Control of methane hydrate formation at the molecular level Tadanori Koga, Department of Materials Science and Engineering, Stony Brook University

2d-detector

Diffuse scattering(surface structure)

High-pressure cell

Neutrons

NG7, NIST Water

Methane

Detector

Natural gas hydrates owe their existence to the ability of water molecules to assemble via hydrogen bonding and form polyhedral cavities in which trapped methane molecules reside. Though initial interest in understanding gas hydrate formation focused on flow assurance to avoid gas pipeline plugging, it is now being considered for applications such as an alternative to desalination technology, potentially a huge natural gas reserve, and natural gas transport alternative to liquefied natural gas (LNG) due to high energy density. A recognizable problem in utilizing the versatility of gas hydrate route is the uncertainty in the hydrate formation process that can take from few minutes to several days. This proposal seeks to undertake a fundamental study to help understand the hydrate nucleation process at the interface. We have custom built a cell to study the natural gas hydrate interfacial phenomenon. A major focus of the study was to measure hydrate nucleation using neutron reflectivity at NIST, which allows detection of nanoscale processes at the earliest stage of the nucleation, and laser light reflectivity, which is sensitive to the micron scale surface structures.

These surface sensitive techniques clarified that the microscopic hydrate formation was always triggered within 1 min within the hydrate stable region in the phase diagram and metastable during the induction period. At the end of the induction period, which was independently determined by methane gas pressure trace experiments, the microscopic nuclei abruptly (within 30s) grew into the micron-scale hydrates.