Quaternary liquid–liquid equilibrium: water–phosphoric acid–1-butanol–2-butanone at 25°C

Mutual solubility and tie-line data are presented for the ternary system, water (W)–phosphoric acid (PA)–1-butanol (BuOH) and water–phosphoric acid–2-butanone (methyl ethyl ketone, MEK) at 25°C, as well as for the quaternary system, water–phosphoric acid–1-butanol–2-butanone, at the same conditions. These systems present an unusual behavior since there are no quaternary tie-line planes and the solubility surface presents a shape like a saddle.