# Air recycling system(CO₂-->O₂) or (CO₂-->fuel)?

I'm not a chemist but I'm working on an eco-friendly project that is supposed to recycle $\ce{CO2}$ from the air and convert it to $\ce{O2}$ or at least a usable fuel source ,the system can use the solar system as an energy source (I know that such system isn't efficient) but for the country in which the project is applicable it would be a great economical benefit (over direct sun power).

-What is the most appropriate chemical reaction to achieve such goal ?

the reaction of course shouldn't emit toxic material(the whole purpose of the project is to benefit the environment, plus the cost of any filter or disposal mechanism isn't affordable)

is there any way to construct a circular system (Regenerative carbon dioxide removal system ) Wikipedia's article doesn't elaborate further.

• If there is a problem in the question please don't down vote ,instead if you don't mind guiding me to correct what ever is wrong. – mahos Jun 3 '13 at 20:34
• Right after I wrote this question I happened to stumble across Wikipedia's article about "Sabatier reaction" ,is this the most efficient method ? – mahos Jun 3 '13 at 21:13
• Welcome to Chemistry.SE. We have the MathJax plugin built into our site to hand chemical formulas, equations, and maths. Check out the faq for more info. – Ben Norris Jun 3 '13 at 22:26
• @mahos - This kind of thing (more specifically, Fischer-Tropsch catalysis using CO2 as a feedstock) is a current active area of research. I feel that your question is a thematic duplicate of this one so I'm going to vote to close on those grounds (not that there's anything wrong with your question, per se), however you should definitely check out the answer, links and discussion over there. – Richard Terrett Jun 4 '13 at 8:50
• I don't think it's quite a duplicate: the other one asked about one very specific fuel synthesis - Tony Marmont's Air Fuel Synthesis. Whereas this one is a general question. – 410 gone Jun 5 '13 at 13:45

This is quite a hot topic at the moment - the current buzz-phrase is power to gas.

There are quite a few conference papers and technical papers, and at least one dedicated conference, for it.

And it's too soon for there to be a known "best" process.

Audi and others are using a modified Sabatier process.

$$\ce{CO2 + 4 H2 -> CH4 + 2 H2O }$$

Others are looking at a modified Fischer-Tropsch process.

$$\ce{(2n +1) H2 + n CO -> C_{n} H_{2n +2} + n H2O}$$
(image courtesy of the RWE power to Gas Project)

Essentially, you've got to prise the Oxygen off the Carbon, which is an energy-intensive process; and then attach the Hydrogen, which is not. But the Hydrogen typically comes from electrolysis of water, which is energy-intensive.

Not only are the processes being prototyped high-energy, but they're high-exergy too, requiring very high heat and / or electricity.

So it's unlikely that this is a better option than using solar power for solar-thermal or photovoltaics, unless the application is long-distance travel, which would require an energy source with a very high energy density. In which case, there are several renewable-fuel synthesisers being prototyped at the moment, but it's too early to tell which is the best.