Study on the Synergistic Properties of Quaternary Phosphonium Bromide Salts with N‑Vinylcaprolactam Based Kinetic Hydrate Inhibitor Polymers

• Published in: Energy & fuels Vol. 28; no. 11; pp. 6803 - 6810
• Main Authors: Magnusson, Carlos D, Kelland, Malcolm A
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 20-11-2014
• Subjects: Applied sciences; Bromides; Copolymers; Crystal growth; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fuels; Hydrates; Inhibitors; Natural gas; Polymers; Synergists; Inhibitor; Kinetics; Hydrates
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/ef501545p

We have evaluated the synergism of five tetraalkyl phosphonium bromide salts with N-vinylcaprolactam based polymers by carrying out high pressure rocking cell experiments with a structure II-forming natural gas mixture. (n-Pe)4PBr was shown to be a superior synergist than (n-Bu)4PBr when used in combination with three different N-vinylcaprolactam based commercial polymers used in kinetic hydrate inhibitor formulations. These are poly­(N-vinylcaprolactam) (PVCap), a N-vinylcaprolactam:N-vinylpyrrolidone 1:1 copolymer, and a N-vinylcaprolactam terpolymer. (n-Pe)4PBr and (n-Pe)4NBr were found to have very similar synergistic capacities and to perform better (n-Bu)4NBr when used with PVCap. (n-Bu)4PBr and (n-Bu)3(iso-Hex)­PBr were better synergists than (n-Bu)4NBr with PVCap. They exhibited the same synergistic performances with PVCap even though (n-Bu)3(iso-Hex)­PBr had been shown to be a better tetrahydrofuran (THF) hydrate crystal growth inhibitor. (n-Bu)3hexadecylPBr showed a synergistic performance similar to that of (n-Bu)4NBr with PVCap. Phe4PBr showed a poor performance as synergist with PVCap. This was in line with a poor THF hydrate crystal growth performance previously reported. By changing the weight ratios of (n-Pe)4PBr and PVCap at the same total weight concentration of 3000 ppm, it was found that the onset temperatures (T o) decreased with increasing amount of (n-Pe)4PBr. The lowest T o was reached for the ratio 29:1 ((n-Pe)4PBr:PVCap). Thus, excellent KHI performance can be obtained with as little as 100 ppm of KHI polymer as long as there is sufficient amount of a good synergist.