Solvation phenomena in association theories with applications to oil & gas and chemical industries

Abstract

Association theories e.g. those belonging to the SAFT family account explicitly for self- and cross-association (solvation) phenomena. Such phenomena are of great practical importance as they affect, often dramatically, the phase behaviour of many mixtures of industrial relevance. From the scientific point of view, solvation phenomena are also very significant because they are present in different types of mixtures and not just those containing two self-associating compounds e.g. water with alcohols or glycols. Mixtures with only one self-associating compound and in some cases even mixtures with two non self-associating compounds may exhibit solvation specifically due to hydrogen bonding or more generally due to Lewis acid-Lewis base interactions. As examples can be mentioned mixtures with polar compounds (water, glycols...) and aromatic hydrocarbons and aqueous ether or ester solutions. This manuscript presents how a specific association thermodynamic model, which employs SAFT's association term, the so-called CPA (Cubic-Plus-Association) equation of state, can be applied in order to account for various types of interactions due to solvation. The role of combining rules in the association term and the cases where explicit treatment of solvation is needed will be illustrated. Copyright © 2008, Institut français du pétrole.