Structural and Thermodynamic Investigations of Nitroalkane + CH4 Hydrates with Structures II and H

Abstract

Thermodynamic promoters improve the thermodynamic stabilities of CH4 hydrates by decreasing their equilibrium pressures (P) and increasing their equilibrium temperatures (T), which result in reduced energy consumption during the preparation, storage, and transportation of the hydrates. In this study, CH4 hydrates containing nitroalkane large guest molecules (LGMs), including 2-methyl-2-nitropropane (tert-nitrobutane, tBuNO2), nitrocyclopentane (cPeNO2), and nitrocyclohexane (cHxNO2) as thermodynamic promoters, were investigated. Structural analyses proved that tBuNO2 and cPeNO2/cHxNO2 form sII- and sH-type hydrates, respectively. All nitroalkanes improved the equilibrium temperatures by 3–12 K. In particular, tBuNO2, which is a solid at ambient temperature, exhibited the strongest promotion effect among the nitroalkane LGMs reported thus far. The dissociation enthalpies (ΔHd) were also determined based on the equilibrium P–T conditions. The ΔHd values significantly varied with the structural type of the hydrate but were nearly independent of the type of the LGM. The structural and thermodynamic results of this study may provide valuable information for the development of CH4 storage and transport technologies.