Aqueous 2-Methylimidazole for CO ₂ /H ₂ Separation: Phase Equilibrium Experiment, Process Modeling and Sensitivity Analysis

Hydrogen is regarded as a promising alternative to fossil fuels; however, approximately 95% of the global hydrogen supply still comes from “gray hydrogen”, with high carbon emissions. Efficient separation of CO2 and H2 is a key challenge in gray hydrogen production. This study proposes a novel H2 recovery process based on an aqueous solution of 2-methylimidazole (2-MeIm). The 2-MeIm aqueous solution possesses both strong CO2 absorption capacity and easy desorption performance, which can reduce energy consumption. Pure component solubility experiments were carried out at temperatures ranging from 283.15 to 353.15 K and pressures ranging from 0 to 2.0 MPa, yielding 66 sets of pure CO2 solubility data and 15 sets of pure H2 solubility data, which were used to regress the binary interaction parameters of the NRTL model. Comparison between the fitted NRTL model parameters and the experimental data indicates that the mean relative error of CO2 is 5.19%, whereas that of H2 is only 0.18%. Further, single-equilibrium-stage phase equilibrium experiments were conducted using a mixed gas stream with a CO2/H2 molar ratio of 40:60 to further validate the accuracy of the fitted NRTL parameters. The results demonstrate that the solubility-based fitted model achieves a mean absolute error (MAE) of 0.03 for gaseous CO2 and a mean relative error (MRE) of 0.93% for liquid-phase CO2, indicating high predictive accuracy. Based on Aspen Plus, this study has developed a rigorous process simulation model with a processing capacity of 100,000 N m3/h. The operating conditions were defined through sensitivity analysis, resulting in the following optimized parameters: 7 theoretical stages for the absorber, an operating pressure of 3.8 MPa, a volumetric gas-to-liquid ratio of 200, and a desorption temperature of 373.15 K. Under these conditions, H2 purity and recovery reached 99.99% and 99.13%, with specific energy consumption of only 260.27 kgoe/t H2 (10.88GJ/t H2). Compared with the conventional Rectisol process, the 2-MeIm-based process not only achieves higher H2 purity and recovery rate, but also significantly reduces total energy consumption by 32.07%. This marked performance enhancement underscores the outstanding energy-saving potential of the 2-MeIm system in the field of H2/CO2 separation.