Measurement of partition coefficients of carboxylic acids between water and triisooctylamine dissolved in various diluents

Tertiary amines dissolved in organic diluents are attractive extractants for the recovery of carboxylic acids from dilute aqueous solutions. This paper reports experimental results for liquid-liquid equilibrium in organic/aqueous two-phase systems containing a tertiary amine (triisooctylamine) and five carboxylic acids, aconitic, citric, lactic, malic, and oxalic acid. Triisooctylamine (tris[6-methylheptyl]amine) was dissolved in various diluents such as chloroform, a mixture (heptane (50 vol %) + 1-hexanol (50 vol %)), and l-octanol. Partition coefficients for individual acids were determined at a temperature of 25 degrees C over a range of amine concentration in each diluent between 2.5 vol % and 60 vol %. Thus, for aconitic, citric, lactic, malic, and oxalic acid the maximum values of partition coefficient were found to be 92.7, 47.0, 28.2, 65.2, and 76.0, respectively. For dilute solutions containing less than 3 mass % of acid, it is energetically preferable to remove the solute from the water through liquid-liquid extraction. Owing to the significant partition coefficients obtained with amine diluent systems, the process generates a small extract stream for subsequent regeneration processing. On the other hand, the recovery of solute by evaporation requires the energy intensive vaporization of water. Liquid-liquid extraction can be considered as an effective process for the recovery organic acids present in wastewater from industries such as distilleries, canneries, and wineries.