Recently, a novel hydrate inhibitor of ionic liquids was identified by Xiao and Adidharma (Chem. Eng. Sci. 2009, 64, 1522-1527) and some researchers have investigated inhibition effects with a variety of ionic liquids. The ionic liquids are reported as dual function inhibitors because they affect not only the thermodynamic equilibrium condition, but also retard nucleation and/or growth time during hydrate formation. However, the reported ionic liquids are mainly based on the immidazolium cation and showed rather kinetic hydrate inhibition characteristic because their thermodynamic inhibition effects are quite weak. To improve the kinetic hydrate inhibition effect, we designed a new specific ionic liquid. Synthesized N-(2-hydroxyethyl)-N- methylpyrrolidinium tetrafluoroborate ([HEMP][BF4]) by taking the following two features into account: 1) being hydrophilic or hygroscopic, and 2) introduction of special functional groups including an oxygen atom or a hydroxyl group for hydrogen bonds with water molecules. This study measures the solid-state 13C NMR spectra for pure CH4 and synthesized natural gas hydrates with or without the ionic liquid and a well-know kinetic inhibitor, poly (N-vinylcaprolactam), PVCap. As expected, the [HEMP][BF4] is found to be a dual function inhibitor with an inhibition effect equal to or stronger than the conventional kinetic inhibitor. Moreover, in situ Raman spectroscopic measurements and pressure monitoring provide microscopic and macroscopic evidence on the synergy effect when the mixture of ionic liquid and the polymer inhibitor is used for efficient hydrate inhibition. It is found that hydrate formation is inhibited or delayed further with a stronger affinity to water molecules and disruption of the hydrate crystals of additional ionic liquid.

Spectroscopic identifications of inhibition effect by an ionic liquid as a synergist on gas hydrate formation

249th National Meeting (2015)

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