NEWARK, Del. — Researchers at the University of Delaware have developed a technique they claim can remove the rubber anti-degradant 6PPD — a substance linked to fish kills in the Pacific Northwest — from end-of-life tires (ELTs).
The process, developed by the university's Center for Plastics Innovation and Department of Chemical and Biomolecular Engineering, "upgrades 6PPD" into safe chemicals and turns leftover crumb rubber into aromatics and carbon black, according to University of Delaware information.
Led by Dion Vlachos, University of Delaware Dan Rich chair in energy, the research tried to remove 6PPD from ELTs via chemical extraction, the university reported Nov. 20.
The process involves heating "millimeter-sized" pieces of tire or crumb rubber in a microwave reactor: using an unidentified chemical solvent to separate the 6PPD from the other molecules present. Once the 6PPD molecules are removed, they can be chemically converted into safe chemicals that can be used or sold for a small price, the team reported.
The rest of the tire, meanwhile, can be safely recycled for use in athletic fields and road surfaces or processed into feedstock materials such as carbon black.
6PPD is used by the tire industry to ensure that the tire components are protected from ozone and oxygen.
However, in the recent years, some researches have raised concerns over a 6PPD transformation product, 6PPD-quinone, which can impact aquatic life, particularly salmon.
Under sun radiation exposure, 6PPD converts to 6PPD-quinone, Vlachos said, or what is called a diketone, or a molecule made up of two ketone groups. One major source for these diketone molecules is the tires themselves.
"You can't put a filter on the environment the way you might have a filter on your household dryer to capture these fibers," said Vlachos, who also directs the Delaware Energy Institute.
According to Vlachos, attempts to break down the tire material using high heat, including pyrolysis, have failed to remove 6PPD from ELTs. The diketone molecules remain in the pyrolysis oil after the process, the research team leader explained.
If the pyrolysis oil is then used in fuel or other materials, the diketone molecules will remain in the product, potentially causing environmental damage.
TheUniversity of Delaware approach has been proved at lab-scale, Vlachos said, adding that a techno-economic analysis showed "the cost looks to be very reasonable."
The U of D research team has protected the novel approach through the University's Office of Economic Innovation and Partnerships.
