Non-Amide Kinetic Hydrate Inhibitors: Performance of a Series of Polymers of Isopropenyloxazoline on Structure II Gas Hydrates

A series of polymers containing the 2-isopropenyl-2-oxazoline (iPOx) monomer have been synthesized by either anionic polymerization or RAFT polymerization. Both homopolymers of varying molecular weight were prepared as well as copolymers with methyl methacrylate (MMA) and N-isopropylmethacrylamide (NIPMAM) comonomers. The iPOx homopolymers were shown to be very poor Structure II tetrahydrofuran hydrate crystal growth inhibitors, indicating weak interaction of the oxazoline group with the hydrate crystal surface. They were also tested for their performance as kinetic hydrate inhibitors on a Structure-II-forming natural gas mixture. The homopolymers showed significant and increasing performance as the molecular weight decreased to 2000 Da. Copolymerization of iPOx with MMA did not improve the KHI performance, but copolymers of iPOx with NIPMAM did show an improvement, although not as good performance as polyNIPMAM homopolymer of similar molecular weight. However, using a 35:20 molar ratio iPOx:NIPMAM copolymer it is possible to obtain good KHI performance and a high cloud point of 70 degrees C in water, which is useful for injection into hot fluids. These results demonstrate that polymers containing predominantly non-amide-based monomers such as iPOx can be useful, high cloud point KHIs. In the case of iPOx polymers the primary inhibition mechanism appears to be nucleation inhibition since hydrate crystal growth inhibition is poor.