Multi-Scale Investigation of the Role of Surface-Active Agents in Gas Hydrate Formation Kinetics

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0854210LeeNaturally-occurring methane hydrates have attracted a lot of public attention because they provide enormous potential as a future energy source. Gas storage in the artificial clathrate form is a safe and economical option, safe because the slow release of gas from a container of hydrate reduces explosion hazards, and economical because the gas storage density at 40 bar is comparable to a compressed gas at 200 bar. On the other hand, hydrate plugs formed inside processing lines are a nuisance to gas and oil industries. A critical obstacle to accelerating or retarding hydrate formation is a lack of understanding of the multi-scale interactions between gas hydrate particles and surface-active agents during hydrate formation. To contrast these interactions, methane (CH4) and carbon dioxide (CO2) hydrate systems will be investigated because surface-active agents generally accelerate CH4 hydrate formation but do not affect or even hinder CO2 hydrate formation. Three sequential stages of hydrate formation will be analyzed at different length scales: nucleation (100 nm), initial growth ( 1 ìm), and layered & agglomerated growth ( 1 mm). Differential scanning calorimetry will be used to quantify the effect of surface-active agents on gas hydrate nucleation by statistical measurements of phase-transitions. The different stages of hydrate growth will be investigated by confocal and transmission electron microscopes to understand how surface-active agents differently affect CH4 and CO2 hydrates in terms of hydrate crystal sizes and porosities. Intellectual Merit: An important hypothesis to be tested is that the adsorption of surface-active molecules onto the hydrate surface rather than their micellization in bulk phase is the main reason for accelerating and inhibiting gas hydrate formation. The adsorption mechanisms to be studied as part of the proposed research will lead to a fundamental understanding of the role of surface-active agents in achieving different morphologies and formation rates of gas hydrates in terms of the microscopic observations. Novel neutron scattering studies of the microscopic, interfacial structure will clarify the configuration and functionality of surface-active agents at the oil-hydrate-water interface. This knowledge on hydrate morphologies and interfacial phenomena will be connected to the macroscopic, scale-up experiments of bulk-phase reaction. Broader Impact: The fundamental understanding of the active role of surfactants and hydrate inhibitors enables controlled self-assembly of liquid-phase water molecules into solid gas hydrates. This understanding can be utilized for fast gas hydrate formation needed for safe natural gas storage and CO2 sequestration, while it can also be used for the investigation of an economical alternative to the 1 billion dollars per year spent on methanol as a hydrate inhibitor. This research will be performed by a close collaboration of two institutions, a Ph.D. granting school (CCNY) and an undergraduate liberal-arts college (Hamilton). The PIs will engage underrepresented high school students via existing programs and will actively involve undergraduate students and graduate students via a summer research exchange program between the two institutions. They will investigate gas hydrate-aided CO2 separation from flue gas to incorporate the thermodynamic, kinetic, interfacial science/engineering, and design aspects of this process into the undergraduate and graduate classes at Hamilton and CCNY.This project is supported by two CBET programs: Interfacial Processes and Thermodynamics; Process and Reaction Engineering