UNIFAC

About: UNIFAC is a research topic. Over the lifetime, 2241 publications have been published within this topic receiving 65265 citations.

Local compositions in thermodynamic excess functions for liquid mixtures

Abstract: A critical discussion is given of the use of local compositions for representation of excess Gibbs energies of liquid mixtures. A new equation is derived, based on Scott's two-liquid model and on an assumption of nonrandomness similar to that used by Wilson. For the same activity coefficients at infinite dilution, the Gibbs energy of mixing is calculated with the new equation as well as the equations of van Laar, Wilson, and Heil; these four equations give similar results for mixtures of moderate nonideality but they differ appreciably for strongly nonideal systems, especially for those with limited miscibility. The new equation contains a nonrandomness parameter α12 which makes it applicable to a large variety of mixtures. By proper selection of α12, the new equation gives an excellent representation of many types of liquid mixtures while other local composition equations appear to be limited to specific types. Consideration is given to prediction of ternary vapor-liquid and ternary liquid-liquid equilibria based on binary data alone.

Statistical thermodynamics of liquid mixtures: A new expression for the excess Gibbs energy of partly or completely miscible systems

Abstract: To obtain a semi-theoretical equation for the excess Gibbs energy of a liquid mixture, Guggenheim's quasi-chemical analysis is generalized through introduction of the local area fraction as the primary concentration variable. The resulting universal quasi-chemical (UNIQUAC) equation uses only two adjustable parameters per binary. Extension to multicomponent systems requires no ternary (or higher) parameters. The UNIQUAC equation gives good representation of both vapor-liquid and liquid-liquid equilibria for binary and multicomponent mixtures containing a variety of nonelectrolyte components such as hydrocarbons, ketones, esters, amines, alcohols, nitriles, etc., and water. When well-defined simplifying assumptions are introduced into the generalized quasi-chemical treatment, the UNIQUAC equation reduces to any one of several well-known equations for the excess Gibbs energy, including the Wilson, Margules, van Laar, and NRTL equations. The effects of molecular size and shape are introduced through structural parameters obtained from pure-component data and through use of Staverman's combinatorial entropy as a boundary condition for athermal mixtures. The UNIQUAC equation, therefore, is applicable also to polymer solutions.

Introduction to chemical engineering thermodynamics

Abstract: Preface 1 Introduction 2 The First Law and Other Basic Concepts 3 Volumetric Properties of Pure Fluids 4 Heat Effects 5 The Second Law of Thermodynamics 6 Thermodynamic Properties of Fluids 7 Applications of Thermodynamics to Flow Processes 8 Production of Power from Heat 9 Refrigeration and Liquefaction 10 Vapor/Liquid Equilbrium: Introduction 11 Solution Thermodynamics: Theory 12 Solution Thermodynamics: Applications 13 Chemical-Reaction Equilibria 14 Topics in Phase Equilibria 15 Thermodynamic Analysis of Processes 16 Introduciton to Molecular Thermodynamics Appendixes A Conversion Factors and Values of the Gas Constant B Properties of Pure Species C Heat Capacities and Property Changes of Formation D Representative Computer Programs E The Lee/Kesler Generalized-Correlation Tables F Steam Tables G Thermodynamic Diagrams H UNIFAC Method I Newton's Method Author Index Subject Index

Group‐contribution estimation of activity coefficients in nonideal liquid mixtures

Abstract: A group-contribution method is presented for the prediction of activity coefficients in nonelectrolyte liquid mixtures. The method combines the solution-of-functional-groups concept with a model for activity coefficients based on an extension of the quasi chemical theory of liquid mixtures (UNIQUAC). The resulting UNIFAC model (UNIQUAC Functional-group Activity Coefficients) contains two adjustable parameters per pair of functional groups. By using group-interaction parameters obtained from data reduction, activity coefficients in a large number of binary and multicomponent mixtures may be predicted, often with good accuracy. This is demonstrated for mixtures containing water, hydrocarbons, alcohols, chlorides, nitriles, ketones, amines, and other organic fluids in the temperature range 275° to 400°K.

A modified UNIFAC model. 2. Present parameter matrix and results for different thermodynamic properties

Abstract: Several years ago a modified UNIFAC (Dortmund, FRG) method was proposed, which shows various advantages when compared with the group contribution methods UNIFAC or ASOG; the latter are used worldwide for the synthesis and design of rectification processes. These advantages were reached by using a modified combinatorial part and by using a large data base to fit temperature-dependent group interaction parameters simultaneously to vapor-liquid equilibrium (VLE), liquid-liquid equilibrium (LLE), h E , and γ ∞ data. The main advantages of the modified UNIFAC method are a better description of the temperature dependence and the real behavior in the dilute region and that it can be applied more reliably for systems involving molecules very different in size. To increase the range of this applicability, the temperature-dependent group interaction parameters of the modified UNIFAC has been fitted for 45 main groups using phase equilibrium information (VLE, h E , γ ∞, LLE) stored in the Dortmund Data Bank. A comprehensive comparison with the results of other group contribution methods confirms the high reliability of the modified UNIFAC (Dortmund) method