Macromolecular and molecular structure of coal and the possible role of pyrolysis-field desorption mass spectrometry in its elucidation

Abstract

Organic matter of coals (vitrinites) consists of macromolecules which contain aromatic and hydroaromatic rings linked by aliphatic bridges. O, N and S heteroatoms occur in furan, quinone, pyridine, pyrrole and thiophene rings and in functional groups. Specific behaviour of coals in the presence of solvents strongly suggests that coal macromolecules are cross-linked spatial systems. Cross-links are believed to be formed by single covalent bonds and larger fragments and by electron-donor-acceptor interactions. Molecular substances (mostly in the m/z 200–400 range) constitute the second phase which occurs in the pores of macromolecular network. Some components of the molecular phase are not extractable. Extractable molecules were identified by gas chromatography-mass spectrometry, high-resolution mass spectrometry and field ionization mass spectrometry. The foregoing two-phase, i.e., macromolecular and molecular, structure of coal implies that mechanistic and kinetic studies of pyrolysis (based on a single-phase, i.e., macromolecular, concept of coal structure) should be re-examined in those cases where discrepancies between experimental and theoretical data occur. The two-phase concept could serve as a key in searching for new methods of investigation of coal structure. Temperature-controlled pyrolysis-mass spectrometry seems to offer a unique possibility in this field.