Researchers at the University of Wyoming have shown that pulverized coal powder can be processed into higher-grade nano-graphite using copper foil, glass containers and a traditional household microwave oven.
The finding is another step in an attempt to find new uses for coal in the Powder River Basin of Wyoming at a time when demand for coal to produce energy is decreasing due to concerns about climate change.
The UW researchers report in a paper published in the journal Nano-Structures & Nano-Objects that they created an atmosphere in a microwave oven where raw coal powder was successfully transformed into nano-graphite, which is used as a lubricant and in products ranging from fire extinguishers to lithium-ion batteries.
This “one-step method with metal-assisted microwave treatment” is a fresh solution that could provide a quick and relatively inexpensive coal conversion technology.
The research team, led by Associate Professor TeYu Chien of the UW Department of Physics and Astronomy, wrote, “This method offers a new way to convert abundant carbon sources into high-value materials with environmental and economic benefits,”
Professor Jinke Tang of the Department of Physics and Astronomy, Professor Brian Leonard of the Department of Chemistry, Professor Maohong Fan of the Department of Petroleum Engineering and the School of Energy Resources, graduate students Rabindra Dulal of Nepal, Joann Hilman of Laramie, Chris Masi of Syracuse, N.Y., and Teneil Schumacher of Buffalo, as well as postdoctoral students Rabindra Dulal of Nepal, Joann Hilman of Laramie, Chris Masi of Syracuse, N.Y.
Although previous research has shown that microwaves can be used to decrease the moisture content of coal and extract sulfur and other minerals, special chemical pretreatment of coal is needed for most of these methods.
The UW researchers in their experiment actually ground raw coal into powder from the Powder River Basin.
Before being placed in a microwave oven, this powder was then put on copper foil and sealed in glass containers with a gas mixture of argon and hydrogen.
Since it was convenient and offered the desired level of radiation, a traditional microwave oven was chosen.
“By cutting the copper foil into a fork shape, the sparks were induced by the microwave radiation and produced an extremely high temperature of more than 1,800 degrees Fahrenheit within a few seconds,” says Masi, lead author of the paper. “This is the reason why you should not put a metal fork in a microwave oven.”
The high temperatures necessary to turn the carbon powder into polycrystalline graphite were produced by the sparks caused by the microwaves, with the copper foil and hydrogen gas also contributing to the process.
Microwave durations of 3 to 45 minutes were involved in the experiment, with an optimum period of 15 minutes.
The researchers suggest that this new carbon conversion process could be optimized and carried out on a larger scale to achieve higher nano-graphite content quality and quantity.
“Finite graphite reserves and environmental concerns for graphite extraction processes make this method of converting coal to graphite a great alternative source for graphite production,”Finite graphite reserves and environmental concerns for processes of graphite extraction make this method of converting coal to graphite a great alternative source for graphite production.
Reference: Christoffer A. Masi, Teneil A. Schumacher, Joann Hilman, Rabindra Dulal, Gaurab Rimal, Bang Xu, Brian Leonard, Jinke Tang, Maohong Fan and TeYu Chien, Jan. 5, 2021, Nano-Structures & Nano-Objects, transforming raw coal powder into polycrystalline nano-graphite by metal-assisted microwave treatment. DOI: 10.1016/j.nanoso.2020.100660