Kinetic Hydrate Inhibitors: The Effect of Pre- or Postpolymerization Solvent Addition on Performance and a Powerful New Glycol Ether Solvent Synergist

Amphiphilic polyamidessuch as poly(N-vinyl caprolactam)(PVCap) and related copolymers have been used as kinetic hydrate inhibitors(KHIs) for over 25 years to combat gas hydrate formation in the oiland gas field. The solvent in which they are made is often a synergistto boost KHI performance. Using PVCap and a variety of glycol ethers,we investigate whether the polymerization of VCap in the synergistsolvent gives a different KHI performance than a PVCap made in a nonsynergisticsolvent, which has had the solvent synergist added afterward. Theresults of high-pressure, slow constant cooling tests (1 & DEG;C/h)in multiple rocking cells using a synthetic natural gas blend suggestthat there is little difference as long as the molecular weight distributionis similar by both methods. In the process of these studies, we alsoidentified a new synergist solvent, dipropylene glycol butyl ether(DPGBE), which showed superb synergy with PVCap. DPGBE also gave excellentsynergy with poly(N-isopropylmethacrylamide) PNIPMAmbut not with poly(N-vinylpyrrolidone) (PVP) or VP:VCapcopolymer. The ability of the solvent to boost the KHI performanceof the polymer may be related to the cloud point of the polymer. Atheory is proposed to explain why sparingly soluble solvents, withthe correct structural features, give the best synergy with low cloudpoint KHI polymers such as PVCap or PNIPMAm.