Usage of Ternary Gas Mixtures to Promote the Capture of Hydrogen into Hydrates: H2/CH4/C3H8 and H2/CH4/C2H6 Case Studies

Following the continuously growing demand and production of hydrogen, effective and high energy-density solutions for its storage need to be explored and validated. The present study deals with the capture of hydrogen into clathrate hydrates, at temperatures above 0 °C and relatively low pressures (<55 bar). As the formation conditions of pure hydrogen hydrates are unsuitable for industrial applications, hydrogen was firstly combined with methane, ethane and propane to form ternary gas mixtures. The role of support gases consisted in fitting both the small and the large cavities of hydrates well, thus ensuring the stability required for the hydrate lattice and allowing to hydrogen molecules to fit easily into the remaining empty cavities. Three different mixtures were selected, and the concentration of each species was defined according to the experimental results achieved in previous studies available in the literature. Chemical promoters were not used at this step, since the goal was to achieve qualitative information about the concentrations of hydrogen achievable with the proposed solution and not to maximize the volume of hydrates produced. For each species and depending on the blend of origin, the concentrations obtained in the hydrate phase were measured and reported in volume and by weight. Under the assumption of 100% cage occupancy, the quantity of each species captured in one cubic meter of hydrate, the energy corresponding to each species and the overall energy stored per unit volume of hydrate were calculated and discussed.