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While filling your tires with nitrogen may not have a major impact on fuel efficiency, the gas plays an important role when it comes time to recycle them. Tire rubber is designed to remain tough and elastic, which is great when you’re riding on them in your road car, but a problem when they’ve reached the end of their useful life.
Unlike used tires from F1 cars, most road tires can’t be easily melted down for recycling purposes. That’s where nitrogen comes in as part of the cryogenic grinding process. This method overcomes the rubber vulcanization that makes melting down old tires challenging and allows them to be recycled.
Cryogenic grinding uses liquid nitrogen to cool shredded rubber to -196 degrees Celsius, at which point a mill breaks it down into smaller particles. Recovered rubber from this kind of cold processing can be incorporated into a wide variety of materials, from new tires to asphalt mixtures and rubber hoses. However, the process produces smooth particles, unlike other methods that yield rougher surfaces that bond more effectively with other polymers. Thus, cryogenic grinding isn’t the right choice for every purpose.
Nitrogen can also help in extreme heat recycling
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Of course, nitrogen does more than help recycle tires. The gas also means tires don’t need topping off as frequently and degrade more slowly. That said, the latter’s benefits are debatable, as most users will replace their tires before that becomes an issue.
Even within the tire recycling process, nitrogen is more than a one-trick pony. The gas is also used at the opposite temperature extreme from cryogenics, in a process called pyrolysis. This breaks down rubber into component gas, liquid, and solid products using extreme heat. However, unlike burning, the process doesn’t use oxygen.
Instead, nitrogen (or hydrogen) is injected into the system to purge oxygen from the air and maintain an inert atmosphere. Displacing oxygen helps prevent unwanted combustion as the extreme heat drives thermal decomposition of the rubber. The process yields syngas, fuel, and a solid residue called carbon black. These materials can then be used as fillers in plastic, in industrial fuels, or as a reinforcing material in tires and other rubber products.