⛽ Oxidation stability of diesel fuel

Petrochemistry PN-EN ISO 12205

Overview

Oxidation stability is a key quality parameter of diesel fuel and other middle distillates, which determines their resistance to chemical degradation under oxygen influence. Fuel oxidation leads to formation of resins, sediments and organic acids, which clog fuel filters, cause wear of injection elements and corrosion of storage tanks.

The method according to ISO 12205 is an accelerated test — it simulates a one-year storage period of diesel fuel by bubbling oxygen through the fuel sample at 95°C for 16 hours. After aging, two types of sediments are determined: insoluble filterable (retained on membrane filter) and insoluble adherent (deposited on glass vessel and cooler walls, washed out with three-component solvent). The sum of both fractions constitutes total insoluble sediments.

According to PN-EN 590 standard, the maximum permissible amount of total insoluble sediments is 25 g/m³. Fuels with FAME addition (biodiesel) typically show lower oxidation stability due to the presence of unsaturated double bonds in esters, which accelerates autoxidation processes.

The test is mandatory in diesel fuel quality certificates and is an important element of quality control at every stage of the logistics chain — from refinery, through storage depots, to fuel stations.

Method principle

350 mL of filtered diesel fuel is placed in an oxidation tube and heated to 95°C ± 1°C in a heating block. Oxygen is bubbled through the sample at a flow rate of 3 L/h for 16 hours. A reflux condenser prevents loss of volatile fractions. After aging, the sample is cooled, filtered through a 0.8 µm pore membrane (filtered sediments) and vessels are washed with three-component solvent (toluene/acetone/methanol) to collect adherent sediments. After solvent evaporation, both types of sediments are weighed and summed.

Applications

• Diesel fuel quality certificate (PN-EN 590) — limit 25 g/m³
• Oxidation stability assessment of diesel/FAME blends (B7, B10, B20)
• Quality control of fuels at storage depots
• Testing the effect of antioxidant additives on fuel durability
• Predicting storage durability of fuels for strategic reserves
• Compatibility assessment of fuel blends from different sources
• R&D research on new fuel formulations

Key parameters

Standard

Standard number

PN-EN ISO 12205:2006

Title (PL)

Przetwory naftowe — Oznaczanie stabilności oksydacyjnej średnich destylatów naftowych

Title (EN)

Petroleum products — Determination of the oxidation stability of middle-distillate fuels

Step-by-step procedure

1. Sample preparation

   Filter diesel fuel sample through 0.8 µm membrane to remove solid contaminants. Measure 350 mL of filtered fuel into glass tube.

   ⏱ Time: 15 min

2. Apparatus preparation

   Wash tubes and condensers with three-component solvent, then acetone. Dry. Mount tube with sample in heating block.

   ⏱ Time: 20 min

3. Condenser and oxygen connection

   Mount reflux condenser on tube. Connect oxygen line with glass tube reaching bottom of tube. Set O₂ flow to 3 L/h.

   ⏱ Time: 10 min

4. Heating to 95°C

   Set block temperature to 95°C ± 1°C. Wait for sample to reach set temperature.

   ⏱ Time: 30 min • 🌡 Temperature: 95°C

5. Oxidation — 16 hours

   Start time counting from reaching 95°C. Bubble oxygen continuously for 16 h. Monitor flow and temperature.

   ⏱ Time: 16 h • 🌡 Temperature: 95°C

6. Sample cooling

   After 16 h turn off heating and oxygen supply. Cool sample to room temperature without dismantling system.

   ⏱ Time: 2 h

7. Filtration — filtered sediments

   Filter cooled sample through pre-weighed 0.8 µm membrane under vacuum. Rinse filtrate with n-heptane.

   ⏱ Time: 30 min

8. Vessel washing — adherent sediments

   Wash tube, condenser and tubes with three-component solvent (toluene:acetone:methanol 1:1:1). Collect rinsings into weighing vessel.

   ⏱ Time: 20 min

9. Drying and weighing

   Dry membrane and vessel with rinsings in oven (110°C). Cool in desiccator. Weigh to 0.1 mg accuracy.

   ⏱ Time: 2 h • 🌡 Temperature: 110°C

10. Result calculation

    Filtered sediments [g/m³] = (sediment mass on filter / 0.350) × 1000. Adherent sediments — similarly. Total = sum of both fractions.

11. Result evaluation

    Compare result with PN-EN 590 limit (≤25 g/m³). For duplicates check repeatability. Round result to 1 g/m³.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Oxygen — supports combustion, do not use near flammable materials and open flame
• Temperature 95°C — burn risk, use heat-resistant gloves
• Toluene, acetone, methanol — flammable and toxic, work under fume hood
• Diesel fuel — flammable, avoid ignition sources
• N-heptane — highly flammable and irritating, use in digestorium
• Safety glasses, nitrile gloves and coat mandatory

Frequently asked questions