Molecular Simulation Of Adsorption And Diffusion Of Nitrogen Compounds In Zeolites

The adsorption properties of pyridine nitrides (including pyridine, 2,6-dimethylpyridine and 2,4,6-trimethylpyridine), Ammonia and amine nitrides (including dimethylamine and trimethylamine) has been investigated by Grand Canonical Monte Carlor simulation method (GCMC). The diffusion properties of Ammonia and amine nitrides(including dimethylamine and trimethylamine) has been investigated by molecular dynamics method (MD) in various zeolites.By comparing the simulated isosteric heats to the values from the literatures, the suitable force fields and reasonable precision were selected to set up the appropriate models for the adsorption systems of pyridine nitrides and amine nitrides in zeolites in the manner of single component simulation by GCMC. Based on these models, the adsorption isotherms, isosteric heats and adsorption sites were predicted. The results are as follows:1. The order of adsorption capacities for pyridine nitrides in holo-silicon type MOR zeolites is pyridine > 2,6-dimethylpyridine > 2,4,6-trimethylpyridine. The sorption capacities for pyridine nitrides in holo-silicon type MOR zeolites at 573K are higher than that at 773K.2. The order of isosteric heats for pyridine nitrides is LTA > MFI > MOR > FAU when the silica/alumina ratio is a constant.3. There is only one adsorption site when pyridine nitrides adsorbed in FAU zeolites and MOR zeolites at the research conditions.4. The order of adsorption capacities is ammonia > dimethylamine > trimethylamine when Ammonia and amine nitrides adsorbed in holo-silicon type MOR zeolites and FAU zeolites.5. The order of isosteric heats for amine nitrides is trimethylamine > dimethylamine > ammonia when the silica/alumina ratio is 1 in these diffferent zeolites with difinite structures.During the simulation of two components system ( benzene and pyridine derivatives blends) by GCMC , we found that several factors such as the structures of zeolites ( including MOR, FAU and MFI), the contents of benzene, the pressure and the silica/alumina ratio will all influence the adsorption selectivities of zeolites to the obsorbed objects. The results demonstrated that the order of sorption selectivity of zeolites to the obsorbed pyridine derivatives is MOR > FAU. The sorption selectivity decreases as the fraction of benzene increases. But the sorption selectivity increases as the fraction of benzene increases for MFI zeolites.The self-diffusion coefficients for ammonia and amine nitrides in holo-silicon MOR zeolites were obtained by molecular dynamics simulation(MD) at different temperatures and adsorption amount. We found that the self-diffusion coefficients increase when the temperature increases but decrease when the adsorption amount increases.