Simulated Distillation of Oils With a Wide Carbon Number Distribution

Abstract

Simulated distillation using gas chromatography is an expedient technique for the determination of boiling range and carbon number distributions of crude oils. A procedure to calculate the uneluted fraction of the oil (from the chromatographic column) exists in the literature. Mathematical equivalence between this procedure and a more intuitive inverse lever-arm principle is established in this paper. Capillary gas chromatography permits the analyses of samples containing higher boiling compounds at temperatures similar to those employed in packed-column chromatography. By using a short (5 m) capillary column, samples containing compounds with carbon numbers up to C 90 can be characterized. However, for accurate measurement of compositions from C 5 -C 44 , a longer capillary column is required. A two-column procedure is developed in this paper to obtain a wide C 5 -C 90 distribution for crude oils. A longer (30 m) column is employed for compositional measurements in the range of C 5 -C 44 . A short (5 m) column is used to obtain carbon number distributions of compounds from C 20 -C 90 . For the two oils analyzed as part of this study, excellent agreement is observed in the overlapping region of the two analyses. The procedure developed in this paper allows for a high-resolution characterization of the C 5 -C 90 fraction of the oil while limiting the uncharacterized portion of the oil to compounds with carbon numbers higher than C 90