GB/T 11136-2025 Determination of bromine index of petroleum hydrocarbons — Electrometric titration method
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1. Method number / full title / English title / replacement relationship
- Standard number: GB/T 11136—2025
- Chinese title: Determination of bromine index of petroleum hydrocarbons — Electrometric titration method
- English title: Determination of bromine index for petroleum hydrocarbons—Electrometric titration
- Replacement relationship: Replaces GB/T 11136—1989 "Determination of bromine index of petroleum hydrocarbons (Electrometric titration method)"; first issued in 1989, this is the first revision.
- Publication/implementation: published on 2025-10-05, implemented on 2026-05-01.
- Custodian: National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC 280).
- Main technical changes compared with the 1989 edition (foreword): a) changed the scope of application (see Chapter 1, Chapter 1 of the 1989 edition); b) deleted the "dead-stop" electrometric titrator, the circuit diagram in Annex A and the corresponding determination steps (see Chapter 5, 5.1, 8.4 and Annex A of the 1989 edition); c) changed the preparation of the starch indicator solution, no longer adding mercury iodide reagent (see 6.18, 7.4 of the 1989 edition); d) changed the preparation of the titration solvent, from "1,1,1- trichloroethane (trichloromethane) and methanol" to "dichloromethane and anhydrous ethanol" (see 6.22, 7.2 of the 1989 edition); e) added the volume precision of standard solution addition during the calibration of potassium bromide-potassium bromate standard solution, "accurate to 0.01 mL" (see 6.23); f) added the optional use of 80 mL titration solvent, and added the corresponding sampling amount requirements in Table 1 (see 7.3, Table 1); g) changed the content of "Report" (see Chapter 9, Chapter 11 of the 1989 edition); h) added the content of "Quality control" (see Chapter 10); i) changed the precision (see Chapter 11, Chapter 10 of the 1989 edition).
2. Scope of application and non-applicability
- This document describes a method for determining the bromine index of petroleum hydrocarbons by electrometric titration.
- Applicable to petroleum hydrocarbons or mixtures with a final boiling point lower than 288 ℃, essentially free of olefins and components lighter than isobutane, such as straight-run and hydrocracked naphtha, reforming feedstock, kerosene and aviation turbine fuel, and other petroleum fractions.
- Bromine index determination range: 5 mg/100g (calculated as Br) to 1000 mg/100g (calculated as Br).
- Method selection guidance given in the introduction (not the scope of application of this document, but method selection notes):
- For petroleum fractions and industrial aliphatic olefins with a bromine index greater than 1000 mg/100g (calculated as Br), use the GB/T 11135 method to obtain more accurate results;
- For the bromine index of industrial aromatics, use the SH/T 1551, SH/T 1767 method;
- For the bromine index of liquid paraffin and white oil, use the NB/SH/T 0995 method.
- Not applicable: no clause separately listed with the wording "not applicable" is provided in the available source.
3. Method principle
Dissolve a sample of known mass in a solvent maintained at a temperature of 0 ℃ to 5 ℃, then titrate with potassium bromide-potassium bromate standard solution. When the free bromine appearing in the solution causes a sudden jump in the potential of the electrometric titrator, the titration endpoint is reached. (See Chapter 4)
4. Reagents and materials (purity / preparation)
Unless otherwise specified, the purity of reagents used in the test is analytical reagent grade.
| Clause | Reagent/material | Purity or requirement | Preparation/notes |
|---|---|---|---|
| 6.1 | Water | Meets the requirements for grade three water in GB/T 6682—2008 | — |
| 6.2 | Glacial acetic acid | Purity ≥99.5% | — |
| 6.3 | Concentrated hydrochloric acid | Purity 36.0% to 38.0% | — |
| 6.4 | Anhydrous ethanol | Purity ≥99.5% | — |
| 6.5 | Dichloromethane | Purity ≥99.5% | — |
| 6.6 | Cyclohexene | Purity ≥98.0% | — |
| 6.7 | Toluene | Purity ≥99.5% | — |
| 6.8 | Potassium dichromate | Primary standard substance, purity ≥99.99% | — |
| 6.9 | Potassium bromide | Purity ≥99.0% | — |
| 6.10 | Potassium bromate | Purity ≥99.8% | — |
| 6.11 | Concentrated sulfuric acid | Purity 95.0% to 98.0% | — |
| 6.12 | Sodium thiosulfate | Purity ≥99.0% | — |
| 6.13 | Potassium iodide | Purity ≥99.0% | — |
| 6.14 | Salicylic acid | Purity ≥99.5% | — |
| 6.15 | Anhydrous sodium carbonate | Purity ≥99.5% | — |
| 6.16 | Sulfuric acid solution (volume ratio 1:5) | — | Carefully pour 1 times the volume of concentrated sulfuric acid into 5 times the volume of water, then mix evenly |
| 6.17 | Potassium iodide solution (150 g/L) | — | Dissolve 150 g potassium iodide in water, dilute with water to 1 L |
| 6.18 | Starch indicator solution (10 g/L) | — | Mix 5 g soluble starch with 3 mL to 5 mL water (if a longer shelf life is needed, add 0.65 g salicylic acid as a preservative); add this paste to 500 mL boiling water, continue boiling for 5 min to 10 min; cool, transfer the upper clear solution to a ground-glass-stoppered bottle and store sealed, shelf life 14 d. Note: A commercially available starch indicator solution (with salicylic acid as preservative) may alternatively be purchased |
| 6.19 | Bromine value standard sample | — | May be purchased commercially; alternatively, weigh a certain amount of cyclohexene and dilute with toluene to prepare different concentrations, place in a sealable container and store in a refrigerator. Calculation of bromine value BV see formula (1): BV = 194.6×m₁/m₂; m₁ is the mass of cyclohexene (g), m₂ is the sum of the mass of cyclohexene and the mass of toluene (g); 194.6 is the conversion factor (159.808/82.14×100) |
| 6.20 | Bromine index standard sample | — | May be purchased commercially; alternatively, weigh a certain amount of bromine value standard sample and dilute with toluene to prepare different concentrations, place in a sealable container and store in a refrigerator. BIstandard = 1000×BV×m₃/m₄; m₃ is the mass of the bromine value standard sample (g), m₄ is the sum of the mass of the bromine value standard sample and the mass of toluene (g) |
| 6.21 | Sodium thiosulfate standard solution (0.05 mol/L) | — | Weigh 12.5 g sodium thiosulfate (Na₂S₂O₃·5H₂O) and dissolve in water, add 0.1 g anhydrous sodium carbonate (for stabilization), dilute with water to 1 L, shake well, store in a polyethylene plastic bottle and let stand for 14 d, then take the upper clear liquid for calibration. Any suitable method may be used for calibration; the calibration result error must not exceed ±0.0002 mol/L; calibrate once every 2 months. Calibration method: weigh 0.09 g primary standard potassium dichromate dried at 120 ℃±2 ℃ to constant mass and place in an iodine flask, dissolve in 25 mL water, add 2 g potassium iodide and 20 mL sulfuric acid solution (1:5), shake well, place in the dark for 10 min, add 150 mL water, titrate with the prepared sodium thiosulfate solution, near the endpoint add 1 mL starch indicator solution, continue titrating until the solution changes from blue to bright green, and simultaneously carry out a blank test. Concentration calculation see formula (3): c(Na₂S₂O₃)=20.395×m₅/(V(Na₂S₂O₃)−V₁); 20.395 is the conversion factor (1000×6/294.19); m₅ is the mass of potassium dichromate (g); V₁ is the blank consumption volume (mL). Alternatively, a commercially available sodium thiosulfate standard solution may be purchased |
| 6.22 | Titration solvent | — | In order, mix 714 mL glacial acetic acid, 134 mL dichloromethane, 134 mL anhydrous ethanol and 18 mL sulfuric acid solution (volume ratio 1:5) to prepare 1 L titration solvent, mix evenly |
| 6.23 | Potassium bromide-potassium bromate standard solution c(1/6KBrO₃)=0.05 mol/L | — | Dry potassium bromide and potassium bromate at 105 ℃±5 ℃ 30 min, weigh approximately 5.1 g potassium bromide and 1.4 g potassium bromate (accurate to 0.01 g) into a beaker, dissolve with water, transfer to a 1000 mL volumetric flask, dilute to the mark with water, and mix well. Calibration method: Take 50 mL glacial acetic acid and 1 mL concentrated hydrochloric acid into a 500 mL iodine flask, place on an ice bath for 10 min; while shaking continuously, simultaneously add 40 mL～45 mL (accurate to 0.01 mL) of this standard solution within 90 s～120 s using a 50 mL burette; immediately stopper, shake, place back in the ice bath, and add 5 mL potassium iodide solution at the mouth of the flask as a liquid seal; after 5 min remove, slowly open the stopper to let the potassium iodide solution flow in, and immediately shake vigorously; rinse the stopper, the edge of the flask, and the inner wall with 100 mL water; rapidly titrate with 0.05 mol/L sodium thiosulfate standard solution, add 1 mL starch indicator solution near the endpoint, and slowly titrate until the blue color disappears. Calibrate the concentration to 4 significant figures. For calculation see formula (4): c=c(Na₂S₂O₃)×V₂/V₃ |
| 6.24 | Potassium bromide-potassium bromate standard solution c(1/6KBrO₃)=0.02 mol/L | — | Accurately measure c(1/6KBrO₃)=0.05 mol/L of potassium bromide-potassium bromate standard solution 80 mL, place in a 200 mL volumetric flask, dilute with water to the mark |
| 6.25 | Quality control (QC) sample | — | A bromine index standard sample or a representative typical routine analysis sample may be used |
5. Instruments and Equipment
| Clause | Equipment | Requirements |
|---|---|---|
| 5.1 | Potentiometric titrator | Any instrument with a high-impedance polarized current source capable of titrating to a preset endpoint may be used; the voltage between the two platinum electrodes should be maintained at about 0.8 V; the sensitivity should be such that the electrode can indicate the titration endpoint when the potential changes by about 50 mV; other suitable types of potentiometric titrators on the market (including certain pH meters) may all be used |
| 5.2 | Platinum electrode | Length about 12 cm, platinum needle diameter about 1 mm, the distance between the two platinum electrodes not exceeding 5 mm, and extending to about 55 mm below the liquid surface |
| 5.3 | Magnetic stirrer | Stirring should be sufficient but must not cause bubbles |
| 5.4 | Titration cell | Jacketed glass vessel with a capacity of about 150 mL or 100 mL; it should be able to circulate coolant so that the temperature of the solution in the vessel is maintained at 0 ℃～5 ℃ |
| 5.5 | Balance | Scale interval 0.0001 g |
| 5.6 | Oven | Controllable temperature 105 ℃±5 ℃ and 120 ℃±2 ℃ |
| 5.7 | Burette | 50 mL, control precision 0.10 mL or smaller |
| 5.8 | Iodine flask | 500 mL, with glass stopper |
| 5.9 | Graduated cylinder | 10 mL, 20 mL, 100 mL |
| 5.10 | Volumetric flask | 100 mL, 200 mL, 1000 mL |
| 5.11 | Pipette | 20 mL, 50 mL |
6. Recommended Operating Conditions
- Titration temperature: Cool the solution in the titration vessel to 0 ℃～5 ℃, and maintain this temperature throughout the titration process (7.2, 7.3).
- Electrode voltage: Maintain the voltage between the two platinum electrodes at about 0.8 V (5.1).
- Endpoint setting: Set the endpoint according to the instrument manual, ensuring that the sensitivity of the platinum electrode circuit meets the requirements of 5.1 (7.4).
- Titration step size: Near the titration endpoint, a titration step size of 0.05 mL is recommended; when the potential reaches the preset value and persists for 30 s or more, the titration endpoint is reached (7.5).
- Standard solution selection (Note, 7.5): When the bromine index is ≥100 mg/100g (calculated as Br), c(1/6KBrO₃)=0.05 mol/L (6.23) is recommended; when the bromine index is <100 mg/100g (calculated as Br), c(1/6KBrO₃)=0.02 mol/L (6.24) is recommended.
- Titration solvent volume: 110 mL or 80 mL (7.3, Table 1).
- Stirring: Turn on the stirrer and adjust to a fast stirring rate, but avoid generating bubbles (7.3).
- Blank requirement: A blank titration must be performed for each batch of titration solvent and reagents, and the volume of potassium bromide-potassium bromate standard titration solution consumed should be less than 0.1 mL; otherwise, replace the reagents and repeat the blank test; perform each blank test twice, take the arithmetic mean as the result, and record V₀ (7.6).
7. Sampling and Sample Preparation
- Sampling: Sample according to the method specified in GB/T 4756 or GB/T 27867 (7.3).
- Weighing: Refer to Table 1 and weigh an appropriate amount of sample into a 150 mL or 100 mL titration vessel (7.3).
- Pre-analysis: Usually the bromine index of the sample is unknown; use 8 g～10 g sample for a pre-analysis test; based on the pre-analysis result, accurately select the sample amount according to Table 1 and re-analyze (7.3 Note).
- Turbidity/phase separation treatment: When testing according to the sample amount in Table 1, if the solution is turbid or separates into two phases, reduce the sample amount (Table 1 Note).
Table 1 Sample Amount
| 110 mL Titration solvent: Bromine index (calculated as Br)/(mg/100g) | 110 mL Titration solvent: Sample amount/g | 80 mL Titration solvent: Bromine index (calculated as Br)/(mg/100g) | 80 mL Titration solvent: Sample amount/g |
|---|---|---|---|
| <10 | 15～20 | <10 | 11～15 |
| 10～100 | 10～15 | 10～100 | 8～11 |
| 100～500 | 8～10 | 100～500 | 6～8 |
| >500～1000 | 4～8 | >500～1000 | 4～6 |
8. Analysis Procedure
7.1 Turn on the potentiometric titrator (5.1), allow the instrument to stabilize, and set the titration parameters according to the instrument manual. 7.2 Circulate a suitable coolant in the jacketed titration vessel and cool the titration vessel to 0 ℃～5 ℃. 7.3 Sample according to the method specified in GB/T 4756 or GB/T 27867. Refer to Table 1 and weigh an appropriate amount of sample into a 150 mL or 100 mL titration vessel, add 110 mL or 80 mL titration solvent to the titration vessel, turn on the stirrer and adjust to a fast stirring rate, but avoid generating bubbles. Allow the liquid in the titration vessel to cool to 0 ℃～5 ℃, and maintain this temperature throughout the titration process. 7.4 Set the endpoint potential. For each instrument, set the endpoint according to the instrument manual, and ensure that the sensitivity of the platinum electrode circuit meets the requirements of 5.1. 7.5 Depending on the titrator equipment, add the potassium bromide-potassium bromate standard solution manually or automatically. Near the titration endpoint, a titration step size of 0.05 mL is recommended; when the potential reaches the preset value and persists for 30 s or more, the titration endpoint is reached. 7.6 Blank test: A blank titration must be performed for each batch of titration solvent and reagents, without adding sample, following the test procedure in 7.1～7.5; the volume of potassium bromide-potassium bromate standard titration solution consumed should be less than 0.1 mL; otherwise, replace the reagents and repeat the blank test. Perform each blank test twice, take the arithmetic mean as the result, and record the volume of potassium bromide-potassium bromate standard titration solution consumed V₀.
9. Qualitative and Quantitative Determination and Calculation Formula
The bromine index of the sample BI is calculated according to formula (5):
BI = [(V − V₀) × c × 7990] / m
Where:
- BI —— Bromine index of the sample, in milligrams per hundred grams calculated as bromine [mg/100g (calculated as Br)];
- V —— Volume of potassium bromide-potassium bromate standard solution consumed by the titrated sample, in milliliters (mL);
- V₀ —— the volume of potassium bromide-potassium bromate standard solution consumed by titrating the blank solvent, in milliliters (mL);
- c —— the concentration of the potassium bromide-potassium bromate standard solution, in moles per liter (mol/L);
- 7990 —— based on the relative atomic mass of bromine and the conversion factor from milliliters (mL) to liters (L), the conversion factor for deriving the mass of bromine consumed per 100 g of sample (mg);
- m —— sample mass, in grams (g).
Related preparation calculation formulas (Chapter 6):
- Formula (1): BV = 194.6 × m₁ / m₂ (bromine value of the bromine value standard sample, g/100g calculated as Br)
- Formula (2): BIstandard = 1000 × BV × m₃ / m₄ (bromine index of the bromine index standard sample, mg/100g calculated as Br)
- Formula (3): c(Na₂S₂O₃) = 20.395 × m₅ / (V(Na₂S₂O₃) − V₁)
- Formula (4): c = c(Na₂S₂O₃) × V₂ / V₃
10. Precision
11.1 Overview: The precision of this document was obtained through collaborative testing by 8 laboratories on 14 samples; determined according to GB/T 6683.1 through inter-laboratory statistical analysis results; the reliability of test results is judged according to the provisions of 11.2 to 11.3 (95% confidence level). Table 2 gives some typical precision values.
11.2 Repeatability (r): For the same operator, in the same laboratory, using the same instrument, according to the same test method, conducting continuous determinations on the same sample, the difference between the two test results obtained shall not exceed the calculated value of formula (6): r = 0.7771 × X₁^0.4641 Where X₁ is the average of two replicate test results, in mg/100g (calculated as Br).
11.3 Reproducibility (R): In different laboratories, by different operators, using different instruments, according to the same test method, conducting determinations on the same sample separately, the difference between the two single, independent test results obtained shall not exceed the calculated value of formula (7): R = 1.6966 × X₂^0.6538 Where X₂ is the average of two single, independent test results, in mg/100g (calculated as Br).
Table 2 Repeatability and reproducibility values corresponding to typical bromine index concentration values (in milligrams per hundred grams, calculated as bromine)
| Bromine index | Repeatability (r) | Reproducibility (R) |
|---|---|---|
| 5.0 | 1.6 | 4.9 |
| 10.0 | 2.3 | 7.6 |
| 50.0 | 4.8 | 21 |
| 100 | 6.6 | 34 |
| 500 | 14 | 98 |
| 800 | 17 | 134 |
| 1000 | 19 | 155 |
11. Report
9.1 Take the arithmetic mean of two replicate determination results as the determination result of the sample. 9.2 When the bromine index is less than 100 mg/100g (calculated as Br), the result is rounded to 0.1 mg/100g (calculated as Br); when the bromine index is greater than or equal to 100 mg/100g (calculated as Br), the result is rounded to 1 mg/100g (calculated as Br).
12. Normative References
Normative references (Chapter 2):
- GB/T 4756 Petroleum liquids—Manual sampling
- GB/T 6682—2008 Water for analytical laboratory use—Specification and test methods
- GB/T 27867 Petroleum liquids—Automatic pipeline sampling
- NB/SH/T 0843 Statistical techniques for the evaluation of test systems in the petrochemical industry
References:
- [1] GB/T 6683.1 Petroleum and related products—Measurement methods and results precision—Part 1: Determination of precision data for test methods
- [2] GB/T 11135 Determination of bromine value of petroleum fractions and industrial aliphatic olefins—Potentiometric titration method
- [3] SH/T 1551 Determination of bromine index of industrial aromatic hydrocarbons—Coulometric titration method
- [4] SH/T 1767 Determination of bromine index of industrial aromatic hydrocarbons—Potentiometric titration method
- [5] NB/SH/T 0995 Determination of bromine index of liquid paraffin and white oil—Potentiometric titration method
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
| Question | Key answer points |
|---|---|
| What is the method principle of this standard? | The sample is dissolved in 0 ℃ to 5 ℃ solvent, titrated with potassium bromide-potassium bromate standard solution; the free bromine causes a potentiometric jump, which is the endpoint (Chapter 4) |
| Applicable bromine index range? | 5 mg/100g (calculated as Br) to 1000 mg/100g (calculated as Br) (Chapter 1) |
| Which samples are applicable? | Petroleum hydrocarbons or mixtures with a final boiling point lower than 288 ℃, essentially free of olefins and components lighter than isobutane, such as straight-run and hydrocracked naphtha, reforming feedstock oil, kerosene, aviation turbine fuel, etc. (Chapter 1) |
| Titration temperature? | 0 ℃ to 5 ℃, maintained throughout (7.2, 7.3) |
| Electrode voltage? | The voltage between the two platinum electrodes is maintained at about 0.8 V (5.1) |
| Endpoint determination conditions? | The potential reaches a preset value and persists for more than 30 s (7.5) |
| Recommended titration step size near the endpoint? | 0.05 mL (7.5) |
| Titration solvent composition? | 714 mL glacial acetic acid + 134 mL dichloromethane + 134 mL anhydrous ethanol + 18 mL sulfuric acid solution (1:5), made up to 1 L (6.22) |
| Titration solvent amount? | 110 mL or 80 mL (7.3, Table 1) |
| How to choose the standard solution concentration? | For bromine index ≥100 mg/100g use 0.05 mol/L; for <100 mg/100g use 0.02 mol/L (7.5 Note) |
| Upper limit of blank consumption? | Should be less than 0.1 mL, otherwise replace reagents and redo (7.6) |
| Number of blank tests and value taken? | Perform two blank tests each time, take the arithmetic mean (7.6) |
| Bromine index calculation formula? | BI = [(V − V₀) × c × 7990] / m (Formula (5)) |
| Result rounding rules? | <100 mg/100g rounded to 0.1 mg/100g; ≥100 mg/100g rounded to 1 mg/100g (9.2) |
| How to take the reported value? | Take the arithmetic mean of two replicate determination results (9.1) |
| Repeatability formula? | r = 0.7771 × X₁^0.4641 (Formula (6)) |
| Reproducibility formula? | R = 1.6966 × X₂^0.6538 (Formula (7)) |
| Precision test scale? | 8 laboratories, 14 samples collaborative test (11.1) |
| What standard is quality control based on? | NB/SH/T 0843 (10.2, 10.3, 10.4, 10.6) |
| Which standards are sampling based on? | GB/T 4756 or GB/T 27867 (7.3) |
| Test water requirements? | Meets GB/T 6682—2008 grade three water (6.1) |
| What to do if the bromine index is greater than 1000 mg/100g? | Use the GB/T 11135 method (Introduction) |
| What method is used for the bromine index of industrial aromatic hydrocarbons? | SH/T 1551, SH/T 1767 (Introduction) |
| What method is used for the bromine index of liquid paraffin and white oil? | NB/SH/T 0995 (Introduction) |
| Conversion relationship between bromine index and bromine value? | When converting bromine index to bromine value, divide by the factor 1000 (Introduction) |
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