Sulfuric acid extraction with trialkylamine: Effect of xylene and n-octanol as modifiers

The equilibrium of sulfuric acid extraction with trialkylamine was measured at 25 °C. Xylene, n-octanol, and their mixtures with a paraffinic solvent were used as diluents. The effects of the diluent composition and of the amine content in the organic phase on extraction equilibrium were investigated. An increase of the xylene content in the diluent shifted the limit of third-phase formation to higher concentrations of acid in the organic phase. No third-phase formation was observed with pure xylene. With n-octanol, the third phase formed only at the highest amine and lowest modifier contents used. The shapes of the amine loading curves indicated preferential formation of the 1:2 acid/amine complex at lower acid concentrations and of the 1:1 complex and its dimer (2:2) in the high-concentration range. At lower acid contents, a positive synergetic effect of the two modifiers on the equilibrium was observed. In systems with n-octanol, the physical extraction with the modifier contributed to the overall acid extraction. The experimental results were correlated with a mathematical model incorporating chemical reactions of acid/ amine complex formation and nonspecific interactions of species present in the organic phase.