Mobility of asphaltene samples studied by 13C NMR spectroscopy

Cerro Negro (CN) and Furrial asphaltenes have been analyzed using both liquid and solid-state C-13 NMR spectroscopy. The spin-lattice relaxation times exhibited by the carbons in the resin containing CN asphaltene samples indicate that these carbons relax more slowly than the equivalent carbons in the resin-free samples. This fact suggests a higher mobility of the molecules in the sample in the presence of resins, CP/MAS experiments showed that, in general, all asphaltene samples have rigid alicyclic structures. This fact is consistent with the presence of condensed aliphatic rings. The results of the measurements of the cross-polarization relaxation times obtained from the variable contact-time CP/MAS experiments indicate that Cerro Negro samples are more "mobile" than Furrial. These findings point toward the presence of a larger number of CH2 chains bonding different ring clusters in the Cerro Negro samples.