Graphene has unique physical properties. It is a naturally-occurring carbon substance. It is a solid that ranges from black to dark gray with metallic luster. It is a highly-refractory material, which is an excellent conductor for heat and electricity. It is also stable at a wide range temperatures. It is also known by the name super conductor due to its low electrical resistance. Graphene comes from natural sources such as coal and plant matter or can be an industrial byproduct such as petroleum koke. Petroleum coke, which is used in the production of aluminum and stainless steel, or for heating, has historically been a source of significant carbon emissions. This industrial byproduct can now be used in a more sustainable way, both environmentally and economically.
Research conducted by the Department of Chemical Engineering at Texas A&M University, funded by Energy Advanced Research Projects Agency - Energy (ARPA-E), has found that a simple modification of the petroleum coke-processing method produces high-quality graphitized graphene. Researchers were able lower the temperature for the coke-to graphite conversion process and reduce the processing time. This allowed it to be applied to high-performance Lithium batteries.
Petroleum coke, also known as carbonized oil residues, is a byproduct of oil refinement. It is produced through fluidized bed coking or delayed coking of crude oils residues. The resulting hard coke has a metallic shine and can be in a granular-like or needle shape. The type of graphite produced by the reaction between coke and carbon dioxide has a crystalline structure that can be distinguished from other types using optical microscopy. It is characterized by a high fixed-carbon content, low sulfur and low ash. It is used for raising the carbon content in high quality steels, alloys, and cast irons.
The researchers reacted CK-1, CK-2, and CK-3 petroleum cokes in an Autoclave with 6M nitric. The post-reaction separation was performed in two steps using centrifugation. Separating the reacted from unreacted coke EEGs was done by centrifugation for 10 min at low speed followed by 20 min at high speed. SEM, Raman and TEM images show that the final products contain single- and multi-layered graphene. The Raman spectrum contains a 2D Peak that is not found in the parent coal. This confirms to us that the centrifugation method has been successful in separating the graphene. The final product, which is similar to graphene, has a high purity and density of crystalline crystals, as well as a low vapor pressur and a wide temperature range. These characteristics make it ideally suited for battery applications. The researchers are working to optimize the process in order to scale it up for commercialization.
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