ASTM D7359 Total F, Cl & S Testing in Aromatic Hydrocarbons by Combustion-IC
ASTM D7359 covers the test for an oxygen-rich pyrohydrolytic environment where the sample is combusted. In the presence of an oxidizing agent, the gaseous by-products of the combusted sample are trapped in an absorption medium, where the hydrogen halides (HX) generated during combustion dissociate into their respective ions, and the sulfur oxides (SOX) formed are further oxidized to SO42-. A sample injection valve automatically injects an aliquot of known volume of the absorbing solution into an ion chromatograph (IC). The anion separation column of the IC separates the halide and sulfate anions. Prior to the conductivity detector on the ion chromatograph, where the anions of interest are detected, the conductivity of the eluent is decreased with an anion suppression device. The system is calibrated with a series of standards containing known levels of fluorine, chlorine, and sulfur, and then unknown samples are analyzed under the same conditions as the standards.
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- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
Overview
ASTM D7359 describes a test method for determining total fluorine, chlorine, and sulfur in aromatic hydrocarbons and their mixtures using oxidative pyrohydrolytic combustion followed by ion chromatography (IC) detection. These halogen and sulfur impurities can cause catalyst poisoning, corrosion, and product quality issues in petrochemical and specialty chemical processes.
This method provides highly sensitive, simultaneous multi-element analysis for trace fluorine, chlorine, and sulfur in aromatic feedstocks and products.
Scope, Applications, and Benefits
Scope
ASTM D7359 applies to aromatic hydrocarbons including benzene, toluene, xylene, styrene, and their mixtures and determines:
- Total fluorine content (µg/g or mg/kg)
- Total chlorine content
- Total sulfur content
- Simultaneous multi-element analysis in a single combustion
Applications
- Aromatic feedstock quality control in petrochemical plants
- Catalyst guard bed protection from halide and sulfur poisoning
- Polymer-grade monomer purity specification compliance
- Reformulated fuel and aromatics extraction quality assurance
- Environmental compliance screening of aromatic emissions
Benefits
- Simultaneous F, Cl, and S determination in a single run
- Very low detection limits (sub-ppm) for sensitive feedstock applications
- IC detection provides excellent selectivity and sensitivity for anions
- Combustion method eliminates matrix interferences from organic compounds
- Supports stringent catalyst protection and product purity requirements
Test Process
Sample Combustion
The sample is combusted in oxygen at high temperature, converting fluorine, chlorine, and sulfur to HF, HCl, and SO₂/SO₃ gases.
1Pyrohydrolysis Absorption
Combustion gases are absorbed in water, forming fluoride, chloride, and sulfate ions.
2Ion Chromatography Analysis
The solution is analyzed by IC, where fluoride, chloride, and sulfate are separated and quantified by conductivity detection.
3Concentration Calculation
Ion concentrations in the absorption solution are back-calculated to element concentrations in the original sample.
4Technical Specifications
| Parameter | Details |
|---|---|
| Standard | ASTM D7359 |
| Test Principle | Oxidative combustion + IC detection |
| Applicable Materials | Benzene, toluene, xylenes, styrene, and mixtures |
| Detection Limits | Typically 0.1–1 mg/kg for F, Cl, S |
| IC Detection | Suppressed conductivity |
| Measured Outputs | F, Cl, S concentrations (mg/kg or µg/g) |
Instrumentation Used for Testing
- Combustion furnace with oxygen and argon/nitrogen supply
- Pyrohydrolysis quartz tube and water absorption vessel
- Ion chromatograph with suppressed conductivity detector
- Anion separation column
- Certified F, Cl, S reference standards for calibration
Results and Deliverables
- Fluorine, chlorine, and sulfur concentrations (mg/kg) in the sample
- Calibration curve linearity and detection limit data
- Comparison to purity specification limits
- IC chromatogram with integrated peak data
- Analytical certificate with measurement uncertainty
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Frequently Asked Questions
Halogens (F, Cl) are powerful catalyst poisons in hydroprocessing and reforming; even sub-ppm levels can deactivate precious metal catalysts, causing significant economic losses.
Yes — the combustion step converts all organic and inorganic forms of F, Cl, and S to their respective ionic forms, providing a true total element measurement regardless of chemical form.
Typical detection limits for chlorine are 0.1–0.5 mg/kg (ppm) depending on sample size and instrument sensitivity; sub-ppm detection is achievable with optimized conditions.
The combustion-IC approach is matrix-tolerant, and the method can be adapted to aliphatic hydrocarbons and other organic matrices with appropriate validation.
Combustion IC offers lower detection limits than portable XRF for sulfur and additionally provides simultaneous halogen (F, Cl) analysis, making it superior for trace multi-element requirements; XRF is faster for higher-concentration screening.
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