ENTHALPIES OF FORMATION OF GAS HYDRATES

摘要

This paper reports the measurement of the enthalpies of gas hydrates for six gas mixtures containing specified amounts of methane,ethane propane,n-butane,iso-butane and carbon dioxide at pressures in the vicinity of 2000 kPa(300 psi)and 6700 kPa(1000 psi)(GPA Research Project No.976 -Part 2).The measurements were made in a multicell differential scanning calorimeter using modified high pressure cells.The gas hydrate was formed by cycling the solution in the vicinity of the ice point.The mass of hydrate formed was calculated from the measurement of the enthalpy of fusion of the remaining ice after the hydrate was formed and then the enthalpy of fusion of the ice after the hydrate was dissociated.The enthalpy of fusion of the ice and the enthalpy of dissociation of the gas hydrate were determined from the calorimeter response during a slow temperature scan from-5 deg C(41 deg F)to 5 deg C(9 deg F)above the hydrate dissociation temperature.The amount of gas released from the dissociation of hydrate was determined from the volume change,measured with a high pressure syringe pump,required to restore the pressure to a known value prior to the hydrate dissociation.The hydrate number(the ratio of the moles of water to moles of gas)has an uncertainty of about 0.2 and the enthalpy of hydrate formation has an uncertainty of about 1.5 %.The results show that the enthalpies of hydrate formation and the occupation number are essentially independent of pressure.