Measurement and application of limiting activity coefficients

Abstract

Infinite dilution activity coefficients (y") in binary liquid mixtures are data of wide practical and theoretical applicability, but their extensive use has been hindered by the experimental limitations of classical vapor-liquid equilibrium techniques. Two new experimental methods for accurate y" determinations are presented. These techniques, both faster and more accurate than classical methods, are complementary, and their applicability to different types of binary systems is discussed. SCOPEThe modern design and modeling of fluid-phase separation equipment require an accurate mathematical representation of chemical activities in a multicomponent liquid mixture. Solution models now use binary data only to represent a multicomponent mixture, and have proven central to the rational design of distillation, absorption, extraction, stripping, or even crystallization units. Although many sets of binary data exist in the literature, the limiting factor in most multicomponent process designs is in the acquisition of valid binary data needed to determine parameters in the mathematical models. For most miscible organic systems, the existing data are in the form of classical VLE (vapor-liquid equilibria) measurements, which are intrinsically slow and difficult experiments. Further, the resulting data, even if accurate, do not contain the most useful information either for a basic understanding of solution behavior or for practical application.It is the purpose of the current study to demonstrate a different approach to gathering the data needed for studying the solution thermodynamics of binary liquid mixtures as well as for designing multicomponent separations. The advantages of using infinite dilution activity coefficients were first proposed over twenty years ago, and their use in design and scale-up has often been demonstrated. However, the actual measurement of such quantities by classical means-either from VLE or LLE data-is very imprecise, and until recently newer experimental methods have been limited in applicability. This work presents two complementary experimental methods for measuring limiting activity coefficients in a wide variety of organic systems. Since these methods are both easier to use and intrinsically more accurate than the classical techniques, the use of limiting activity coefficients presents useful, new experimental and analytical approaches. CONCLUSIONS AND SIGNIFICANCELimiting activity coefficient (7%) data are most effective both in the description of binary mixtures and in the scale-up to multi-component systems. The limiting activity coefficient characterizes the behavior of a single solute molecule completely surrounded by solvent. As such, it generally indicates a maximum nonideality and offers incisive information to the theorist, since the order-disorder effect disappears; it also offers economy of effort to the experimentalist, since this datum has wider applicability than a measurement at any other concentration.The major reason that yx methods have been little used lies in the dif...

Activity coefficients at infinite dilution of {N-methyl-2-pyrrolidinone (NMP), orN,N- dimethylformamide (DMF), or dimethyl sulfoxide (DMSO)+ 1-heptyne, or 1-octyne } using comparative ebulliometry

“…A differential or comparative ebulliometric technique for measuring the activity coefficient at infinite dilution γ ∞ i has been described by Null (5) and also by Eckert et al (6) It involved boiling a solution in an ebulliometer, connected to condensers through a manifold to a second ebulliometer in which only pure solvent was boiling. Thomas et al (7) has described improvements to the technique, which included most notably the ability to measure a This paper is in memory of Professor Max McGlashan.…”

Determinação do coeficiente de atividade na diluição infinita (<FONT FACE=Symbol>g&yen;</FONT>) através da micro-extração em fase sólida (SPME)

“…O coeficiente de partição do soluto entre o revestimento e a fase gasosa foi calculado a partir da Equação 1 (1) onde K é o coeficiente de partição do soluto; C f e C g são as concentrações no revestimento da fibra e na fase gasosa, no equilíbrio; n f e n o são a massa extraída pelo revestimento da fibra e a massa introduzida no recipiente; V f e V g são os volumes do revestimento da fibra e do recipiente, respectivamente.…”

“…Soluções modelos usam dados binários para representar as misturas multicomponentes quando do projeto de unidades de destilação, absorção, extração, "stripping" ou mesmo de cristalização. Embora existam muitos dados na literatura referentes a sistemas binários, a maioria dos projetos de processos multicomponentes exige o cálculo do coeficiente de atividade na diluição infinita para a obtenção de dados binários válidos, necessários para a determinação dos parâmetros nos modelos matemáticos 1 . As medidas dos coeficientes de atividade na diluição infinita de solutos em uma fase estacionária são normalmente feitas de duas maneiras: pelo método estático, ou através da cromatografia gasosa (CG).…”

Experimental Investigation and Modeling of Activity Coefficient at Infinite Dilution of Solutes Using Dicationic Solvent Based on Pyrrolidinium as a New Stationary Phase in Gas Chromatography

“…This parameter describes the behavior of a solute completely surrounded by solvent molecules. AcHow to cite this paper: Yahyaee, A., Nazifi, M., Kianpour Several methods were developed for the measurement of γ∞ such as dilutor technique (DT) [6] [7], inert gas stripping [6], differential ebulliometry [8], head space [9] and dew point techniques [10]. However, there are some drawbacks, in terms of time, cost and material, associated with each method.…”