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D2549-23 – Standard Test Method Technical Guide
ASTM D2549-23 outlines a standard test method for separating representative aromatics and nonaromatics fractions from high-boiling oils using elution chromatography. This method is essential for analyzing hydrocarbon mixtures in the petroleum industry.
📐 Scope and Applicable Boiling Ranges
The test method applies to hydrocarbon mixtures with boiling points between 232 °C and 538 °C (450 °F to 1000 °F). It includes procedures for both 2 g and 10 g sample sizes. For samples boiling below 232 °C but with a 5 % point above 178 °C per Test Method D2887, an alternative approach is provided in Appendix X1.
| 📏 Sample Size | 🎯 Boiling Range | 📌 Alternative Condition |
|---|---|---|
| 2 g or 10 g | 232 °C – 538 °C (450 °F – 1000 °F) | For samples <232 °C with 5% >178 °C (see Appendix X1) |
⚙️ Test Procedure and Elution Sequence
A weighed sample is charged to a glass column packed with activated bauxite and silica gel. The nonaromatics fraction is eluted with n-pentane, followed by the aromatics fraction using diethyl ether, chloroform, and ethyl alcohol.
| ⚗️ Step | 🧪 Solvent | 🎯 Fraction |
|---|---|---|
| 1 | n-Pentane | Nonaromatics |
| 2 | Diethyl Ether | Aromatics |
| 3 | Chloroform | Aromatics |
| 4 | Ethyl Alcohol | Aromatics |
⚠️ Caution: Some components may not elute under standard conditions for certain sample types. Consider using Test Method D2007 as an alternative.
📊 Definitions and Composition of Fractions
The nonaromatics fraction is the n-pentane eluate, composed of paraffinic and naphthenic hydrocarbons for straight-run materials, and may include olefins for cracked stocks. The aromatics fraction is desorbed with polar solvents and contains aromatics, condensed naphthenic-aromatics, aromatic olefins, and heteroatom compounds (sulfur, nitrogen, oxygen).
💡 These fractions are suitable for further analysis using methods like D2425, D2786, or D3239 for hydrocarbon type determination.
❓ Frequently Asked Questions
🔍 What is the purpose of ASTM D2549-23?
To separate high-boiling oils into representative aromatics and nonaromatics fractions for compositional analysis.
💡 What solvents are used for elution?
n-Pentane for nonaromatics, and diethyl ether, chloroform, and ethyl alcohol for aromatics.
⚡ Can this method handle low-boiling samples?
Yes, with an alternative procedure for samples with a 5 % point above 178 °C (see Appendix X1).
📌 What defines the aromatics fraction?
The aromatics fraction includes aromatics, condensed naphthenic-aromatics, aromatic olefins, and heteroatom compounds.