Citric acid (2-hydroxypropane-1,2,3-tricarboxylic
acid) is a tricarboxylic acid, naturally presents in several fruits,
vegetables, and in the milk. Commercially, citric acid is usually found as a
white crystalline solid and it has several industrial applications. This acid is
widely used in food and pharmaceutical industries because of its various
functions, such as acidulant, food preservative, chelating agent, carbonic gas
fixer, humectant, emollient, and others. In this work, the authors aimed at the
study of citric acid solvent extraction in order to establish the composition
of the organic phase and to obtain thermodynamic and kinetic data for the
chosen system.
Discontinuous
extraction experiments in a single stage were performed from a synthetic
solution of citric acid, with the typical concentration (10% w/v) observed in
industrial fermented musts. Exploratory experiments were carried out by using
different organic phases in order to select the most suitable solvent phase to
further continuous extraction tests in a mechanically agitated column. The
selected organic phase composition was: Alamine® 336, ExxalTM 13
tridecyl alcohol, and the aliphatic diluent EscaidTM 110.
The effects of the
contact time and of the concentrations of extractant and modifier on the citric
acid extraction were also studied. Among the investigated conditions, the best
one was 10 minutes of contact time, 30% w/v of Alamine® 336,
and 10% w/v of ExxalTM 13 tridecyl alcohol. For this condition,
the equilibrium isotherm (28°C ± 2°C) was determined, and the equilibrium
constant was calculated (36.8 (mol·L-1)-1.5). It was
considered that trioctylamine and citric acid complexation reaction occurred
mainly with non-dissociated citric acid form because the aqueous feed
solutions’ pH was lower than the citric acid pKa1. It was found that 1.5
molecules of the extractant, on average, were required to react with one citric
acid molecule, which could indicate that reactions with different
extractant/citric acid ratios occurred simultaneously.
Next, the rate
constants for the direct and inverse reactions, 2.10 (mol·L-1)-1.5·s-1 and
5.69 × 10-2 s-1, respectively, were calculated.
Coefficients of determination (R2) values higher than 0.93 were
found in these calculations, suggesting that the results obtained using a
computer modeling would be very close to those results obtained experimentally.
Therefore, the
present work provided data required to future modelling, design, and simulation
of citric acid solvent extraction processes.
Article by Estêvão
Magno Rodrigues Araújo, et al, from Federal University of Minas Gerais (UFMG),
Belo Horizonte, Brazil.
Full access: http://mrw.so/CmhDm
Image by Marina Nadal, from Flickr-cc.
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