Association Mechanism Between Propionic Acid and Trioctylamine

Tertiary amines dissolved in diluents are attractive extractants for recovery of carboxylic acids from dilute aqueous solutions. Quantitative Fourier transform infrared (FTIR) analysis of organic solutions containing various concentrations of trioctylamine (TOA), n-octanol, and propionic acid was carried out, and liquid-liquid equilibrium was investigated using TOA in n-octanol as the solvent. The fraction of ion-pair association between TOA and propionic acid in the organic phase was quantitatively determined by FTIR. The apparent reactive extraction equilibrium constant, K11, was calculated using the quantitative FTIR spectrum and the equilibrium data. The results show that the fraction of ion-pair association depends on diluent concentration, complex dissolution for propionic acid, and association between TOA and propionic acid. The K11 based on quantitative FTIR has the same loading trend as that from the equilibrium data.