Publication Date

Spring 2017

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biomedical, Chemical & Materials Engineering

Advisor

Liat Rosenfeld

Keywords

crystallization, cyclopentane, hydrate, morphology, rheology, surfactant

Subject Areas

Materials Science; Chemical engineering; Petroleum engineering

Abstract

Gas hydrates pose economic and environmental risks to the oil and gas industry when plug formation occurs in pipelines. A novel approach using interfacial rheology was applied to understand cyclopentane clathrate hydrate formation in the presence of nonionic surfactant to achieve hydrate inhibition at low percent weight compared to thermodynamic inhibitors. The hydrate-inhibiting performance of low (CMC) concentrations of Span 20, Span 80, Pluronic L31, and Tween 65 at 2 C on a manually nucleated 2 μL droplet showed a morphological shift in crystallization from planar shell growth to conical growth for growth rates below 0.20 mm^2/min. Monitoring the internal pressure of a droplet undergoing planar hydrate crystallization provided a strong correlation (up to R=-0.989) of decreasing interfacial tension to the shrinking area of the water-cyclopentane interface. Results from the high-concentration batch of surfactants indicated that while initial hydrate growth is largely suppressed, the final stage of droplet conversion becomes rapid. This effect was observed following droplet collapse from the combination of large conical growths and low interfacial tensions. The low-concentration batch of surfactants saw rapid growth rates that diminished once hydrate shell coverage was completed. The most effective surfactant was the high-concentration Tween 65 (0.15 g/100mL), which slowed hydrate growth to 0.068 mm^2/min, nearly an order of magnitude slower than that found for pure water at 0.590 mm^2/min. High molecular weight (1845 g/mol) and HLB (10.5) close to 10 contribute to a large energy of desorption at an interface and are believed to be the sources of Tween 65's hydrate-inhibiting properties.

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