Acryloyl piperidine/pyrrolidine statistical and block copolymers as hydrate inhibitors: effects of cloud point temperature and copolymer microstructure

Abstract

Ongoing investigations on the polymer chemistry and physical properties of kinetic hydrate inhibitors (KHIs) have led to several theories attempting to interpret their inhibition mechanisms during hydrate nucleation and growth, crucial for flow assurance in offshore facilities. Namely, numerous reports have studied the relationship between the hydrophobicity, cloud point temperatures (CPTs) and copolymer microstructures of KHIs and their abilities to reduce hydrate formation. To verify these theories, statistical and block copolymers with various compositions (0, 30, 50, 70, 100 mol.%) of acryloyl pyrrolidine (APy) with acryloyl piperidine (APi) were synthesized and sI methane hydrate growth kinetics were measured at 2 °C and 4646 kPa. All tested KHI samples reduced methane consumption to <25 % of that of an uninhibited system. Poly(APi) with bigger amide rings and lower CPT acted as a poorer KHI than the more hydrophilic poly(APy). The statistical copolymers with a wide range of CPTs from 4 to 48 °C showed that KHI performance was not influenced by CPT, as the sI hydrate growth rate exhibited a nearly linear relationship with respect to copolymer composition. On the other hand, results of block copolymers suggest that the thermoresponsive behavior of these surfactant-like additives might play a role during hydrate growth inhibition. The block copolymer with 30 mol.% APi acted as the best KHI amongst all tested samples, while the block copolymer with 70 mol.% APi acted as the poorest. The results were significantly different from the statistical copolymers with similar composition; thus, copolymer microstructure is also a factor to consider during KHI design.