Reactive extraction of gallic acid from aqueous solution with Tri-n-octylamine in oleyl alcohol: Equilibrium, Thermodynamics and optimization using RSM-rCCD

Abstract Concern of the recovery of important constituents found in nature, industrial waste streams and fermentation broth, the present study is aimed to recover gallic acid (HGA) from aqueous solution using tri-n-octylamine (TOA) in a non-toxic diluent, oleyl alcohol (OA). The optimal conditions for maximum extraction of HGA (90.1 %) are determined as (i) initial concentration of HGA (CHGA,o) = 0.0588 mol/L, (ii) initial TOA concentration ( C ¯ TOA,o ) = 0.2762 mol/L, (iii) pH = 2.0 and (iv) temperature (T) = 25.0 oC, at atmospheric pressure (101.325 kPa), using response surface methodology (RSM) with rotatable central composite design (rCCD). The statistical analysis with ANOVA is used to model fitness and shows a high coefficient of determination (R2 = 97%). At optimum conditions, the insights of reactive extraction are determined using differential evolution (DE) approach, a bio-inspired algorithm. The apparent stoichiometric coefficient (number moles of acid per mole of extractant, m = 1.28) of reactive extraction, overall equilibrium constant (KE = 85.77) and individual equilibrium constants (K11 = 110.32 and K21 = 1106.77) are calculated. Thermodynamic study at four different temperatures (20, 30, 40 and 50 oC) is also carried out to determine enthalpy (ΔH = -12.97 J/mol), entropy (ΔS = -3.77 J/mol.K) and Gibb’s energy change (ΔG = -12370.44 to -5399.96 J/mol.K) of reactive extraction.