Surface Chemical Heterogeneity of Low Rank Coal Characterized by Micro-FTIR and Its Correlation with Hydrophobicity

Micro-Fourier transform infrared (micro-FTIR) spectroscopy was used to correlate the surface chemistry of low rank coal with hydrophobicity. Six square areas without mineral impurities on low rank coal surfaces were selected as testing areas. A specially-designed methodology was applied to conduct micro-FTIR measurements and contact angle tests on the same testing area. A series of semi-quantitative functional group ratios derived from micro-FTIR spectra were correlated with contact angles, and the determination coefficients of linear regression were calculated and compared in order to identify the structure of the functional group ratios. Finally, two semi-quantitative ratios composed of aliphatic carbon hydrogen, aromatic carbon hydrogen and two different types of carbonyl groups were proposed as indicators of low rank coal hydrophobicity. This work provided a rapid way to predict low rank coal hydrophobicity through its functional group composition and helped us understand the hydrophobicity heterogeneity of low rank coal from the perspective of its surface chemistry.

Automated summary

Micro-FTIR spectroscopy was used to study the correlation between surface chemistry and hydrophobicity of low rank coal. Functional group ratios derived from the spectra were proposed as indicators of hydrophobicity, revealing heterogeneity in hydrophobicity among low rank coal samples.