Thermal Chemistry of Nitrogen in Kerogen and Low-Rank Coal

X-ray photoelectron spectroscopy (XPS) was used to identify the forms of nitrogen present in Green River Type I and Bakken Type II kerogen concentrate samples and to follow the changes in nitrogen forms in the tars and chars produced upon pyrolysis. Pyrrolic nitrogen is the most abundant form of nitrogen, followed by pyridinic, amino, and quaternary types. XPS results show that upon devolatilization at 510 °C, the resultant kerogen tar and char contain mostly pyrrolic and pyridinic forms while amino groups are preferentially released into the tar. A portion of the quaternary nitrogen initially present in the Bakken kerogen appears in the 510 °C char and tar. Similar transformations were found for low-rank coal. These transformations occur at lower temperatures at long pyrolysis times for both kerogen and low-rank coal. Severe pyrolysis of the devolatilized kerogen char (T = 630−810 °C) results in the appearance of an asymmetric carbon (1s) line shape indicative of very large polynuclear “graphitic-like” units. This transformation is accompanied by an increase in the relative abundance of quaternary nitrogen forms. Quaternary and pyridinic nitrogen forms become the dominant forms in severely pyrolyzed kerogen chars.