A study has found that pulverised coal powder can be converted into nano-graphite using a household microwave oven, an advance that could keep coal economically viable.
The team from the University of Wyoming have had their findings published in the journal Nano-Structures & Nano-Objects. They believe this discovery will mark a step forward in the effort to find alternative uses for Wyoming’s Powder River Basin coal, at a time when demand for coal to generate electricity is declining due to climate change concerns.
Researchers reported that they created an environment in a conventional microwave oven to successfully convert raw coal powder into the higher value nano-graphite, which is used as a lubricant and in items ranging from fire extinguishers to lithium ion batteries.
“This method provides a new route to convert abundant carbon sources to high-value materials with ecological and economical benefits,” said the team, led by associate professor TeYu Chien, in UW’s Department of Physics and Astronomy.
While previous research has shown that microwaves can be used to reduce the moisture content of coal and remove sulphur and other minerals, most methods require specific chemical pre-treatment of the coal. The UW researchers explained how in their experiment, they simply ground raw Powder River Basin coal into powder.
The powder was then placed on copper foil and sealed in glass containers with a gas mixture of argon and hydrogen, before being placed in the microwave oven: chosen because of convenience, according to the team, and because it produced desired levels of radiation.
Chris Masi, the paper’s lead author, explained that by cutting the copper foil into a fork shape, sparks were induced by the microwave radiation, generating a temperature of over 1,800 degrees Fahrenheit within a few seconds.
These high temperatures were necessary to transform the coal powder into polycrystalline graphite, with the copper foil and hydrogen also contributing to the process. While the experiment was reported to include microwave durations ranging from three to 45 minutes, the optimal duration was found to be 15 minutes.
The scientists hope that this new method of coal conversion could be refined and performed at a larger scale, to yield a higher quality and quantity of nano-graphite materials.
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