Study of the Gas Hydrate Antiagglomerant Performance of a Series of Mono- and Bis-amine Oxides: Dual Antiagglomerant and Kinetic Hydrate Inhibition Behavior

Abstract

Antiagglomerants (AAs) are surfactants used in the upstream oil industry to prevent gas hydrate plugging in flow lines. Most, if not all, AAs used in the field today are cationic quaternary ammonium surfactants and function using the “hydrate-philic” mechanism. In this study, we have synthesized a series of butylated mono- and bis-amine oxide surfactants with aliphatic tails with chains of 9–17 carbon atoms and either amide or ester spacer groups. Their performance as hydrate-philic AAs has been investigated in a sapphire autoclave and sapphire rocking cells with a Structure II-forming natural gas mixture. There was generally good agreement regarding the performance and relative ranking of the surfactants between the two sets of equipment. The AA performance of the amine oxide surfactants depended on many factors, including the polar head and spacer groups, tail length, subcooling at hydrate onset, salinity, and the composition of the hydrocarbon fluid. Amido amine oxide surfactants performed better than the equivalent ester amine oxide, probably due to the stronger hydrogen-bonding ability of the amide group. The bis-amine oxide surfactants were designed with optimum interamine distance for best Structure II crystal growth inhibition and performed better as AAs than did the mono-amine oxide surfactants. The amido bis-amine oxide surfactants showed reasonable seawater biodegradation rates over 28 days, giving biological oxygen demand values of 25–40%. The bis-amine oxide surfactants in particular also showed a strong kinetic hydrate inhibition effect, which could be very useful for field applications. Thus, these surfactants could be used first as kinetic hydrate inhibitors (KHIs), and if for any reason hydrate formation does occur they could also function as AAs to prevent hydrate blockages under certain conditions.