Raúl H. López

Monte Carlo Simulation Strategies for Predicting CO2/CH4 Adsorption onto Activated Carbons from Pure Gas Isotherms

The problem of predicting the adsorptive properties of activated carbon (AC) towards a mixture of gases from the simple knowledge of the adsorption properties of the pure components is addressed, with special reference to the CO2/CH4 mixture. The adsorption process for the pure gases and their mixtures was simulated using the Grand Canonical Monte Carlo (GCMC) method and the calculations were then used to analyze experimental isotherms for the pure gases and for mixtures with different molar fractions in the gaseous phase. It was shown that the pore-size distributions (PSDs) “sensed” by each of the pure probe gases was different one from the other and also from the PSDs “seen” by the mixture. A mixing rule for combining the PSDs corresponding to the pure gases is proposed for obtaining predictions regarding the adsorption of the corresponding mixtures, which are then compared with those arising from the classical IAST approximation. For this purpose, selectivity curves for CO2 relative to CH4 have been calculated and compared with experimental values. It was concluded that, for the adsorbate/adsorbent system under study, the proposed GCMC mixed model was capable of predicting the binary adsorption equilibrium, and especially the selectivity, more accurately than the IAST.

Is the Alexander–Orbach Conjecture Suitable for Treating Diffusion in Correlated Percolation Clusters?

How does a particle diffuse inside a percolation cluster? This question is of both scientific and practical importance, e.g. in drug-controlled release and vapour adsorption. Diffusion in fractal media is characterized by the fracton dimension, ds. The Alexander and Orbach conjecture indicates that ds = 4/3 for diffusion in classical percolation clusters and, after much research on the subject, it is still provides a very good approximation for ds in the case of uncorrelated percolation cluster structures. However, what happens to the value of ds when a particle is moving inside a correlated percolation cluster? In this work, this problem is studied via Monte Carlo computer simulation. Our results show that the Alexander and Orbach conjecture is not always fulfilled.

On the universal behavior of sorption isotherms in disordered mesoporous solids

Abstract Adsorption–desorption isotherms in disordered mesoporous solids, described by the Dual Site-Bond Model, are obtained through Monte Carlo simulations and their behavior is correlated to the topological properties of the porous networks and to their percolation properties, extending previous results to the general case of variable connectivity networks. A quasi-universal curve is found which may be useful in the problem of obtaining pore size distributions from the analysis of experimental Adsorption–desorption isotherms.