Systematic Study of Polyglyoxylamides as Powerful, High-Cloud-Point Kinetic Hydrate Inhibitors

A series of polyglyoxylamides (PGAms) have been synthesized and investigated for performance as kinetic hydrate inhibitors (KHIs) in slow constant cooling high-pressure rocking cell experiments using a structure II-forming synthetic natural gas mixture at 76 bar initial pressure. We found that the KHI performance improved as the size of the alkyl pendant group was increased. The best performing PGAm, poly(pyrrolidinyl glyoxylamide) (PPyGAm-I), gave an onset temperature of 8.2 degrees C at 2500 ppm. The KHI performance was improved by increasing the polymer concentration or by adding the high-flash point solvent n-butyl glycol ether (nBGE) as a synergist. For example, using 7500 ppm of PPyGAm-I, the onset temperature was lowered to 3.8 degrees C (giving a subcooling of 15.7 degrees C, compensating for the drop in pressure at T-o). A mixture of 2500 ppm PPyGAm-I and 7500 ppm nBGE gave an onset temperature of 5.1 degrees C. Combined with a high cloud point (T-Cl = 79 degrees C), this makes PPyGAm-I a strong candidate for potential industrial use. The seawater biodegradability of the PGAms in this study was found to be low, 4-17%, according to the 28-day marine OECD306 test protocol. However, this can be improved by changing the polymer's end groups, grafting, or by utilizing the polymer's susceptibility to acid hydrolysis.