Liquid–Liquid Equilibria of Butyric Acid, Water, and Methyl Isobutyl Ketone with the Aid of Biological Buffer as a Green Auxiliary Agent

Biological buffer has a significant impact on aqueous organic phase equilibria in extraction processes. This study investigated the effect of biological buffer on the efficacy of butyric acid extraction from aqueous solution utilizing methyl isobutyl ketone (MIBK) as the extraction solvent. The liquid–liquid equilibria (LLE) of quaternary systems of methyl isobutyl ketone (MIBK) + butyric acid + water + biological buffer MOPS [3-(N)-morpholino propane sulfonic acid], HEPES (2-(4-(2-hydroxyethyl)-1-piperazinyl)­ethanesulfonic acid), or EPPS (4-(2-hydroxyethyl)-1-piperazine propanesulfonic acid) were determined at temperature T = 303.15 K (30 °C) and P = 0.1 MPa (atmospheric pressure). The addition of EPPS to the butyric acid aqueous solution resulted in superior extraction efficacy compared to the other biological buffers, as determined by experimental data. Generally, the extraction performance was in the order EPPS > MOPS > HEPES, which represented the buffering-out strength as well. The non-random two-liquid (NRTL) and UNIversal QUAsi Chemical (UNIQUAC) models fit well with the actual LLE data of the quaternary systems. The σ-profile analysis was also evaluated in this study. Additionally, a potential process flow sheet using biological buffer and MIBK solvent was suggested for removing butyric acid from its aqueous solution.