As everyone who hasn’t been living on the dark side of the moon for the last 50 years will know by now, carbon dioxide (CO2) has at least the potential to contribute to global warming.
Another effect that is talked about slightly less often but which is equally important is that it contributes to the acidification of the oceans, with potentially disastrous consequences for food chains.
It has been called
“global warming’s evil twin”
by Jane Lubchenco , the then chief of the American National Oceanic and Atmospheric Administration (NOAA). [1]
So, what do we do with the CO2 we produce and will continue to produce, albeit in hopefully ever smaller quantities?
1. Carbon Capture
Some of it is captured right at the point of production and the technology to do this is reasonably advanced.
It generally revolves around using a base to capture the slightly acidic CO2, although other technologies such as membrane separation are used as well.
There are also ideas to use similar principles to scrub CO2 out of ambient air, an endeavour of ginormous proportions should it ever materialise. [2,3]
Bypassing the problems of carbon capture for the time being let’s ask the question:
2. Now that we’ve got the CO2 what do we do with it?
Chemically speaking, CO2 is a rather useless molecule.
It reacts slightly acidic with water and that’s practically it.
Energetically speaking it is dead.
It is so stable that any attempt to turn it into something useful (e.g. so-called platform molecules such as cyclic carbonates) requires a significant input of energy or otherwise harsh and undesirable reaction conditions.
There are potentially interesting solutions to this problem on the bench-scale level, however, none of them have matured to the commercial level. [4,5]
There are many uses for CO2 as the gas that it is.
2. Common uses of CO2
2.1 Supercritical CO2
When heated and pressurised it can be turned into its supercritical state and used in applications such as decaffeinating coffee or tee, as well as dry cleaning, water-less dyeing, extraction of flavours and fragrances, or even cannabis oil, etc.[6]
2.2 Carbonification of soft drinks
Another use is the carbonification of soft drinks such as sparkling water and lemonades as well as beer.
An afterthought…
Due to the Covid-19 crisis, global production of goods has decreased.
This also means that less CO2 has been produced and captured.
This might even cause an increase in price of sodas and beers! [7]
2.3. Enhanced oil recovery
A third use is in enhanced oil recovery.
CO2 enhanced oil recovery (video)
Here, CO2 is pumped into oil fields which are approaching the point of depletion to pump the last little amounts of oil out.
The above three uses have in common that they are, well, commercially used.
However, much more CO2 is produced than can be used in such ways.
Hence the question arises:
What do we do with the rest?
3. Carbon storage
This is where the ‘S’ in CCS comes in — Storage.
How and where does one store millions of tons of a gas?
One possible answer has already been alluded to in the third use of CO2 mentioned above. It is possible to inject the CO2 into depleted oil and gas fields. The infrastructure to pump a gas into an oil field is practically already there while the field is still being exploited.
The problem becomes then one of transport.
CO2 is most often captured at industrial plants far away from possible storage sites.
A looped system could be envisaged: Natural gas is combusted in a power station.
This generates CO2 which is captured and subsequently fed back into the same reservoir the natural gas was taken from.
In simplistic terms: Put a lid on it — done!
Of course, it is never that simple. Now, security concerns raise their ugly little heads:
It has to be made sure that the lid stays on because a massive CO2 leak (caused by material fatigue or by a terrorist attack) would kill all animal life in a large area around the leak. The subsequent consequences for plant life are uncertain.
So will C.C.S. mitigate climate change?
Summarising this little overview of possibilities and problems one could say that CCS is an interim technology.
Capturing CO2 is important to supply CO2 to the industries requiring it for their operations.
Storing it so that it doesn’t do too much harm is important too.
But the best solution and the long term goal is to find ways to satisfy our needs without producing CO2.
[1] https://web.archive.org/web/20120712003629/http://www.huffingtonpost.com/2012/07/09/ocean-acidification-reefs-climate-change_n_1658081.html [Last accessed on June 14th]
[2] https://en.wikipedia.org/wiki/Direct_air_capture [Last accessed on June 14th]
[3] https://www.climate-kic.org/news/climeworks-raises-over-67-million-to-expand-carbon-dioxide-removal/[Last accessed on June 14th]
[4] https://www.ornl.gov/news/nano-spike-catalysts-convert-carbon-dioxide-directly-ethanol [Last accessed on June 14th]
[5] http://inhabitat.com/new-machine-turns-co2-into-fuel/ [Last accessed on June 14th]
[6] https://www.science-by-trianon.com/post/why-reduce-the-environmental-impact-of-industrial-solvents [Last accessed on June 14th]
[7] https://www.ouest-france.fr/economie/consommation/pourquoi-boire-un-bon-soda-ou-une-biere-risque-de-vous-couter-cher-6855480 [Last accessed on June 14th]
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