Excess Volumes VEm Research Articles

Temperature Dependence of the Volumetric Properties of Binary Mixtures Containing Polyethers and 1-Propanol

Excess molar volumes (VEm) were measured at 288.15, 298.15, and 308.15 K and atmospheric pressure as a function of composition with a continuous dilution dilatometer for the binary mixtures of 1-propanol [CH3CH2CH2OH] with glymes [CH3O(CH2CH2O)mCH3, m=1,2,3, and 4]. With these results and other thermodynamic data from the literature, the following mixing quantities have been reported over the complete range of concentration or at equimolar concentration: α, volume expansivity; αE, excess volume expansivity; (∂VEm/∂T)P, and (∂HE/∂P)T at 298.15 K. The Prigogine–Flory–Patterson theory (PFP) of liquid mixtures has been applied to estimate interaction, free-volume, and internal-pressure contributions to VEm and to estimate the different mixing quantities for the mixtures. The calculated values using the PFP theory were then compared at 298.15 K with the experimentally obtained results. The PFP theory predicts excess volume VEm values rather well, while the calculated value of (∂VEm/∂T)P and (∂HE/∂P)T by using the Flory theory show general variation with the chain length of the glyme. The (∂VEm/∂T)P and (∂HE/∂P)T show deviations between theoretical and experimental values that are slightly larger in systems with lower glyme.

HEm and VEm thermodynamic surfaces for binary mixtures in the near critical region

Abstract Even for such simple mixtures as (argon+methane), the excess enthalpy HEm and the excess volume VEm in the near critical region are about two orders of magnitude higher than for the liquid mixture at low temperatures and pressures near ambient conditions. Mixtures for which the critical temperatures are close together, and for which the critical pressures are far apart, have similar HEm (x,p,T) and VEm (x,p,T) surfaces, and near critical isotherms show double maxima in the supercritical fluid region. Mixtures for which the critical pressures are close together, and the critical temperatures are far apart, also have similar HEm (x,p,T) and VEm (x,p,T) surfaces, but isobars on the surfaces are ‘S’ shaped. The shapes of these near-critical excess-function surfaces can be understood from an inspection of the enthalpy, or residual enthalpy curves of the mixture and of the pure components. Examples of both are given. Attention is drawn to the large value that these excess functions can have close to a pure component critical point.