A team from the University of Calgary and Rice University has used flash joule heating (FJH) (earlier post) to convert low-value asphaltenes—a by-product of crude oil refining—into a high-value carbon allotrope, asphaltene-derived flash graphene (AFG).
Flash graphene from asphaltenes. (A) Schematic conceptualization of sustainable valorization of asphaltene. (B) Photograph of ground asphaltene powder, the FJH jig during a flash treatment event, AFG, and a TEM image of the AFG flakes.
Asphaltenes are heavy macromolecules in the high-temperature residuum of petroleum distillation; they impede the crude oil processing via a number of mechanisms and lower the economic value of the crude oil. Asphaltenes are thus deemed as low-value by-products with little to no real-world application and commercial use in today’s market.
Worldwide reserves of asphaltenes are currently estimated to be between 1 to 2 trillion barrels; poor biodegradability, ignitability, and reactivity raise concerns over their reuse and/or disposal. Isolated via conventional separation techniques, asphaltenes are typically combusted for reuse as transportation fuels and/or discarded in tailing ponds and landfills.
However, the team noted:
Asphaltenes are rich in carbon (~70 to 80%), and such a carbon-rich material with diverse and appealing physicochemical characteristics, for example, high aromaticity, heteroatom content, polar functional groups, and double bond equivalent numbers, can have great potential as an inexpensive and readily available feedstock for developing carbon-based structural and functional materials.
Consequently, research on the valorization of asphaltenes has sparked over the past few years. To date, efforts have been invested in developing carbon fibers, carbon electrodes, porous carbon foam/scaffolds, and carbon nanosheets from asphaltenes. However, a green recycling or upcycling solution that will simultaneously convert low-value asphaltene into high-value carbon materials/allotropes and develop end products appropriate for a myriad of engineering applications is still unrealized.
Here, we report the bulk-scale conversion of asphaltenes into a stable, naturally occurring form of carbon, namely, graphene, using a single-step, low-cost, energy-efficient, recyclable, scalable, and sustainable technique called flash joule heating (FJH).—Saadi et al.
Because the FJH process is a resistive/ohmic heating process that requires the source material to be electrically conductive, and because asphaltene is a poor conductor, the researchers added a minimal amount [20 weight % (wt %)] of conductive carbon black (CB) to the raw asphaltene powder.
The conductive homogeneous mixture is lightly compressed inside a quartz tube between two copper electrodes. High-voltage electric discharge from a capacitor bank brings the source mixture to temperatures higher than 3000 K in less than 100 ms, effectively converting into AFG with a process yield of ~45% and an AFG yield above 95%.
After successful conversion, we develop nanocomposites by dispersing AFG into a polymer effectively, which have superior mechanical, thermal, and corrosion-resistant properties compared to the bare polymer. In addition, the life cycle and technoeconomic analysis show that the FJH process leads to reduced environmental impact compared to the traditional processing of asphaltene and lower production cost compared to other FJH precursors. Thus, our work suggests an alternative pathway to the existing asphaltene processing that directs toward a higher value stream while sequestering downstream emissions from the processing.—Saadi et al.
Saadi MASR, Advincula PA, Thakur MSH, Khater AZ, Saad S, Shayesteh Zeraati A, Nabil SK, Zinke A, Roy S, Lou M, Bheemasetti SN, Bari MAA, Zheng Y, Beckham JL, Gadhamshetty V, Vashisth A, Kibria MG, Tour JM, Ajayan PM, Rahman MM. (2022) “Sustainable valorization of asphaltenes via flash joule heating.” Sci Adv. doi: 10.1126/sciadv.add3555