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  • Review Article
  • Published:

Microwave-assisted biorefineries

Nature Reviews Clean Technology volume 1, pages 269–287 (2025)Cite this article

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Abstract

Microwaves offer volumetric heating with a higher energy efficiency than conductive–convective heat transfer in conventional approaches. The emerging application of microwave heating in biorefineries is a low-emission strategy to produce bio-based chemicals and materials. In this Review, we discuss the use of microwaves in biorefinery applications, including lignocellulose pretreatment, bioactive substance extraction, pyrolysis and hydrothermal treatment. Experimental evidence suggests that microwaves increase reaction rates, product yield and selectivity; however, these outcomes do not always occur. It is important that microwave-assisted techniques are assessed under controlled conditions to allow a fair comparison with conventional processing. Microwaves can induce hotspots in heterogeneous, multiphasic systems, which have reaction-specific impacts on the chemistry of the system. If not controlled, hotspot generation might cause potential catalyst deactivation or risk of reactor explosion. Pilot-scale systems for solid-phase processing such as pyrolysis have already been demonstrated, whereas large-scale microwave-assisted liquid-phase processing could face problems such as low microwave absorptivity in hot water and limited microwave penetration for large volumes. Further work is needed to develop standard protocols to clarify the advantages of microwaves in wide-ranging biorefinery systems to lay the foundation of technological transfer.

Key points

  • Microwave processing could enable the development of energy-efficient biorefineries for lignocellulose pretreatment, extraction of bioactive substances, pyrolysis, hydrothermal treatment and fine chemical production.

  • Unlike conventional heating methods, the reacting matrix, including the feedstocks, solvents and additives, needs to be strong microwave absorbers for effective heating to occur under microwaves.

  • Non-equilibrium localized heating under microwaves, known as the hotspot effect, has been widely linked to the increased reaction rate and selective production observed in microwave experiments; however, there is not yet any empirical evidence on the universality of this link.

  • The feasibility of pilot-scale and field-scale microwave-assisted biorefineries has been experimentally demonstrated, especially for solid-phase processing such as pyrolysis.

  • Techno-economic assessments and life-cycle analyses indicate that microwave processing potentially has a lower cost and carbon footprint than conventional techniques; however, such a conclusion cannot be extrapolated to contexts outside the discussed studies and independent assessments are still required for new projects in real-life scenarios.

  • Hotspot monitoring and control alongside advances in microwave reactors could help to expedite the industrial-scale use of microwave-assisted biorefineries.

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Fig. 1: Biomass feedstocks and the corresponding treatments.
Fig. 2: Hotspots and the landscape of microwave-assisted biorefinery.
Fig. 3: Environment impacts of microwave processing.

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Acknowledgements

I.K.M.Y. acknowledges the financial support provided by Tsinghua-NUS Joint Research Initiative Fund (WBS: A-8002524-00-00).

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Authors and Affiliations

  1. Department of Civil and Environmental Engineering, National University of Singapore, Singapore, Singapore

    Qiaozhi Zhang, Zhuo Li, Zhuoyue Liu, Yudha Dwi Prasetyatama & Iris K. M. Yu

  2. Sobono Private Limited, Singapore, Singapore

    Wee Khoon Oh

  3. NUS Environmental Research Institute, National University of Singapore, Singapore, Singapore

    Iris K. M. Yu

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  1. Qiaozhi Zhang
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Contributions

Q.Z., Z. Li, Z. Liu and Y.D.P. researched data for the article. All authors contributed substantially to discussion of the content. W.K.O. specifically contributed to discussion related to scale-up of biorefineries. All authors wrote the article. I.K.M.Y. reviewed and/or edited the manuscript before submission.

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Correspondence to Iris K. M. Yu.

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W.K.O. is the Manager Director of Sobono Private Limited, which focuses on sustainable technologies including bioresource utilization for renewable energy production. The other authors declare no competing interests.

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Zhang, Q., Li, Z., Liu, Z. et al. Microwave-assisted biorefineries. Nat. Rev. Clean Technol. 1, 269–287 (2025). https://doi.org/10.1038/s44359-025-00033-5

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