CHEMICAL, QUASI-CHEMICAL AND PERTURBATION THEORIES FOR ASSOCIATING FLUIDS
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Pure fluids and mixtures of species that hydrogen bond behave differently from systems that interact only through dispersion forces. The deviations from classical behavior often are sufficiently large that conventional equations of state and activity models cannot be used without the introduction of large, conditiondependent empirical parameters. Consequently, three different classes of theories have been developed specifically to treat hydrogenbonding systems. The first is based on the assumption that when molecules hydrogenbond, they react to form new species and consequently is referred to as chemical theory. The second is based on latticefluid theory that is used to describe different types of specific interactions and is known as quasichemical theory. The last is based on the solution of integral equations using a potential function that mimics that of a hydrogen bond. It is shown here that these three approaches give essentially equivalent results. This allows one to relate the parameters in the perturbation theory to the equilibrium constant and hence greatly improves its utility for real systems. All three theories are compared with simulation data. Copyright 1991 American Institute of Chemical Engineers
