Molecular simulation of cage occupancy and selectivity of binary $THF-H_2$ s2 hydrate

Abstract

The hydrogen capacity of the binary $THF-H_2$ sII hydrate is determined by the cage occupancy and by the selectivity of guest molecules. Grand canonical Monte Carlo (GCMC) simulation is used to study the cage occupancy and selectivity of guest molecules from the equilibrium configuration of the binary sII hydrate. The cage framework is regarded as a rigid body and the number of guest molecules is varied to preserve the grand canonical ensemble. The occupancy and selectivity were investigated at a temperature of 270K for pressures ranging from 0.1 to 200 MPa. It was found that most large cages select THF as guest molecules while small cages include only hydrogen molecules. Multiple occupancy of hydrogen, up to 4 molecules in large cages and 2 molecules in small cages, was found as the pressure increases. GCMC results show that the hydrogen capacity is approximately 1.1 wt% at 200 MPa.