Effects of salting-out and salting-out extraction on the separation of butyric acid

The effects of salting-out and salting-out extraction on the separation of butyric acid from the simulated solution were investigated. Ammonium sulfate, monosodium phosphate and calcium chloride were screened out and showed outstanding salting-out ability under acidic conditions, resulting in a butyric acid-rich top phase with a concentration multiple of 6.5-18.7 and an increased selectivity of butyric acid to acetic acid from 4 to 13.8-50.0. However, the salting-out effect of inorganic salt decreased with the acid concentration, indicating that this method was not effective for separation of butyric acid at low concentration. In contrast, salting-out extraction system composed of monosodium phosphate and ethanol exhibited excellent extraction efficiency for both butyric acid (∼99%) and acetic acid (∼90%). The partition coefficient and recovery yield of butyric acid increased with the acid concentration and system composition, while decreased with the hydrophobicity of extractant. Finally, two-step salting-out and salting-out extraction was employed, as a result, the total recovery yield of butyric acid and acetic acid were 99.4-99.5% and 88.5-88.9%, respectively.