Kinetic study of CH4 hydrate formation in the presence of tetrabutylphosphonium chloride (TBPC)

Methane hydrate is considered as an excellent choice for transporting and storing natural gas. To improve the hydrate formation conditions, adding semiclathrate hydrate formers was strongly recommended. The major objective of this study was to investigate formation kinetics of tetrabutylphosphonium chloride (TBPC) + CH4 semiclathrate hydrate. Using isobaric kinetics measurement, the experiment was conducted systematically with various pressures (P: 4.0 MPa, 6.0 MPa), temperatures (282.1 K, 275.2 K, subcooling degree of 6 K), and salt concentrations (w: 0.05-0.30 mass fraction). Total gas consumption, normalized gas consumption, salt-to-hydrate conversion, rapid growth rate, and gas consumption percentage were calculated. The results revealed that for TBPC + CH4 hydrate salt-to-hydrate conversion was greatly affected by the concentration of TBPC. And the gas consumption percentage was found to reach 0.5 in the first 2 h for TBPC + CH4 hydrate. For designing gas storage process and fast hydrate formation process, the system with (w = 0.05, P = 6.0 MPa, subcooling degree of 6 K) and system with (w = 0.10, P = 6.0 MPa, T = 282.1 K) were recommended, respectively.