Phase equilibria and dissociation enthalpies for tetra-n-butylammonium chloride semiclathrate hydrates formed with CO2, CH4, and CO2Â +Â CH4

In this work, a high pressure micro-differential scanning calorimeter (HP µ-DSC) was employed to measure the phase equilibrium data and dissociation enthalpies of tetra-n-butylammonium chloride (TBAC) semiclathrate hydrate formed in the presence of CO2, CH4, and CO2 + CH4. The TBAC concentration varied from 1.0 mol% to 5.0 mol%, and the operating pressure changed from 1.0 MPa to 5.0 MPa. It was found that the phase boundary of TBAC semiclathrate hydrate formed at 3.3 mol% TBAC was lower than that obtained at 1.0 mol% and 5.0 mol% TBAC in the presence of CO2 + CH4, and the hydrate dissociation enthalpy obtained at 3.3 mol% TBAC was larger than that obtained at 1.0 mol% and 5.0 mol% TBAC. This result indicates that TBAC semiclathrate (TBAC·29.7H2O) formed at the stoichiometric concentration (3.3 mol%) was more stable than that formed at 1.0 mol% and 5.0 mol% TBAC in the presence of CO2 + CH4. In addition, pure TBAC semiclathrate hydrate and the mixed TBAC + CO2 + CH4 semiclathrate hydrate were found to coexist at 1.0 mol% TBAC. The hydrate dissociation enthalpy for the mixed TBAC + CO2 + CH4 semiclathrate hydrate formed at 3.3 mol% TBAC was found to increase with the increase of pressure. This is probably because a larger amount of the CO2 + CH4 gas mixture was incorporated into the TBAC semiclathrate hydrate at a higher pressure.