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D6313-99 – Standard Test Method Technical Guide
🔬 Scope and Applicability
This test method, designated ASTM D6313-99, covers the determination of total sulfur in aromatic hydrocarbons, their derivatives, and related chemicals. It is specifically validated for typical sulfur concentrations from 0.005 to 10 mg/kg.
The method is applicable to a wide variety of aromatic compounds including benzene, toluene, cumene, p-xylene, o-xylene, cyclohexane, phenol, cresols, xylenols, and other oxygenated aromatic compounds. Higher sulfur concentrations may be analyzed by extending the range through acceptable dilution techniques.
| 🟦 Material Category | 📏 Example Compounds | 🎯 Validated Sulfur Range (mg/kg) |
|---|---|---|
| Basic Aromatic Hydrocarbons | Benzene, Toluene, Xylenes | 0.005 – 10 |
| Oxygenated Aromatics | Phenol, Cresols, Xylenols | 0.005 – 10 |
| Extended Range (via dilution) | All applicable materials | > 10 |
⚙️ Test Configurations and Procedure
The analysis is performed using a high-temperature hydrogenolysis furnace operating at 1200 to 1300°C. All sulfur compounds are broken down and reduced to hydrogen sulfide (H₂S), which is then measured by difference photometry based on its colorimetric reaction with lead acetate.
The standard outlines two distinct instrument configurations:
- Reductive Configuration: A specific amount of sample is injected into an air stream, thoroughly mixed with excess hydrogen, and introduced into the pyrolysis furnace. The atmosphere remains reducing throughout the process.
- OxyhydroPyrolysis Configuration: The sample is initially burned in an air stream within the furnace. The resulting combustion products are then released into a hydrogen-rich atmosphere where they are chemically reduced to H₂S.
| 🟦 Configuration | 🔬 Injection & Atmosphere | ⚡ Detection Principle |
|---|---|---|
| Reductive | Sample in air, mixed with H₂ prior to pyrolysis | H₂S + Lead Acetate (Difference Photometry) |
| OxyhydroPyrolysis | Sample pyrolyzed in air, then exposed to H₂ | H₂S + Lead Acetate (Difference Photometry) |
⚠️ Safety Consideration: This standard does not address all safety concerns. Specific precautionary statements regarding the handling of reagents and operation of the high-temperature furnace are located in Sections 7.5, 7.6, 8, and 11.4 of the complete standard. Appropriate safety and health practices must always be established.
💡 Technical Tip: For conformance with specification limits, observed or calculated values must be rounded off in accordance with the rounding-off method of Practice E 29. The user should refer to Terminology D 4790 for definitions of other standard terms used in this test method.
📊 Key Terminology and References
Difference Photometry: An analytical method where the photometric property of a colorimetric reactant (e.g., lead acetate) is measured as a baseline reading, exposed to the analyte, and then remeasured. The difference in response is proportional to the concentration.
Oxyhydropyrolysis: The act of first burning a material in a pyrolysis furnace to create combustion products, and then exposing those products to a hydrogen-rich atmosphere to reduce them for detection.
The method relies on several referenced ASTM standards, including D 1193 (Reagent Water), D 3437 and D 3852 (Sampling and Handling of Cyclic Products and Phenol), and D 4052 (Density Measurement).
❓ Frequently Asked Questions
🔍 What is the specified concentration range for D6313-99?
The test method is designed for aromatic compounds with typical sulfur concentrations from 0.005 to 10 mg/kg. Higher concentrations require sample dilution.
💡 What chemical reaction is used for detection?
Sulfur compounds are reduced to hydrogen sulfide (H₂S) in the pyrolysis furnace. The H₂S then reacts with lead acetate, producing a colorimetric change measured by difference photometry.
⚡ What is the required pyrolysis temperature?
The hydrogenolysis pyrolysis furnace must be maintained at a temperature of 1200° to 1300°C to ensure complete breakdown and reduction of sulfur compounds.
📌 Which ASTM practice governs the rounding of test data for conformance?
Practice E 29 (Using Significant Digits in Test Data to Determine Conformance with Specifications) must be followed when rounding off observed or calculated values.