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.     

用离子液体作催化剂和夹带剂时在反应萃取精馏塔中乙酸甲酯和正丁醇酯交换反应的模拟

A new reactive and extractive distillation process with ionic liquids as entrainer and catalyst (RED-IL) was proposed to produce methanol and n-butyl acetate by transesterification reaction of methyl acetate with n-butanol. The RED-IL process was simulated via a rigorous model, and high purity products of methanol and n-butyl acetate can be obtained in such a process. The effects of reflux ratio, feed mode, holdup, feed location, entrainer ratio and catalyst concentration on RED-IL process were investigated. The conversion of methyl acetate and purities of products increase with the holdup in column, entrainer ratio and catalyst content. An optimal reflux ratio exists in RED-IL process. Comparing to the mixed-feed mode, the segregated-feed mode is more effective, in which the optimal feed locations of reactants exist.     

乳酸提纯反应精馏新工艺非平衡级稳态模拟

Purification of lactic acid by reactive distillation (RD) is a novel technology which has many excellent characteristics compared with traditional technologies. This paper presented a non-equilibrium model for lactic acid purification RD pilot column. An Improved Separation Efficiency Function (ISEF) was proposed based on de-coupling and pseudo-homogenous assumptions, which greatly improved the solving efficiency and made this model suitable for practical application. Simulation results were consistent with the experiments in different conditions, and the simulation results outperformed the simulator ASPEN PLUS in which the equilibrium stage assumptions were adopted. The static characteristics of the pilot setup were also investigated. The analysis result could help to accelerate the commercialization of the lactic acid purification RD technology.     

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.     

Batch Extractive Distillation in a Column with a Middle Vessel

Batch extractive distillation was studied in a column with a middle vessel. The process was simulated by a constant holdup model and solved by two point implicit method. Acetone and methanol mixture was separated in such a setup using water as solvent. The simulation agrees well with experimental results. The experimental and simulation results show that the solvent at the bottom and the product at the top of the column can be withdrawn simultaneously for a long period of time. It needs more time for the solvent to reach high purity than that required for the more volatile component to reach high purity, so that the time to withdraw solvent from the bottom is delayed.     

带有中间储罐的塔用于间歇萃取精馏

Batch extractive distillation was studied in a column with a middle vessel. The process was simulated by a constant holdup model and solved by two point implicit method. Acetone and methanol mixture was separated in such a setup using water as solvent. The simulation agrees well with experimental results. The experimental and simulation results show that the solvent at the bottom and the product at the top of the column can be withdrawn simultaneously for a long period of time. It needs more time for the solvent to reach high purity than that required for the more volatile component to reach high purity, so that the time to withdraw solvent from the bottom is delayed.     

基于Aspen Plus的气流床煤气化炉三段平衡模型(英文)

A three stage equilibrium model is developed for coal gasification in the Texaco type coal gasifiers based on Aspen Plus to calculate the composition of product gas, carbon conversion, and gasification temperature. The model is divided into three stages including pyrolysis and combustion stage, char gas reaction stage, and gas phase reaction stage. Part of the water produced in the pyrolysis and combustion stage is assumed to be involved in the second stage to react with the unburned carbon. Carbon conversion is then estimated in the second stage by steam participation ratio expressed as a function of temperature. And the gas product compositions are calculated from gas phase reactions in the third stage. The simulation results are consistent with published experimental data.     

非理想多组分混合物中质量传递过程基于Maxwell-Stefan扩散理论的建模及数值分析(英文)

The Intalox metal tower packing was used to simulate an industrial relevant extractive distillation column for purifying azeotropic multicomponent mixture.In order to explain the inconsistencies in the modeling of transfer process in nonideal multicomponent distillation column,a method was developed with equilibrium stage models(EQ)and non-equilibrium model(NEQ)incorporated with Maxwell-Stefan diffusion equations in the framework of AspenONE  simulator.Dortmund Modified UNIFAC(UNIFAC-DMD)thermodynamic model was employed to estimate activity coefficients.In addition,to understand the reason for the diffusion against driving force and the different results by EQ and NEQ models,explicit investigations were made on diffusion coefficients, component Murphree efficiency and mass transfer coefficients.The results provide valuable information for basic design and applications associated with extractive distillation.     

Experimental and simulation of the reactive dividing wall column based on ethyl acetate synthesis

Reactive dividing wall column(RDWC) is a highly integrated unit which combines reaction distillation(RD) with dividing wall column separation technology into one shell, and it realized the chemical reaction and the separation of multiple product fractions simultaneously. In this paper, the reaction of esterification with acetic acid and ethanol to produce ethyl acetate was used as the research system, experiments and simulations of the RDWC were carried out. This system in the traditional process mostly used the homogeneous catalyst(e.g. sulfuric acid). However, in view of the corrosion of the equipment caused by the acidity of the catalyst, we used the heterogeneous catalysts – iron exchange resins – Amberlyst15 and proposed a novel catalyst loading method. Firstly,the reliability of the model of the simulation was verified by the experimental study on the change of liquid split ratio and reflux ratio. After that, the four-column model was established in Aspen Plus to analyze the effects of the amount of azeotropic agent, reflux ratio and acetic acid concentration. Finally, for a fair comparison, the economic analysis was conducted between traditional RD column and RDWC. The results showed that RDWC can save34.7% of total operating costs and 18.5% of TAC.     

工业PTA溶剂脱水过程动态模拟与分析

Dynamic model for dehydration process of industrial purified terephthalic acid solvent is investigated to understand and characterize the process.A temperature differential expression is presented,which ensures the equation to convergence and short computation time.The model is used to study the dynamic behavior of an azeotropic distillation column separating acetic acid and water using n-butyl acetate as the entrainer.Responses of the column to feed flow and aqueous reflux flow are simulated.The movement of temperature front is also simulated.The comparison between simulation and industrial values shows that the model and algorithm are effective.On the basis of simulation and analysis,control strategy,online optimization and so on can be implemented effectively in dehydration process of purified terephthalic acid solvent.     

Simulation of a plant scale reactive distillation column for esterification of acetic acid

Most of the reactive distillation (RD) simulation studies rely upon very scarce laboratory scale experimental data available in literature. In the present work, an industrial scale RD finishing column for ethyl acetate production is simulated using rate based model of Aspen Plus™. Available activity coefficient data could not predict composition profiles of the industrial column. Therefore, a new set of NRTL model parameters is established for this system using the vapor–liquid equilibrium data available in literature. This new set of data was used in the non-equilibrium, rate based model of Aspen Plus™. Baring the variation in concentration profile due to fluctuations caused by pseudo-steady-state behavior of industrial unit, the predicted concentration profile closely matches the plant data. The simulation results for stage efficiencies, component generation rates, and the effect of the organic reflux rate on ethanol conversion and ethyl acetate purity are also presented and discussed.     

混合离子液体催化反应精馏合成乙酸正己酯

离子液体催化反应精馏是提高酯交换平衡反应转化率的一种绿色有效方法。以离子液体1-丙基磺酸-3-甲基咪唑三氟甲烷磺酸盐（［PSO₃HMIm］［OTf］）和离子液体1-辛基-2,3-二甲基咪唑双（三氟甲烷磺酰）亚胺盐（［OMMIm］［Tf₂N］）的混合物作为乙酸甲酯和正己醇进行酯交换反应合成乙酸正己酯的催化剂,测定了酯交换反应动力学。探讨了混合比、反应温度、反应物初始摩尔比、催化剂浓度对反应速率和乙酸甲酯转化率的影响,考察了催化剂的回收性能。利用实验数据回归得出混合离子液体催化酯交换反应动力学方程。在反应动力学的基础上进行了乙酸甲酯和正己醇的酯交换反应精馏流程模拟,分析了理论板数、回流比、进料位置及反应段塔板数、催化剂用量、持液量等参数对反应精馏塔的影响。在优化的操作条件下,获得纯度为0.9993的乙酸正己酯产品。     

Simulation study on a reactive distillation process of methyl acetate hydrolysis intensified by reaction of methanol dehydration

Methyl acetate (MeOAc) recovery from the polyvinyl alcohol (PVA) production is a difficult and heavy energy consuming process. In this work, a reactive distillation (RD) process of MeOAc hydrolysis intensified by methanol (MeOH) dehydration, as an auxiliary reaction, was proposed. Two different feeds with the mole ratio of MeOAc to MeOH at 1:1 and 1:9 were studied, and the effect of the operating pressure, the feed location and the reflux ratio on the RD column was analyzed. The simulations of reactive distillation were performed using a three phase non-equilibrium model implemented by gPROMS. As the limit of the reaction rate of MeOH dehydration, it is impossible to get 100% conversion of MeOAc and MeOH by a single RD column. Therefore, two novel processes for recovery of methyl acetate in PVA production were developed. The simulation results show that the high purity of dimethyl ether (DME) could be achieved with a complete conversion of MeOAc, and a large amount of energy demand and equipment costs can be reduced.     

PDMS/ZSM-5膜的制备及渗透汽化分离水中乙酸正丁酯和乙酸乙酯

为探究出适合分离水中的乙酸正丁酯和乙酸乙酯的新型渗透汽化膜材料,选用沸石ZSM-5 对聚二甲基硅氧烷(PDMS)材料进行填充改性,以聚偏氟乙烯(PVDF)为支撑层,采用刮涂法制备PDMS/ZSM-5/PVDF复合膜渗透汽化分离水中的乙酸正丁酯和乙酸乙酯。采用SEM、接触角测量仪、FTIR、TGA和XRD等对膜材料物理化学性能进行表征,考察了膜材料的溶胀行为及渗透汽化性能。结果表明,ZSM-5在 PDMS 膜中分散均匀,且没有发生化学作用,并提高了膜材料的疏水性和热稳定性。随着ZSM-5添加量的增加,膜在乙酸正丁酯和乙酸乙酯的溶胀度和待分离组分在膜材料中的扩散速率不断增加。随着进料浓度和温度的增加,渗透通量不断增大,分离因子先增大后减小。随着ZSM-5在PDMS/ZSM-5/PVDF复合膜中含量的增加,总渗透通量增加,而分离因子呈现先增加后减小的趋势。当添加量为10%（质量）时,分离因子达到最大值。对于乙酸正丁酯/水体系,渗透通量和分离因子最大值分别为319 g·m ^-2·h ^-1和131;而对于乙酸乙酯/水体系,渗透通量和分离因子最大值分别为1385 g·m ^-2·h ^-1和121。     

Experimental study and process simulation of n-butyl acetate produced by transesterification in a catalytic distillation column

The production of n-butyl acetate by transesterification of methyl acetate with n-butanol, catalyzed by acidic ion-exchange resin NKC-9, was experimentally investigated in a homemade catalytic distillation column with a diameter of 80 mm. A non-equilibrium stage model for describing the catalytic distillation process was established and solved with Newton-Homotopy method. The effect of feeding mode, reflux ratio, material molar ratio and number of reactive sections on the conversion of methyl acetate was investigated. The experimental results agree well with those obtained by the theoretical simulation calculations, indicating the accuracy and reliability of the non-equilibrium model. It can be concluded that the non-equilibrium model established in this paper can provide theoretical guidance for the further process design and optimization.     

H3PW12O40/酸改性硅藻土催化剂的制备、表征及催化合成乙酸正丁酯

以硫酸改性后的硅藻土为载体,Keggin结构磷钨酸为活性组分,通过浸渍法制备出负载型催化剂H₃PW₁₂O₄₀/改性硅藻土,并对催化剂进行傅里叶变换红外光谱（FTIR）、X射线衍射（XRD）、扫描电镜（SEM）、X射线能谱（EDS）和N₂-程序升温脱附（N₂-TPD）表征。结果表明：酸改性后硅藻土的微孔增大增多,比表面积增大。H₃PW₁₂O₄₀均匀分布在改性硅藻土载体上,负载后磷钨酸仍保持Keggin结构。以H₃PW₁₂O₄₀/改性硅藻土为催化剂催化乙酸和正丁醇液相合成乙酸正丁酯,通过正交试验探索优化工艺条件。在较优工艺条件下,即w(40%H₃PW₁₂O₄₀/改性硅藻土)=1.1%（基于反应物质量）,n(酸)∶n(醇)=1∶3,125℃反应2.0h,酯化率高达98.1%。催化剂重复催化使用5次,酯化率仍可达86.1%。H₃PW₁₂O₄₀/改性硅藻土可作为催化合成乙酸正丁酯的高效催化剂,具有活性高、用量少、价格低廉、制备简单、后处理简便、无废液排放等优点。     

Investigations on the Synthesis of Methyl Acetate in a Heterogeneous Reactive Distillation Process

The production of methyl acetate in a reactive distillation process – prior art for 15 years – is often used as an example to study the basic phenomena of reactive distillation. The present paper deals with a theoretical and experimental analysis of methyl acetate synthesis in a reactive distillation column. A design method based on the interpretation of reactive distillation line diagrams is used to identify the main process parameters and to provide a foundation for experimental investigation. The significant influence of the reflux ratio on the conversion in the column is shown by mini plant experiments using supported ion exchanger in the form of Raschig rings as a heterogeneous catalyst. These experiments demonstrate the catalytic quality of this packing material. To simulate the reactive distillation column with a simple stage-to-stage method, the separation efficiency of the catalytic rings is investigated. Comparison of experimental and simulation results reveals that a simple model based on the assumption of simultaneous chemical and phase equilibrium describes the experimental data quite well over a wide range of reflux ratios. Furthermore, simulation results show that the conversion depends less on the number of reactive stages than on the use of two feed stages.     

Hydrolysis of methyl acetate via catalytic distillation: Simulation and design of new technological process

An equilibrium stage model was developed for the simulation of the catalytic distillation process of methyl acetate (MeOAc) hydrolysis. In the model, the influences of the reactive kinetics, residence-time, liquid holdup, and separation efficiency of the catalytic packing were considered. The model predicted the conversion of MeOAc and the mass ratio of acetic acid to water in the hydrolysis mixture. The predictions were in good agreement with experimental data. A novel process was designed based on the results of theoretic analysis and the simulation research. This new process had a higher conversion of MeOAc compared with the results in previous research and was found to be energy efficient. Optimal effect parameters and design factors of new technology on energy consumption and conversion were also determined and summarized as the following: the position of side draw is 18th to 19th stages, the catalytic distillation (CD) column pressure is at 350 kPa, the volume ratio of reflux to feed is 6–8, mole ratio of feed water to MeOAc is 3.5–4.5, and the mass ratio of side withdrawal to feed is 0.32–0.34.