Effect of hydrothermal treatment on the carbon structure of Inner Mongolia lignite
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Effect of hydrothermal treatment on the carbon structure of Inner Mongolia lignite Peng Liu1 • Dexiang Zhang2
Received: 5 December 2019 / Revised: 17 July 2020 / Accepted: 29 July 2020 Ó The Author(s) 2020
Abstract Understanding the structural properties of lignite during hydrothermal treatment would aid in predicting the subsequent behavior of coal during the pyrolysis, liquefaction, and gasification processes. Here, hydrothermal treatment of Inner Mongolia lignite (IM) was carried out in a lab autoclave. The distribution of carbon in the lignite was monitored via solid 13C nuclear magnetic resonance spectroscopy, and the functional groups of oxygen in lignite were determined by Fourier transform infrared spectroscopy. The curve-fitting method was used to calculate the content of the functional groups quantitatively. The results show that hydrothermal treatment is an effective method for upgrading the lignite. The side chains of the aromatic ring in lignite are altered, while the main macromolecular structure remains nearly the same. The hydrothermal treatment of IM could be divided into three temperature-dependent stages. The first stage (\ 493 K) is the decomposition reaction of oxygen functional groups, where the O/C ratio decreases from 0.203 in raw IM to 0.185 for the IM treated at 493 K. In the second stage (493–533 K), hydrolysis of functional groups and hydrogen transfer between water and lignite occur. Here, the ratio of methylene to methyl increases from 0.871 in IM-493 to 1.241 for IM-533, and the content of quinone generates from the condensation of free phenol increased. The third stage ([ 533 K) involves breakage of the covalent bond, and the content of CH4 and CO in the emission gas clearly increase. Keywords Lignite Hydrothermal treatment Carbon structure Solid
1 Introduction Lignite is an abundant fossil fuel resource and will continue to be an important energy source in the foreseeable future. Because of its high moisture content (25 wt%– 60 wt%), the drying/dewatering is an integral step for & Peng Liu [email protected] & Dexiang Zhang [email protected] 1
National-Local Joint Engineering Research Center of Biomass Refining and High-Quality Utilization, Institute of Urban and Rural Mining, Changzhou University, Changzhou 213164, Jiangsu, China
2
Department of Chemical Engineering for Energy Resources, East China University of Science and Technology, Shanghai 200237, China
13
C nuclear magnetic resonance
lignite applications that require high efficiency. Hydrothermal treatment (Butler et al. 2007; Sakaguchi et al. 2008; Katalambula and Gupta 2009; Ullah et al. 2018), a non-evaporative technique, is considered an effective method for dewatering and upgrading lignite. The process enables an improvement in the slurry properties of coal (Yu et al. 2012; Fu and Wang 2014; Zhang et al. 2018) and can reduce the viscosity of the coal-water slurry. Moreover, hydrothermal treatment not only promotes the hydro-liquefaction activity during coal liquefaction (Li et al. 2020) but also increases
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