The studied quaternary reaction system is water + sec-butyl alcohol + sec-butyl acetate + acetic acid.

The liquid-liquid equilibrium data for this quaternary system were determined at 303.15–333.15 K and atmosphere pressure.

The LLE model was established with consideration of the chemical equilibrium of the reversible reaction.

The measured LLE data were used to correlate the binary interaction parameters of the NRTL and UNIQUAC models.