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A New Chemical Recipe Raises Prospect of Inexpensive Fuel


metal-organic framework

This tubelike molecule, called a MOF, can transform ethane (small structures with light blue dots) into ethanol (structures with added red dots). Credit: NIST

Cheap fuel: A lot of people would like to bring down the cost of gas, and not just for running car engines. Natural gas derivatives like liquid methanol can become the basis for chemicals that make everything from paint to plywood. Methanol, however, often gets its start from the gas component methane, and moving the gas safely and storing it costs a lot of money.

The liquid form would be a lot easier, safer, and less expensive to use. But transforming methane to methanol, on an industrial scale, drives up the cost, because the reaction requires a lot of added energy, in the form of heat. About 1560 degrees Fahrenheit of heat, in fact. When nature does the conversion it is more efficient: It happens at room temperature.

Some honeycomb-shaped molecules created in a lab are coming closer to that bit of alchemy. They have not done it yet, but they have recently pulled off a related feat, turning ethane, another natural gas component, into liquid ethanol. “Chemists have been trying to do things like this for a long time,” says Jeffrey Long from the University of California at Berkeley, who is one of those chemists.

The molecules are called metal-organic frameworks, or MOFs. They are laboratory-built, formed from metal atoms that are linked together by organic, carbon-based molecules. The result does look something like a honeycomb, or a box of drinking straws built on a microscopic scale. Long and his colleagues built one around iron atoms, called it Fe-MOF-74, and patented it.

When the scientists ran ethane through the frameworks, they learned that a lot of it was converted to ethanol at the end of the process, they reported two weeks ago in Nature Chemistry. The iron catalyzed the reaction, by but the rigid framework was key to keeping the iron exposed so it could do that job. The entire structure holds the iron open, free to react with the substances flowing by it.

The goal, chemists say, is not to turn natural gas into whiskey—ethanol is the alcohol we drink—or any other beverage. MOFs are “tunable,” meaning chemists can slightly alter their properties to react with other gas components. The hope is that deliberate tuning will eventually let them move on to methane and move it to liquid methanol at close to room temperature, and that is an intoxicating prospect.

The views expressed are those of the author and are not necessarily those of Scientific American.

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