of reactive distillation columns using tray-by-tray, phase equilibrium and kinetic based models. The proposed formulation uses disjunctions for conditional trays to apply the MESH and reaction kinetics equations for only the selected trays in order to reduce the size of the nonlinear programming subproblems. Solution of the model yields the optimal feed tray locations, number of trays, reaction zones, and operating and design parameters. The disjunctive program is solved using a logic-based outer-approximation algorithm where the MILP master problem is based on the big-M formulation of disjunctions, and where a special initialization scheme is used to reduce the number of initial NLP subproblems that need to be solved. Two examples are presented that include reactive distillation for the metathesis reaction of 2-pentene and for the production of ethylene glycol. The results show that the proposed method can effectively handle these difficult nonlinear optimization problems.     

Determination of catalytic packing characteristics for reactive distillation

Catalytic distillation still expands its field of applications. New structured catalytic column internals have been developed in recent years and new studies have been reported. A modern structured catalytic packing MULTIPAK^® is a subject of the investigations presented in this paper.

Important parameters of MULTIPAK^® have been examined experimentally in a 250 mm ID laboratory column: pressure drop for dry, prewetted and irrigated packings, flooding line and mass transfer coefficients for the gas and liquid phases.

The correlations obtained have been incorporated into a software tool for the simulation of catalytic distillation processes and simulations have been performed assuming methyl acetate synthesis as a model process. The calculations have been verified using the experiments performed for the same synthesis in a 50 mm ID catalytic distillation column operating continuously and thus reflecting industrial applications. It is concluded that the model represents the real process with satisfactory accuracy, although some deviations can be observed, especially within the reactive zone.     

离子液体催化反应精馏合成乙酸乙酯

利用1-己基吡啶四氟硼酸盐离子液体作溶剂和催化剂,在催化反应精馏塔内合成乙酸乙酯。结果表明该离子液体具有催化活性,反应的选择性为100%,分离后的1-已基吡啶四氟硼酸盐离子液体重复使用5次,其活性没有明显变化。考察了回流比、进料比、溶剂和催化剂用量对酯化反应结果的影响,优化了反应的工艺条件,适宜的反应条件为:物料比n(乙酸):n(乙醇)=1.1:1,离子液体用量n(乙酸):n(离子液体)=8:1,回流比为3。     

乙酸戊酯酯化反应精馏过程系统控制模拟及分析

反应精馏技术是将反应和精馏两个单元操作耦合在一个设备中同时进行,其非线性给反应精馏过程的平稳操作和过程控制提出了更高的要求。目前,反应精馏过程控制研究都是针对特定反应体系进行的有针对性的研究,对于乙酸戊酯反应体系的控制研究少有报道。本文利用Aspen Plus和Aspen Dynamic 软件对乙酸戊酯的反应精馏过程进行动态模拟,针对塔釜产品组成要求提出温度控制和组成控制两种不同的控制方案,对两个控制系统分别进行±10%的进料流量扰动测试和酸醇比为1:1、1.2:1的进料组成扰动测试。研究了不同扰动对产品质量的影响并比较了两种方案在不同扰动干扰下的控制效果。结果表明:进料组成扰动会对两个控制方案造成较大影响;温度控制方案的控制稳定性要好于组成控制方案。