Extraction of 4-Hydroxybenzoic Acid with Aliquat 336: Equilibrium Studies

• Published in: Solvent extraction and ion exchange Vol. 23; no. 2; pp. 213 - 230
• Main Authors: Santos, Celina M. L., Ismael, M. Rosinda C., Gameiro, M. Lurdes F., Carvalho, Jorge M.R.
• Format: Journal Article
• Language: English
• Published: Taylor & Francis Group 01-03-2005
• Subjects: Aliquat 336; carboxylic acid extraction; Debye-Huckel; Pitzer model
• ISSN: 0736-6299; 1532-2262
• DOI: 10.1081/SEI-200044398

This paper reports a study of the extraction of 4-hydroxybenzoic acid with a mixture of trialkylmethylammonium chlorides (Aliquat 336) dissolved in a mixture of ShellSol T and ShellSol A. The experimental results revealed that the extraction of undissociated 4-hydroxybenzoic acid (HA) with Aliquat 336 (QCl) can be described by the following equation:
while the extraction of anionic 4-hydroxybenzoic acid (A
−
) with Aliquat 336 is described by the following equation:
The thermodynamic equilibrium constants in terms of the aqueous phase for the reactions above were evaluated to be, respectively, K
1,ext
0
=10
(2.18±0.15)
and K
2,ext
0
=10
(0.81±0.11)
at 298 K. The non-ideality of the aqueous phase was taken into account by applying a Setchenov equation for non-dissociated 4-hydroxybenzoic acid, the extended Debye-Hückel equation for dissociated 4-hydroxybenzoic acid, and the Pitzer model for other species in the aqueous solution. The use of K
1,ext
0
and K
2,ext
0
equilibrium constants allowed simulating the dependence of the distribution coefficient (D) on pH in the range 1.5-8.5. The equilibrium results showed that the presence of 1-decanol (ROH) in the organic phase complicates the extraction process. This can be explained by an interaction between QCl and ROH, which reduces the concentration of free QCl. The formation of QCl:ROH species in the organic phase was postulated and the correspondent equilibrium constant was found to be (3.3±0.3)/M.