Understanding the interplay between collective properties and performance of antiagglomerants used in gas hydrate management has been a major issue in a variety of scientific and industrial contexts, including climate change modeling, hydrocarbon extraction, natural gas storage, and planetary surface chemistry. Gas hydrates are ice-like inclusion compounds consisting of polyhedral hydrogen-bonded water cages stabilized by guest gas molecules. They are not chemical compounds because no strong chemical bonds exist between water and gas molecules. They are formed under high pressure and low temperature conditions, such as those found in deep oceans and pipelines. The gas molecules able to be trapped into the water cages are usually small. Of particular interest are the hydrocarbon hydrates that can form blockages in oil and gas pipelines.
There are three major stages associated with hydrate plug formation in pipelines: nucleation, growth, and agglomeration. To manage hydrates in pipelines, hydrate inhibitors are used. They are differentiated depending on their mode of action: thermodynamic hydrate inhibitors, such as methanol and monoethylene glycol, shift the stability conditions of hydrates to lower temperatures and higher pressures, but require large amounts to be effective. Low dosage hydrate inhibitors, instead, are effective at low concentrations. Kinetic hydrate inhibitors and antiagglomerants (AAs) are the two main low dosage hydrate inhibitor classes. AAs, mostly surface-active surfactants, are usually amphiphilic chemicals with complex hydrophobic tails and hydrophilic headgroups. They allow the hydrate particles to form, but keep them dispersed yielding transportable slurries. When AAs adsorb at the oil-hydrate interface, the hydrophobic tails preferably point toward the hydrocarbon phase, possibly inducing an effective repulsion when two hydrates approach each other. When the AAs polar headgroups are adsorbed on the hydrate surface, they could interfere with the hydrate growth. While the use of AAs is increasing in subsea projects across the industry, their mechanisms of action remain poorly understood. Such understanding is necessary to improve their cost-effectiveness and expand the range of conditions over which their use is safe and convenient.
F. Sicard* and A. Striolo, Role of Structural Rigidity and Collective Behaviour in the Molecular Design of Gas Hydrates Anti-Agglomerants, Mol. Syst. Des. Eng. 6, 713-721 (2021).
F. Sicard*, T.Bui, D. Monteiro, Q. Lan, M. Ceglio, C. Burress and A. Striolo, Emergent properties of antiagglomerant films control methane transport: implications for hydrate management, Langmuir 34 (33), 9701-9710 (2018).
T. Bui, F. Sicard, D. Monteiro, Q. Lan, M. Ceglio, C. Burress and A. Striolo*, Anti-agglomerants affect Gas Hydrate Growth, J. Phys. Chem. Lett. 9, 3491-3496 (2018).
* Corresponding author
last update: Jan 2021