Multiscale Analysis on CH₄–CO₂ Swapping Phenomenon Occurred in Hydrates

Abstract

Swapping CH 4 with CO 2 in hydrocarbon hydrates is renowned as an eco-friendly method for potential energy production and climate change mitigation. To fully understand the CH 4 −CO 2 replacement process, in situ Raman spectroscopy combined with long-term macroscopic measurements were carried out by putting CH 4 hydrates into gaseous CO 2 at temperatures ranging from 273.2 to 281.2 K. A kinetic model based on gas diffusion theory was modified. Results showed that the gas swapping process started with surface reaction followed by gas diffusion in hydrate phase. At hydrate surface, the average occupancy of CH 4 decreased without dramatic fluctuations, suggesting that the replacements were not simply composed of a series of dissociation and reformation process. A rise in temperature was found to effectively increase the gas swapping rates and strengthen the gas diffusion in hydrate phase. In situ Raman results together with gas consumption data were fitted by the kinetic model. The calculated gas-hydrate interfacial area revealed the foamy nature of hydrates. Fitting parameters representing the gas diffusion coefficient were of the same order of magnitude as the water mobility in hydrate phase, which implied that the replacements were limited by the mobility of water molecules.

Microscopic measurements on the decomposition behaviour of methane hydrates formed in natural sands

“…4, which represent the kinetic characteristics of hydrate decomposition in the six particle size deposits and bulk hydrate, respectively. We can clearly observe the Raman peak of the water molecules in the main structure of the hydrate caused by vibration of the H-O bond and distributed in the Raman shi range of 2830-3600 cm À1 , which is also observed by Zhou et al 45 and Schicks et al 46 Compared with the bulk hydrate decomposition process, it was found that the behavior of the hydrate formed in sediment was signicantly different. As shown in Fig.…”

Clathrate hydrates: recent advances on CH4 and CO2 hydrates, and possible new frontiers

“…43 Many studies, including field campaigns, continue to be conducted to determine the optimal operation conditions (T, P, addition of liquid vs. gaseous CO2) to enhance CH4 removal from hydrates. [44][45][46][47][48][49][50] Because it is a very aggressive hydrate former, H2S is proposed as an additive for this application, 48,51 and it could help improving the kinetics of the CO2/CH4 swap process.…”

Methane hydrate formation in an oil–water system in the presence of lauroylamide propylbetaine

“…Detailed information concerning the two devices can be found elsewhere. 30 The SEM images were obtained using Hitachi S-4800 equipped with a cryo-SEM preparation system (Quorum). The measurement time was limited to 40 minutes to avoid the potential dissociation of the formed hydrate.…”

“…As seen, the surface of the hydrate sample is porous and the pore size is generally below 5 mm, which agrees with literature. 30 However, the morphology of the samples formed from the 0.18 wt% LPB solution is greatly changed. No pores are found on the surface.…”