Fiber medicine

Could we make cars from petroleum residues?


A new way to make carbon fiber could turn refinery byproducts into high-value, ultralight structural materials for cars, planes and spacecraft.

As the world strives to improve the efficiency of cars and other vehicles to reduce greenhouse gas emissions and improve the range of electric vehicles, the search for materials that are ever lighter and strong enough for use in car bodies is underway.

Lightweight carbon fiber materials, similar to the material used for some tennis racquets and bicycles, combine exceptional strength with low weight, but have been more expensive to produce than comparable steel or aluminum structural elements. Now, researchers from[{” attribute=””>MIT and elsewhere have come up with a way of making these lightweight fibers out of an ultracheap feedstock: the heavy, gloppy waste material left over from the refining of petroleum, material that refineries today supply for low-value applications such as asphalt, or eventually treat as waste.

Not only is the new carbon fiber cheap to make, but it offers advantages over the traditional carbon fiber materials because it can have compressional strength, meaning it could be used for load-bearing applications. The new process is described on March 18, 2022m in the journal Science Advances, in a paper by graduate student Asmita Jana, research scientist Nicola Ferralis, professor Jeffrey Grossman, and five others at MIT, Western Research Institute in Wyoming, and Oak Ridge National Laboratory in Tennessee.

Circle of Carbon Fibers

A circle of carbon fibers which have a diameter of about 10 micrometers. Credit: Nicola Ferralis

The research began about four years ago in response to a request from the Department of Energy, which was seeking ways to make cars more efficient and reduce fuel consumption by lowering their overall weight. “If you look at the same model car now, compared to 30 years ago, it’s significantly heavier,” Ferralis says. “The weight of cars has increased more than 15 percent within the same category.”

A heavier car requires a bigger engine, stronger brakes, and so on, so the reducing the weight of the body or other components has a ripple effect that produces additional weight savings. The DOE is pushing for the development of lightweight structural materials that match the safety of today’s conventional steel panels but also can be made cheaply enough to potentially replace steel altogether in standard vehicles.

Composites made from carbon fibers are not a new idea, but so far in the automotive world they have only been used in a few very expensive models. The new research aims to turn that around by providing a low-cost starting material and relatively simple processing methods.

Human Hair and Carbon Fiber

A human hair and carbon fiber, with a clear ruler on the bottom half of the image. The human hair, pictured in a vertical orientation, is thicker (about 60 micrometers) than the carbon fiber behind it. Credit: Nicola Ferralis

Carbon fibers of the quality needed for automotive use cost at least $10 to $12 per pound currently, Ferralis says, and “can be way more,” up to hundreds of dollars a pound for specialized application like spacecraft components. That compares to about 75 cents a pound for steel, or $2 for aluminum, though these prices fluctuate widely, and the materials often rely on foreign sources. At those prices, he says, making a pickup truck out of carbon fiber instead of steel would roughly double the cost.

These fibers are typically made from polymers (such as polyacrilonitrile) derived from petroleum, but use a costly intermediate step of polymerizing the carbon compounds. The cost of the polymer can account for more than 60 percent of the total cost of the final fiber, Ferralis says. Instead of using a refined and processed petroleum product to start with, the team’s new approach uses what is essentially the dregs left after the refining process, a material known as petroleum pitch. “It’s what we sometimes call the bottom of the barrel,” Ferralis says.

“Pitch is incredibly messy,” he says. It’s a hodgepodge of mixed heavy hydrocarbons, and “that’s actually what makes it beautiful in a way, because there’s so much chemistry that can be exploited. That makes it a fascinating material to start with.”

It’s useless for combustion; although it can burn, it’s too dirty a fuel be practical, and this is especially true with tightening environmental regulations. “There’s so much of it,” he says, “the inherent value of these products is very low, so then it is often landfilled.” An alternative source of pitch, which the team also tested, is coal pitch, a similar material that is a byproduct of coking coal, used for example for steel production. That process yields about 80 percent coke and 20 percent coal pitch, “which is basically a waste,” he says.

Working in collaboration with researchers at Oak Ridge National Laboratory, who had the expertise in manufacturing carbon fibers under a variety of conditions, from lab scale all the way up to pilot-plant scale, the team set about finding ways to predict the performance in order to guide the choice of conditions for those fabrication experiments.

“The process that you need to actually make a carbon fiber [from pitch] is actually extremely minimal, both in terms of energy requirements and in terms of the actual processing you need to do,” says Ferralis.

Jana explains that pitch is “made of these heterogeneous sets of molecules, where you would expect that if you change the shape or the size, you would expect the properties to change drastically”, whereas an industrial material should have very consistent properties.

By carefully modeling how bonds form and crosslink between constituent molecules, Jana was able to develop a way to predict how a given set of processing conditions would affect the properties of the resulting fiber. “We were able to replicate the results with such accuracyshe says, “to the point where companies could take these graphs and be able to predict” characteristics like fiber density and modulus of elasticity.

The work produced results showing that by adjusting the starting conditions, it was possible to make carbon fibers that were not only tensile-resistant, like most of these fibers, but also compressive-resistant, meaning that ‘they could potentially be used in carrier applications. This opens up entirely new possibilities for the utility of these materials, they say.

The DOE’s call was for projects to bring the cost of lightweight materials below $5 a pound, but the MIT team believes their method can do better than that, hitting something like $3 a pound, although they have not yet done a detailed economic analysis. analysis.

“The new route we are developing is not just a cost effect,” says Ferralis. “It could open up new applications, and it doesn’t have to be vehicles.” Part of the complication of making conventional fiber composites is that the fibers must be formed into a fabric and laid out in precise, detailed patterns. The reason is, he says, “to compensate for the lack of compressive strength.” It’s a matter of engineering to overcome the shortcomings of the material, he says, but with the new process all that extra complexity wouldn’t be necessary.

Reference: “Atoms to Fibers: Identifying New Processing Methods in Pitch-Based Carbon Fiber Synthesis” by Asmita Jana, Taishan Zhu, Yanming Wang, Jeramie J. Adams, Logan T. Kearney, Amit K. Naskar, Jeffrey C. Grossman and Nicola Ferralis, March 18, 2022, Scientists progress.
DOI: 10.1126/sciadv.abn1905

The research team included Taishan Zhu and Yanming Wang from MIT, Jeramie Adams from Western Reserve University, and Logan Kearney and Amit Naskar from Oak Ridge National Laboratory. The work was supported by the US Department of Energy.