INVESTIGATION OF THE HYDROGEN STORAGE CAPACITY OF HYDRATES WITH MONTE CARLO SIMULATIONS Papadimitriou, Nikolaos I.; Tsimpanogiannis, Ioannis N.; Stubos, Athanassios K.; Peters, Cor J.
In the present work Grand Canonical Monte Carlo simulations are implemented in order to evaluate the hydrogen storage capacity of hydrates under a wide range of conditions. Hydrates of sII and sH type with or without promoter have been examined. Concerning hydrates of pure H2, our results show that sII hydrates can store up to 3.3 wt. % H2 and sH up to 3.6 wt. % in the pressure range examined (up to 500 MPa). The small cavities of the sII hydrate as well as the small and medium cavities of the sH hydrate are occupied by one H2 molecule at most. The occupancy of the large cavities of both types of hydrates highly depends on pressure. At 400 MPa, the average occupancy of the large cavity of the sII hydrate is 2.8 while the respective value for the sH hydrate is 5.5. Binary hydrates of H2 and promoter present a reduced H2 uptake (less than 1.1 wt. % for sII and less than 1.4 wt. % for sH hydrates). There rather limited values are attributed to the single occupancy of the cavities that are not occupied by the promoter molecules. Furthermore, the results of our simulations do not support the suggestion that the H2 uptake of the binary (sII) H2-THF hydrate can be “tuned” by adjusting the THF concentration in the equilibrium solution. Finally, binary sH hydrates with the promoter occupying the medium instead of the large cavities could be an alternative approach to increase hydrogen uptake.
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