Thermal Dissociation Behavior and Dissociation Enthalpies of Methane–Carbon Dioxide Mixed Hydrates (original) (raw)

Enthalpies of Dissociation of Pure Methane and Carbon Dioxide Gas Hydrate

2014

In this study the enthalpies of dissociation for pure methane and pure carbon dioxide was calculated using a hydrate equilibrium data obtained in this study. The enthalpy of dissociation was determined using Clausius-Clapeyron equation. The results were compared with the values reported in literature obtained using various techniques. Keywords—Enthalpies of dissociation, methane, carbon dioxide, gas hydrate, natural gas.

Experimental determination of dissociation temperatures and enthalpies of methane, ethane and carbon dioxide hydrates up to 90 MPa by using a multicycle calorimetric procedure

Fuel, 2022

This work presents the application of a multicycle procedure to determine the dissociation temperature and enthalpy of gas hydrates using high-pressure microcalorimetry (HP-µDSC). In the multicycle procedure, a sample of water in contact with the gas undergoes successive cooling and warming cycles below hydrate dissociation temperature, increasing the conversion of water into hydrate. This technique has been previously used in literature to increase water conversion during carbon dioxide hydrate formation up to 2.0 MPa, but its applicability has not been assessed for higher pressures and with different guest molecules. New experimental equilibrium data for methane, ethane, and carbon dioxide hydrates were obtained through HP-µDSC up to 90 MPa using the multicycle procedure. The advantages and limitations of the method are discussed. Dissociation temperatures are in good agreement with data previously obtained from a HP-µDSC standard method, which confirms the reliability to determine this property by both methods. Nevertheless, the enthalpy of hydrate dissociation obtained by the direct integration of thermograms provided by the HP-µDSC standard method is not accurate. Thus, it is usually calculated by using the Clapeyron equation from equilibrium temperature and pressure data obtained by the HP-µDSC standard method, as presented in previous work. The new dissociation enthalpies presented in this work were obtained experimentally by direct integration of thermograms using the multicycle procedure, which provides accurate data as the conversion is very high (above 97% of water converts into hydrate), the baselines are clearly established, and no exothermic peak related to metastable phases is observed.

Thermally Assisted Dissociation of Methane Hydrates and the Impact of CO2 Injection

The largest amount of methane gas is trapped in lessconventional natural gas resources, such as methane hydrates. It is estimated that these reserves of methane gas, in the form of hydrates, are larger than all of the conventional resources of methane gas combined. [U.S. Energy Information Administration (EIA), Independent Statistics and Analysis, Potential of Gas Hydrates Is Great, but Practical Development Is Far of, http://www.eia.gov/todayinenergy/detail.cfm?id=8690\]. Methane extraction from hydrates can be coupled with carbon dioxide sequestration to make this process carbon-neutral. A large-scale laboratory reactor is used to simulate the conditions existing in permafrost hydrate sediments to study the hydrate formation and dissociation processes. The dissociation process occurs via a cartridge heat source (to simulate the down-hole combustion) and carbon dioxide injection, to study the CO2 sequestration behavior. The hydrate sediment studied was formed with 50% saturation of hydrate by pore volume and the dissociation of this sediment was done using different combinations of high and low heating rates (100 W and 20 W) and high and low CO2 injection rates (1000 and 155 mL/min). Two baseline tests were conducted without any addition of heat at CO2 injection rates of 155 and 1000 mL/min, for comparison. The results indicate that, at a constant heating rate, the number of moles of methane recovered decreases with an increasing flow rate of CO2 injection, whereas the number of moles of CO2 sequestered increases as the CO2 injection flow rate increases. At 50% initial hydrate saturation (SH) and a heating rate of 100 W, the number of moles of methane recovered decreased from 96 to 58 when the CO2 injection rate was increased from 155 mL/ min to 1000 mL/min, respectively. Whereas, at 50% initial saturation and a heating rate of 100 W, the number of moles of CO2 sequestered increased from 13 to 40 when the CO2 injection rates were increased from 155 mL/min to 1000 mL/min. The recovery efficiency improved from 18% to 22% to 60% when the heating rate was increased from 0 to 20 W to 100 W, respectively, at 1000 mL/min CO2 injection.

Heat capacity and heat of dissociation of methane hydrates

AIChE Journal, 1988

The objective of this study was to determine the heat capacity and heat of dissociation of methane hydrates. A technique has been devised which circumvents the two major problems encountered in measuring gas hydrate heat capacity: the need to impose a mechanical pressure during the measurement and the need to have an absolutely pure hydrate sample. The technique was shown to be successful utilizing high-pressure, constant-volume cells in a differential scanning calorimeter.