⛽ Ash content in petroleum products
Gravimetric determination of ash content in petroleum products by burning the sample and ashing the residue in a muffle furnace at 775°C.
Overview
Determination of ash content is one of the basic quality tests for petroleum products. Ash is the non-combustible mineral residue that remains after complete combustion of a petroleum product sample. It consists mainly of metal oxides (iron, vanadium, nickel, sodium, calcium) originating from petroleum feedstock or external contamination (rust, sand, sediments).
High ash content in heavy fuels causes erosion and high-temperature corrosion of gas turbines, boilers and marine engines. In lubricating oils, ash may indicate wear or contamination. In petroleum waxes, ash indicates improper product purification. Ash content control is required by product standards PN-EN 590 (diesel fuel), PN-C-96024 (fuel oil), ASTM D396 and marine specifications.
The gravimetric method according to ISO 6245 involves burning a measured sample of petroleum product in a porcelain or platinum vessel, then ashing the carbon residue in a muffle furnace at 775°C to constant ash mass. The scope of application covers products with ash content from 0.001% to 0.180% m/m.
The test is routinely performed in refinery laboratories, fuel quality control laboratories and accredited laboratories dealing with petroleum product testing.
Method principle
A measured portion of sample (up to 100 g) is placed in a previously ashed and weighed porcelain (or platinum) vessel. The sample is ignited and allowed to burn until only ash and carbon residue remain. The vessel is then placed in a muffle furnace heated to 775°C ± 25°C and ashed until complete removal of carbon (white or light gray ash). After cooling in a desiccator, the vessel is weighed to 0.1 mg accuracy. The result is expressed as mass percent of ash in the sample.
Applications
- Quality control of diesel and fuel oils (PN-EN 590)
- Testing of heavy oils (marine fuels HFO, RMG, RMK)
- Purity assessment of petroleum waxes and paraffins
- Lubricating oil control — detection of metallic contaminants
- Crude oil and distillation fraction testing
- Turbine and boiler fuel specifications
- Refinery process monitoring
Key parameters
| Parameter | Value |
|---|---|
| Determination range | 0.001–0.180% m/m |
| Ashing temperature | 775°C ± 25°C |
| Weighing accuracy | 0.1 mg |
| Sample mass | Up to 100 g (selected according to expected ash content) |
| Repeatability | 0.003% m/m (for content <0.01%) |
| Determination time | 4–8 h (with ashing) |
Standard
- Standard number
- PN-EN ISO 6245:2008
- Title (PL)
- Przetwory naftowe — Oznaczanie popiołu
- Title (EN)
- Petroleum products — Determination of ash
Step-by-step procedure
1. Vessel preparation
Ash the porcelain vessel (crucible) in muffle furnace at 775°C for at least 10 minutes. Cool in desiccator to room temperature.
2. Vessel weighing
Weigh the cooled vessel on analytical balance to 0.1 mg accuracy. Repeat ashing and weighing until difference does not exceed 0.5 mg.
3. Sample measurement
Weigh sample portion (select mass according to Table 1 of standard, to obtain up to 20 mg ash). For heavy oils — approx. 10–50 g, for light oils — up to 100 g.
4. Preliminary combustion
Initiate sample combustion (ignite with flame or igniter). Allow to burn freely under fume hood until flame extinguishes and dark carbon residue remains.
5. Combustion assistance
If sample is difficult to ignite (waxes, heavy oils), add a few drops of light petroleum as combustion initiator. Do not allow vigorous boiling.
6. Ashing in muffle furnace
Place vessel with carbon residue in muffle furnace heated to 775°C ± 25°C. Ash until complete removal of carbon (white/gray ash, constant mass).
7. Cooling
Remove vessel from furnace with tongs and place in desiccator. Cool to room temperature (approx. 30–45 min).
8. Ash weighing
Weigh vessel with ash to 0.1 mg accuracy. Repeat ashing (15 min) and weighing until difference between successive weighings is ≤0.5 mg.
9. Result calculation
Ash content [% m/m] = (ash mass / sample mass) × 100. Report result to 0.001% accuracy.
10. Quality control and cleaning
Perform determination in duplicate. Check compliance with repeatability limits. Clean vessels with toluene and re-ash.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Muffle furnace | Nabertherm L 9/11, Carbolite CWF 1100, Snol 8.2/1100 | 8 000–25 000 PLN |
| Analytical balance (d=0.1 mg) | Mettler Toledo ME204, Sartorius Secura 224, Radwag AS 220.R2 | 5 000–15 000 PLN |
| Combustion vessels (porcelain/platinum) | Porcelain crucible 50 mL or platinum, JIPO/Rosenthal | 30–200 PLN (porcelain), 3 000–8 000 PLN (platinum) |
| Desiccator with silica gel | Glass desiccator Ø 200 mm with stopcock, Duran/Simax | 400–1 200 PLN |
| Gas burner or electric igniter | Bunsen burner, piezoelectric igniter | 200–500 PLN |
| Crucible tongs | Stainless steel crucible tongs, length 300 mm | 100–300 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Silica gel (indicator) | 112926-00-8 | Desiccant for desiccator, indicator type (color change) |
| Toluene | 108-88-3 | Analytical grade, for washing vessels after combustion |
| Light petroleum (petroleum ether) | 8032-32-4 | For assisting ignition of difficult-to-ignite samples, low flash point |
Health and safety (OHS)
- Muffle furnace 775°C — serious burn risk, use heat-resistant gloves and tongs
- Sample combustion — flammable vapors, work under fume hood or in digestorium
- Light petroleum — flammable and volatile, store away from fire
- Hot vessels — do not place directly on bench, use ceramic pads
- Safety glasses and laboratory coat mandatory