Vapour–liquid equilibrium of carboxylic acid–alcohol binary systems: 2-Propanol + butyric acid, 2-butanol + butyric acid and 2-methyl-1-propanol + butyric acid

Isothermal vapour–liquid equilibrium (VLE) data were measured for alcohol–carboxylic acid systems using a dynamic recirculating apparatus operated isothermally. For super-atmospheric pressures, a stainless steel version of the apparatus was used with sight glasses in the Cottrell pump and liquid and condensate sampling chambers to observe flow patterns. Data are presented for 2-propanol + butyric acid, 2-butanol + butyric acid, and 2-methyl-1-propanol + butyric acid at 333.15 K, 353.15 K, and 373.15 K. To account for vapour phase non-ideality the iterative procedure of Prausnitz et al. [J.M. Prausnitz, T.F. Anderson, E.A. Grens, C.A. Eckert, H. Seih, J.P. O’Connell, Multicomponent Vapor–Liquid and Liquid–Liquid Equilibria, Prentice Hall, Englewood Cliffs, NJ, 1980], based on the chemical theory and corresponding states correlations, was used to obtain true species concentrations, association constants (Kii), and from these liquid phase activity coefficients. The Lewis fugacity rule was used for the true species fugacity coefficient. For the low pressures and moderate temperatures of the study, only dimerization of the acid in the vapour phase was considered. Satisfactory modelling of the data was obtained with the NRTL equation and also, for the direct (EOS) method, with the cubic-based Soave–Redlich–Kwong equation of state and the Wong–Sandler mixing rules. The high non-ideality of the vapour phase for the mixtures studied was confirmed by the considerable departure of the vapour phase correction factors, Φi, from unity. The thermodynamic consistency of the data is shown by the area test and the more rigorous Van Ness point and direct tests.