Resolution and quantification of ring type aromatics by HPLC method using n-hexane elution

A method is described for the ring-type separation of aromatic fraction of crude oils. The crude oils were dissolved in n-hexane to precipitate asphaltenes. The n-hexane dissolved portion of the crude oil was separated into saturates, aromatic types, and polars using high performance liquid chromatography. The aromatics were differentiated into monoaromatics (1R), diaromatics (2R), triaromatics (3R), tetraaromatics (4R), and polyaromatics (5R+). This method was applied to four commercial Saudi Arabian crude oils namely Arab Berri, Arab Light, Arab Medium, and Arab Heavy having API gravity in the range 28.0-38.5. The HPLC separation was carried out by n-hexane elution on a amino propylsilane silica column. The hydrocarbon group types were determined on weight percent basis. The saturates and total aromatics were found decreasing with decreasing. API gravity while polars and asphaltenes increased. This trend may be due to the reason that the condensed polycyclic compounds and heteroatomic contents increase with decreasing API gravity in crude oils. This method may be applied to other crude oils for aromatic types determination.