Improvement of hydrogen clathrate formation by reverse micelles and optimization of the formulative parameters
Résumé
The efficient storage of hydrogen is a critical enabling technology for its wider application in energy sectors, encompassing stationary and portable power generation, as well as transportation. Current methodologies for hydrogen storage, such as high-pressure compression (up to 70 MPa), liquefaction at cryogenic temperatures (20 K), and adsorption onto metal hydrides, all present significant drawbacks [1]. Clathrate hydrates, ice-like crystalline structures formed under moderate temperature and pressure conditions, offer a potentially transformative approach. These inclusion compounds feature a hydrogen-bonded network of water molecules that can encapsulate small guest molecules, including hydrogen, methane, and carbon dioxide. While their formation poses operational challenges in the oil and gas industry due to pipeline blockages, clathrate hydrates have gathered significant research interest for their potential in gas separation and storage/transportation applications. In this contest, clathrate hydrates of hydrogen form at relatively low pressures (e.g., ca. 10 MPa) when a co-former compound is added and could represent a valid alternative in the field of hydrogen storage and transportation for large, stationary applications [2]. In that case, however, the gravimetric amount of stored hydrogen drops to less than 1 wt % from ca. 5.6 wt % without a co-former. Another factor restraining the entrapment of hydrogen into a clathrate matrix appears to be of a kinetic origin, in that the mass transfer of hydrogen into clathrates is limited by the macroscopic scale of the gas–water interfaces involved in their formation. Thus, the enhanced formation of binary (hydrogen + co-former) hydrates would represent a major achievement in the attempt to exploit those materials as a convenient means for storing hydrogen, even for large-size aerospace installations [3]. The aim of this work falls within the PRIN 2022 PNRR project entitled “Low-cost, high-safety hydrogen storage into chemically-enhanced clathrate hydrates for energy storage in planetary infrastructures” (Brave New Worlds, CUP D53D2301693000, funded by the European Union – Next Generation EU) led by the University “G. d’Annunzio” of Chieti – Pescara, the University “Aldo Moro” of Bari, and the National Institute for Astrophysics of Catania as a research units. We present some developments of a kinetically efficient method for preparing hydrogen hydrates, which is based on the formation of amphiphile-aided reverse micelles to reduce the size of hydrate forming gas–water interfaces down to tens of nanometers, and macroemulsions/binary systems. Both in nano- and macro-systems, the THF concentration has been tuned in the range of stability of the clathrates at constant pressure of 10 MPa and temperature of 270 K, starting from its maximum amount and decreasing until the formation of clathrates ceased. We prepared different solutions of 80%, 60%, 40%, 30%, and 20% in THF with respect to the maximum stochiometric concentration of 5.56% for the reverse micelles system; regarding the macroemulsion system, the THF was tuned at 13%, 16% and 19% in function of the partition coefficient between water and isooctane. We found that the kinetics of hydrate formation was enhanced, and also the amount of hydrogen enclathrated was increased as compared to the non-adjuvanted system. It was also observed that a value of 40% of THF is the minimal concentration to stabilize the formation of clathrates. Bibliography [1] Di Profio P, Arca S, Rossi F, Filipponi M. Int J Hydrogen Energy 2009;34:9173–80. [2] Di Profio P, Arca S, Germani R, Savelli G. J Fuel Cell Sci Technol 2007;4:49–55. [3] Di Profio P, Canale V, Germani R, Arca S, Fontana A. J Colloid Interface Sci 2018;516:224–3