US EPA

1596853 

Journal Article 

Extraction of benzene and naphthalene carboxylic acids using quaternary ammonium salts as a model study for the separation of coal oxidation products 

Kawamura, K; Nagano, H; Okuwaki, A 

2005 

1 

Separation Science and Technology
ISSN: 0149-6395
EISSN: 1520-5754 

40 

13 

2761-2771 

English 

10.1080/01496390500326503 

WOS:000233305000012 

http://://WOS:000233305000012
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The ion-pair solvent extraction of benzene- and
naphthalene-carboxylic acids has been investigated as a model study for the separation of coal
oxidation products, which are formed by treatment with alkaline solutions at high temperatures.
It was possible that benzene- and naphthalene-dicarboxylic acids are extracted into several types
of organic solvents with quaternary ammonium ions. The extraction equilibrium constants (K(ex))
for benzoic acid, 1,2-benzenedicarboxylic acid, 1,3-benzenedicarboxylic acid, 1-naphthoic acid,
2-naphthoic acid, 2,3-naphthalenedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid into
chloroform were determined at 20 degrees C. The difference of K(ex) among the aromatic acids was
sufficiently large for designing a separation method for these aromatic acids. It was unexpected
that the extraction of dicarboxylic acids was slower than that of monocarboxylic acids, although
the ion-pair formation of aromatic carboxylate ion with quaternary ammonium ion is normally
considered as a diffusion control reaction in aqueous phase. Thus, this fact suggests that the
phase transfer of the ion-pair from aqueous to organic phase is the rate-determining step.
Liner-free-energy relationship was observed for the monocarboxylic acids using different
quaternary ammonium salts while that was ambiguous for the dicarboxylic acids. This is due to the
steric influence of the counter ions for the magnitude of K(ex).. 

ion-pair solvent extraction; aromatic carboxylic acid; coal oxidation products; hydrothermal reaction products; quaternary ammonium salt