Thermodynamic modeling of hydrogen-water systems with gas impurity at various conditions using cubic and PC-SAFT equations of state

Hydrogen (H-2) has emerged as a viable solution for energy storage of renewable sources, supplying off-seasonal demand. Hydrogen contamination due to undesired mixing with other fluids during operations is a significant problem. Water contamination is a regular occurrence; therefore, an accurate prediction of H-2-water thermodynamics is crucial for the design of efficient storage and water removal processes. In thermodynamic modeling, the Peng-Robinson (PR) and Soave Redlich-Kwong (SRK) equations of state (EoSs) are widely applied. However, both EoSs fail to predict the vapor-liquid equilibrium (VLE) accurately for H-2-blend mixtures with or without fine-tuning binary interaction parameters due to the polarity of the components. This work investigates the accuracy of two advanced EoSs: the Schwartzentruber and Renon modified Redlich-Kwong cubic EoS (SR-RK) and perturbed-chain statistical associating fluid theory (SAFT) in predicting VLE and solubility properties of H-2 and water. The SR-RK involves the introduction of polar parameters and a volume translation term. The proposed workflow is based on optimizing the binary interaction coefficients using regression against experimental data that cover a wide range of pressure (0.34 to 101.23 MPa), temperature (273.2 to 588.7 K), and H-2 mole fraction (0.0004 to 0.9670) values. A flash liberation model is developed to calculate the H-2 solubility and water vaporization at different temperature and pressure conditions. The model captures the influence of H-2-gas (CO2) impurity on VLE. The results agreed well with the experimental data, demonstrating the model's capability of predicting the VLE of hydrogen-water mixtures for a broad range of pressures and temperatures. Optimized coefficients of binary interaction parameters for both EoSs are provided. The sensitivity analysis indicates an increase in H-2 solubility with temperature and pressure and a decrease in water vaporization. Moreover, the work demonstrates the capability of SR-RK in modeling the influence of gas impurity (i.e., H-2-CO2 mixture) on the H-2 solubility and water vaporization, indicating a significant influence over a wide range of H-2-CO2 mixtures. Increasing the CO2 ratio from 20% to 80% exhibited almost the opposite behavior of H-2 solubility compared to the pure hydrogen feed solubility. Finally, the work emphasizes the critical selection of proper EoSs for calculating thermodynamic properties and the solubility of gaseous H-2 and water vaporization for the efficient design of H-2 storage and fuel cells.