SULFUR-CONTAINING AND NITROGEN-CONTAINING PHENOL-FORMALDEHYDE CO-RESITES FOR PROBING THE THERMAL-BEHAVIOR OF HETEROATOMIC FORMS IN SOLID FUELS

In order to probe the formation of sulfur- and nitrogen-containing gas es during the pyrolysis and combustion of coals and other solid fuels, non-softening model substrates are required. In this respect, phenol- formaldehyde (PF) resins are ideal since they readily facilitate the i ncorporation of individual heteroatomic functions into a highly crossl inked matrix. A series of sulfur- and nitrogen-containing co-resites h ave been prepared using phenol with, as the second component, thiophen e, dibenzothiophene, diphenylsulfide, benzyl phenyl sulfide, thioaniso le, 8-hydroxyquinoline and 2-hydroxycarbazole. A mole ratio of 3 : 1 ( phenol: heteroatom-containing component) was adopted in order to ensur e that a reasonably high degree of crosslinking was achieved. Resoles containing diphenyldisulfide were also prepared but, due to the compar able bond strengths of the S-S and C-O linkages, a curing temperature of only 130 degrees C was used to avoid cleavage of the disulfide bond . The virtually complete elimination of ether and methylol functions f rom the resoles by curing at 200 degrees C was monitored by solid-stat e C-13 nuclear magnetic resonance (n.m.r.) spectroscopy. The resultant resites were also characterized by sulfur K-edge X-ray absorption nea r-edge structure (XANES.) spectroscopy, X-ray photoelectron spectrosco py (X.p.s.) and differential scanning calorimetry (d.s.c.). Simple air oxidation was found to selectively convert the aliphatic-bound sulfur to a mixture of sulfones and sulfoxides. Applications of the resites in fuel science are described. Copyright (C) 1996 Elsevier Science Ltd .