Use of Columns with Coupled Heat and Material Flows in Separation of Multicomponent Zeotropic Mixtures

The possibility of bringing real distillation processes to thermodynamically reversible distillation is considered. Distillation systems involving partially or fully thermally coupled columns are suggested for the separation of ternary mixtures. The transformation of the optimal flowsheet in response to variation of feed composition is studied. Recommendations are provided as to the choice of an energy saving distillation design.__________Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 3, 2005, pp. 264–268.Original Russian Text Copyright © 2005 by Ivanova, Timoshenko.     

多效蒸发海水淡化系统中CO2化学解吸的模拟

为有效降低不凝气对降膜蒸发过程的影响和优化蒸发器结构参数,建立了多效蒸发(MED)海水淡化系统中CO₂化学解吸的数学模型,通过对实际海水淡化装置的模拟,得到了系统CO₂的解吸速率及其影响因素,并通过与前人研究成果和MED海水淡化厂实际运行数据对比分析,验证了模型的正确性并且证明具有更高的精度。结果表明,蒸发温度是决定化学反应速率的关键因素,蒸发温度越高,反应速率越快,在海水加热到饱和温度阶段,海水盐度和pH值也显著影响化学反应速率;碳酸盐离子浓度因海水蒸发而增大,有助于CO₂的化学解吸;随着各效蒸发器内蒸发温度的降低,液膜中传质系数降低,CO₂解吸速率逐效降低。     

The importance of glycerol in the fatty acid industry

Historically, glycerol, a valuable by product of the fatty acid insutry, is priced higher in the market-place than any of the common fatty acids. Glycerol “credit” from fat-splitting, frequently in time of economic stress, makes the difference between a profitable stearic acid operation and an economically unsound one. Theoretical yields of glycerol for the common fats and oils range from 9–13.5%; practical plant yields, corrected for FFA and upgrading yield losses, are 9–12.8% on 100% glycerol basis, or 10.3–14.8% on an 88% glycerol basis. Glycerol “credit” per pound of fatty acid ranges from 1 to 3 cents/pound. Upgrading “sweetwaters” from splitting operations in the fatty acid industry requires removal of dissolved salts, elimination of color, and fat and oil impurities, concentration (evaporation of water) and/or distillation. For Twitchellized sweetwaters this generally involves (a.) lime treatment. (b.) filtration, (c.) evaporation to half-crude, (d.) precipitation of excess lime, (e.) filtration, (f.) evaporation to a concentration of 88–90%, and probably, (g.) distillation. For autoclave or continuous process sweetwaters the upgrading includes (a.) light lime treatment, (b.) filtration, (c.) evaporation concentration to 88–90%, and probably, (d.) distillation. Glycerol may also be upgraded by ion-exchange processing followed by evaporation concentration in which distillation may be eliminated. Ion-exclusion (Dow process) is also feasible. Many special triglyceride products are required of different fatty acid homolog distribution than those of the parent or hydrogenated fats and oils. These are prepared by splitting the fats or hydrogenated oils, fractionating the fatty acids, upgrading the glycerol, and recombining the desired fractionated acids with glycerol by reesterification. One example is high lauric triglyceride from coconut oil suited for use as a coco butter substitute.     

Distillation with Chemical Reaction and Apparatus Selection

Abstract

Reactive distillation was studied practically and theoretically for the esterification of succinic anhydride with methanol to produce in a first step monomethyl succinate and in a second one dimethyl succinate and water. It was shown that simulations using the ASPEN PLUS rigorous distillation model RADFRAC corresponds with experimental data quite well. With this fundament further calculations were performed simulating several kinds of reactive and distillation equipment. On basis of this, an apparatus selection is made related on energy consumption and relative conversion. Key parameters, as reaction velocity for the reaction term and the relative volatility (α from 1.2 to 14), affect markedly the selection of the apparatus of choice. The reaction column is the apparatus of choice for fast reactions and high volatilities considering the energy input. For low relative volatilities the choice is between the reaction column or the reactor with evaporation, depending on whether operating costs or investment costs are taken into account.     

Classification of the Phase Diagrams of Real Batch Distillation

A model is suggested and all possible phase diagrams are constructed for real batch distillation. The model suggested is topologically similar to the model of open equilibrium evaporation: both are characterized by the same singular points and unity K-and -lines.     

Reactive distillation: Non-ideal flow behaviour of the liquid phase in structured catalytic packings

Reactive distillation, the combination of chemical reaction and multistage distillation, is one of the most important industrial applications of the multifunctional reactor concept. The most promising column internals for reactive distillation are the so-called structured catalytic packings that combine favourable characteristics of traditional structured packings and heterogeneous catalysts. The non-ideal flow behaviour of the gas and the liquid phase is a fundamental aspect in multiphase reactor design since it has a strong influence on the reactor performance. In this study, liquid phase residence time distributions for the catalytic structured packing MULTIPAK^® were measured by means of conductivity measurements under different liquid and gas flow rates and evaluated with differential models.     

Purification of glass melts in the As-Se system with vacuum distillation

The behavior of macrocomponents and impurities during vacuum distillation of glass melts in the As-Se system with arsenic concentrations of 30 and 40 at % in closed and open systems has been investigated. The possibility of using vacuum distillation in an open system for purifying arsenic selenide glass melts from oxygen and hydrogen impurities has been demonstrated.     

Enzymatic Synthesis of an Isopropyl Ester by Alcoholysis of Camellia Oil

A camellia oil-based isopropyl ester (CO-IPE) was successfully synthesized by enzymatic alcoholysis with camellia oil (CO), and its physiochemical properties were analyzed. Three commercial immobilized lipases (Lipozyme RM IM, Lipozyme TL IM and Novozym 435) were screened, and Novozym 435 was the best one. The optimal reaction conditions were achieved at 240 U/g of Novozym 435 loading, a substrate molar ratio of 5:1 (isopropanol/CO), and 24 h of reaction time at 55 °C. Under the above conditions, the content of CO-IPE was obtained as 89.83%. Purity of CO-IPE further increased to be 96.95% after separation by rotary evaporation and molecular distillation. The viscosity of the synthesized CO-IPE showed itself to be about six times lower than that of CO, and the refractive index of the CO-IPE (1.449) was nearer to 1 in contrast to that of CO. It suggested that CO-IPE could be more intensively applied in the cosmetic industry.     

蒸氨系统改扩建工艺设计

为脱除氨水中的水分,利用蒸馏原理扩建蒸氨系统。介绍了蒸氨系统的工艺流程;对主要工艺参数进行了物料衡算和热量衡算;确定了蒸氨塔的内径、塔板浮阀数和理论塔板数,对设计中工艺过程可能出现的问题进行了讨论。     

Method for analyzing the structures of reactive distillation diagrams

A method for analyzing the structures of reactive distillation phase diagrams in systems involving several chemical reactions is proposed and described in detail by the example of the reactions 2C D and D A + B. An algorithm for determining the position of the chemical equilibrium manifold in the concentration simplex, its dimension, and the types of singular points is put forward.Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 1, 2005, pp. 7–18.Original Russian Text Copyright © 2005 by Tishaeva, Shuvalov, Pisarenko, Serafimov.     

Liquid-holdup regions research of novel reactive distillation column for C5 fraction separation

Recent advances in technologies of reactive distillation (RD) offer various design concepts for chemical processes. For separation of cracking C5 fraction, one of the main challenges is improving the conversion of cyclopentadiene (CPD) and the recovery of isoprene (IP). In the current work, a novel reactive distillation column with several liquid-holdup regions was designed, since it allows long residence time and provides flexibility for narrowing the efficiency gap between reaction and distillation. By use of Aspen Plus, a corresponding mathematic model was established and verified to be accurate. Following that, comprehensive studies were carried out for the design of liquid-holdup regions position. Details and principles about the separation performance with the liquid-holdup regions were revealed and optimized parameters were determined with 100 theoretical plates, feed position of 35th plate, and four liquid-holdup regions at 25th, 60th, 75th and 90th plate. The designed RD column could wellmeet the technical requirement, and influence of other important factors including residence time, operating pressure and reflux ratio was further investigated.     

反应精馏技术的关键问题分析

反应精馏是为增强反应与精馏效果而将两种单元操作进行耦合的多功能新技术。因既有化学反应又有精馏过程,反应精馏过程需考虑气液相平衡、气液质量传递、催化剂内扩散(非均相反应精馏)以及动力学等因素的相互作用,导致该过程存在定态多重性、动力学复杂性。文章系统地综述了近年来国内外科研工作者对反应精馏实验和理论的研究进展,分析了反应精馏技术工业应用中存在的关键问题,并对未来的发展方向进行了展望。     

Lipase-mediated plant oil hydrolysis—Toward a quantitative glycerol recovery for the synthesis of pure allyl alcohol and acrylonitrile

Plant based triacylglycerides are a sustainable feedstock for the chemical, bioenergy, food and cosmetic sector. While fatty acids conversion has been intensively studied, processes for glycerol valorization have been scarce. In contrast to chemical hydrolysis of plant triacylglycerides enzymatic hydrolysis methods provide a cleaner glycerol stream. This study focuses on the selection of a commercial lipase capable of quantitative hydrolysis of rapeseed- and high oleic sunflower oils. Enzymatic process using only water as the reaction medium allows simplified recovery of pure glycerol. Among the six commercial lipase preparations tested, Candida rugosa lipase was identified as the most effective biocatalyst. Catalytic behavior in buffer and pure water was equivalent. Glycerol generated using a washed lipase was recovered by just three purification steps. The FTIR spectrum of the recovered glycerol was equivalent to pure glycerol standard. Over the entire recovery process, 82%–88% of the theoretical glycerol yield could be obtained. Purified glycerol was further didehydroxylated to allyl alcohol by a formic acid mediated open distillation process. The enriched allyl alcohol had a quality, which allows to use it for the synthesis of bio-based acrylonitrile.     

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.     

Simulation and optimization of the thermally coupled reactive distillation column for producing toluene diisocynate

Toluene diisocyanate is an important chemical intermediate prepared by phosgenation reaction with two steps named cold and thermal phosgenation, respectively. The thermal phosgenation reaction is a complex reactive distillation process with high energy consumption and multiple targets of reaction and separation, so it is of great significance to optimize the step. The reactive distillation model of the thermal phosgenation was established for an industrial installation by aspen plus, and the effects of the different parameters of temperatures, residence times, etc., were investigated firstly; then a thermally coupled reactive distillation column was presented to perform the thermal phosgenation process, and the optimal operation and configuration parameters were obtained by simulation. The results showed that the proposed process can save the heat and cold energy with 7.29% and 32.78%, respectively, and reduce the total annual cost by about 17.11%.     

Mathematical study of thermal explosion of a magnesium particle with allowance for metal evaporation

A catastrophe/ignition manifold for a model of thermal explosion of a magnesium particle is constructed. The model takes into account the chemical oxidation reaction, metal evaporation, and convective heat exchange with the ambient gas. This made it possible to determine the types of heat dynamics of the particle in the plane of bifurcation parameters of the model (to locate ignition, extinction, and regular-heating regions), to find the kinetic constants in the empirical law of ignition on the basis of experimental data, and to show the stability of the integral parameter of the ignition delay in relation to sets of kinetic constants determined for mathematical models with and without account for metal evaporation. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 2, pp. 39–46, March–April, 1998.     

多目标遗传算法在反应精馏优化中的应用

反应精馏是反应与精馏的复合过程,因其具有选择性强、投资少、能耗低等优点而受到研究者们的广泛关注,并且在工业生产中得到广泛的应用。利用人工神经网络（ANN）模型来模拟反应精馏过程。在建立ANN模型时,首先用ASPEN软件模拟计算出多组数据以弥补实验数据不多的不足,并在此基础上用多目标遗传算法（GA）进行操作条件的优化。优化结果表明,多目标遗传算法结合ANN对反应精馏进行优化是可行的,而且具有很高的精度。以合成乙酸乙酯的反应精馏过程为例说明上述模拟和优化方法。     

Analysis of Distillation Using the Mass-Transfer Equation in Multicomponent Mixtures

The vector equation of mass transfer in multicomponent systems, the conditions for the existence of singular points, and the temperature distributions along the height of a two-section distillation column are analyzed.__________Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 4, 2005, pp. 407–414.Original Russian Text Copyright © 2005 by Serafimov, Timoshenko.     

黄磷尾气副产甲酸钠制备甲酸分离技术研究

云南省化工研究院研发了用多聚磷酸酸化黄磷尾气副产的甲酸钠制取高浓度甲酸的工艺,针对该特殊的反应体系,对其分离技术进行了研究。对减压蒸馏、圆盘蒸发、微波蒸发、喷雾干燥、闪蒸等几种方式进行了比较,考察了几种方式下甲酸的蒸发强度及产品甲酸的浓度,从而找到较适合本体系的分离方式。经过比较,几种方法中除了闪蒸外都可以实现酸化产物的连续分离,但综合比较了各种方法的数据后,认为选择喷雾干燥的方式比较适合本体系的分离。     

Modelling of homogeneously catalysed reactive distillation processes in packed columns: Experimental model validation

The design of reactive distillation processes requires reliable and accurate models to significantly decrease the expensive and time consuming experimental work. Different modelling approaches of varying complexity are available in the open literature. However, only few publications exist in which the question of the optimal modelling depth is discussed for homogeneously catalysed processes. Unlike these publications, we used experimental data in the present study to compare them with simulation results using different modelling depths for homogeneous reactive distillation processes. The nonequilibrium-stage model using the Maxwell–Stefan equations, the nonequilibrium-stage model using effective diffusion coefficients, the equilibrium-stage model including reaction kinetics, and the equilibrium-stage model assuming chemical equilibrium were investigated. The homogeneously catalysed transesterification of dimethyl carbonate with ethanol, for which pilot-scale experimental data were available, was used as a test system.