SH/T 0630-1996 Petroleum products—Determination of bromine number and bromine index—Electrolytic method

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Card type: Test method

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

• Standard number: SH/T 0630-1996
• Chinese name: Petroleum products—Determination of bromine number and bromine index—Electrolytic method
• English name: not provided in the available source
• Replacement relationship: not provided in the available source
• Other: confirmed in 2004; approved by China Petrochemical Corporation 1996-05-24, implemented in 1996-12-01

2. Scope of application and non-applicability

• This standard specifies the method for determining the bromine number and bromine index of samples by the electrolytic method.
• Applicable to petroleum products such as gasoline, kerosene, diesel, lubricating oil, wax oil, and light and heavy aromatic hydrocarbons.
• Bromine number determination range: 0.1～300 gBr/100g.
• Bromine index determination range: 0.2～1000 mgBr/100g.
• Not applicable: not provided in the available source.

3. Method principle

When the sample is injected into a special electrolyte containing a known amount of bromine, the unsaturated hydrocarbons in the sample undergo an addition reaction with the bromine in the electrolyte. The bromine consumed by the reaction is replenished by electrolysis at the electrolytic anode: 2Br⁻ - 2e⁻ → Br₂. By measuring the quantity of electricity consumed to electrolytically replenish the bromine, according to Faraday's law of electrolysis, the bromine number or bromine index of the sample can be calculated.

4. Reagents and materials (purity / preparation)

4.1 Reagents

• Glacial acetic acid: analytical reagent.
• Benzene (or dichloromethane): analytical reagent. Note: benzene is a toxic reagent; during use, avoid skin contact and inhalation of benzene vapor, and use it under good ventilation conditions and wear protective gloves.
• 95% ethanol: analytical reagent.
• Potassium bromide: chemical reagent.

4.2 Materials

• Water: all distilled water or deionized water.
• Standard samples: 10 gBr/100g or 100 mgBr/100g, or standard samples of different concentrations as required. A series of bromine number and bromine index standard samples provided by the Research Institute of Petroleum Processing may be used (national secondary reference materials, standard numbers GBW(E)060114～060121).

4.3 Solution preparation

• Potassium bromide solution: take 100 g potassium bromide and dissolve it in 100 mL water, place in a 100 mL narrow-mouth bottle with a stopper for later use.
• Bromine number electrolyte: sequentially take 50 mL potassium bromide solution, 450 mL 95% ethanol, 400 mL benzene (or dichloromethane), and 100 mL glacial acetic acid in a 1 L narrow-mouth bottle with a stopper, shake well for later use.
• Bromine index electrolyte: sequentially take 68 mL potassium bromide solution, 600 mL 95% ethanol, 200 mL benzene (or dichloromethane), and 132 mL glacial acetic acid in a 1 L narrow-mouth bottle with a stopper, shake well for later use.
• Note: During the preparation of the electrolyte, never add glacial acetic acid immediately after taking the potassium bromide solution, so as to avoid the appearance of free bromine in the electrolyte.

5. Apparatus and equipment

• Microcoulometric titrator: BR-1 type bromine number and bromine index analyzer, with a balance current not lower than 300 mA, a detection sensitivity not lower than 0.1 mgBr/100g, an electrolysis current that can vary with the measurement signal, and a forward and reverse pulse electrolysis function, or an instrument of equivalent performance. The instrument and the titration cell are both patented products, with patent numbers ZL 94 2 0280.4 and ZL 93 2 15743.2 respectively. Such instruments can be produced and supplied by Jianghuan Analytical Instrument Co., Ltd., and are supervised by the petroleum product standardization centralized unit.
• Titration cell: its structure is shown in Figure 1 (Figure 1 is a schematic diagram of the titration cell structure, including measuring electrode, titration cell cover, stirrer bar, electrolytic anode, anode chamber, ion exchange membrane, cathode chamber cap, cathode chamber, electrolytic cathode, electrolytic anode fixing cap, cathode chamber cover, electrolytic cathode fixing cap, drying tube, drying tube installation hole, liquid replacement port, measuring electrode installation hole, sample injection port, cathode chamber installation hole, electrolytic anode installation hole).
• Syringes: 0.25, 1, 2, 5, 100 mL.
• Microsyringes: 0.5, 1, 5, 10, 50, 100 μL.
• Narrow-mouth bottles with stoppers: 100 mL, 1 L.
• Injection needles: 7 gauge or 9 gauge, length 80 mm.

6. Recommended operating conditions

• Instrument debugging: respectively inject 80 mL electrolyte into the cleaned anode chamber of the titration cell (when determining bromine number, inject 6.2.1 bromine number electrolyte; when determining bromine index, inject 6.2.2 bromine index electrolyte), and inject 5 mL electrolyte into the cathode chamber (same as above). Place the titration cell on the fixed position of the stirrer, and connect the electrodes according to the markings on the electrode wires. Note: avoid direct exposure of the titration cell to strong light.
• Turn on the instrument power switch, and adjust the stirring speed until the titrating solution forms a vortex without generating bubbles.
• Operate according to the instrument manual. Taking the BR-1 type analyzer as an example: select the given value according to the parameters given in Table 1, for example, select the given value as 5, press the A, E keys in sequence, then press the numeric keys, and finally press the confirm key; the instrument automatically starts electrolysis and equilibration; when the endpoint is reached, the buzzer sounds and the injection display light turns on, indicating that the instrument has reached equilibrium and instrument calibration or sample analysis can be carried out.
• Table 1 Reference values for given selection:
  • Bromine number ≥10 gBr/100g: given value 8～7
  • Bromine number <10 gBr/100g: given value 9.5～8
  • Bromine index ≥10 mgBr/100g: given value 8～7
  • Bromine index <10 mgBr/100g: given value 9.5～8
  • (Note: some values source-text extraction in Table 1 contain noise, requires confirmation against the source standard (source-text extraction))

7. Sampling and sample preparation

• Rinse the syringe three to five times with the sample to be analyzed, and draw an appropriate amount of sample according to the parameters given in Table 2.
• Table 2 Reference sample amounts:
  • Bromine number gBr/100g:
    • >100: reference sample amount 1.0～10 μL
    • 100～10: reference sample amount 10～100 μL
    • 10～1.0: reference sample amount 100～500 μL
    • 0.1～1.0: reference sample amount 500～1000 μL
  • Bromine index mgBr/100g:
    • 1000～10: reference sample amount 10～2000 μL (the original numerical range source-text extraction contains noise, requires confirmation against the source standard (source-text extraction))
    • 10～1.0: reference sample amount 100～2000 μL (the original numerical range source-text extraction contains noise, requires confirmation against the source standard (source-text extraction))
    • <1.0: reference sample amount 100～500 μL (the original numerical range source-text extraction contains noise, requires confirmation against the source standard (source-text extraction))
• For some heavy petroleum distillates and some non-liquid petroleum products that cannot be directly drawn with a syringe, the weighing dilution method may be used: weigh 0.100～0.500 g sample into a 10 mL volumetric flask, dilute to the mark with benzene, and mix well. Then directly draw this diluted sample from the volumetric flask with a syringe; at this time, input the density of the diluted sample in the parameters. At the test temperature, the density of the diluted sample ρ₀ (g/mL) is calculated according to formula (1): ρ₀ = m / V₀ Where: m— weighed amount of sample, g; V₀—total volume of the diluted solution, mL.

8. Analysis steps

• When the instrument injection display light is on, input various parameters, including volume (μL), density at the sampling temperature (g/mL), delay time (s) into the instrument, then press the start key; the injection display light turns off, the instrument automatically starts counting the delay time, and the prepared sample is quickly injected into the titration cell through the sample injection port of the titration cell.
• Note: a) Inputting or changing various parameters must be carried out while the injection display light is on. b) The start key can be pressed only after the parameters have been input and confirmed to be correct. If an input error is found, it can be corrected before pressing the start key. At this time, simply press the function key of the item to be corrected, then input the correct number, and the erroneous number will be cleared. When analyzing the same sample under the same conditions, starting from the second injection, it is not necessary to re-input the parameters; simply press the start key after the injection display light is on to perform injection analysis. c) When analyzing a new sample, attention must be paid to whether various parameters need to be changed; otherwise erroneous results will occur.
• When the delay time is up, the instrument automatically performs titration; at the endpoint, the buzzer sounds, and the digital display sequentially shows the gBr, mC values or the mgBr, mC values. At this time, if the results need to be printed, press the print key, and the instrument will print out the parameters and results. After the results are printed, the instrument immediately automatically executes the baseline equilibration instruction, quickly reaches a new equilibrium, the injection display light turns on, and the next analysis can be carried out.

9. Qualitative and quantitative determination and calculation formulas

• When analyzing a sample, if parameters such as sample volume and density have not been input, or if there is an error in parameter input, or if an instrument of the same performance that only displays the quantity of electricity is used, the results can be calculated according to the given formula based on the quantity of electricity displayed by the instrument.
• The bromine number of the sample X (gBr/100g) is calculated according to formula (2): X = (Q × 79.9 × 100) / (96500 × V × ρ) = (Q × 0.0828) / (V × ρ) Where: Q— quantity of electricity displayed by the instrument, mC; V— injection volume of the sample used for analysis, μL; ρ— density of the sample used at the sampling temperature during analysis, g/mL; 96500— Faraday constant, C/mol; 79.9—1 mass of the molar bromine anion, g/mol; 100— mass of the sample, g.
• The bromine index of the sample X₁ (mgBr/100g) is calculated according to formula (3): X₁ = (Q₁ × 79.9 × 100 × 1000) / (96500 × V₁ × ρ₁) = (Q₁ × 82.8) / (V₁ × ρ₁) Where: Q₁, V₁ and ρ₁ are the same as 2), Q and V in formula (ρ); 1000—g and mgBr are conversion factors; the other terms are the same as in formula (2)).

10. Precision

Judge the reliability of the test results according to the following provisions (95% confidence level).

• Repeatability: The difference between two results obtained by the same operator in repeated determinations shall not exceed the value in Table 3.
• Reproducibility: The difference between two results obtained by different operators in different laboratories shall not exceed the value in Table 3.
• Table 3 Precision values:
  • Bromine number, gBr/100g, range 1～100: repeatability 0.09X, reproducibility 0.16X
  • Bromine index, mgBr/100g, range <3.0: repeatability 0.3, reproducibility 0.5
  • Bromine index, mgBr/100g, range >3～500: repeatability 0.09X, reproducibility 0.16X
  • Note: X is the average of two results.
  • Note: This precision was obtained from statistical tests of 15 laboratories, with bromine numbers in the range 1～100 gBr/100g and bromine indices in the range 0.8～500 mgBr/100g, using 17 samples. (The original text bromine index range source-text extraction contains noise, requires confirmation against the source standard (source-text extraction))

11. Report

• Take the arithmetic mean of two repeated determination results as the determination result of the sample.
• When the bromine number is less than 1 gBr/100g, the result shall be reported to 0.1 gBr/100g; when the bromine number is from 1 to less than 100 gBr/100g, the result shall be reported to 1 gBr/100g; when the bromine number is equal to or greater than 100 gBr/100g, the result shall be reported as an integer.
• When the bromine index is less than 100 mgBr/100g, the result shall be reported to 0.01 mgBr/100g; when the bromine index is equal to or greater than 100 mgBr/100g, the result shall be reported as an integer.

12. Normative references

Not provided in the available source.

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