Evidence of chemical pathways of humification: a study of aquatic humic substances heated at various temperatures

The effects of thermal evolution on the composition and structure of aquati c humic substances (HS) heated at temperatures from 100 degreesC to 500 deg reesC in presence of helium were investigated using elemental analysis, FTI R and solid state C-13 CP/MAS NMR spectroscopy, and Py-GC/MS spectrometry. Elemental composition results showed that with increasing heating temperatu res, there was an increase in the atomic H/C ratio and a decrease in the at omic O/C ratio in the HS. FTIR, solid state C-13 CP/MAS NMR, and Py-GC/MS r esults showed decreases in amounts of oxygen-containing groups followed by their subsequent disappearance at higher temperatures. Formation of aromati cs was observed at expense of aliphatics at higher temperatures. This study has given a substantial amount of information on mass loss, structural evo lution, and the degree of maturity as the humic substances are heated with increasing temperatures, suggesting that thermal evolution may play an impo rtant role in the contribution of the HS as a precursor of coal like organi c materials. (C) 2001 Elsevier Science B.V. All rights reserved.