Phase equilibria of semiclathrate hydrates for methane + tetra n-butylammonium chloride (TBAC), carbon dioxide + TBAC, and nitrogen + TBAC aqueous solution systems

• The dissociation data of gas + TBAC semiclathrate hydrates were measured.
• Three gases: methane, carbon dioxide and nitrogen are studied.
• TBAC dramatically shifts the hydrate formation (dissociation) conditions to the stabilized region.
• By increasing the concentration of TBAC its promotion effect increases.

The equilibria of semiclathrate hydrates for the systems of tetra-n-butylammonium chloride (TBAC) + water + gas (methane, carbon dioxide, or nitrogen) and TBAC + water were measured. The experiments were performed in the temperature range of 277.1–293.2 K and the pressure range of 1.02–9.83 MPa at 0.05, 0.15, and 0.22 mass fraction of TBAC. An isochoric pressure-search method was employed to generate the phase equilibrium data. The experimental results show that the presence of TBAC moderates the hydrate formation (dissociation) conditions remarkably (in the concentration ranges studied in this work). Moreover, pressure reduction is dependent on TBAC concentration. By increasing the concentration of TBAC from 0.05 mass fraction to 0.22 mass fraction, its promotion effect increases and the pressure–temperature curves of the double gas + TBAC semiclathrate shift to the stabilized regions. The isobaric dissociation temperature of TBAC + methane semiclathrates is close to that of TBAC + carbon dioxide semiclathrates.

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