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 preferred adsorption sites of light alkanes (methane, ethane, propane. n-butane, i-propane and neopentane) in silicalite and ZSM-5. In order to compare their performance the same simulation conditions were used in all the calculations. The effect of using specific and generic force fields to represent the zeolite was also investigated. For the molecules studied, the MC and MD methods furnished comparable adsorption energies, although the MD results are slightly better when compared to experiments. For the linear akanes, the MM results are qualitatively correct but only when a specific force field 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 used to represent the zeolite. The Linear alkanes (C-1-C-4) showed equal probability of being found in both the straight and sinusoidal channels while the branched alkanes prefer the channel intersections. (C) 1999 Elsevier Science B.V. All rights reserved.