Robust optimization of the heteroextractive distillation column for the purification of water/acetic acid mixtures using p-xylene as entrainer

The separation of water and acetic acid mixtures is a challenging task in the terephthalic acid production process. This study addresses the techno-economical optimization of an heteroextractive distillation column that uses p-xylene as entrainer. The optimization of this column is performed by means of robust optimizers belonging to the BzzMath library, coupled with the detailed process simulation of the downstream section performed with the commercial software SimSci PRO/II. A comparison with respect to the commercial simulator optimizer and a quantification of benefits are given. Results show that the BzzMath robust optimizer reaches a lower Total Annual Cost (−3.5%) with respect to the commercial software optimization. Finally, the comparison with other entrainers proposed in literature for the advanced distillation of the water/acetic acid mixtures demonstrates the economical and operational appeal of this process configuration.     

Entrainer selection for the synthesis of fatty acid esters by Entrainer-based Reactive Distillation

In this research it is demonstrated that, due to the similarities between Entrainer-based Reactive Distillation and azeotropic distillation, the same selection rules can be applied to select a suitable entrainer. From a list of suitable entrainers for the azeotropic distillation of isopropanol and water, cyclohexane and isopropyl acetate are chosen. Residue curve maps, simulations of the distillation section of the column, and simulations of the total Entrainer-based Reactive Distillation concept show that both can be used as an entrainer in Entrainer-based Reactive Distillation. Whether the Entrainer-based Reactive Distillation concept will be feasible, depends strongly on the kinetics of the reaction.     

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.     

Inter-integration reactive distillation with vapor permeation for ethyl levulinate production: Equipment development and experimental validating

Ethyl levulinate, one of the main derivatives of levulinic acid (LA), is of significant potential as platform chemicals for bio-based materials. The esterification of LA was generally carried out in a conventional batch reactor or in a conventional reactive distillation column. However, traditional methods are hard to deal with equilibrium limited reactions and azeotropic issues. Therefore, the inter-integration reactive distillation with vapor permeation (R-VP-D) process, which integrated reaction, vapor permeation, and distillation into one single unit, is proposed in this paper and validated in the pilot-scale experiments. A comparative study is made between a pilot-scale RD column with and without VP module. Owing to the water-selective VP membrane and the ingenious design of related apparatuses, the R-VP-D process reveal a superiority in LA conversion of 21.9% maximum higher than RD without VP process and removing of product water about 53.6% from VP module, which indicates its promising industrial application in process intensification field.     

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。     

Fatty acid esterification by reactive distillation. Part 1: equilibrium-based design

Esters of fatty acids are currently produced in batch processes. In this study we present an innovative process based on reactive distillation (RD). The synthesis of a several fatty esters is possible in the same RD set-up, making possible the development of a continuous multipurpose process. Conceptual design is presented as a systematic methodology based on thermodynamic analysis combined with computer simulation. This approach sets also targets for limited experimental work. The methodology is illustrated by the esterification of lauric acid with 2-ethylhexanol and methanol, the heaviest and lightest alcohol in the C₁-C₈ series. The first part presents the design of a RD set-up based on chemical equilibrium. Both reactions can be accommodated in the same hardware, but with different operation procedures. The alternative with alcohol reflux is suitable for heavy alcohols that form heterogeneous azeotropes with water. Another alternative with acid reflux can accommodate both light and heavy alcohols, and may be seen as a generic process for fatty acid esterification.     

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%.     

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.     

DESIGN STRATEGY FOR ACETIC ACID RECOVERY

Acetic add is recovered from dilute aqueous solutions by extraction followed by azeotropic distillation. The heat required for distillation accounts for the major proportion of the cost of the process. Therefore, the proper selection of the entrainer is of great importance. In this paper, a procedure for preliminary entrainer selection is developed combining the well proved heuristic approaches and the latest developments for the synthesis phase based on residue curve maps and liquid-liquid equilibria plots. The energy requirements for the most promising entrainers are calculated using a commercial process simulator. It was found that methyl tert-butyl ether is a promising entrainer for the acetic acid dehydration process.     

甲烷磺酸锌的合成、表征及其催化酯化反应性能的研究

合成了甲烷磺酸锌,并利用红外、热重分析对其结构进行表征。热重分析结果表明,实验所合成的甲烷化磺酸锌分子中含有3个结晶水;ZnO含量的实测值与理论计算值基本相符。以甲烷磺酸锌作为催化剂,研究其催化正丁醇与冰乙酸反应生成乙酸正丁酯中各种因素对酯化率的影响。反应条件为：醇酸摩尔比1．2／1,催化剂用量1％(以酸的摩尔数计量),带水剂环己烷2．5mL,反应时间2．5h,反应温度为回流温度,最高酯化率可达到89．9％。甲烷磺酸锌在催化酯化反应过程中可以重复使用6次,酯化率仍然达到88．4％。     

Energy saving in acetic acid process using an azeotropic distillation column with a side stripper

Dilute acetic acid is obtained primarily from fermentation and synthesis processes and cannot be produced by simple distillation due to relatively low volatility of acetic acid compared to water. Instead, an azeotropic distillation is applied to increase the concentration of dilute acetic acid. When acetic acid is extracted from a dilute aqueous solution using a solvent mixture of ester and alcohol, its recovery requires an energy-intensive azeotropic distillation. In the water stripping process that follows azeotropic distillation, two distillation columns handle the acetic acid and water mixture in similar composition. Therefore, the two columns can be combined as a side stripper connected to the azeotropic distillation column. The energy-saving effect is examined with the HYSYS (Aspentech Corporation) evaluation of the process. Compared to the conventional process, the modified process suggests 39% reduction in heating duty and 24% coolant savings. The economic analysis shows 32% decrease in investment and 36% utility savings. Based on heat utilization analysis, the thermodynamic efficiency is enhanced by 11%.     

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.     

对甲苯磺酸催化合成乙酸丁酯的研究

研究了以对甲苯磺酸为催化剂 ,乙酸和正丁醇为原料合成乙酸丁酯 ,并考察了影响反应的因素。结果表明 ,醇酸摩尔比为 1 2∶1,催化剂用量为 0 8g(乙酸为 0 2mol的情况下 ) ,带水剂环己烷为 5ml,反应时间为 2 0h是最适宜的反应条件 ,酯化率达 96 9%     

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%。     

NMP萃取精馏分离醋酸和水的过程模拟

利用化工模拟软件Aspen Plus采用萃取精馏法,以N-甲基吡咯烷酮(NMP)为萃取剂,对生产中醋酸和水分离进行了模拟计算,并与普通精馏法进行比较。结果表明,NMP是一种良好的萃取剂,能够很好的实现醋酸和水的分离;与普通精馏法相比,同样分离指标下萃取精馏法的能耗降低了69.8%,每吨醋酸蒸汽消耗量由10.5 t降低至3.2 t,表明萃取精馏分离醋酸和水,节能显著,优于普通精馏,为醋酸和水分离的优化操作和设计提供依据。     

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.     

Recovery of Formic Acid and Acetic Acid from Waste Water Using Reactive Distillation

Processing of biobased feedstock materials may lead to formation of multicomponent azeotropic mixtures. Reactive separations provide an opportunity to circumvent azeotropes by changing the substance properties through chemical reactions. Exemplarily several effluents from black liquor processing contain aqueous mixtures of low molecular weight fatty acids such as formic acid and acetic acid. These mixtures form inseparable azeotropes. Separation of the system formic acid–acetic acid–water by esterification with methanol was investigated. Reactive distillation experiments in batch and continuous mode confirmed complete removal of formic acid in a first step. Acetic acid may then be isolated by distillation or by reactive distillation.     

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。     

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.     

从工业废水中回收乙酸的方法研究进展

随着我国工业水平的不断提高, 含有乙酸的废水产生量越来越大。乙酸的含量一般在1%～30%(质量分数), 使废水不仅表现为强酸性, 而且化学耗氧量高, 不易直接排放。乙酸与水不易分离也使乙酸废水在工业上难以处理, 研究从废水中回收乙酸的方法具有重要意义。本文简要介绍了近几年国内外从工业废水中回收乙酸的进展, 主要包括膜分离法、吸附法、萃取法、萃取酯化法、精馏法, 并分析了每种方法的优缺点以及当前的研究水平。指出:双极膜电渗析和渗透汽化法适合乙酸质量分数在1%左右的废水处理;吸附法和反应萃取法适用于乙酸含量在10%以下的废水处理, 30%以下的乙酸废水可以借助反应精馏进行分离。最后分析了膜分离法和吸附法处理含乙酸废水的工业应用尚需解决的关键问题。