NMR and Viscosity Investigation of Clathrate Hydrate Formation and Dissociation

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• 作者：Shuqiang Gao ; Walter G. Chapman ; and Waylon House
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2005
• 出版时间：September 14, 2005
• 年：2005
• 卷：44
• 期：19
• 页码：7373 - 7379
• 全文大小：190K
• 年卷期：v.44,no.19(September 14, 2005)
• ISSN：1520-5045

文摘

To better understand clathrate hydrate mechanisms, nuclear magnetic resonance (NMR) andviscosity measurements were employed to investigate tetrahydrofuran (THF) hydrate formationand dissociation processes. In NMR experiments, the proton spin lattice relaxation time (T₁) ofTHF in deuterium oxide (D₂O) was measured as the sample was cooled from room temperaturedown to the hydrate formation region. The D₂O structural change around THF during this processwas examined by monitoring the rotational activation energy of THF, which can be obtainedfrom the slope of ln(1/T₁) vs 1/T. No evidence of hydrate precursor formation in the hydrateregion was found. T₁ measurements of THF under constant subcooling temperature indicatethat THF hydration shells do not undergo much structural rearrangement during induction.The T₁ of THF was also measured as the sample was warmed back to room temperature afterhydrate dissociation. T₁ values of THF after hydrate dissociation were consistently smaller thanthose before hydrate formation and never returned to original values. It was proposed that thisdifference in T₁ after hydrate dissociation indicates that the THF-D₂O solution is moremicroscopically homogeneous than before hydrate formation. In viscosity experiments, aChampion Technologies hydrate rocking cell (CTHRC) was used to probe the residual viscosityphenomenon after Green Canyon (GC) gas hydrate as well as THF hydrate dissociation. Theresidual viscosity reported in the literature was observed after GC hydrate dissociation but notafter THF hydrate dissociation. Because GC hydrate behavior involves significant amounts ofgas mass transfer while THF hydrate does not, one might conclude that the residual viscosityobserved after GC hydrate dissociation was likely caused by the supersaturated gas concentrationand its general effect on solvent viscosity, not necessarily by a clathrate water structure lingeringfrom the solid.