Impact of Low-Dosage Inhibitors on Clathrate Hydrate Stability

Summary: Development of more capable low-dosage hydrate inhibitors (LDHI) is of crucial importance to oil and gas industry. Those efforts have been severely hindered so far by lack of clear understanding of molecular-level mechanisms, both thermodynamic and kinetic, which make certain chemical compounds into efficient inhibitors. An accurate representation of intermolecular potentials between polymeric low dosage inhibitors and hydrate-water-gas surfaces is essential for modelling systems containing these components. A two-stage computational study was undertaken of two proven LDHIs, polyvinylpyrrolidone (PVP) and polyvinylcaprolactam (PVCap), in aqueous solutions under various conditions. We have first carried out ab initio density functional theory (DFT) calculations for PVP and PVCap polymers with molecular weight spanning from monomers to polymeric chains. Molecular dynamics were then employed to investigate thermodynamic and kinetic processes that affect hydrate nucleation and growth. Comparison with experiments has also shown that calculated potential is able to mimic the characteristic behaviour of methane hydrate and PVP complexes.