Structural Design of Poly(2-amino-2-oxazoline)s for Kinetic Hydrate Inhibition of Natural Gas and Methane Hydrates

Abstract

Kinetic hydrate inhibitors (KHIs) are chemical substances that prevent gas hydrate plugging of oil and gas production flow lines. The main ingredient in a KHI formulation is one or more water-soluble amphiphilic polymers. We recently presented the first results on the KHI performance of a new class of amphiphilic polymers, namely, poly(2-dialkylamino-2-oxazoline)s, which showed good potential as KHIs. In this work, this class of novel KHIs has been investigated in more detail using both structure I and structure II hydrate-forming gases to optimize the polymer structure for best performance and with higher cloud point temperature for wider field applications. All polymers were tested in high-pressure rocking cells using the slow (1 °C/h) constant cooling test method. The best poly(2-dialkylamino-2-oxazoline)s tested at 2500 ppm contained 5-membered and 6-membered heterocyclic pendant groups and performed similarly to a commercial KHI polymer, poly(N-vinyl caprolactam) (PVCap), with both gases and with higher cloud point temperature (T_CP) than PVCap, thereby expanding the workability temperature range. The effect of salinity on KHI performance has also been studied, along with high flash point glycol solvents as synergists in combination with the best performing polymers. The onset temperature using the 2500–5000 ppm polymer could further be lowered by about 2–3 °C by the addition of 5000 ppm butylated glycol ethers. Hence, this work demonstrates the broader potential of poly(2-dialkylamino-2-oxazoline)s as KHIs.