Salting-out extraction of carboxylic acids

Developing economic and feasible technology for recovery of carboxylic acids is a challenge for their industrial production. Salting-out extraction of carboxylic acids (formic, acetic, propionic, lactic, succinic, and citric acids) was studied using a system composed of ethanol and ammonium sulfate. The system parameters influencing the extraction efficiency, such as tie line length, phase volume ratio, acid concentration, temperature, and system pH were evaluated. The results showed that partition coefficient of carboxylic acids increased or decreased linearly as tie line length increased, and strongly depended on the system pH. However, the varied phase volume ratio alone the selected tie line, acid concentration and temperature nearly had no effect on the partition coefficient of carboxylic acids in this system, although the recovery increased obviously as the phase volume ratio increased. Correlation of the hydrophobicity (ClogP) of carboxylic acids with natural logarithm of partition coefficient (ln K), indicated that the extraction efficiency was improved as hydrophobicity of carboxylic acids increased.