乙酰丙酸乙酯的反应精馏模型及隔壁塔节能优化设计

乙酰丙酸乙酯是一种潜在的生物质基平台化合物,在工业上具有很高的应用价值。乙酰丙酸乙酯传统的生产方法主要为间歇反应法,效率较低,产物分离困难且工艺流程较长。因此,本文提出了反应精馏工艺生产乙酰丙酸乙酯,在以中试实验结果为依据的基础上,使用Aspen Plus模拟软件建立了工艺流程,并考察了回流比、进料位置、进料摩尔比以及理论塔板数等关键参数,得到了常规单塔反应精馏工艺生产乙酰丙酸乙酯的最优配置。而后,为了得到纯度大于99.9%的乙酰丙酸乙酯,本文进一步提出了反应精馏双塔精制流程以及反应精馏隔壁塔流程,并通过对两种流程所得到的产品纯度以及能耗的对比,验证了反应精馏隔壁塔工艺生产乙酰丙酸乙酯的有效性以及在节能方面较大的优势。     

Production of ethyltert-butyl ether fromtert-butyl alcohol and ethanol catalyzed byβ-zeolite in reactive distillation

The synthesis of ethyl tert-butyl ether (ETBE) from a liquid phase reaction between tert-butyl alcohol (TBA) and ethanol (EtOH) in reactive distillation has been studied.β-Zeolite catalysts with three compositions (Si/Al ratio=13, 36 and 55) were compared by testing the reaction in a semi-batch reactor. Although they showed almost the same performance, the one with Si/Al ratio of 55 was selected for the kinetic and reactive distillation studies because it is commercially available and present in a ready-to-use form. The kinetic parameters of the reaction determined by fitting parameters with the experimental results at temperature in the range of 343–363 K were used in an ASPEN PLUS simulator. Experimental results of the reactive distillation at a standard condition were used to validate a rigorous reactive distillation model of the ASPEN PLUS used in a simulation study. The effects of various operating parameters such as condenser temperature, feed molar flow rate, reflux ratio, heat duty and mole ratio of H₂O : EtOH on the reactive distillation performance were then investigated via simulation using the ASPEN PLUS program. The results were compared between two reactive distillation columns: one packed withβ-zeolite and the other with conventional Amberlyst-15. It was found that the effect of various operating parameters for both types of catalysts follows the same trend; however, the column packed withΒ-zeolite outperforms that with Amberlyst-15 catalyst due to the higher selectivity of the catalyst.     

基于样条插值模型的间歇精馏模拟与预测控制

以Aspen Batch Distillation（ABD）中的间歇精馏仿真系统为过程原型,提出了利用过程的模拟测试数据来建立间歇精馏过程的样条插值简化模型（spline interpolation model, SIM）。结合变回流比下的动态修正函数,构造出了一种简单实用的动态模型。该模型可有效模拟不同组分浓度下回流比发生变化时馏出液浓度和流量的动态变化情况。以该模型作为预测模型,进一步提出了一种变回流比的预测控制（model predictive control, MPC）算法来使馏出液浓度按照期望的设定值变化。控制仿真结果表明该控制方案计算简单,同时具有较好的控制效果。     

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™.     

Recovery of lactic acid by batch reactive distillation

Lactic acid, being virtually a non‐boiling compound, is difficult to separate from its aqueous solution by conventional methods such as distillation. It is necessary to convert it to the relatively volatile ester and the separation of the ester, followed by hydrolysis, is recommended as an appropriate method of recovery. In the present work, we explore and investigate a novel reactive distillation strategy to perform esterification, distillation and hydrolysis in a single unit. The experiments were performed in a batch reactive distillation set‐up and the results have been explained with the help of an appropriate model. An unsteady state mathematical model based on an equilibrium stage concept was developed for batch reactive distillation. A pseudo‐homogeneous model was used for the determination of reaction kinetics. The effect of operating parameters such as feed concentration, mole ratio, catalyst loading, boil‐up rate, etc. on the recovery of lactic acid was studied with the help of simulation and experimental results. The feasibility issue of reactive distillation has been discussed based on the results obtained. Copyright © 2006 Society of Chemical Industry     

Heat-integrated reactive distillation process for synthesis of fatty esters

Catalytic reactive distillation (RD) offers novel opportunities for manufacturing fatty acid alkyl esters involved in specialty chemicals and at a larger scale in biodiesel. The integration of reaction and separation into one RD unit, corroborated with the use of a heterogeneous catalyst, provides major benefits such as low capital investment and operating costs. This work presents a novel heat-integrated process based on reactive distillation that aims to reduce furthermore the energy requirements for biodiesel production, leading to competitive operating costs. Despite the high degree of integration, the process is well controllable using an efficient control structure proposed in this work. Rigorous simulations embedding experimental results were performed using computer aided process engineering tools, such as AspenTech Aspen Plus and Aspen Dynamics. The RD column was simulated using the rigorous RADFRAC unit with RateSep (rate-based) model, and explicitly considering three phase balances. Steady-state and dynamic simulation results are given for a plant producing 10 ktpy fatty acid methyl esters (FAME) from methanol and waste vegetable oil with high free fatty acids (FFA) content, using sulfated zirconia as green catalyst. The heat-integrated RD process eliminates all conventional catalyst related operations, efficiently uses the raw materials and the reactor volume offering complete conversion of the fatty acids and allowing significant energy savings. Remarkably, compared to previously reported RD processes, the energy requirements of this process are about 45% lower - only 108.8 kW h/ton biodiesel - while the capital investment cost remains the same as no additional equipment is required.     

Study of heterogeneously catalysed reactive distillation using the D+R tray—A novel type of laboratory equipment

Recently, novel equipment for heterogeneously catalysed reactive distillation, the D+R tray, has been introduced by Schmitt et al. (2009). The present work reports results of measurements of the separation capacity of D+R trays. Furthermore, results of reactive distillation experiments on two test systems are presented that show that the D+R tray can be used routinely for laboratory studies of heterogeneously catalysed reactive distillation. As test systems, the esterifications yielding butyl acetate and hexyl acetate were chosen. Reactive distillation using catalytic packings was studied previously in detail ( [Parada, 2008], [Schmitt et al., 2004] and [Schmitt et al., 2005]) with the same test system. The experiments of the present work are carried out so that a direct comparison is possible. For both test systems, the most important process parameters such as feed rate and mass of catalyst were systematically varied. High conversions of the reactants and high purities of the products were achieved. The reproducibility of the results is excellent. The study shows that the D+R tray is a novel laboratory equipment that facilitates fast and flexible investigations of heterogeneously catalysed reactive distillation processes and that it can be used for studying process designs of columns equipped with either catalytic packings or trays.     

Continuous transesterification of biodiesel in a helicoidal reactor using recycled oil

The main problem with biodiesel is the high cost of oils made from oleaginous crops. For this reason, various raw materials have been analysed with a view to reducing production costs and obtaining a product that can compete with the price of petrodiesel. Recycled oil is one of the most promising alternatives in the production of biodiesel because not only is the cheapest raw material but it also avoids the expense of treating the oil as a residue.Another way to reduce costs is to make the process more economical. Conventional technology uses sodium hydroxide as the basic catalyst and large-scale batch reactors, whose mechanical agitation requires high energy consumption due to residence times of at least 60 min and temperatures of 60 °C.In this paper we use a recycled pretreated oil to compare conventional transesterification with continuous transesterification in a tubular reactor. In this reactor the reactants (oil, methanol and sodium hydroxide) flow through a helicoidal tube submerged in a heating bath at 60 °C. The reactor has five outlets distributed non-uniformly to enable samples to be taken at different reaction times. This is to reduce the reaction time and avoid the need for mechanical agitation. With the aim of improving the quality of the biodiesel obtained, we varied the helicoidal system by incorporating a static micromixer and supplying energy in the form of ultrasound from the heating bath. This reactor produced biodiesel and glycerine at compositions roughly equal to those obtained in the batch process (89% FAME content at 75 min) but did so continuously (2.5 mL/min) and just 13 min after the reactants were integrated in a single line using a T device. Both the oil and the biodiesel were characterized and analysed in accordance with European standard UNE EN14214 for biodiesel.     

Evaluation of configuration alternatives for multi-product polyester synthesis by reactive distillation

Reactive distillation (RD) combines reaction and separation in an integrated setup that is able to reduce the energy use, improve productivity and selectivity, and increase the efficiency. In previous work, we showed the design, modeling and experimental validation of a RD process for synthesis of unsaturated polyesters. The results of our previous work clearly demonstrated that reactive distillation is indeed a very promising alternative for the polyesters synthesis.This study explores the best suitable internals and various feed configurations of a reactive distillation process for unsaturated polyester synthesis. Multi-product simulations were performed to find the operational parameters for producing different grades of polyester in the same equipment. The product transition time during product changeover is determined for various configurations and product grades. The selection criteria for the best configuration are the minimum requirements of volume and energy to produce 100 ktpy polyesters.The results of the rigorous simulations carried out in Aspen Custom Modeler shows that the best configuration has the reactive stripping section as a packed or trayed bubble column, and the reactive rectifying section as a packed column. With respect to the feed configuration, the feeding of monoesters to the RD column significantly intensifies the polyester process as compared to an anhydrous reactant fed to the column. Moreover, the product transition time in this configuration is also significantly reduced as compared to the other configurations.     

Reactive pressure swing batch distillation by a new double column system

Ethyl-acetate is generally produced by the esterification reaction of ethanol with acetic-acid. Since the reaction is equilibrium-limited, the use of reactive distillation is an attractive option. A new double-column system is suggested for ethyl-acetate production by applying reactive pressure swing batch distillation. The system was investigated by a feasibility study based on the analysis of reactive and non-reactive residue curve maps. Two different process options were found to be feasible. In the first option, the reactive column operates at the lower pressure (1.01 bar), and the non-reactive column that removes ethyl-acetate from the system operates at the higher pressure (10 bar). The second option allows the reactive column to operate at the higher pressure (10 bar), and the non-reactive column removes water at the lower pressure (1.01 bar). The first process option was studied by rigorous simulation based on less simplifying assumptions using a professional dynamic simulator. The influence of the most important operation parameters was also studied.     

Effects of system parameters on the performance of CO2-selective WGS membrane reactor for fuel cells

Performing water gas shift (WGS) reaction efficiently is critical to hydrogen purification for fuel cells. In our earlier work, we proposed a CO₂-selective WGS membrane reactor, developed a one-dimensional non-isothermal model to simulate the simultaneous reaction and transport process and verified the model experimentally under an isothermal condition. Further modeling investigations were made on the effects of several important system parameters, including inlet feed temperature, inlet sweep temperature, feed-side pressure, feed inlet CO concentration, and catalyst activity, on membrane reactor performance. The synthesis gases from both autothermal reforming and steam reforming were used as the feed gas. As the inlet feed temperature increased, the required membrane area reduced because of the higher WGS reaction rate. Increasing the inlet sweep temperature decreased the required membrane area more significantly, even though the required membrane area increased slightly when the inlet sweep temperature exceeded about 160 °C. Higher feed-side pressure decreased the required membrane area as a result of the higher permeation driving force and reaction rate. A potentially more active catalyst could make the membrane reactor more compact because of the enhanced reaction rate. The modeling results have shown that a CO concentration of less than 10 ppm is achievable from syngases containing up to 10% CO.     

Modeling and simulation of an industrial slurry phase ethylene polymerization reactor: effect of reactor operating variables

A hierarchical and computationally efficient mathematical model was developed to explain the polymerization of high-density polyethylene (HDPE) in an isothermal, industrial, continuous stirred tank slurry reactor (CSTR). A modified polymeric multi-grain model (PMGM) was used. Steady-state macroscopic mass balance equations were derived for all species (namely, monomer, solvent, catalyst and polymer) to obtain the final particle size and the required monomer and solvent input rates for a given catalyst input and the reactor residence time. The interphase mass transfer coefficients were calculated for the industrial CSTR using the operating data on the reactor. The present model was tuned with some data on an isothermal industrial reactor and the simulation results were compared with data on another set of industrial reactor. The comparison revealed that the present tuned model is capable of predicting the productivity and the polymer yield at various catalyst feed rates and the mean residence times. The effects of variation of two operating variables (catalyst feed rate and mean residence time) on the productivity, the polymer yield, the polydispersity index (PDI) and the operational safety were analyzed. The present study indicated that an optimal value of the reactor residence time (for maximum productivity per catalyst particle) exists at any catalyst feed rate.

     

乳酸提纯新工艺动态建模仿真和控制系统设计

基于非平衡级和拟均相假设,建立了乳酸提纯反应精馏新工艺实验装置的动态机理模型.通过改进的数值计算方法提高了模型的求解效率,设计并实现了包含物性估算系统的模型仿真平台,以促进新工艺的工业化应用.利用仿真平台对新工艺装置进行了动态特性分析,在此基础上设计了两种单端质量控制方案:直接物料平衡和间接物料平衡方案.在不同类型和幅度的过程扰动下,分析比较了两种控制方案的调节性能.结果表明直接物料平衡方案控制品质优于间接物料平衡方案,可在不同扰动情况下满足过程的产品质量和转化率的联合控制要求.非平衡级动态机理模型能够反映反应精馏过程的动态特性,分析发现反应精馏过程有着独特的过程特性,基于机理模型的仿真平台是分析反应精馏特性的有效工具.     

基于Aspen Polymer的聚酯聚合反应研究及流程模拟

通过Aspen Polymer对对苯二甲酸和乙二醇进行逐步聚合生成聚酯的反应进行了研究。并采用间歇反应器模块分析了进料比、压力、温度对反应的影响,结果表明进料比为1.2～2.0是比较合适的,低压高温有利于聚合反应的进行。但过低的压力导致较低的反应速率而使反应时间增加,过高的温度也导致副产物大幅度增加。因此选择压力为0.001～0.2MPa,温度为260～285℃,在间歇反应器内进行逐步降压和逐步升温反应,并在此基础上,设计模拟了压力逐步降低、温度逐步升高的连续生产工艺流程并进行优化。经过优化后的连续生产工艺流程最终反应器出口聚合度达到121.1。     

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.     

二异丁烯反应精馏生产过程控制策略设计

二异丁烯是一种重要的化工中间体,近年来研究者提出了以催化裂化C₄为原料、采用反应精馏技术同时生产高纯二异丁烯和汽油添加剂的新工艺。由于反应精馏过程中非线性程度高,稳定控制困难,使得采用反应精馏技术生产二异丁烯过程的控制策略研究较少。采用Aspen dynamic软件进行动态模拟,针对反应精馏生产二异丁烯过程开发了温度控制方案、组分温度联合控制方案和组分温度串级控制方案。对3个控制系统进行（±10）%的进料流量扰动和（±5）%组成扰动测试并进行对比。结果表明：组分温度串级控制方案在添加扰动的情况下依然保证了二异丁烯质量分数99%,三异丁烯质量分数小于10%以及异丁烯转化率大于99%的要求,并且最终稳定时间约5 h,具有更好的抗干扰性能。研究结果能够为二异丁烯产品的生产工艺工业化应用提供设计依据。     

Synthesis and characterization of a novel unsaturated polyester based on poly(trimethylene terephthalate)

Unsaturated aromatic polyesters were obtained by glycolysis of poly(trimethylene terephthalate) with cis-2-buten-1,4-diol followed by a solid-state polymerization. The glycolysis was performed in a batch mode as well as through a continuous process in a twin screw extruder. The degradation and subsequent rebuilding of the polymer chain during the course of reaction was followed by means of inherent and melt viscosity measurements, and ¹H NMR terminal group analysis of the intermediates and the final products. Structural investigations revealed that this new approach resulted in melt processible unsaturated polyesters with cross-linkable sites having similar characteristics to that of the virgin saturated polyester. Although the processing temperature for the different reaction steps was sufficiently high (180−260 °C), no thermally induced cross-linking of the incorporated unsaturated bonds could be evidenced indicating that the obtained products remained stable during the production stage. For comparison purposes, a commercial unsaturated polyester (Vestodur^©) was included in the investigations. UV irradiation of thin polyester films did not result in cross-linked products but in cis-trans isomerization of the incorporated bisoxybutenyl unit.     

考虑不同产品选择性目标的乙醇胺反应精馏塔模拟与优化

提出以环氧乙烷和液氨为原料，水为催化剂，反应精馏塔合成乙醇胺的工艺。分别以一乙醇胺（MEA）和二乙醇胺（DEA）的选择性最大为目标，探讨了在同一反应精馏塔中实现不同产物选择性目标的可行性和可达到的最大选择性。研究在Aspen Plus模拟软件上进行，通过考察操作压力、水进料量、进料氨烷比、再沸比、环氧乙烷进料位置等参数对反应精馏的影响规律，取得实现不同产物选择性目标的参数优化调节方法。研究表明，大的氨烷比、水进料量和再沸比有利于提高MEA选择性，小的氨烷比、水进料量和再沸比则有利于提高DEA选择性，在优化条件下，MEA选择性可达70.30%，DEA选择性可达41.89%。与文献方法比较，采用反应精馏合成乙醇胺具有明显的优越性和操作柔性。     

常规间歇萃取精馏分离苯-环己烷的研究

通过一个常规间歇萃取精馏实验装置,考察了不同萃取剂在不同回流比及萃取溶剂加入速率情况下对分离苯-环己烷共沸体系的影响。结果表明,二元混合溶剂能够解决单一溶剂的选择性与溶解性相矛盾的问题;且在同等条件下,综合性能优于单一溶剂;随着溶剂加入速率和操作回流比的增加,产品的产量逐渐提高,尤其重要的是混合溶剂间歇萃取精馏技术与简单溶剂间歇萃取精馏技术相比并不复杂。     

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.