MOLECULAR-INTERACTIONS IN TRI-N-BUTYL PHOSPHATE-DILUENT MIXTURES

This model considers both specific chemical and nonspecific physical c ontributions to excess Gibbs energy. Competitive chemical equilibria a re evaluated to describe specific chemical interactions. Molecular siz e, shape difference, and regulation solution terms, based on the ''tru e'' species, are used to describe nonspecific physical interactions. P arameter estimates are obtained by fitting vapor-liquid equilibrium an d hydrogen and phosphorus NMR shift data for three tri-n-butyl phospha te (TBP) and diluent binary mixtures. The thermodynamic equilibrium co nstant for the TBP dimer is a shared parameter since this complex appa rently exists in all binary mixtures. At 22 degrees C, its value is 6. 65 based on the behavior of TBP diluted with either benzene, chlorofor m, or n-heptane. Thermodynamic equilibrium constants for the 1:1 TBP/c hloroform and TBP/benzene complexes are 37.88 and 1.34, respectively. The 1:2 chloroform/TBP dimer complex has an equilibrium constant of 37 .57. Model parameters are used to predict excess molar volumes and ent halpies. Commonly reported stability constants are shown to be concent ration dependent.