Excess thermodynamic properties of chainlike mixtures. II. Self-associating systems: predictions from soft-SAFT and molecular simulation

Abstract

The excess thermodynamic behaviour of self-associating binary mixtures of chainlike molecules is studied using modified statistical associating fluid theory, the so-called soft-SAFT equation of state. The chainlike molecules are described as Lennard-Jones spherical segments tangentially bonded together. The associating Lennard-Jones chains are modelled considering additional embedded off-centre square-well bonding sites. This model, which accounts explicitly for the most important microscopic features of real non-associating and associating chainlike molecules, such as repulsive and attractive forces between chemical groups, the connectivity of the segments to form the chains and the specific interactions (association), is also solved using the Monte Carlo molecular simulation technique. Comparisons between theoretical predictions and simulation results for selected mixtures are made in order to assess the adequacy of the theory in predicting excess properties. Agreement between simulation and soft-SAFT predictions indicates that the theory is able to provide a good description of the major excess properties. The theory is used also to study the effect of the molecular parameters on the excess properties of self-associating binary mixtures, with particular emphasis on the effect of association (including the bonding energy and number of associating sites) and chain length. The thermodynamic behaviour of these systems is governed by a delicate interplay between two important effects: the bond breaking of the structure formed by the associating molecules and the interstitial accommodation of the non-associating chains within the branched multimeric structure of the associating fluid. The theory is able to explain qualitatively the most salient features of the excess properties in real systems, including positive, negative and sigmoidal shape behaviour. After an in depth analysis of the effect of the association and chain length, an application of soft-SAFT that includes some quantitative comparisons with experimental excess volumes for n-alkane + 1-alcohol binary mixtures is presented.

Prediction of Thermodynamic Derivative Properties of Pure Fluids through the Soft-SAFT Equation of State

“…The different extensions and implementations of soft-SAFT − made it readily applicable to phase equilibria calculations of different types of fluids, including associating and nonassociating fluids, linear, homonuclear and heteronuclear chains, pure fluids, and binary and ternary mixtures. The equation is also applicable to the calculation of interfacial , and critical properties of pure fluids and mixtures. , Another recent extension of the equation, performed by Blas and co-workers, deals with the calculation of excess thermodynamic properties. − Until now, soft-SAFT has been applied to correlate and predict the phase behavior of several experimental systems, showing excellent agreement in all cases. − A challenging test would be to check the capability of the equation to provide other thermodynamic properties, such as derivative properties. In particular, it should be investigated if the equation provides the physics behind derivative properties, such as some of the singularities observed experimentally.…”

Group contribution methodology based on the statistical associating fluid theory for heteronuclear molecules formed from Mie segments

“…Properties such as the excess volume 145 at a pressure of p = 0.10132 MPa. The continuous curves represent the predictions with SAFT-γ Mie group contribution approach, and the dashed curves the corresponding description with SAFT-γ SW. 66,67 and enthalpy have been the subject of numerous studies, 115 including among others the seminal work of Flory and coworkers [138][139][140] and more recently the work of Blas and coworkers [141][142][143] within the SAFT framework. An example of the performance of the SAFT-γ Mie approach is illustrated in Figure 15, where the predictions of the theory are compared to experimental data for the excess speed of sound (u E ) of selected n-hexane + n-alkane binary mixtures 144 (cf.…”

Excess Thermodynamics of Mixtures Involving Xenon and Light Linear Alkanes by Computer Simulation

“…27 In Table 9, the theoretical predictions from dos Ramos et al are compared with the present results and experimental data for the equimolar excess functions studied. As can be seen, simulation data and SAFT predictions deviate from experimental results in the same qualitative way for the systems xenon + propane and xenon + butane, the SAFT values being closer to the experiment than the simulation data.…”