Surfactant Effect on Hydrate Crystallization Mechanism

Abstract

SURFACTANT EFFECT ON HYDRATE CRYSTALLIZATION MECHANISM by Kevin Dann 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), medium (≈CMC), and high (>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.

Surfactant Effect on Hydrate Crystallization at the Oil–Water Interface

“…Temperature control is achieved by the implementation of a programmable temperature regulator via a solid-state Peltier component. A full description of the programmable temperature regulator is described in ref 26.…”

The Effect of the Hydrate Antiagglomerant on Hydrate Crystallization at the Oil–Water Interface

“…The hydrate that starts to form at the steel surface may be nucleated by the seed hydrates that stick to the steel surface. 23 As recognized by Figures 3 and 4, the time required for a full encapsulation of the water droplet with the hydrate shell depends on the subcooling. Due to the low subcooling (3.7 °C), which acts as the driving force to propagate the hydrate front at the cyclopentane−water interface, the encapsulation of the water droplet by the hydrate shell was completed in 1 h (Figure 4e), while only 10 min was needed at 1 °C as shown in Figure 3c.…”

“…As can be seen from Figure b,c, both the steel and the seed crystals can induce the hydrate growth. The hydrate that starts to form at the steel surface may be nucleated by the seed hydrates that stick to the steel surface . As recognized by Figures and , the time required for a full encapsulation of the water droplet with the hydrate shell depends on the subcooling.…”