Storage and Transportation of Hythane: Thermodynamics, Kinetics, and Stability Studies Using the Gas Hydrates Process

Hydrogen-rich natural gas, popularly known as Hythane or HRNG, has been recently recognized as a safer hydrogen transport and storage mode. At the same time, the conventional method of transporting Hythane has significant safety concerns primarily due to hydrogen embrittlement probabilities. The prime focus of the research on Hythane storage and transportation is necessary to develop Hythane as an immediate solution toward achieving the hydrogen economy. The current study proposes to convert the gaseous components into gas hydrate pellets using the gas hydrate process, thus keeping them enclosed inside hydrogen-bonded water cages to minimize the chance of embrittlement. In this work, Hythane storage using gas hydrate technology has been studied with three different Hythane gas mixtures having hydrogen concentrations of 8, 15, and 30 mol % in methane under 6.0 MPa, a relatively lower pressure for hydrogen gas mixtures. A detailed study includes phase equilibria and micro-DSC study, which helped design a growth kinetics study followed by Hythane hydrate pellet formation and stability investigation. In order to improve the Hythane hydrate growth for industrial applications, additives including sodium dodecyl sulfate (SDS), sodium dodecyl benzenesulfonate (SDBS) (kinetic hydrate promotors), and tetrahydrofuran (THF) (thermodynamic hydrate promotors) were explored. Thermodynamic and kinetic studies were performed for each additive system. Hythane mole consumption and induction time analysis revealed relatively high hydrogen storage and faster hydrate growth with THF kinetics. SDS and SDBS also showcased improved and better Hythane hydrate formation than pure water; however, it also showed foam generation and lower stability; whereas THF has less energy-intensive and stable hydrate formation due to mixed hydrate formation. The hydrate formation study was extended to store Hythane gas in the hydrate pellets under a controlled environment. Hythane with 30% hydrogen showed the highest hydrogen storage in the form of gas hydrates, where Hythane gas hydrate pellets (Hythane 30 + THF system) were found stable at 1 MPa and 283.15 K for 15 days. Based on the observations and findings of this study, a commercially exploitable process flow diagram to produce, store, and transport Hythane gas hydrate pellets is also proposed.