Selective recovery of pyruvic acid from two and three acid aqueous solutions by reactive extraction

With single-stage extraction, approximately 40% of the acetic acid (AA) is preferentially and selectively recovered from the aqueous three-acid solution using 0.1 M trioctylamine (TOA) in 1-octanol. Pyruvic acid is the only solute positively affected by an increase in the TOA concentration; however, the purity of the final extract is compromised by co-extracted acids. The distribution coefficient (KD) values obtained in three-acid solutions are lower than those obtained in single-acid solutions, showing the antagonistic effects due to the presence of other acids. However, in two-acid solutions, the presence of lactic acid (LA) at an initial concentration of about 7-20% (0.05-0.15 M) of that of PA (0.75-0.85 M) causes an increase of 33-80% on the KD of the latter. Using 0.6 M TOA in 1-octanol, 92% of initial PA is recovered from the two-acid solution. The competition with the other acid(s) for ion pair formation and its marked hydrophilicity hinders the extraction of LA from multiple acid solutions. Thus, a successful selective separation is achieved for the three acids present in the aqueous phase. A further increase in the initial concentration ratio of LA to PA in two-acid solution results in reduced KD values for the latter. The maximum separation factor of 54.3 is obtained at the lowest acid ratio (AR, 0.19) and highest TOA concentration (0.6 M). Hence, reactive extraction can be successfully employed to selectively recover PA from two and three-acid aqueous solutions.