Simultaneous Determination of Boiling Range Distribution of Hydrocarbon, Sulfur, and Nitrogen in Petroleum Crude Oil by Gas Chromatography with Flame Ionization and Chemiluminescence Detections

Abstract

We present a quick and efficient gas chromatographic method to simultaneously determine the boiling range distribution of hydrocarbon (C), sulfur (S), and nitrogen (N) in crude oils by a high temperature–CNS simulated distillation (HT-CNS SimDis) analyzer. The analyzer is a gas chromatograph equipped with flame ionization (FID) and sulfur and nitrogen chemiluminescence (SCD and NCD) detectors with simulated distillation features. The hydrocarbon yield profile of crude oil obtained by FID response was applied to calculate S and N content in various isolated fractions such as naphtha, kerosene, diesel, and vacuum gas oil. This method was used to analyze 10 different crude oils of variable composition. A fraction of crude oil that boils above the atmospheric equivalent temperature (AET) of 700 °C does not elute fully and forms a coke inside the chromatographic column. As a result, it is not possible to quantify total sulfur and total nitrogen content in the high-boiling vacuum residue (VR) fraction (565 °C and above) of crude oil by this method. However, we have addressed this issue by calculating sulfur in the VR fraction as a difference between total sulfur in crude oil (using X-ray fluorescence or combustion methods) and sulfur in the rest of the fractions (using HT-CNS SimDis). A similar technique was employed to determine nitrogen in the VR fraction of crude oil. The gas oil reference standard with known boiling range distribution was used to check the system suitability and generate the response factor for the calculation of hydrocarbon yield, and VGO NS Reference (internal nitrogen/sulfur QC standard) was used as a calibration standard for sulfur and nitrogen quantification. Currently, there is no single method available for the simultaneous determination of C, S, and N present in crude oil. This method produces detailed temperature distribution of S and N in a crude oil sample that cannot be obtained by either total sulfur and total nitrogen analysis or analysis of sulfur and nitrogen in discrete distillation cuts. As a result, this technique is extremely valuable to the refining industry for the valuation of crude oil, plant troubleshooting, and optimization of refinery processes.