(244e) Equilibrium of Gas Hydrates Using Molecular Dynamics Simulations

Gas hydrates are non-stoichiometric crystalline compounds consisting of water and gas molecules. In gas hydrates, water molecules are connected with each other by hydrogen bonds to form a specific crystal structure named as ?cavity' and gas molecules are captured in cavities. There is no chemical bonding between gas molecules and gas molecules. Gas hydrates are stabilized at low temperature and high pressure conditions, and cause a plugging problem in gas/oil transportation line while natural gas hydrates has a potential to be used as a future energy resources. Equilibrium conditions of various gas hydrates (methane, ethane, propane, ?, etc) have been calculated using Molecular Dynamic Simulation (MD) for a unit cell structure of gas hydrate. In the simulation, we used ?link cell' to calculate short range forces and Ewald sum technique to calculate long range electrostatic forces. The Gaussian thermostat was used to maintain a temperature. For water molecules Jorgansen's TIP4P model was used. With the MD simulation, we calculated the chemical potential for theoretical empty cavities of various gas hydrates based on the distortion theory that assumes the distortion of the hydrate structure due to size of gas molecules captured in water cavity structure. 0.01 to 0.1 ps time step is used during simulation. As an attempt to apply MD simulation to calculate the reference state of gas hydrate, we demonstrate lattice distortion of structure I and II gas hydrates. The chemical potentials for the theoretical empty cavity of various gas hydrates have been calculated and the capacity expansion due to temperature has been also calculated.