A new hydrogen bond in coal

The hydrogen bonds in four coals with different rank and different sulfur content were checked using the in situ diffuse reflectance FTIR (DRIFT) method. Besides the hydrogen bonds formed by -OH and -COOH groups, there exists a new kind of hydrogen bond (SH-N) formed by the -SH in the thiophenols or mercaptans and the nigrogen in pyridine-like compounds in coal. The absence of this shoulder peak in the IR spectra of low rank coals (even high sulfur) can be attributed to the high content of -COOH groups, and consequently the strong and broad absorbance in carboxylic acid dimers in this range covers the weak absorbance of SH-N. However, when the low rank coals were heated to 620degreesC in Ar atmosphere and the -COOH disappears, the peak of SH-N clearly occurs. To summarize all the work on this new hydrogen bond, we assign it to the position of about 2514 cm(-1).