Characterization of Molecular Structure of Bituminous Coal and Anthracite by 13C NMR, FT-IR, Raman and Modeling Techniques

Abstract

[Purposes] While extensive research has been conducted on the evolution of coal′s molecular structure during coalification, the heterogeneity and complexity of coal continue to impede the accurate and precise quantitative characterization of its structural evolution mechanism. [Methods] Through maceral identification, vitrinite reflectance, industrial quality, elemental analysis, and spectral analysis, the carbon skeleton structure and occurrence state of functional groups of bituminous coal (FS1) and anthracite coal (ZY1) were determined. Two molecular structure models were established by computer-aided molecular design. [Finding] The results show that with the progress of coalification, the loss rate of methylene is faster than that of methyl in the process of bituminous coal to anthracite, the aromaticity is enhanced, the aliphatic chain of aromatic ring becomes shorter and the degree of branching is higher, the oxygen-containing functional groups is gradually reduced, the crystallinity of coal is enhanced, and the chemical structure of coal tends to be mature and stable. At the sometime, the content of aliphatic carbon in coal decreases, the content of aromatic carbon increases, and the content of methyl carbon and methylene carbon decreases. After several attempts, the bonding mode between aromatic carbon, aliphatic side chain, and oxygen functional group was determined, and the final molecular structure models were obtained: C175H162O13N2 (FS1), C190H159O5N3 (ZY1). These models well reflect the real structure of coal, and the simulated 13C NMR spectra are in good agreement with the experimental spectra. The above research provides a theoretical reference for the molecular structure evolution of coal with different metamorphic degrees, and provides a method for establishing high-reliability molecular structure characterization.

Keywords

• coal
• 13c nmr
• ft-ir
• raman
• molecular structure model