Sustainable production of graphene from petroleum coke using electrochemical exfoliation
Petroleum coke is a solid, carbonaceous by-product of oil refining and is normally used for heating or as an anode in aluminum and steel production. These applications contribute to carbon emissions, but here we show that petroleum coke has another potential avenue: as a precursor for graphene production. This path presents an environmentally and economically sustainable use for a low-value industrial stream. Electrochemical exfoliation is used to produce graphene nanosheets from petroleum coke, rather than graphite. The final product is separated from the unreacted material by a two-step centrifuging process. SEM and TEM images confirm that the final product contains few-layered nanosheets, and the Raman spectra confirm that the exfoliated coke product is indeed graphene. Post-annealing of this product substantially increases the electrical conductivity. This new finding holds potential for the petroleum industry to produce a value-added nanomaterial and enhance the economic impact of slurry oil and slurry oil-derived coke streams by orders of magnitude; this route also allows these streams to be directed away from high-emissions uses.To get more news about
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With the continuing rise in concern over sustainable resource use, the petrochemical industry faces challenges in managing each of its product streams. Even by-products of oil refining, such as petroleum coke, are difficult to utilize sustainably; coke is produced by heating slurry oils and decant oils from refinery units such as Fluid Catalytic Crackers. Coke is used as a fuel for heating in several industries, and the combustion of coke produces more CO2 per fuel mass than coal1. Coke is also used in the steel and aluminum industries as an anode for smelting, a process that also emits greenhouse gases2. These concerns highlight the global need to repurpose existing petroleum streams such as coke and its precursor oils toward sustainable end-uses (Fig. 1).
Here, we demonstrate the use of petroleum coke as a feedstock for carbon nanomaterial production. Graphene, in particular, is an exciting target because of its ongoing deployment into a range of application fields including batteries, supercapacitors, structural materials, transparent electronics, and flexible wearable devices3,4. It is highly desirable to expand the suite of graphene precursors to include existing industrial by-products.
In addition, petroleum coke provides an additional feedstock for graphene production. Natural graphite is a finite source; it is estimated that 800 million tons can be recovered worldwide5. Furthermore, much of it is difficult to use or unusable for graphene production because only 10-15% of natural graphite is actually graphitic carbon; most of it is amorphous and contains silicate minerals or metals5. In contrast, needle coke can be consistently produced with high graphitic content and low impurity concentrations. Global needle coke production was at 1.1 million tons per year as of 2020, and it is expected to increase to 1.5 million tons per year by 20266. However, these numbers are based on the demand for needle coke for the steel and lithium-ion battery industries; needle coke production can be significantly increased to meet additional demand if needed. Although petroleum (and therefore petroleum coke) is also a finite resource, progress has been made toward producing needle coke from renewable feedstocks such as biomass7 or plastic waste8. Not only can needle coke be a more permanent feedstock for graphene production, but this avenue also the petroleum portfolio away from high-emission end-uses.
Graphite-derived graphene is well-documented9,10,11, but coke-derived graphene has not been extensively explored. Prior work on the production of graphene from coke has largely focused on graphene oxide (GO) and explored the effect of crystallinity on the resulting lateral size10,12,13. Ball-milling coke with stearic acid has also been explored14, but questions remain about the distinction between the parent material and the final graphene-like product, particularly in their Raman signature. This is likely related to a lack of effective separation procedures in place.
