Comment by photochemsyn

3 years ago

The article is interesting but technically weak. If we focus on the process of generating a stream of pure CO2 from the atmosphere (where CO2 is at ~420 parts per million at present), things become a bit more clear.

Note first that the global biosphere is capturing CO2 into organic molecules at about 15 times the rate that fossil fuel consumption dumps geologically stable carbon deposits into the atmosphere. However, almost all of this biological carbon is respired back into the atmosphere by microbes, fungi, insects and animals who use the material as a food source. The reason atmospheric CO2 is rising is that the biosphere doesn't have the capacity to absorb the added CO2. Keep in mind that plant growth is a quite slow process compared to industrial activity.

So let's say we generate a stream of pure CO2 from the atmosphere - but how? If we got the electricity to do this (for pumping air over CO2 filters etc.) from fossil fuels, it's a futile cycle. The energy source has to be fossil-free for this to make sense as a CO2 extraction process.

Now, the oil industry has mostly been using their CO2 streams for enhanced oilfield recovery, i.e. they pump the CO2 down into the wells and it comes back out carrying the dregs of the oil with it. When processed into fuel, the injected CO2 goes back into the atmosphere.

Another use of a pure CO2 stream is to jack greenhouse CO2 up to ~1000 ppm, which has a significant effect on plant growth rates under controlled nutrient conditions. Most of the CO2 is released back into the atmosphere as well.

In terms of storing the CO2 in some stable form, this is rather energy-intensive. The two options that make the most sense are carbon fiber materials and diamond, the latter being harder to make (but very cool and sci-fi, enter the Diamond Age). Other options like making limestone (CaCO3) are tricky (where do you get all the calcium from). These are the only long-term removal options that make sense.

Claims that pumping CO2 down wells is a good idea for long-term storage are fraudulent. Claims that coal can be burned and used for electricity while capturing all the CO2 by the above process are fraudulent. The DOE public-private programs like FutureGen that promoted this were fraudulent, to the tune of billions of dollars of fraud.

The other option for captured CO2 is to use it make methane and jet fuel, for long-distance air travel, rocketry, maybe global shipping. Here we have zero effect on atmospheric CO2 content as what comes out goes back in. This is comparable to biosphere activity, i.e. it's steady-state. Costs for this process might be 10X that for current fossil fuel production, but it's the long-term fuel solution. Given the high costs, electric vehicles form most local transportation will be far more efficient.