Experimental results

 

Pure CO2

20% CO2, 80% N2 Mixture

The methane hydrates were placed in a clean vessel and pressurized with pure CO2 to determine how much methane could be exchanged.

NMR spectra showing a decrease in the amount of methane trapped in the hydrates with exchange time. Even after 24 hours, some methane remains in the hydrate.

Raman spectra showing accumulation of CO2 in the hydrate with reaction time.

NMR and Raman data taken together indicate exchange of CH4 for CO2 in the hydrates at high pressure. Additionally, it was observed that the hydrate crystals restructure from SII to SI during the exchange.

time

Therefore, the reaction that occurs for gas exchange can be described by:

The authors proposed that using a mixture of N2 and CO2 could allow for the recovery of more methane since nitrogen is smaller than carbon dioxide and could more easily displace methane trapped in the small SI hydrate cages.

Using the experimental results, the authors were able to determine how the exchange occurs as a function of time.

NMR spectra showing that CO2 is still trapped in the hydrate when the vessel is pressurized with the nitrogen/carbon dioxide mixture.

NMR spectra indicating that CH4 is displaced from the SI hydrate crystals when using the nitrogen/carbon dioxide mixture.

Results indicate that CO2 is still exchanged into the hydrate and that the methane trapped in the SI crystals decreases when exposed to the nitrogen/carbon dioxide mixture.

Comparison of Gas Composition

Methane recovery from the hydrate as a function of exchange time with either pure carbon dioxide or a mixture of carbon dioxide and nitrogen.

Comparison shows that more CH4 is recovered when CO2/N2 mixture is used (with the difference coming from methane trapped in the SI cages).

This means that more CH4 can be recovered while avoiding the expensive CO2 separation process!