Supercritical fluids Lennard-Jones

Excess Chemical Potential (3pex of the Lennard-Jones Fluid at Supercritical Temperatures... 

A mode coupling theory is recently developed [135] which goes beyond the time-dependent density functional theory method. In this theory a projection operator formalism is used to derive an expression for the coupling vertex projecting the fluctuating transition frequency onto the subspace spanned by the product of the solvent self-density and solvent collective density modes. The theory has been applied to the case of nonpolar solvation dynamics of dense Lennard-Jones fluid. Also it has been extended to the case of solvation dynamics of the LJ fluid in the supercritical state [135],... 

In the present work, we performed MC simulations at different operation conditions, constant fluid density and constant pressure, for calculating K2 to investigate the distribution behavior in the supercritical region. We selected C02, benzene, and graphitic slitpore as a model system by adopting the Lennard - Jones (LJ) potential function for intermolecular interactions. 

Here, k is the Boltzmann constant. The Lorentz-Bcrthelot rule has been adopted for the parameters working between different species of the mixture and the values are thus yilk= 9.% K and a j2=3.405 x 10 1 m, which correspond to the interaction parameters of neat argon. The critical temperature of the Lennard-Jones monoatomic fluids ) evaluated by the integral equation theory is 1.321 multiplied by ( f/k ), which is equal to 111.9 K and 223.8 K for the component 1 and 2, respectively. The temperature set in our present calculation is higher than any of these critical temperature. Thus the fluids discussed in this work are always at supercritical state. 

We propose the study of Lennard-Jones (LJ) mixtures that simulate the carbon dioxide-naphthalene system. The LJ fluid is used only as a model, as real CO2 and CioHg are far from LJ particles. The rationale is that supercritical solubility enhancement is common to all fluids exhibiting critical behavior, irrespective of their specific intermolecular forces. Study of simpler models will bring out the salient features without the complications of details. The accurate HMSA integral equation (Ifl) is employed to calculate the pair correlation functions at various conditions characteristic of supercritical solutions. In closely related work reported elsewhere (Pfund, D. M. Lee, L. L. Cochran, H. D. Int. J. Thermophvs. in press and Fluid Phase Equilib. in preparation) we have explored methods of determining chemical potentials in solutions from molecular distribution functions. 

The adsorption of gas mixtures has been extensively studied. For example, Wendland et al. [64] applied the Bom—Green—Yvon approach using a coarse grained density to study the adsorption of subcritical Lennard-Jones fluids. In a subsequent paper, they tested their equations with simulated adsorption isotherms of several model mixtures [65]. They compared the adsorption of model gases with an equal molecular size but different adsorption potentials. They discussed the stmcture of the adsorbed phase, adsorption isotherms, and selectivity curves. Based on the vacancy solution theory [66], Nguyen and Do [67] developed a new technique for predicting the multicomponent adsorption equihbria of supercritical fluids in microporous carbons. They concluded that the degree of adsorption enhancement, due to the proximity of the pore... 

In order to ascertain whether the 3-regime behavior observed in the experimental vibrational lifetimes is indeed a result of local density enhancements, Goodyear and Tucker [12] computed both vibrational lifetimes and local density enhancements from molecular dynamics simulation for a model solute-solvent SCF solution. These authors considered a diatomic solute in a 2-dimensional supercritical Lennard-Jones fluid of 1150 atoms (Fig. 1). In this model, each of the solute atoms was designated as a Lennard-Jones site, and the Lennard-Jones parameters between solute and solvent atoms were taken to be the same as those between solvent atoms. The vibrational lifetimes were computed using the standard, classical Landau-Teller expression [69,70,72,73,78], i.e. 

Figure 10. Simulated vibrational lifetimes for a simple diatomic solute in a 2-dimen-sional Lennard-Jones supercritical fluid along two isotherms see text.

Yoshii, N. and S. Okazaki 1997, A large-scale and long-time molecular dynamics study of supercritical Lennard-Jones fluid. An analysis of high temperature clusters . J. Chem. Phys. 107, 2020. 

Goodyear, G., M. Maddox, and S. C. Tucker, Density inhomogeneities in the compressible regime of a supercritical Lennard-Jones fluid ., submitted. 

Sweatman, M. B. 2001. Phys. Rev. E. Weighted density funchonal theory for simple fluids Supercritical adsorption of a Lennard-Jones fluid in an ideal slit pore. 63 031102. 

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