Morphology study of structure I methane hydrate formation on water droplets in the presence of kinetic inhibitors

• Main Author: Lessard, Lindsay Dianne.
• Format: Thesis
• Language: English
• Published: McGill University 2006
• Subjects: Engineering; Chemical; Methane hydrate
• Online Access: http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99520

Gas hydrates are non-stoichiometric crystalline compounds that occur when water molecules hydrogen bond to form cavities which can be stabilized by the presence of a guest molecule such as a gas or volatile liquid. Hydrates have been problematic in the oil and gas industry for several years as they may block pipelines and damage equipment. It is therefore of great interest to find environmentally safe inhibitors which can prevent hydrates from forming or from growing large enough to block pipelines. The purpose of my study was to observe the effect of kinetic inhibitors on the morphology of methane structure I hydrate using a high pressure crystallizer. Two kinetic inhibitors were studied, poly(VP/VC), a lactam ring copolymer, and antifreeze protein. Experiments were carried out on droplets with and without memory at pressures ranging from 5000 kPa to 10,000 kPa. There was no evident trend in induction times since nucleation is a stochastic process. Surface coverage time of each droplet was measured and found to be fastest on the water droplet followed by that of the poly(VP/VC) droplet and finally the AFP droplet, confirming that the two kinetic inhibitors studied were in fact effective at inhibiting hydrate growth. Since hydrate growth, unlike nucleation, can reliably be measured we can definitively conclude that AFP has a greater kinetic inhibiting effect on hydrate growth. During hydrate decomposition, it was observed in all experiments that the water droplet decomposed first followed by the poly(VP/VC) droplet and the AFP droplet. It is proposed that since the polymer chains and protein molecules bind to the hydrate crystals, this reduces the surface area of hydrate skin exposed, slowing the rate of decomposition.