Experimental and Theoretical Equilibrium Insights in the Reactive Extraction of Pimelic Acid with Tri-n-octylamine in Natural Solvents

Abstract

The theoretical and experimental studies on the reactive extraction of pimelic acid (PA) from dilute aqueous solutions with tri-n-octylamine (TOA) in three different green and natural solvents namely, rice bran oil, sunflower oil (SFO), and soybean oil are carried out. In addition, physical extraction (extraction with pure solvent, natural oil) is also studied to determine the partition and dimerization constants. The experiments on reaction equilibria were performed to calculate the extraction efficiencies with variable TOA concentration, PA concentration, type of diluent/solvent, and temperature at atmospheric pressure (101.325 ± 1 kPa). The acid distribution coefficient (KD), degree of extraction (E, %), and loading factor (Z) were calculated as the extraction efficiencies to recover the PA from aqueous solution. The maximum KD (7.76) and extraction yield (88.58%) were obtained for initial PA concentration (CH2P,o= 0.2497 kmol·m–3) with 0.687 kmol·m–3 TOA concentration (C̅S,o) dissolved in sunflower oil. The overall stoichiometry and reaction equilibrium constant (KE) and individual acid-extractant complexation constants (K11, K12, K21, and K31) of 1:1, 1:2, 2:1, and 3:1 PA–TOA complexes in the organic phase and their complex concentrations (C11, C12, C21, and C31) are determined using an equilibrium chemical model and bioinspired genetic algorithm, differential evolution, for better understanding of the reaction mechanism. Moreover, based on extraction conditions, the thermodynamic study is carried out to determine the change in enthalpy (−1320.11 J·mol–1), entropy (−3.63427 J·mol–1·K–1), and Gibbs free energy (−254.72 J·mol–1·K–1) of reactive separation of PA with TOA–SFO.