Zum Zusammenhang zwischen idealen und realen Gemischen bei der Destillation

The Relation Between the Distillation of Ideal and Real Mixtures A complete theory exists for the distillation of ideal mixtures, i.e., mixtures with constant relative volatilities. This theory allows one to answer any questions that arise during the distillation of multicomponent systems using simple algebraic equations. The concepts of ideal mixtures can, at least quantitatively, be used for the distillation of real multicomponent systems, no matter how complex, as shown in this work. The understanding of the basic principles for the distillation of these mixtures is, therefore, remarkably simplified.     

A unified description of the distillation of ideal mixtures

It is shown that the distillation of multicomponent ideal mixtures may be regarded as a superposition of the distillation of ternary mixtures and that the equation describing the distillation of ternary mixtures may be reduced to one single fundamental equation. This fundamental equation contains the lightest, the heaviest and one intermediate boiling component and is equally valid for distillation based on theoretical trays as well as packings. It applies to the distillation at total and finite reflux and also includes the limiting cases of reversible distillation or distillation with a mass transfer resistance either on the gas or on the liquid side. This reduction of the distillation of multicomponent mixtures to the distillation of a ternary mixture and to one single equation greatly simplifies the understanding of the complexities of multicomponent distillation.     

Synthesis,experiments and simulation of heterogeneous batch distillation processes

The presence of azeotropes in multicomponent mixtures complicates the design of batch distillation separation processes widely used in pharmaceutical and speciality chemical industries. Most of those processes include the use of a homogeneous entrainer to ease the separation. We describe novel methods to break azeotropes using an entrainer that is partially miscible with one of the initial binary mixture components. We depict some of the advantages of heterogeneous batch distillation processes: more design alternatives for the separation of an azeotropic binary mixture than with homogeneous batch distillation, batch distillation boundary crossing thanks to a controlled reflux of the entrainer-rich phase, simplified distillation sequences as a consequence of less distillation tasks. Three examples based on the separation of non-ideal azeotropic or close boiling point binary mixtures through heterogeneous batch distillation are simulated using a commercial batch distillation package. Experiments validate the simulated separation of a minimum boiling azeotropic mixture.     

Batch‐Rektifikation azeotroper Gemische in Verstärkungs‐ und Abtriebskolonnen

Batch distillation is an efficient unit operation which allows the separation of a multicomponent mixture into its pure constituents in a single column. However, the separation of azeotropic mixtures by distillation is quite difficult because at the azeotrope the liquid and the gas have the same composition and, in turn, the driving force for distillation disappears. A systematic presentation of batch distillation processes for the separation of binary azeotropic mixtures using an entrainer is given.     

预测非理想多元混合物精馏点效率的新模型

提出一个新的计算非理想多元元精馏物系Murphree点效率的方法,在计算塔板上鼓泡液体中汽液两相间的传质通量时,充分考虑了在扩散路径上混合物组成的变化所产生的影响,同时根据多相湍流动力学的原理计算了鼓泡液体中汽、液相的接触面积．利用这个新模型对6个多元非理想混合物的计算,表明它能够准确地预测某些组元点效率的奇异性,而且预测的精度明显地优于现有其他方法,证明它是一个有效的、可靠的非理想多元精馏点效率预测方法.     

Determination of vapor pressure/molecular weight correlations from droplet evaporation data

A rapid method is presented for the determination of vapor pressure/molecular weight correlations for homologous hydrocarbon mixtures. By comparing droplet evaporation data to discretized theoretical continuum mass flux rates which employ two parameter exponential vapor pressure/molecular weight correlations, best fit pressure correlation parameters are determined. The present technique is applied to the multicomponent oil mixture, 100 pale oil, which is modeled as a fifteen component system. Postulating the mixture is thermodynamically ideal, best fit pressure correlations are determined which result in less than 5% error between theory and experiment. It is shown the hydrocarbon vapor pressure calculated from the derived pressure correlation is in satisfactory agreement with pressures calculated from distillation data and the Clausius Clapeyron relation.     

Minimum-reflux regime of simple distillation columns

A general algorithm for calculating minimum reflux ratios in simple distillation columns used for the separation of ideal and nonideal (including azeotropic) homogeneous multicomponent mixtures is proposed. The algorithm deals with various splits: direct, indirect, intermediate, and with one distributed component. The algorithm is mathematically rigorous, developed on the basis of the geometrical theory of distillation, and makes it possible to consider the special features of nonideal mixtures (tangent pinch, necessity of using nonadiabatic columns).     

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.     

进料组成改变对隔板塔经济性影响的模拟

完全热耦合精馏相比传统精馏可以减少设备投资和操作费用,可代替传统精馏分离多组分混合物。对隔板塔（完全热耦合精馏塔）用于分离三组分混合物时的可操作性和经济性进行了研究。采用严格模拟方法,针对4种不同的进料组成设计了4种不同的隔板塔,并得出各个隔板塔气相和液相分割比对隔板塔年度总费用（TAC）的关系曲线,研究了当进料组成改变时4种隔板塔的经济性。     

Kontinuierliche Thermodynamik – ein Weg zur Behandlung komplexer Vielstoffsysteme

Continuous Thermodynamics – An Approach to the Treatment of Multicomponent Mixtures. In the chemical industry, complex multicomponent mixtures such as petroleum fractions or polymer systems are of great importance. Characterization experiments on such mixtures mostly result only in continuous distribution functions. In contrast, equations of chemical thermodynamics include the mole fractions of the individual components. An approach suitable for overcoming these difficulties is provided by continous thermodynamics, which is based directly on continuous distribution functions. Here, applications relating preferentially to vapor-liquid equilibrium involved in the calculation of distillation columns are discussed. Continuous thermodynamics is seen to provide distinct advantages over the traditional approach, i.e. the pseudo-component method.     

Optimal retrofit of a side stream column to a dividing wall column for energy efficiency maximization

A side distillation column is widely used to separate multicomponent mixtures into three products. However, this kind of column consumes considerable amounts of energy due to thermodynamic restrictions and the nature of the distillation process. Retrofit of the side distillation column to a dividing wall column (DWC) can result in significant energy savings. This study evaluated a systematic method for optimal retrofit of a side stream column to a DWC. The minimum energy requirement for the separation of a multicomponent mixture was used for a feasibility study. Subsequently, design and optimization was performed using shortcut, rigorous and response surface methodology. One case study was illustrated to demonstrate the proposed methodology. The results showed that the optimal retrofit of a side distillation column to the DWC could not only save a significant amount of energy, but also increase the capacity. This study highlights the potential for retrofitting a side stream column to a DWC from a techno economic point of view.     

Systematic exploration of the applicability of the idiomatic vapor balance rule to distillation column consolidation

For N-component distillation (N ≥ 3), consolidation between different column sections is an inevitable manipulation when synthesizing complex distillation configurations. In the consolidation, the idiomatic vapor balance (IVB) rule, in which the larger vapor flowrate in the two columns before consolidation will be chosen as the balanced vapor flowrate at the consolidation point, has been widely used. However, the applicability of the IVB rule has not been verified, which is of essential importance to the accuracy of the distillation configuration synthesis. In the present study, the applicability of the IVB rule to distillation column consolidation was systematically explored by rigorous method for the first time. First, the separation of ideal and non-ideal three-component mixtures with variable compositions was studied, and the optimized configurations before and after consolidation were determined by a rigorous method. The results indicated that for the separation of an ideal mixture, the IVB rule was applicable for the whole composition range, while for the separation of a non-ideal mixture, the IVB rule was only applicable for very limited composition range. Finally, two cases of synthesizing distillation configurations for the separation of non-ideal mixtures were studied to verify the remarkable deviations the IVB rule may cause. The results indicated that the applicability of the shortcut method using the IVB rule to the distillation configuration synthesis depended on the composition of the non-ideal mixture, and a remarkable error might result and the truly optimal configuration might be missed if the IVB rule is applied to a non-ideal mixture.     

Systematic exploration of the applicability of the idiomatic vapor balance rule to distillation column consolidation

For N-component distillation(N ≥ 3), consolidation between different column sections is an inevitable manipulation when synthesizing complex distillation configurations. In the consolidation, the idiomatic vapor balance(IVB) rule, in which the larger vapor flowrate in the two columns before consolidation will be chosen as the balanced vapor flowrate at the consolidation point, has been widely used. However, the applicability of the IVB rule has not been verified, which is of essential importance to the accuracy of the distillation configuration synthesis.In the present study, the applicability of the IVB rule to distillation column consolidation was systematically explored by rigorous method for the first time. First, the separation of ideal and non-ideal three-component mixtures with variable compositions was studied, and the optimized configurations before and after consolidation were determined by a rigorous method. The results indicated that for the separation of an ideal mixture, the IVB rule was applicable for the whole composition range, while for the separation of a non-ideal mixture, the IVB rule was only applicable for very limited composition range. Finally, two cases of synthesizing distillation configurations for the separation of non-ideal mixtures were studied to verify the remarkable deviations the IVB rule may cause. The results indicated that the applicability of the shortcut method using the IVB rule to the distillation configuration synthesis depended on the composition of the non-ideal mixture, and a remarkable error might result and the truly optimal configuration might be missed if the IVB rule is applied to a non-ideal mixture.     

Pressure relief of nonideal mixtures: Composition trajectories and residue curve maps

During the course of a pressure relief discharge from a vessel containing a multicomponent liquid mixture, composition changes occur that affect the properties of the vessel contents. In this work, a model of the dynamic relief process for ternary, nonideal, homogeneous mixtures is developed, under the assumption of vapor-only venting. Opening/reclosing of the relief valve introduces state-events, which require reinitialization of the model at each state transition. The relationship between the pressure relief model and the concept of residue curves, which describe simple-distillation processes, is demonstrated. It is known that the presence of azeotropes and distillation boundaries in mixtures restricts the composition trajectories of simple-distillation processes, as well as continuous distillation columns at total reflux. In this work, the residue-curve analogy is extended to vapor-only pressure-relief, where vapor composition changes directly affect the operation of the pressure-relief device. Examples of dynamic relief processes are developed for ternary mixtures with varying nonideality.     

A generalized procedure for the prediction of multicomponent adsorption equilibria

Prediction of multicomponent adsorption equilibria has been investigated for several decades. While there are theories available to predict the adsorption behavior of ideal mixtures, there are few purely predictive theories to account for nonidealities in real systems. Most models available for dealing with nonidealities contain interaction parameters that must be obtained through correlation with binary‐mixture data. However, as the number of components in a system grows, the number of parameters needed to be obtained increases exponentially. Here, a generalized procedure is proposed, as an extension of the predictive real adsorbed solution theory, for determining the parameters of any activity model, for any number of components, without correlation. This procedure is then combined with the adsorbed solution theory to predict the adsorption behavior of mixtures. As this method can be applied to any isotherm model and any activity model, it is referred to as the generalized predictive adsorbed solution theory. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2600–2610, 2015     

Definition von Destillationslinien bei der Trennung von Mehrstoffgemischen

Definition of Distillation Lines in the Separation of Multicomponent Mixtures. In recent years “distillation lines” have been used for the assessment of the separation behaviour of multicomponent mixtures, with these distillation lines being defined differently by different authors. The theory of distillation of multicomponent mixtures shows that it is appropriate to distinguish between residue lines and rectification lines. While the profile of residue lines is determined solely by the thermodynamic phase equilibrium, that of rectification lines also depends upon the mass transfer model used. By analogy with VDI Guideline 2761: “Thermal Separation Processes in Process Engineering”, it is proposed that residue lines and rectification lines are designated by the collective term distillation lines.     

Global optimization of multicomponent distillation configurations: 2. Enumeration based global minimization algorithm

We present a general Global Minimization Algorithm (GMA) to identify basic or thermally coupled distillation configurations that require the least vapor duty under minimum reflux conditions for separating any ideal or near‐ideal multicomponent mixture into a desired number of product streams. In this algorithm, global optimality is guaranteed by modeling the system using Underwood equations and reformulating the resulting constraints to bilinear inequalities. The speed of convergence to the globally optimal solution is increased by using appropriate feasibility and optimality based variable‐range reduction techniques and by developing valid inequalities. The GMA can be coupled with already developed techniques that enumerate basic and thermally coupled distillation configurations, to provide for the first time, a global optimization based rank‐list of distillation configurations. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2071–2086, 2016     

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.     

Design and synthesis of multicomponent thermally coupled distillation flowsheets

The design and synthesis of thermally coupled distillation flowsheets for separations of five-component mixtures are studied. Four types of possible configurations are identified when simple and complex columns are both considered in a flowsheet. A universal design procedure is developed for design of any types of the identified configurations based on the abstraction of the three basic units in the flowsheets. Two examples demonstrated that this shortcut design method can be used in design of any types of the identified multicomponent thermally coupled distillation flowsheets, as well as give very good initializations for rigorous simulation of such configurations. Moreover, with a proposed computer representation of all the types of the feasible configurations, a synthesis algorithm is developed for synthesizing of multicomponent complex distillation flowsheets with both simple and complex columns. It is practical by the proposed methods for optimal design of multicomponent distillation systems in an extended search space to include the complex distillation flowsheets for industrial problems.     

Comparison of methods for characterization of complex mixtures

Comparative calculations of several methods of characterization for three multicomponent mixtures that include paraffin, naphthene, and aromatic fractions are shown. Each method requires different experimental information about the mixtures but all use the numerical Gauss-Legendre quadrature. The results show that characterization making direct use of the TPB distillation curve is the most suitable approach for characterizing complex multicomponent mixtures.