A review of the co-pyrolysis of low-rank coals and microalgae biomass for fuel production

• Interactions between coal and biomass volatiles enhance coal decomposition. • Co-pyrolysis mechanisms may be influenced by the coal: algae feed ratio. • Lower temperature ranges are suitable for the production of liquid fuel. • The blending ratio influences gas, liquid, and char yields. • Catalysts in the co-pyrolysis process enhance the bio-oil quality. This review comprehensively examines recent advancements in the co-pyrolysis of low-rank coal and microalgae biomass. The co-pyrolysis process aims to improve coal conversion efficiency and enhance the quality of pyrolysis products while integrating renewable biomass to facilitate cleaner fuel production. The article highlights significant research progress in coal-microalgae pyrolysis studies, concentrating on pyrolysis reactions and the underlying reaction mechanisms involving low-rank coals and various microalgae species. Key factors influencing product yield distribution, such as feedstock composition, pyrolysis temperature, heating rate, catalyst use, and reaction time, are analysed in detail. The findings indicate that optimising the blend ratio between coal and biomass substantially enhances bio-oil yield, while pyrolysis temperature significantly impacts product distribution. The heating rate is crucial for promoting pyrolysis reactions, and catalysts play a vital role in improving the efficiency of the co-pyrolysis process, particularly by increasing oil yield and improving its quality. Furthermore, the combined effect of pyrolysis temperature and blend ratio greatly influences char properties. The review concludes by emphasizing both the challenges and opportunities in implementing co-pyrolysis technology for low-rank coal and microalgae biomass, while also offering future perspectives on the practical application of this novel process.