[thedoc (OP)]

Bert Latamore asked the Naked Scientists:
   
Recently as part of your alternative energy podcast you interviewed a scientist who is breaking apart the H2O bond to get hydrogen for fuel. Could we instead break apart atmospheric CO2 to recover pure carbon, which then could be turned into a several very pure artificial oil, gasoline, aviation fuel, etc. using solar and wind power? This has several advantages: It eliminates the issues of variability in solar and wind. the resulting fuel can be distributed using the existing infrastructure and used in today's vehicles. It also allows us to take control of the world climate. If we want to decrease average world temperatures all we have to do is produce more carbon than we urn and either use it in non-combustible products such as graphine or sequester it. If in the future the temperatures start dropping too low we can decrease production by a planned amount and withdraw and use some of that sequestered carbon.

I enjoy your podcasts.

What do you think?

[CliffordK]

Plants, of course, are efficient at converting relatively low amounts of atmospheric carbon dioxide into hydrocarbons plus free oxygen (generally using solar energy, but also using artificial light).

Theoretically one could take carbon dioxide (or a carbon dioxide compound such as calcium carbonate or sodium bicarbonate) and break the carbon-oxygen bonds to release free oxygen and produce either a carbon compound (diamond or graphite), or produce a hydrocarbon (with the addition of hydrogen from water).  However, doing so would take a lot of energy. 

[chiralSPO]

It is possible to heat CO₂ enough to break it apart. Incredibly high temperatures are needed to push the reaction to C and O₂, but at more reasonable temperatures (still above 2000 °C), and with a catalyst, one can break CO₂ into O₂ and CO, which is useful as a fuel, or for making fuels (more on this below). (see one reference here: http://energy.columbia.edu/files/2012/11/5_-Jensen_Sundrop_CO2_Splitting_Jensen_4-10a.pdf)

Solar-driven electroreduction of CO₂ and a proton source (such as water) can produce organic compounds, but we are still really bad at this compared to plants. Formic acid (H₂CO₂) and methanol (H₄CO) are about the limit that we can make directly in the lab, and even with these it is not energy efficient enough to be useful yet.

However we have developed quite efficient technology (http://en.wikipedia.org/wiki/Fischer%E2%80%93Tropsch_process) for making hydrocarbon fuels out of CO and water, or from CO₂ and H₂. (It's the same reaction because at these temperatures CO + H₂O CO₂ + H₂ http://en.wikipedia.org/wiki/Water-gas_shift_reaction). The only practical difference between the two is where the energy is stored--either one stores energy during reduction of CO₂ to CO, or in reduction of H₂O to H₂. It is also possible to convert essentially any type of organic matter into hydrocarbon fuels using this method--I believe South Africa turned most of their garbage into diesel during the embargo, and have been using this technology since.

[evan_au]

Could we break apart atmospheric CO2 to recover ...very pure artificial oil, gasoline, aviation fuel, etc?

You could, but it would take far more energy than was released when we originally burned the gasoline, aviation fuel, etc. It would take significant resources to capture the CO₂ and process it chemically (a widespread distribution network is already in place for liquid fuels, so this would just need some tweaking).

Plants already process CO₂ during photosynthesis, using energy from the Sun. At present, we mostly use this recycled CO₂ to (very inefficiently) produce fruit, grains and beef which we consume, and wood which we burn. But some genetic engineering projects are trying to produce strains of algae that will more efficiently turn CO₂ into liquid oils which could be refined into biodiesel.