Partition behavior of monocarboxylic acids in salting-out extraction systems of monohydric alcohols and dipotassium phosphate

Abstract

Abstract Extraction of organic acids has been attracted much attention due to their hydrophilicity, pH-dependence and structural diversity. Partition behavior of seven monocarboxylic acids with different chemical structures, including formic acid, acetic acid, n-propionic acid, n-butyric acid, n-valeric acid, glycollic acid and lactic acid, have been investigated in salting-out extraction systems (SOES) composed of monohydric alcohol (ethanol, isopropanol, n-propanol, or tert-butanol)/K2HPO4. The relative hydrophobicity of the equilibrium phases in the SOES has been characterized by the Gibbs energy of transfer for methylene group from the salt-rich bottom phase to the solvent-rich top phase. The effects of the structures of target products and organic extractants, SOES composition, system pH and temperature on partition behavior were investigated. The results showed that natural logarithm of partition coefficient (ln K) of target products increased linearly with their calculated 1-octanol/water partition coefficient (Clog P), but decreased with the calculated 1-octanol/water partition coefficient of organic extractant. The partition coefficient of target products increased or decreased linearly as tie line length, which depends on their hydrophobicity. The partition coefficient and recovery decreased with the increasing of system pH values. In addition, the increasing of temperature will decreased the extraction efficiency of monocarboxylic acids, because the salting-out extraction is an exothermic process.