New vapor−liquid equilibrium (VLE) PTx data for two binary mixtures morpholine with 1-butanol and morpholine with 3-methyl-1-butanol under 13 conditions have been measured through a Sweitoslawski-type ebulliometer. Each set of experimental PTx data has been correlated by five activity coefficient models using a Gauss−Newton (GN) optimization procedure, Wilson single parameter, Wilson single-set data treatment, and two versions of the UNIFAC method. Comparisons were also made between available literature values and published data with the present experimental vapor−liquid equilibrium PTx data. The azeotropic points have been determined using the method of Mixon et al.

Experimental PTx data have been measured and reported for three binary mixtures containing morpholine under 18 conditions using a Sweitoslawski-type ebulliometer. The measured pressure (P), temperature (T), and liquid­(x) composition (PTx) data were correlated by five popular excess free-energy models using the Gauss–Newton (GN) optimization algorithm to obtain the vapor composition and optimized parameters simultaneously. In general, the Margules model had been found to be the best in vapor composition predictions. UNIFAC predictions for the activity coefficients and vapor compositions were also made for each dataset to evaluate the suitability of group interaction parameters published for two UNIFAC versions. However, the results were not compatible with the predictions by the two-parameter models. The binary mixtures studied in the present work exhibited negative deviations from Raoult’s law with a few exceptions. A comparison made between the measured vapor pressure data and the available literature data for four pure components showed good agreement. When the Tx data of methanol–morpholine mixture at 74.26 and 101.32 kPa were compared with the published data, large deviations were observed for the data at 101.32 kPa. Moreover, the pair of activity coefficients at infinite dilution data for each binary system were predicted using Margules and UNIFC models.