FTIR quantitative analysis upon solubility of carbon disulfide/N-methyl-2-pyrrolidinone mixed solvent to coal petrographic constituents

• A formula is created based on the FTIR spectra to calculate extract yield (YE).
• High linear correlation is found between the calculated YE and the direct one.
• The most representative groups reflecting the structure of coal include four types.
• The distribution of various functional groups in the extracts was analyzed.

In this paper, the carbon disulfide/N-methyl-2-pyrrolidinone mixed solvent was used to extract all the petrographic constituents of Huaibei Tongting coal and Xuzhou Pangzhuang coal. The Fourier transform infrared spectroscopy (FTIR) analysis upon the raw coals and their extraction residues was carried out and the peak fitting for all absorption peaks was conducted to gain the peak areas of some major functional groups by PeakFit. Based on this, a new method was created to calculate the extract yields of all coal petrographic constituents and the distribution ratios of all functional groups in the extracts were analyzed. The results show that the calculated extract yield has good linear correlation compared with the actual one. The functional groups, which are the most representative and able to reflect coal structures precisely, mainly include 4 types, i.e. aromatic C = C skeletal vibration, aromatic C–H stretching vibration, aliphatic CH2 and CH3 asymmetric stretching vibration, R3CH vibration and stretching vibration of hydrogen-bonded –OH and phenolic compounds. The distribution ratios of all functional groups in collinites of Tongting coal are very high on average, with small difference between each functional group, while the distribution ratios in Pangzhuang coal are opposite.