Solvent Extraction of Citric Acid with Different Organic Phases

Abstract

The present work 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 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, Exxal TM 13 tridecyl alcohol, and the aliphatic diluent Escaid TM 110. Next, the effects of the contact time and of the concentrations of extractant and modifier on the citric acid extraction were 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 Exxal TM 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 occurs mainly with non-dissociated citric acid form, because the aqueous feed solutions’ pH is lower than the citric acid pKa1. It was found that 1.5 molecules of the extractant, on average, are required to react with one citric acid molecule, which can indicate that reactions with different extractant/citric acid ratios occur 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 (R 2 ) 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 provides data required to future modelling, design, and simulation of citric acid solvent extraction processes.