Thermodynamic and Kinetic Effect of a Dual-Function Inhibitor on Gas Hydrate Formation

The unexpected formation of gas hydrates during production and transportation processes in petroleum industries has caused serious problems, blocking oil and gas pipelines with safety hazards. To cope with this trouble, the gas hydrate community has searched for hydrate inhibitors that have great performance and cost effectiveness. Recently, the ionic liquids (ILs) have been suggested as novel hydrate inhibitors that are able to act in both thermodynamic and kinetic ways which are designated as dual-function inhibitors. In this study, we suggest a non-ionic liquid compound, morpholine as a dual-function inhibitor. We observed that this inhibitor shifts the hydrate phase equilibrium curve and reduces the hydrate formation rate as well. The formation kinetics of gas hydrates in the presence of morpholine was found to be better than two comparators of 1-ethyl-3-methylimidazolium tetrafluoroborate and polyvinylpyrrolidone. In addition, a series of microscopic analyses (powder X-ray diffraction, solid-state ¹³C NMR and Raman spectroscopy) were adopted to identify their crystal structure and molecular behavior during hydrate formation. Such inhibition effects of morpholine are thought to be mainly attributed to the nucleophilicity of the ring compound forming hydrogen bonds between surrounding water molecules. Moreover, it can be speculated that the more energy is required to form the structure II hydrate in the presence of morpholine instead of the structure I CH₄ hydrate with milder formation conditions.