Planned cut in European CO2 Emissions

power plant emissions (uncredited photo)

The above image is uncredited and was found on the site Environment Canada.

As reported by Reuters, the German utilities company RWE is the largest polluter in Europe. RWE has just announced plans to work with two other companies, Linde and BASF, to scrub CO2 (carbon dioxide) from emissions of its coal-burning operations. The coal is burned to generate electrical power and CO2 is the major product of burning any form of carbon or nearly any carbon derivative (either coal in an electricity plant or the hydrocarbon that fuels your car).

The scrubbing process for RWE has not been figured out yet, though Linde is a company that specializes in handling gases and BASF is a multifaceted chemical company, so the team seems powerful and experienced. However, according to the article, doubts have been expressed by others that the technology can be made practical on what would be a huge scale.

This CO2 scrubbing seems like a good thing if it can been made to happen. It is worth mentioning that scrubbing CO2 out of gas streams or air is pretty commonplace on a small scale, and there are a number of simple methods that work well. However, just because it can be done by young students in a science lab doesn’t mean that the process is trivial, especially when the scale is enormous.

In fact, the $25 million dollar “Virgin Earth Challenge” is aimed at another version of “the CO2 problem”: British businessman Richard Branson, in collaboration with Al Gore, announced this challenge to stimulate research and development aimed at removing CO2 from the earth’s atmosphere. If successful, this concept would be a remediation of our atmosphere, or a clean-up to try to reverse the process of global warming that is largely caused by burning fossil fuels.

You might wonder what happens to the CO2 when it is “scrubbed” (it can’t just disappear magically). Scrubbing of CO2 typically generates the carbonate ion, CO3(2-) by reaction with sodium hydroxide or lithium hydroxide. Calcium hydroxide is also used, for example in the re-breathing apparatus used by some underwater divers. If you follow the calcium hydroxide link in the previous sentence, you’ll be taken to “General Chemistry Online”, which has a discussion of the relative merits of these various hydroxides and a class of chemicals called amines, all of which undergo chemical reactions with CO2 (and can therefore remove it from the air). General Chemistry Online has a further link to a US Department of Energy (DOE) website that addresses CO2 sequestration, or scrubbing, except that the link is currently broken, so you might want to try here to see what DOE has to say. I have emailed author Fred Senese of Frostburg State University about the broken link.

The lithium hydroxide link in the previous paragraph takes you to a publicly-released US military document that refers to both deep-sea diving and removal of CO2 from the atmosphere in submarines.

What needs to be said, and Professor Senese addresses this nicely, is that lithium and sodium are caustic (sodium hydroxide is the ingredient in lye). Calcium hydroxide is a little less troublesome. However, the materials used in CO2 sequestration are typically harmful if simple (they can give you chemical burns). Realizing this might give you some more insight into why it isn’t a trivial thing to scrub tons of CO2 as it tries to exit a coal-fired electricity-generating plant. Bubbling gas through a saturated or concentrated sodium hydroxide solution, for example, will generate sodium carbonate. Boiling away the water (which requires a lot of heat) will give you solid sodium carbonate. I’m not sure where RWE plans to put all of the material generated by CO2 scrubbing, but I was under the impression that landfill space was rapidly being filled already (we’ll have to lok into this more!).

Some readers will be thinking- what about photosynthetic plants? We can discuss them, and related bacteria, at a later date.

© James K. Bashkin, 2007

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  1. I see a major problem with using these metal hydroxides to capture carbon dioxide. Let’s take calcium hydroxide as an example:
    Calcium carbonate is the source of calcium hydroxide. It would be pointless to heat calcium carbonate to end up with calcium hydroxide (via calcium oxide and the release of carbon dioxide) so it could capture carbon dioxide to end up with more calcium carbonate. Lots of energy would be consumed in the process which mostly comes from fossil fuels. This would only end up releaseing more carbon dioxide than captured.

    I have a reference to the chemical equations in the url.

  2. Thanks for the comments and for backing them up with sound chemistry. I agree entirely. When I said “less troublesome”, I meant that the calcium system should be easier to handle in cases like the example of rebreathing apparatus I cite than lithium or sodium hydroxide. That is not a valid analogy to massive, industrial scale CO2 capture, however, as your comments make abundantly clear.

    I’m trying to keep an open mind about the planned CO2 capture program, and I find it attractive in theory, but the solid waste issues, plus your excellent points, make this “plan” seem less than ideal, at least without some new chemistry being developed.

    Of course, developing new chemistry is what we do as chemists, so it is nice to have important motivation. Unfortunately, RWE has already mentioned land fill as final resting place of the captured CO2, and I’d be most comfortable with an approach that didn’t generate solid waste, given what I’ve read about landfills closing all over the place because they are filling up (sorry- no reference yet).

    Thanks again for your chemically-insightful and extremely clear commentary!

  3. I forgot to sign my response!
    James K. Bashkin

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