Effect of rare earth oxides on the formation of gaseous products from low rank coal pyrolysis

ABSTRACT

Rare earth elements and their compounds can be used as catalysts or promoters for pyrolysis of organic matter including those in coal, but relevant investigations, especially regarding the role of rare earth materials in coal pyrolysis are very scarce. This study focuses on the effect of cerium oxide (CeO₂) and lanthanum oxide (La₂O₃) on the formation of gaseous products from low-rank coal pyrolysis by means of gas chromatography (GC). The mechanisms of two kinds of rare earth oxides (REOs) involved in the coal pyrolysis are also discussed tentatively. Results show that CeO₂ can promote the formation of CO₂ (400°C–600°C), CO (550°C–650°C), CH₄ (300°C–500°C), C₂H₆ and C₃H₈ (350°C–750°C), and it is believed to catalyze the bond breaking reactions of the aliphatic side chain, carboxyl group and phenolic hydroxyl group, or the bridge bonds between aromatic nuclei. The catalytic effect of CeO₂ on the breaking of bridge bonds is likely to be completed by the movement of oxygen vacancies (i.e., oxygen storage and release ability of CeO₂) in the water vapor environment. In addition, the results also reveal that it is La₂O(CO₃)₂, not La₂O₃, playing a role in coal pyrolysis, which can promote the formation of CO₂ (500°C–750°C), H₂ and unsaturated hydrocarbons (350°C–500°C), and could be considered to be a catalyst for dehydrogenation at low-medium temperature. The mechanism of CO₂ formation catalyzed by La₂O(CO₃)₂ is probably related to the decomposition of oxygen-containing ligands formed by La(III) and carboxyl group at high temperature.

KEYWORDS:

• Rare earth oxide
• catalytic pyrolysis
• low rank coal
• gas composition analysis
• catalytic mechanism

Acknowledgments

The authors gratefully acknowledge the financial support of the National Natural Science Foundation of China (51974323), Inner Mongolia Science and Technology Plan (201602015) and Natural Science Foundation of Inner Mongolia (2018LH05029 and 2020MS05070).

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [51974323]; Natural Science Foundation of Inner Mongolia of China [2018LH05029,2020MS05070]; Inner Mongolia Science and Technology Plan [201602015].

Notes on contributors

Lingkun Rong

Lingkun Rong (1983-), male, an associate professor in Inner Mongolia University of Science and Technology, who holdsa Ph.D.degree in mineral processing engineering, mainly engaged in research on clean conversion and comprehensiveutilization of low rank coal, such as coal drying, coal pyrolysis, coal gasification, coal water slurry and briquette, etc.Email: [email protected].

Baolu Cui

Baolu Cui (1996-), male,  a graduate student in Inner Mongolia University of Science and Technology, mainly studying coal pyrolysis. Email: [email protected].

Yin Qu

Yin Qu (1982-), male, an engineer in Baotou ecological environment monitoring station of Inner Mongolia Autonomous Region, mainly responsible for environmental monitoring of key pollution sources. Email: [email protected]

Jialei Sun

Jialei Sun (1995-),Male, Master, School of Mineral Engineering, Inner Mongolia University of Science and Technology, mainly studying clean coal technology.  Email:[email protected]

Fengjun Jia

Fengjun Jia (1961-), male, professor, Inner Mongolia University of Science and Technology, and his research interests focus on coal chemical engineering.  Email:[email protected]

Wenxiu Li

Wenxiu Li (1970-), male, lecturer, Inner Mongolia University of Science and Technology, mainly engaged in research on coal chemical engineering. Email: [email protected].

Mo Chu

Mo Chu (1966-), female, Professor, China University of Mining and Technology-Beijing, mainly engaged in coal chemical conversion and clean utilization. Email: [email protected]

Wanzhong Yin

Wanzhong Yin (1970-), Male, Professor, Northeastern University, mainly engaged in mineral flotation theory and technology, efficient separation of complex polymetallic ores and mineral materials. Email: [email protected]