Most carbohydrates, especially in the absence of oxygen, can be reduced thermally to charcoal (carbon) and steam. Sugars can be acted upon by acids to form a mass of carbon, with the liberation of water or steam. I was wondering what’s the simplest molecule that can be directly converted into elemental carbon (NOT carbon dioxide, carbon monoxide, or methane) and water . The absolute smallest molecule would be formaldehyde (H-C-OH), but I don’t know if it can be decomposed like more complex carbohydrates can.
Aagh, got the formula for formaldehyde wrong, it should be H-CO-H. But other than that…
All carbon compounds can be reduced to carbon by some chemical method, including CO2, formaldehyde, methanol etc. Sugars can be turned into carbons simply by heating or reaction with a dehydrating reagent as (i) they already contain many carbon-carbon bonds and (ii) They can lose water easily to leave nothing but carbon e.g C12H22O11 (sucrose) to C12 + 11H2O.
In terms of simlpicity the simplest stable carbon compound that can be turned into C is CO (in terms of atoms) or methane (in terms of weight).
In the lab (mainly for carbon 14 dating see http://www.colorado.edu/INSTAAR/RadiocarbonDatingLab/methods.html ) CO2 is reduced to graphite by the use of an iron catalyst and Hydrogen at about 600 C. I am sure the same method would work for methanol and formaldehyde
That’s surprising, because coal gas is produced by the reaction C + H2O = CO + 2H. And in biochemistry plants don’t actually extract oxygen from carbon dioxide; through a series of intermediate reactions they essentially hydrogenate carbon dioxide into carbohydrates, the oxygen being left over from the water the plant took in.
The reason I brought this up is because I’ve often thought that a practical means of extracting oxygen from carbon dioxide would be a boon to manned space travel. But I’ve never read anything where it was even considered, except for the idea of using plants in greenhouses. I had thought this was because reducing carbon dioxide was supposed to be enormously difficult compared to, say, electrolyzing water. The reduction of carbohydrates was the only example I knew of where you had a fairly easy straightforward way of ending up with elemental carbon.
note that carbohydrates to carbon is not reduction - it is simply dehydration (which is why a dehydrating agent such as sulfuric acid is used or simply heating)
carbon dioxide to oxygen is not trivial due to the large amount of energy needed.
The best way to do what you want is to turn the carbon dioxide into water (and methane or carbon) and then electrolyse it into oxygen. See oregonstate.edu/~atwaterj/h2o_gen.htm and the links at the bottom for how it is done in practice.