不同热集成变压精馏工艺分离乙酸乙酯/正己烷共沸物的优化与控制

基于变压精馏分离乙酸乙酯/正己烷共沸体系两塔的温差,利用Aspen Plus软件,以年度总成本最小为目标函数,对部分及完全热集成变压精馏工艺进行了稳态模拟及优化。在此基础上,利用Aspen Dynamics软件开发了多种控制结构,通过引入不同进料流量及组成的扰动测试控制结构的有效性。结果表明,完全热集成变压精馏工艺比部分热集成变压精馏工艺的经济性稍好。动态响应结果表明,部分热集成变压精馏工艺的压力?补偿温度控制结构可有效处理不同程度的干扰,能有效提高控制结构对干扰的响应速度,缩短达到新稳态的时间,保证乙酸乙酯和正己烷产品纯度在99.9wt%之上;而完全热集成变压精馏工艺的组分?温度串级控制结构仅能处理较小的组分和流量干扰,实现稳健控制,无法处理较大的干扰。综合比较两种工艺的经济性和可控性,认为部分热集成变压精馏工艺分离乙酸乙酯/正己烷共沸体系优于完全热集成变压精馏工艺。     

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.     

变压精馏分离乙醇-氯仿共沸物的动态特性

基于乙醇-氯仿二元共沸体系的压力敏感特性,利用Aspen Plus软件,以年度总费用(TAC)最小为目标函数,模拟和优化了变压精馏稳态工艺,所得乙醇和氯仿产品纯度均大于99.9%(质量分数).利用稳态模拟考察了不同热集成变压精馏工艺的经济性.利用Aspen Dynamics软件考察了不同热集成变压精馏工艺的动态特性,建立了不同热集成变压精馏工艺的稳健控制方案.结果表明:完全热集成工艺与无热集成和部分热集成工艺相比,经济性最优;组成-温度串级控制结构可较好地控制无热集成和部分热集成流程,压力-补偿温度控制结构在完全热集成工艺中可实现稳健的控制;虽然完全热集成工艺经济性最优,但部分热集成工艺的可控性优于完全热集成工艺.本文研究对工业分离含低碳醇的二元共沸物热集成变压精馏工艺有一定的参考价值.     

热集成变压精馏分离水-异丙醇-二异丙胺的工艺模拟

在分析水-异丙醇-二异丙胺体系共沸特性的基础上,提出了热集成变压精馏工艺. 采用UNIQUAC-RK方程计算气液相平衡数据,并利用实验数据在模拟压力范围内(0.004~1.0 MPa)对UNIQUAC方程中的二元交互作用参数进行修正. 利用ASPEN PLUS过程模拟软件中的RADFRAC严格精馏模型,对提出的热集成变压精馏工艺进行过程模拟与参数优化. 得到了热集成变压精馏分离水-异丙醇-二异丙胺体系的最佳工艺参数、塔内气液浓度分布及精馏塔设备参数等,并通过实验对模拟结果进行验证. 结果表明,热集成变压精馏工艺比常规的变压精馏工艺约节能34.3%.     

萃取精馏分离苯/环己烷共沸体系模拟与优化

以糠醛作为萃取剂分别使用常规萃取精馏、隔壁塔萃取精馏和差压热集成萃取精馏对苯和环己烷体系进行分离研究,使用流程模拟软件Aspen Plus V8.4进行模拟分析,对初步设计的三稳态流程,分别进行灵敏度分析,使用多目标遗传算法对过程进行整体优化以获得最优结构参数。结果表明,隔壁塔萃取精馏和差压热集成萃取精馏相对于常规萃取精馏所需再沸器热负荷可分别减小21.5%和15.7%。对三工艺流程进行经济性分析,发现与常规流程相比,隔壁塔萃取精馏的年总费用下降了6.0%,而差压热集成萃取精馏年总费用增加了50.8%,为萃取精馏分离苯/环己烷共沸体系工业化设计提供了理论依据和设计参考。     

变压精馏分离乙酸甲酯-甲醇-乙酸乙酯体系的设计与控制

聚丙烯醇的生产过程会产生乙酸甲酯-甲醇-乙酸乙酯共沸混合物,如果不及时处理,必然会造成环境污染和资源浪费。本文采用变压精馏的方式,针对乙酸甲酯-甲醇-乙酸乙酯体系设计了两种产品顺序不同的变压精馏分离序列,并采用遗传算法以年度总费用最小为目标,对两种分离序列进行优化设计以获得最优的设计参数。优化结果表明,两种变压精馏分离方案的设备投资费用分别为5.6×10⁵ USD/a和5.7×10⁵ USD/a,能耗费用分别为8.8×10⁵USD/a和1.0×10⁶USD/a。此外,对具有经济优势的变压精馏分离方案进行了控制结构的构建,使该过程在面对进料流量扰动和进料组分扰动时仍能维持稳定,稳定之后的三种产品纯度仍能维持在设定值附近。     

Exploration of a heat-integrated pressure-swing distillation process with a varied-diameter column for binary azeotrope separation

The pressure-swing distillation (PSD) processes with varied-diameter columns (VDCs) for separating methanol–chloroform and n-heptane–isobutanol are studied. Furthermore, two heat-integrated PSD processes, partial integration and full heat integration, are discussed with ordinary and VDCs. The results show that whether it is heat integrated or non-heat integrated, the processes using VDC have an advantage in the economy. Based on the minimum total annual cost (TAC), the dynamic controllability without and with full heat integration for an azeotrope system methanol/chloroform is explored. The dynamic controllability without and with partial heat integration for the azeotrope system n-heptane/isobutanol is discussed. The results indicated that compared with the dynamic responses without heat integration process, the heat-integrated PSD with a VDC did not increase the control difficulty while maintaining its economy. More azeotropic systems should be studied to investigate their economics and control effects, which will benefit PSD design and industrial application.     

A semicontinuous approach for heterogeneous azeotropic distillation processes

The separation of azeotropes has substantial energy and investment costs, and the available methods require high capital costs for reconstruction of process plants. As an alternative, a semicontinuous configuration that utilizes an existing plant with minor modifications has been explored. In this paper, a semicontinuous, heterogeneous azeotropic distillation process is proposed and acetic acid dehydration process is used as a case study. To carry out the simulation work, Aspen HYSYS^® simulation software is used along with MATLAB^® and an interface program to handle the mode-transition of the semicontinuous process. Sensitivity analyses on operating parameters are performed to identify the process limits. Comparisons are made to conventional heterogeneous azeotropic distillation, and dividing-wall distillation column on the annual cost. The results proved that the semicontinuous system is the best setup in terms of total annual costs and energy requirements.     

甲醇-苯共沸体系变压精馏分离工艺的动态控制

基于甲醇和苯共沸体系的压敏性,利用Aspen Plus和Aspen Dynamics软件对变压精馏分离该体系的稳态工艺进行了模拟和优化,研究了该工艺的动态特性,提出了控制产品纯度的3种控制结构：基础控制结构、比例控制结构和双比例与温度?组分联合控制结构,通过对控制结构添加±20%的组分和流量干扰测试控制结构的稳定性. 结果表明,基础控制结构基本能实现稳健控制,但不能解决组分干扰引起的产品纯度偏差过大等问题;比例控制结构可实现相对稳健的控制,但改进效果不显著;双比例与温度?组分联合控制结构在受到20%进料和组分干扰后,产品纯度能较快恢复至设定值的99.90%,实现稳健控制.     

Design and control of reactive distillation–recovery distillation flowsheet with a decanter for synthesis of N-propyl propionate

Reactive distillation (RD) for the synthesis of n-propyl propionate (ProPro) is operated with an excess of the reactant n-propyl alcohol (ProOH). It is simulated as a two-column system which can be easily controlled compared with a single reactive column which is operated neat, because the recovery column acts conceptually as a composition analyzer. The optimal steady-state design of the two-column system with the minimal total annual cost (TAC) is screened first. Then, an effective control scheme is established to handle feed disturbances. Only tray temperatures are required in the dynamic control two-column process. The product purity is held close to the set value 99.5 mol% and large deviation is prevented.     

热集成变压精馏分离乙二胺-水共沸体系的模拟优化

针对乙二胺-水共沸物组成对压力较为敏感的特性,采用部分热集成变压精馏工艺分离该共沸物。先利用Aspen Plus软件对该工艺进行稳态模拟,再以理论塔板数、进料位置、回流比为优化变量,水和乙二胺的纯度为约束,以年度总费用（total annual cost,TAC）为目标函数建立乙二胺-水共沸体系分离系统的优化设计模型。采用列队竞争算法对该分离过程主要工艺参数进行优化,得到了变压精馏分离乙二胺-水体系的最佳工艺操作参数及设备参数。模拟结果表明,利用算法对多变量进行同时优化可得到更具经济效益的分离系统,与传统优化结果相比,可降低TAC约7.31%。在此基础上,对高压塔的操作压力进行优化分析,将其由2atm提升至4atm（1atm=101325Pa）,并对流程其他参数进行优化,可显著降低TAC约24.62%。进一步,采用部分热集成比普通变压双塔精馏降低TAC约21.87%     

Application of a simulated annealing algorithm to design and optimize a pressure-swing distillation process

The design and optimization of pressure-swing distillation (PSD) have a critical impact on its economics. An optimization method based on simulated annealing algorithm (SAA) was proposed. The move generator and cooling schedule of the SAA were discussed, and suitable parameter settings were investigated. Two cases of PSD with and without heat integration were optimized by the SAA-based optimization method using procedures of pressure specified and pressure optimized. The results of the process without heat integration were compared with conventional optimization methods. For the acetone-methanol system, the total annual cost (TAC) shows a 5.69% decrease with the pressure specified and a 17.32% decrease with the pressure optimized. For the methanol-chloroform system, the TAC shows a 1.79% decrease with the pressure specified and a 9.04% decrease with the pressure optimized. The SAA-based optimization method has the advantages of a high probability to obtain the global optimum, automatic calculation, and less computing time.     

甲醇-丙酮共沸物分离的研究进展

主要介绍了甲醇-丙酮共沸物系变压精馏和萃取精馏两种分离方法的研究进展。经过比较,萃取精馏方法在经济成本方面更具有显著优势。关于萃取精馏,首先阐述了萃取剂的选取以及近些年来萃取剂的研究,主要集中在3个方面:传统单一溶剂、各种盐类和离子液体。其次还介绍了各种萃取剂所对应的气液平衡模型的应用情况和操作条件的优化等方面,并对萃取精馏及其萃取剂的应用提出了展望。     

变压-塔顶蒸汽再压缩精馏分离甲苯-正丁醇体系优化工艺

针对变压精馏分离甲苯-正丁醇的高能耗问题,采用塔顶蒸汽再压缩热泵技术对变压精馏进行改造。利用Aspen Plus流程模拟软件,以年度总费用(TAC)最小为目标函数,利用序贯迭代法确定变压精馏、变压-塔顶蒸汽压缩式热泵精馏的最优工艺参数。从节能和经济的角度对工艺进行评价,结果表明:变压-塔顶蒸汽压缩式热泵精馏更具有优势。     

Implementation of Ethanol Dehydration Using Dividing-Wall Heterogeneous Azeotropic Distillation Column

In this article, the design and optimization procedures of a dividing-wall column for heterogeneous azeotropic distillation (DWC-A) using cyclohexane as an entrainer for ethanol dehydration are investigated. The proposed procedures can detect the optimal values of the design variables and thereby guarantee the minimum energy requirements, which is related to the minimum CO₂ emissions and the lowest total annual cost (TAC). Since ethanol and water form an azeotrope under atmosphere pressure, a conventional heterogeneous azeotropic distillation sequence (CHADS), including an azeotropic column and a recovery column, is usually used to perform the ethanol dehydration process. However, due to high energy requirements and equipment investments of CHADS, the TAC is at a relatively high level. DWC-A can be used to eliminate the condenser of the second column and decrease the degree of back-mixing. Both CHADS and DWC-A are simulated with Aspen Plus®, and the results show that DWC-A has an energy saving of 42.17% and the TAC reduction of 35.18% along with higher thermodynamic efficiency and reduction in greenhouse gas emissions.     

隔板塔共沸精馏分离二氯甲烷-乙腈-水-硅醚体系

以二氯甲烷-乙腈-水-硅醚为分离体系,采用自制隔板塔小试装置,研究了共沸剂回流比和液相分配比等操作参数对隔板塔分离效果的影响。实验结果表明,当气相分配比R_v为0.5,共沸剂回流比为3时,液相分配比R_l在[0.12,0.2]范围内,隔板塔分离效果较好。在实验的基础上,采用Aspen Plus软件对隔板塔共沸精馏工艺进行模拟,考察了隔板塔共沸精馏工艺最佳操作区域及节能效果。模拟结果表明,特定分离要求下,隔板塔存在一个使再沸器热负荷最小的最佳操作区域,在此最佳操作区域内,R_l和R_v相互关联,呈一一对应关系;与三塔串联简单精馏工艺相比,完成相同的分离任务,隔板塔共沸精馏工艺再沸器节能32.74%,冷凝器热负荷减少33.70%,乙腈回收率由66.47%提高到96.01%,且大幅降低设备投资。     

Optimal design of mixed acid esterification and isopropanol dehydration systems via incorporation of dividing-wall columns

This study explores the design of a reactive distillation system and that of a heterogeneous azeotropic system by incorporating dividing-wall column (DWC). The first system involves the esterification of mixed acid (acetic acid and propionic acid) with methanol. Simulation studies are carried out for conventional reactive distillation sequence as well as for reactive dividing-wall distillation system. Both systems are optimized by an iterative optimization procedure. Optimal design results show that the reactive dividing-wall system saves steam consumption by 45.2% and reduces total annual costs (TAC) by 34.5%. The second case investigated is a heterogeneous azeotropic distillation system involving dehydration of crude isopropyl alcohol with cyclohexane as entrainer. Two optimal separation systems are generated, including one with a single-dividing wall column and one with a double-dividing wall column. In comparison with an energy-efficient azeotropic distillation sequence containing two stripping columns by Chang et al. (2012) [1], simulation results show that the former two systems can cut steam usage further by 6.0%. The two systems save about 5.4–6.1% in terms of TAC. DWCs prove to be superior to the convention distillation systems with respect to both cost and energy efficiency.     

Solute recovery from ionic liquids: A conceptual design study for recovery of styrene monomer from [4-mebupy][BF4]

Extractive distillation using ionic liquids (ILs) is a promising technology to separate the close-boiling mixture ethylbenzene/styrene. A proper solvent regeneration is crucial to obtain a technical and economic feasible process. In this work, several regeneration technologies were studied to recover styrene from the IL [4-mebupy][BF₄] using Aspen Plus. Stripping with a hot gas (N₂ or ethylbenzene), supercritical CO₂ extraction, distillation by adding a co-solvent, and evaporation were investigated. It was found that the IL that was fed as solvent to the extractive distillation column should have a purity of at least 99.6 wt% to maintain the purities of the top and bottom products from the extractive distillation column. This purity could not be obtained with an evaporator using mild conditions (T = 130 °C, T_condenser ≥ 20 °C). From the process models and the economic evaluation for a typical production capacity of 500,000 mta, the conclusion can be drawn that evaporation using very low pressures (P < 10 mbar) and stripping with ethylbenzene are the most promising technologies to recover styrene monomer from the IL [4-mebupy][BF₄].     

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.     

变压精馏分离甲苯-乙醇体系的经济最优化设计

甲苯-乙醇体系的共沸组成与相对挥发度对压力比较敏感,可用变压精馏分离该体系。利用Aspen化工流程模拟软件,以年度总费用最小为目标函数,以NRTL为热力学计算模型,采用序贯迭代法确定普通、部分热集成和完全热集成的变压精馏最优工艺参数。结果表明完全热集成更具有优势。