Nitrogen functionality in coals and coal-tar pitch determined by X-ray photoelectron spectroscopy

Abstract

The forms of nitrogen in several Australian coals, a coal-tar pitch, mesophase prepared from the coal-tar pitch, and the isotropic phase in equilibrium with the mesophase, have been determined by X-ray photoelectron spectroscopy. In agreement with previous studies, nitrogen in the coals was found to be present predominantly in pyrrolic and pyridinic forms, with the proportion of pyrrolic being greater than pyridinic in each case. A N(1s) component near 401.5 eV was assigned to a protonated or oxide form of pyridinic nitrogen. On this basis, the total proportion of pyridinic nitrogen is comparable with the reported value determined by X-ray absorption near-edge structure spectroscopy for a US bituminous coal. Pyrrolic nitrogen was also found to be the predominant form of nitrogen in coal-tar pitch. The nitrogen content, and the ratio of pyrrolic to pyridinic functional forms, were essentially the same in coal-tar pitch mesophase as in the precursor pitch from which it was prepared. It was concluded that mesogens do not discriminate against the inclusion of nitrogen in 5- or 6-membered rings, but that other nitrogen functionalities such as amines appear to be excluded.