Researchers at Texas A&M University and ExxonMobil are developing a method to reprocess petroleum coke—a byproduct of refining crude oil—into graphene, using a chemical process called electrochemical exfoliation. This open-access study was published in NPJ 2D Materials and Applications.
Simplified schematic of refinery operations and products: there is a need to push these petroleum streams toward products with low end-use emissions, such as carbon nanomaterials. Saha et al.
Crude oil is a mixture of many different hydrocarbons, with light portions going to natural gas while the heaviest portions form viscous or even solid materials. One of the many products that comes from refining crude oil is solid petroleum coke.
Although there are many ways to utilize petroleum coke—such as electrodes for steel and aluminum production—these processes release carbon emissions. For this reason, the industry is looking for low-emissions, high-value materials that can be derived from crude oil.
A possible solution is repurposing the carbon-rich petroleum coke to generate graphene, a versatile sheet-like material composed of a single layer of carbon atoms. Conventionally, graphene is exfoliated from graphite. The researchers investigated whether any chemical processes would facilitate graphene production from fossil fuel-derived materials.
We know that petroleum coke contains graphene-like materials. Our challenge was to isolate the graphene from the starting material.
The researchers placed coke into an electrolyte solution with a working electrode and a counter electrode. When they applied voltage to the working electrode, the ionic species or negative ions from the electrolyte migrated in between the graphene sheets in a process called intercalation.
When the coke is expanded, the graphene separates. Negative ions are created and move into the spaces between the graphene sheets, completing the coke byproduct and graphene separation.
Many graphene applications require high conductivity, but whether the graphene from petroleum coke could achieve such performance was unknown. The graphene created from the coke had a conductivity of 50 siemens per meter compared to a typical lithium-ion battery, whose electrical conductivity is about 150-160 siemens per meter. With a heat treatment called annealing, the researchers could boost the conductivity even higher, making it comparable to electrodes in lithium-ion batteries.
Saha, S., Lakhe, P., Mason, M.J. et al. (2021) “Sustainable production of graphene from petroleum coke using electrochemical exfoliation.” npj 2D Mater Appl 5, 75 doi: 10.1038/s41699-021-00255-8