When crude oil is processed, a lot of grungy byproducts are left over. A new study indicates that a couple of those substances can be used to make low-cost carbon fibers, which could in turn find use in less costly carbon fiber composites.
The composite material that we know as carbon fiber typically consists of woven carbon fibers combined with an epoxy binder.
And yes, the material tends to be expensive. That's because polyacrylonitril, which is a precursor chemical that commonly gets spun to create the fibers, is itself quite pricey. As a result, scientists have been searching for more cost-effective carbon fiber sources for some time now.
One previously considered candidate are molecular substances known as asphaltenes. These are components of crude oil, and they're separated from that oil during the refinement process. As you can guess by their name, they're used in the production of asphalt, among other applications.
They can also be spun into the form of carbon fibers, although those fibers tend to break easily. The fiber yield is also relatively low following the final heat-treatment step of the spinning process, in which the asphaltene fibers are carbonized.
With these drawbacks in mind, Prof. Mani Sarathy and colleagues at Saudi Arabia's King Abdullah University of Science and Technology (KAUST) recently looked to another crude oil processing byproduct – resins.
"Previous studies of oil residues have suggested that resins stabilize asphaltene molecules, highlighting their strong molecular affinity," says Edwin Guevara Romero, a researcher in Sarathy's lab. "This led us to hypothesize that blending asphaltenes with resins could create a synergistic feedstock for carbon fiber production."
In laboratory tests, such asphaltene-resin blends were found to flow better than asphaltenes alone, allowing them to be spun at lower, more energy-efficient temperatures. The fibers were also less prone to breakage after carbonization, resulting in performance similar to that of existing moderate-to-high-strength isotropic carbon fibers.
And as an added bonus, collecting the asphaltenes and resins should make the remaining crude-oil-processing leftovers easier to deal with.
"Traditionally, oil residues have been used in very low-value applications such as road surfacing," says Sarathy. "By extracting the heaviest asphaltenes and resins for high-value carbon fiber manufacturing, the remaining residual oils can also be more easily processed to produce cleaner fuels or valuable small molecules, further improving the economics of the process."
A paper on the research was recently published in the journal Fuel.
Source: KAUST