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Chain-length-controllable upcycling of polyolefins to sulfate detergents

Nature Sustainability volume 7, pages 1681–1690 (2024)Cite this article

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Abstract

Escalating global plastic pollution and the depletion of fossil-based resources underscore the urgent need for innovative end-of-life plastic management strategies in the context of a circular economy. Thermolysis is capable of upcycling end-of-life plastics to intermediate molecules suitable for downstream conversion to eventually high-value chemicals, but tuning the molar mass distribution of the products is challenging. Here we report a temperature-gradient thermolysis strategy for the conversion of polyethylene and polypropylene into hydrocarbons with tunable molar mass distributions. The whole thermolysis process is catalyst- and hydrogen-free. The thermolysis of polyethylene and polyethylene/polypropylene mixtures with tailored temperature gradients generated oil with an average chain length of ~C14. The oil featured a high concentration of synthetically useful α-olefins. Computational fluid dynamics simulations revealed that regulating the reactor wall temperature was the key to tuning the hydrocarbon distributions. Subsequent oxidation of the obtained α-olefins by sulfuric acid and neutralization by potassium hydroxide afforded sulfate detergents with excellent foaming behaviour and emulsifying capacity and low critical micelle concentration. Overall, this work provides a viable approach to producing value-added chemicals from end-of-life plastics, improving the circularity of the anthropogenic carbon cycle.

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Fig. 1: Controlling the hydrocarbon product distribution from plastic thermolysis.
Fig. 2: Tuning the molar mass of hydrocarbon products from PP and mixed PE75/PP25 thermolysis.
Fig. 3: Upcycling PE thermolysis oil into sulfate detergents.
Fig. 4: Determination of the wettability of PE-, PP-, PE75/PP25- and SDS-detergents.
Fig. 5: Physicochemical properties of sulfate detergents.

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Data availability

Additional data are provided in the Supplementary Information, and all the raw files are available via Dryad at https://doi.org/10.5061/dryad.41ns1rnq0 (ref. 51). Source data are provided with this paper.

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Acknowledgements

This work is based on the project supported by NSF Award No. DMR-2411680. We acknowledge the Chemistry Chromatography Center at Virginia Tech and M. Ashraf-Khorassani for providing assistance with the GC–MS experiments.

Author information

Authors and Affiliations

  1. Department of Chemistry, Virginia Tech, Blacksburg, VA, USA

    Nuwayo Eric Munyaneza & Guoliang Liu

  2. Department of Mechanical Engineering, Virginia Tech, Blacksburg, VA, USA

    Ruiyang Ji & Rui Qiao

  3. Department of Chemical Engineering, Virginia Tech, Blacksburg, VA, USA

    Adrian DiMarco & Guoliang Liu

  4. Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, CO, USA

    Joel Miscall, Lisa Stanley & Nicholas Rorrer

  5. BOTTLE Consortium, Golden, CO, USA

    Joel Miscall, Lisa Stanley & Nicholas Rorrer

  6. Department of Materials Science and Engineering, Macromolecules Innovation Institute, Virginia Tech, Blacksburg, VA, USA

    Guoliang Liu

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Contributions

G.L. conceived and supervised the project. G.L. and N.E.M. designed the research. N.E.M. performed the thermolysis and sulfation experiments. J.M., L.S. and N.R. evaluated the molar masses of the plastic feedstocks and thermolysis products. N.E.M. and A.D. conducted materials characterization of plastic waste-based detergents. R.Q. and R.J. performed the computational fluid dynamics studies. G.L. and N.E.M. wrote the original manuscript. All authors contributed to manuscript proofreading and editing.

Corresponding authors

Correspondence to Rui Qiao or Guoliang Liu.

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Competing interests

G.L. and N.E.M. have filed a patent based on this work: PCT/US2024/026720. The remaining authors declare no competing interests.

Peer review

Peer review information

Nature Sustainability thanks Yue Liu, Fan Zhang 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. 1–30, Scheme 1, Tables 1–10, Results, Discussion and computational fluid dynamics simulations.

Reporting Summary

Source data

Source Data Fig. 1

GC chromatograms of PE-oil and PE-wax.

Source Data Fig. 2a

Bar graphs of wax, oil and gas yield from plastics.

Source Data Fig. 2b

Pie charts of acyclic and naphthene product breakdown.

Source Data Fig. 2c

GC chromatograms of PP-oil and PP-wax.

Source Data Fig. 2d

GC chromatograms of PE/PP mixture oil and wax.

Source Data Fig. 3b

Proton NMR of PE thermolysis oil.

Source Data Fig. 3b

Proton NMR of PE-oil-derived AHS.

Source Data Fig. 3c

13C NMR of PE-oil-derived AHS.

Source Data Fig. 4c

Contact angle measurements of plastic-waste-based detergent solutions and SDS.

Source Data Fig. 5b

Drainage time experiments of detergents and paraffin oil mixtures.

Source Data Fig. 5c and 5d

Effect of detergent concentration on surface tension.

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Munyaneza, N.E., Ji, R., DiMarco, A. et al. Chain-length-controllable upcycling of polyolefins to sulfate detergents. Nat Sustain 7, 1681–1690 (2024). https://doi.org/10.1038/s41893-024-01464-x

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