Organic nitrogen forms of different rank coals in Handan-Fengfeng mining area, China

Nitrogen is one of the common elements in coal. The occurrence forms of nitrogen in coal are various and vary with coal rank. Based on X-ray photoelectron spectroscopy (XPS), taking Handan-Fengfeng mining area as an example, organic nitrogen forms of different rank coals(R_ran=1.08%-3.67%) were studied, and the variation of the relative abundance of each organic nitrogen with rank was further discussed. The results show that four kinds of nitrogen forms are considered for the coals according to binding energies of N 1s XPS sub-peaks, corresponding to N-6, N-5, N-Q and N-X. N-5 is the most abundant organic nitrogen and its relative abundance decreases as coal rank increases, while N-Q shows opposite trend. The variation of the relative abundance of N-6 with rank shows “increasing-decreasing-stable” trend, and N-X accounts for 9.1%-35.1% of the total organic nitrogen, whose changing with coal rank is not obvious. Protonated pyridinic nitrogen, a type of N-Q, which dominates in lignite, almost disappears at a coal rank range from R_ran 1.08% to R_ran 1.47% due to the loss of oxygen groups and deprotonation, resulting in the absence of N-Q sub-peaks in the XPS spectra.