Thermodynamics

Now that we are deep enough into the Anthropogenic Global Warming crisis that only the whackiest of whackaloons are still denying its existence or the serious impacts it is going to have on planetary livability, a whole different type of whacky thought is filling the airwaves. These have to do with a variety of techniques to suck CO2 out of the sky and turn atmospheric carbon into something useful like carbon nanotubes or alternative fuels.

These schemes are no doubt possible. The problem is that they don’t solve the actual problem, which isn’t carbon in the air, it is about making energy by putting carbon in the air. To talk about that, we need to talk about thermodynamics.

The Laws of Thermodynamics are pretty fundamental science. They cannot, in the normal universe where we live, be violated. They were once summed up to me in this analogy which helps to keep track of them*:

1st Law: You can’t win.
2nd Law: You can’t even break even.
3rd Law: You can’t get out of the game.

The one we are most worried about here is the 2nd Law, which essentially says that any time energy changes states, there is a net increase in entropy. In other words, every time you use energy to do something, you lose a bit of energy. It is the 2nd Law that makes perpetual motion machines impossible.

Relating this to schemes to pull carbon out of the air and make it useful, it is important to realize we don’t just toss CO2 into the air for the fun of it. For the most part we do it to use the energy released when you combine carbon with oxygen, be it energy to drive our cars/planes/ships or energy to generate electricity. We do this because the act of combining carbon with oxygen releases energy in the form of heat (which is a whole different chemistry lecture we should save for Beer Friday). We can do the same thing backwards, strip the oxygen off of the carbon, but that takes energy, and (this is where the 2nd Law comes in) a little bit more energy than it produced during the original combination.

So all of those schemes you see that will turn CO2 into something useful, no matter how efficient they are, will require more energy than we gained when we created the CO2 in the first place. So it makes way more sense to simply not produce the CO2 in the first place. instead, we could use the energy we would dedicate to sucking it out of the air and making carbon nanotubes out of it back into doing whatever job we wanted to do with the energy we gained in the first place when we added the oxygen to the carbon. As a bonus, we can still make the carbon nanotubes out of any of a zillion existing carbon sources we have on the planet, be they plants, rocks, or hydrocarbons, without the need to waste a bunch of energy stripping oxygen off of the carbon.  That way the carbon stays out of the atmosphere, we use less energy, and we are all better off.

The reality is that the “technological fix” of climate change is nothing shocking, cutting edge or freaky; it is in our hand right now. It is no more complicated than stopping the taking of carbon out of the ground to combine with oxygen for cheap energy when there is an abundance of alternatives available. But it starts with recognizing this “cheap” form of energy is a false economy, as is betting the future on big fans and diamonds from the sky.

*there is a 4th Law, but since it was developed later, and then determined to be more fundamental, the physics community called it the “0th Law”, just to reinforce those points. In the analogy above, it would be translated as “We are all playing the same game”

4 comments on “Thermodynamics

  1. What you’re missing is consideration of the quality of different stores of energy. To oversimplify it, if I have an energy source that is essentially clean and unlimited, but low quality and an energy source that is dirty, but high quality, if I can use the low quality source to clean up the mess from the high quality source, it doesn’t matter that I use more energy in total. It becomes effectively a transfer of energy from the low quality system to the high one, with a commensurate hit in efficiency. But if my low quality source is clean and unlimited, efficiency doesn’t matter. Unless you’re arguing it’s the latent heat that’s causing climate change, in which case were screwed no matter what.

    1. Well, we area few generations away from latent heat being an issue, but it will someday (see Tom Murphy). You do point out though that the issue is storage. Gasoline is easy to store, move around, and suck energy out of; wind less so. However, it emphasizes the point that the problem being solved is an energy production one, not an atmospheric shift one. Pulling diamonds out of the sky is addressing the wrong problem when it comes to climate change, and there will always be easier, cheaper sources of carbon that the atmosphere, even at 400+ ppm.

  2. Patrick, your explanation of thermodynamics rates at a very low first year level. The second law of thermodynamics has an important qualifier in that it only applies in a closed system. The earth is not a closed system, it is an open system with energy entering and leaving the system at differing rates.

    As for your chemical comment, it shows a profound misunderstanding of how chemical reactions actually work and would get you laughed out of a second year (possibly first year) chemistry class. During combustion carbon dioxide is generated as is heat and water. A subsequent reaction to remove that carbon dioxide from the atmosphere is in no way related to the amount of heat generated in the initial combustion reaction that formed the CO2.

    Finally your understanding of how processes to remove carbon dioxide from the atmosphere actually work is lacking. The plans do not involve stripping the carbon atoms from the oxygen atoms in the CO2 molecule, they either involve using chemical processes to generate a phase-change in the carbon dioxide or simply enabling a chemical reaction between the carbon dioxide molecule and a suitably reactive compound like an amine or even using something as simple as running it over activated carbon. Simple subsequent reactions can then be used (often with a catalyst) to subsequently regenerate the amine/activated carbon at a relatively low cost in energy. The output of the process is not carbon and oxygen but concentrated carbon dioxide gas that can be used in greenhouses or in other chemical reactions or sequestered (if that is your desire).

    1. Sorry, Blair, this was not exactly meant to be a dissertation. I am assuming most of my readers didn’t do graduate work in chemistry, so there is a need to simplify. The allegorical shorthand for thermodynamics certainly lacks in rigour, but makes for a good shorthand explanation, and is pretty memorable. Since you raised the point, I have traced the original quote (which I have carried around in my head since undergrad) back to physical chemist C.P. Snow, but I digress.

      I think where we got off to a misunderstanding is where I started by talking about (and linking to) fancy schemes to pull CO2 out of the air and make something useful like fuel out of it, not simple sequestration schemes that make CO2 available for greenhouses or deep aquifer storage. The former is (I argue) a flawed way to address the problem of burning fossil hydrocarbons for cheap energy, because it will require more energy to make the fuel from the CO2 than you will extract from the fuel while making the CO2. In this case, the second law does apply (by Kelvin’s definition) as we can consider the fuel-in to fuel-out system a “closed” one, unless we choose to add energy to the system (which we can do), but defeats the alleged purpose.

      I maintain that it will require more energy to strip oxygen off of CO2 than we will gain by adding oxygen to carbon. Pulling the CO2 out of the atmosphere, or separating it from contaminants in the powerplant flue, is not even a problem I wanted to address here, and it can be done pretty efficiently with catalysts.

      If however, we choose to only make the CO2 into a solid or squeeze it into a deep reservoir in liquid form, then we don’t need to pull it out of the air, but can tap directly into the source at power plants and capture it there. Problem is what to do with it then, and whether the energy required to do the capture/storage makes the entire process worthwhile, when compared to the readily available alternatives.

Leave a Reply to Patrick Johnstone Cancel reply