Analysis of Impurities in Propane/Propylene Streams Using a Pulsed-Flame Photometric Detector (PFPD)

Importance of the Topic

The accurate detection of trace sulfur species such as hydrogen sulfide (H2S) and carbonyl sulfide (COS) in propane/propylene (C3) and ethylene/ethane (C2) streams is critical for the petrochemical industry. Even minute amounts of these contaminants can corrode infrastructure, poison catalysts, and compromise polymer product quality. A rapid, sensitive, and robust analytical approach is therefore essential to ensure feedstock purity, process efficiency, and equipment longevity.

Objectives and Study Overview

This study presents a streamlined gas chromatographic method employing a pulsed-flame photometric detector (PFPD) for quantifying sulfur impurities in C2 and C3 feedstocks. Key goals include achieving detection limits below 0.1 ppmv, demonstrating linear response across relevant concentration ranges, and verifying long-term system stability under routine operating conditions.

Methodology and Instrumentation

A custom-configured OI Analytical S-PRO Select GC System fitted with a 5383 PFPD formed the core of the analytical setup. Automated loop injection and dual electronically actuated valves enabled precise, reproducible sample introduction. Separation was accomplished on an Agilent J&W Low Sulfur Select column (60 m × 0.32 mm ID) with helium carrier gas at 1.2 mL/min. Oven programming commenced at 40 °C, held for 10 min, followed by a ramp of 30 °C/min to 180 °C, culminating in a total runtime of 15.2 min. The PFPD was optimized for sulfur detection in linearized mode with a square-root function enabled. A dual time-gate approach provided simultaneous sulfur and hydrocarbon chromatograms from a single detector.

Calibration and Validation

Certified permeation devices for H2S, COS, and methyl mercaptan (MeSH) served as calibration standards over ranges of 0.083–1.881 ppmv (H2S), 0.093–2.083 ppmv (COS), and 0.032–0.719 ppmv (MeSH). Ten-point calibration curves exhibited excellent linearity (R2 ≥ 0.999). A two-week repeatability study with 110 replicate injections yielded relative standard deviations of 10.96% (H2S), 4.31% (COS), and 8.81% (MeSH), confirming system robustness.

Main Results and Discussion

Analysis of spiked matrices demonstrated clear separation of sulfur compounds from propane/propylene, ethylene/ethane, and methane streams. While COS resolution was consistently robust, H2S presented coelution challenges in C2 matrices due to its elution between ethylene and ethane peaks. Adjusting split ratios and matrix dilutions allowed for optimized detection without significant interference. Typical split ratios ranged from 10:1 to 100:1, depending on matrix composition.

Benefits and Practical Applications

• Fast throughput with total run times under 16 minutes per sample.
• High sensitivity enabling detection below 0.1 ppmv for critical sulfur species.
• Automated loop injection ensures reproducibility and minimal operator intervention.
• Single-detector dual-channel capability reduces instrument footprint and maintenance.
• Applicable to a variety of gas matrices without extensive method reconfiguration.

Future Trends and Opportunities

Emerging directions include hyphenation of GC-PFPD with mass spectrometry for enhanced compound identification, incorporation of microfluidic sampling for on-line process monitoring, and development of data-driven predictive maintenance models. Further miniaturization and integration into portable platforms could enable field deployment for real-time feedstock quality control and rapid troubleshooting in petrochemical plants.

Conclusion

The presented GC-PFPD method delivers a rapid, reliable, and reproducible approach for trace sulfur analysis in C2 and C3 feedstocks. Its high sensitivity, robust calibration, and versatility across diverse gas matrices make it an attractive solution for routine quality assurance in petrochemical operations.

Reference

1. Market Study: Polypropylene (3rd Edition), Ceresana, 2014. ASTM Standard D6228-10, Determination of Sulfur Compounds in Gaseous Fuels by GC-PFPD, ASTM International, 2010.