NB/SH/T 0916-2015 Determination of biodiesel (fatty acid methyl esters) content in diesel fuel — Infrared spectroscopy method

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Card type: Test method

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

• Standard number: NB/SH/T 0916—2015
• Chinese name: Determination of biodiesel (fatty acid methyl esters) content in diesel fuel — Infrared spectroscopy method
• English name: Standard test method for determination of biodiesel (fatty acid methyl esters) content in diesel fuel oil using mid infrared spectroscopy
• Replacement relationship: This standard is first published (not provided in the available source regarding replacement of other standards).
• Adoption relationship: Modified adoption using the redrafting method of ASTM D7371-14 "Determination of biodiesel (fatty acid methyl esters) content in diesel fuel — Infrared spectroscopy method".
• Technical differences from ASTM D7371-14: Some referenced standards are modified to the corresponding national standards or industry standards of our country; to comply with standard drafting regulations, the explanation regarding units of measurement in clause 1.2 of ASTM D7371-14 has been deleted.
• Publication/implementation: published on 2015-10-27, implemented on 2016-03-01; issued by the National Energy Administration.
• Drafting organization: Sinopec Research Institute of Petroleum Processing; main drafters: Yang Yurui, Xu Yupeng.
• Custody: National Technical Committee for Standardization of Petroleum Products and Lubricants, Subcommittee on Petroleum Fuels and Lubricants (SAC/TC280/SC1); proposed by: China Petrochemical Corporation.

2. Scope of application and non-applicability

• This standard specifies a method for determining the content of biodiesel (fatty acid methyl esters (FAME)) in diesel fuel.
• It is applicable to the determination of fatty acid methyl ester content in diesel fuel with a volume fraction of 1%~20%.
• It is only applicable to the determination of fatty acid methyl ester (FAME) content; biodiesel containing fatty acid ethyl esters (FAEE) will produce a negative bias.
• Note: Using an appropriate attenuated total reflection (ATR) accessory, the measurement range can be expanded to a volume fraction of 1%~100%, but when the volume fraction exceeds 20%, the precision of this standard is not applicable.
• Method application (Chapter 5): 5.1 biodiesel is a commercial fuel, used as an additional component for diesel fuel blending; 5.2 this standard is applicable to quality control during the production and sales of biodiesel blended fuels (the source text at this location has noise at source-text extraction, requires confirmation against the source standard (source-text extraction)).

3. Method principle

• 4.2 This standard uses Fourier transform mid-infrared spectroscopy, an attenuated total reflection (ATR) sample cell, and partial least squares (PLS) calculation.
• By collecting spectral data of the test sample in the wavenumber range of 4000 cm⁻¹~650 cm⁻¹, the volume fraction of biodiesel is determined according to the calibration equation established in Appendix A (see 12.6, 12.7).
• The infrared spectrum is the negative logarithm of the ratio of the single-beam infrared spectrum of the test sample to the single-beam Fourier transform infrared spectrum of dry air (or nitrogen) (see A.2.2).

4. Reagents and materials (purity / preparation)

• 8.1 Spectroscopic grade (preferred) or analytical reagent grade chemicals should be used; other grades of reagents may also be used, provided that the reagent is first determined to be of sufficiently high purity and will not reduce the accuracy of the measurement.
• 8.2 BD100 (pure biodiesel): The BD100 biodiesel used for calibration and quality control shall meet the specification requirements of GB/T 20828—2014; it shall be biodiesel of typical fatty acid methyl esters. The calibration sample used to determine the precision of this standard method is soybean methyl ester. Derived esters from other feedstocks, such as animal fat, canola oil, jatropha oil, palm oil, rapeseed oil, and waste cooking oil, may also be used, but the number of standard samples prepared using waste cooking oil methyl ester shall not exceed 50% of the calibration samples.
• 8.3 Middle distillate fuel: The middle distillate fuel standard samples used for calibration, verification, and quality control shall meet the specification requirements of GB 252—2011, and shall not contain biodiesel or biodiesel feedstock; they should be represented by pre-blended known mineral oils (different crude oil sources, low aromatic content, high aromatic content, etc.), see the calibration set in Appendix A.2. Note: In GB 252—2011 Table 1, the cetane number requirement is not greater than 45, but Note 5 of Table 1 stipulates that the cetane number of each grade of light diesel produced from intermediate-base or naphthenic-base crude oil is allowed to be less than 40 (for those with special requirements, it shall be determined by both supplier and buyer); in order to increase the applicability of the calibration model, middle distillate fuels with a cetane number not less than 40 may be used for calibration, verification, and quality control standard samples.
• 8.4 Diesel cetane number check fuel (DCCF- low): low cetane number (see Appendix B.2 alternative feedstock).
• 8.5 Diesel cetane number check fuel (DCCF- high): high cetane number.
• 8.6 Diesel cetane number check fuel (DCCF- ultra-high): ultra-high cetane number.
• 8.7 Acetone: analytical reagent.
• 8.8 Toluene: analytical reagent.
• 8.9 Methanol: analytical reagent.
• 8.10 Mixed solvent: equal-volume mixture of toluene, methanol, and acetone.

5. Instruments and equipment

• 7.1 Fourier transform mid-infrared spectrometer: including infrared light source, liquid attenuated total reflection (ATR) sample cell, scanning interferometer, detector, A/D converter, computer, and sample introduction method, and shall meet:
  • Scanning range: 4000 cm⁻¹~650 cm⁻¹
  • Resolution: 4 cm⁻¹
• 7.1.2 The noise signal level is determined using the single-beam spectrum of air or nitrogen; the single-beam spectrum can be obtained by averaging multiple scans of FTIR, but the total scanning time is not provided in the available source (source-text extraction doubtful point, requires confirmation against the source standard (source-text extraction)). If there is interference from water vapor and carbon dioxide, the instrument should be purged with dry air or nitrogen. In the spectral range of 1765 cm⁻¹~1725 cm⁻¹, the spectral noise at 100% transmittance shall be lower than 0.3%.
• 7.2 Liquid attenuated total reflection sample cell
  • 7.2.1 Attenuated total reflection (ATR) conical sample cell specifications are shown in Table 1; suitable for low, medium, and high concentration FAME measurements.
  • 7.2.2 Horizontal attenuated total reflection (ATR) sample cell: ATR of ZnSe material is mounted on a horizontal plate; the absorption intensity at 1745 cm⁻¹ shall not exceed 1.2 absorbance units, and it is suitable for calibration of high concentration FAME; an appropriate crystal length and angle should be selected so that the maximum absorbance at 1745 cm⁻¹ does not exceed 1.2 absorbance units.
• Table 1 ATR Conical sample cell specifications (the source table header at source-text extraction has noise, requires confirmation against the source standard (source-text extraction)):
  • ATR Crystal material: aSe (as in the source text, requires confirmation against the source standard (source-text extraction))
  • Light focusing optical element/structure: cone, non-optical focusing element and cell body; circular cross-section intersects with the tail of the coaxial cone
  • Cone angle: 60°
  • Crystal length: 36.83 mm~39.37 mm
  • Crystal diameter: 3.175 mm
  • Incident angle at sample interface: 53.8°
  • Maximum range of incident angle: ±1.5°
  • Standard absorbance: 0.38 AU±0.02 AU (source text "0.38AU0.02AU", requires confirmation against the source standard (source-text extraction))
  • Cell body material: 316 stainless steel
  • Gasket: Chemrez or Kalrez O type ring (as in the source text, requires confirmation against the source standard (source-text extraction))
  • Other: square ketone 1428 cm⁻¹ band (as in the source text, requires confirmation against the source standard (source-text extraction))

6. Recommended operating conditions

• Sample temperature: Before analysis, the sample temperature should be kept constant at 15 ℃~27 ℃ (see 9.2.1, 12.1).
• Spectral acquisition range: 4000 cm⁻¹~650 cm⁻¹ (see 12.6).
• Calibration model spectral intervals (without baseline correction):
  • Low concentration model: 1800 cm⁻¹–1692 cm⁻¹ and 1327 cm⁻¹–940 cm⁻¹ (see 12.7.1.1, A.2.3.1)
  • Medium concentration model: 1800 cm⁻¹–1700 cm⁻¹ and 1399 cm⁻¹–931 cm⁻¹ (see 12.7.1.3, A.2.3.2)
  • High concentration model: 1851 cm⁻¹–1670 cm⁻¹ and 1371 cm⁻¹–1060 cm⁻¹ (see 12.7.1.5, A.2.3.3)
• Modeling method: mean centering + 3 latent variables (principal factors); if the standard deviation of validation based on 4 latent variables is lower, it may also be used, but the reason for using 4 latent variables should be recorded (see A.2.3.1, A.2.3.2, A.2.3.3).
• Purge: It is best to purge the spectrometer with dry air or nitrogen to remove water vapor; purging is best performed before analysis and stabilized for several hours; the corresponding reference background spectrum should be measured when acquiring each sample spectrum; the spectrometer should be sealed and dry, and accessories should be sealed (see Note to 6.3).

7. Sampling and sample preparation

• 9.1 General requirements
  • 9.1.1 When using this test method to analyze fuel samples, sampling shall be carried out in accordance with the procedures in GB/T 4756.
  • 9.1.2 Before testing, excessively high sample temperature should be avoided.
  • 9.1.3 Samples shall not be stored in leaking containers; if a sample is found to be leaking, it should be discarded and a new sample should be obtained again.
• 9.2 Sample handling during analysis
  • 9.2.1 When using FTIR to determine the test sample, control the sample temperature at 15 ℃~27 ℃; all samples should be equilibrated at room temperature (15 ℃~27 ℃) before analysis.
  • 9.2.2 After sample analysis, if the sample needs to be retained, it should be resealed.
• 6.5 Insoluble water in the test sample will lead to erroneous measurement results; before injecting the sample into the spectrometer sample cell, filter turbid or water-containing samples with dry filter paper.

8. Analysis Steps

• 12.1 Before analysis, the sample temperature should be kept constant within 15 ℃~27 ℃.
• 12.2 Clean any residual fuel in the sample cell according to the instrument requirements; rinse the sample cell with sufficient solvent or the sample to be tested to ensure it is completely flushed clean; for substances that are difficult to remove such as BD100, rinse with the mixed solvent in 8.10; blow dry the residual solvent with dry air or nitrogen.
• 12.3 Collect the background spectrum according to the method provided by the instrument.
• 12.4 Before analyzing an unknown sample, by collecting the spectrum of a quality control sample, compare the predicted biodiesel concentration with the known value of the quality control sample to ensure the instrument is operating normally; a sufficient amount of quality control sample should be added to the sample cell, and the sample cell should be rinsed with at least 3 times the sample cell volume of quality control sample.
• 12.5 Inject a sufficient amount of fuel sample into the sample cell, ensuring that the sample cell is rinsed with at least 3 times the sample cell volume of fuel sample. Note: Biodiesel and biodiesel blend fuels containing high concentrations are difficult to remove from the ATR crystal surface, and it is necessary to rinse several times between two samples with the sample to be tested or with solvent; if in doubt, repeat steps 12.5 and 12.7 and compare the results to ensure the rinsing is complete and thorough.
• 12.6 Collect spectral data of the sample in the wavenumber range 4000 cm⁻¹~650 cm⁻¹.
• 12.7 Determine the volume fraction of biodiesel according to the calibration equation established in Appendix A.
  • 12.7.1.1 Use the low-concentration calibration model to predict the biodiesel concentration in the fuel sample (see A.2.3.1), with spectral intervals 1800 cm⁻¹–1692 cm⁻¹ and 1327 cm⁻¹–940 cm⁻¹, without baseline correction.
  • 12.7.1.2 If the biodiesel volume fraction predicted in 12.7.1.1 is equal to or lower than 10.00%, use the low-concentration calibration model (see A.2.3.1) to predict the biodiesel concentration.
  • 12.7.1.3 If the biodiesel volume fraction predicted in 12.7.1.2 is greater than 10.00%, use the medium-concentration calibration model (see A.2.3.2) to predict the biodiesel concentration in the fuel sample, with spectral intervals 1800 cm⁻¹–1700 cm⁻¹ and 1399 cm⁻¹–931 cm⁻¹, without baseline correction.
  • 12.7.1.4 If the biodiesel volume fraction value predicted in 12.7.1.3 using the medium-concentration calibration model is less than or equal to 10.50%, the reported value is determined by the low-concentration calibration model; if the biodiesel volume fraction predicted in 12.7.1.3 is greater than 10.50% and less than or equal to 30.00%, then this value is used as the reported value.
  • 12.7.1.5 If the biodiesel volume fraction predicted in 12.7.1.4 is greater than 31.00%, use the high-concentration calibration model (see A.2.3.3) to predict the biodiesel concentration, with spectral intervals 1851 cm⁻¹–1670 cm⁻¹ and 1371 cm⁻¹–1060 cm⁻¹, without baseline correction.
  • 12.7.1.6 If the biodiesel volume fraction predicted in 12.7.1.5 using the high-concentration calibration model is lower than or equal to 31.00%, use the medium calibration model to determine the reported value; if the predicted biodiesel volume fraction is greater than 31.00% (determined by 12.7.1.5), then this value is used as the reported value.
• Note (after 12.7.1.6): The sample cell should be thoroughly cleaned after use; first clean any water-soluble substances in the sample cell with acetone; soak the sample cell in an aqueous ethanol (or methanol) solution of 30% for at least 1 h, then clean with acetone and dry; do not clean the ZnSe crystal with acid or alkali.
• 10.1 Before using the instrument, calibrate according to the procedure in Appendix A; calibration may be performed by the manufacturer or supplier at instrument acceptance; if the instrument is repaired, it should be recalibrated, and the verification procedure also needs to be redone.
• 10.2 Before using the instrument, verify according to the procedure in Appendix A; verification only needs to be performed when the instrument is initially put into use, recalibrated, and repaired.
• 11 Quality control check: 11.1 Measure the concentration of at least one biodiesel quality control sample every day to determine the quality control status of the test method; this quality control sample is consistent with the samples routinely analyzed in composition and model applicability. 11.2 A test method that is out of statistical control cannot be used until the cause of the out-of-control condition has been identified and corrected. 11.3 If the correction of the out-of-control condition requires repairing the instrument or recalibrating the instrument, then before using this method to determine the biodiesel content of samples, the instrument performance verification described in A.3 should be performed.

9. Qualitative and Quantitative and Calculation Formulas

• 13 Calculation: The volume fraction of biodiesel (fatty acid methyl esters) is converted from mass fraction to volume fraction by the calibration and verification standard samples according to formula (1).
  • V = M₀ × (D₀ / D) …… (1)
  • Where: V—— biodiesel (fatty acid methyl esters) volume fraction, %; M₀ — biodiesel (fatty acid methyl esters) mass fraction, %; D—— relative density of the calibration and verification sample at 20 ℃ (determined according to method GB/T 1884); D₀ — relative density of the BD100 biodiesel feedstock of the calibration and verification sample at 20 ℃ (determined by method GB/T 1884).
  • Note: The correspondence between the formula symbols and the description in the original text source-text extraction is noisy, requires confirmation against the source standard (source-text extraction).
• Calibration model (Appendix A):
  • A.1.1 Use partial least squares (PLS) to establish the calibration model; the calibration set is divided into three groups: A group 0.00%~10.00%, B group 10.00%~30.00%, C group 30.00%~100%.
  • A.1.2 Measure the density of the calibration sample blend components at 20 ℃ according to GB/T 1884.
  • A.1.3 For each calibration sample, convert the biodiesel mass fraction to volume fraction according to formula (1).
  • A.2.3.1 Low-concentration calibration model (0.00–10.00%): spectral intervals 1800 cm⁻¹–1692 cm⁻¹ and 1327 cm⁻¹~940 cm⁻¹, without baseline correction, mean centering and 3 latent variables.
  • A.2.3.2 Medium-concentration calibration model (10.00%–30.00%): spectral intervals 1800 cm⁻¹–1700 cm⁻¹ and 1399 cm⁻¹~931 cm⁻¹, without baseline correction, mean centering and 3 latent variables.
  • A.2.3.3 High-concentration calibration model (optional, 30.00%–100%): spectral intervals 1851 cm⁻¹–1670 cm⁻¹ and 1371 cm⁻¹~1060 cm⁻¹, without baseline correction, mean centering and 3 latent variables; the use of the model can be limited by the sample cell accessory.
• Instrument performance verification (A.3):
  • A.3.1 Verification sample preparation: similar to but not exactly the same as the calibration set samples; at least cover 95% of the calibration sample concentration range; the number of verification samples is generally 3 times the latent variables in the calibration equation (the multiplier is unclear in the source transcription and remains unverified); for a PLS model with 3 principal components, the number of standard samples required for verification is at least 20.
  • A.3.3.1 Verification standard deviation SEQ is calculated according to formula (A.1) (the original formula details source-text extraction are missing, requires confirmation against the source standard (source-text extraction)).
  • A.3.3.2 If SEQ is lower than PSEQ (the sum of standard deviations of replicate measurements), the instrument can be used for testing.
  • A.3.3.3 If SEQ is higher than PSEQ, calculate the F value by dividing the square of SEQ by the square of PSEQ; compare the F value with the critical F value using the degrees of freedom in the numerator q and the degrees of freedom in the denominator DOF (PSEQ); the values of PSEQ and DOF (PSEQ) are shown in Table A.2, and the critical values of F are shown in Table A.3.
  • A.3.3.4 If the F value is less than or equal to the critical F value in the table, the instrument can be used for testing.
  • A.3.3.5 If the F value is greater than the critical F value in the table, the instrument cannot be used for testing.
• Table A.2 Allowable sum of standard deviations: calibration 0.21, degrees of freedom 56 (only the "calibration" row is seen in the original text, requires confirmation against the source standard (source-text extraction)).
• Table A.3 Critical F values: degrees of freedom 20/21/22/23/24/25/30/35/40 corresponds to critical F value 1.76/1.75/1.74/1.72/1.71/1.70/1.66/1.63/1.61.

10. Precision

• 15.1 Precision: The precision test of this method was conducted among 5 laboratories, using 16 samples with fatty acid methyl ester volume fractions ranging from 1%~20%; the precision of the test method was determined by statistical test results from 5 laboratories; the summary table is shown in Table 2 and Table 3.
• 15.1.1 Repeatability: For biodiesel with a fatty acid methyl ester volume fraction between 1.00%~20.00%, the difference between two replicate results obtained by the same operator using the same instrument under the same conditions on the same sample should not exceed the value calculated by formula (2):
  • Repeatability = 0.01505 (X + 14.905) …… (2)
  • Where: X—— the average of two replicate results of biodiesel volume fraction, %.
• Table 2 Typical repeatability values (%):
  • Biodiesel volume fraction 1.00 → Repeatability 0.24
  • 2.00 → 0.25
  • 5.00 → 0.30 (the original text "00" "VH9" etc. source-text extraction is noisy, requires confirmation against the source standard (source-text extraction))
  • 10.00 → 0.37
  • 20.00 → 0.53
  • 50.00 → undetermined
  • 90.00 → undetermined
  • 100.00 → undetermined
• 15.1.2 Reproducibility: For biodiesel with a fatty acid methyl ester volume fraction of 1.00%~20.00%, the difference between two independent test results obtained by different operators in different laboratories on the same test sample shall not exceed the value calculated by formula (3):
  • Reproducibility = 0.04770 (X + 14.905) ...... (3)
  • Where: X—— the average of the two measured biodiesel volume fraction results, %.
• Table 3 Typical reproducibility values (%):
  • Biodiesel volume fraction 1.00 → Reproducibility 0.76
  • 2.00 → 0.8 (original text "0.8", requires confirmation against the source standard (source-text extraction))
  • 5.00 → 0.95
  • 10.00 → 1.19
  • 20.00 → 1.66
  • 50.00 → undetermined
  • 90.00 → undetermined
  • 100.00 → undetermined
• 15.2 Bias: The content of this section in the original text source-text extraction is severely missing, with only phrases such as "suitable reference material" visible, requires confirmation against the source standard (source-text extraction).

11. Report

• 14 Report: Report the volume fraction of biodiesel (fatty acid methyl esters) in the test sample (%), to the nearest 0.01%.

12. Normative References

• GB 252—2011 Automotive diesel fuel
• GB/T 1884 Standard test method for density of crude petroleum and liquid petroleum products (hydrometer method)
• GB/T 4756 Standard practice for manual sampling of petroleum liquids
• GB/T 13377 Determination of density or relative density of crude petroleum and liquid or solid petroleum products — Capillary-stoppered pyknometer and graduated bicapillary pyknometer methods
• GB/T 11139 Calculation of cetane index of distillate fuels
• GB/T 20828—2014 Biodiesel (BD100) for blending with diesel engine fuels
• SH/T 0604 Determination of density of crude petroleum and petroleum products (U-shaped vibrating tube method)
• SH/T 0694 Calculation of cetane index of middle distillate fuels (four-variable equation method)
• NB/SH/T 0843 Evaluation of analytical testing systems in the petrochemical industry — Statistical techniques
• ASTM E1655 Standard for infrared multivariate calibration analysis (Standard practices for infrared multivariate quantitative analysis)
• Note: The title of Chapter 2 source-text extraction is ": Normative references", which should be "2 Normative references", requires confirmation against the source standard (source-text extraction).

13. Source and verification

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