Properties of Inhibitors of Methane Hydrate Formation via Molecular Dynamics Simulations

• Published in: Journal of the American Chemical Society 2005-12, Vol.127 (50), p.17852-17862
• Main Authors: Anderson, Brian J, Tester, Jefferson W, Borghi, Gian Paolo, Trout, Bernhardt L
• Format: Article
• Language: English
• Subjects: Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Methods of crystal growth; physics of crystal growth; Physics; Theory and models of crystal growth; physics of crystal growth, crystal morphology and orientation
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0554965

Within the framework of a proposed two-step mechanism for hydrate inhibition, the energy of binding of four inhibitor molecules (PEO, PVP, PVCap, and VIMA) to a hydrate surface is estimated with molecular dynamic simulations. One key feature of this proposed mechanism is that the binding of an inhibitor molecule to the surface of an ensuing hydrate crystal disrupts growth and therein crystallization. It is found through the molecular dynamic simulations that inhibitor molecules that experimentally exhibit better inhibition strength also have higher free energies of binding, an indirect confirmation of our proposed mechanism. Inhibitors increasing in effectiveness, PEO < PVP < PVCap < VIMA, have increasingly negative (exothermic) binding energies of −0.2 < −20.6 < −37.5 < −45.8 kcal/mol and binding free energies of increasing favorability (+0.4 ≈ +0.5 < −9.4 < −15.1 kcal/mol). Furthermore, the effect of an inhibitor molecule on the local liquid water structure under hydrate-forming conditions was examined and correlated to the experimental effectiveness of the inhibitors. Two molecular characteristics that lead to strongly binding inhibitors were found:  (1) a charge distribution on the edge of the inhibitor that mimics the charge separation in the water molecules on the surface of the hydrate and (2) the congruence of the size of the inhibitor with respect to the available space at the hydrate-surface binding site. Equipped with this molecular-level understanding of the process of hydrate inhibition via low-dosage kinetic hydrate inhibitors we can design new, more effective inhibitor molecules.