This chapter delves into the application of supersonic flow phase change behavior for CO2 separation in CO2-rich natural gas (NG) offshore processing, highlighting its pivotal role in CCUS technology. A condensation model based on real gas thermodynamics was developed to accurately assess CO2 heat and mass transfer. Compared to the ideal gas model, the real gas model demonstrates superior prediction accuracy for supersonic CO2 condensation (RMSE = 0.0147). Sensitivity analysis reveals that the ideal gas model underestimates liquid CO2 fraction at the Wilson point by 2.8% and overestimates latent heat by 20.1% at that point. A predictive model for Wilson point supercooling, pressure, and expansion rate was established, facilitating future CO2 separation predictions in supersonic flows. Innovatively integrating the entropy transfer equation into the Euler–Euler–Euler real gas numerical model enables simulation of the CH4-CO2 system’s carbon capture process. Model accuracy was verified through CO2 condensation and supersonic separator experiments. Simulation outcomes indicate that optimal CO2 separation efficiency and minimized energy consumption occur with inlet heterogeneous droplet mass concentrations between 5 and 7.5 kg/m3. Analysis of supersonic nozzle and separator simulations shows that higher pressures enhance CO2 condensation efficiency; under supercritical and constant pressures, lowering inlet temperature or increasing CO2 mole fraction significantly boosts condensation rates. Regarding separation, increasing inlet heterogeneous droplet mass concentration from 0.1 to 7.5 kg/m3 escalates carbon separation from 3.33 to 4.43 t/h. Energy loss per kilogram of condensed CO2 decreases from 436.57 to 329.56 kJ/kg, indicating easier decarburization with higher foreign core concentrations. Furthermore, economic parameter analysis comparing supersonic CO2 capture technology with other separation methods underscores its potential. Key future challenges include obtaining adequate experimental and simulation data, optimizing structural designs and operating parameters, and enhancing the effectiveness of supersonic CO2 capture technology in addressing global energy and environmental challenges.