Multi - scale perspective on hydrothermal treatment dewatering of lignite: Synergistic regulation of structural evolution and lightening of pyrolysis tar
Shucheng Liu , Haojie Yang , Yichao Zhang , Qingzhou Zeng , Fugui Liu , Keli Zhu , Jun Zhang , Hongyu Zhao , Ming Zeng
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引用次数: 0
Abstract
Hydrothermal treatment dewatering (HTD) is a promising method for upgrading lignite. However, the mechanistic links between its structural modifications and the regulation of pyrolysis tar remain unclear. In this paper, the cascade effect of HTD on the physicochemical structure and pyrolysis tar components of lignite is systematically revealed by combining multi-scale characterization techniques (XPS, FTIR, BET) with Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS). The results show that the HTD process (330°C) can significantly reduce the moisture content (12.4 %→2.7 %) and oxygen content (38.00 %→31.89 %) of lignite. Moreover, the cleavage of O-containing groups and the decomposition of aliphatic chains drive the aromatization of organic structure during the HTD process. The XPS results show that the proportion of aromatic carbon content increased from 48.74 % to 70.85 %. These changes also directly affect the composition of the pyrolysis tar of lignite. The Py-GC/MS results indicate that the contents of aliphatic hydrocarbons and O-containing compounds in the tar continuously decrease with increasing HTD temperature, while the proportion of aromatic hydrocarbons significantly rises to 30.57 %. The content of phenolic compounds follows a non-linear trend, first increasing and then decreasing due to the hydrolysis and decomposition of hydroxyl functional groups. Additionally, the HTD process promotes the lightening of pyrolysis tar. For instance, the relative content of small-molecule aliphatic hydrocarbons (C4-C9) increases to 64.45 %, and the relative proportion of monocyclic aromatic hydrocarbons reaches 78.81 %. HTD is an effective method to improve quality of pyrolysis tar. The underlying mechanism is attributed to the synergistic effects of the distribution characteristics of functional groups, radical enrichment, and suppressed cross-linking. The research results provide key theoretical support for regulating the hydrothermal process of lignite and for preparing light tar with high added value.
期刊介绍:
The Journal of Analytical and Applied Pyrolysis (JAAP) is devoted to the publication of papers dealing with innovative applications of pyrolysis processes, the characterization of products related to pyrolysis reactions, and investigations of reaction mechanism. To be considered by JAAP, a manuscript should present significant progress in these topics. The novelty must be satisfactorily argued in the cover letter. A manuscript with a cover letter to the editor not addressing the novelty is likely to be rejected without review.