NITROGEN TRANSFORMATIONS IN COAL DURING PYROLYSIS

X-ray photoelectron spectroscopy (XPS) was used to identify and quanti fy the changes in organically bound nitrogen forms present in the tars and chars of coals after pyrolysis. For fresh coal, pyrrolic nitrogen is the most abundant form of organically bound nitrogen, followed by pyridinic, quaternary, and amino types. Some of the quaternary nitroge n species initially present in coal are lost upon mild pyrolysis, prio r to hydrocarbon devolatilization. These quaternary species are attrib uted to pyridinic or basic nitrogen species associated with hydroxyl g roups from carboxylic acids or phenols. A portion of the quaternary ni trogen species is lost at the very earliest stage of pyrolysis. Upon d evolatilization, the resultant tar and char contain mostly pyrrolic an d pyridinic forms; however, a portion of the quaternary nitrogen initi ally present in the coal appears in the coal char and tar. The relativ ely strong bonding interactions associated with these quaternary speci es suggests that there may be other quaternary nitrogen, in addition t o protonated pyridines, in low-rank coal. For low-rank coal, amino gro ups are preferentially released and concentrate in the tar. XPS analys is of chars and tars produced during rapid heat-up (10(4) deg/s) pyrol ysis show similar trends. However, severe pyrolysis of the devolatiliz ed char results in the appearance of an asymmetric carbon (1s) line sh ape indicative of very large polynuclear ''graphitic-like'' units. Thi s transformation is accompanied by a rise in the relative number of qu aternary nitrogen forms and occurs over a relatively narrow temperatur e range. Quaternary and pyridinic nitrogen forms become the dominant f orms in severely pyrolyzed chars. The relatively low level of quaterna ry nitrogen in the rapid heat-up chars indicates that very large polyn uclear aromatic structures are not fully developed under these pyrolys is conditions.