| When confined within the small pores of many absorbent materials, fluids exhibit a variety of novel properties and phenomena. These phenomena are poorly understood at present. However, they play a decisive role in many important industrial, biological and geological processes. In this work, the behavior of fluids and fluid mixtures in microporous materials is studied using a combination of computer simulation, statistical mechanical theory and experimental techniques. The systems of particular interest are methane and other common constituents of natural gas on a single graphite surface or in slit carbon pores.;In our experimental investigation, we measured adsorption isotherms of methane and ethane in activated carbon (AC610) and activated carbon fibers (KF1500 and A10) at pressures up to 10 MPa and at temperatures between 313 and 373 K using a modified direct weighing densimeter. By combining theoretically calculated results with the pore size distribution calculated from previously obtained data, we are able to compare our simulation and theoretical results with those of our experiments.;In our simulation and theoretical investigation, fluid-fluid interactions are modeled by Lennard-Jones potentials. Solid-fluid interactions are modeled by both a uniform 10-4-3 adsorbent-adsorbate potential and a periodically varying adsorbent-adsorbate potential. Simulation techniques used in this work include canonical, grand canonical and Gibbs ensemble Monte Carlo simulation methods. A nonlocal density functional theory used is the one due to Kierlik and Rosinberg. The properties studied include multilayer adsorption, isosteric heat of adsorption, layering transitions, freezing transitions, adsorption hysteresis, capillary condensation, the commensurate-incommensurate transition, vapor-liquid equilibrium and selectivity. The influence of major variables (pore size, structure, temperature, pressure and intermolecular potential) on these properties has been studied. The simulation results and theoretical predictions are compared with experimental results whenever experimental data are available. They are generally in good agreement. Several techniques and results are presented for the first time. Examples include (a) prediction of freezing transitions using molecular simulation methods, (b) resolution of the system size effect on the critical behavior of two-dimensional fluids, (c) application of the Gibbs ensemble simulation technique to study of vapor-liquid equilibrium in two-dimensional adsorbed films, (d) enhancement of the efficiency of particle insertion in simulation studies of adsorption problems by using a biased sampling technique based on the solid-fluid potential, and (e) more realistic choice of the dimensions of a simulation cell to account for the structure of a substrate surface. |
