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The replacement process of CH 4 from CH 4 hydrate formed in NaCl solution by using pressurized CO 2 was investigated with a self-designed device at temperatures of 271.05, 273.15 and 275.05 K and a constant pressure of 3.30 MPa. The mass fraction of the NaCl solution was either 0.5 wt% or 1.0 wt%. The effects of temperature and concentration of NaCl solution on the replacement process were investigated. Experimental results showed that high temperature was favorable to the replacement reaction but high NaCl concentration had a negative effect on the replacement process. Based on the experimental data, kinetic models of CH 4 hydrate decomposition and CO 2 hydrate formation in NaCl solution were established. The calculated activation energies suggested that both CH 4 hydrate decomposition and CO 2 hydrate formation are dominated by diffusion in the hydrate phase.

CO2 flooding is an important method for improving oil recovery for reservoirs with low permeability. Even though CO2 could be miscible with oil in regions nearby injection wells, the miscibility could be lost in deep reservoirs because of low pressure and the dispersion effect. Reducing the CO2–oil miscibility pressure can enlarge the miscible zone, particularly when the reservoir pressure is less than the needed minimum miscible pressure (MMP). Furthermore, adding intermediate hydrocarbons in the CO2–oil system can also lower the interfacial tension (IFT). In this study, we used dead crude oil from the H Block in the X oilfield to study the IFT and the MMP changes with different hydrocarbon agents. The hydrocarbon agents, including alkanes, alcohols, oil-soluble surfactants, and petroleum ethers, were mixed with the crude oil samples from the H Block, and their performances on reducing CO2–oil IFT and CO2–oil MMP were determined. Experimental results show that the CO2–oil MMP could be reduced by 6.19 MPa or 12.17% with petroleum ether in the boiling range of 30–60 °C. The effects of mass concentration of hydrocarbon agents on CO2–oil IFT and crude oil viscosity indicate that the petroleum ether in the boiling range of 30–60 °C with a mass concentration of 0.5% would be the best hydrocarbon agent for implementing CO2 miscible flooding in the H Block.

In this work, binary gas mixtures of 92 mol % CH 4 /CO 2 and ternary gas mixtures of 87 mol % CH 4 /5 mol % C 2 H 6 /CO 2 were studied as simulate associated petroleum gas. It mainly consists of two parts: one is the hydrate phase equilibrium of the binary and ternary gas mixtures both in water and 0.293 mol % tetra-n-butyl ammonium bromide (TBAB) solution by isochoric pressure-search method, and the other is the enthalpy of hydrate dissociation calculated by the Clausius−Clapeyron equation. The hydrate phase equilibrium measured temperature ranged from 278.61 to 289.46 K and pressure from 2.12 to 10.06 MPa with 24 points in total. The results show that the hydrate phase equilibrium line of 87 mol % CH 4 /5 mol % C 2 H 6 /CO 2 + water was shifted about 2.4 K toward the higher temperature compared to that of 92 mol % CH 4 /CO 2 + water. After adding 0.293 mol % TBAB, it could be found that the hydrate phase equilibrium line of binary gas mixtures and ternary gas mixtures in 0.293 mol % TBAB(aq) were shifted about 5.3 and 2.7 K toward the higher temperature compared to that of water. Besides, the enthalpy of the hydrate dissociation in 0.293 mol % TBAB(aq) is much higher than that in water. Average enthalpy of the hydrate dissociation of binary gas mixture hydrate increased from 62.46 kJ/ mol in water to 160.21 kJ/mol in 0.0293 mol % TBAB(aq). Meanwhile the average enthalpy of hydrate dissociation of ternary gas mixture hydrate increased from 72.89 kJ/mol in water to 181.61 kJ/mol in 0.0293 mol % TBAB(aq).

Hydrate-based separation and capture technology, as a green and economical gas separation technology, can be used to purify biogas by removing CO 2 to increase the calorific value and energy density. To achieve pilot-scale biogas separation, a 15 L pilot-scale reactor with novel jet impingement stream was designed for fast and efficient CH 4 recovery and CO 2 capture and pure CH 4 was obtained by multistage separation in this work. Hydrate nucleation and growth were enhanced by jet impingement stream in aqueous solution with 5.0 wt % tetrabutylammonium bromide. The space velocity of the reactor reached a maximum value of 557 h −1 ; the gas uptake reached up to 1.00 mol/L at 4.0 MPa; and the fastest time to reach 80% of the rate of gas uptake was about 2.5 min at 3.0 MPa and 277 K. The effects of the pressure and temperature driving force on the CH 4 concentration in residual gas, CH 4 recovery rate, CO 2 capture ratio, and gas hydration rate were studied. By a four-stage hydrate-based gas separation process, the CH 4 concentration could be increased from 50.0 to about 95.1%. This work provides insights for the industrial application of continuous hydrate-based biogas separation.