Tires are dirty business, and we're not just talking about the mud they gather as they roll beneath your car. Manufacturing rubber is a resource-intensive process that is heavily reliant on petroleum, but now scientists are claiming a chemical breakthrough that replaces the key molecule in conventional tires with one sourced from grass and trees instead, all without affecting the tire's color, shape or performance.

The environmental impact of tire production has prompted a years-long search for a more sustainable method. These efforts have focused on the main component of rubber, a molecule called isoprene. To make isoprene, molecules in petroleum are thermally broken apart and the molecule is isolated from hundreds of other chemicals and purified, at which point it organizes itself into long polymer chains.

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Conveniently, isoprene can also be derived from natural sources. While researchers have explored the possibility of using sugars derived from biomass to make tire rubber, doing so on anything near the scale required is no easy feat. In 2010, for example, Goodyear described a method of engineering bacteria to ramp up the microbial production of isoprene, while the cloning of a key enzyme to produce man-made isoprene in 2012 offered yet another potential way forward.

Now researchers at the University of Minnesota are claiming a new breakthrough in the area, by way of a chemical process that combines the boosting of natural microbial fermentation with catalytic refining, similar to the process used to refine petroleum.

The chemical process combines the boosting of natural microbial fermentation with catalytic refining (Credit: University of Minnesota)

It begins with the microbial fermentation of plant sugars, such as glucose, into something called itaconic acid. This acid is then mixed with hydrogen, causing a chemical reaction that results in something called methyl-THF.

And the third step, which is where the breakthrough lies, involves using a recently discovered catalyst called Phosphorous Self-Pillared Pentasil to dehydrate the methyl-THF into isoprene. This method resulted in catalytic efficiency as high as 90 percent, with most of the product being isoprene, something the researchers say gives the prospect of renewable isoprene a real boost and could even lead to other advanced rubber-based products.

"The performance of the new P-containing zeolite catalysts such as S-PPP was surprising," says Paul Dauenhauer, a University of Minnesota associate professor of chemical engineering and lead author of the new study. "This new class of solid acid catalysts exhibits dramatically improved catalytic efficiency and is the reason renewable isoprene is possible."

The research was published in the journal ACS Catalysis.

Source: University of Minnesota

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