Salting-out effect on complexation extraction of monocarboxylic acids

Based on reversible chemical complexation, the complexation extraction is a highly effective and selective separation method which can be used to extract the monocarboxylic acid from its dilute solution. Using trialkylamine as the complex agent, the n-octanol as 'active' polar diluent, the kerosene and toluene as 'inert' diluent, the complexation extractions of acetic acid and butyric acid from their dilute solutions were studied respectively. The salting-out effects of different kinds of salts used (sodium nitrate, sodium chloride and sodium sulfate) on the extraction process were investigated. Experimental results show that extraction distribution ratio increases with the increase of salt concentration, and the salting-out effects on acetic acid are in the order of sodium nitrate < sodium chloride < sodium sulfate. However, the order of the salt-out effects on butyric acid is the inverse of that on acetic acid. The interaction mechanisms among the extractant, carboxylic acid and the salt were analyzed. Based on the experimental data, an empirical equation for the salting-out effect was proposed.