Thermal chemistry of nitrogen in kerogen and low-rank coal

X-ray photoelectron spectroscopy (XPS) was used to identify the forms of ni trogen 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 nit rogen, followed by pyridinic, amino, and quaternary types. XPS results show that upon devolatilization at 510 degrees C, the resultant kerogen tar and char contain mostly pyrrolic and pyridinic forms while amino groups are pr eferentially released into the tar. A portion of the quaternary nitrogen in itially present in the Bakken kerogen appears in the 510 degrees C char and tar. Similar transformations were found for low-rank coal. These transform ations 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 degrees C) results in the appearance of an asymmetric carbon (Is) line shape indicative of very large polynuclear "graphitic-like" units. Thi s 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.