Interfacial Tension of Hydrogenated and De-Hydrogenated Organic Hydrogen Carriers: Implications for Hydrogen Geological Storage

Abstract Organic Hydrogen Carriers (OHCs) have emerged as a promising solution for efficient hydrogen storage, addressing one of the key challenges towards enabling hydrogen economy. As the demand for renewable energy and decarbonization intensifies, the need for reliable and efficient large-scale storage and hydrogen transport becomes increasingly crucial. OHC technology offers a promising approach that enables hydrogen to be geologically stored in a liquid form, allowing for safe and convenient handling, distribution, and utilization. The ability of subsurface formations to store geologically is determined by their wetting properties and interfacial forces. These factors significantly impact residual saturations, fluid flow dynamics, injection, withdrawal rates, and containment reliability. To our knowledge, literature has yet to report these properties for most OHCs at natural geological physio-thermal conditions. Therefore, we have measured the interfacial tension of methyl-cyclohexane (MCH; hydrogenated OHC) and toluene (de-hydrogenated MCH) in the presence of one molar NaCl solution at natural physio-thermal geological conditions (T = 298-343 K and P = 1-20 MPa). MCH and toluene were used as a surrounding phase, and one molar NaCl was used as a drop phase. The results suggest that IFT values decrease with temperature and increase with pressure. This is caused by the increased intermolecular interaction of one liquid to the other liquid molecule due to pressure increase, thus increasing the IFT. Similarly, temperature reduces the density of both liquids, causing a reduction in IFT. However, MCH has higher IFT values than the toluene at pressure and temperature conditions similar to the toluene. 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 IFT value for MCH was 54 mN/m (density = 0.7599 g/ml) compared to the toluene = 38 mN/m (density = 0.84762 g/ml). Our findings pave the way towards optimizing safety for sub-surface hydrogen storage, offering a readily scalable solution to enhance energy security and support the transition to a sustainable, carbon-neutral future.