The liquid-liquid equilibrium (LLE) for the system water + ethanol + ethyl
tert-butyl ether (ETBE) has been studied in the temperature range of (288.1
5 to 308.15) K. The NRTL equation and UNIQUAC method were used to regress t
he experimental data. The UNIFAC method was used to predict the phase equil
ibrium in the system using the interaction parameters determined from exper
imental data between groups CH2, CH2O, OH, and H2O. The UNIQUAC and NRTL eq
uations fit the experimental data with a root mean square deviation of 0.36
% for each, while the UNIFAC method predicted the results with a root mean
square deviation of 0.65%.