Predicting liquid-liquid equilibria of amine extraction of carboxylic acid through solvation energy relation

Abstract

Long-chain, aliphatic tertiary amines (e.g., Alamine 336 or 308) dissolved in suitable organic solvents are known to be effective extractants for carboxylic acids. A log-basis approach SERAS (solvation energy relation for amine systems) has been proposed to estimate the properties and liquid-liquid equilibria (LLE) of amine/diluent/organic acid associated systems containing protic and nonprotic components. The model combines the solvatochromic parameters of solvation energy of solution with the thermodynamic factors derived from a group-contribution method, i.e., UNIFAC-Dortmund activity-coefficient model. The reliability of the model has been analyzed against the LLE data for distribution of pyruvic (2-oxopropanoic) acid between water and Alamine 308 (triisooctylamine) dissolved in C-6-ring-included diluents of proton-donating and -accepting (cyclohexanone, methylcyclohexanol), polar (1,2-dichlorobenzene), and inert (toluene) types. The proposed solvatochromic approach SERAS is expected to be an improvement in data fit clarifying the simultaneous impact of hydrogen bonding, solubility, and thermodynamic factors of components on LLE. The model matches the experimental data, yielding a mean relative error of +/- 13.9%. The results were also correlated using a version of the mass-action law, i.e., a chemodel approach comprising the formation of one or two acid-amine complexes.