Prediction of thermodynamic derivative properties of fluids by Monte Carlo simulation

Abstract

We compute second order derivatives of the Gibbs energy by Monte Carlo simulation in the isobaricÈisothermal ensemble for Ñuids made of rigid and Ñexible molecules and test the accuracy of the simple interactions potential. The thermal expansivity and the isothermal compressibility can be calculated directly during a simulation run. The total heat capacity is obtained as the sum of the residual heat capacity computed using the Ñuctuation method and the ideal heat capacity, which cannot be determined by Monte Carlo simulation and must be taken from experimental data. The JouleÈThomson coefficient is obtained by the combined use of thermal expansivity and total heat capacity. The Ñuctuation method proves to converge very well, with limitation at low pressure for the JouleÈThomson coefficient. The Ñuctuation method has been extensively tested on pure light hydrocarbons (methane, ethane and butane) in the vapour and liquid states. In the case of methane, we used a united atom Lennard-Jones potential (D.J. Oprzynski, A. and J. Mo ller, Mu ller Fischer, Mol. Phys., 1992, 75, 363). Detailed comparison with experimental heat capacities, volumetric properties and JouleÈThomson coefficients at pressures up to 100 MPa showed excellent agreement. The inversion of the JouleÈThomson e †ect is predicted with an excellent accuracy. In the case of ethane and n-butane, we used an anisotropic united atoms potential (P. Ungerer, C.

Molecular Dynamics Simulations of Volumetric Thermophysical Properties of Natural Gases

“…Therefore, considering the results reported in this work, molecular dynamics approach is not able to lead to predictions that may be used for natural gas production, processing or transportation purposes in the present situation. Nevertheless, we think that results reported in this work, and by other authors in the literature (Lagache et al, 2001;Lagache et al 2004), are very promising, and the use of molecular simulation approach to predict complex natural gas like mixtures properties should not be discarded. Therefore studies are being carried out by the authors with the next main objectives: i) Improvement of forcefield parameterizations.…”

“…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. The authors used a united atom potential.…”

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

“…Since then, E. Bourasseau has demonstrated that this potential correctly represented the properties of long chain alkanes (Bourasseau et al, 2002b) and M. Lagache obtained good predictions of thermodynamic quantities derived for ethane and butane (Lagache et al, 2001). This performance should be credited to the physical meaning of the parameters obtained by optimization.…”

“…The work of B. Neubauer had already established the feasibility for calculating one of the properties of natural gases containing several components, with highly encouraging results . It was therefore tempting to grapple with a more difficult problem, namely the prediction of derivative thermodynamic quantities: heat capacity, thermal (Jorgensen, 1986;Lagache et al, 2001). It is in fact possible to calculate the derivative of a mean quantity X with respect to an intensive variable Y by considering the covariance of X and the extensive quantity Z associated with Y:…”

Development and Application of Molecular Simulation Methods for the Screening of Industrial Zeolite Adsorbents

“…This has allowed linear and branched alkane adsorption for a significant range of zeolites to be addressed [10][11][12][13][14][15]. Meanwhile, our group has investigated the adsorption of aromatics in faujasites, a delicate problem in which the location of cations and the electrostatic interactions play a major role [16,17]. The location of cations is also a delicate issue, because it is not always available from experimental measurements and it may be influenced by the presence of water, which is often co-adsorbed in laboratory measurements or in industrial processes.…”