Evaluating polymeric inhibitors of ethane clathrate hydrates

• Four polymers were investigated as kinetic inhibitors of ethane clathrate hydrates.
• Sever formation conditions of gas hydrates were simulated.
• Induction time and total amount of enclathrated ethane were measured.
• The performance was correlated with hydrogen-bond interactions calculated by computational modeling.

Inhibitions of gas hydrates under sever conditions such as high subcooling temperature using kinetic hydrate inhibitors (KHIs) is practically challenging. However, KHIs are favorable than thermodynamic inhibitors (THIs) because of economical and environmental reasons. Therefore, fundamental understandings of polymers performance in high severity conditions are essential to rationally design effective KHIs for this type of application. In this paper, polyvinylpyrrolidone, polyethyloxazoline and low and high Mw of polyethylene glycol (200 MW and 20,000 MW) were investigated as kinetic ethane clathrate hydrates inhibitors. Performance was evaluated in terms of the induction time to nucleation and the total number of moles of ethane enclathrated in the hydrate. The induction time to nucleation was observed to scale in order of increasing performance as polyethylene glycol (20,000 MW), polyvinylpyrrolidone, polyethylene glycol (200 MW), and polyethyloxazoline. Polyethylene glycol leads to the lowest yield of ethane in the clathrate hydrate, while polyethyloxazoline and polyvinylpyrrolidone lead to similar high yields near the polymer-free system. The performance observed was supported by computational modeling using density functional theory (DFT), where infra-red (IR) band shifts were calculated for the polymer surrogates in hydrated forms. Additionally, bond distance, interaction energy, and atom charge of polymer surrogates molecules in the hydrated state were calculated. These calculations were correlated with the performances of polyvinylpyrrolidone and polyethyloxazoline as kinetic inhibitors of ethane clathrate hydrates.