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Title: Molecular Simulation of Clathrate Hydrate Nucleation, Growth and Inhibition
Author: Hawtin, Robert William
ISNI:       0000 0001 3547 5880
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2007
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Gas hydrates are solid crystalline mixtures of water and small gas molecules, such as those found in natural gas. They are stable at temperatures and pressures commonly found on the seafloor and in sub-sea pipelines for the transportation of natural gas. It is the propensity of gas hydrates to cause blockages in pipelines that necessitates the addition of inhibitors to prevent hydrate formation. Recent work has focused on developing 'low dosage hydrate inhibitors', LDHls, which act to delay nucleation or prevent growth while present at low concentrations, but identifying new chemicals to provide more active LDHls has been hindered by the absence of a clear molecularlevel understanding of their activity. Molecular Dynamics simulations designed to shed light on the molecular-level processes of gas hydrate nucleation and inhibition are presented in this thesis. Nucleation of a model methane hydrate has been simulated with and without the presence of known LDHls. Nucleation in the absence of any additives has been investigated by a range of methods, including 'local phase assignment'. Hydrate has been shown to form a dynamic cage structure with elements of hydrate structures I and II. It is proposed that the stable bulk hydrate structure arises out of this dynamic structure. Crystal growth has been calculated to be favourable for clusters in excess of 200 hydrate-like water molecules in size, thus providing an estimate for the critical cluster size in these systems. In a system including the kinetic inhibitor polydimethylaminoethylmethacrylate (PDMAEMA) hydrate growth from a seed crystal of 225 water molecules was accelerated compared to the uninhibited system. Repeated simulations and statistical analysis showed the magnitude of the promotion effect to be greater with increased levels of PDMAEMA immersion. Binding of the PDMAEMA to the surface of the hydrate was seen, which is in agreement with current theories of inhibitor activity. The simulations and protocol have also been extended in systems containing other kinetic inhibitors.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available