Proton magnetic resonance thermal analysis of petroleum derived asphaltene

The thermal transformations in petroleum derived asphaltene in a temperature range from 40 to 420 degrees C was studied using proton magnetic resonance thermal analysis (PMRTA). Stacked plot of H-1-NMR signals and residual hydrogen suggest the gradual structural transition of asphaltene from largely rigid material to one having a high degree of molecular mobility at 300 degrees C. From the results of solid echo curve fitting analysis, an increasing Weibull time constant and decreasing power may be taken as gradual shifting of rigid structure to a more mobile one. No clear abrupt changes are observed relating to liquid phase transition and the formation of coke precursor from asphaltene in the temperature range up to 420 degrees C. The second moment, M-2T(V-T), is sensitive to molecular dynamics and also to concentration and distribution of protons and unpaired electrons in the molecular lattice. The value of M(2T)16 provides an appropriate measure to study the extent to which molecular lattice of asphaltene was mobilized by thermal destabilization. The asphaltene has extremely high fluidity compared with those derived from coals at 400 degrees C. From PMRTA of reheated samples, first heat treatment up to 450 degrees C have resulted in irreversible thermal transformations.