Phase Equilibria and the Crystallographic Properties of TBAB-CO2 Semiclathrate Hydrates

Understanding the crystal properties of semiclathrate hydrates is important for their potential application in gas storage and separation. In this work, the phase equilibria of TBAB-CO2 hydrates were measured and hydrates formed from the solutions where TBAB concentrations ranged from 0.01 to 0.32 mass fraction were analyzed using Raman and powder X-ray diffraction. Results showed that the equilibrium pressure of TBAB-CO2 hydrate was more sensitive to temperature than that of simple CO2 hydrate, and the equilibrium temperature also got increased with a rise in TBAB concentration. By measuring the hydrate samples formed at 274 K and 3 MPa, the simple CO2 hydrates could be found distributed randomly and discontinuously in the samples, while the TBAB-CO2 hydrate crystals were relatively large. The simple CO2 hydrate was found to coexist with TBAB-CO2 hydrate, and the TBAB center dot 38H(2)O was the only semiclathrate hydrate structure regardless of the initial concentrations of TBAB. When the TBAB concentration was high, the simple CO2 hydrate was assumed to grow competitively with TBAB-CO2 hydrate