Implementation and Operation of a Dividing‐Wall Distillation Column

The design and construction of a prototype of a dividing‐wall distillation column was possible by integrating previous knowledge in process intensification, energy savings, theoretical control properties, and closed‐loop dynamics of thermally coupled distillation sequences. In order to achieve the predicted energy savings for this class of complex distillation column, a dividing wall and a side tank were implemented in order to manipulate the internal flows associated with energy consumption. The reaction between ethanol and acetic acid was conducted within the prototype, and the experimental results indicate that a heterogeneous mixture of ethyl acetate and water is obtained as the top product. The temperature profile measured during the experimental run can be used for controlling the batch distillation column in cyclic operation mode.     

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。     

Analysis of the Start‐up Process for Reactive Distillation

The start‐up procedure of a distillation column is a time‐ and energy‐consuming process. Further, the products during the start‐up time are off specification and cannot easily be recycled as for conventional distillation but must costly be disposed of. In this paper, a process model to simulate the barely analyzed start‐up procedure for a reactive distillation from the cold and empty state to steady state is presented. The start‐up of a reactive distillation column has been modeled with gPROMS. The advantage of a cold and empty start‐up is the consistent and reproducible initialization. Commercial simulators do not give the opportunity to start form a cold and empty state, e.g., a column modeled with Hysys must be shut down from a steady state to be able to model the complete start‐up process, which is not possible, for example, for a batch process. Also, a change in the describing equations and discontinuities in process variables is difficult to handle within the simulation. In this paper, the start‐up strategies normally used for distillation without reaction are examined and applied to reactive distillation. It will be shown that the widely used strategy of total reflux is not suitable for reactive distillation. A simplified model to derive a time constant which describes the influence of parameter setting changes, like heating power, reflux ratio and feed composition on the start‐up time, is introduced and validated.     

Optimization of Reactive Dividing‐Wall Distillation Column for Ethyl t‐Butyl Ether Synthesis

Ethyl t‐butyl ether (ETBE) was synthesized via reaction of ethanol and isobutene by means of a reactive dividing‐wall distillation column (RDWC). The RDWC was simulated using the RADFRAC model of Aspen Plus. Multi‐response optimization by response surface methodology (RSM) with desirability function approach was applied for maximizing product purities and minimizing energy requirements and CO₂ emissions simultaneously with a constraint that the difference in pressure drop across the dividing wall should be zero. The prediction from the RSM optimization agrees well with the simulation. The optimized RDWC provided an excellent purity of 99.99 mol % of the product ETBE with about one‐third reduction in energy requirements and CO₂ emissions as compared to reactive distillation.     

Design and Control of Ionic Liquid‐Catalyzed Reactive Distillation for n‐Butyl Acetate Production

A simulation study of n‐butyl acetate production with the [Hpy][HSO₄] ionic liquid catalyst was performed. Due to the lack of phase equilibrium data, the binary interaction parameters of the NRTL model for ionic liquid and reactive species were calculated by the COSMO‐RS technique. A reactive distillation process with recycled ionic liquid stream was proposed, and the column configuration was optimized by minimization of the total annual capital. The novel process is considerably efficient and economic compared to the traditional reactive distillation process of nonionic liquids. With the steady‐state parameters, a plant‐wide control structure was further developed to evaluate the robustness of the control system by exerting the disturbances of feed flow rate and feed composition. Dynamic simulation results suggest that the control scheme with a composition controller is timely and effective.     

反应精馏过程图解设计法研究进展

反应精馏是伴有化学反应的精馏过程 ,具有设备紧凑、能量集成等优点。文章总结介绍了 80年代中期以来国内外有关反应精馏过程设计的研究进展 ,重点分析了图解设计法理论研究的现状和局限性 ,指出了反应精馏过程图解设计法的发展方向。     

反应精馏过程的研究进展

反应精馏是化学反应和精馏过程耦合为一体的单元操作,已成为当今的重要研究领域。本文综述了反应精馏过程的模拟计算和设计方法,介绍了过程控制中的多定态问题,总结了反应精馏的工业应用情况,指出了研究中应注意的重要因素,并指出了未来的研究方向。     

精馏塔进料位置图解法探讨

叙述了精馏塔进料位置对全塔效率的影响.认为不在最佳位置进料会导致全塔效率下降,而不是理论塔板数增多;不能用下移进料位置提高塔顶的含量,也不能用上移进料位置提高塔底的含量;工程设计中可在最佳进料位置附近几块塔板的塔圈上增设进料口,操作中可通过改变进料口使塔长期处于最佳工况.     

连续反应精馏合成丁酸乙酯

本研究采用对甲苯磺酸为催化剂,用试验与Aspen Plus模拟相结合,研究了反应精馏合成丁酸乙酯的工艺。首先对反应精馏装置进行试验研究,并利用Aspen Plus对其进行模拟,模拟结果与试验结果较吻合。在此基础上,对本工艺流程进行了试验研究及模拟设计,得到了可行的工艺方案。该方案得到的产品纯度理论上可达到99.5%以上,且具有流程简单、废水排放量少,设备投资低等优点。     

Temperature Inferential Control of Heat‐Integrated Distillation Column Based on Variable Sensitive Stage Temperature Set‐point

Heat‐integrated distillation is an improved distillation technique with remarkable energy‐saving potential. A control scheme with a variable sensitive stage temperature set‐point is proposed to solve the control problem of a heat‐integrated distillation column (HIDiC). An online estimator is designed to support the variation of the set‐point. The locations of the stage temperature measurements are carefully selected based on a combination strategy with three steps. First, the sensitive stages are selected. Then, the following stages are determined by a PCA‐based method. Finally, a maximum differentiation method provides the remaining measurement selections. According to the profile parameters estimated by the proposed estimator, the set‐point of the sensitive stage temperature is adjusted adaptively to reduce the influence of the disturbances. Two commonly‐used PID controllers, the sensitive temperature control and the temperature differential control, are developed as the comparative study. The simulation results show that the proposed control scheme has a distinct advantage in restraining different disturbances.     

Multiple Analysis in a Reactive Distillation Column for the Synthesis of tert‐Amyl Methyl Ether

tert‐Amyl methyl ether (TAME) is produced via reactive distillation. A simulation is set up and controlled on Aspen HYSYS v 8.0 for generating the highest purity of TAME. This simulation includes a plug‐flow reactor and a reactive distillation column. Emphasis was put on finding the optimal operating conditions of the reactive distillation column in order to get the maximum purity of TAME. The operational parameters were reflux ratio, number of reactive stages in the distillation column, and condenser pressure. The results indicated the optimal reflux ratio and condenser pressure which could be adapted to industrial scale.     

Predictions for Start‐Up Processes of Reactive Distillation Column via Artificial Neural Network

The time consumed in starting up the unit with appropriate holdups can form an important part of the total distillation time, particularly for reactive distillation systems with large holdups. Also, the products formed during the start‐up time are off specification, and are not easily recycled as for traditional distillation, but must be carefully disposed of, which can be very costly. A back‐propagation algorithm artificial neural network model is presented as a tool to assess the start‐up process for a given reactive distillation system. All the data required for training and testing the artificial neural network have been generated using the CHEMCAD simulator, version 5.2–0. The values for the learning rate, momentum term, and gain term of the artificial neural network have been taken as 0.01, 0.6, and 1.0, respectively. From the case studied in this work, it can be seen that a good start‐up policy can reduce both the energy and time requirements in the start‐up phase of reactive distillation processes. Results from predictions show the time consumed in the start‐up period has an average error of 2.833 %, and a maximum error of 7.600 %, for the case studied here. The accuracy of the model will depend upon the data available and the type of model being approximated.     

Coproduction of Ethyl Acetate and n‐Butyl Acetate by Using a Reactive Dividing‐Wall Column

The performance of the reactive distillation dividing‐wall column for coproduction of ethyl acetate and butyl acetate was experimentally studied. n‐Butanol and ethanol are raw reaction materials that react with acetic acid in the reaction zone to produce n‐butyl acetate and ethyl acetate, respectively. n‐Butyl acetate is not only a product, but also acts to remove water generated by the esterification reactions. The effects of various parameters, such as catalyst loading per stage, reflux ratio, liquid split and molar feed ratios, ethyl acetate/n‐butyl acetate purity, pressure drop, and total energy consumption, are investigated. Results show that ethanol could be completely converted and the products could be easily separated, which shows great industrial application potential in the coproduction of ethyl acetate and n‐butyl acetate.     

反应精馏技术的进展

简述了反应精馏技术的研究开发现状及工业应用;介绍了反应精馏技术的概念设计和开发方法;比较了设计反应精馏过程的各种数学模型,并且指出非平衡池模型是有广阔应用前景的设计方法;最后,简要讨论了在实验和模拟基础上进行过程放大的相关问题。     

反应精馏过程图解法设计策略研究

从反应精馏过程图解法设计的理论研究出发,探讨了反应空间、转换组成变量以及剩余曲线等应用范围和局限性;通过分析反应精馏操作线方程的变化,提出了图解法设计反应精馏过程的策略;（1）用奇异点判断法结合实验数据可判定应用反应精馏过程的可行性;（2）借助反应空间可判断该过程能否在单塔中得到完全分离;（3）图解法设计的多种设计结果及相应对策。采用实例验证了该策略的可行性。     

Synthesis and Analysis of Reactive Dividing-Wall Distillation for Methylal Production

By means of water as an extractant, the two-feed and three-feed reactive distillation production processes of methylal are synthesized and analyzed. The effects of water on the methylal reactive distillation (RD) production is investigated. Thermally coupled two-feed and three-feed reactive dividing-wall columns are proposed and analyzed. The two-feed and three-feed RD processes are compared. The three-feed thermally coupled reactive dividing-wall column (DWC) exhibits an outstanding ability of energy and cost savings. Results from this work could be helpful for further development and application of RD or reactive DWC in methylal production.     

反应精馏研究进展及应用前景

对反应精馏技术在工艺和模拟方面的研究进展进行了概述 ,简单介绍了反应精馏的关键技术并对反应精馏的应用前景进行了展望。     

Control System Design for a Single Feed ETBE Reactive Distillation Column

Reactive distillation (RD) is advantageous for the Ethyl Tert‐Butyl Ether (ETBE) synthesis. The steady state model of an ETBE reactive distillation column created using the simulator HYSYS is analyzed to synthesize effective control structures. Since the column exhibits input multiplicity with the dual process objectives of ETBE RD (isobutene conversion and ETBE purity), inferential variables are selected. A control structure that organizes a sensitive tray temperature in the stripping section using the reboiler duty and maintains the temperature difference of reactive trays using the reflux flow, is found to be most suitable. A decentralized PI controller and constrained Model Predictive Controller (MPC) are implemented, and performances are compared for set point tracking and disturbance rejection. MPC control algorithms are implemented in MATLAB and interfaced with HYSYS. Constrained MPC (CMPC) is found to be effective for load disturbance rejection, which frequently occurs in the single feed configuration.     

连续反应精馏合成乙酸异丙酯

以乙酸和异丙醇为原料通过连续反应精馏合成乙酸异丙酯,实验研究了影响反应的因素,结果表明最佳合成条件为：酸醇比1：1．2,回流比3,异丙醇的进料流量2mL／min,硫酸用量为乙酸体积的2％,乙酸异丙酯的最大收率为92．5％。     

Energy Saving in Crude Oil Atmospheric Distillation Columns by Modifying the Vapor Feed Inlet Tray

Optimization of a typical crude oil atmospheric distillation unit and reduction of energy conservation were carried out through modifying the implementation and change in the flash zone of the tower. A conventional procedure in such units involves the combination of liquid and vapor product of the prefractionation train surge drum upon introduction to the tower. However, it is theoretically illustrated and represented by simulation means that introducing the vapor feed into the upper stages of the distillation column separately can lead to an energy saving of 12.6 % in the condenser duty, an increased liquid‐to‐gas flow (L/G) at certain points of the column, and hence to a reduction in diameter and investment costs of new tower designs of approximately US$ 0.7 million a^–1. The proposal can be put into practice without the need of additional equipments or additional cost of difficult rerouting the streams. An industrial case study of a steady‐state crude oil distillation unit is given by simulation provision of AspenHysys™.