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Equilibrium studies on the extraction of lactic acid by means of a mixed extractant (a mixture of tri-n-octylamine and Aliquat 336 in decanol) are carried out. Different ratios between the two extractants are investigated, and the obtained results are compared with those using the individual extractants. The effect of the initial pH of the aqueous solution on the extraction extent is followed in a large interval. The equilibrium pH values are also measured. The obtained results give grounds to conclude that the mixture of a tertiary amine and a quaternary ammonium salt is more efficient than the individual extractants. This makes it particularly appropriate for the recovery of lactic acid from fermentation broth.

The extraction of lactic acid with tri-n-octylamine (TOA) or tri-iso-octylamine (TIOA) dissolved in a mixture of dodecane and a different alcohol was investigated under various experimental conditions. The influence of extractant, modifier, and diluent concentrations on the overall and overall particular distribution coefficients was determined. The obtained results and the observed phenomena were discussed by taking into consideration the mechanism of extraction and the concentration of the interaction product in the aqueous phase.

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Recently, new processes for recovery of monocarboxylic acids have been studied. Among these processes, liquid−liquid extraction has had special attention. This process of extraction is attractive if an adequate solvent is used, which shows high selectivity and efficiency, does not affect the thermal stability of products, and requires low energy consumption. In the present work, extraction equilibria of the systems tributyl phosphate and trioctylamine in organic diluents (decan-1-ol and dodecane), water, and each of five lower monocarboxylic acids were measured at the temperature (20 ± 1) °C. For each studied acid are obtained different extraction isotherms in dependence on the composition of the organic phase. From the treatment of experimental data it is shown that the estimated values of the equilibrium extraction constant and the apparent number of extractant molecules reacting with one molecule of monoacid depend not only on the organic phase composition but also on how they are determined.

The effect of the modifier 1-decanol on the extraction of tartaric acid by the extractants tri-noctylamine (TOA), quaternary ammonium chloride (Aliquat 336), or their mixture in the diluent n-dodecane was studied at different pH values. The effect of the modifier was examined as a function of the initial pH value of the aqueous solution for the three extractants mentioned above. A positive, negative, or no effect of the modifier on the distribution coefficient of tartaric acid was observed in the different cases.

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