Lennard-Jones fluid adsorption simulation

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... 

This section is devoted to studying the 2D Lennard-Jones model in order to serve as the basis in applying Steele s theory. In Section IVA the main studies about that model are summarized and commented on. In Section IVB, the most useful expressions for the equation of state of the model are given. In Section IVC we present results about the application of these equations, which are compared with other theoretical approaches to studying adsorption of 2D Lennard-Jones fluids onto perfectly flat surfaces. In Section FVD, the comparison with experimental results is made, including results for the adsorption isotherms, the spreading pressure, and the isosteric heat. Finally, in Section IVE we indicate briefly some details about the use of computer simulations to model the properties both of an isolated 2D Lennard-Jones system and of adsorbate-adsorbent systems. 

FIG. 11 Theoretical adsorption isotherms for a Lennard-Jones fluid on a perfectly flat surface [213] at reduced temperature 0.8. Legend is the same as in Fig. 10, except KM = Knight and Monson [225] computer simulation. 

Adsorption of hard sphere fluid mixtures in disordered hard sphere matrices has not been studied profoundly and the accuracy of the ROZ-type theory in the description of the structure and thermodynamics of simple mixtures is difficult to discuss. Adsorption of mixtures consisting of argon with ethane and methane in a matrix mimicking silica xerogel has been simulated by Kaminsky and Monson [42,43] in the framework of the Lennard-Jones model. A comparison with experimentally measured properties has also been performed. However, we are not aware of similar studies for simpler hard sphere mixtures, but the work from our laboratory has focused on a two-dimensional partly quenched model of hard discs [44]. That makes it impossible to judge the accuracy of theoretical approaches even for simple binary mixtures in disordered microporous media. 

The small spheres are fluid molecules, and the large spheres are immobile silica particles. The top visualizations are for a disordered material and the bottom visualizations are for an ordered material of the same porosity. The visualizations on the left are for the saturated vapor state, and those on the right are for the corresponding saturated liquid state, (b) Simulated adsorption and desorption isotherms for Lennard-Jones methane in a silica xerogel at reduced temperature kT/Sfi = 0.7. The reduced adsorbate density p = pa is plotted vs the relative pressure X/Xo for methane silica/methane methane well depth ratios ejf/Sff = 1- (open circles) and 1.8 (filled circles) [44]. (Reproduced with permission from S. Ramalingam,... 

We first compare our SDA results for the excess adsorption per unit of surface area with the grand canonical Monte Carlo (GCMC) simulation results of van Megen and Snook (vMS) [11]. Calculations were carried out for a Lennard-Jones (LJ) fluid with parameters modeling ethylene in a slit-like carbon pore with a 10-4-3 potential for the solid-fluid potential [12] (see next section). The excess adsorption per unit area, F, is defined as... 

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