Microwave-Assisted Pyrolysis of Low-Rank Coal

Microwave-assisted pyrolysis (MAP) of low-rank coal has emerged as a transformative route for converting high‐moisture, oxygen‐rich lignite and sub‐bituminous coals into valuable chemical feedstocks and fuels. Unlike conventional thermal methods, MAP employs dielectric heating to deliver energy directly into the coal matrix, thereby promoting rapid and uniform temperature rise, minimising heat losses and enabling selective bond cleavage. This approach facilitates enhanced devolatilisation, yielding higher proportions of liquid tar fractions and syngas with improved calorific value, while producing a char residue tailored for downstream gasification or soil amendment. Recent advances in in situ spectroscopy and synchrotron imaging have elucidated fundamental reaction pathways—dehydration, depolymerisation and deoxygenation—and revealed the development of interconnected pore networks that accelerate mass transfer. Integration of CO₂ or steam as reactive agents during pyrolysis allows simultaneous gasification, generating hydrogen-rich syngas and capturing carbon in solid char. Engineering efforts focus on continuous‐flow microwave reactors with optimised resonator designs and process intensification strategies, offering routes to decentralised energy production and partial decarbonisation in regions reliant on low‐rank coal reserves.

Research from Nature Portfolio

Recent studies have deployed advanced imaging to track microstructural evolution in lignite under microwave fields, demonstrating that selective heating of mineral inclusions generates internal porosity enhancements that drive tar yields up by more than 30 %. In parallel, a modular microwave reactor concept has been validated at pilot scale, where renewable electricity powers pyrolysis and catalytic upgrading of syngas to liquid hydrocarbons. This system achieved a 40 % reduction in net CO₂ emissions relative to conventional coal‐to‐liquid processes, illustrating the potential for negative‐carbon footprint fuel production.

Microwave-Assisted Pyrolysis of Low-Rank Coal publication trend

The graph below shows the total number of articles in microwave-assisted pyrolysis of low-rank coal across all publications each year (not limited to Nature Index journals).

Technical terms

Dielectric heating: Heating mechanism whereby polar materials absorb microwave radiation and convert it to thermal energy.

Low-rank coal: Coal type characterised by high moisture and oxygen content, such as lignite and sub-bituminous coal.

Char: Solid carbonaceous residue remaining after pyrolysis, frequently used as a feedstock for gasification or soil amendment.

Tar: Condensable liquid hydrocarbons produced during pyrolysis, valued for use as chemical intermediates or fuel blending components.

Syngas: Synthesis gas composed primarily of hydrogen and carbon monoxide, generated via pyrolysis and gasification processes.

Cold gas efficiency: Ratio of chemical energy in produced syngas to the energy input of the feedstock, used to assess gasification performance.

References

1. Kinetic and thermodynamic investigations of CO2 gasification of coal chars prepared via conventional and microwave pyrolysis. International Journal of Coal Science & Technology (2020).
2. Influence of the microwave irradiation dewatering on the combustion characteristics of Chinese brown coals. IOP Conference Series Earth and Environmental Science (2018).
3. PYROLYSIS AND KINETIC STUDY OF THERMAL DEGRADATION OF WALNUT SHELLS AND INDIGENOUS COAL. Journal of Chemistry and Technologies (2022).