A number of companies are working on technologies to extract carbon dioxide from the air, and *seem* to be making practical advances. The technologies seem to differ somewhat in the specifics, but they seem to all involve passing air over some chemical – liquid or solid – that preferentially absorbs or adsorbs carbon dioxide. The CO2 is then stored for sequestration, selling to customers such as greenhouses, or, in the future, conversion to a hydrocarbon fuel.

The machines are all necessarily big, require a lot of money and materials to manufacture, and undoubtedly require a lot of maintenance. At least some of them use an ill-defined fluid that absorbs the CO2; there would necessarily be loss of the fluid over time, along with the stuff getting gunked up with pollen and dust and everything else. To make a difference on a planetary scale to reduce the CO2 levels, a *lot* of these things would need to be produced, and they would doubtless require a whole lot of power input.

To me it seems like it would be a whole lot easier to simply crank out a few terawatts of nuclear powerplants to start replacing coal and gas plants, but, whatever. I’m in favor of people developing whatever technologies that might work and make a profit. If these systems can be made self-contained (equipped with PV arrays to power themselves, packed into shipping containers) and good and rugged… sure, why not. You could park these things pretty much anywhere, since CO2 is pretty much anywhere, but there are some places where it would obviously make more sense. Downwind of major CO2 sources – urban areas for example – and near transportation infrastructure so that the captured CO2 can be collected for transport to the processing or utilization center.

On one hand, if these things can be made into standard shipping containers, it should theoretically be possible to park these things pretty much anywhere. On top of skyscrapers might seem a good location…. they’d be out of the way and might be located somewhere with constant wind, requiring minimal power input; but the more you distribute these things, the more difficult it becomes to deal with the produced CO2. if a rooftop unit produces a ton of compressed CO2… what do you do with it? Are you going to build pipelines all over town, or will you have to airlift the containers hither and yon? On the other hand, unproductive areas could be used for large-scale CO2 capture; deserts, of course, but presumably also arctic locations (assuming cold doesn’t screw up the system). Given the current dropoff in NFL viewership due to the anti-anthem protests, perhaps those great big stadiums could be seized via eminent domain. The roofs could be covered with PV arrays, the interiors and parking lots filled with CO2 absorbers. This would turn those useless monstrosities into something that would at the very least clean up the air in the immediate vicinity; by centralizing the CO2 capture into large arrays, the CO2 storage and processing could be made pretty efficient.

There are doubtless vastly cheaper ways to procure methane fuel, but the use of systems like this could in theory make something like SpaceX’s BFR rocket system a virtually self-contained system. Locate the launch facility near the ocean or a river for ready access to large quantities of water; build a very powerful energy system (again, nukes would be preferable, but PV/wind turbines could be used if there was sufficient area); build a vast CO2 capture system and chemical reactors to convert CO2 and hydrogen from the seawater into methane fuel. Would this system make economic sense, compared to simply shipping in the methane from conventional sources? Mmmm…. very likely no. But it would be very useful on other levels. Politically and economically it would insulate the launch system from fluctuations in the market and difficulties with propellant transport logistics. And perhaps most importantly, nailing down and perfecting the system on Earth would be very useful for learning how to do it on Mars, where you *have* to make your own fuel. Twenty years ago I built a chemical reactor that converted CO2 and water into a range of propellants such as methanol and methane… the system was small enough to fit in a suitcase, though of course at that scale efficiency wasn’t so spectacular. But if a small group of knuckleheads can cobble together a system like that on a small SBIR Phase 1 contract, then it’d be readily doable on a large scale.