Phase equilibrium for clathrate hydrates formed with difluoromethane and N-methylpiperidine for hydrate-refrigeration system

This paper reports the pressure-temperature conditions for the three-phase aqueous liquid + hydrate + vapor equilibrium in the hydrate formed with water, difluoromethane and methylpiperdine as large molecule guest compound (LMGC). The aim of the study is to obtain a hydrate formed in mild pressure-temperature conditions which could be applied to various technologies. To measure the pressure-temperature phase equilibrium, isochoric method^[1] was used. The pressure and temperature ranges of the present measurements are from 61.9 to 104.2 kPa and from 259.3 to 272.2 K. Obtained results were comparatively mild conditions than the phase equilibrium p-T condition of the structure I hydrates formed with water + difluoromethane. To alleviate the phase equilibrium condition, the LMGCs showed its significance through this study. In addition, the cage structure of formed hydrates was measured by powder X-ray diffraction measurements. The hydrate samples were made using the difluoromethane and N-methylpiperidine. The measurement results indicated the cage structure of hydrate as structure H. Thus, the molecular size of difluoromethane was confirmed as the suitable size for the small cages of structure H.