Analysis of sulfur in oils according to ASTM D2622 method

Significance of the Topic

Monitoring sulfur levels in oils is essential to meet environmental regulations, protect engine components, and ensure product quality in the petrochemical industry.

Objectives and Study Overview

This study demonstrates the determination of sulfur in various oil matrices using X-ray fluorescence (XRF) spectroscopy in accordance with ASTM D2622.
The main goals were:

• To establish a calibration curve based on six sulfur standards.
• To assess method repeatability and stability across different sample cells.
• To analyze unknown crude oil, heavy oil, and oil residue samples and compare results with certified values.

Methodology and Equipment Used

The analysis was performed on a Thermo Scientific ARL PERFORM’X 4200 W XRF spectrometer configured with a 5 GN+ rhodium X-ray tube, helium purge, multi-filter primary beam system, multiple crystals, and dual detectors.
Key features include the LoadSafe design with liquid cassette recognition, the Secutainer vacuum powder collector, and an optional helium shutter for goniometer protection.

Calibration procedure:

1. Preparation of six oil standards by ASTM D2622.
2. Acquisition of net sulfur intensities (S net = S Ka1,2 – background).
3. Correlation of intensity with sulfur concentration in parts per million to generate the calibration curve.

Repeatability and stability tests:

• Analysis of a single oil residue sample across three liquid cells (A, B, C), each measured in triplicate.
• Calculation of mean, standard deviation, and relative standard deviation.

Unknown sample analysis:

• Four oil samples (crude oil, heavy oil, and two oil residues) prepared and measured in triplicate per cell.
• Comparison of measured sulfur levels with certified values.

Main Results and Discussion

The calibration curve exhibited excellent linearity, with a standard error of estimate of 0.015 %.

Stability test outcomes for the oil residue sample demonstrated high repeatability across cells A, B, and C, with standard deviations below 0.012 %.

Unknown sample analysis yielded sulfur concentrations within 0.03 % of certified values and relative standard deviations under 0.25 %, confirming both accuracy and precision of the method.

Benefits and Practical Applications

The ARL PERFORM’X XRF system offers:

• Rapid, non-destructive sulfur quantification in oils.
• Minimal sample preparation via liquid cells.
• High analytical stability and safety features to prevent sample damage.
• Compliance with ASTM standards for routine QA/QC in refineries and laboratories.

Future Trends and Potential Applications

Emerging developments may include:

• Automation of sample handling and data processing for high-throughput analysis.
• Integration of advanced chemometric models and machine learning for improved calibration stability.
• Extension to multi-element screening in complex matrices.
• On-line or in-line XRF monitoring for real-time process control.
• Enhanced tube and detector technologies to further lower detection limits.

Conclusion

The Thermo Scientific ARL PERFORM’X XRF spectrometer delivers reliable, accurate, and precise sulfur determinations in oil samples following ASTM D2622 guidelines. Its robust design, safety features, and high reproducibility make it an ideal tool for petrochemical quality control and regulatory compliance.

Reference

ASTM D2622: Standard Test Method for Sulfur in Petroleum and Petroleum Products by Wavelength Dispersive X-ray Fluorescence Spectrometry