Insights into the phase behaviour of tetra-n-butyl ammonium bromide semi-clathrates formed with CO2, (CO2 + CH4) using high-pressure DSC

Abstract This work investigated the phase behaviour of tetra- n -butyl ammonium bromide (TBAB) semi-clathrates formed with CO 2 , and (CO 2  + CH 4 ) gas mixture using high-pressure differential scanning calorimetry (HP DSC). The phase equilibrium data of TBAB semi-clathrate formed with (40% CO 2  + 60% CH 4 ) in mole fraction were obtained at four TBAB molar concentrations (0.29%, 0.62%, 1.38%, and 2.57%). It was found that (TBAB + CO 2  + CH 4 ) mixed hydrate formed at 2.57% TBAB was more stable than that formed at 0.29%, 0.62%, and 1.38% TBAB, and two types of TBAB semi-clathrate (type A and type B) formed at the same time in the presence and absence of the (CO 2  + CH 4 ) gas mixture. The dissociation enthalpy of TBAB hydrate formed at 0.62% TBAB was higher than those obtained at 0.29%, 1.38%, and 2.57% TBAB. Besides, the phenomenon of liquid CO 2 evaporation was confirmed in the (TBAB + CO 2 ) hydrate formation system with the pressure varying from 3 MPa to 5 MPa. The endothermic heat of liquid CO 2 evaporation was found to be much larger than that for the dissociation of (TBAB + CO 2 ) semi-clathrate hydrate.