The hybrid ionic liquid (IL) − amine solvents have demonstrated high efficiency in CO2 capture. However, rigorous simulations of carbon capture processes employing IL-amine blended solvents have been scarce. This study presents detailed thermodynamic modeling and process simulations for carbon capture in the steel process and natural gas combined cycle (NGCC) power plant. We investigated two hybrid solvent systems, i.e., [BMIM][BF4]/PZ/MDEA and [BMIM][TF2N]/PZ/MDEA with the blended amine PZ/MDEA used as a benchmark. The phase equilibria of the CO2-PZ-MDEA-H2O-IL system was regressed with the NRTL model. The CO2 molar loading in the lean solvent (αlean) and mass fraction of ILs (xIL) in the mixture solvent were optimized to minimize the regeneration energy (Qreg) of the capture processes. The results indicate that the [BMIM][TF2N]/PZ/MDEA-based process is most energy-efficient (Qreg = 2.845 GJ/tCO2 at αlean = 0.14 and xIL = 1.0 wt%) for the steel plant and (Qreg = 2.749 GJ/tCO2 at αlean = 0.08 and xIL = 1.5 wt%) for the NGCC power plant. Compared to the PZ/MDEA-based benchmark process, IL's inclusion led to a 2.90 % and 0.11 % reduction in the regeneration energy for the steel process and NGCC power plant, respectively, demonstrating the benefit of introducing IL into the amine solvents for CO2 capture.

Direct Air Capture (DAC) is regarded as an effective method to decrease the concentration of CO2 in the atmosphere and thus alleviate the greenhouse effect. This article conducts a comparative analysis of the CO2 emissions of 12 state-of-the-art DAC technologies. The evaluations consider regional (EU, USA, and China) and temporal (years 2023, 2030, and 2050) energy supply variations. It is found that the CO2 emissions generally decrease over time for all the different regions considered. The best CO2 emission performance is found in Europe, followed by the United States and China. The evaluation also finds that currently a substantial number of DAC technologies could not achieve net-negative emission, especially for China. In 2050, most of the DAC technologies are found to perform significantly better in terms of their negative emission performance. We also found that the utilization of fossil fuels, especially coal, needed to operate the DAC process, substantially hinders its ability to achieve net-negative emission. Electrochemical-based technologies are found to outperform others in all scenarios, especially when powered with renewable electricity. The DAC technologies relying on steam-based sorbent regeneration can greatly reduce their CO2 emission when low-carbon energy is used for steam generation. Finally, in all the different scenarios, the DAC technologies incorporating high-temperature calcination regenerations exhibit the worst performance due to the lack of low-emission energies for generating fired heat.