GB/T 268-1987 Petroleum products — Determination of carbon residue — Conradson method

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GB/T 268-1987, Petroleum products — Determination of carbon residue — Conradson method, specifies the determination of the carbon residue left after evaporation and pyrolysis of petroleum products as an indicator of their relative tendency to form coke.

Evidence note: The content of this page was compiled from the original text of this standard held in the Origin Standard library (where marked [to be verified], the source is [source unclear]); for individual values and the current status, please refer to the original standard page and the product certificate.

Scope: Used to determine the amount of carbon residue left after evaporation and pyrolysis of petroleum products, providing an indicator of the relative coking tendency of petroleum products. Generally used for petroleum products that are partly decomposed and relatively non-volatile in atmospheric distillation. For petroleum products containing ash-forming components (determined by GB 508, “Petroleum products — Determination of ash”), results with a high carbon residue value will be obtained, the magnitude of the error depending on the amount of ash formed. For some heavy residual fuel oils, coking feedstocks and similar oils that are not easily charged into a Conradson coking bulb, this method is preferable for determining carbon residue. The carbon residue values determined by this method and by ZBE 30001, “Petroleum products — Determination of carbon residue — Ramsbottom method”, are not numerically the same, and no satisfactory correlation between the two can be found. Notes in the original: a. Engine oils: the carbon residue value was once considered an indicator of the amount of carbonaceous deposits formed by engine oils in the combustion chamber, but in view of the additives present in many petroleum products this now appears doubtful. Detergent additives that form ash will increase the carbon residue value but usually reduce the tendency to form deposits. b. Diesel fuels: diesel fuels containing amyl nitrate give high carbon residue values; for diesel fuels free of amyl nitrate, or for base fuels intended for blending with amyl nitrate, the carbon residue value has an approximate relationship with combustion chamber deposits. c. Petroleum products containing ash-forming additives: the carbon residue value may be unrelated to the tendency to form deposits and may be higher than the corresponding tendency to form deposits. The carbon residue value of burner fuels can roughly estimate the tendency of the fuel to form deposits in evaporating-pot and sleeve-type burners; the carbon residue value of diesel fuel free of amyl nitrate broadly corresponds to combustion chamber deposits. Determining the carbon residue value of gas oil is useful for guiding gas oil gasification production; the carbon residue values of crude oil residues, cylinder oils and heavy lubricating oils are useful for guiding lubricating oil production.

Principle: A weighed sample is placed in a crucible and subjected to destructive distillation. The residue is strongly heated for a specified time, i.e. cracking and coking reactions take place. At the end of the specified heating time, the crucible containing the carbonaceous residue is placed in a desiccator to cool and is weighed, and the carbon residue value is calculated (expressed as a mass percentage of the original sample).

Apparatus: Petroleum products Conradson carbon residue apparatus (see Figure 1). 2.1 Porcelain crucible: fully glazed, wide-mouth type, outside diameter at the rim 46 to 49 mm, capacity 29 to 31 mL. 2.2 Inner iron crucible: with an annular flange, capacity 65 to 82 mL, flange inside diameter 53 to 57 mm, outside diameter 60 to 67 mm; crucible height 37 to 39 mm; with a lid having no conduit but a closed vertical hole, the horizontal hole in the lid being about 6.5 mm in diameter, and this hole must be kept clean; flat bottom outside diameter 30 to 32 mm. 2.3 Outer iron crucible: top outside diameter 78 to 82 mm, height 58 to 60 mm, wall thickness about 0.8 mm, with a suitable iron lid; before each test spread a layer of about 25 mL of dry sand evenly on the bottom of the crucible, or such an amount of sand that the lid of the inner iron crucible almost touches the top lid of the outer iron crucible. 2.4 Nichrome wire tripod: made of nichrome wire about 2.0 to 2.3 mm in diameter; the opening is sized to support the bottom of the outer iron crucible so that it is at the same level as the bottom surface of the flame shield. 2.5 Round iron hood: made of thin iron sheet; lower cylindrical section 120 to 130 mm in diameter and 50 to 53 mm high; upper section is a chimney, inside diameter 50 to 56 mm, height 50 to 60 mm; a conical transition section connects the upper and lower sections in the middle; total height 125 to 130 mm; at the top of the chimney there is a 50 mm high flame bridge (made of nichrome wire or iron wire about 3 mm in diameter) to control the height of the flame above the chimney. 2.6 Flame shield: insulating body, ceramic heat-resistant block, refractory ring or hollow metal box; may be round or square; diameter or side length 150 to 175 mm, height 32 to 38 mm; in the middle there is an inverted conical hole lined with metal, larger at the top and smaller at the bottom; hole top diameter 89 mm, hole bottom diameter 83 mm; when a refractory ring type flame shield is used, no metal lining is needed because the ring is made of hard heat-resistant material. 2.7 Burner: Meker type or equivalent burner with a port diameter of about 25 mm. High-temperature furnace: for calcining porcelain crucibles, 800 ± 20 °C (the original reads “800 20C”, [to be verified] ([source unclear])). Desiccator. Hot crucible tongs. Analytical balance: accurate to 0.0001 g (for weighing crucibles and carbon residue); accurate to 0.005 g (for weighing samples). Figure 1 labels: 1 — flame shield; 2 — dry sand; 3 — burner; 4 — nichrome wire tripod; 5 — porcelain crucible; 6 — inner iron crucible; 7 — outer iron crucible; 8 — horizontal hole; 9 — round iron hood.

Reagents and reference materials: Glass beads: about 2.5 mm in diameter, cleaned and dried for use (the original does not state a purity grade). Dry sand: for spreading on the bottom of the outer iron crucible, about 25 mL before each test (the original does not state a purity grade). The available material does not provide other reagents.

Key conditions: Pre-ignition stage: strong flame heating (but not smoking), controlled within 10 ± 1.5 min. Oil vapour burning stage: controlled to be completed within 13 ± 1 min (the original reads “within 131 min”, [to be verified] ([source unclear])). Flame during the burning stage: make the ignited oil vapour burn evenly, with the flame rising above the chimney but not exceeding the flame bridge. Strong heating stage: when the sample vapour stops burning and no blue smoke is visible above the hood, immediately increase the gas burner flame again so that the bottom and lower part of the outer iron crucible are cherry red, and maintain this accurately for 7 min. Total heating time (including the pre-ignition and burning stages): should be controlled within 30 ± 2 min (the original reads “within 302 min”, [to be verified] ([source unclear])). Burner position: place the burner head about 50 mm below the outer iron crucible. Cooling: after removing the gas burner, allow the apparatus to cool until no smoke is visible (about 15 min); transfer the porcelain crucible to a desiccator, cool for 40 min and weigh. Porcelain crucible pretreatment: calcine in a high-temperature furnace at 800 ± 20 °C for 1.5 to 2 h, then clean and dry for use. Viscous or wax-containing petroleum products: preheat to 50 to 60 °C before shaking to mix.

Calculation and results: The Conradson carbon residue value X [(% ) mass/mass] of the sample or of the 10 % distillation residue is calculated according to the following equation: X = m₁ / m₀ × 100 where: m₁ — mass of carbon residue, g; m₀ — mass of sample, g.

Quality control: Judge the reliability of the test results according to the values in Figure 2 (95 % confidence level). 8.1 Repeatability: the difference between two results obtained by the same operator shall not exceed the repeatability value shown in Figure 2. 8.2 Reproducibility: the difference between two results provided by two laboratories shall not exceed the reproducibility value shown in Figure 2. Figure 2 precision chart coordinate information (extracted from [source unclear], [to be verified] ([source unclear])): Ordinate values: 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 3, 4 (the original lists 43, 0.5, 0.2, 0.1, 0.05, 0.02, 0.01, 0.005, etc., [to be verified] ([source unclear])). Abscissa: mean Conradson carbon residue, %, marked 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 3, 4, 10, 20, 30. The original does not give a specific table of precision values, only Figure 2.

Normative references: GB 508 Petroleum products — Determination of ash GB 6536 Petroleum products — Determination of distillation GB 255 Petroleum products — Determination of distillation range ZBE 30001 Petroleum products — Determination of carbon residue — Ramsbottom method ISO 6615—1983 Petroleum products — Determination of carbon residue — Conradson method Annex A (reference): the relationship between the carbon residue values determined by the two methods, GB 268 Conradson carbon residue and ZBE 30001 Ramsbottom carbon residue. Owing to the limitations of the conditions of the two test methods, Conradson carbon residue and Ramsbottom carbon residue, there is no precise correlation between the results obtained by the two methods. An approximate correlation (Figure A) has been derived by others from the cooperative test results of 18 representative petroleum products and verified with test data from about 150 samples (samples that did not take part in the cooperative test). For non-universal petroleum products, the test results obtained by the two methods may not fall near the correlation curve of Figure A. This approximate correlation should be used with caution for samples with low carbon residue values. Figure A coordinate information (extracted from [source unclear], [to be verified] ([source unclear])): the ordinate is Ramsbottom carbon residue (ZBE 30001) (mass/mass), the abscissa is Conradson carbon residue (GB 268) (mass/mass), the abscissa being marked 0.2, 0.3, 0.6, 1, 2, 3, 4, 6, 10, 20, 30, 40, 60, 80, 100. Additional notes: This standard is technically administered by the Research Institute of Petroleum Processing. This standard was drafted under the responsibility of the Research Institute of Petroleum Processing. The main drafter of this standard was Li Zifeng. This standard was first published in 1964.

Verification note: [To be verified] and [source unclear] mark points that still need to be checked against the original standard text; they do not mean the values have been verified. Do not use these values or procedures directly as a basis for work.

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