How THF Tunes the Kinetics of H₂–THF Hydrates? A Kinetic Study with Morphology and Calorimetric Analysis

Abstract

Hydrogen (H 2 ) is a clean energy that holds great promise as a sustainable alternative to fossil fuels. H 2 storage has gained increasing research interest in recent decades. Hydrate-based H 2 storage technology in the presence of thermodynamic promoters is promising for large-scale H 2 storage due to the mild storage conditions required, the nonexplosive nature, and the easy recovery of the stored H 2 . However, sluggish H 2 hydrate formation kinetics and low H 2 storage capacity pose major challenges for large-scale applications. In this study, we aim to elucidate the tuning effect of tetrahydrofuran (THF) no more than its stoichiometric concentration (5.56 mol %) on H 2 −THF hydrate kinetics based on systematically designed kinetic experiments with morphology observation at macroscale complemented with microscale characterization of the synthesized H 2 −THF hydrates. 3.5 mol% THF yielded a superior H 2 gas uptake of 2.36 v/v compared to 5.56 mol % THF. The H 2 −THF hydrate morphology transited from slurry-like in the aqueous phase to plate-like at the gas−liquid interface with increasing THF concentration (C THF ). Single H 2 molecules were identified to be enclathrated in the 5 12 small cages of the H 2 −THF sII hydrate for all C THF based on spectroscopic analysis. THF and binary H 2 −THF hydrates were identified, and the ratio of the THF hydrate to the H 2 −THF hydrate increased with increasing C THF based on calorimetric analysis. Higher H 2 gas uptake achieved with C THF less than 5.56 mol % was closely linked to the morphology of the H 2 −THF hydrate, which in turn was controlled by C THF . The coexistence and the ratio of THF and H 2 −THF hydrates under various C THF first reported in our study suggested that optimizing C THF was key in achieving high H 2 gas uptake. These findings provide insights for understanding the tuning effect of H 2 −THF hydrates at multiscales and guide the optimization of thermodynamic promoter concentrations in future large-scale hydrate-based H 2 storage applications.

How Do Varying THF Concentrations Affect the CH4 Cage Occupancy in CH4+THF sII Hydrates? A Thermodynamic Approach

“…In the similar directions, Seo et al investigated the CH 4 +THF hydrates and provided evidence via Raman and NMR studies that CH 4 molecules do occupy large cages of sII hydrates at low concentrations of THF. In some of the recent studies, the tuning effect has been focused during H 2 –THF hydrate formation for its relevance in storage-related applications. , Therefore, in this study, we have also considered the large cage occupancy of CH 4 in the CH 4 +THF sII hydrate system during the modeling, and additionally, we have introduced the guest–guest interaction parameter to the Langmuir constant evaluation as well. The change in equilibrium conditions due to the presence of THF has been taken into account through the changes in the reference hydrate vapor pressure and the Langmuir constant values.…”