Phase equilibria for Kr hydrate formed with 2,2-dimethylbutane, methylcyclohexane and 1-methylpiperidine

This paper reports the thermophysical properties of hydrates in the (krypton + 1-methylpiperidine, 2,2-dimethylbutane or methylcyclohexane + water) system. Phase equilibrium conditions were measured in the temperature ranges from 274.6 K to 297.3 K at the corresponding equilibrium pressures between 0.532 MPa and 6.246 MPa in the (krypton + 1-methylpiperidine + water) system. In the temperature ranges from 291.2 K to 297.0 K and 290.6 K to 296.8 K, the equilibrium pressure was between 4.035 MPa to 8.936 MPa and 3.993 MPa to 9.128 MPa, in the (krypton + 2,2-dimethylbutane + water) system and (krypton + methylcyclohexane + water) system, respectively. These results indicate that hydrates can be formed under the condition of lower temperature and pressure in the (krypton + 1-methylpiperidine + water) system than in the other two systems. The crystallographic structure of (krypton + 1-methylpiperidine) hydrate was thereby identified to be structure H at 183 K based on the Powder X-ray diffraction (PXRD) measurements. Dissociation heat of (krypton + 1-methylpiperidine) hydrate was estimated to be 73.5 kJ/mol, that is smaller than that of structure II hydrates containing krypton. These results support the potential for (krypton + 1-methylpiperidine) structure H hydrate to be utilized in hydrate-based technologies.