Shuanshi Fan

Capturing CO2 by forming hydrate is an attractive technology for reducing the greenhouse effect. The most primary challenges are high energy consumption, low hydrate formation rate, and separation efficiency. This work presents efficient capture of CO2 from simulated flue gas (CO2 (16.60 mol %)/N2 binary mixtures) by formation of semiclathrate hydrates at 4.5 and 7.1 °C and feed pressures ranging from 2.19 to 7.31 MPa. The effect of 0.293 mol % tetra-n-butyl ammonium bromide (TBAB) and tetra-n-butyl ammonium fluoride (TBAF) on the hydrate formation rate, reactor space velocity, and CO2 separation efficiency was studied in a 1 L stirred reactor. The results showed the hydrate formation rate constant increased with increasing feed pressure and reached the maximum at 2.82 × 10−7 mol2/(s·J) with TBAB and 8.26 × 10−7 mol2/(s·J) with TBAF. The space velocity of the hydrate reactor increased with increasing feed pressure and reached a maximum of 13.46 h−1 with TBAB and 25.96 h−1 with TBAF. CO2 recovery was about 50%, and the optimum CO2 separation factor with TBAF was 36.98, which was about 4 times higher than that with TBAB in the range of feed pressure. CO2 could be enriched to 90.40 mol % from simulated flue gas under low feed pressure by two stages of hydrate separation with TBAF. The results demonstrated that TBAB, especially TBAF, could accelerate hydrate formation. The space velocity of the hydrate reactor with TBAB or TBAF was higher than that with THF. CO2 could be easily enriched in the hydrate phase by two stages of hydrate separation under gentle conditions.

The methane hydrate was formed in a pressure vessel 38 mm in id and 500 mm in length. Experimental works on gas production from the hydrate-bearing core by depressurization to 0.1, 0.93, and 1.93 MPa have been carried out. The hydrate reservoir simulator TOUGH-Fx/Hydrate was used to simulate the experimental gas production behavior, and the intrinsic hydration dissociation constant (K0) fitted for the experimental data was on the order of 104 mol m-2 Pa-1 s-1, which was one order lower than that of the bulk hydrate dissociation. The sensitivity analyses based on the simulator have been carried out, and the results suggested that the hydrate dissociation kinetics had a great effect on the gas production behavior for the laboratory-scale hydrate-bearing core. However for a field-scale hydrate reservoir, the flow ability dominated the gas production behavior and the effect of hydrate dissociation kinetics on the gas production behavior could be neglected.

Hydrate formation data of CO2-rich mixtures, three binaries (CO2 + CH4, CO2 + C2H6 and CO2 + N2) and one quaternary (CO2 + CH4 + C2H6 + N2), in water and aqueous sodium chloride solutions were measured. The measurements were carried out in a transparent sapphire cell by applying an isothermal pressure search method in the temperature range 264 K to 284 K and the pressure range 0.5 MPa to 5.0 MPa.