Kinetic Hydrate Inhibitors: The Effect of Pre- or Postpolymerization Solvent Addition on Performance and a Powerful New Glycol Ether Solvent Synergist
Malcolm A. Kelland, Erik G. Dirdal, Janronel Pomicpic, Hiroharu Ajiro, Aniruddha Nag
Abstract
High Resolution Image Download MS PowerPoint Slide Amphiphilic polyamides such 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 oil and gas field. The solvent in which they are made is often a synergist to boost KHI performance. Using PVCap and a variety of glycol ethers, we investigate whether the polymerization of VCap in the synergist solvent gives a different KHI performance than a PVCap made in a nonsynergistic solvent, which has had the solvent synergist added afterward. The results of high-pressure, slow constant cooling tests (1 °C/h) in multiple rocking cells using a synthetic natural gas blend suggest that there is little difference as long as the molecular weight distribution is similar by both methods. In the process of these studies, we also identified a new synergist solvent, dipropylene glycol butyl ether (DPGBE), which showed superb synergy with PVCap. DPGBE also gave excellent synergy with poly( N -isopropylmethacrylamide) PNIPMAm but not with poly( N -vinylpyrrolidone) (PVP) or VP:VCap copolymer. The ability of the solvent to boost the KHI performance of the polymer may be related to the cloud point of the polymer. A theory is proposed to explain why sparingly soluble solvents, with the correct structural features, give the best synergy with low cloud point KHI polymers such as PVCap or PNIPMAm.