ANALYSIS OF SULFUR CONTAINING COMPOUNDS IN PETROLEUM FUELS AND DISTILLATES USING DEANS SWITCHING WITH AN IMPROVED HIGH TEMPERATURE FLAME PHOTOMETRIC DETECTOR

Importance of the Topic

In petroleum refining, precise characterization of sulfur compounds is critical for meeting stringent environmental regulations and optimizing hydrotreating and hydrocracking processes. Detailed profiling of dibenzothiophene (DBT) homologues informs catalyst selection and operating conditions to achieve ultra–low sulfur fuels and efficient process performance.

Objectives and Study Overview

This work demonstrates the use of an improved high-temperature flame photometric detector (FPD) on an Agilent 7890B gas chromatograph combined with a Deans switching system. The study aims to separate and quantify C0–C4 alkylated DBTs in a variety of feedstocks—including low sulfur diesel, light cycle oil (LCO) and heavy vacuum gas oil—while minimizing hydrocarbon quenching and extending analysis to heavier distillate fractions via backflush.

Methodology and Instrumentation

A capillary flow technology (CFT) Deans switch heartcut approach transfers the DBT region from a non-polar HP-1 column to a mid-polar DB-17HT column for enhanced separation. The primary column (30 m×0.25 mm×0.25 µm) operates at a constant He flow of 1.25 mL/min; the secondary column (30 m×0.25 mm×0.15 µm) at 2.20 mL/min. Oven programming ramps from 40 °C to 250 °C at 10 °C/min, then to 350 °C at 15 °C/min. The FPD features a thermally isolated emission block (150 °C) and transfer line heated up to 360 °C, enabling sulfur detection at temperatures above 300 °C. Backflush capability protects the column set when analyzing high-boiling fractions.

Main Results and Discussion

Heartcutting into the DB-17HT column significantly reduces co-elution with hydrocarbons, yielding clear chromatographic resolution of DBT, C1–C4 homologues and multidimensional alkylated DBTs. Calibration in the 1–100 ppm range achieved sensitivities of 2.5 pg S/sec. The approach successfully profiled sulfur species in low sulfur diesel and LCO, and handled heavy gas oil fractions to 620 °C simulated distillation boiling point without column damage.

Benefits and Practical Applications

• Enhanced selectivity and sensitivity for sulfur speciation in complex matrices
• Reduced quenching and improved quantitation of trace DBT homologues
• Backflush protects columns and shortens cycle times when analyzing heavy feedstocks
• Valuable tool for refining process optimization, quality control and regulatory compliance

Future Trends and Potential Applications

Advancements may include shorter, thinner-film secondary columns for even heavier heartcuts, expansion to multi-ring sulfur and other heteroatom species, integration with automated sampling for high-throughput analysis, and coupling with chemometric techniques and real-time process monitoring systems.

Conclusion

The combination of a high-temperature FPD with a CFT Deans switch on the Agilent 7890B GC offers a robust and versatile platform for detailed sulfur compound profiling in petroleum feeds and fuels. This method supports the industry’s drive toward ultra–low sulfur products and efficient catalyst utilization.

Instrumentation Used

• Gas chromatograph: Agilent 7890B with MMI inlet
• Detector: High-temperature Flame Photometric Detector (FPD) with emission block and transfer line heaters
• Primary column: HP-1, 30 m×0.25 mm×0.25 µm
• Secondary column: DB-17HT, 30 m×0.25 mm×0.15 µm
• Capillary Flow Technology (CFT) Deans switch system with backflush capability
• Carrier gas: Helium, constant flow mode
• Oven program: 40 °C (0 min) to 250 °C at 10 °C/min, then to 350 °C at 15 °C/min