Separation of Butyric Acid with Methyl Isobutyl Ketone and Zwitterionic Buffers (EPPS/MOPSO/HEPES/TAPS) Based on Liquid Liquid Equilibrium Experiments and a Quantum Chemistry Approach

Abstract

The aim of this study is to examine the ATPS consisting of butyric acid, water, MIBK, and a biological buffer at T = 293.15 K and atmospheric pressure. The zwitterionic buffer effect as a green auxiliary agent was also investigated using four different biological buffers, i.e., N-[tris (hydroxymethyl)methyl]-3-aminopropanesulfonic acid (TAPS), 2-hydroxy-3-(morpholin-4-yl)propane-1-sulfonic acid (MOPSO), 4-(2-hydroxyethyl)-1-piperazine propanesulfonic acid (EPPS), and 2-(4-(2-hydroxyethyl)-1-piperazinyl)-ethanesulfonic acid (HEPES). Based on the experimental findings, the performance of extraction followed the sequence HEPES > MOPSO > EPPS > TAPS, which also indicated the effectiveness of buffering-out. Two thermodynamic models, the nonrandom two-liquid (NRTL) and the universal quasi-chemical (UNIQUAC), successfully correlated the experimental ATPS LLE data. The enthalpies of mixing were used to predict the sigma profile and energy interactions of butyric acid, water, MIBK, and the zwitterionic buffer. The molecular interaction via excess enthalpies of water and butyric acid was greater than that of MIBK and butyric acid. In addition, quantum chemical calculations were performed to study the interactions between MIBK–water and MIBK–butyric acid via the reduced density gradient (RDG). The results showed that the separation of butyric acid with MIBK from an aqueous solution was dominated by hydrogen bonding and vdW forces.