Abstract
The cleavage of the aliphatic chain or ether bond connecting the polycyclic aromatic hydrocarbons in coal can be achieved by not only hydrogenation reduction but also oxidative acid treatment. In this paper, coal samples from Wucaiwan in Xinjiang were pretreated with HNO3 followed by mixed acids/ultrasound treatment. The depolymerized coal samples obtained under different pH conditions were then separated by fractional washing. The structures and properties of the resulting coal samples were studied by elemental analysis, FT-IR, XRD, TG–DTA, TEM, UV–Vis, and PL. The results showed that when pH = 0.012, the obtained coal samples were fragments stripped off from the raw coal samples by ultrasound in strong acid conditions, aliphatic hydrocarbons linked with oxygen-containing groups such as nitro group, a small amount of small aromatic molecules and mineral salts; when pH = 1.99–4.09, the obtained coal samples were polycyclic aromatic hydrocarbons linked with oxygen-containing groups such as nitro group,possessing the annulus wall of multilayer graphene fragment structures built up by sp2 carbons, and they are typical fluorescent substances of carbon nanoparticle structure. The former has no solubility in organic solvents, while the latter can be well dissolved in polar solvents such as acetone. All the depolymerized coal samples obtained under different pH conditions exhibited good absorption and ability of fluorescence emission.Graphical
Highlights
During the coal gasification and liquefaction processes, hydrogen can cleave the alkane chain or ether bond between the macromolecules in coal structures in the presence of catalyst to obtain liquid hydrogenated products (Chen et al 2015; Li et al 2015; Guo et al 2015)
The results showed that when pH = 0.012, the obtained coal samples were fragments stripped off from the raw coal samples by ultrasound in strong acid conditions, aliphatic hydrocarbons linked with oxygen-containing groups such as nitro group, a small amount of small aromatic molecules and mineral salts; when pH = 1.99–4.09, the obtained coal samples were polycyclic aromatic hydrocarbons linked with oxygen-containing groups such as nitro group,possessing the annulus wall of multilayer graphene fragment structures built up by sp2 carbons, and they are typical fluorescent substances of carbon nanoparticle structure
To study the structure change of the coal sample before and after the pretreatment by HNO3, FT-IR, X-ray diffraction (XRD), and TGDTG analysis were performed on three samples in Table 1 and the results are shown in Fig. 1, 2
Summary
During the coal gasification and liquefaction processes, hydrogen can cleave the alkane chain or ether bond between the macromolecules in coal structures in the presence of catalyst to obtain liquid hydrogenated products (Chen et al 2015; Li et al 2015; Guo et al 2015). The cleavage of these weak bonds can be achieved by hydrogenation reduction and acid oxidation. Only presented a method for the preparation of coal-based carbon nanoparticles, and aid in revealing the coal structures on a molecular level, at the same time, it can provide useful information for the developing technique of mild conversion of coal
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