Simulation of Isoenthalps and Joule-Thomson Inversion Curves of Pure Fluids and Mixtures

Abstract

This paper examines the molecular simulation of expansion and compression processes of fluids under common non-isothermal conditions. It is shown that accurate isoenthalps can be traced if simulated configurational properties obtained from the particular molecular force-field adopted are complemented by experimentally-based data for the ideal-gas contributions to the heat capacity. The simulation of inversion curves is also analyzed and found to be particularly challenging as conventional extrapolation techniques have limited applicability. Several approaches were investigated to overcome such difficulties including (1) simulation of several isobars and isoenthalps, (2) thermodynamic integration, and (3) histogram reweighting techniques. Contrary to the results of a recent study, our calculations show that the Johnson et al., equation of state does provide a good description of the inversion curve for the Lennard-Jones fluid. Isoenthalps and the inversion curve for a model gas condensate mixture were also simulated; calculations of this sort could be used to identify conditions at which isoenthalpic decompression leads to heating of hydrocarbon reservoir fluids.

Joule–Thomson inversion curves of mixtures by molecular simulation in comparison to advanced equations of state: Natural gas as an example

“…via compressibility [30,31] or via thermal expansivity [32], to simulate the JT inversion curve. Work on more complex fluids is still scarce, examples are Escobedo et al [33] (nitrogen), Chacín et al [35] (carbon dioxide), Lísal et al [36] (R32), Kristóf et al [37] (hydrogen sulphide), or a recent work of our group [25] dealing with fifteen different pure substances (including methane, carbon dioxide, R134a, R143a, R152a) and the mixture air. Two publications, dealing with multi-component natural gas mixtures, should be mentioned: Escobedo et al [33] predicted the JT inversion curve for a seven-component system, but compared it to cubic EOS data only.…”

“…Work on more complex fluids is still scarce, examples are Escobedo et al [33] (nitrogen), Chacín et al [35] (carbon dioxide), Lísal et al [36] (R32), Kristóf et al [37] (hydrogen sulphide), or a recent work of our group [25] dealing with fifteen different pure substances (including methane, carbon dioxide, R134a, R143a, R152a) and the mixture air. Two publications, dealing with multi-component natural gas mixtures, should be mentioned: Escobedo et al [33] predicted the JT inversion curve for a seven-component system, but compared it to cubic EOS data only. A favourable comparison between simulation and experiment was presented by Lagache et al [38] regarding the JT inversion pressure of a 20-component mixture for one specified temperature.…”

“…Most publications on JT inversion curves by molecular simulation are based on the spherical Lennard-Jones (LJ) model [26][27][28][29][30][31][32][33], which is appropriate only for simple molecules like methane and the noble gases. However, this simple potential model is well suited to further develop molecular simulation techniques for determining JT inversion as reliable simulation data is available for comparison.…”

From Organic Geochemistry to Statistical Thermodynamics: the Development of Simulation Methods for the Petroleum Industry

“…This author having also proposed an alternative method adapted to the calculation of dew pointsfor which the direct algorithm is unstable-it was decided not to further pursue the development of this type of algorithm. In fact, Escobedo in the meantime proposed an algorithm for isenthalpic calculations (Escobedo and Chen, 2001) and the azeotrope calculation algorithms progressed (Pandit and Kofke, 1999). It would have been difficult to stand up to this competition.…”

Molecular Dynamics Simulations of Volumetric Thermophysical Properties of Natural Gases

“…Simulations were performed in the NVT ensemble with a united atom approach for alkanes leading to viscosity deviations of 7 % and 11 % for the gaseous and liquid states, respectively. Escobedo and Chen, 2001, developed a NPT Monte Carlo study for the prediction of JouleThomson inversion curves for several fluids, including pure methane and a gas condensate mixture (with alkanes up to C7), leading to reliable predictions. Lagache et al, 2001, reported a study in which NPT Monte Carlo simulations were performed to compute second order derivatives of the Gibbs energy for simple alkanes up to butane and for the methane -ethane binary mixture.…”