Determination of Carbon, Hydrogen, and Nitrogen in Hydrocarbons (CHN828)

Importance of the Topic

The quantitative analysis of carbon, hydrogen, and nitrogen is a cornerstone in the ultimate characterization of hydrocarbon materials.
It underpins calculations of energy content, material balances, refining yields and emission potentials when hydrocarbons are used as fuels.

Objectives and Overview

This application note demonstrates a robust procedure for CHN determination in various hydrocarbon samples using the LECO CHN828.
A modified ASTM D5291 protocol is applied to achieve accurate results with low detection limits, especially for nitrogen in low-N matrices.

Instrumentation Used

• LECO CHN828 combustion analyzer with vertical quartz furnace and pure oxygen environment
• Afterburner module for sulfur compound removal
• Infrared detector cells for CO₂ (carbon) and H₂O (hydrogen)
• Thermal conductivity detector for N₂ (nitrogen)
• Helium carrier gas and selectable dose loops (3 cm³ or 10 cm³)

Methodology

Samples (0.07–0.14 g) are weighed into tin foil cups, tin capsules or copper capsules with COM-AID additive to ensure uniform combustion and prevent sample loss.
Cups and capsules may be left open to purge entrapped atmosphere or closed with an atmospheric blank correction.
Key procedural steps:

• System conditioning with reference or sample replicates
• Blank determination to verify baseline stability (std dev ≤ 0.001 % with helium)
• Calibration/drift correction using certified phenylalanine standards over fractional masses
• Sample analysis sequence with programmed furnace (950 °C) and afterburner (850 °C) flows
• Optional atmospheric blank for tin foil and copper capsule analyses

Main Results and Discussion

Typical data demonstrate high accuracy and precision across sample types:
– Residual oil: C ≈ 83.5 % ± 0.2, H ≈ 13.2 % ± 0.04, N ≈ 0.07 % ± 0.01
– Paraffin oil: C ≈ 86.4 % ± 0.1, H ≈ 14.1 % ± 0.02, N below detection limit
– Mineral oil: C ≈ 84.4 % ± 0.2, H ≈ 14.2 % ± 0.04, N below detection limit
Precision is maintained when using either tin cups, capsules or copper capsules, with appropriate blank corrections for trapped atmosphere.

Benefits and Practical Applications

• Rapid and reproducible CHN data for quality control in petrochemical and lubrication industries
• Simple linear calibration procedures reduce operational complexity and cost
• High sensitivity for low-nitrogen samples supports emissions and fuel-quality assessments
• Flexible sample container options accommodate oils with varying volatility and viscosity

Future Trends and Potential Applications

Ongoing developments may include automated sample handling and integration with complementary detectors (e.g., sulfur, oxygen).
Miniaturized combustion systems and advanced data analytics will further streamline CHN analysis in research and industrial laboratories.
Green analytical approaches may reduce reagent consumption and system footprint.

Conclusion

The LECO CHN828 coupled with a modified ASTM D5291 protocol delivers reliable, high-precision carbon, hydrogen, and nitrogen determinations for a variety of hydrocarbon matrices.
Appropriate sample preparation and blank correction techniques ensure data integrity at low nitrogen levels.

References

• ASTM D5291: Standard Test Methods for Instrumental Determination of Carbon, Hydrogen, and Nitrogen in Petroleum Products and Lubricants
• LECO CHN828 Series Operator’s Instruction Manual