Published: Journal of Chromatographic Science, Volume 33, Number 3, March 1995, pp. 133-138.

Simulated Distillation of Oils With a Wide Carbon Number Distribution
Lawrence A. Neer and Milind D. Deo

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 C₉₀ can be characterized. However, for accurate measurement of compositions from C₅–C₄₄, a longer capillary column is required. A two-column procedure is developed in this paper to obtain a wide C₅–C₉₀ distribution for crude oils. A longer (30 m) column is employed for compositional measurements in the range of C₅–C₄₄. A short (5 m) column is used to obtain carbon number distributions of compounds from C₂₀–C₉₀. 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 C₅–C₉₀ fraction of the oil while limiting the uncharacterized portion of the oil to compounds with carbon numbers higher than C₉₀.

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