Polyvinyldialkylamine Oxides─A Powerful Class of Kinetic Hydrate Inhibitors

Abstract

One of the chemical methods to prevent gas hydrate formation in oil and gas operations is the deployment of kinetic hydrate inhibitors (KHIs). During the past decade, polyamine oxides have been shown to be powerful KHIs. Here, we present the first study on polyvinyldialkylamine oxides as KHIs. First, Structure II tetrahydrofuran hydrate crystal growth inhibition was observed to be the most powerful when the alkyl group in the polymer was n-butyl (PVBu₂AO). High-pressure tests in steel rocking cells were carried out, with both methane and a synthetic natural gas (SNG) mixture. Slow constant cooling and isothermal testing were used. The butylated polymer was also the best in the gas hydrate experiments, with the lowest molecular weight polymer, PVBu₂AO-LMw (Mw ca. 20,000 g/mol), giving the best results. It performed better than poly(N-vinyl caprolactam) (PVCap) with both gases and with both test methods, even though PVCap had a lower and more optimized molecular weight of about 4000 g/mol. The high flash point solvent, n-butyl glycol ether (nBGE), was shown to be an excellent synergist. For example, in isothermal tests with SNG using 5000 ppm of PVBu₂AO-LMw and 5000 ppm of nBGE, hydrate formation onset was delayed about 1.5 days at 70 bar and 13.1 °C subcooling. The same blend using 101 bar of methane at 8.1 °C subcooling gave no hydrates in 18 h, but hydrates did form after ca. 12–18 h at 10.9 °C subcooling. In summary, polyvinyldialkylamine oxides were shown to be a powerful new class of KHI polymers which could probably be further optimized for even higher performance, for example, at lower molecular weight.