Studies on some zwitterionic surfactant gas hydrate anti-agglomerants

Low dosage hydrate inhibitors (LDHIs) are a recently developed hydrate control technology, which can be more cost-effective than traditional practices such as the use of thermodynamic inhibitors e.g. methanol and glycols. Two classes of LDHI called kinetic inhibitors (KHIs) and anti-agglomerants (AAs) are already being successfully used in the field. This paper describes efforts to develop new classes of AAs based on zwitterionic surfactants. The chemistry of the new surfactants is described along with experiments to determine their performance carried out in high pressure cells and a wheel loop. The results indicate positive performance for some products but not as good as a commercial quaternary ammonium-based surfactant AA. It was also shown that best results were obtained if the two ionic groups are spaced far apart from each other in the molecule. The best AA molecule tested was 3-[N,N- dibutyl-N-(2-(3-carboxy-pentadecenoyloxy)propyl)]ammonio propanoate. It performed well in sapphire cell tests at up to 15.9 °C subcooling. Its performance was fairly good in the wheel loop at 13.4 °C subcooling, but failed at 16.5 °C subcooling. 3-[N,N-dibutyl-N-(2- hydroxypropyl)ammonio]propanoate was also shown to be an excellent synergist for polyvinylcaprolactam KHIs.