LIQUID-LIQUID EQUILIBRIA OF ACETIC, FORMIC, AND OXALIC ACIDS BETWEEN WATER AND TRIBUTYL-PHOSPHATE PLUS DODECANE

The purpose of this work is to study the extractive capacity of an org anophosphorus compound to recover carboxylic acids from the waste wate r resulting from the ozonation process for the bleaching of pulp in or der to reduce the environment pollution. In this work, the selected so lvent was composed of a mixture of tributyl phosphate (60 vol %) with dodecane (40 vol %) and the solutes under consideration were acetic, f ormic, and oxalic acids. With no exception, it is the undissociated ac id that is extracted by the solvent. Ternary system solubility diagram s water + carboxylic acid + tributyl phosphate and tie-line data were established at the temperature of 25 degrees C. In comparison with the conventional extraction solvents such as alcohols, ketones, or ethers , which involve the solvation of the acid by donor bonds, the more bas ic donor properties of phophorus-bonded oxygen compounds show the stro nger extractive capacity of this group of extractants. Furthermore, th e carbon-bonded oxygen solvents are much more soluble in water and hen ce involve a costly solvent recovery. With regard to the tertiary amin e extractants, which have low residual solubilities in water and high extractive power for several acids, the selectivity of organophosphoru s compounds with respect to an individual carboxylic acid can be consi dered as an attractive property of this category of solvent. In this s tudy, partition coefficients between 0.27 and 1.25 were determined for the separate acids.