Free-radical behaviors of co-pyrolysis of low-rank coal and different solid hydrogen-rich donors: A critical review

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2023-10, Vol.474, p.145900, Article 145900
• Main Authors: Wu, Lei, Guan, Yining, Li, Changcong, Shi, Lei, Yang, Sasha, Rajasekhar Reddy, B., Ye, Gan, Zhang, Qiuli, Liew, Rock Keey, Zhou, Jun, Vinu, R., Lam, Su Shiung
• Format: Article
• Language: English
• Subjects: Co-pyrolysis; Detection technology; Free radical behaviors; Hydrogen-rich donors; Low-rank coal
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2023.145900

•Soild “rich-hydrogen” donors act as “hydrogen sources” for coal pyrolysis.•Existing detection methods of free radicals indirectly reflect their properties.•Free radical behaviors signally affect the yield and quality of pyrolysis products.•Pyrolysis temperature is the most key influence factors of free radical behaviors.•Effects of free radical behaviors on coke/semi-coke and tar are more attention. Low-cost and accessible “hydrogen source” are the key to reducing the cost of coal hydropyrolysis technology. The mechanism of hydrogen supply is a crucial scientific issue in this technology. Solid “hydrogen-rich” donors, such as biomass, waste plastics, oil shale, and coal liquefaction residue, possess favorable characteristics such as affordability, abundant availability, high volatility and a high H/C ratio, which are considered ideal solid “hydrogen sources” for coal hydropyrolysis. The co-pyrolysis reactions between low-rank coal and solid “hydrogen donor” follow the mechanism of free radical reactions. Moreover, a clear investigation of the free-radical behaviors and synergistic interactions between them can clarify the hydrogen supply mechanism in the co-pyrolysis process of solid “hydrogen-rich” donors, resulting in the controlled production of high-quality oil and gas products. This review systematically summarizes the free-radical behaviors during the co-pyrolysis of low-rank coal and solid “hydrogen-rich” donors: Three detection methods of free radicals and their applications are first introduced. Then, the factors influencing the free-radical behaviors during the co-pyrolysis are discussed, and the influences of the free-radical behaviors on the products obtained by the co-pyrolysis are analyzed. Finally, the results and challenges of free-radical behaviors are outlined. This work is intended to provide a comprehensive and scientific basis for completing the mechanism of free-radical reactions in the co-pyrolysis of low-rank coal and solid “hydrogen-rich” donors.