Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel Full Length Article Study on the structural evolution of semi-chars and their solvent extracted materials during pyrolysis process of a Chinese low-rank coal Liangping Zhang a , Song Hu a,b, ⁎ , Kai Xu a, ⁎ , Long Jiang a , Yi Wang a , Sheng Su a,b , Yiming Xiao a , Lianying Shan b , Wenzhong Shen c , Huafei Li d , Gang Chen a,b , Jun Xiang a,b a State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074, Hubei, PR China b China-EU Institute for Clean and Renewable Energy at Huazhong University of Science and Technology, Wuhan 430074, Hubei, PR China c State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, Shanxi, PR China d Engineering Training Centre of Huazhong University of Science and Technology, Wuhan 430074, Hubei, PR China GRAPHICAL ABSTRACT Proposed conversion process of the chemical structure of Shenfu low-rank coal during low-temperature pyrolysis, especially considering the solvent extracted metaplast materials (SEMMs) in semi-chars. ARTICLE INFO Keywords: Pyrolysis Semi-char Metaplast Structural evolution ABSTRACT The structural evolution of coal during pyrolysis process has been studied for a long time but remains unclear, mainly due to the extraordinary complexity of coal structure. The present study aimed to further identify the chemical structural evolution of different parts in the semi-chars obtained by low-temperature pyrolysis of a Chinese low-rank coal (Shenfu coal). Semi-chars and their solvent extracted materials (oil, resin, asphaltene and preasphaltene) were analyzed by 13 C nuclear magnetic resonance (NMR) mass spectrometry, diffuse reflectance Fourier transform-infrared spectroscopy (DRIFTs) and ultraviolet (UV) fluorescence spectroscopy, separately. The results showed that 23.8% weight loss occurred during the whole pyrolysis process at 435 °C and half of the weight loss was achieved in the initial five minutes. By contrast, amount of the extracts in semi-chars (solvent extracted metaplast materials) decreased more dramatically in the initial stage of the pyrolysis, and 51.8% of the extracts disappeared in the initial one minute. Oil and preasphaltene showed higher thermal sensitivity than asphaltene and resin. Considerable content of metaplast materials with 1–2 rings (especially in oil and/or as- phaltene) were produced along with the pyrolysis process. Condensed aromatic structures in semi-chars were relatively stable and mainly decomposed in the initial stage of pyrolysis which could be attributed to the dra- matically decomposition of some active aromatic structures with ≥ 4 rings (especially the components in ex- tracts such as preasphaltene). The results provided a new insight into the structural evolution of coal during low- temperature pyrolysis process, which specially considered the detailed information of the solvent extractable metaplast materials in semi-chars. https://doi.org/10.1016/j.fuel.2017.11.043 Received 10 April 2017; Received in revised form 26 July 2017; Accepted 14 November 2017 ⁎ Corresponding authors at: China-EU Institute for Clean and Renewable Energy at Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan 430074, PR China (S. Hu). Room 504, State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan 430074, PR China (K. Xu). E-mail addresses: husong@hust.edu.cn (S. Hu), xukai@hust.edu.cn (K. Xu). Fuel 214 (2018) 363–368 0016-2361/ © 2017 Elsevier Ltd. All rights reserved. T