⚗️ Aromatic hydrocarbon content in diesel fuel
In short
Determination of monoaromatic, diaromatic and polyaromatic hydrocarbon content in diesel fuel and middle distillates by HPLC method with refractive index detection (RI). The test is performed according to PN-EN 12916:2016; Monoaromatics range: 5–40% m/m (typical). The procedure comprises 10 steps (about 4 h 15 min in total); it is used for: Diesel fuel quality control (polyaromatics limit ≤8.0% m/m), Monitoring of hydrorefining processes in refineries, Testing of middle distillates — jet fuel (Jet A-1), kerosene.
At a glance
- Standard: PN-EN 12916:2016
- Category: Petrochemistry
- Procedure steps: 10
- Total time of stages: 4 h 15 min
- Monoaromatics range: 5–40% m/m (typical)
- Diaromatics range: 1–15% m/m
- Polyaromatics range: 0.1–10% m/m
Overview
Aromatic hydrocarbons are undesirable components in diesel fuel for several reasons: they reduce cetane number (longer ignition delay, harsh engine operation), increase particulate matter (soot) and nitrogen oxide (NOₓ) emissions and possess carcinogenic properties (especially polycyclic aromatics — PAH). Fuel Quality Directive 2009/30/EC limits polycyclic aromatic hydrocarbon (polyaromatics) content in diesel fuel to maximum 8.0% m/m.
PN-EN 12916 method enables rapid and accurate separation and quantitative determination of three types of aromatic hydrocarbons: monoaromatics (1 ring — e.g. toluene, xylenes), diaromatics (2 rings — e.g. naphthalene) and polyaromatics (≥3 rings — e.g. anthracene, pyrene) in middle distillates with boiling range 150–400°C.
HPLC analysis is industry standard in diesel fuel quality control in refineries and fuel depots. Test is routinely performed with every diesel fuel production batch and in fuel quality monitoring by Trade Inspection and Energy Regulatory Office (URE). Results are also used to optimize hydrorefining processes (HDS/HDN) aimed at reducing aromatic content.
Method is equivalent to ASTM D6591 (IP 548) — both standards give comparable results and are widely accepted in international trade.
Method principle
Diesel oil sample, dissolved in hexane, is introduced onto HPLC column packed with modified silica gel with aminosilyl phase (NH₂). Normal phase separates hydrocarbons by type: saturated (aliphatic + naphthenic) elute first, then monoaromatics, diaromatics and finally polyaromatics. Detection is performed using refractive index detector (RI — Refractive Index Detector), which measures difference in refractive index between eluate and pure solvent. Each aromatic type gives separate peak on chromatogram. Content is calculated based on calibration with standard mixtures of known concentrations of individual aromatic types. Result expressed in % m/m.
Applications
- Diesel fuel quality control (polyaromatics limit ≤8.0% m/m)
- Monitoring of hydrorefining processes in refineries
- Testing of middle distillates — jet fuel (Jet A-1), kerosene
- Assessment of fuel impact on exhaust emissions (soot, NOₓ)
- Control of imported fuels (Customs Service)
- Testing of alternative fuels — biodiesel (FAME), HVO, GTL
- Diesel fuel formulation optimization (blending)
Key parameters
| Parameter | Value |
|---|---|
| Monoaromatics range | 5–40% m/m (typical) |
| Diaromatics range | 1–15% m/m |
| Polyaromatics range | 0.1–10% m/m |
| Polyaromatics limit (EU Directive) | ≤8.0% m/m |
| Repeatability | ±0.5% m/m (monoaromatics), ±0.3% m/m (diaromatics), ±0.2% m/m (polyaromatics) |
| Column | Aminosilyl (NH₂), 250 mm × 4.6 mm, 5 µm |
Standard
- Standard number
- PN-EN 12916:2016
- Title (PL)
- Przetwory naftowe — Oznaczanie typów węglowodorów aromatycznych w destylatach średnich — Metoda wysokosprawnej chromatografii cieczowej z detektorem refrakcji (HPLC-RI)
- Title (EN)
- Petroleum products — Determination of aromatic hydrocarbon types in middle distillates — High performance liquid chromatography method with refractive index detection
Step-by-step procedure
-
Mobile phase preparation
Degas n-hexane HPLC grade by ultrasound or helium purging (15 min). Filter through 0.45 µm membrane filter. Fill HPLC solvent reservoir.
-
Column conditioning
Flush aminosilyl column with hexane at flow 1.0 mL/min for min. 30 min. Check RI detector baseline stability.
-
Calibration solution preparation
Prepare standard mixtures containing known amounts of hexadecane, toluene, naphthalene and phenanthrene in hexane (3–5 concentration levels). Each solution ~100 mg/mL total concentration.
-
Calibration
Inject calibration solutions (injection volume 5–20 µL). Record chromatograms. Integrate peaks of individual fractions. Build calibration curves (peak area vs % m/m).
-
Sample preparation
Dissolve ~100 mg diesel oil in 1 mL hexane. Filter through 0.45 µm PTFE syringe filter. Transfer to HPLC vial with septum.
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Chromatographic analysis
Inject sample (5–20 µL). Isocratic hexane flow 1.0 mL/min. Analysis time ~20–30 min. Chromatogram should show separate peaks: saturates, monoaromatics, diaromatics, polyaromatics.
-
Integration and calculations
Integrate peaks of individual aromatic fractions. From calibration curves calculate content of each type in % m/m. Sum of fractions = 100%.
-
Quality control
Analyze control sample (certified reference material) every 10 samples. Check standard retention time (drift <2%). Monitor column back pressure.
-
Column regeneration
After series of analyses flush column with hexane/dichloromethane mixture (90:10) to remove heavy fractions. Then return to pure hexane.
-
Reporting
Result: monoaromatics = X.X % m/m, diaromatics = Y.Y % m/m, polyaromatics = Z.Z % m/m, total aromatics = sum. Compare polyaromatics with limit ≤8.0% m/m.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| HPLC system with RI detector | Agilent 1260 Infinity II, Waters Alliance e2695, Shimadzu Prominence-i | 150,000–350,000 PLN |
| Aminosilyl HPLC column | Agilent Zorbax NH₂ 250×4.6 mm 5 µm, Waters Spherisorb NH₂ | 1,500–3,500 PLN |
| Refractive index detector (RI) | Agilent 1260 RID, Waters 2414 RI Detector | 40,000–80,000 PLN (in HPLC system) |
| Autosampler | Agilent 1260 ALS, Waters 2707 | 50,000–90,000 PLN (in system) |
| Isocratic pump | Agilent 1260 Iso Pump, flow 1.0 mL/min hexane | in HPLC system |
| Chromatography software | Agilent OpenLab CDS, Waters Empower 3 | 15,000–40,000 PLN (license) |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| n-Hexane HPLC grade | 110-54-3 | Mobile phase and sample solvent, purity ≥97%, filtered 0.45 µm, degassed |
| Naphthalene (diaromatics standard) | 91-20-3 | Purity ≥99%, certified, for diaromatic fraction calibration |
| Phenanthrene (polyaromatics standard) | 85-01-8 | Purity ≥98%, for polyaromatic fraction calibration |
| 1-Methylnaphthalene | 90-12-0 | Monoaromatic/diaromatic standard, purity ≥97% |
| Hexadecane (saturated standard) | 544-76-3 | Saturated (aliphatic) fraction representative, purity ≥99% |
| Toluene (monoaromatic standard) | 108-88-3 | HPLC grade purity, for monoaromatics calibration |
Health and safety (OHS)
- n-Hexane — flammable (H225), neurotoxic with chronic exposure (H373), work under fume hood
- Naphthalene — harmful (H302), suspected carcinogen, use gloves
- Phenanthrene and polycyclic aromatics — potentially carcinogenic, avoid skin contact
- Dichloromethane — suspected carcinogen (H351), narcotic, ventilation mandatory
- Diesel oil — irritant, flammable, safety goggles and protective gloves
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN 12916:2016 — “Petroleum products — Determination of aromatic hydrocarbon types in middle distillates — High performance liquid chromatography method with refractive index detection”.
How does this method work?
Diesel oil sample, dissolved in hexane, is introduced onto HPLC column packed with modified silica gel with aminosilyl phase (NH₂). Normal phase separates hydrocarbons by type: saturated (aliphatic + naphthenic) elute first, then monoaromatics, diaromatics and finally polyaromatics.
What is the measuring range and accuracy?
Monoaromatics range: 5–40% m/m (typical); Diaromatics range: 1–15% m/m; Polyaromatics range: 0.1–10% m/m; Polyaromatics limit (EU Directive): ≤8.0% m/m.
How long does the test take?
The times given for the individual stages add up to approximately 4 h 15 min. The procedure comprises 10 steps.
What equipment is required?
HPLC system with RI detector, Aminosilyl HPLC column, Refractive index detector (RI), Autosampler, Isocratic pump, Chromatography software. Indicative cost of the core instrument (HPLC system with RI detector): 150,000–350,000 PLN.
Where is this test used?
Diesel fuel quality control (polyaromatics limit ≤8.0% m/m); Monitoring of hydrorefining processes in refineries; Testing of middle distillates — jet fuel (Jet A-1), kerosene; Assessment of fuel impact on exhaust emissions (soot, NOₓ); Control of imported fuels (Customs Service); Testing of alternative fuels — biodiesel (FAME), HVO, GTL; Diesel fuel formulation optimization (blending).
What safety precautions apply?
n-Hexane — flammable (H225), neurotoxic with chronic exposure (H373), work under fume hood; Naphthalene — harmful (H302), suspected carcinogen, use gloves; Phenanthrene and polycyclic aromatics — potentially carcinogenic, avoid skin contact; Dichloromethane — suspected carcinogen (H351), narcotic, ventilation mandatory; Diesel oil — irritant, flammable, safety goggles and protective gloves.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN 12916.