In situ Raman investigation on mixed CH4-C3H8 hydrate dissociation in the presence of polyvinylpyrrolidone

• Published in: Fuel
• Main Authors: Tang, Cuiping, Zhou, Xuebing, Li, Dongliang, Zhao, Xiangyong, Liang, Deqing
• Format: Report
• Language: English
• Published: ELSEVIER SCI LTD 2018
• Subjects: Energy & Fuels; Engineering; Gas hydrate; Dissociation; Kinetic inhibitor; Raman spectra; Chemical; METHANE HYDRATE; MOLECULAR-DYNAMICS; KINETIC INHIBITORS; CRYSTAL-GROWTH; WATER DROPLETS; DECOMPOSITION; PROPANE; SPECTROSCOPY; SYSTEMS; Methane hydrate
• Online Access: http://ir.gig.ac.cn/handle/344008/43643; https://doi.org/10.1016/j.fuel.2017.11.063

The dissociation of hydrates containing kinetic inhibitors is important for the treatment of gas hydrate blockages in pipelines. In this work, the dissociation of natural gas hydrates in the presence of polyvinylpyrrolidone (PVP) was investigated by Raman spectroscopy and cryo-scanning electron microscope (SEM). The natural gas hydrates were formed from a synthetic natural gas mixture composed of CH4 (95.0 vol%) and C3H8 (5.0 vol%). The results showed that the crystallographic structure of the formed hydrate was structure II (sII) with CH4 encaged in both small and large cages and C3H8 in large cages. Raman spectra showed that PVP could not be captured by the sII hydrate cage and had no influence on the structural type of the hydrate. However, PVP inhibited the occupancy of CH4 molecules in the large cages. The dissociation of hydrates in the presence of PVP was slower than without PVP. No other transient structure was observed during the dissociation and gas hydrate cages were suggested to collapse as an entity, without the interference of PVP. The microstructure of the gas hydrates appeared to change from close-to-spherical to scale-like when PVP was added.