Membrane reactors in chemical production processes and the application to the pervaporation-assisted esterification

When appropriate membrane was used for the assistance of chemical and biochemical equilibrium reactions, it is possible to enhance the yield and the purity of the reaction product by selectively adding educts or selectively removing products and to a lower the energy input and the reaction time compared to conventional process. In this paper a review on membrane reactors with special emphasis on membrane-assistance of esterification reactions and a continuous tube membrane reactor for the pervaporation-assistance of the esterification are presented. The heterogeneously catalyzed esterification of ethanol and acetic acid to ethyl acetate and water was investigated as a typical chemical equilibrium reaction. The selective and simultaneous water separation from the reaction mixture of the esterification with polyvinyl alcohol pervaporation membranes is considered to be an interesting process alternative to the conventional distillation process. Compared to the distillation process, for the pervaporation-assisted process a decrease of the energy input of over 75% and of the investment and operating coasts of over 50% each was calculated.     

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.     

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.     

带侧线反应精馏-渗透汽化生产乙酸乙酯集成过程模拟与分析

针对乙酸酯化法生产乙酸乙酯分离过程复杂、能耗大的缺点,提出了一种带侧线反应精馏-渗透汽化（RD-PV）集成过程。通过反应精馏塔侧线采出和渗透汽化膜组件及时移出水分,促进酯化反应向正反应方向进行,在达到乙酸高转化率的同时使乙酸乙酯产品达到高纯度。研究了反应精馏塔侧线采出位置、采出比、反应段塔板数、精馏段塔板数以及膜组件个数等对年度总成本（TAC）的影响,获得了TAC达到最小的过程参数。与传统双塔精馏分离过程对比,RD-PV集成过程节省能耗26.6%,但膜材料价格对RD-PV集成过程的TAC有较大影响,随着渗透汽化技术的成熟,当膜材料价格低于1913 CNY·m^-2时,RD-PV集成过程在经济上占据优势。     

A new hybrid membrane separation process for enhanced ethanol recovery: Process description and numerical studies

Ethanol is a biofuel, produced through the fermentation of sugars derived from biomass. Its usefulness as a fuel is limited by the energy intensive nature of the ethanol separation process. The ethanol recovery process is inefficient due to the dilute nature of the fermentation product and the presence of the ethanol?water azeotrope. This investigation presents a new hybrid separation process for energy efficient ethanol recovery. The new process is a hybrid of distillation and pervaporation. However, as opposed to most other hybrid processes, the distillation and pervaporation processes are combined into single unit. An overview of the proposed system was provided and differences to the conventional separation process were highlighted. A mathematical model was derived to explain the transport phenomena occurring in the hybrid process. The model was then used to compare the process to distillation. It was shown that the hybrid process is capable of breaking the ethanol-water azeotrope. It was also demonstrated that the pervaporation process, which is associated with both material and energy transfer, induces partial condensation of the vapor and thereby affects the efficiency of vapor?liquid contacting. Simulations were presented to show the impact of reflux ratio and pervaporation flux on the performance of the process.     

The use of dilute acetic acid for butyl acetate production in a reactive distillation: Simulation and control studies

The recovery of dilute acetic acid, which is widely found as a by-product in many chemical and petrochemical industries, becomes an important issue due to economic and environmental awareness. In general, separation of acetic acid in aqueous solution by conventional distillation columns is difficult, requiring a column with many stages and high energy consumption. As a result, the primary concern of the present study is the application of reactive distillation as a potential alternative method to recover dilute acetic acid. The direct use of dilute acetic acid as reactant for esterification with butanol to produce butyl acetate in the reactive distillation is investigated. Simulation studies are performed in order to investigate effect of the concentration of dilute acetic acid and key process parameters on the performance of the reactive distillation in terms of acetic acid conversion and butyl acetate production. In addition, three alternative control strategies are studied for the closed loop control of the reactive distillation. The control objective is to maintain the butyl acetate in a bottom product stream at the desired purity of 99.5 wt%.     

甲基异丁基酮分离过程中精馏-渗透汽化集成工艺的研究

对丙酮一步法生产甲基异丁基酮(MIBK)部分精馏流程进行了工艺分析,MIBK脱轻塔进料液中少量水的存在使MI-BK脱轻塔运行不稳定,进而影响MIBK合成液的整个分离过程。针对这个问题,提出了精馏-渗透汽化集成的工艺方案,省去MIBK脱轻塔。建立了渗透汽化小试实验,研究了NaA分子筛膜的渗透汽化过程以及分离性能。用Aspen Plus软件对精馏-渗透汽化集成工艺进行了模拟,与精馏过程相比,在MIBK产品质量与收率相同情况下,操作成本降低了20%,总成本可降低15%。     

固体酸催化合成乙酸异戊酯的研究

用自制固体酸代替浓硫酸作为催化剂 ,对乙酸和异戊醇酯化制备乙酸异戊酯进行研究。取得较为满意的结果 ,酯化率高 ,且产品质量好。探索出生产乙酸异戊酯的较佳工艺条件     

从杂醇油中异戊醇制取乙酸异戊酯

阐述了用精密蒸馏法,从杂醇油中分出异戊醇,并用硫酸和杂多酸为催化剂,与醋酸酯化制备乙酸异戊酯的反应条件。     

十二烷基磺酸铁催化合成乙酸异戊酯

对乙酸与异戊醇在十二烷基磺酸铁为催化剂作用下的酯化反应进行了研究，考察了反应时间、催化剂用量、醇酸摩尔比等因素对乙酸异戊酯收率的影响。实验结果表明较好的反应条件为：乙酸用量为0.1mol，醇酸摩尔比为1．1：1，十二烷基磺酸铁用量为1．6g(约2．0mmol)，带水剂环己烷用量为6HlL，反应40min，酯收率达95．2％，催化剂重复使用5次仍保持较高活性。产品经折光率、红外光谱表征。     

三氯化铁催化合成乙酸异戊酯

研究了以三氯化铁为催化剂乙酸与异戊醇的酯化反应,考察了反应时间、催化剂用量、醇酸摩尔比等因素对乙酸异戊酯收率的影响。实验结果表明,较好的反应条件为:乙酸用量0.1 mol,醇酸摩尔比:1.2∶1,三氯化铁用量(0.2mol/L)10 mL,带水剂环己烷用量8 mL,反应30 m in,酯收率达93.5%。产品经折光率、红外光谱表征。     

反应精馏合成醋酸正丁酯的模拟和优化

利用Aspen Plus模拟了合成醋酸正丁酯的反应精馏过程,并分析各工艺参数对产品纯度和再沸器热负荷影响。通过优化得出最佳工艺参数为:理论塔板数为16;精馏段、反应段和提馏段塔板数分别为5、7和4;醋酸和正丁醇的进料塔板数分别为5和7;酸醇进料比为1:1;回流比为1。在此条件下产品醋酸正丁酯的纯度达99.55%;乙酸的转化率达99.71%,再沸器的能耗较低。     

萃取、共沸精馏技术联用回收废液中的醋酸

针对化工生产过程中产生的稀醋酸溶液难以回收高纯度醋酸的问题,首先采用乙酸乙酯和苯的混合溶剂萃取浓缩稀醋酸溶液;再通过精馏蒸出溶液中的萃取剂和部分水;最后采用乙酸丁酯作为挟带剂,用共沸精馏法分离得到醋酸。得到的醋酸质量分数达96.84%,回收率达84.97%。对工业化回收稀醋酸溶液中的醋酸有一定的实用价值。     

Simulation of a hybrid pervaporation–distillation process

This study explores the possibility of simulating a hybrid pervaporation membrane process with the help of Aspen Plus? (Aspen Tech) flowsheeting. Because Aspen Plus does not contain membrane modules in its Model Library, the pervaporation membrane is simulated within Excel Visual Basic for Applications (VBA). Excel VBA is then linked with Aspen Plus to perform the hybrid simulation. In this way, the user can control the simulation even during the calculations.Case studies, in which industrially relevant hybrid distillation–pervaporation processes are simulated, are used to test the program. First, the dehydration and recycling of ethanol in an industrial plant is looked at, to explore whether an economic improvement can be established with a hybrid process. Secondly, the same is done for the purification of acetic acid in an industrial plant. The results presented here indicate the value of this software as a design tool.     

Thermodynamic efficiency of membrane-assisted distillation processes

Membrane processes are considered as comparably mild separation processes offering the potential for significant energy savings compared with azeotropic distillation processes. Despite higher investment and material costs, they are of particular interest for improving the energy efficiency in the chemical industry. However, energy savings of more than 20%–30% are rarely reported and even a general superiority can be disputed. To further elucidate this controversial, the current study pursues a quantitative assessment of the thermodynamic efficiency of pervaporation and vapor permeation processes with stand-alone distillation and hybrid membrane-assisted distillation processes for the separation of azeotropic mixtures. The results confirm the case-dependent potential of distillation processes to outperform membrane-assisted separations in terms of energy efficiency, considering proper heat integration. Although energy efficiency is becoming significantly important, it should be considered in the context of economic performance to determine an optimal trade-off and to select the best process alternative during conceptual process design.     

乙酸与丁醇酯化反应和渗透蒸发耦合过程研究

以硫酸锆催化乙酸和丁醇的酯化反应为例对渗透蒸发和酯化反应耦合过程进行研究 ,考察了温度、反应物初始摩尔比、膜面积与反应液体积比和催化剂浓度对耦合过程的影响。     

A techno‐economic comparison of various process options for the production of 1,1‐diethoxy butane

BACKGROUND: Acetals can be considered important bio‐based diesel additives. The production of most of these compounds, from an alcohol and an aldehyde, suffers from low conversion due to thermodynamic limitations. These limitations can be overcome through the removal of the by‐product water. Previous studies showed that the in situ dehydration options of reactive distillation and pervaporation membrane reactor integration offer little advantage or at least not at reasonable unit dimensions. The aim of the present work is the development of a membrane based process and comparison with other alternatives (based on experimental data). RESULTS: Three different membrane processes were developed. The one in which the reaction mixture is recycled over a first dehydration membrane module and subsequently through a simple distillation column, was found to give the highest overall conversion (100%) at low recycle rates and reasonable membrane area. This process was techno‐economically compared with other possible alternatives: (1) a process based on a conventional tubular reactor and several distillation columns; and (2) a process based on reactive distillation. CONCLUSIONS: Efficient water removal by membranes avoids possible azeotropes in downstream distillation units making them much simpler, reducing considerably the unit sizes and the energy demand (40% lower). Copyright © 2012 Society of Chemical Industry     

Process analysis and optimisation of hybrid processes for the dehydration of ethanol

Promising hybrid processes for ethanol dewatering consist of different combinations of distillation with adsorption and/or vapour permeation. This paper presents an analysis and optimisation of these hybrid processes using non-equilibrium models and an evolutionary algorithm. Four different membrane assisted configurations are compared with a benchmark process consisting of distillation and pressure swing adsorption. In total 12 cases were investigated while assuming different feed and product compositions at different production capacities: three ethanol mass fractions in feed 45, 80, 92 wt.%, two product purities 99.6, 99.95 wt.% and two production capacities 25,000, 250,000 m³/year. The influence of decisive operating and structural variables on important target variables such as total membrane area is demonstrated. Finally, the processes are evaluated regarding operating costs and energy consumption depending on product purity and production capacity. The operating costs of the membrane assisted configurations differ only in a small range of −3% to 6% from those of the benchmark. The energy consumption of the membrane assisted configurations without distillation is up to 30% lower compared to the benchmark. Especially the combination of vapour permeation and adsorption is a promising alternative allowing for producing ethanol with high purities at lower operating pressures compared to the vapour permeation as stand alone process.     

Esterification of Acetic Acid and Ethanol in a Flow‐Through Membrane Reactor Coupled with Pervaporation

The esterification of acetic acid is an important industrial process for the synthesis of ethyl acetate. A membrane reactor with a sulfonated polyethersulfone/polyethersulfone/non‐woven fabrics composite catalytic coupled with a poly(vinyl alcohol) pervaporation membrane was applied in continuous esterification of ethanol with acetic acid in a flow‐through mode. High equilibrium conversion was obtained for esterification in a closed‐loop mode. For the pervaporation‐assisted esterification in this mode, the experimental conversion was very close to the theoretical value.     

ASPEN模拟反应精馏生产醋酸甲酯及工业化探讨

采用Aspen Plus软件模拟催化反应精馏生产醋酸甲酯的工艺过程。考察操作压力、醋酸进料位置、回流比和醋酸/甲醇进料比对反应精馏塔塔顶醋酸甲酯纯度的影响。得出反应精馏塔优化操作条件为:操作压力1atm、醋酸在第5块板进料、回流比为1.9、酸醇比为1.6。在模拟计算的基础上,初步探讨工业化装置设计的技术关键点。