Analysis and prediction of input multiplicity for the reactive flash separation using reaction-invariant composition variables

In this study, we introduce a new approach for predicting and analyzing the input multiplicity in reactive flash separation processes. Specifically, we have identified necessary conditions to detect these multiple states in reactive flash separations using reaction-invariant composition variables. The presence of the input multiplicity is studied for the reactive systems of MTBE and TAME production to illustrate the capabilities of our methodology. For these reactive systems, we report the existence of multiple states for different operating conditions. In summary, our strategy can be applied with any reactive system and thermodynamic model, assuming that all reactions are reversible and in thermodynamic equilibrium and the operating conditions are away from the retrograde region. In general, our method is a robust procedure for the multiplicity analysis in flash separation of multi-reactive and multi-component systems.     

Hybrid reactive distillation systems for n-butyl acetate production from dilute acetic acid

The recovery of dilute acetic acid, regarding as a waste stream in many chemical and petrochemical processes, becomes an important issue due to economic and environmental awareness. In this work, a simulation study on the direct utilization of dilute acetic acid to produce n-butyl acetate via esterification with butanol in a reactive distillation is presented by using Aspen Plus. The performance of a hybrid reactive distillation with a pretreatment unit, i.e., a conventional distillation or a pervaporation, is investigated. For a single reactive distillation system, it is found that higher overall energy of the system is required when the concentration of acetic acid is lowered. By considering the enrichment of acetic acid in the reactive distillation column feed from 35 to 65 wt.%, a hybrid pervaporation–reactive distillation requires lower energy than both the conventional distillation–reactive distillation system and the single reactive distillation.     

背包进料的背包式反应精馏生产甲缩醛的模拟

提出了一种具有背包进料的背包式反应精馏生产甲缩醛的新工艺,将部分甲醇直接加入到背包反应器中.应用过程模拟软件Aspen Plus对工艺过程进行了模拟计算,采用RADFRAC严格计算模型模拟精馏塔部分,采用NRTL方程模拟反应器部分,重点考察了进料方案和甲醇进料量对新工艺过程的影响.模拟结果表明,当仅在最靠近塔顶的背包反...     

Design and control of butyl acrylate reactive distillation column system

In this study, the design and control of a reactive distillation column system for the production of butyl acrylate has been investigated. The proposed design is quite simple including only one reactive distillation column and an overhead decanter. The optimal design is selected based on the minimization of total annual cost (TAC) for the overall system. At this optimized flowsheet condition, output multiplicity was found with reboiler duty or feed ratio as the bifurcation parameter. The highest purity stable steady state was selected as the base case condition for the control study. The overall control of this system can be achieved with no on-line composition measurements. Simple single-point tray temperature control loop is designed to infer final product purity. From results of dynamic simulation, the proposed control strategy performs very well in rejecting various disturbances while maintaining butyl acrylate product at high purity. One of the important finding in this paper is that it is better to operate this reactive distillation column not at the exact feed stoichiometric balance point for better operability reason. The control performances of the proposed operating point and the operating condition right at the exact stoichiometric balance point will be compared.     

1-氯-1,1-二氟乙烷反应精馏工艺的定态模拟研究

提出了以偏氯乙烯为原料生产1-氯-1,1-二氟乙烷的反应精馏新工艺,并运用Aspen Plus软件对实现该工艺的反应精馏塔的定态行为进行了数值模拟研究。模拟研究结果表明：将化学反应过程和产物、副产物及残余反应物的分离过程集成在-个塔内实现是可能的,不仅能够得到高纯度的产品,同时还能提高反应选择性,减少副产物的生成量。相比于目前采用的传统生产工艺,反应精馏新工艺能够大大减少工艺环节和节省设备投资。案例研究显示,对于相同的偏氯乙烯加料量,1-氯-1,1-二氟乙烷产品的产量提高6．4％,副产物1,1,1-三氟乙烷的产量降低70．6％。     

A novel process for the synthesis of unsaturated polyester

Traditionally polyester production is done in a batch reactor equipped with a separation column for a batch distillation. A promising alternative for the intensification of this process is reactive distillation. The aim of this paper is to study the conceptual design of reactive distillation and to find out whether reactive distillation is potentially interesting compared to batch reactor process. Therefore, a reactive distillation model is developed and sensitivity analysis is used to obtain the design and operational parameters for the reactive distillation process. These parameters are the required number of stages, required residence time, feed ratio, reflux ratio and temperature of feed stream. The model predicts the polymer attribute, isomerization and saturation composition of the polymer in the range of industrial polyester production data. The simulation study shows that the total production time of polyester in a continuous reactive distillation system is reduced from 12 h to 1.5-2 h compared to the industrial batch reactor process. The equilibrium conversion is also raised by 7% compared to the conventional process. The model demonstrated that reactive distillation has the potential to intensify the process by factor of 6-8 in comparison to the batch reactor.     

An integrated reactive distillation process for biodiesel production

An integrated reactive distillation process for biodiesel production is proposed. The reactive separation process consists of two coupled reactive distillation columns (RDCs) considering the kinetically controlled reactions of esterification of the fatty acids (FFA) and the transesterification of glycerides with methanol, respectively. The conceptual design of the reactive distillation columns was performed through the construction of reactive residue curve maps in terms of elements. The design of the esterification reactive distillation column consisted of one reactive zone loaded with Amberlyst 15 catalyst and for the transesterification reactive column two reactive zones loaded with MgO were used. Intensive simulation of the integrated reactive process considering the complex kinetic expressions and the PC-SAFT EOS was performed using the computational environment of Aspen Plus. The final integrated RD process was able to handle more than 1% wt of fatty acid contents in the vegetable oil. However, results showed that the amount of fatty acids in the vegetable oil feed plays a key role on the performance (energy cost, catalyst load, methanol flow rate) of the integrated esterification–transesterification reactive distillation process.     

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。     

反应精馏过程中的多稳态分析

Reactive distillation processes for synthesis of ethylene glycol （EG） and ethyl tert-butyl ether （ETBE） were modeled with the simulation package ASPEN PLUS. The input multiplicity and output multiplicity were discussed with the method of sensitivity analysis for both cases. In EG production process, steady state multiplicities were studied in terms of effective liquid holdup volume and boil-up ratio. In ETBE synthesis process, the user kinetic subroutine was supplied into ASPEN PLUS firstly, and then the composition, temperature and reaction-rate profiles within the reactive distillation column were presented in detail. A set of stable solution branches based on distinct initial guesses for a range of boil-up ratio were found in EG synthesis. Input multiplicities were observed for a range of reboiler duty at several values of reflux ratio for ETBE synthesis process. These results can be used to avoid excessive energy consumption and achieve optimum design of reactive distillation column.     

反应精馏隔壁塔生产乙酸正丁酯的优化与控制

对反应精馏隔壁塔生产乙酸正丁酯过程进行了模拟、优化与控制的系统研究。利用Aspen Plus软件模拟乙酸甲酯与正丁醇的酯交换反应过程,以年总费用（TAC）为目标函数进行过程优化,通过稳态敏感性分析及相对增益矩阵（RGA）判据得到不同的操纵变量与控制变量匹配关系,以此为基础,在Aspen Dynamics平台建立了若干控制结构并进行分析对比。结果表明,利用两股反应物呈比例进料可较为有效地抵抗进料扰动,最后提出的无再沸器热负荷与混合物进料量比值（Q_r/F）控制的改进控制结构CS3,在降低反应精馏隔壁塔控制过程超调量方面有较大的优越性。     

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。     

三氯氢硅歧化反应精馏生产硅烷的模拟简

The reactive distillation process for producing high purity monosilane via trichlorosilane redistribution reaction was simulated. Rigorous RadFrac block was employed in Aspen Plus simulation package. Accurate results could be given when the chemical kinetics was taken into account in the equilibrium stage model. A single column process was used for the verification of previous studies. The results showed that 99.9% purity monosilane could be achieved in the reactive distillation. A pumparound block was employed to reduce the condenser duty with inexpen- sive coolant. The effects of operating pressure, feed stage location, liquid holdup per stage and pumparound loca- tion were also investigated. The energy consumption was limited, but the refrigerant temperature was too low, which is the fatal disadvantage. Therefore, a double columns process was developed to increase the condenser tem- perature. The simulation results demonstrated that a reasonable temperature could be achieved by varying the recy- cle stream location.     

2,3-丁二醇分离纯化中反应精馏的实验和模拟

对反应萃取-水解精馏法分离发酵液中2,3-丁二醇工艺中的水解精馏进行了实验和模拟研究。实验验证了4,5-二甲基-2-丙基-1,3-二氧戊环(DPD)水解精馏得到2,3-丁二醇的可行性。采用Aspen Plus建立反应精馏模型,以UNIFAC为热力学方程,RadFrac为反应精馏模块,对常压下DPD的水解精馏进行模拟,模拟结果与实验结果吻合较好。以2,3-丁二醇的收率为主要优化目标,考察最佳塔板数、进料位置、进料比、回流比和塔顶馏出比。模拟结果表明,在最佳操作条件下,塔釜2,3-丁二醇的收率为0.981,摩尔分率为0.150。     

Simulation studies on reactive distillation for synthesis oftert-amyl ethyl ether

In this work, a reactive distillation column in which chemical reactions and separations occur simultaneously is applied for the synthesis of tert-amyl ethyl ether (TAEE) from ethanol (EtOH) and tert-amyl alcohol (TAA). A rate-based kinetic model for liquid-phase etherification and an equilibrium stage model for separation are employed to study the reactive distillation. The calculation is carried out using the commercial software package, Aspen Plus. Simulations are performed to examine the effects of design variables, i.e., a number of rectifying, reaction and stripping stages on the performance of reactive distillation column. It has been found that an optimal column configuration for the TAEE production under the study is designed with no rectifying, 4 reaction and 8 stripping stages. With such an appropriate specification of the reactive distillation column, the effects of various operating variables on the TAA conversion and TAEE selectivity are further investigated and the results have shown that the reflux ratio and operating pressure are the most important factors to the operation of the reactive distillation.     

Feasibility study of a thermally coupled reactive distillation process for biodiesel production

Biodiesel fuel represents an interesting alternative as a clean and renewable substitute of fossil fuels. A typical biodiesel production process involves the use of a catalyst, which implies high energy consumptions for the separation of the catalyst and the by-products of the reaction, including those of undesirable side reactions (such as the saponification reaction). A recently proposed process involves the use of short-chain alcohols at supercritical conditions, avoiding the use of a catalyst and the occurrence of the saponification reaction. This process requires fewer pieces of equipment than the conventional one, but its high energy requirements and the need of special materials that support the reaction conditions makes the main product, biodiesel fuel, more expensive than petroleum diesel. In this work, a modification of the supercritical process for the production of biodiesel fuel is proposed. Two alternatives are proposed. The process involves the use of either reactive distillation or thermally coupled reactive distillation. Simulations have been carried out by using the Aspen One™ process simulator to demonstrate the feasibility of such alternatives to produce biodiesel with methanol at high pressure conditions. A design method for the thermally coupled system is also proposed. Both systems have been tested and the results indicate favorable energy performance when compared to the original scheme. Furthermore, the thermally coupled system shows lower energy consumptions than the reactive distillation column.     

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。     

用于生产TAEE的反应精馏和全蒸发的混合过程

In this study, a reactive distillation column in which chemical reaction and separation occur simultaneously is applied for the synthesis of tert-amyl ethyl ether （TAEE） from ethanol （EtOH） and tert-amyl alcohol （TAA）. Pervaporation, an efficient membrane separation technique, is integrated with the reactive distillation for enhancing the efficiency of TAEE production. A user-defined Fortran subroutine of a pervaporation unit is developed, allowing the design and simulation of the hybrid process of reactive distillation and pervaporation in Aspen Plus simulator. The performance of such a hybrid process is analyzed and the results indicate that the integration of the reactive distillation with the pervaporation increases the conversion of TAA and the purity of TAEE product, compared with the conventional reactive distillation.     

From simulation studies to experimental tests in a reactive dividing wall distillation column

The design and control of thermally coupled distillation sequences have been studied since many years, but the real implementation occurred until middle of the 1980s using a single shell divided by a wall named dividing wall distillation column. In this work, experimental results for the production of ethyl acetate in a reactive dividing wall distillation column are presented for first time. The experimental results are in agreement with those obtained using steady state simulations with AspenONE Aspen plus. These experimental results are important since it is possible to validate most of the previous results generated using simulations.     

异丙醇-环己烷萃取精馏过程模拟与优化

利用化工流程模拟软件Aspen Plus对异丙醇-环己烷共沸物系的双塔连续萃取精馏过程进行了模拟计算与优化。首先根据溶剂相似相溶原理,先初选出糠醛和硝基苯作为备选溶剂,再通过汽液平衡试验及ChemCAD模拟筛选,确定糠醛为最适宜溶剂,选择NRTL模型作为物性方法,使用RadFrac模块进行模拟计算,并利用灵敏度分析模块对各工艺参数进行优化。结果表明,最适宜工艺方案为：萃取精馏塔理论塔板数为30,原料在第26块板进料,溶剂在第12块板进料,物质的量回流比为1.8,溶剂质量比为3∶1;溶剂回收塔理论板数为15,进料位置在第10块板,物质的量回流比为1.0。分离效果可达到环己烷质量分数为99.74%,异丙醇质量分数为99.61%。模拟和优化结果为分离过程的优化操作和设计提供了依据。     

The second law optimal state of a diabatic binary tray distillation column

A new numerical procedure to minimize the entropy production in diabatic tray distillation columns has been developed. The method was based on a least square regression of the entropy production at each tray. A diabatic column is a column with heat exchangers on all trays. The method was demonstrated on a distillation column separating propylene from propane. The entropy production included contributions from the heat transfer in the heat exchangers and the mass and heat transfer between liquid and vapor inside the distillation column. It was minimized for a number of binary tray distillation columns with fixed heat transfer area, number of trays, and feed stream temperature and composition. For the first time, the areas of heat exchange were used as variables in the optimization. An analytical result is that the entropy production due to heat transfer is proportional to the area of each heat exchanger in the optimal state. For many distillation columns, this is equivalent to a constant driving force for heat transfer. The entropy production was reduced with up to 30% in the cases with large heat transfer area and many trays. In large process facilities, this reduction would ideally lead to 1-2 GWh of saved exergy per year. The most important variable in obtaining these reductions is the total heat transfer area. The investigation was done with a perspective to later include the column as a part in an optimization of a larger process. We found that the entropy production of the column behaved almost as a quadratic function when the composition of the feed stream changed. This means that the feed composition is a natural, easy variable for a second law optimization when the distillation column is a part of a process. The entropy production was insensitive to variations in the feed temperature.