CO2 could be stored below ocean floor

Date:
March 7, 2022
Source:
National University of Singapore
Summary:
Climate change is one of the most pressing challenges facing
humanity. To combat its potentially catastrophic effects, scientists
are searching for new technologies that could help the world reach
carbon neutrality. One potential solution that is drawing growing
attention is to capture and store carbon dioxide (CO2) emissions
in the form of hydrates under ocean floor sediments, kept in place
by the natural pressure created by the weight of the seawater
above. A major question, however, has been how stable this stored
CO2 would be for the extended periods of storage required to keep
the carbon in place and out of the atmosphere. A research team has
shown that CO2 hydrates, under the ocean's cold and high-pressure
environment, can remain stable in oceanic sediments for up to 30
days. Going forward, the team says, the same process can be used
to validate the stability of CO2 hydrates for much longer periods.



FULL STORY ========================================================================== Climate change is one of the most pressing challenges facing humanity. To combat its potentially catastrophic effects, scientists are searching
for new technologies that could help the world reach carbon neutrality.


==========================================================================
One potential solution that is drawing growing attention is to capture
and store carbon dioxide (CO2) emissions in the form of hydrates under
ocean floor sediments, kept in place by the natural pressure created by
the weight of the seawater above. A major question, however, has been
how stable this stored CO2would be for the extended periods of storage
required to keep the carbon in place and out of the atmosphere.

Now researchers from the National University of Singapore's (NUS)
Department of Chemical and Biomolecular Engineering have demonstrated
the first-ever experimental evidence of the stability of CO2 hydrates
in oceanic sediments - - an essential step in making this carbon storage technology a viable reality.

"It's the first of its kind experimental evidence that we hope is going
to spur further activity on this technology development," said Professor Praveen Linga, the lead researcher of the study. The team's findings --
part of a project funded through the Singapore Energy Centre -- were
first published in scientific journal Chemical Engineering Journal.

Using a specially designed laboratory reactor the NUS team showed that
CO2 hydrates can remain stable in oceanic sediments for a period of up
to 30 days.

Going forward, the team says, the same process can be used to validate
the stability of CO2 hydrates for much longer periods.

Trapped in ice-like substances At low-temperature and under high-pressure conditions created by the ocean, CO2 can be trapped within water
molecules, forming an ice-like substance. These CO2 hydrates form at
a temperature just above the freezing point of water and can store as
much as 184 cubic metres of CO2 in one cubic meter of hydrates.



==========================================================================
The presence of huge volumes of methane hydrates in similar locations
around the world and their safe existence presents a natural analogy
to support the belief that CO2 hydrates will remain stable and safe if
stored in deep-oceanic sediments.

The research team says that this technology could eventually be developed
into a commercial-scale process, allowing countries like Singapore to efficiently sequester more than two million tons of CO2 annually as
hydrates to meet emission reduction targets.

Ocean floor conditions Working with specially designed equipment, Prof
Linga and his team recreated the conditions of the deep ocean floor,
where temperatures range between 2DEGC to 6DEGC and pressures are 100
times higher than what we experience at sea level. Creating a macro-scale reactor that could maintain such conditions was challenging and is one
of the reasons why experiments to test the stability of CO2 hydrates
were previously not possible. The NUS team overcame this challenge using
an in-house designed pressurised vessel, lined with a silica sand bed,
which imitated ocean sediments.

The team was able to form solid hydrates on top and within the silica
sand bed and transitioned the pressurised vessel to mimic oceanic
conditions to observe the stability of the formed solid CO2 hydrates in sediments. Under pressurised conditions, the hydrates were observed for
14 to 30 days and were found to show a high degree of stability.



==========================================================================
This hydrate technology would allow nations to sequester large volumes
of carbon emissions in deep-ocean geological formations in addition to
how it is currently stored in depleted oil and gas reserves and saline
aquifer formations. For countries like Singapore, which has set a target
to become carbon neutral by 2050, the technology could be a significant
tool for reducing CO2 emissions.

"In order to achieve carbon-neutrality targets, we have to look at
new options that provide scale and speed to sequester CO2. Deep-ocean sequestration in sediments as CO2 hydrates is a promising solution,"
said Prof Linga.

The next step for the team will be to scale up the experiment's volume
and timescale.

"From an experimental standpoint, we are planning to scale up by 10 times
along with further innovations to develop quantifiable tools and methods
for the technology," said Prof Linga. Moving forward, he said, the team
aimed soon to demonstrate six months stability for the CO2 hydrates.

The team's recently announced funding under the Low-Carbon Energy
Research Funding Initiative from the Singapore government to develop cutting-edge low- carbon energy technology solutions will greatly support
the development of this storage technology. With the planned future experiments, the team hopes to develop and validate models that can
predict the stability of CO2 hydrates thousands of years into the future.

========================================================================== Story Source: Materials provided by
National_University_of_Singapore. Note: Content may be edited for style
and length.


========================================================================== Related Multimedia:
* Lab_set-up,_CO2_hydrates_and_diagram ========================================================================== Journal Reference:
1. M Fahed Qureshi, Junjie Zheng, Himanshu Khandelwal, Pradeep
Venkataraman,
Adam Usadi, Timothy A Barckholtz, Ashish B Mhadeshwar, Praveen
Linga.

Laboratory demonstration of the stability of CO2 hydrates in
deep-oceanic sediments. Chemical Engineering Journal, 2022; 432:
134290 DOI: 10.1016/ j.cej.2021.134290 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220307113139.htm

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