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End-of-life tire decontamination from 6PPD and upcycling

Nature Chemical Engineering volume 1, pages 597–607 (2024)Cite this article

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Abstract

N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) is a ubiquitous rubber antioxidant and antiozonant that extends the lifetime of common rubber products, such as those found in tires. It transforms into a quinone derivative following certain environmental conditions. 6PPD and the quinone can leach into the environment and cause severe morbidity to aquatic life at diminutive concentrations, with health effects on humans still not fully understood. With legislation on the horizon to ban 6PPD entirely, developing effective methods for its removal and conversion to safe compounds is essential. Here we show that 6PPD survives microwave-assisted pyrolysis and escapes in the oil product, rendering decontamination essential. We introduce a decontamination strategy that removes 6PPD from end-of-life tires before it enters the broader ecosystem. We demonstrate the catalytic upgrade of 6PPD to safe chemicals and the valorization of crumb rubber to aromatics and carbon black using microwave-assisted pyrolysis.

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Fig. 1: Heating performance, product distribution and morphological evolution in microwave pyrolysis of EOL tires.
Fig. 2: Solvent screening for 6PPD extraction.
Fig. 3: Temperature profiles and extraction rates of 6PPD in a continuous-phase extraction set-up.
Fig. 4: Catalytic deconstruction of 6PPD.
Fig. 5: Techno-economic analysis of the proposed decontamination and upcycling strategy.

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Acknowledgements

This work was supported by the National Science Foundation (grant no. OIA – 2119754). B.C.V. acknowledges a Graduate Research Fellowship through the National Science Foundation (grant no. 1940700). Crumb rubber was generously supplied by Liberty Tire Recycling. This research used beamline 7-BM (QAS) of the National Synchrotron Light Source II, a US DOE Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory (contract no. DE-SC0012704). Beamline operations were supported in part by the Synchrotron Catalysis Consortium (US DOE, Office of Basic Energy Sciences; grant no. DE-SC0012335). We thank L. Ma, N. Marinkovic and S. N. Ehrlich at the National Synchrotron Light Source II for their assistance with the XAS measurements. The TGA–MS used here is part of the Center for Plastics Innovation, an Energy Frontier Research Center funded by the US DOE, Office of Science, Basic Energy Sciences (grant no. DE-SC0021166).

Author information

Authors and Affiliations

  1. Center for Plastics Innovation, Newark, DE, USA

    Sean Najmi, Pooja Bhalode, Brandon C. Vance, Esun Selvam, Weiqing Zheng & Dionisios G. Vlachos

  2. Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE, USA

    Montgomery Baker-Fales, Brandon C. Vance, Esun Selvam, Kewei Yu & Dionisios G. Vlachos

Authors
  1. Sean Najmi
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  2. Pooja Bhalode
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  3. Montgomery Baker-Fales
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  8. Dionisios G. Vlachos
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Contributions

S.N. conceptualized the work and performed a formal analysis. S.N., P.B., M.B.-F., B.C.V., E.S., K.Y. and W.Z. performed the investigations. S.N., P.B., M.B.-F., B.C.V., E.S., K.Y. and W.Z. created the methodology. S.N., P.B., B.C.V., E.S., K.Y., W.Z. and D.G.V. wrote the original draft, whereas S.N. reviewed and edited it. D.G.V. administered the project and acquired funding.

Corresponding author

Correspondence to Dionisios G. Vlachos.

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Competing interests

S.N. and D.G.V. are inventors on a patent application related to this work filed by the University of Delaware. The other authors declare no competing interests.

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Nature Chemical Engineering thanks Ning Yan and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–26 and Tables 1–6.

Source data

Source Data Fig. 1

Temperature data, pyrolysis oil yields.

Source Data Fig. 2

Extraction data and COSMO solubility.

Source Data Fig. 3

Temperature data, extraction yields.

Source Data Fig. 4

XAS data, conversions and product yields.

Source Data Fig. 5

Costs and profitability index values.

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Najmi, S., Bhalode, P., Baker-Fales, M. et al. End-of-life tire decontamination from 6PPD and upcycling. Nat Chem Eng 1, 597–607 (2024). https://doi.org/10.1038/s44286-024-00110-9

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