Coal structure and its evolution in catalytic hydrogenation are studie
d in this work. The hydrogenation experiments were performed in tubing
bomb reactors, in the absence of solvent, with an initial pressure of
10 MPa of H-2, and for a reaction time of 30 min; iron sulfide was th
e catalyst precursor. The characterization of the solid residues was p
erformed by different techniques, especially solvent swelling in pyrid
ine and surface and porosity studies. The swelling values are related
to the topological structure rather than to the density in noncovalent
cross-linkages. The evolution of that structure is monitored by calcu
lating the average number of carbon atoms between cross-link points, f
inding that at mild hydrogenation conditions (350 degrees C for low-ra
nk coals, 400 degrees C for bituminous coals) the solid residues prese
nt a structure with longer chains of aromatic clusters than in the par
ent coals. This would seem to be due to the release of heteroatom-cont
aining moieties and the prevention of cross-linking reactions by the c
atalyst. The textural characterization showed that there is a relation
ship between the increase of the skeletal density and chain length; th
e structure becomes more compact and ordered in the absence of low mol
ecular weight or noncovalently bonded material.