Comparison of the Kinetic Hydrate Inhibition Performance of Block and Statistical N-Alkylacrylamide Copolymers

Abstract

Various classes of water-soluble polymers have been used for over 2 decades as kinetic hydrate inhibitors (KHIs) to prevent the plugging of flowlines with gas hydrates. Many of these polymers are polyvinyl-based and are synthesized by radical polymerization of the corresponding vinylic monomers. When two or more co-monomers are used, this will give statistical copolymers. In this study, we compare the KHI performance of statistical and block copolymers made from N-isopropylacrylamide (NIPAM) with both N,N-dimethylacrylamide (DMA) and 2-hydroxyethylacrylamide (HEAA). The copolymers were made using similar procedures and have very similar molecular weights and PDI (dispersity) values to enable good KHI performance comparison. The copolymers were tested in high pressure rocking cells using a structure II-forming synthetic natural gas mixture using a slow constant cooling method. All of the 1:1 block copolymers, at 2500 or 7000 ppm, gave statistically significant lower average onset temperatures than the equivalent 1:1 statistical copolymers by about 1 °C. For the 3:1 NIPAM:HEAA statistical and block copolymers, the performances were more similar. These 3:1 ratios were also the best performing copolymers, probably reflecting the higher percentage of the more hydrophobic NIPAM co-monomer.