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

Abstract

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.

Kinetic Hydrate Inhibition from Thermoresponsive Poly(2-amino-2-oxazoline)s: Size and Shape of the Hydrophobic Groups Are Critical for Performance

“…For a set of 5–6 experiments, we typically observe 10–15% margin of error in T o and T a values which was also the case in this study. A typical full set of data for 6 cells has been reported . The variation in T o and T a values is due to the stochastic nature of the hydrate nucleation process.…”

Comparing the Kinetic Hydrate Inhibition Performance of Linear versus Branched Polymers

“…Gas hydrate formation is a stochastic process. Results for four sets of tests in five rocking cells for one polymer using the same test method as this study were recently reported, demonstrating the reproducibility . Thus, five tests allow for ranking of polymers as long as the average T o value for two different polymers is sufficiently different, as warranted by the p-value obtained in a t test.…”

Attempts to Improve the Performance and Biodegradation of Kinetic Hydrate Inhibitors–More Lessons Learned

“…This method has been shown previously to give comparable performance ranking as isothermal tests in autoclaves . The reader is referred to past studies for details about the test procedure and analysis. − For the SNG tests, the start pressure was 76 bar. This gave 20.5 °C as the hydrate equilibrium temperature (HET) found from calculations performed in the PVTSim software of Calsep .…”

“…A typical variation between 20 identical rocking cell tests has been reported. 25 ■ RESULTS AND DISCUSSION Project 1 − Polyesterlactams. PVCap and VCap copolymers are some of the most powerful KHIs tested to date, especially when blended with good synergists which can also be the solvent.…”