Download Chemical theory for mixtures containing any number of alcohols

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Fluid Phase Equihbria 102 (1994) 61 84
Chemical theory for mixtures containing
any number of alcohols
Scott W. C a m p b e l l
Department of Chemical Engmeering, Umverslty of South FlorMa, Tampa, FL 33620-5350, USA
Received November 8, 1993, accepted an final form May 9, 1994
Abstract
In a previous paper (Pradhan et al_, 1993 Fluid Phase Equlhbrm, 84 183 206) Flory-Hugglns theory, regular
solution theory, and the use of chemical equihbrxa to model hydrogen bonding were combined to form a simple
association model for ternary mixtures containing two alcohols and an alkane In this paper the model is extended
to represent systems containing any number of alcohols and alkanes The chemical equdlbria approach, thought to
be complicated for systems containing more than two alcohols, is actually found to be quite feasible if a suitable
means of counting the associated complexes xs used
The model does not require cross-association equilibrium constants for alcohols to be the geometric mean of the
self-association constants However, this assumption is tested on binary vapor hquld eqmhbrlum data for alcohol
systems and is found to provide acceptable results
In addmon to binary mixtures of alcohols, the model is apphed to binary mixtures of an alcohol and an alkane,
ternary mixtures containing two alcohols and an alkane, and ternary mixtures comprising three alcohols It compares
favorably with the Wdson equatmn and has potentially fewer adjustable parameters
Finally, the model xs compared with statistical assocmtmg fluid theory (SAFT) and the two approaches are found
to be strikingly similar
Keywords Theory, Vapor-hqmd equlhbrla, Associated
1. Introduction
The highly non-ideal solution behavior shown by alcohol-hydrocarbon systems is often
attributed to hydrogen bonding of alcohol molecules. In a mixture of an alcohol with an Inert
species, tt IS generally believed that hydrogen bonding causes the alcohol to form a distribution
of associated complexes and that this distribution changes as the mole fraction of the inert
species changes
Although the thermodynamic properties of such mixtures have been modelled with local
composition equattons and a variety of empirical expressions, it has been of recent interest to
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