Ring distribution, aromatic asphaltenes

The CCB-distillate fraction contains no ash or asphaltenes (n-Heptane insolubles at reflux). It has a low and narrow molecular weight distribution (Mn 290), and contains a very narrow aromatic ring distribution (3, 4, 5, and 6 rings). Table I gives the... 

CCB was fractionated into six asphaltene-free distillate fractions of varying boiling ranges and an asphaltene-rich non-distillable residue. Characterization of the distillate and the non-distillable fractions indicate significant differences in the asphaltene, ash, aromaticity, molecular weight and aromatic ring distributions. 

Table III. Aromatic Ring Distribution in Major Classes Found in EDS Asphaltenes...

The concept that molecular weight and polarity play a role in determining the composition of an asphaltene fraction is very realistic but does not present any indication of the nature of the polynuclear aromatic systems in the asphaltene fraction of petroleum. Thus, the purpose of this chapter is to present new data that provide indications of the ring-size distribution in petroleum asphaltenes. The evidence is accumulated by asphaltene fractionation and subsequent examination of the fractions by high-performance liquid chromatography (HPLC) using a UV detector. 

The application of thermal techniques to study the nature of the volatile thermal fragments from petroleum asphaltenes has produced some interesting data relating to the polynuclear aromatic systems (18-22). These thermal techniques have produced strong evidence for the presence of small polynuclear aromatic systems (one to four rings) (14), and application of the techniques to the various functional fractions has confirmed the general, but unequal, distribution of these systems throughout asphaltenes. 

The method is subject to the limitation of the sensitivity of polynuclear aromatic systems. Furthermore, some of the asphaltene material (<2% w/w) was irreversibly adsorbed on the adsorbent. In this case, the missing material is presumably highly polar and any deviation from the ring-size distribution outlined in the foregoing discussion is not believed to be significant enough to influence the general conclusions about the nature of the polynuclear aromatic systems in petroleum asphaltenes. 

---