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.     

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。     

侧反应器反应精馏方法生产醋酸甲酯的模拟

采用强酸性阳离子交换树脂催化醋酸与甲醇反应精馏生成醋酸甲酯,可避免硫酸作为催化剂的不足。但该非均相催化反应受平衡限制,且达到平衡时间较长,采用传统反应精馏塔难以提供足够反应空间。文中设计侧反应器与精馏塔耦合新工艺,采用Aspen Plus软件模拟研究了侧反应器数量、位置,原料进料位置,回流比,醇酸比等对反应精馏过程的影响。结果表明,当装置具有7个侧反应器,反应器间隔4块板,在优化的操作条件下,醋酸甲酯质量分数可达99.1%。     

Process alternatives for methyl acetate conversion using reactive distillation. 1. Hydrolysis

In a polyvinyl alcohol (PVA) plant, reaction stoichiometry indicates that equal molar of methyl acetate is generated for every mole of PVA produced. This work explores an alternative to convert methyl acetate back to acetic acid (raw materials of PVA plant), methyl acetate (MeAc) hydrolysis. The design and control of methyl acetate hydrolysis using reactive distillation is studied. Because of the small chemical equilibrium constant (∼0.013) and unfavorable boiling point ranking (MeAc being the lightest boiler), the reactive distillation exhibits the following characteristics: (1) total reflux operation and (2) excess reactant (water) design. The proposed flowsheet consists of one reactive distillation column with a reactive reflux drum, two separation columns, and one water-rich recycle stream. A systematic design procedure is used to generate the flowsheet based on the total annual cost (TAC). Two dominate design variables are: recycle flow rate (for the degree of excess in water) and the overhead impurity level of acetic acid in the product column (to avoid tangent pinch). Finally, the operability of the hydrolysis plant is evaluated. A plantwide control structure is developed followed by process identification and controller tuning. The results show that reasonable control performance can be achieved using simple temperature control for feed flow and feed composition disturbances.     

Design of entrainer-enhanced reactive distillation for the synthesis of butyl cellosolve acetate

An innovative entrainer-enhanced reactive distillation (RD) process is presented, which aims to the production of high-purity butyl cellosolve acetate from butyl cellosolve and acetic acid via an esterification reaction. This entrainer-enhanced RD process can procure technical advantages from both heterogeneous azeotropic distillation and RD. Solvents such as cyclohexane, ethylene dichloride, toluene, and octane are considered as candidates in this esterification RD process. The function of entrainers is to simplify the separation between water and acetic acid. For this purpose, the proper entrainer to use is thus evaluated based on its mutual solubility with water in two liquid phases. Simulation results reveal that total annual cost can be substantially reduced when cyclohexane, toluene, and octane are used as entrainers in the RD column. The octane-enhanced RD provides the most economical design in this studied case.     

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.     

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.     

共沸蒸馏在化工生产中的应用与研究进展

共沸蒸馏为共沸物或相对挥发度接近于1的非理想物系的分离过程提供了选择。介绍了蒸馏残余曲线图的热力学原理,并以反应蒸馏生产乙酸乙酯工艺为例说明了蒸馏残余曲线图在流程设计等方面的应用。分别从夹带剂选择、过程设计、过程集成强化、过程控制等角度阐述了共沸蒸馏过程相关理论研究进展;在应用方面,主要综述了乙醇、异丙醇稀溶液、稀乙酸等脱水及回收利用情况,共沸蒸馏过程强化反应蒸馏、变压共沸蒸馏、共沸蒸馏耦合膜分离研究进展情况以及反应蒸馏工艺的局限性,并对其未来的发展前景作了展望。     

Optimization of coproduction of ethyl acetate and n-butyl acetate by reactive distillation☆

Based on a previous investigation, a simulation model was used for optimization of coproduction of ethyl acetate and n-butyl acetate by reactive distil ation. An experimental setup was established to verify the simulated results. The effects of various operating variables, such as ethanol feed location, acetic acid feed location, feed stage of reaction mixture of acetic acid and n-butanol, reflux ratio of ethyl acetate reactive distillation column, and distil-late to feed ratio of n-butyl acetate column, on the ethanol/n-butanol conversions, ethyl acetate/n-butyl acetate purity, and energy consumption were investigated. The optimal results in the simulation study are as follows:ethanol feed location, 15th stage;acetic acid feed location, eighth stage;feed location of reaction mixture of acetic acid and n-butanol, eighth stage;reflux ratio of ethyl acetate reactive distillation column, 2.0;and distillate to feed ratio of n-butyl acetate, 0.6.     

Analysis of reactive distillation using the esterification of acetic acid as an example

The uncatalyzed esterification of acetic acid is described in the literature as a typical example of reactive distillation. Many rigorous models were validated using this esterification as an example. Process proposals for the production of pure ethyl acetate from ethanol and acetic acid have been determined using short-cut methods with the assumption of chemical equilibrium only. In this publication, the limitations of this esterification are clarified, using a rigorous model that was developed. The reasons why reactive distillation appears to be unfavorable for this esterification are explained. It is, however, theoretically possible to obtain ethyl acetate in high purity with different variants of the process. Different process variants are examined in this work. Construction variables that are important for the design of reactive columns, such as the number of reactive separation stages and the holdup in the column, are analyzed. Furthermore, the influence of variables dependent on the component system, such as the phase equilibrium of the reactive system and the reaction kinetics on the conversion in the column, are described. It can be shown that the short-cut methods published so far for reactive distillation, which assume chemical equilibrium, are inadequate.     

催化精馏酯化法回收稀醋酸

采用催化精馏技术处理稀醋酸溶液,以乙醇为反应物,使醋酸转化为醋酸乙酯。催化剂选用自制的填料型SO42-/Al2O3-Al固体酸催化剂,实验考察了回流比、醇酸比、乙醇进料流量、稀醋酸浓度等因素对催化精馏过程的影响。     

Kinetics of acetic acid esterification over ion exchange catalysts

Computer simulation showed that catalytic distillation is an attractive process for the removal of dilute acetic acid from wastewater. Selection of catalysts and kinetic data have been obtained for the design of the catalytic distillation column. Kinetic measurements were conducted in a batch reactor. Methanol was added to the dilute acetic acid solutions and reacted with the acid in water to form methyl acetate and water. The reaction can be catalyzed by solid acid catalysts. It was found that Amberlyst 15 was an effective catalyst for this reaction. The effects of stirrer speed, reaction temperature, reactant concentration and catalyst loading on reaction rate were investigated. A complete kinetic equation for describing the reaction catalyzed by Amberlyst 15 was developed. This equation can be used in the simulation and design of the catalytic distillation column for removing acetic acid from wastewater.     

催化精馏合成乙酸乙酯的工业试验

以固体酸为催化剂,在中试催化精馏塔中进行了乙酸与乙醇反应制备乙酸乙酯的工业试验,试验塔的精馏段塔径为600 mm,内装陶瓷规整填料,反应精馏段塔径为1 000mm,内装7层立体催化精馏塔板.采用连续操作,考察了不同的回流比、釜酸质量分数、进料流量对反应和分离过程的影响,同时测定了塔板上气液相质量分数的分布.通过试验得到...     

催化精馏合成醋酸甲酯的研究

以强酸型阳离子交换树脂为催化剂,在直径为40 mm的填料塔内对催化精馏合成醋酸甲酯进行了研究。实验塔的三段填料高度分别为810、270、450 mm,填料段之间放置直径为60 mm、高度为175 mm的2节催化剂床层,并在塔釜放置催化剂。采用连续操作,着重考察了醇酸进料摩尔比、醋酸进料位置、甲醇进料位置和回流比对催化精馏合成醋酸甲酯的影响。在选定实验条件下,塔顶醋酸甲酯的质量分数可达到98.43%,醋酸的转化率达到99.13%。     

Simulation of continuous packed bed reactive distillation column for the esterification process using activity based kinetic model

A mathematical model for the continuous packed bed reactive distillation process of esterification of acetic acid with methanol is developed. The kinetic rate equation, which plays a major role for the performance of reactive distillation and it is the part of model, is required for the liquid phase reversible esterification reaction. The mineral sulphuric acid is used as the catalyst. The kinetic experiments are carried out under different temperatures in the range of 305.15 to 333.15 K and catalyst concentrations in the range of 0.1267 mole H⁺/lit to 0.6537 mole H⁺/lit. From that experimental data the kinetic model is developed and the same is used for the simulation of reactive distillation process. Equilibrium stage model, in which the vapour and the liquid leaving a stage are assumed to be in equilibrium with each other, has been used for the simulation of reactive distillation process by incorporating our kinetic model. Conversion of acetic acid as function of reflux ratio and reboiler ratio has been predicted. The liquid composition and temperature profiles versus stage number have been also predicted. Finally, the optimum operating conditions obtained from the simulation results for high pure methyl acetate by reactive distillation process.     

Synthesis of vinyl acetate monomer from synthesis gas

Previous attempts to synthesize vinyl acetate monomer (VAM) from synthesis gas involve routes that require a costly recycle of acetic acid through a carbonylation reactor. Two new routes to VAM from synthesis gas that avoid this acetic acid recycle have been investigated. One of these new routes synthesizes VAM from acetic acid via the intermediacy of ketene. Ketene is hydrogenated to acetaldehyde, and the acetaldehyde is reacted directly with ketene to produce VAM. The second route synthesizes VAM from the carbonylation of dimethyl ether to acetic anhydride followed by reaction of the acetic anhydride with acetaldehyde in a reactive distillation column to produce VAM and acetic acid. The co-produced acetic acid is hydrogenated to form the acetaldehyde required in the reactive distillation.     

Theoretical Investigations on the Quaternary System n‐Butanol,Butyl Acetate,Acetic Acid and Water

Reactive distillation has been established for different processes, for example, the production of MTBE and TAME. Numerous publications have shown experimental and theoretical results of such etherification processes. The present paper deals with a theoretical background for an esterification process. The investigations will be carried out with the quaternary system consisting of n‐butanol, butyl acetate, acetic acid and water. For this system, not often used in literature, the chemical equilibrium constant and a suitable reaction kinetic has to be found. The different singular points will be checked and the kind of singularity will be determined. Residue curve maps will show the shape of simulations from different starting points. The differences between a simple distillation process and a reactive distillation process will be demonstrated.     

Removal of acetic acid from water by catalytic distillation. Part 1: Experimental studies

Catalytic distillation experiments were carried out in a 100 mm diameter column for the removal of dilute acetic acid from water. The column was installed with a novel internal composed of alternating a dualflow tray and a catalyst basket. Amberlyst 15 was used as a catalyst to accelerate the esterification of acetic acid with methanol. The effects of various operating parameters on the acid removal were investigated. For the feed which contains 2.5 to 9.9 wt% of acetic acid in water, more than 50 wt% of acetic acid can be recovered as methyl acetate in the 1.5 meter high test column.     

醋酸废水回收利用技术研究

从稀醋酸水溶液中回收醋酸是酸性工业废水处理中一项很重要的问题,对于资源再利用和环境污染控制等方面都具有重要意义。作为废水处理和资源回收相结合的过程,现在通常采用的方法是:共沸精馏;简单蒸馏;溶剂萃取,然后精馏回收溶剂;超临界流体萃取或氧化;吸附。本文针对先行方法存在的不足,提出并详细介绍SO42-/Al2O3-Al催化剂条件下的催化精馏反应回收醋酸的原理及意义。     

反应精馏法制备醋酸甲酯的研究

以醋酸、甲醇为原料,以浓硫酸为催化剂,对反应精馏法制备醋酸甲酯的过程进行了实验研究。着重考察了回流比、进料中醋酸摩尔分率、塔板数及混酸进料位置等因素对反应转化率和塔顶产品中醋酸甲酯含量的影响,并得出最佳的工艺条件。