Solar Heat Powered Machine Turns CO2 Back Into Fuel

Usually, solar powered hydrogen-generating systems use the light from the Sun falling down an electric solar panel which makes electrolysis happen. By studying another type of water splitting technology, scientists from the Sandia National Laboratories realized that if they put CO2 instead of water in the reaction chamber, they’ll eventually achieve a “reverse combustion”, and turn carbon dioxide back into fuel (actually syngas, which is a building block for the fuel).

This is the simple description, of course – the machine, made of a metal cylinder, is called the CR5 (Counter Rotating Ring Receiver Reactor Recuperator) is working on the principle that heat triggers a thermo-chemical reaction in an iron-rich composite material. This material is fabricated in a fashion that it is able to give up an oxygen molecule when exposed to extreme heat, and then receive an oxygen molecule once it cools down.

Rich Diver, the inventor of this device, is enthusiastic that his device could eventually work as the ultimate carbon sequestration machine and that it could recycle carbon dioxide from industrial plants and turn it back into gasoline, diesel, or kerosene. He assumes that the process can become at least twice as efficient as natural photosynthesis.

The machine is designed with a chamber on each side. One side is hot, the other cool. Running through the center is a set of 14 Frisbee-like rings rotating at one revolution per minute. The outer edge of each ring is made up of an iron oxide composite supported by a zirconium matrix. Scientists use a solar concentrator to heat the inside of one chamber to 1,500 º C, causing the iron oxide on one side of the ring to give up oxygen molecules.

As the affected side of the ring rotates to the opposite chamber, it begins to cool down and carbon dioxide is pumped in. This cooling allows the iron oxide to steal back oxygen molecules from the CO2, leaving behind carbon monoxide. The process is continually repeated, turning an incoming supply of CO2 into an outgoing stream of carbon monoxide.

“Our short-term goal is to get this to a few percent efficiency,” says says James Miller, a chemical engineer with Sandia’s advanced materials laboratory. “It might seem like a low number, but we like to compare that to photosynthesis, which is actually a very inefficient way to use sunlight.”

Diver’s initial approach towards producing hydrogen with extreme temperatures is also pursued in various countries such as Japan, France and Germany. The only existing prototype of this kind (in the form of CO2 sequestration machine) has been tested this fall and gave excellent results. However, it will take another estimated 15 to 20 years for it to become commercial, in Diver’s view, to decrease its cost and increase the fuel production efficiency.


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