⛽ Carbon residue (micro)
In short
Micro method for carbon residue: a weighed test portion is heated in a glass vial to 500 °C under a stream of nitrogen, and the residue is weighed. The test is performed according to PN-EN ISO 10370:2014-12; Range: 0.10–30.0 % (m/m); below 0.10 % — 10 % (V/V) distillation residue (clause 1). The procedure comprises 6 steps; it is used for: Diesel fuel — at most 0.30 % (m/m) on the 10 % distillation residue (Journal of Laws 2024, item 1018, Annex 3 item 8), Paraffinic diesel fuel — the same requirement (Journal of Laws 2025, item 426, Annex 3), Products yielding more than 0.10 % (m/m) residue — result equivalent to the Conradson method in the range 0.10–25.0 % (m/m) (clause 1, Annex A).
At a glance
- Standard: PN-EN ISO 10370:2014-12
- Category: Petrochemistry
- Procedure steps: 6
- Range: 0.10–30.0 % (m/m); below 0.10 % — 10 % (V/V) distillation residue (clause 1)
- Pyrolysis temperature: 500 °C under a stream of nitrogen (clause 4)
- Nitrogen: low oxygen content, 99.998 % (V/V) or better; delivery pressure 0–200 kPa (5.1)
Overview
STATUS (as of 30.10.2026). PN-EN ISO 10370:2014-12 — English version, published 17.12.2014, implements EN ISO 10370:2014 and ISO 10370:2014 [IDT]; it replaced PN-EN ISO 10370:1999 (Polish version). Polish title according to the PKN card: “Przetwory naftowe — Oznaczanie pozostałości po koksowaniu — Metoda mikro”; the card has no withdrawal note. ISO 10370:2014 (second edition) replaced ISO 10370:1993 and its Cor 1:1996; among other things it incorporated the results of an interlaboratory study of the 10 % (V/V) distillation residue procedure for middle distillates in 4 ml vials.
SCOPE (clause 1). Determination of carbon residue in the range 0.10–30.0 % (m/m) left after evaporation and pyrolysis of petroleum products under specified conditions. The value is an approximation of the tendency of a product to form carbonaceous deposits under similar degradation conditions and may help to compare products within the same class — results are interpreted with care. For products yielding more than 0.10 % (m/m), the results are equivalent to the Conradson method (ISO 6615) in the range 0.10–25.0 % (m/m) (Annex A). Products consisting essentially of distillate material that may yield less than 0.10 % (m/m) are tested on a 10 % (V/V) distillation residue (7.3). Ash-forming constituents (as defined by ISO 6245) and non-volatile additives add to the result and are included in the value reported; organic nitrates in certain distillate fuels give abnormally high results — the presence of alkyl nitrate is detected according to ISO 13759 (Note 2).
SAMPLE AND VIALS (6.1, 7.1, clause 8, Table 1). Glass vials of 2 ml; for very low residues (below about 0.20 % (m/m)) vials of 4 ml. The test portion mass depends on the expected residue: above 5.0 % — (0.15 ± 0.05) g; 1.0–5.0 % — (0.50 ± 0.10) g; 0.2–1.0 % — (1.50 ± 0.50) g; 10 % distillation residue of middle distillates, below 0.3 % — (3.00 ± 0.50) g in a 4 ml vial. Middle distillates that may yield less than 0.30 % (m/m) are tested via the 10 % distillation residue. Vials are discarded after use. A control sample may be included in each batch — a typical sample tested at least 20 times in the same apparatus; batch results are accepted when the control result is within the mean ± three standard deviations.
LEGAL REQUIREMENTS. Diesel fuel: carbon residue on the 10 % distillation residue at most 0.30 % (m/m). The limit applies to the product before a cetane improver is added; if commercial fuel exceeds it, the presence of nitrates is checked according to PN-EN ISO 13759, and an additive found releases the finished fuel from this limit, but not the product before additives are added (Journal of Laws 2024, item 1018, Annex 3 item 8 and footnote 6). The same requirement applies to paraffinic diesel fuel (Journal of Laws 2025, item 426, Annex 3).
WHAT WE DO NOT GIVE HERE. The publicly available text of the standard ends at Table 1 (8.3). We do not give the heating programme and nitrogen flows (clause 9), the calculation (clause 10), the precision data (clause 12) or Annex A. The American method ASTM D4530 on the same subject states that up to 12 samples, including a control sample, can be run simultaneously in the holder.
Method principle
A weighed test portion is placed in a glass vial and heated in a controlled manner to 500 °C under a stream of inert gas (nitrogen) for a specific time. Volatiles formed during the reactions are swept away by the gas, and the carbonaceous residue is weighed (clause 4). The result is the whole residue produced under the evaporation and pyrolysis conditions described in the standard (definition 3.1).
Applications
- Diesel fuel — at most 0.30 % (m/m) on the 10 % distillation residue (Journal of Laws 2024, item 1018, Annex 3 item 8)
- Paraffinic diesel fuel — the same requirement (Journal of Laws 2025, item 426, Annex 3)
- Products yielding more than 0.10 % (m/m) residue — result equivalent to the Conradson method in the range 0.10–25.0 % (m/m) (clause 1, Annex A)
- Comparing the tendency of products of the same class to form carbonaceous deposits (clause 1, Note 1)
Key parameters
| Parameter | Value |
|---|---|
| Range | 0.10–30.0 % (m/m); below 0.10 % — 10 % (V/V) distillation residue (clause 1) |
| Pyrolysis temperature | 500 °C under a stream of nitrogen (clause 4) |
| Nitrogen | low oxygen content, 99.998 % (V/V) or better; delivery pressure 0–200 kPa (5.1) |
| Test portion mass | from (0.15 ± 0.05) g to (3.00 ± 0.50) g depending on the expected residue (Table 1) |
| Weighing | to the nearest 0.1 mg (6.6, 8.2–8.3) |
| Requirement for diesel fuel | at most 0.30 % (m/m) on the 10 % distillation residue (Journal of Laws 2024, item 1018) |
Standard
- Standard number
- PN-EN ISO 10370:2014-12
- Title (PL)
- Przetwory naftowe — Oznaczanie pozostałości po koksowaniu — Metoda mikro
- Title (EN)
- Petroleum products — Determination of carbon residue — Micro method
Step-by-step procedure
-
Sample preparation
The sample is stirred thoroughly, warming it first if necessary to reduce its viscosity; liquids are transferred to the vials with a rod or syringe, and solids are heated or frozen with liquid nitrogen and shattered into manageable pieces (7.2).
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10 % distillation residue (middle distillates)
When the result may be below 0.30 % (m/m), the sample is distilled according to ISO 3405 in a clean 125 ml flask with six anti-bumping beads (the thermometer may be replaced by a stopper). Heating is stopped when 88 ml of distillate has been recovered, the flask is cooled for 5 min, the residue is swirled and 2.5–3.0 ml is immediately transferred to a pre-weighed 4 ml vial, excluding the beads (7.1, 7.3).
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Weighing the vials
Clean vials, handled with forceps, are weighed to the nearest 0.1 mg (8.1–8.2).
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Test portion
A test portion of the mass given in Table 1 is placed in the bottom of the weighed vial without touching the walls and reweighed to the nearest 0.1 mg; the vials (up to 12) are placed in the holder, noting the position of each relative to the index mark (8.3).
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Control sample
A control sample may be included in the batch; batch results are accepted when its result is within the mean ± three standard deviations established from at least 20 tests in the same apparatus (8.3).
-
Coking and weighing the residue
The portions are heated in the oven to 500 °C under nitrogen, and after cooling the residue is weighed; the heating programme and gas flows are given in clause 9 and the calculation in clause 10 of the standard, outside the publicly available text.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Glass vials | 2 ml, outside diameter 12 mm, height about 35 mm; 4 ml (height about 72 mm) for very low residues; single use (6.1, 8.1) | — |
| Coking oven | top-loading chamber of about 85 mm × 100 mm, heating to 500 °C at 10–40 °C/min, nitrogen purge of the chamber, thermocouple next to the vials, lid sealing out air, condensate trap (6.3) | — |
| Vial holder | aluminium block of about 76 mm diameter and 17 mm thickness with 12 holes (6.4) | — |
| Thermocouple | iron-constantan, with exterior read-out, range including 450–550 °C (6.5) | — |
| Analytical balance | 0.1 mg sensitivity (6.6) | — |
| Cooling vessel | desiccator or similar tightly closed vessel without desiccant (6.7) | — |
| Eyedropper or small rod | for transferring the sample to the vials (6.2) | — |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Nitrogen | 7727-37-9 | low oxygen content — 99.998 % (V/V) or better, with regulation providing a delivery pressure of 0–200 kPa (in practice at least 140 kPa) (5.1) |
Health and safety (OHS)
- The standard warns that its use may involve hazardous materials, operations and equipment, and that the user establishes the safety and health practices (warning before clause 1)
- Vapours and smoke from pyrolysis leave the oven outlet (Figure 1) — they are vented according to the instrument instructions
- Liquid nitrogen for shattering solid samples (7.2) and petroleum samples — according to their safety data sheets
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 10370:2014-12 — “Petroleum products — Determination of carbon residue — Micro method”.
How does this method work?
A weighed test portion is placed in a glass vial and heated in a controlled manner to 500 °C under a stream of inert gas (nitrogen) for a specific time. Volatiles formed during the reactions are swept away by the gas, and the carbonaceous residue is weighed (clause 4).
What is the measuring range and accuracy?
Range: 0.10–30.0 % (m/m); below 0.10 % — 10 % (V/V) distillation residue (clause 1); Pyrolysis temperature: 500 °C under a stream of nitrogen (clause 4); Nitrogen: low oxygen content, 99.998 % (V/V) or better; delivery pressure 0–200 kPa (5.1); Test portion mass: from (0.15 ± 0.05) g to (3.00 ± 0.50) g depending on the expected residue (Table 1).
How long does the test take?
The procedure comprises 6 steps. The standard does not give a duration for every stage — the laboratory's own procedure decides.
What equipment is required?
Glass vials, Coking oven, Vial holder, Thermocouple, Analytical balance, Cooling vessel, Eyedropper or small rod.
Where is this test used?
Diesel fuel — at most 0.30 % (m/m) on the 10 % distillation residue (Journal of Laws 2024, item 1018, Annex 3 item 8); Paraffinic diesel fuel — the same requirement (Journal of Laws 2025, item 426, Annex 3); Products yielding more than 0.10 % (m/m) residue — result equivalent to the Conradson method in the range 0.10–25.0 % (m/m) (clause 1, Annex A); Comparing the tendency of products of the same class to form carbonaceous deposits (clause 1, Note 1).
What safety precautions apply?
The standard warns that its use may involve hazardous materials, operations and equipment, and that the user establishes the safety and health practices (warning before clause 1); Vapours and smoke from pyrolysis leave the oven outlet (Figure 1) — they are vented according to the instrument instructions; Liquid nitrogen for shattering solid samples (7.2) and petroleum samples — according to their safety data sheets.
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 ISO 10370.