Volume 23: Sustainable Energy Solutions for a Post-COVID Recovery towards a Better Future: Part VI

Peculiarity of CO2/H2 Hydrate Decomposition: The Equilibrium Decomposition Temperature Seems to be Affected by Different H2 Molecule Occupation Yan Xie, Yujie Zhu, Tao Zheng, Jinrong Zhong, Changyu Sun*, Guangjin Chen*, JingChun Feng*

Abstract

It is well known that H2 molecule can more easily migrate between hydrate cages and realize multiple molecule occupation due to its small molecular diameter. In this work, several splitting DSC endothermic peaks for CO2/H2 hydrate decomposition in constant pressure and 29.5% CO2 + 70.5% H2 gas composition were unexpectedly found through a high pressure micro-differential scanning calorimeter (HP μ-DSC). These DSC decomposition peaks have the typical characteristics with several different hydrates coexisting. The dissociation temperatures corresponding to these peaks showed obvious regularity that the temperatures for those first peaks and last peaks are almost close to the equilibrium decomposition temperature of the CO2/H2 hydrate with the similar gas phase component and pure CO2 hydrate respectively. We speculate that the occurrence of this peculiar phenomenon may be mainly due to the different occupation of H2 molecules in CO2/H2 hydrate cages. This led to the metastable change of hydrate equilibrium conditions, and therefore resulted into the delayed decomposition. Raman spectra confirmed the various occupation of H2 molecules in CO2/H2 hydrate cages under this experimental conditions. The finding in this study may provide some new insights into the deeper understanding of the physical/chemical properties behind clathrate hydrates in the future.

Keywords CO2/H2 hydrate, splitting DSC endothermic peaks, metastable hydrate equilibrium conditions, different H2 molecule occupation