Computer simulation of vapor–liquid equilibria of linear quadrupolar fluids. Departures from the principle of corresponding states

Abstract

Improved vapor-liquid equilibria predictions for Lennard-Jones chains from the statistical associating fluid dimer theory: Comparison with Monte Carlo simulations Vapor-liquid equilibria of different quadrupolar linear Kihara fiuids have been studied, by using the Gibbs ensemble Monte Carlo technique. Coexistence curves for fiuids with elongations L * = LI u= 0.3, 0.6, and 0.8 and different quadrupoles are given. We analyze the effect of quadrupole moment on critical properties. Quadrupole moment increases the critical temperature, pressure, and density. The magnitude of the increase depends on both anisotrop~ a~d qu~~~ole moment. A new way of reducing the quadrupole is proposed, so that the vanatlon of cnhcal properties due to the quadrupole follows a universal behavior. Quadrupole provokes deviations from the principle of corresponding states. A broadening of the coexistence curve is observed due to the quadrupole. The quadrupole moment increases the slope of the vapor pressure curve vs temperature inverse. Simulation data are used to describe vapor-liquid eqUilibria of carbon dioxide. Good agreement between simulation and experiment is achieved.4166

Accurate Simulations of the Vapor−Liquid Equilibrium of Important Organic Solvents and Other Diatomics

“…Easier choices 3,31 are possible, but in this case the parameters depend slightly on the particular thermodynamic states used to fit them. Moreover, we have found 19,20 that reduced critical temperatures are independent of elongation for the Kihara potential when a reduced dipole/quadrupole density is properly defined and we have made use of this fact here. The equations used in this work were Alternatively, eq 3 can be written as…”

“…34 No systematic deviation was observed for the most complicated molecular shape or for the presence of internal rotation in the case of perfluorethane. We previously studied this case for carbon dioxide, with excellent results, 20 and we can predict that a model of carbon dioxide without quadrupole would have a critical temperature 60 K lower than the quadrupole model of actual CO 2. We have shown that this behavior is general when reduced quadrupole density is properly defined.…”

“…In Monte Carlo (MC) or Molecular Dynamics (MD) simulation, parameters have the same straightforward physical meaning as in theories but mathematical instruments are conceptually as simple as Newton equations in molecular dynamics or the generation of random numbers in Monte Carlo. 17 In the last few years, we have indeed performed extensive computations on molecular models 18 mimicking linear or quasi-linear or simple nonlinear molecules, including in some cases dipole 19 or quadrupole 20 interactions. These models correspond to a large number of organic solvents widely used in the chemical industry.…”

Determination of phase diagrams via computer simulation: methodology and applications to water, electrolytes and proteins

“…In fact TIP4P provides a quadrupole moment and a ratio dipole/quadrupole in much better agreement with experiment. The effect of a quadrupole moment on the vapor-liquid equilibria of molecular models is well known [232,233,234]. However it seems that the role of the quadrupole on water properties has been overlooked in spite of some warnings about its importance [235,236,237,218,238,239].…”

Current advances in Monte Carlo methods

“…Examples of applications of the method that have appeared in the past year include calculations of phase diagrams for diatomic Lennard-Jones molecules [31], dipolar and quadrupolar fluids [32,33], a realistic potential model for methanol [34] and methyl iodide [35]. Extensions of the technique to reactive and associating systems [36] as well as ionic systems [37] are available.…”