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Tuesday, October 9, 2012

Navy wants to make fuel out of seawater

Gizmag took a look at Navy efforts to turn sewater into jet fuel, using a well-understood but extremely inefficient process called the Fischer-Tropsch reduction. here's the description:

The NRL process begins by extracting carbon dioxide and hydrogen from seawater. To do this, it uses a three-chambered electrochemical acidification cell. As seawater passes through this, it’s subjected to a small electric current. This causes the seawater to exchange hydrogen ions produced at the anode with sodium ions. As a result, the seawater is acidified.

Meanwhile, at the cathode, the water is reduced to hydrogen gas and sodium hydroxide is formed. The cells recover dissolved and bound carbon dioxide by re-equilibrating carbonate and bicarbonate to carbon dioxide gas from the acidified seawater. The end product is hydrogen and carbon dioxide gas. As a bonus, the sodium hydroxide is added to the leftover seawater to neutralize its acidity.

In the next step, the hydrogen and carbon dioxide are passed into a heated reaction chamber with an iron catalyst. The gases combine and form long-chained unsaturated hydrocarbons with methane as a by-product. The unsaturated hydrocarbons are then oligomerized – that is, they are made to form longer hydrocarbon molecules containing six to nine carbon atoms. Using a nickel-supported catalyst, these are then converted into jet fuel.

As with most chemistry, the problem is scale: It's one thing to do something in a beaker, something else to do it in 10,000-gallon tanks, where mixing and heat exchange and other issues become very, very complicated.

Read the whole article here - it's very good.