Molecular simulation of alkene adsorption in zeolites

The adsorption isotherms of various alkenes and their mixtures in zeolites such as silicalite- 1 ( MFI- type), theta- 1 ( TON- type), and deca- dodecasil 3R ( DDR- type) were calculated using the grand canonical Monte Carlo ( GCMC) approach. Additionally, the adsorption of alkene alkane mixtures was simulated. The GCMC approach was combined with the configurational-bias Monte Carlo ( CBMC) method. Effective Lennard - Jones parameters for the interaction between the oxygen atoms of all- silica zeolites and the sp(2)- hybridized groups of linear alkenes were determined using a united atom force field. They were adjusted to the experimental adsorption data of silicalite- 1 ( MFI). The inflection behaviour of the 1- heptene isotherm was investigated in detail. It is shown that, in the inflection region, the 1- heptene molecules alter their end- to- end length depending on their location. The occurrence of a maximum in the mixture adsorption isotherms is attributed to two effects: entropic effects and non- ideality effects. From the mixture simulations some general conclusions concerning the separation of hydrocarbons with silicalite- 1 can be drawn. The transferability of the Lennard - Jones parameters to other zeolites was investigated. Simulations of adsorption isotherms in the zeolites theta- 1 and DD3R and their comparison with experimental data indicate the possibility of transferring the parameters to other all- silica zeolites.