Abstract
Organic Hydrogen Carriers (OHCs) present an auspicious resolution for competent hydrogen storage, which is essential for realizing a hydrogen-based economy. As the demand for green energy and the need to reduce carbon emissions increase, the importance of safe and effective large-scale hydrogen storage and transportation grows. OHC technology allows hydrogen to be stored underground in liquid form, making it a practical, safe, and efficient method for handling, distributing, storing, and utilizing hydrogen. The distribution of OHCs at the pore scale, the storage capacity of these at the reservoir scale, and the security of their confinement are all greatly affected by interfacial properties. These variables include the equilibrium contact angle (θE), interfacial tension (IFT) between the solid and brine phase (γSL) and solid and OHC phase (γsohc). Nevertheless, due to the technological limitations associated with experimentally obtaining these parameters, they are frequently computed using Young’s equation and Neumann’s equation of state. There is a limited availability of data about θE, γsl, and γsohc, especially about OHCs storage potential, which has not been documented in existing literature.
Therefore, we have integrated Young’s equation and Neumann’s equation of state to theoretically calculate three parameters (θE, γSL, and γsohc) for methyl-cyclohexane (MCH; hydrogenated OHC) and toluene (de-hydrogenated MCH) under reservoir conditions (T = 298-343 K and P = 1-20 MPa; salinity one molar NaCl) with fluid-fluid IFT and advancing and receding contact angles as input parameters for the possible geo-storage of OHCs in carbonate reservoirs.
The study’s findings indicate an increase in 9e with pressure, while there is a drop in γsohc as pressure increase, this behavior is caused by the increased intermolecular interaction between liquid molecules and solid surface, thus increasing the wettability and decreasing the solid-OHC IFT. Additionally, γsl does not show any change in values due to pressure increase, this is due to the negligible change in density of brine with increase in pressure. However, temperature increase causes a reduction in θE and γsl, whereas, increase in γsohc. The results also depict that toluene has higher values for θE than the MCH and lower values for γsl, and γsohc than the MCH at similar pressure and temperature conditions. This is due to the difference in density of a similar compound’s hydrogenated and de-hydrogenated form. For instance, at 10 MPa and 323 K, the density value for MCH is 0.7599 g/ml compared to the toluene = 0.84762 g/ml. The results emphasize the incorporation of OHCs in carbonate reservoirs as an effective approach to improve hydrogen storage potential, tackling thermodynamic, kinetic, and safety issues in hydrogen geo-storage systems. This highlights the necessity of enhancing OHC interactions with geological substrates to boost hydrogen storage efficiency and aid in the progression of sustainable energy solutions.
