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The Latest in Coffee Grounds Energy Technology

Empty the grounds, add some lye ... hey, you've got a methane trap going.
(Photo: Robert Wolkaniec/Shutterstock)

(Photo: Robert Wolkaniec/Shutterstock)

Coffee grounds are for many of us just something we throw in the compost (or the trash), but the wonderful World Wide Web provides numerous alternatives, including soap and wood stain. You can now add energy storage to the list. Turns out, coffee grounds make for a simple, cheap way to trap and store methane gas.

Methane, the main ingredient in natural gas, burns considerably cleaner than other fossil fuels. It also happens to be a greenhouse gas, with a global warming potential roughly 30 times as high as carbon dioxide. (Humans produce just shy of two-thirds of the atmosphere's methane.)

Coffee grounds make for a simple, cheap way to trap and store methane gas.

That's led scientists and engineers to devote a fair amount of time to figuring out how to collect the gas, sticking pipes in everything from landfills to cows with the goal of storing methane for later use in cars or power plants. The trouble is, storing methane is often a complicated and dangerous matter—it's usually contained in heavily compressed gas cylinders at up to 250 times ordinary atmospheric levels.

But there are other options—in particular, carbon. "[C]arbon-based materials are ideal candidates for methane and other gas capture/storage as they are light, durable and relatively cheaper to produce," postdoctoral fellow Christian Kemp and colleagues at Ulsan National Institute of Science and Technology write in the journal Nanotechnology. "In fact, the cost of carbon-based materials used in methane adsorption can be further reduced if the carbon source is readily available and of no inherent value, i.e. waste material."

In other words, spent coffee grounds might make a good methane storage system. Kemp and other members of the Center for Superfunctional Materials decided to test out the theory. Their first step: "Spent coffee grounds (Kirkland, 100% Colombian coffee, dark roast fine ground) were obtained in house," they explain, using the academic lingo for "we made cheap coffee and saved the grounds."

They next stirred those grounds into a mix of water and potassium hydroxide, better known as lye, which they then dried and heated at temperatures between 700ºC and 900ºC. This produced activated carbon—the same stuff used in water filters and deodorizers. (Above 900ºC, their equipment mysteriously disintegrated, possibly because it came into contact with molten lye, the researchers note.) Finally, the team rinsed their sample in water to remove the lye.

The team then set out to see how much methane they could force into this sample of their activated carbon. Their results: about 70 grams of methane per kilogram of activated carbon, at roughly 14 percent of the pressure of a typical compressed natural gas tank—considerably less than Department of Energy's 2000 objective of 238 grams of methane per kilogram of carbon at the same pressure. A number of other projects have met that goal, but, Kemp and colleagues write, at much greater effort and cost.

Now you have one more thing to do with your coffee grounds.

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