Improvements in the experimentation and the representation of thermodynamic properties (iso-p VLE and y^E) of alkyl propanoate + alkane binaries

This paper presents the experimental measurements of isobaric vapor-liquid equilibria (iso-p VLE) and excess volumes (v^E) at several temperatures in the interval (288.15 to 328.15) K for six binary systems composed of two alkyl (methyl, ethyl) propanoates and three odd carbon alkanes (C5 to C9). The mixing processes were expansive, v^E > 0, with (δv^E/δT)_p > 0, and endothermic. The installation used to measure the iso-p VLE was improved by controlling three of the variables involved in the experimentation with a PC. Experimental iso-101.32 VLE data showed a positive consistency with Fredenslund's point-to-point method. Systems of methyl propanoate + heptane and ethyl propanoate + heptane presented azeotropes (x_az,T_az) at (0.844, 351.86) and (0.481, 366.61), respectively. Representations were obtained of pv^E = φ(x,T) and h^E = φ(x,T), using a model proposed previously [Ind. Eng. Chem. Res. 2010, 49, 406], and the behavior of the binary systems studied was interpreted. An adequate extended version of the same model was used to perform a stepwise correlation of the different properties according the following order (x,T,_cp^E)→(x,T,h^E) →(x,T,g^E), positively valuing the multiproperty correlation. The paper conducts a comparison with the results obtained by applying the nonrandom two-liquid (NRTL) model, which were acceptable with the exception of the inadequate reproduction of values of the second derivative of the Gibbs function. The universal functional activity coefficient (UNIFAC) group contribution model did not give a satisfactory representation of the properties for the binaries of this work.