Mathematical model for a semicontinuous esterification process with recycle between terephthalic acid and ethylene glycol

A new mathematical model has been derived for a semicontinuous recycle esterification process that consists of two reactors, one has the recycle flow to or from another and the discharge flow of the main flow and another has only recycle flow without the discharge flow. This model can give useful information about the optimum design of a new plant through the predictions of oligomer characteristics such as concentrations of carboxyl and hydroxyl end groups, number-average molecular weight, number-average degree of polymerization, esterification and saponification degree, diethylene glycol content, melting point, concentrations of ethylene glycol and water in the vapor phase, and so on.     

TPA和EG连续生产PET的第一酯化反应器操作模拟

对乙二醇(EG)和对苯二甲酸(TPA)连续生产对苯二甲酸乙二酯(PET)的第一酯化反应器进行了数学模拟。数学模型中包括了反应动力学方程、气液平衡和气液传质方程,使模拟结果接近于工厂实践。此外对不同停留时间、不同的反应器操作温度及压力、不同的进料 EG/TPA 的 mol比,进行了模拟计算,得出了反应器出口各种产物的组成随操作参数的变化,并对各操作参数的范围和对反应的影响进行了评述。     

Modeling of semibatch direct esterification reactor for poly(ethylene terephthalate) synthesis

A comprehensive kinetic model for a semibatch direct esterification reactor has been developed. The solid-liquid equilibirium of terephthalic acid was considered in the modeling. Effects of the monomer feed ratio, reaction temperatures, and oligomer addition on the conversion, degree of polymerization, and the formation of diethylene glycol were studied. © 1996 John Wiley & Sons, Inc.     

A mathematical model for a continuous esterification process with recycle between terephthalic acid and ethylene glycol

A new mathematical model for a continuous recycle esterification process has been derived by basically the same procedure as the continuous process of a cascade type, reported earlier, which includes material and heat balances. Such a model can give extensive information about the optimum design of a new plant through the predictions of oligomer characteristics (concentrations of carboxyl and hydroxyl end groups, number average molecular weight, number average degree of polymerization, esterification and saponification degree, DEG content, melting point of oligomer, etc.), distillate properties (concentrations of EG and water in the vapor phase), heat transfer area, mass flow rate of heating medium, amount of heat supplied by heating medium, enthalpy moving with recycle, and amount of heat removed from each reactor. © 1992 John Wiley & Sons, Inc.     

反应条件对环氧大豆油酯化反应的影响研究

通过调节温度、投料比、投料方式、催化剂、阻聚剂用量等条件,合成了一系列环氧大豆油丙烯酸酯低聚物。采用紫外光固化制备固化膜,并测定了固化膜的凝胶含量。实验结果表明,产物的酯化程度随着反应温度的升高而增大,但过高的温度增加了产物的黏度。适当提高体系中环氧大豆油含量,改变投料方式,合适的催化剂和阻聚剂用量,有利于提高合成产物的酯化程度。最终得出反应温度120℃、n(环氧大豆油)∶n(丙烯酸)=1.12∶1、将环氧大豆油与阻聚剂预先混合,再滴加丙烯酸与催化剂的混合物的投料方式、w(阻聚剂)=0.15%,为最佳反应条件。     

Modeling of poly(ethylene terephthalate) reactors: 4. A continuous esterification process

A mathematical model has been developed for the direct, continuous esterification process. Influence of process and operational variables, including temperature distribution, residence time distribution, bis(hydroxyethyl)terephthalate recycle, pressure, and ethylene glycol (EG) to terephthalic acid ratio on the reactor performance have been investigated in a range as close to industrial practice as possible. The variables influencing the amount of EG reflux (which governs the energy economy) and side products (which govern the product quality) have been discussed. This investigation provides an analysis of a continuous, direct esterification process, and the results indicate strategies for optimizing productivity and product quality.     

Optimal temperature profiles for parallel-consecutive reactions with deactivating catalyst

A cocurrent tubular reactor with temperature profile control and recycle of moving deactivating catalyst has been investigated. For the temperature-dependent catalyst deactivation, the optimization problem has been formulated in which a maximum of a profit flux is achieved by the best choice of temperature profile and residence time of reactants for the set of catalytic reactions A+B→R and R+B→S with desired product R, the rates of reactions have been described separately for every reagent by the expressions containing (temperature dependent) reaction rate constants, concentrations of reagents, catalyst activity, as well as catalyst concentration in the reacting suspension and a measure of the slip between reagents and solid catalyst particles. The algorithms of maximum principle have been used for optimization. The optimal solutions show that a shape of the optimal temperature profile depends on the mutual relations between activation energies of reactions and catalyst deactivation. It has been proved that the optimal temperature profile is a result of the compromise between the overall production rate of desired reagent R (production rate in the first reaction minus disappearance rate in the second one), necessity of saving of reagents residence time (reactor volume) and necessity of saving catalyst; the most important influence on the optimal temperature profile is associated with necessity of saving the catalyst. When catalyst recycle ratio increases (mean number of catalyst particles residing in reactor increases), optimal temperatures save the catalyst, as the optimal profile is shifted in direction of lower temperatures. The same is observed when catalyst slip increases (catalyst residence time in reactor increases). Despite of variation in the catalyst concentration the optimal profile is practically the same because the decay rate is affected only by instantaneous activity of catalyst. When reactor unit volume price decreases, catalyst residence time increases, whereas optimal temperature profile is shifted to lower temperatures. When economic value of unit activity of outlet catalyst increases (catalyst with a residual activity still has an economic value), catalyst saving should be more and more intense. As far as possible, the optimal profile is shifted in direction of lower temperatures, whereas the optimal residence time is still the same. Then the optimal profile is isothermal at the level of minimum allowable temperature, whereas the catalyst is saved as its residence time in reactor decreases.     

Acid-catalysed dehydration of alcohols in supercritical water

At pressures exceeding its critical pressure water retains its ionic properties to temperatures of 400 °C or more. In water under these conditions trace amounts of Arrhenius acids dissociate and selectively catalyse the dehydration of alcohols, diols, and polyols. High yields of the desired dehydration product (ethene from ethanol, propene from propanol, acetaldehyde from ethylene glycol, and acrolein from glycerol) can be obtained with a residence time of less than one minute. However, for ethanol the equilibrium conversion appears to be less than predicted by ideal solution thermochemical calculations. This may be due to catalyst deactivation, or it may be an effect of hydrogen bonding between the water and the reactant alcohol. The dehydration of n-propanol proceeds by a first order reversible reaction whose equilibrium is close to that predicted by thermodynamics. Because these dehydration reactions proceed rapidly with a high degree of specificity, they appear to be good candidates for industrial exploitation.     

UV固化萜烯聚酯丙烯酸酯的合成研究

以松节油-马来酸酐(TMA)、一缩乙二醇(DEG)、邻苯二甲酸酐(PA)、丙烯酸(AA)为主要原料合成了涂料用紫外光固化(UV)萜烯聚酯丙烯酸酯(TPEA)预聚物。通过分子质量、酯化率及涂膜性能测试以及GPC,TG分析以考察了原料物质的量比、合成工艺、反应温度等对TPEA树脂合成及涂膜性能的影响。结果表明,适宜的工艺条件为:TPEA酯化反应温度125℃,n(TMA)∶n(DEG)∶n(PA)∶n(AA)=1∶2.2∶0.5∶2,采用两步法,制备出的TPEA树脂综合性能较好。     

原位聚合法生产全消光聚酯的技术探究

在自主研发的功能性纳米TiO2母液中加入乙二醇,经稀释、离心和接地消除静电后,通过在线添加技术注入酯化釜后低聚物管线注射系统,经原位聚合制得全消光聚酯(PET)及纤维。与半消光PET及其他常规PET产品系列的制备工艺相比,全消光PET制备宜采用较低的反应温度,并通过调整终缩聚真空度来控制产品的黏度。与功能母粒添加法相比,原位聚合法制得的全消光PET产品及其纤维的质量更稳定,尤其是染色均匀性更好,产品优等品率提升5.6%。     

以分子组份为对象的PTA间歇酯化反应模拟

为了研究对苯二甲酸和乙二醇间歇酯化过程中的低聚合反应，建立了一数学模型，模型能被用以估计转化率、低聚组份的浓度和低聚物的分布，分析了乙二醇／对苯二甲酸摩尔比对转化率、低聚物浓度、低聚物分子量及分子分布的影响。     

Identification of kinetics of direct esterification reactions for PET synthesis based on a genetic algorithm

In this study we propose a method to identify the kinetics of direction esterification reactions for polyethylene terephthalate (PET) based on a genetic algorithm. The reaction rate parameters could be identified successfully by using a genetic algorithm and plant data. The effects of key operating variables (temperature, pressure, monomer feed ratio and residence time) on the reactor performance were also investigated. It was observed that the reactor performance strongly depends on the degree of dissolution of the solid terephthalic acid (TPA) in the reaction mixtures.     

五釜工艺聚酯工业装置的稳态模拟

针对大型连续PTA直接酯化法PET工艺过程装置,以Aspen Plus和Polymers Plus为模型开发工具,建立了以反应和传质过程机理为基础的稳态模型。结果表明:该模型中包括了酯化反应、缩聚反应、二甘醇生成反应、链降解反应和乙醛生成等主副反应,且考虑了端羧基对酯化反应的自催化效应;更重要的是模型考虑了酯化阶段PTA在酯化反应器中的溶解过程和终缩聚阶段小分子的脱挥,并建立了小分子脱挥的传质系数与缩聚反应器内聚合度、黏度、温度和搅拌器转速等的关联;在此模型基础上模拟研究了第一酯化反应操作温度对各反应器出口指标的影响,指出酯化段的酯化率有一个适宜的控制范围。     

Effects of operation variables on the recovery of lactic acid in a batch distillation process with chemical reactions

In this study, the feasibility of recovery of lactic acid by batch reactive distillation using cation exchange resin as a catalyst was investigated. For the recovery of lactic acid, two reactions, esterification and hydrolysis, are involved and hence, an apparatus with two distillation columns was developed and operated in a batch mode to ensure enough residence time in the reboiler and column. The effects of operation variables such as catalyst loading, reactant mole ratio, feed concentration, type of alcohols and partial condenser temperature on the yield were studied. In this study, the reaction products of the esterification (methyl lactate and water) were distilled to the hydrolysis part to be recovered into pure lactic acid. The yield of lactic acid increased as catalyst loading in the esterification part increased and reactant mole ratio and feed lactic acid concentration decreased. Methanol as a reactant gave higher yield than any other alcohols. The yield of recovered lactic acid was as high as 90%. The yield of lactic acid was closely related to the boiling temperature of the reaction mixture in the esterification part     

A fundamental analysis of continuous flow bioreactor models and membrane reactor models to process industrial wastewaters

We analyse the steady-state treatment of industrial wastewaters in a continuous flow bioreactor and in an idealised continuous flow membrane reactor. The reaction is assumed to be governed by Contois growth kinetics, which is often used to model the growth of biomass in wastewaters containing biodegradable organic materials. We show that a flow reactor with idealised recycle has the same performance as an idealised membrane reactor and that the performance of a non-idealised membrane reactor is identical to an appropriately defined continuous flow bioreactor with non-idealised recycle. The performance of all three reactor types can therefore be obtained by analysing a flow reactor with recycle. The steady-states of the model are found and their stability determined as a function of the residence time. The performance of the reactor at large residence times is obtained. In the limit as the residence time becomes very large, all three reactor configurations have identical performances. Thus the main advantage of using a membrane reactor, or a flow reactor with recycle, for the treatment of industrial wastewaters and slurries is to improve the performance at low residence times.     

One-Step Synthesis of W/O and O/W Emulsifiers in the Presence of Surface Active Agents

The main goal of this study was to describe the method of the synthesis of the dodecyl-, tetradecyl-, hexadecyl- and octadecyl-propylene glycol emulsifiers in the presence of selected anionic and nonionic surfactants. Acyl propylene glycol emulsifiers were produced by esterification of propane–1,2-diol (propylene glycol, PG) with C_12:0–C_18:0 fatty acids in the presence of anionic sodium dodecyl sulfate (SDS) and nonionic-poly(ethylene glycol) monolaurate (PEGML). The presence of SDS and PEGML in the reaction system caused microemulsion formation. Depending on the structure and amount of the surfactant in the system reactions proceeded at different rates and with different efficiency levels. The esterification of propylene glycol carried out under applied conditions causes products with the desired contents of propylene glycol monoesters (MAPG) to be obtained in a one-step reaction. Knowledge of the reaction kinetics creates the possibility to program the composition and properties of the synthesized emulsifiers. The interaction of nonionic, lipophilic MAPG with anionic, hydrophilic SDS or nonionic, hydrophilic PEGML influences the hydrophile–lipophile balance (HLB) values of the products which may be used to stabilize water-in-oil (W/O) and oil-in-water (O/W) emulsions. Use of the synthesized compounds allows stable emulsions to be prepared which include the following vegetable fats in the oil phase: mango oil, palm oil, shorea butter and hydrogenated soybean oil.     

Synthesis of poly(alkylene succinate) biodegradable polyesters I. Mathematical modelling of the esterification reaction

Synthesis of three biodegradable aliphatic polyesters, namely poly(ethylene succinate), poly(propylene succinate) and poly(butylene succinate) is presented using the appropriate diols and succinic acid in the presence of tetrabutoxytitanium as catalyst. A theoretical mathematical model for the esterification reaction, based on the functional group approach, is developed and applied successfully in the simulation of all experimental data. Values for the kinetic rate constants are proposed for different catalyst molar ratios and comonomer chemical structure. It was found that the presence of the metal catalyst used leads to a poor activity of self-catalyzed acid and the main kinetic rate constant of the esterification reaction correlates well with the square root of the catalyst concentration. Different glycols do not influence much the number average degree of polymerization (NADP) values of the oligomers produced, even thought they slightly affect esterification rates in the order BG>PG>EG. In contrast, these values are affected by the amount of catalyst, with larger catalyst molar ratio giving polymer with bigger average molecular weight. These results were verified from measurements of the final polyester average molecular weight obtained at different polycondensation temperatures. Finally, from theoretical simulation results it was found that although higher initial ratios of glycol to succinic acid are useful to increase the esterification rate, they lower the NADP of the oligomers formed at a fixed conversion of acid end groups.     

Synthesis and characterization of ethoxyethyl α‐cyanoacrylate and reaction intermediates

Ethoxyethyl α‐cyanoacrylate was synthesized by first making oligo(ethoxyethyl α‐cyanoacrylate) through a condensation reaction of ethoxyethyl cyanoacetate with paraformaldehyde, followed by a depolymerization of the oligomer at an elevated temperature in an acidic atmosphere with a high vacuum. The ethoxyethyl cyanoacetate was in turn synthesized from an esterification of ethoxyethanol and cyanoacetic acid. The molecular structure of the target monomer and the corresponding intermediates were corroborated by IR and ¹H‐NMR. Solvents having a lower polarity led to the formation of oligomers having higher molecular weights. The molecular weight distribution of the oligomer revealed that the reaction of ethoxyethyl cyanoacetate with formaldehyde followed a mechanism comprising monomer activations, anionic reactions, and chain scissions. DSC thermograms demonstrated the cured ethoxyethyl α‐cyanoacrylate was nearly amorphous, containing little or low crystallinity. Mechanical testing data indicated that the cured ethoxyethyl α‐cyanoacrylate was a hard adhesive with higher toughness than the conventional ethyl α‐cyanoacrylate. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1758–1773, 2003     

Synthesis of flexible polyarylate by interfacial polycondensation

Products with hydroxyl ends were synthesized from the esterification of bisphenol-A, terephthalic acid and ethylene glycol. These ester products were then used for synthesis of polyarylate by interfacial polycondensation. Not only the relative concentrations of reactants for esterification but also the conditions for interfacial polycondensation, such as the monomer ratio between two phases and the reaction time, play significant roles in affecting the properties of final products. Under proper synthesis conditions, the polyarylate formed could possess equivalent thermal characteristics and much higher impact strength in comparison with unmodified polyarylate due to the incorporation of flexible aliphatic segments from ethylene glycol. X-ray diffraction showed the existence of aliphatic segments would induce small degree of orderly alignment locally in structure.     

PBT酯化反应过程中影响因素的分析

以钛酸四丁酯为催化剂,将对苯二甲酸和1,4-丁二醇进行酯化反应,并利用卡氏水份仪、气相色谱仪和全自动电位滴定仪对反应过程中的馏出液样品和酯化物固体样品进行相关分析,考察了温度、催化剂加入量、原料配比等因素对酯化反应过程及酯化程度的影响,优化了间歇酯化反应的工艺条件,为连续化工艺过程优化提供了基础数据。