SH/T 0411-1992 Determination of aromatic hydrocarbon content in liquid paraffin (colorimetric method)

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Card type: Test method

1. Method number / full name / English name / replacement relationship

• Standard number: SH/T 0411-92
• Chinese full name: Determination of aromatic hydrocarbon content in liquid paraffin (colorimetric method)
• English name: not provided in the available source
• Replacement relationship: replaces SY 2857-82
• Approval/implementation: approved by China Petrochemical Corporation 1992-05-20, implemented on 1992-05-20
• First issued: year 1975 (see additional notes)

2. Scope of application and non-applicability

• Applicable to the determination of liquid paraffin that does not contain alcohols and olefins and has an aromatic hydrocarbon content less than 1 g/kg.
• If the aromatic hydrocarbon content in the liquid paraffin is greater than 1 g/kg, it should first be diluted with aromatic-hydrocarbon-free liquid paraffin.
• Not applicable: liquid paraffin containing alcohols and olefins (the source limits the scope of application by 'does not contain alcohols and olefins' and does not separately list non-applicability clauses).

3. Method principle

Sulfuric acid-formaldehyde reagent is used to react with aromatic hydrocarbons to develop color; under certain conditions, the colored solution is used to determine the content by colorimetric method.

4. Reagents and materials (purity / preparation)

• 3.1 Silica gel: 30～100 mesh, fine-pore silica gel for chromatography.
• 3.2 Sulfuric acid: analytical reagent.
• 3.3 Formaldehyde solution: analytical reagent.
• 3.4 Anhydrous ethanol: chemical reagent.
• 3.5 Petroleum ether: 30～60 ℃, free of aromatic hydrocarbons.
• 3.6 Preparation of sulfuric acid-formaldehyde reagent: mix sulfuric acid and formaldehyde solution uniformly in the ratio 99.5:0.5 (m/m); the reagent is stored in a brown narrow-neck ground-glass-stoppered bottle. If the reagent is found to have color or precipitate, it must not continue to be used.
• Appendix A Active test solution: a benzene-n-heptane binary mixture with a benzene content of 10% (V/V).
• Note: 'm/[unreadable character]' in 3.6 is source-text extraction noise and should be m/m; requires confirmation against the source standard (source-text extraction).

5. Instruments and equipment

• 4.1 72 type spectrophotometer.
• 4.2 Syringe: 50 μL and 1 mL (the source '501 AL and 1MLa' is source-text extraction noise; requires confirmation against the source standard (source-text extraction)).
• 4.3 Volumetric flask: 10 mL (the source 'IOMLo' is source-text extraction noise; requires confirmation against the source standard (source-text extraction)).
• 4.4 Weighing bottle: 30 mm × 60 mm.
• 4.5 Separatory funnel: 250 mL.
• 4.6 Stopwatch.
• 4.7 Rubber bulb.
• 4.8 Funnel.
• 4.9 Analytical balance.
• 4.10 Refractometer.
• 4.11 Constant-temperature oven.
• 4.12 Qualitative white porcelain plate.
• 4.13 Adsorption column (see figure below; figure omitted in the source).
• Appendix A: silica gel activity determination tube (see Figure A1; figure omitted in the source); 10 mL graduated cylinder, graduation 0.1 mL.

6. Recommended operating conditions

• Silica gel activation: dry at 100～110 ℃, then activate at 150～160 ℃ for more than 5 h.
• Standard solution preparation temperature: about 25 ℃.
• Color development shaking: shake vigorously by hand 4～5 times, then shake by hand at a frequency of 100～110 times per minute for 2 min; or place in a shaker and shake at a frequency of 160～200 times per minute for 3 min.
• Cuvette: light path 3 cm (the absorbance of the cuvettes should be close).
• Standing: 10 min (at this time turn on the colorimeter to stabilize the voltage).
• Wavelength and output voltage: the source only states 'colorimetric determination is carried out at a certain wavelength and output voltage'; the specific values are not provided in the available source.
• Silica gel activity determination: the test should be carried out at constant temperature (when the operating time is not long, room temperature can be regarded as constant).

7. Sampling and sample preparation

• 5.2 Preparation of aromatic-hydrocarbon-free liquid paraffin and purification of aromatic hydrocarbons:
  • 5.2.1 According to the ratio of silica gel to liquid paraffin, inject a certain amount of liquid paraffin into an adsorption column already packed with silica gel (when packing the column, it should be uniform top and bottom and suitably loose or tight), so that it flows naturally downward through the silica gel, and collect the dearomatized liquid paraffin. Collect in fractions, continuously testing with sulfuric acid-formaldehyde reagent; once color develops, stop collection immediately; the obtained product is aromatic-hydrocarbon-free liquid paraffin.
  • 5.2.2 After preparing aromatic-hydrocarbon-free liquid paraffin, add aromatic-hydrocarbon-free petroleum ether of known refractive index to the adsorption column to wash out the non-aromatic hydrocarbon components remaining on the silica gel. When the refractive index of the effluent is the same as that of the aromatic-hydrocarbon-free petroleum ether, then use dried compressed air to blow all the petroleum ether out of the adsorption column.
  • 5.2.3 After the petroleum ether has been blown out, add anhydrous ethanol to the adsorption column as a displacing agent to desorb the aromatic hydrocarbons from the silica gel; wash the desorbed liquid with distilled water in a separatory funnel 4～5 times to remove ethanol, then filter with quantitative filter paper to remove trace moisture. The obtained component is pure aromatic hydrocarbons; the average refractive index of the pure aromatic hydrocarbons at 20 ℃ should be greater than 1.49000.
• Sample dilution: when the aromatic hydrocarbon content is greater than 1 g/kg, first measure the refractive index to estimate the content, dilute with aromatic-hydrocarbon-free liquid paraffin to less than 1 g/kg, and record the dilution factor.

8. Analytical procedure

• 5.1 Activation of silica gel: take 30～100 mesh silica gel, boil and wash several times with distilled water under stirring, and test with silver nitrate until no chloride radical is present and it is neutral. Then dry in a constant-temperature oven at 100～110 ℃, then activate at 150～160 ℃ for more than 5 h; after removal, immediately place in a desiccator to cool, and measure its activity (see Appendix A); when the activity is greater than 10, it can be used.
• 5.3 Drawing the working curve:
  • 5.3.1 Using aromatic hydrocarbons purified from the liquid paraffin to be tested and aromatic-hydrocarbon-free liquid paraffin, prepare a series of standard solutions with contents of 0, 0.2, 0.4, 0.6, 0.8 and 1.0 g/kg. The standard solutions should be prepared at a temperature of about 25 ℃.
  • 5.3.2 Use a microsyringe to draw 50 μL of each of the above standard solutions and place them respectively in six clean, dry 10 mL volumetric flasks; add sulfuric acid-formaldehyde reagent from a burette up to the mark of the volumetric flask, insert the ground-glass stopper tightly and immediately shake vigorously by hand 4～5 times, then shake by hand at a frequency of 100～110 times per minute for 2 min or place in a shaker and shake at a frequency of 160～200 times per minute for 3 min, pour into a cuvette with a light path of 3 cm, after standing for 10 min, use aromatic-hydrocarbon-free liquid paraffin as blank, carry out colorimetric determination at a certain wavelength and output voltage, and record the absorbance.
  • 5.3.3 Using the measured results and the corresponding aromatic hydrocarbon concentrations as coordinates, draw the absorbance-aromatic hydrocarbon concentration working curve.
  • 5.3.4 If the feedstock oil or the photoelectric colorimeter is changed, a new working curve should be prepared.
  • 5.3.5 When the aromatic hydrocarbon content in the sample is less than 1 g/kg, measure the absorbance according to the operating procedure in 5.3.2, and directly find the corresponding aromatic hydrocarbon content from the working curve.
  • 5.3.6 When the aromatic hydrocarbon content in the sample is greater than 1 g/kg, first measure the refractive index of the sample, estimate the aromatic hydrocarbon content, then dilute with aromatic-hydrocarbon-free liquid paraffin until the aromatic hydrocarbon content is less than 1 g/kg, determine according to 5.3.2, and record the dilution factor.
• Appendix A Silica gel activity determination method (supplementary item):
  • A2 Analytical procedure: weigh 10 g of the silica gel whose activity is to be measured, carefully load it into a dry, clean silica gel activity determination tube whose lower opening is lightly plugged with degreased cotton or glass fiber, tap the tube wall to make the packing uniform and suitably loose or tight. Immediately use 20 mL of active test solution [a benzene-n-heptane binary mixture with a benzene content of 10% (V/V)] and inject it from the upper opening into the silica gel activity determination tube, and connect a 10 mL graduated cylinder with graduations of 0.1 mL to the lower opening; after the test solution has all penetrated into the silica gel, add 3 mL anhydrous ethanol; after it has all penetrated into the silica gel, add distilled water for desorption; when the effluent is about 6～7 mL, take 1 drops at the outlet and perform a spot test with sulfuric acid-formaldehyde reagent to check for the presence of aromatic hydrocarbons; check once every 0.5 mL in this way until aromatic hydrocarbons are detected, and record the volume of effluent (including the portion used for the spot test in the estimate).

9. Qualitative and quantitative determination and calculation formulas

• 6.1 When the aromatic hydrocarbon content in the sample is less than 1 g/kg, use the measured absorbance to directly find the corresponding aromatic hydrocarbon content on the working curve.
• 6.2 When the aromatic hydrocarbon content in the sample is greater than 1 g/kg, its aromatic hydrocarbon content X is calculated according to the following formula: X = (n + 1) X₁ Where: n— dilution increase factor; X₁—aromatic hydrocarbon content after dilution, g/kg.
• 6.3 Report the aromatic hydrocarbon content in the sample as g/kg, take the arithmetic mean of the two results of duplicate determination, and take the positive value as the result of the sample.
• Appendix A3 Silica gel activity Y (mL benzene/100 g silica gel) is calculated according to formula (A1): Y = 100 V · C / [(1 − C) m] …(A1) Where: V— amount of effluent (pure n-heptane), mL; C— concentration of aromatic hydrocarbons in the active test solution, % (V/V); m— amount of silica gel used, g. As in the above operation: m = 10, C = 10% (V/V), then Y = 100 V × 10% / [(1 − 10%) × 10] = 1.11 V.
• Note: In the formula 6.2, the definitional relationship between “n+1” and “dilution increase multiple” is as in the original text; in source-text extraction, “X,” should be X₁, requires confirmation against the source standard (source-text extraction).

10. Precision

• Repeatability: The difference between two results of duplicate determinations shall not be greater than the following values:
  • Aromatic hydrocarbon content ≤ 10 g/kg: permissible difference 1 g/kg
  • Aromatic hydrocarbon content > 10 g/kg: 10% of the smaller result
• Note: In the original table, the unit source-text extraction for “less than or equal to 10” and “greater than 10” is shown as “[unreadable character]kg/[garbled unit]”, which should be g/kg, requires confirmation against the source standard (source-text extraction).
• Appendix A Silica gel activity determination: The difference between two results of duplicate determinations and their arithmetic mean shall not be greater than ±0.1～0.2 mL, rounded to one decimal place.

11. Report

• Report the aromatic hydrocarbon content in the sample as g/kg, taking the arithmetic mean of two results of duplicate determinations, and take the positive value as the sample result (see 6.3).
• Other report format requirements are not provided in the available source.

12. Normative references

• The main text of the original does not list a separate “Normative references” section.
• Appendix A is a supplementary element (silica gel activity determination method).
• Additional notes: This standard is technically administered by Fushun Research Institute of Petroleum and Petrochemicals; drafted by Fushun Research Institute of Petroleum and Petrochemicals; first published in 1975.

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick Q&A reference