New Solar Reactor Prototype Unveiled

chrb writes "Scientists from the California Institute of Technology and the Swiss Federal Institute of Technology have unveiled a new solar reactor prototype that directly converts carbon dioxide or water into carbon monoxide or hydrogen, respectively. The abstract is available in Science. Quoting the BBC writeup: 'The prototype ... uses a quartz window and cavity to concentrate sunlight into a cylinder lined with cerium oxide, also known as ceria. Ceria has a natural propensity to exhale oxygen as it heats up and inhale it as it cools down. If, as in the prototype, carbon dioxide and/or water are pumped into the vessel, the ceria will rapidly strip the oxygen from them as it cools, creating hydrogen and/or carbon monoxide. ...The prototype is grossly inefficient, the fuel created harnessing only between 0.7% and 0.8% of the solar energy taken into the vessel. Most of the energy is lost through heat loss through the reactor's wall or through the re-radiation of sunlight back through the device's aperture. But the researchers are confident that efficiency rates of up to 19% can be achieved through better insulation and smaller apertures. Such efficiency rates, they say, could make for a viable commercial device."

Re:Hmmm

[otis wildflower]

If it can be used to manufacture methane (or, ideally, longer hydrocarbons such as butanol) it can be used to generate carbon-neutral vehicle fuel from water and atmospheric CO2.

not new

[wizardforce]

This is water thermochemical cracking and it isn't new. Not by a long shot. Most of the attention has been on the Sodium Manganese, Sulfur Iodine and this cycle which really hasn't been terribly efficient comparatively. The Cerium cycle which this thermochemical cracking system uses works at a much higher temperature than the other cycles as well. See here [wikipedia.org] for details.

Water thermochemical cracking is probably the most efficient method of converting solar energy to chemical energy that we have, perhaps that even exists considering the inefficiency of electrolysis.

Re:Hmmm

[wizardforce]

If only you knew just how useful Carbon Monoxide is in industrial synthesis. Methanol, Acetic acid, Oxalic acid, various synthetic hydrocarbons, catalytic metal complexes like Co2(CO)8, ethylene glycol and a ton of others.
CO+3HS => CH4 + H2O
CO+2H2 => CH3OH
CO+CH3OH => CH3COOH
CO+2H2+CH2O => ethylene glycol via hydroformylation
2CO+5H2 => ethanol + H2O via anaerobic fermentation
etc. etc. etc.

Re:CO2 to CO. What WHAT?

[wizardforce]

1) CO is very useful industrially being used to produce various organic molecules including Methanol, Acetic acid, catalytic metal complexes, hydrocarbons, alcohols etc.

2) this process does produce oxygen:
2Ce2O3 + 2CO2 => 2CO + 4CeO4
4CeO4 + extreme heat => 2Ce2O3 + O2

Yup

[Scareduck]

Carbon monoxide is the starting point for Fischer-Tropsch synthesis [wikipedia.org].

Ideal Process Description

[Black Gold Alchemist]

Here's just a description of the reactions and why you want CO and gasoline. You want gasoline as the end product because gas is our infrastructure. You don't want methane, alcohol, or some other fuel, because conversion of vehicles to such fuels is virtually impossible with EPA regulations. Instead you want normal (though high octane) gasoline fuel.

What you get with this system is overall:
CO2 + H2O + heat -> gasoline + O2

The first step is to reduce CO2 and H2O:
Ce2O3 + CO2 -> 2CeO2 + CO (at low temperature)
Ce2O3 + H2O -> 2CeO2 + H2 (at low temperature)
4CeO2 + heat -> 2Ce2O3 + O2 (high temperature)

Next, it you don't have the right mixture of CO2 to H2O, you can do the following:
CO2 + H2 + heat <-> CO + H2O

Next, you create methanol:
CO + 2H2 -> H3COH

Finally, you create gasoline via the methanol to gasoline process:
H3COH -> gasoline + H2O

Now, where do you get the CO2? From CO2 traps, like soda lime:
CO2 + Mg(OH)2 -> MgCO3 + H2O (in alkaline solution)
MgCO3 + heat -> MgO + CO2 (heat)

You could power this CO2 trapper off of waste heat from the engine. This system could be up to 50-60 percent efficient at converting solar energy into gasoline. This is a vast improvement of biofuels, which are often less than 1% efficient. Gasoline engines are only 10% efficient, so the scheme is less efficient than electric cars + solar panels. However, the hydrogen and CO (especially) could be used as reducing agents to reduce metals such as iron and zinc. These metals would then be burned in metal-air fuel cells to provide power on demand. You also need hydrogen to produce ammonia and other industrial chemicals.