Single stage process for converting coal into graphite

“This method provides a new route to convert abundant carbon sources to high-value materials with ecological and economic benefits”Te-Yu Chien

Researchers at the University of Wyoming have shown how to easily and cheaply convert coal powder into graphite using just copper foil, glass containers and a standard microwave oven. With the demand for coal declining due to climate change, this breakthrough in pulverizing coal powder into nano-graphite – which is used as a lubricant and in a range of products such as lithium-ion batteries and fire extinguishers – could help identify new uses for coal.

Although previous studies had used microwaves to reduce the moisture content of coal, as well as remove sulfur and other minerals, these approaches tend to depend on chemical pre-treatment of the coal and are problematic due to the complexity and interpretation of the results. However, as reported in the journal Nano-Structures & Nano-Objects [Masi et al. Nano-Struct. Nano-Objects (2020) DOI: 10.1016/j.nanoso.2020.100660], here raw coal powder was converted into nano-graphite in a single stage approach based around four factors: high temperature, a reducing environment, a catalyst and microwave radiation.

Raw coal was first ground into powder, before it was positioned on copper foil and sealed in a glass vial with a gas mixture of argon and hydrogen, and then put into a conventional household microwave oven. Sparks produced by the microwaves made the high temperatures required to change the coal powder into polycrystalline graphite, a process that was also facilitated by the copper foil and hydrogen gas. On testing microwave durations of up to 45 minutes, it was found that the best duration was 15 minutes.

With finite graphite reserves and environmental concerns about how it is extracted, this new approach to coal conversion could be refined to offer a higher quality and quantity of nano-graphite materials. As team leader TeYu Chien said, “This method provides a new route to convert abundant carbon sources to high-value materials with ecological and economic benefits”.

Further research is needed to assess if their approach is viable at a larger scale, and if it is possible to extract or isolate the converted graphite from the non-converted matrix. However, modifying the recipe could lead to new possibilities of treating coal and other materials of interest, and the team have already tried using plastic powder from a conventional plastic water bottle. Various functional and complex materials could also be produced by changing the metal used, or the temperature, or varying the source materials to target different areas, while modifying the environment could provide different reactions such as doping.