Analyses on thermal stability of lignites and its derived humic acids

ABSTRACT

The thermal stabilities of humic acids (HAs) are critical for its effective utilization and relate closely with raw lignites. Thus, this work is to study the relationship of thermal stability between lignites and its derived HAs using Thermogravimetry – Fourier Transform Infrared Spectroscopy (TG-FTIR) and Differential Scanning Calorimetry Measurement (DSC) techniques. The TG-FTIR results indicated that the intensities of peaks from the evolution gases (H₂O, CO₂, CO, CH₄) during thermal treatment of Zhaotong lignite (ZL) and its derived HAs (denoted as ZLHA) are higher compared with the Mile lignite (ML) and its derived HA (denoted as MLHA). TG-FTIR and DSC measurements of lignites showed that the thermal stability of ML is better than that of ZL, and the more oxygen containing functional groups existed in ZL. Similarly, the results indicated that the contents of oxygen containing functional groups of ZLHA are higher than that of MLHA. On the other hand, DSC experimental data showed that the MLHA has smaller peaks on the DSC profiles, which showed that MLHA has longer aliphatic chain and less oxygen containing functional groups. Briefly, the results obtained from TG-FTIR and DSC measurement are consistent. The thermal stabilities of HAs are highly associated with the physicochemical property of raw lignites.

KEYWORDS:

• Humic acids
• lignites
• thermal stability
• TG-FTIR
• DSC

Additional information

Funding

This work was supported by the National Natural Science Foundation of China under Grant [No. 21766013]; and Analysis and Measurement Foundation of Kunming University of Science and Technology under Grant [No. 2019T20070105].

Notes on contributors

Yanhong Li

Yanhong Li is a Ph.D. candidate in chemical engineering in the Key Laboratory of Coal Science and Technology of Ministry of Education and Shanxi Province at the Taiyuan University of Technology. He received his B.E. from the Xinyang Normal University in 2004 and M.S. from the Key Laboratory of Coal Science and Technology of Ministry of Education and Shanxi Province at the Taiyuan University of Technology in 2007. Yanhong Li is a associate professor in the Faculty of Chemical Engineering, Kunming University of Science and Technology. His research has focused on energy and chemical engineering, such as biomass, coal, and petroleum.

Yuanqin Zhang

Yuanqin Zhang received her B.E. Degree in Chemical Engineering and Technology from Tianjin University Renai college in 2018. She is currently pursuing her M.S. in Chemical Engineering at Kunming University of Science and Technology under the supervision of Dr. Yanhong Li. Her research has focused on coal chemical industry.

Liping Chang

Liping Chang is a Professor in the Key Laboratory of Coal Science and Technology of Ministry of Education and Shanxi Province at the Taiyuan University of Technology. She received her Ph.D. degree from the Taiyuan University of Technology in 2004. She has been a visiting scientist at Monash University, Australia, during 2002. Her research interests include the formation and the control of sulfur and nitrogen pollutants in the coal conversion, the gas purification, the lignite upgrading, the cooperative control of pollutants from the coal, and the structure and the reactivity of the coal.

Changyu Zi

Changyu Zi received her B.E. Degree in energy chemical engineering from Northeast PetroleumUniversity in 2017. She is currently pursuing her M.S. in Chemical Engineeringat KunmingUniversity of Science and Technology under the supervision of Dr. Yanhong Li. Her research has focused on coal chemical industry.

Guangbing Liang

Guangbing Liang received his B.S. Degree in applied chemistry from Northeast Petroleum University in 2018. He is currently pursuing his M.S. in Chemical Engineering at Kunming University of Science and Technology under the supervision of Dr. Yanhong Li. His research has focused on biomass solid waste treatment and coal tar pitch.

Dengfeng Zhang

Dengfeng Zhang was granted Ph.D. degree by the Institute of Process Engineering (IPE) of Chinese Academy of Sciences (CAS) in Beijing in 2011. He is now a Professor of Faculty of Chemical Engineering, Kunming University of Science and Technology. He has been majoring in environmental engineering and his research mainly involves CO₂ capture and sequestration (CCS), unconventional natural gas exploration and production, etc.

Wei Xie

Wei Xie was granted Ph.D. degree by the Discipline of Chemical Engineering of the University of Newcastle, Australia in 2013. He received his B.E. from the Xinyang Normal University in 2004 and M.S. from the Key Laboratory of Coal Science and Technology of Ministry of Education and Shanxi Province at the Taiyuan University of Technology in 2007. Wei Xie is a research fellow at the University of Newcastle, Australia. His research has focused on energy and chemical engineering, such as coal science and technology.