We report the phase diagram and structure of the binary clathrate hydrate (abbreviated as hydrate) of methane + trans-1,3,3,3-tetrafluoropropene (HFO-1234ze(E)) guest molecules by phase equilibrium measurements, powder X-ray diffraction measurements, and molecular dynamics simulations. The four-phase (methane-rich gas + water + HFO-1234ze(E) liquid + solid clathrate hydrate) equilibrium data in the system were measured in the temperature range of 274.3 K to 280.2 K. At temperatures from 274.3 K to 276.6 K, the phase equilibrium pressures of the binary hydrate were lower, by a maximum of 0.27 MPa, than those in a pure methane structure I clathrate hydrate system three phase equilibrium line. This indicates that the hydrate formed from the binary mixture was different from a simple methane hydrate. Powder X-ray diffraction measurements were performed on the binary hydrate sample prepared at 274.3 K and pressures from 2.65 to 2.94 MPa. The X-ray diffraction measurements revealed that a structure II hydrate was formed in the system. This is somewhat surprising as the longest molecular dimension of HFO-1234ze(E) is similar to that of 2-methylbutane that forms a structure H hydrate. To clarify some of the aspects of the behavior of the binary hydrate, molecular dynamics simulations were performed. These calculations show that the HFO-1234ze(E) molecules do not form hydrogen bonds with the cage water molecules but are closely interacting with the cage water molecules via electrostatic and van der Waals interactions.
ASJC Scopus subject areas
- Materials Chemistry