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The electric vehicle revolution is here, and that means good news for fans of zero emission travel. Now attention is turning to untangling the EV supply chain from a sticky web of fossil energy inputs. For one solution, the A-list tire manufacturer Bridgestone is focusing its efforts on sustainable tires made with synthetic rubber, derived from just about anything other than virgin petroleum.
Sustainable Tires And The Synthetic Rubber Problem
Tires made of natural rubber dominated the auto industry in the early years, beginning in the 19th century. However, the most sustainable tires of today are not necessarily the ones made from plant rubber.
Only one type of rubber-producing plant, the Hevea brasiliensis tree, has broken into the commercial rubber market. Its reputation is clouded by disease, climate change, and deforestation issues. Those problems are intensifying alongside the rising demand for rubber. Diversifying the natural rubber supply chain could help on the sustainability end. Soybeans, the shrubby weed guayule, and dandelions are some of the candidates under exploration. However, the alternatives are far from scaling up, to meet demand.
In the 20th century tire manufacturers began supplementing natural rubber with a synthetic version. The go-to source today is butadiene, a byproduct of the petroleum refining process. Aside from the petroleum angle, that raises a serious supply chain concern. Whenever the global pace of petroleum extraction finally begins to decline — hopefully in time to prevent catastrophic climate change — the supply of butadiene will decline along with it.
Sustainable Tires From Ethanol
For a solution, researchers at the US Department of Energy’s Pacific Northwest Natural Laboratory have been kicking supply chain diversity up a notch. The idea is to skip over the part about producing natural rubber from plants. Instead, the PNNL team has been focusing on converting ethanol to butadiene.
In terms of sustainable tires, corn ethanol comes with some serious baggage of its own. However, corn is just one potential resource.
“Nearly all of the country’s ethanol currently comes from the starch in corn grain, but ethanol can also be produced from other types of biomass,” PNNL points out, listing the up-and-coming algae industry, food waste, human waste, industrial waste, and old tires among the alternative ethanol feedstocks.
The challenge is to develop an efficient, cost-effective catalyst to shepherd the ethanol-to-butadiene conversion process along, and PNNL has found it
“When it’s mixed with ethanol, the catalyst works by first breaking off ethanol’s hydrogen atoms, which creates acetaldehyde (a compound that occurs naturally in coffee, ripe fruit and bread). Further reactions continue to rearrange atoms and bonds until butadiene forms,” PNNL explains.
Bridgestone Wants Sustainable Tires For Your New EV
The PNNL catalyst first emerged in 2018 and underwent further refinement with an assist from the Energy Department’s Bioenergy Technologies Office and a collaboration with Bridgestone. In the most recent development, the Energy Department’s Industrial Efficiency and Decarbonization Office is providing another $10 million or so to push the catalyst into commercial development.
Bridgestone is partnering with PNNL in the three-year project, and they seem pretty confident about the potential for moving sustainable tires into the marketplace. In a press release dated December 16, PNNL noted that Bridgestone is already laying plans for a pilot plant to be located in Akron, Ohio.
Bridgestone also described the research project in October, stating that it is tasked with designing, building, and operating a pilot plant aimed at demonstrating “an innovative, potentially more sustainable and cost-effective approach to obtaining butadiene from ethanol.”
The Long Road To Sustainable Tires
The road from sustainable butadiene to sustainable tires will be a long one. The ethanol-to-butadiene pilot plant is expected to answer some key questions about lifecycle carbon emissions as well as commercial viability. Bridgestone will also need to evaluate how the butadiene performs in tires.
“Butadiene is a key ingredient in tires today and typically represents the No. 1 ingredient (by volume) in synthetic rubber that is derived from fossil fuels,” the company notes. “The goal of this project is to assess, and hopefully prove, the economic viability of deriving butadiene from ethanol conversion versus fossil fuel conversion.”
As described by Bridgestone, the 12-month period starting in October 2024 will focus on designing the pilot plant. Construction should begin by the end of 2025, with operation to follow in 2026.
Beyond The Sustainable EV Of The Future: Group Hug For US Taxpayers
Of course, the most sustainable tires are the ones that go on buses and other modes of alternative transportation, including feet, bicycles, and various sorts of two-wheeled electric vehicles. Failing that, cleaning up the supply chain for EV tires is a good step in the right direction.
Bridgestone and other tire industry stakeholders have their work cut out for them. Sustainable tires sounds good on paper, but the elements of lifespan and performance are also crucial factor. In the electric vehicle space, for example, tire quality can have a significant impact on battery range (see more EV tire background here).
If the Bridgestone-PNNL collaboration does meet expectations for sustainability, lifespan, and performance, tires will not be the only consumer products to be freed from the fossil energy supply chain, and US taxpayers can give themselves a pat on the back for that.
“If America wore a pair of shoes, the soles would be made of butadiene. This molecule is the building block for just about every major synthetic plastic or rubber,” noted PNNL Laboratory Relationships Manager Corinne Drennan back in 2018, in an Energy Department article describing how researchers at the lab developed the new catalyst.
Earlier, non-commercial methods for converting ethanol to butadiene deployed weak catalysts, and they required an additional purification step. The PNNL team, headed up by researcher Vanessa Dagle, and came up with a one-step catalyst based on silver nitrate and zirconyl nitrate, supported on a platform of silica. The new catalyst separates out the hydrogen to form acetaldehyde, which then self-assembles into crotonaldehyde, and from there into crotyl alcohol. The process is complete when the alcohol is dehydrated.
The lab reported a 70% conversion rate for their one-step process. In contrast, previous catalysts required multiple pass-throughs to reach that goal. “The catalyst also does not require pre-preparation of the ethanol; aqueous ethanol (ethanol with water in it) can be used,” Drennan noted.
The incoming administration has pledged to support fossil energy stakeholders. However, unless they can figure out a way to slow or even halt the Bridgestone-PNNL collaboration, the ripple effect will go beyond sustainable tires to impact the supply chain for all sorts of petroleum-dependent products. If you have any thoughts about that, drop a note in the comment thread.
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Photo (cropped): Sustainable tires could be made with butadiene derived from algae, food waste, and other renewable resources instead of petroleum, if a new research project pans out (courtesy of Pacific Northwest National Laboratory).
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