Optimizing the Kinetic Hydrate Inhibition Performance of N‑Alkyl‑N‑vinylamide Copolymers

The generation of gas hydrates in gas and multiphase flowlines can cause blockages, leading to downtime, economic losses, and even potential accidents. Injecting kinetic hydrate inhibitors (KHIs) is an effective way to prevent gas hydrate formation. Most KHI formulations are built around water-soluble polymers containing amide groups. On the basis of past work on N-alkyl-N-vinylamide polymers from our group, we have now been able to become much closer to designing the optimum KHI for this class of polymers. In this study, we have synthesized four N-alkyl-N-vinylamide monomers, where the alkyl group is n-propyl, isopropyl, n-butyl, and isobutyl. These have been copolymerized successfully with N-methyl-N-vinylacetamide and N-vinylformamide to form a series of copolymers with low molecular weights. We have investigated their KHI performance using a slow constant cooling method with a synthetic natural gas mixture in high-pressure rocker cells at 76 bar. All of the new N-vinylamide copolymers show good KHI performance. The average onset temperature of the best copolymer, N-vinylformamide:N-isobutyl-N-vinylformamide copolymer, at 2500 ppm concentration in deionized water was 8.2 °C. This decreased considerably to 4.7 °C (ca. 15.3 °C subcooling) when 10 000 ppm of n-butyl glycol ether solvent was added, demonstrating good synergy between the polymer and solvent. Two of the best copolymers were further investigated at varying concentrations in the range of 1000–7500 ppm and showed increased performance as the dosage increased.