The environmental, social, and economic concerns regarding fossil fuels necessitate the demand for an efficient energy mix utilising renewable resources like biomass for sustainable development. Recent interest in the thermochemical conversion of coal and biomass into bioenergy via co-pyrolysis processes is gaining importance. This review critically assesses the behaviour of different types of coal and biomass blends during co-pyrolysis from various perspectives, including the effects of temperature, blending ratios, heating rate, synergistic and inhibitive behaviours, heat transfer mechanisms, nature of products, and their future applications. The possible synergies arising due to differences in the compositions of coal and biomass are discussed. In addition, the synergistic effect on co-pyrolysis yield is critically presented. Moreover, it is analysed that the co-pyrolysis offers higher yields of liquid and gaseous fuels compared to individual feedstock coal and biomass. Co-pyrolysis of coal and biomass can be promoted from a scientific standpoint; however, further research is still required for the integration of new technologies to enhance the effectiveness of co-pyrolysis.

A review on characteristics and synergistic behaviour of coal-biomass blends in co-pyrolysis process for bioenergy generation
    Abstract
    1 Introduction
    2 Overview of coal and biomass as an energy source
    3 Influencing factors for the reactivity characteristics of coal and biomass co-pyrolysis
        3.1 Effect of temperature on co-pyrolysis
        3.2 Impact of blending ratios on co-pyrolysis of the coal and biomass
        3.3 TGA of coal-biomass blends
        3.4 Effect of initial weight on TGA​
        3.5 Effect of heating rate
        3.6 Effect of blending on product characteristics
    4 Possible synergistic effects
        4.1 Hydrogen transfer reaction
        4.2 Catalytic effects of AAEM
        4.3 Heat transfer
        4.4 Co-pyrolysis kinetics behaviour
    5 Product analysis
        5.1 Nature of co-pyrolysis oil
        5.2 Nature of co-pyrolysis char
        5.3 Nature of gaseous compounds
    6 Future recommendations
    7 Conclusive remarks
    References

• Maham Tauseef(U.S.‑Pakistan Centre for Advanced Studies in Energy (USPCAS‑E), National University of Sciences and Technology (NUST), Sector H‑12, Islamabad 44000, Pakistan)
• Nida Naeem(U.S.‑Pakistan Centre for Advanced Studies in Energy (USPCAS‑E), National University of Sciences and Technology (NUST), Sector H‑12, Islamabad 44000, Pakistan)
• Tahreem Assad Khan(U.S.‑Pakistan Centre for Advanced Studies in Energy (USPCAS‑E), National University of Sciences and Technology (NUST), Sector H‑12, Islamabad 44000, Pakistan)
• Abeera Ayaz Ansari(U.S.‑Pakistan Centre for Advanced Studies in Energy (USPCAS‑E), National University of Sciences and Technology (NUST), Sector H‑12, Islamabad 44000, Pakistan)
• Asif Hussain Khoja(U.S.‑Pakistan Centre for Advanced Studies in Energy (USPCAS‑E), National University of Sciences and Technology (NUST), Sector H‑12, Islamabad 44000, Pakistan, Department of Chemical and Environmental Engineering (ChEE), University of Cincinnati, Cincinnati, OH 45221‑0012, USA) Corresponding author
• Muzzamail Hussain(State Key Laboratory of Multi‑Phase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China)
• Xi Zeng(State Key Laboratory of Multi‑Phase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China, School of Ecology and Environment, Beijing Technology and Business University, Beijing 100048, China)
• Arslan Khan(Laboratory of Alternative Fuels and Sustainability, School of Chemical and Materials Engineering, National University of Sciences and Technology, Islamabad 44000, H‑12, Pakistan)
• Ramza Akram(School of Interdisciplinary Engineering and Science (SINES), National University of Sciences and Technology (NUST), Sector H‑12, Islamabad 44000, Pakistan)