Kinetic Hydrate Inhibition with Poly(N-isopropyl methacrylamide) and Triisopentylamine Oxide Blends–Evidence for First Amine Oxide Mixed Clathrate Hydrate

Kinetic hydrate inhibitors (KHIs) are chemicals that prevent the formation of gas hydrates to avoid plugging of oil and gas production flow lines. The main ingredient is a water-soluble amphiphilic polymer, usually a polyamide, which is often mixed with synergists to boost the performance. Earlier, we reported on the excellent synergetic performance of poly(N-isopropyl methacrylamide) (PNIPMAm) with trialkylamine oxides, in particular triisopentylamine oxide (TiPeAO). A unique concentration-performance was observed, whereby the performance appeared to decrease above about 1500–2000 ppm. In addition, an unusual double pressure drop was observed in slow constant cooling (1.0 °C/h) tests with methane and a blend of 5000 ppm each of PNIPMAm and TiPeAO. We now report a wider KHI study using methane as the gas phase in which we probe the concentration and structural properties of both chemicals that produce the inverse concentration effect, the double pressure drop, and the nature of the two drops. The first drop was found to be due to mixed hydrate formation with methane and TiPeAO as the guest molecules, while the second drop is due to the failure of the KHI to inhibit methane hydrate formation. This is the first report of a mixed clathrate hydrate containing an amine oxide and opens up the possibility of exploring amine oxide-based clathrate hydrates for applications including gas storage and gas separation.