‘Green’ cars that could run on CO2 and sunlight

A team is working on creating building blocks for synthetic liquid fuels to reduce CO2 emissions.

London: A team at Sandia National Laboratories is working on creating building blocks for synthetic liquid fuels that could reduce carbon dioxide emissions significantly.
Their cerium-oxide-based system can convert CO2 into carbon monoxide, and can also turn water into hydrogen.

The machine, called the Counter Rotating Ring Receiver Reactor Recuperator (CR5) consists of two chambers separated by rotating rings of cerium oxide. As the rings spin, a large parabolic mirror concentrates solar energy onto one side, heating it to 1500 degree Celsius and causing the cerium oxide there to release oxygen gas into one of the chambers, whence it is pumped away.

As the ring rotates further it takes the deoxygenated ring off the heat and allows it to cool before it swings round to the other chamber. CO2 is pumped into the second chamber, causing the cooled cerium to steal back an oxygen molecule, producing carbon monoxide and cerium oxide.

The process also works with water instead of CO2, with the reaction this time producing hydrogen.

Once the reactor starts producing a steady stream of hydrogen and carbon monoxide, the gases can be converted into a synthetic liquid fuel. Initially, the team plan to use CO2 captured from power-plant exhaust flues to produce their synthetic fuel but eventually plan to use CO2 extracted directly from the air.

"That is a huge challenge in itself, and we opted to focus on one hard problem at a time," New Scientist quoted James Miller, a combustion chemist at Sandia, as saying.

The reactor concentrates solar energy using mirrors, in a chamber containing calcium oxide. At 400 degree Celsius, heat causes the calcium oxide to react with CO2 to form calcium carbonate. This calcium carbonate is again heated to 800 degree Celsius, to release pure CO2 and revert back to calcium oxide.

This pure CO2 is pumped into a second reactor, where heat zinc oxide at 1700 degree Celsius produces oxygen molecules and zinc metal. The temperature is then lowered and CO2 and steam are pumped in, which react with the pure zinc to form syngas, a mixture of hydrogen and carbon monoxide, – and zinc oxide once again.

"This area holds out the promise for technologies that can produce large amounts of carbon-neutral power at affordable prices, which can be used where and when that power is needed," he says.

"It is one of the few technology areas that could truly revolutionise our energy future.


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