ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Liquid-liquid equilibria of butyric acid for solvents containing a phosphonium ionic liquid

Ján Marták and Štefan Schlosser

Institute of Chemical and Environmental Engineering, Faculty of Chemical and Food Technology, Slovak University of Technology, Radlinského 9, 81237 Bratislava, Slovakia

E-mail: stefan.schlosser@stuba.sk

Received: 14 June 2007  Revised: 2 August 2007  Accepted: 3 August 2007

Abstract: L/L equilibrium data of butyric acid (BA) in aqueous solutions contacted with the solvents containing ionic liquid (IL), trihexyl-(tetradecyl)phosphonium bis 2,4,4-trimethylpentylphosphinate (Cyphos IL-104), and a related model are presented. IL-104 and its solutions in dodecane were found to be effective solvents of BA. The values of the distribution coefficients of BA were higher than those for solvents with the widely used extractant trioctylamine, especially at low acid concentrations and were also several-fold higher than those of lactic acid (LA). IL extracted BA only in its undissociated form (BAH) at pH well below pK _a of the acid. The loading of IL was independent of IL concentration and it achieved a value higher than four at saturation. Complexes with 1–5 molecules of BA per one IL molecule were supposed in the mass action model in which the reactive formation of complexes (BAH) _p (IL)(H₂O)₂ was supposed. Up to 10 % of the total extracted BA was extracted physically by dodecane as a monomer and dimer, in the solvent. The water content in the organic phase steeply decreased with the BA concentration, which was caused by splitting water-IL reverse micelles due to the formation of the BAH/IL complexes.

Keywords: extraction - L/L equilibria - butyric acid - phosphonium ionic liquid - modelling

Full paper is available at www.springerlink.com.

DOI: 10.2478/s11696-007-0077-5

Chemical Papers 62 (1) 42–50 (2008)