Dynamic simulation of multicomponent distillation

A program has been developed for the dynamic simulation of large scale chemical processes. The simulator has a highly modular structure and an explicit integration routine which is capable of handling large systems of stiff ordinary differential equations. The use of an explicit method reduces computer storage requirements and greatly simplifies the writing of new modules. Unit subroutines have been written which are capable of describing multicomponent distillation columns without resorting to conventional thermodynamic equilibrium calculations. The absence of these iterative routines reduces computation time and allows tray efficiencies to be handled in a more natural manner than is possible with Murphee efficiencies. The program also includes an advanced thermodynamic property package based on the Peng Robinson equation of state. An industrial process consisting of two distillation columns with a combined total of seventy-five mass transfer stages, has been successfully simulated and the computed results have been compared with dynamic data collected from plant tests.     

Prediction of multicomponent distillation efficiencies

The prediction of multicomponent distillation efficiencies from binary data is highly desirable as it is physically impossible to perform the experimental study of all the systems of industrial importance.In the present work a new method of predicting ternary efficiencies is presented. The validity of the method is assessed comparing experimental ternary distillation lines with predicted distillation lines. Experimental results obtained in a 38mm diameter seven plate sieve-plate column with the binary systems cyclohexane/n-heptane, cyclohexane/toluene and n-heptane/toluene and the ternary system cyclohexane/n-heptane/toluene are used for such comparison.Experimental results obtained with the ternary system show the existence of Murphree efficiencies greater than unity for the intermediate component. Such interesting physical situations are also predicted using the new method.     

A computer-controlled pilot-plant distillation unit and studies on multicomponent distillation

A pilot-plant unit for distillation studies consists of a tray column, an on-stream process analyzer and a process computer. The analyzer system is based upon a quadrupole mass spectrometer, and provides means for on-line concentration measurements of both liquid and vapor samples with multicomponent mixtures. A study of multicomponent plate efficiencies is presented. Experimental results with water/ethanol/n-butanol mixture show that the Murphree vapor phase efficiencies of the components differ markedly.     

A matrix method for multicomponent distillation sequences

We describe a simple‐to‐use “matrix” method for obtaining all the basic distillation configurations and additional thermally coupled configurations that separate a zeotropic multicomponent feed into essentially pure product streams. This provides an opportunity to rank‐list the configurations for a given application subject to criteria of interest. The only information needed to generate the configurations is the number of components in the feed. We have successfully enumerated all the configurations for feeds containing up to eight components. The method can also be used to generate nondistillation and hybrid separation configurations, and even easy‐to‐retrofit configurations. We illustrate the use of this method by applying it to the highly energy‐intensive problem of petroleum crude distillation. We have identified more than 70 new configurations that could potentially have lower heat duty than the existing configuration. A significant number of these could reduce the heat demand by nearly 50%. © 2009 American Institute of Chemical Engineers AIChE J, 56: 1759–1775, 2010     

Murphree and vaporization efficiencies in multicomponent distillation

A quantitative comparison between Murphree and vaporization efficiencies is presented based on ternary distillation data for the systems acetone/methanol/ethanol, acetone/benzene/chlorobenzene, benzene/toluene/mxylene and n-hexane/methylcyclopentane/benzene. The influence of experimental errors on calculated values of Murphree efficiencies is also analysed.It is shown that the vaporization efficiency model fails to describe the behaviour of distillation plates and it is suggested that Murphree's model gives a more useful representation of the behaviour of distillation columns.     

The role of liquid mixing in evaporation of complex multicomponent mixtures: modelling using continuous thermodynamics

This paper investigates the part played by internal mixing in the evaporation of droplets of mixtures with large numbers of components. Continuous thermodynamics—the use of probability density functions rather than discrete components to represent composition—is applied as the mixture model, and continuous mixture formulations of the liquid phase transport equations and diffusivities are developed. Sample calculations are presented for a mixture with a single distribution function as well as for mixtures with two widely separated distributions (“dumbbell” mixtures, composed of very light and very heavy fractions). The calculations show that internal mixing generally has a smaller influence on droplet behaviour for a mixture with a large number of components than it does for a binary mixture, and give some guidance as to when a well-mixed droplet model may—or may not—be a good approximation for practical work.     

Calculation of multicomponent distillation of non-ideal mixtures by a short-cut method

The Smith-Brinkley method has been modified for use in computing non-ideal multicomponent distillations. The procedure proposed is of particular advantage for rapid calculating hydrocarbon fractionators.     

Horizontal reactive distillation for multicomponent chiral resolution

A novel horizontal reactive distillation apparatus and a new overall process scheme are proposed for continuous multicomponent chiral resolution via reversible enantioselective acylation of a chiral (racemic) substrate by a chiral (racemic) acyl donor. The process enables simultaneous production of up to four enantiomers with enhanced chiral purity. Kinetic studies, miniplant experiments, and process simulation results are described for a model lipase‐catalyzed reaction: (R)‐enantioselective transesterification of (R,S)‐1‐n‐butoxy‐2‐propanol with (R,S)‐1‐methoxy‐2‐acetoxypropane to produce (R)‐1‐n‐butoxy‐2‐acetoxypropane, (R)‐1‐methoxy‐2‐propanol, and the two unreacted (S)‐enantiomers of the (R,S)‐reagents. A horizontal, compartmentalized reactive distillation vessel is specified instead of a conventional reactive distillation column to provide longer liquid‐phase residence time needed for adequate conversion. Low vapor‐traffic pressure drop allows operation under vacuum at reduced temperatures for good enzyme stability and enantioselectivity. The general technology has potential as a means to producing a wide range of chiral synthons used in asymmetric syntheses of chiral pharmaceuticals and other biologically active products. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2603–2620, 2013     

Species grouping in multicomponent adsorption calculations

The validity of the assumption of species grouping, which combines several adsorbable species into a fewer number of pseudo-species in adsorption calculations, was examined by comparing the equilibrium concentrations obtained from exact calculations with those obtained with the use of the assumption. It was found that if the adsorption affinities of the individual species exhibited by their single-species isotherms are of the same order of magnitude, the use of the species grouping assumption yields acceptable results. This procedure applies to three situations, including those in which (a) all the species are grouped into a single pseudo-species; (b) the various species are combined into several (but fewer) pseudo-species; and (c) only some of the species are grouped, while the others remain individual species.     

Efficiency-based nonequilibrium modeling of industrial-scale multicomponent distillation columns

An efficiency-based nonequilibrium model is proposed to simulate two industrial distillation columns. In this model, the behavior of trays is studied by considering the mass transfer at interphase. The interphase mass transfer is simply evaluated by the simultaneous solution of the vapor material balance equation and the definition of the Murphree efficiency. A MATLAB code is developed to implement the simulation procedure. For verification, the product compositions and plate temperatures are compared with the reported experimental data. The discrepancy of the experimental and simulation results is about 0.5% and 20% for the temperature and the product compositions for both columns, respectively.     

Estimates of energy consumption and selection of optimal distillation sequence for multicomponent distillation

An estimate has been obtained of the energy consumption on 1 mol of separated mixture based on thermodynamic balances for processes that use mechanical and heat energy. Only irreversible losses depend on the order of separation for mixtures in mechanical systems, while for the systems using the heat, the order of separation also affects the reversible energy consumption. In the latter case, in order to obtain a reversible estimate of the heat consumption, one should solve the problem of selecting the order of separation. An algorithm has been obtained for its solution that enables one to approximately choose the order of separation at the stage of preliminary calculations knowing only the properties of the feed.     

Surface tension effects in binary and multicomponent distillation

Surface tension effects play an important role in the performance of distillation columns. In the present work they are analysed using experimental resIt is shown that marked differences exist between the behaviour of the different binary systems and that the observed binary efficiency differences canSo far as the ternary system is concerned it is clear that for most of the experimental duration lines two distinct zones have to be considered as theIt is pointed out that in the ternary diagram the region of high values of foam height corresponds to the region of larger values of component efficien     

Modeling a non-equilibrium distillation stage using irreversible thermodynamics

We compare transport equations derived from non-equilibrium thermodynamics to a classical rate model developed over the last 20 years, in terms of their ability to calculate the heat and mass fluxes by modeling a segment of a packed distillation column. We show, using water and ethanol separation as an example, that there is a significant coupling between heat and mass transfer. Neglect of this transport coefficient leads to variations in the magnitude, even the sign of the calculated heat flux, while the mass flux is less affected.     

连续精馏分离乙酸乙酯与丙酮体系的模拟研究

对制备超细高氯酸铵产生的废液即乙酸乙酯-丙酮混合液的分离过程进行了模拟研究.采用Aspen Plus化工模拟软件中的RadFrac模块进行连续精馏模拟,分别考察了塔板数、进料位置、回流比及塔顶出料量对分离效果的影响.结果表明:对于处理流量3 kg/h乙酸乙酯-丙酮的混合液,精馏塔在塔板数40,进料位置第16块塔板,回流...     

连续精馏法对加氢裂解C_9芳烃预处理的研究

对乙烯生产过程中的主要副产物加氢裂解C9芳烃的用途简要概括;提出采用连续精馏法预处理加氢裂解C9芳烃,切除重组分,提取其中的C9芳烃馏分。实验中探讨塔釜温度、进料量、出料量、提馏段高度及精馏段高度对分离过程的影响,并采用最小方差法关联实验数据、牛顿迭代法迭代,实验值和关联值相差较小,实验结果准确、可靠。在优化条件下,可以将C9芳烃馏分的质量分数由原料中的29.701 0%提高至86.784 6%,收率73.048 6%。为进一步的放大实验提供了依据。     

Simulation of continuous reactive distillation by a homotopy-continuation method

Reactive distillation was studied theoretically for the esterification of acetic acid with ethanol to produce ethyl acetate and water, using second-order reversible kinetics. Because of the high degree of interaction among the iteration variables, convergence was difticult-to-impossible to achieve with Newton's method. Consequently, a robust homotopy-continuation method was applied to solve the simultaneous nonlinear equations used to model the reactive-distillation system. Case studies for several different specifications were conducted to show how design variables affect the reactive-distillation system.