Researchers convert coal powder to graphite in a microwave oven

Using copper foil, glassware and a conventional household microwave oven, University of Wyoming researchers have demonstrated that crushed coal powder can be converted to nano-graphite with a higher value.

This discovery is another step forward in the search for alternative uses for Wyoming Powder River coal, at a time when demand for coal for electricity generation is declining due to concerns about climate change.

In a paper published in the journal Nano-structures & Nano-objects, UW researchers report that they created an environment in a microwave oven to convert crude coal powder to nano-graphite, which is used as an incinerator and in items from fire extinguishers to lithium-ion batteries . This “one-step method with metal-assisted microwave handling” is a new approach that could represent a simple and very inexpensive coal conversion technology.

“This approach provides a new path to convert abundant carbon resources into high-value products with ecological and economic benefits,” wrote the research team, led by Professional Professor TeYu Chien, in Department UW Physics and Astronomy.

Others involved in the project were Professor Jinke Tang, in the Department of Physics and Astronomy; Professional Professor Brian Leonard, in the Department of Chemistry; Professor Maohong Fan, in the Department of Petroleum Engineering and School of Energy Resources; graduate students Rabindra Dulal, of Nepal, Joann Hilman, of Laramie, Wyo., Chris Masi, of Syracuse, NY, and Teneil Schumacher, of Buffalo, Wyo .; and postdoctoral researchers Gaurab Rimal, from Nepal, and Bang Xu, China.

Although previous research has shown that a microwave can be used to reduce the moisture content of coal and remove sulfur and other minerals, most such methods require a special chemical pretreatment of the coal. In their experiment, UW researchers are just adding Basin River Powder raw coal to powder.

That powder was then placed on copper foil and sealed in glass containers with a gas mixture of argon and hydrogen, before being placed in a microwave oven. A standard microwave oven was chosen because of its convenience and because it provided the desired levels of radiation.

“By cutting the copper foil in the shape of a fork, the sparks were absorbed by the microwave radiation, generating a very high temperature of over 1,800 degrees Fahrenheit within a few seconds,” says Masi, lead author of the paper. “That’s why you shouldn’t put a metal fork inside a microwave oven.”

The sparks caused by the microwave created the high temperature required to convert the coal powder to polycrystalline graphite, with the copper foil and hydrogen gas also contributing to the process.

Although the test included microwave times ranging from 3 to 45 minutes, 15 minutes was found to be the optimal time.

The researchers say this new method of coal conversion could be refined and made at a larger scale to provide both higher quality and quantity of nano-graphite materials.

“Preserved sources of graphite and environmental concerns for graphite extraction methods make this method of converting coal to graphite another good source of graphite production,” the experts wrote.

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