NB/SH/T 0902-2015 Determination of the separability value of asphaltene-containing heavy fuel oils induced by n-heptane phase separation — Optical scanning method

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Card type: Test method

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

• Method number: NB/SH/T 0902—2015
• Chinese full title: Determination of the separability value of asphaltene-containing heavy fuel oils induced by n-heptane phase separation — Optical scanning method
• English name: Standard test method for measuring n-heptane induced phase separation of asphaltene-containing heavy fuel oil as separability number by an optical scanning device
• Replacement relationship: This standard is first published (the replaced standard number is not provided in the available source)
• Adoption relationship: Modified adoption using the redrafting method of ASTM D7061-12 "Determination of n-heptane-induced phase separability value of asphaltene-containing heavy fuel oils — Optical scanner method"
• Publication/implementation: published on 2015-10-27, implemented on 2016-03-01
• Issuing authority: National Energy Administration
• Drafting organization: Petrochemical Research Institute of PetroChina Company Limited
• Main drafters: Liang Yingchun, Wang Chunyan, He Jing, Yu Hao, Xiao Zhanmin
• Custodian: National Technical Committee for Standardization of Petroleum Products and Lubricants, Subcommittee on Petroleum Fuels and Lubricants (SAC/TC280/SC1)
• Technical differences from ASTM D7061-12: In the normative references, some referenced standards in ASTM D7061-12 are changed to corresponding Chinese national standards and industry standards; in Annex A, GB 25989 is used to replace ASTM D396 (in GB 25989, the fuel oils in F-D2, F-R1, F-R2, F-R3 have the same or better quality than the fuel oils in ASTM D396 4#, 5#, 6#); in Annex A, petroleum fuels containing heavy fractions from petroleum refining (RST4 and MT4) included in GB/T 29114 are supplemented; this standard corrects the precision formula.

2. Scope of application and non-applicability

• Scope of application: Specifies a quantitative determination method for measuring, on site or in the laboratory, using optical scanning equipment, the degree of difficulty of phase separation (i.e., the separability value) of fuel oil dissolved in toluene after addition of n-heptane; applicable to asphaltene-containing heavy fuel oils.
• Non-applicability: This standard cannot be used to predict whether oils are mutually soluble before mixing, but it can be used to determine the separability value of oils after they have been mixed (see 5.3).

3. Method principle

• 4.1 Dissolve the sample, then add n-heptane to flocculate asphaltenes, causing oil phase separation. The phase separation rate is determined by measuring the increase in light transmittance of the sample from the bottom to the top of the sample tube (a portion of the sample tube) over a period of time. The separability value is calculated from the standard deviation of the average light transmittance after multiple scans.
• 4.2 First mix the sample with toluene; the mixing ratio depends on the type of sample (see Annex A). Take 2 mL of sample-toluene solution and mix with 23 mL n-heptane. After pipetting 7 mL of the sample-toluene-n-heptane mixture into a glass tube, begin rapidly inserting it into the optical scanning device.
• 4.3 Use the optical scanning device to vertically scan and record the light transmittance of the glass tube containing the oil-toluene-n-heptane mixture. Starting at a position 10 mm from the bottom of the glass tube, scan once every 0.04 mm and record the light transmittance until 55 mm at the top of the glass tube, and calculate the average light transmittance of 125 scan readings. Then repeat scanning the glass tube once every 60 s for 15 min. Calculate the separability value based on the results of 16 scans and report it.

4. Reagents and materials (purity / preparation)

• 7.1 Toluene: chemically pure.
• 7.2 n-Heptane: chemically pure.
• Warning: Toluene and n-heptane are flammable; vapors are harmful and flammable.
• Other materials: polytetrafluoroethylene-coated magnetic stirring bar (6.9).

5. Instruments and equipment

• 6.1 Computer: built-in software used to control the instrument. Data are stored on the computer hard disk.
• 6.2 Optical scanner: The instrument shall be calibrated according to the instrument manufacturer's operating instructions. The instrument has a pulsed infrared light source read head with a wavelength of 850 nm. The detector is located opposite the light source and detects the light transmittance of the sample glass tube. For each scan, the read head moves up and down along the glass tube, scanning the entire glass tube upward and automatically measuring the light transmittance once. The read head scans once from bottom to top, with a time interval of 60 s, for a total of 16 measurements. A schematic diagram of the measurement principle is shown in Figure 1. The measured light transmittance is automatically recorded on the computer hard disk and further processed according to the method in Chapter 10 and Annex B.
• 6.3 Cylindrical transparent glass tube: capacity 15 mL, outer diameter 16 mm, inner diameter 12 mm, length 140 mm. Used as sample container.
• 6.4 Pipette or automatic pipette: specific specifications are not provided in the available source (requires confirmation against the source standard (source-text extraction)).
• 6.5 Graduated cylinder: 25 mL.
• 6.6 Glass bottle with stopper: 250 mL.
• 6.7 Transparent glass bottle with stopper: 50 mL.
• 6.8 Balance: scale interval 0.01 g (the numbering of 6.4~6.13 in the source text is source-text extraction confusing, requires confirmation against the source standard (source-text extraction)).
• 6.9 Polytetrafluoroethylene-coated magnetic stirring bar.
• 6.10 Stirrer.
• 6.11 Timer: scale interval 0.1 s (numbering in the source text requires confirmation against the source standard (source-text extraction)).
• 6.12 Graduated cylinder: 25 mL, A grade.
• 6.13 Heating furnace.
• Note: The correspondence between the numbering and content of 6.4~6.13 in the source text is misaligned due to source-text extraction noise, requires confirmation against the source standard (source-text extraction).

6. Recommended operating conditions

• The optical scanner shall be started at least 1 h in advance (9.1).
• The sample is placed in a 60 °C heating furnace for 24 h to ensure homogeneity (9.2).
• Perform the test at room temperature (20 °C~25 °C) (9.7).
• Scanning wavelength 850 nm; scanning interval 60 s; a total of 16 scans, lasting 15 min; scanning range from 10 mm to 55 mm from the bottom of the glass tube, scanning once every 0.04 mm, for a total of 125 readings (4.3, 6.2).
• Stir the mixture for 90 min ± 5 min (9.4).

7. Sampling and sample preparation

• 8.1 Sample according to GB/T 4756.
• 8.2 For solid or viscous oil samples, before sampling and mixing, the viscosity may be reduced by heating (for example, on a hot plate, in an oven, or wrapped with a heating jacket or steam tape) to ensure that the sample should be flowable. Sample according to GB/T 27867.
• 9.2 The sample is placed in a 60 °C heating furnace for 24 h to ensure homogeneity.
• 9.3 Remove the sample from the heating furnace and shake for 1 min to ensure thorough mixing.
• 9.4 Weigh 5 g ± 0.01 g of sample with a balance, dilute with toluene in a 250 mL transparent glass bottle with stopper (6.6), with a dilution ratio from 1:3 to 1:20, so that the light transmittance baseline is below 15%. Carefully add the magnetic stirring bar to avoid loss of the sample-toluene mixture. Shake the transparent glass bottle with stopper until the sample no longer adheres to the bottom of the bottle. Place the transparent glass bottle with stopper on a magnetic stirrer and stir the mixture for 90 min ± 5 min.
• For dilution ratios, see Annex A Table A.1 (sample and toluene dilution ratios).

8. Analytical procedure

• 9.1 The optical scanner shall be started at least 1 h in advance. For detailed operation, see Annex B and Annex C.
• 9.2 The sample is placed in a 60 °C heating furnace for 24 h to ensure homogeneity.
• 9.3 Remove the sample from the heating furnace and shake for 1 min to ensure thorough mixing.
• 9.4 Weigh 5 g ± 0.01 g of sample, dilute with toluene in a 250 mL transparent glass bottle with stopper, with a dilution ratio from 1:3 to 1:20, so that the light transmittance baseline is below 15%. Add the magnetic stirring bar and stir for 90 min ± 5 min.
• 9.5 Use a graduated cylinder (6.12) to measure 23 mL of n-heptane into a 50 mL transparent glass bottle with stopper (6.7), then use a pipette to transfer 2 mL of the sample-toluene mixture prepared in 9.4 into the 50 mL transparent glass bottle with stopper, and rapidly shake the mixture 6 times (the source text "6." requires confirmation against the source standard (source-text extraction)).
• 9.6 Use a pipette to transfer 7 mL of the sample-toluene-n-heptane mixture prepared in 9.5 into a screw-capped cylindrical transparent glass tube (6.3) within 10 s, and tighten the screw cap. If the transfer time exceeds 10 s, terminate the test and start again.
• 9.7 At room temperature (20 °C~25 °C), quickly place the cylindrical transparent glass tube with a screw cap into the optical scanner and immediately start the test. Note: Record the transmittance through the cylindrical transparent glass tube with a screw cap every 60 s within 15 min, and store it on the computer hard drive via software.
• 9.8 After the measurement is completed, remove the cylindrical transparent glass tube with a screw cap from the optical scanner and clean it with toluene in a fume hood.

9. Qualitative and Quantitative and Calculation Formulas

• 10.1.1 Perform the calculation manually using a spreadsheet program (see Appendix B) or automatically using software Heavy Fuel V.1.0 (see Appendix C).
• 10.1.2 Measure the transmittance of the cylindrical transparent glass tube with a screw cap between 10 mm~55 mm (from the bottom of the glass tube at 10 mm), and calculate the average transmittance of this region per minute (Xₙ).
• 10.1.3 Calculate the total average transmittance of 16 scans (X_T).
• 10.1.4 Calculate the separability value S of the sample using the standard deviation formula according to formula (1):

S = √[ Σ(Xₙ − X_T)² / (n − 1) ] ………………(1)

Where:

• Xₙ —— average transmittance per 60 s;

• X_T —— average value of Xₙ (X_T = (X₁ + X₂ + … + X₁₆) / 16);

• n —— number of repeated measurements, n = 16.

• 10.2 Interpretation of results: The separability value can be used to measure the difficulty of oil phase separation after the sample is added to n-heptane. Phase separation is caused by asphaltene flocculation and precipitation. As asphaltenes settle in the solution, the transmittance of the sample changes. If the transmittance changes quickly, the separability value is high. A higher separability value indicates poor storage stability of the oil, while a lower separability value indicates good storage stability of the oil. The separability value is expressed as a percentage transmittance value.

• 5.1 Application of the method: When the separability value is between 0–5, the oil is considered to have high storage stability, and asphaltenes are not easily flocculated. When the separability value is between 5–10, the storage stability of the oil is low. When the separability value is above 10, the storage stability of the oil is very low, asphaltenes are easily flocculated, or flocculation has already begun.

• 5.2 This standard is applicable to refineries and oil product users. The method is suitable for evaluating the storage stability of oil products. Users can use this standard to control and optimize the refining process, and it can be used to evaluate the storage stability of oil products before, during, or after storage.

• 5.3 This standard cannot be used to predict whether oil products are mutually soluble before mixing, but it can be used to determine the separability value of oil products after mixing. Oils with low separability values and oils with high separability values are easily miscible with other oil products.

10. Precision

• 12.1 Precision: The precision of this standard was determined in 2011 through interlaboratory cooperative testing. The reliability of test results shall be judged according to the following provisions (95% confidence level).
• 12.1.1 Repeatability (r): The difference between two test results obtained by the same operator using the same instrument under the same operating conditions and according to the same test method on the same sample in continuous measurements shall not exceed the repeatability requirements in formula (2) and Table 1.

r = 1.3485 (S + 0.05) ^ 0.5 ………………(2)

Where: S —— average of two replicate determinations, applicable range: 0.1~16. (Note: The exponent source-text extraction in the original formula is “®.S”, suspected to be 0.5, requires confirmation against the source standard (source-text extraction))

• 12.1.2 Reproducibility (R): The difference between two single, independent test results obtained by different operators in different laboratories on the same sample according to the same test method shall not exceed the reproducibility requirements in formula (3) and Table 1.

R = 2.494 (S + 0.05) ^ 0.5 ………………(3)

Where: S —— average of two single, independent determination results, applicable range: 0.1~16. (Note: The exponent source-text extraction in the original formula is “"S”, suspected to be 0.5, requires confirmation against the source standard (source-text extraction))

• Table 1 Typical values of precision (the original table source-text extraction is misaligned; the following are identifiable data, requires confirmation against the source standard (source-text extraction)):

• 12.2 Bias: Currently, there is no reference standard material available to determine the storage stability of oil products (i.e., the separability value measured by this standard), so the bias cannot be determined.

11. Report

Report the following information:

• 11.1 Toluene dissolution ratio (see Appendix A).
• 11.2 Sample separability value, accurate to 0.1.

12. Referenced Documents

• GB/T 4756 Petroleum liquids — Manual sampling
• GB 25989 Furnace fuel oils
• GB/T 27867 Petroleum liquids — Automatic pipeline sampling
• GB/T 29114 Gas turbine liquid fuels
• ASTM D396 Standard specification for fuel oils
• ASTM D975 Standard specification for diesel fuel oils
• ASTM D2880 Standard specification for gas turbine fuel oils
• GB/T 1.1—2009 (mentioned in the foreword, used for standard drafting rules)

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.

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