GB/T 11135-2013 Determination of bromine value of petroleum fractions and industrial aliphatic olefins — Potentiometric titration method

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Applies to the determination of the bromine value of the following samples: petroleum fractions whose 90% distillation temperature (determined by GB/T 6536) is below 327 °C and which contain no components lighter than isobutane, such as gasoline (including leaded gasoline, unleaded gasoline and oxygenated fuels), kerosene and all distillate oils meeting the conditions of Table 1.

Evidence note: the content of this page is compiled from the original text of this standard held in the Origin Standard library (where marked [to be verified] the original is [source unclear]); for individual values and for the current status, refer to the original pages of the standard and the product certificate. Verification note: [to be verified] and [source unclear] mark places where the original text of the standard still has to be checked and do not mean that verification has been completed. Do not use these values or steps directly as a basis for work.

Scope: For the determination of the bromine value of the following samples: petroleum fractions whose 90% distillation temperature (determined by GB/T 6536) is below 327 °C and which contain no components lighter than isobutane, such as gasoline (including leaded gasoline, unleaded gasoline and oxygenated fuels), kerosene and all distillate oils meeting the conditions of Table 1. Industrial olefins with a bromine value between 95 g/100g and 165 g/100g. Industrial olefins are generally mixtures of aliphatic mono-olefins, such as industrial propylene trimer, propylene tetramer, butene dimer, and mixtures of nonene, octene and heptene. Table 1 Determination range of the bromine value of petroleum fractions | 90% distillation temperature / °C | Maximum bromine value / (g/100g) | | --- | --- | | ≤205 | 175 | | 205-327 | 10 | NOTE: Precision has been determined only for industrial olefins with a bromine value in the range 95 g/100g to 165 g/100g. Other notes: the bromine value reflects the amount of substances that can react with bromine but cannot be used to identify the type of substance. Annex A gives the bromine value results of compounds determined by potentiometric titration; only the compounds given in Annex A may be used for the determination of olefinic unsaturation. To convert a bromine value into a bromine index, multiply by a factor of 1 000. For petroleum hydrocarbon mixtures with a bromine value below 1.0 g/100g, however, GB/T 11136 or SH/T 0630 is recommended for a more accurate result; for samples with a bromine value below 0.5 g/100g, GB/T 11136, SH/T 0630 or the aromatic bromine index methods SH/T 1551 and SH/T 1767 may be used. The scope of each standard method should be noted when selecting the method. Not applicable: the material available provides no explicit "not applicable" clause (the 1989 edition wording "not applicable to oils containing alcohol, ketone, ether and amine additives" has been deleted).

Principle: A sample of known mass is dissolved in a solvent maintained at 0 °C to 5 °C and titrated with potassium bromide-potassium bromate standard solution. The end point is reached when the free bromine appearing in the solution causes a sudden change in the potential of the potentiometric titrator (see clause 4, summary of method).

Apparatus: Potentiometric titrator: any instrument with a high-impedance polarized current source that can titrate to a preset end point may be used; the voltage between the two platinum electrodes is maintained at about 0.8 V, and the sensitivity is such that the electrodes can indicate the end point for a potential change of about 50 mV. Other suitable potentiometric titrators on the market, including some pH meters, may also be used. 6.2 Titration cell: a jacketed glass vessel about 120 mm high with an internal diameter of about 45 mm, able to keep the solution in the vessel at 0 °C to 5 °C (here the original reads [source unclear] "0? to 5 °C" [to be verified] [source unclear]). 6.3 Magnetic stirrer. 6.4 Electrodes: a pair of platinum wire electrodes about 12 mm long, 1 mm in diameter and 5 mm apart. Immersed to a depth of about 55 mm in the solution. Clean periodically with 65% nitric acid and rinse with water before use. 6.5 Burette: 10 mL, with a control accuracy of 0.05 mL or finer. 6.6 Volumetric flasks: 50 mL and 1000 mL. 6.7 Pipettes: 2 mL, 5 mL and 10 mL. 6.8 Iodine flask: 500 mL.

Reagents and reference materials: Reagent purity: all reagents used in the test are of analytical grade. If reagents of other purity are used, their influence on the accuracy of the result shall be shown to be small. 7.2 Water: grade 3 water according to GB/T 6682-2008. 7.3 Glacial acetic acid. WARNING: toxic, corrosive, flammable. Handle in a fume cupboard; avoid splashing eyes, skin and clothing. 7.4 Potassium bromide-potassium bromate standard solution (Br₂ content 0.2500 mol/L): dry potassium bromide and potassium bromate at 105 °C for 30 min, then dissolve 51.0 g of potassium bromide and 13.92 g of potassium bromate in water and dilute to 1 L. Standardization: add 50 mL of glacial acetic acid and 1 mL of concentrated hydrochloric acid to a 500 mL iodine flask and cool in an ice-water bath for about 10 min. While shaking the flask continuously, add 5 mL ± 0.01 mL of the potassium bromide-potassium bromate standard solution from a calibrated 10 mL burette at 1 or 2 drops per second. Stopper immediately, shake well and return to the ice-water bath. Then add 5 mL of potassium iodide solution at the mouth of the flask. After 5 min remove the flask from the ice-water bath, open the stopper slowly and let the potassium iodide solution run into the flask, shaking vigorously. Rinse the stopper, mouth and walls with 100 mL of water, then titrate rapidly with 0.1 mol/L sodium thiosulphate solution. Near the end point add 1 mL of starch indicator and titrate slowly until the blue colour disappears. Equation (1): c = (V₁·c₂)/(5×2). c: molar concentration of the potassium bromide-potassium bromate solution (calculated as Br₂), mol/L; V₁: volume of sodium thiosulphate consumed, mL; c₂: molar concentration of the sodium thiosulphate, mol/L; 5: volume of the potassium bromide-potassium bromate solution, mL; 2: number of electrons transferred in the redox reaction of the potassium bromide-potassium bromate solution. The difference between two determinations and their mean shall not exceed ±0.002 mol/L, otherwise the standardization is repeated. 7.5 Methanol. WARNING: toxic, flammable. Vapour inhalation may cause blindness or death; keep away from heat and open flame. 7.6 Potassium iodide solution (150 g/L): dissolve 150 g of potassium iodide in water and dilute to 1 L. 7.7 Sodium thiosulphate standard solution (0.1 mol/L): dissolve 25 g of sodium thiosulphate (Na₂S₂O₃·5H₂O) in water, add 0.1 g of sodium carbonate (Na₂CO₃) and dilute to 1 L, shaking thoroughly. Any standardization method suitable for sodium thiosulphate standard solution may be used, but the error of the standardization result shall not exceed ±0.0002 mol/L. Standardize periodically so that a concentration change of 0.0005 mol/L is detected in good time. NOTE: commercial reference materials may be purchased. 7.8 Starch solution: mix 5 g of water-soluble starch with 3 mL to 5 mL of water (0.65 g of salicylic acid may be added as a preservative if necessary). Add this paste to 500 mL of boiling water and continue boiling for 5 min to 10 min. Cool, transfer the clear supernatant to a glass-stoppered bottle and store sealed. NOTE: commercial starch solution (with salicylic acid as preservative) may be purchased. 7.9 Sulphuric acid solution (1:5): carefully pour 1 volume of concentrated sulphuric acid into 5 volumes of water and mix well. WARNING: toxic, strongly corrosive, strongly oxidizing. Handle in a fume cupboard; avoid splashing eyes, skin and clothing. 7.10 Titration solvent: prepare 1 L of titration solvent from 714 mL of glacial acetic acid, 134 mL of 1,1,1-trichloroethane (or dichloromethane), 134 mL of methanol and 18 mL of 1:5 sulphuric acid solution, and mix well. 7.11 1,1,1-Trichloroethane. WARNING: harmful by inhalation; high concentrations may cause unconsciousness or death. Handle in a fume cupboard; avoid contact with eyes and skin, which it irritates. 7.12 Dichloromethane. NOTE: 1,1,1-trichloroethane is an ozone-depleting chemical; dichloromethane is currently used in its place.

Key conditions: Titration cell temperature: 0 °C to 5 °C, maintained throughout the titration (see 9.2). Potentiometric titrator: voltage between the two platinum electrodes maintained at about 0.8 V; the sensitivity indicates the end point for a potential change of about 50 mV (see 6.1). End-point determination: the potential reaches the preset value and can be maintained for at least 30 s (see 9.5). Titration solvent volume: 110 mL (see 9.3). Stirring: switch on the stirrer and adjust the speed so that no bubbles appear in the solution (see 9.3). Potassium bromide-potassium bromate standard solution volume: shall not exceed 10 mL (see 9.1). Sample volume: shall not exceed 20 mL (see 9.1). The reaction mixture shall not separate into layers during the titration (see 9.1).

Calculation and results: The bromine value B of the sample (g/100g) is calculated by equation (2): B = (V - V₀) × c × 15.98 / m where: V is the volume of potassium bromide-potassium bromate standard solution consumed in titrating the sample, mL; V₀ is the volume of potassium bromide-potassium bromate standard solution consumed in titrating the blank, mL; c is the molar concentration of the potassium bromide-potassium bromate standard solution (calculated as Br₂), mol/L; 15.98 is the conversion factor derived from the relative molecular mass of Br₂ (calculated as Br₂) and the conversion from millilitres (mL) to litres (L), giving the grams of bromine consumed per 100 g of sample; m is the mass of sample entering the titration cell, g. (Equation (2) in the original is [source unclear], reading "B-(Y-Vo201X15.98"; the doubt is [to be verified] [source unclear].)

Quality control: Precision: judge the reliability of the test results as specified below (95% confidence level). NOTE: the precision data of this standard method were obtained with 1,1,1-trichloroethane as sample diluent and titration solvent; investigation has shown that the precision data are applicable after replacement of 1,1,1-trichloroethane by dichloromethane. 11.1.1 Repeatability: the difference between two repeat determination results obtained by the same operator, in the same laboratory, using the same apparatus, on the same sample shall not exceed the value in Table 5. 11.1.2 Reproducibility: the difference between two single and independent results obtained by different operators, in different laboratories, using different apparatus, on the same sample shall not exceed the value in Table 5. Table 5 Repeatability and reproducibility | Sample type | Repeatability / (g/100g) | Reproducibility / (g/100g) | | --- | --- | --- | | Petroleum fractions with a 90% distillation temperature below 205 °C | 0.11X^0.70 | 0.72X^0.78 | | Petroleum fractions with a 90% distillation temperature between 205 °C and 327 °C | 0.11X^0.89 | 0.78X^0.67 | | Industrial aliphatic olefins | 3 | 12 | NOTE: X is the mean of the determination results. (In Table 5 of the original, the repeatability/reproducibility values in the two petroleum fraction rows are [source unclear] and noisy, for example "0.11890", "0.72X278" and "0.78×067"; [to be verified] [source unclear].) 11.2 Bias: since the bromine value is a result defined by this method, the bromine value determined by this method has no bias.

Normative references: GB/T 6536 Standard test method for distillation of petroleum products at atmospheric pressure GB/T 6682-2008 Water for analytical laboratory use — Specification and test methods (ISO 3696:1987, MOD) GB/T 11136 Standard test method for bromine index of petroleum hydrocarbons — Electrometric titration SH/T 0630 Standard test method for bromine value and bromine index of petroleum products — Coulometric titration SH/T 1551 Determination of bromine index in aromatic hydrocarbons — Coulometric titration SH/T 1767 Determination of bromine index of industrial aromatic hydrocarbons — Potentiometric titration

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