Comparative experimental and modeling studies of the viscosity behavior of ethanol + C7 hydrocarbon mixtures versus pressure and temperature

The viscosity of the binary system ethanol + n-heptane has been measured with a falling-body viscometer for seven compositions as well as for the pure compounds in the temperature range (293.15 to 353.15) K and up to 100 MPa with an experimental uncertainty of 2%. At 0.1 MPa the viscosity has been measured with a classical capillary viscometer (Ubbelohde) with an uncertainty of 1%. A total of 208 experimental measurements are reported for this binary system. The viscosity behavior of this binary system is interpreted as the results of changes in the free volume, and the breaking or weakening of hydrogen bonds. The excess activation energy for viscous flow of the mixtures is negative with a maximum absolute value of 0.3 kJ·mol, indicating a very weakly interacting system and showing a negative departure from ideality. The data of this binary system as well as those recently measured for ethanol + toluene have been used in a study of the performance of some viscosity models with a physical and theoretical background. The evaluated models are based on the hard-sphere scheme, the concepts of the free-volume and the friction theory, and a model derived from molecular dynamics. In addition to these models, the simple mixing laws of Grunberg-Nissan and Katti-Chaudhri are also applied in the representation of the viscosity behavior of these ethanol + C7 hydrocarbon systems. Overall a satisfactory representation of the viscosity of these two binary systems is found for the different models within the considered T,P range taken into account their simplicity.