SIMULATION OF METHANE CONTAINING AIR MIXTURE SORPTION IN SILICALITE
Molecular dynamics simulation technique has been used to investigate nitrogen and methane sorption process in silicalite and sorption of composite methane-containing gas mixture in silicalite. Zeolite type silicalite as hydrophobic material can be useful for making gas sensor, which has response for nonpolar molecules such as methane. The purpose of this work is the investigation of composite air mixture sorption selectivity in silicalite. Simulation has been performed in LAMMPS package. System for research includes 2 × 2 × 2 ZSM-5 unit cells (2304 atoms), 2340 nitrogen molecules, 270 oxygen molecules, 60 water molecules and 30 methane molecules. Bonded intramolecular interactions for all types of molecules and for zeolite framework are represented by two harmonic potentials - one for bond-stretch and one for an-gle-bend - and by torsion angle potential (for modeling rotate along bond). Interatomic potential are presented in Lennard-Jones form. TIP3P model is used for water. Simulations are accomplished using periodic boundary condition. Duration of calculation amount to 18 ns, simulation timestep - 0.5 fs. System temperature varies from 223 K to 473 K. All particles are integrated with NVT ensemble. There are no molecules inside zeolite structure at the initial time. Maximum sorption rate of methane and nitrogen molecules are determined on temperature dependence and come to ~300 K for methane. Inflection point is find out on temperature dependence of maximum zeolite loading and fall on 323 K. We consider that inflection may be caused by dominance of surface adsorption. The study of process sorption for methane-containing air mixture is performed at 273 K and 323 K. The research shows appreciable increase of methane percentage in sorbate mixture from 1 % to 5 % in compared to initial mixture, insignificant increase of oxygen percentage and small decrease of nitrogen one. Water sorption occur in very short time range ~1 ps only on zeolite surface. The results received in study are evidence that hydrophobic ZSM-5 can be used as gas-sensitive film for methane sensor.