Investigation of New Classes of Amide and Non-amide Kinetic Hydrate Inhibitors

Abstract

The formation of gas hydrates can cause pipeline blockage during the transportation of gas and oil products, which is one of the main challenges for flow assurance in the petroleum industry. It is uneasy to remove gas hydrates once they have formed in gas and oil transportation pipelines, so the primary method of managing the blockage risk of gas hydrates is to prevent gas hydrates from forming. Compared to other gas hydrates inhibition methods, such as water removal, thermodynamic inhibition, hydraulic and thermal methods, injection of kinetic hydrate inhibitors (KHIs) can be an efficacious and more economical method for some fields. Most reported KHIs are amide-containing polymers that are soluble in water, e.g., poly (N-vinyl caprolactam) (PVCap) and poly (N-isopropyl methacrylamide) (PNIPMAM). However, the cloud points of many amide-containing KHI polymers are relatively low, making injection difficult, and they will lose their inhibition effect if the hydrate subcooling is above about 10-12 oC for long periods. These two aforementioned weaknesses limit the application range of current amidebased KHIs. Therefore, there is a need to develop KHIs with improved inhibition performance as well as high cloud point. In addition, the kinetic hydrate inhibition mechanism is still not fully understood. Addressing these issues has been the motivation for the research presented in this thesis. My PhD studies involved two main projects. (i) Improving the inhibition performance of traditional amide-containing KHI polymers; (ii) Investigating novel classes of polymers with alternative hydrophilic groups to the amide group to determine if they can give superior performance and/or compatibility. The inhibition performance tests of KHI polymers were mainly carried out in high-pressure rocking cells using synthetic natural gas mixture. The slow constant cooling method was deployed as the standard screening method for KHI performance ranking. My thesis consists of ten publications. Eight of the papers are published in the journal of Energy & Fuels, and two of the papers are published in the journal of Chemical Engineering Science.

In summary, the inhibition performance of several series of amidecontaining KHI polymers, including N-alkyl-N-vinylamide, 3-methylene-2-pyrrolidone, N-vinyl caprolactam, and acrylamide polymers, were improved by using treatments like N-alkylation, ring expansion, end-capping modification, copolymerization, and combination of synergist solvents. Tailor-made polypeptides as well as several classes of non-amide polymers, including polyvinylsulphonamides, amine oxide polymers, zwitterionic poly (sulfobetaine methacrylate)s, and polyvinylaminals, have been shown to give excellent inhibition performance. Most of these novel KHIs gave promising high cloud points. In addition, the inhibition mechanisms were discussed with respect to the inhibition performance results of KHIs and their various structures.