Tetrahydrofuran Hydrate Crystal Growth Inhibition by Trialkylamine Oxides and Synergism with the Gas Kinetic Hydrate Inhibitor Poly(N-vinyl caprolactam)

We have determined the crystal growth inhibition of tetrahydrofuran (THF) hydrates with trialkylamine oxides. Our studies indicate that, within this class, tri-n-butylamine oxide (TBAO), tri-iso-pentylamine oxide (TiPAO), and tri-n-pentylamine oxide (TPAO) are the best THF hydrate crystal growth inhibitors, the butylated derivative being the best of these three. This contrasts with tetraalkylammonium bromide salts, where the pentylated and not the butylated species gives the stronger THF hydrate crystal growth inhibition. A possible explanation is discussed. The THF hydrate crystal growth inhibition performance of TBAO is reduced when one of the butyl groups is replaced by various other organic groups but still shows significant activity. The hydrate inhibition performance of trialkylamine oxides was illustrated by testing their ability as synergists to enhance the performance of the well-known kinetic hydrate inhibitor, polyvinylcaprolactam. In high pressure rocking cell tests using a SII-forming natural gas mixture, TPAO was found to be a better synergist than either TBAO, the best THF hydrate crystal growth inhibitor, or TiPAO. We speculate that adsorption onto hydrate crystal surfaces may not be the only synergistic kinetic hydrate inhibition mechanism operating and that the more hydrophobic TPAO is perturbing the nucleation of hydrate more than the less hydrophobic TBAO.