Computer simulations of the adsorption process of light alkanes in high-silica zeolites

The methods of molecular mechanics (MM), molecular dynamics (MD) and Monte- Carlo (MC) were used to compute adsorption energies and to determine the pr eferred adsorption sites of light alkanes (methane, ethane, propane. n-buta ne, i-propane and neopentane) in silicalite and ZSM-5. In order to compare their performance the same simulation conditions were used in all the calcu lations. The effect of using specific and generic force fields to represent the zeolite was also investigated. For the molecules studied, the MC and M D methods furnished comparable adsorption energies, although the MD results are slightly better when compared to experiments. For the linear akanes, t he MM results are qualitatively correct but only when a specific force fiel d is used to describe the zeolite. For the branched alkanes the MM results are comparable to the MD and MC ones even when a generic force field is use d to represent the zeolite. The Linear alkanes (C-1-C-4) showed equal proba bility of being found in both the straight and sinusoidal channels while th e branched alkanes prefer the channel intersections. (C) 1999 Elsevier Scie nce B.V. All rights reserved.