Ž . Fluid Phase Equilibria 146 1998 161–173 Quaternary liquid–liquid equilibria of systems with two partially miscible solvent pairs: 1-octanol q 2-methoxy-2-methylpropane q water q ethanol at 258C Alberto Arce ) , Manuel Blanco, Ana Soto Chemical Engineering Department, UniÕersity of Santiago de Compostela, E-15706 Santiago, Spain Received 4 November 1997; accepted 17 December 1997 Abstract Ž . Liquid–liquid equilibrium LLE data were determined for the quaternary system 1-octanol q 2-methoxy-2- Ž . methylpropane MTBE q water q ethanol at 258C and atmospheric pressure. The full range of compositions was covered by using pseudoternary systems, each one corresponding to a plane in the tetrahedral phase diagram. The tie-lines for the quaternary mixtures did not always lie within the plane for the corresponding pseudoternary system. The LLE data for the quaternary system, and for its constituent ternary subsystems, were Ž . correlated using the NRTL a s 0.1, 0.2 or 0.3 , UNIQUAC and TK-Wilson equations. Each correlation afforded similar binary interaction parameters for the partially miscible pairs common to the ternary subsystems. Moreover, these parameters differed little from those obtained for these solvent pairs in the quaternary system. The LLE data were predicted using the UNIFAC method and also using the above-mentioned correlation equations, fixing each binary interaction parameter to the value or mean value obtained by correlating the LLE data for the constituent ternary subsystems. q 1998 Published by Elsevier Science B.V. All rights reserved. Keywords: Data; Liquid–liquid; Quaternary; 1-octanol; 2-Methoxy-2-methylpropane; Water; Ethanol 1. Introduction Although quaternary mixtures are frequently encountered in liquid–liquid extraction processes, there has been little attention paid to them as compared to ternary mixtures. In the early 1980s, Ruiz w x and co-workers 16–21 published several interesting papers dealing with quaternary systems and ) Corresponding author. 0378-3812r98r$19.00 q 1998 Published by Elsevier Science B.V. All rights reserved. Ž . PII S0378-3812 98 00212-X