SH/T 0793-2007 Determination of aromatic carbon content in hydrocarbon oils (High-resolution nuclear magnetic resonance method)

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Card type: Test method

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

• Standard number: SH/T 0793—2007
• Chinese full title: Determination of aromatic carbon content in hydrocarbon oils (High-resolution nuclear magnetic resonance method)
• English title: Standard test method for aromatic carbon contents of hydrocarbon oils by high resolution nuclear magnetic resonance spectroscopy
• Replacement relationship: not provided in the available source (the foreword only states modified adoption of ASTM D5292-99 (2004), and does not mention replacement of an old version of the standard)
• Adoption relationship: modified adoption of ASTM D5292-99 (2004)
• Publication/implementation: published on 2007-08-01, implemented on 2008-01-01
• Issuing body: National Development and Reform Commission of the People's Republic of China
• Drafting organization: Sinopec Research Institute of Petroleum Processing
• Main drafter: Wang Jing

2. Scope of application and non-applicability

• 1.1 specifies methods for determining aromatic hydrogen content (procedure A and procedure B) and aromatic carbon content (procedure C) in oils using a high-resolution nuclear magnetic resonance (NMR) spectrometer. Applicable samples include kerosene, heavy distillate oils, mineral oils, lubricating oils, liquids derived from coal, and other fractions that are completely soluble in chloroform at room temperature.
• 1.1 detection limits: for pulsed Fourier transform spectrometers, generally 0.1% (mole fraction) aromatic hydrogen atoms and 0.5% (mole fraction) aromatic carbon atoms; continuous-wave spectrometers are only suitable for measuring aromatic hydrogen atoms, with a detection limit generally of 0.5% (mole fraction) aromatic hydrogen atoms.
• 1.2 reporting units are mole fraction of aromatic hydrogen atoms and mole fraction of aromatic carbon atoms.
• 1.3 is not applicable to samples containing more than 1% (mass fraction) of olefins or phenolic compounds.
• 1.4 does not include determination of the mass fraction of aromatic hydrocarbons in oils (because the NMR signals of saturated hydrocarbons and aliphatic substituents on aromatic hydrocarbon molecules appear in the same chemical shift region); to determine the mass and volume content of aromatic hydrocarbons, chromatographic or mass spectrometric methods may be used.
• 1.5 uses SI (International System of Units) units.
• 1.6 does not provide recommendations for all safety issues involved.

3. Method principle

• 4.1 uses a continuous-wave or pulsed Fourier transform high-resolution nuclear magnetic resonance spectrometer to obtain a ¹H nuclear magnetic resonance spectrum from a deuterated chloroform solution of the sample. TMS is preferred as the internal standard, and its chemical shift assignment in ¹H and ¹³C nuclear magnetic resonance spectra is 0ppm.
• 4.3 The aromatic carbon content of the sample is obtained by comparing the integral of the aromatic carbon region (chemical shift 100ppm–170ppm) in the ¹³C spectrum with the sum of the integrals of the aliphatic carbon region (-10ppm–70ppm) and the aromatic carbon region (100ppm~170ppm).
• 4.4 Because of the influence of residual chloroform (chemical shift 7.25ppm) in the solvent mainly composed of deuterated chloroform, the integral of the aromatic hydrogen region must be corrected for the NMR spectral peak.
• 4.5 The integrals of the aliphatic hydrogen region and the aliphatic carbon region must be corrected for the NMR spectral peak because of the influence of the chemical shift internal standard TMS (chemical shift 0.0ppm in both ¹H and ¹³C spectra).

4. Reagents and materials (purity / preparation)

• 7.1 Reagent purity: reagents of chemical purity or above should be used in all test procedures.
• 7.2 Deuterated chloroform: for ¹H NMR, residual chloroform in deuterated chloroform must be less than 0.2% (volume fraction). Warning: harmful to health, highly toxic, suspected carcinogen, swallowing may be fatal, inhalation is harmful, combustion produces toxic vapors.
• 7.3 Tetramethylsilane (TMS): chemical shift internal standard reagent for ¹H and ¹³C NMR spectra.
• 7.4 2,4- Chromium(III) pentanedionate: also called chromium acetylacetonate, used as a relaxation reagent for ¹³C NMR spectra, generally at a content of 97% (mass fraction).
• 9.4 If TMS is used as the chemical shift internal standard: when measuring ¹H spectra, use deuterated chloroform containing TMS at 0.03% (volume fraction); when measuring ¹³C spectra, use deuterated chloroform containing TMS at 1% (volume fraction); the deuteration degree of all deuterated chloroform is not less than 99.8%.
• Table 2 Relaxation reagent: 2,4- Chromium(III) pentanedionate, recommended only for ¹³C NMR, used as a solution at a concentration of 20mmol/L (about 10mg/mL).
• 9.8.2 If a relaxation reagent is used, weigh 10mg 2,4- Chromium(III) pentanedionate per milliliter of final solution and add it directly to the sample tube containing the test specimen.

5. Instruments and equipment

• 6.1 High-resolution nuclear magnetic resonance spectrometer: a high-resolution continuous-wave (CW) or pulsed Fourier transform (FT) nuclear magnetic resonance spectrometer, which can be operated according to the conditions listed in Table 1 and Table 2, and can produce all peaks whose spectral width and coupling constants are within the conventional ranges of chemical shifts and coupling constants for the nucleus being detected.
• 6.2 Sample tube: a glass tube with an outer diameter of 5mm or 10mm, and compatible with a continuous-wave (CW) or pulsed Fourier transform (FT) spectrometer.

6. Recommended operating conditions

Table 1 Instrument conditions for ¹H NMR samples and continuous-wave (CW) measurement:

• Solvent: deuterated chloroform
• Sample concentration: for distillate oils, the concentration can be as high as 50% (volume fraction)
• Sample temperature: instrument ambient temperature
• Internal lock: recommended
• Sample spinning rate: generally 20Hz
• Radio-frequency power level: recommended
• Signal-to-noise ratio level: the signal-to-noise ratio of the highest peak in the aliphatic hydrogen region is greater than 5:1
• Chemical shift calibration: preferably TMS (0.0ppm), at a concentration of 0.03% (volume fraction)
• Integration: aliphatic hydrogen region -0.5ppm–5ppm; aromatic hydrogen region 5ppm–10ppm

Table 2 Instrument conditions for ¹H and ¹³C NMR spectra samples and pulsed Fourier transform measurement:

• Solvent: deuterated chloroform
• Sample concentration: for ¹H NMR, instrument operating conditions must be optimized, and the concentration can be as high as 5% (volume fraction); for ¹³C NMR, for distillate oils the concentration can be as high as 50% (volume fraction), and for liquids derived from coal it can be as high as 30% (volume fraction)
• Relaxation reagent: 2,4- Chromium(III) pentanedionate, recommended only for ¹³C NMR, used as a solution at a concentration of 20mmol/L (about 10mg/mL)
• Sample temperature: instrument ambient temperature
• Internal lock: deuterium (deuterated chloroform used for ¹H NMR)
• Sample spinning rate: recommended by the instrument manufacturer, generally 20Hz
• Pulse flip angle: about 30°
• Pulse delay time: >10s; >3s (with relaxation reagent); >60s (without relaxation reagent)
• Pulse: only for ¹³C NMR, broadband covering the entire frequency range of ¹H, gated decoupling during ¹³C data acquisition, decoupling rise time less than 2ms
• Sampling memory size: for ¹H, select and set a minimum digitization rate of 0.5Hz/ points; for ¹³C set a minimum digitization rate of 1.2Hz/ points, and increase storage space and zero-fill value if necessary
• Spectral width: for ¹H NMR at least 15ppm and centered as close as possible to 5ppm; for ¹³C NMR at least 250ppm and centered as close as possible to 100ppm
• Filter bandwidth: set equal to or greater than the spectral width and allowed by the instrument filter hardware
• Exponential window: set at least equal to the digitization rate
• Signal-to-noise ratio: the signal-to-noise ratio of the highest peak in the smaller integration region is greater than 20:1; the signal-to-noise ratio of the highest deuterated chloroform peak appearing at a chemical shift between 75ppm and 80ppm is greater than 60:1
• Chemical shift calibration: for ¹H NMR, preferably TMS (0.0ppm), at a concentration of 0.03% (volume fraction); for ¹³C NMR, preferably TMS (0.0ppm), at a concentration not greater than 1% (volume fraction); if this peak is not used for calibration, the middle peak of the deuterated chloroform triplet is set to 77.0ppm
• Integration: for ¹H NMR, aliphatic hydrogen region -0.5ppm–5ppm, aromatic hydrogen region 5ppm–10ppm; for ¹³C NMR, aliphatic carbon region -10ppm–70ppm, aromatic carbon region 100ppm–170ppm

7. Sampling and test specimen preparation

• 8.1 Obtain a representative sample to be tested by GB/T 4756 or an equivalent method. If measurement is not started immediately, store it in a cool place.
• 8.2 The minimum sample amount required by this method is about 10mL. When necessary, it should be sufficient to allow two determinations.
• 8.3 Before preparing the next lower-level sample, all higher-level samples must be homogeneous. If there are any external impurities, such as suspended particles like rust, pass the sample to be tested through a clean small funnel containing a piece of glass fiber, and allow the filtered oil sample to drip directly into a clean, dry small bottle or a NMR sample tube containing deuterated chloroform.
• 8.4 If the sample contains waxy substances, heat the sample in the container to about 60℃, and mix the sample with a high-shear mixer before sampling. To maintain sample homogeneity, it is sometimes necessary to use a pipette that has been heated to about 60℃ to transfer part of the sample into a NMR tube containing deuterated chloroform.
• 8.5 To ensure the validity of the test results, the sample must be completely dissolved in deuterated chloroform. Carefully check to ensure that the final solution is homogeneous and free of undissolved particles.
• 9.5 If it is inconvenient to prepare the test solution directly in a NMR sample tube according to the following procedure, the test solution may be prepared in a small bottle, and after adding solvent and dissolving the sample, transferred to a NMR sample tube. Ensure that the final solution concentration is appropriate and that no contamination occurs during transfer.

8. Analytical procedure

• 9.1 This chapter describes three different procedures: procedure A for determining aromatic hydrogen content (clause 9.6) and procedure B (clause 9.7), as well as procedure C for determining aromatic carbon content (clause 9.8).
• 9.2 The analyst may select the analysis procedure according to the NMR spectrometer used and the analysis item to be determined (aromatic hydrogen content or aromatic carbon content).
• 9.3 To ensure the best performance of the NMR spectrometer in the application of these procedures, Appendices A and ASTM E386 should be used in combination with the NMR spectrometer manufacturer's instructions.

Procedure A—— uses a continuous wave (CW) NMR spectrometer to determine ¹H NMR:

• 9.6.1 Use a pipette to transfer a homogeneous sample into a NMR sample tube matched to the CW spectrometer, usually a capped NMR sample tube with an outer diameter of 5mm.
• 9.6.2 Add deuterated chloroform to the NMR sample tube to produce a final oil solution with a concentration in the solvent of up to 50% (volume fraction). The concentration of oil in the solvent should be optimized for the spectrometer when used but may be as high as the above value; carefully check to ensure the final solution is homogeneous and free of undissolved particles.
• 9.6.3 Acquire data using the instrument conditions shown in Table 1, and plot the CW ¹H NMR spectrum. If TMS is used as an internal standard, assign the chemical shift value of this peak as 0.0ppm.
• 9.6.4 Integrate two chemical shift regions, from 5.0ppm–10.0ppm (A region) and from -0.5ppm–5ppm (B region). See Appendix A for suggested integration procedures.
• 9.6.5 Subtract from the total integral value of the A region the integral contribution of the residual chloroform solvent peak (which is the 7.25ppm peak in the hydrogen spectrum); if the residual chloroform peak is not obvious, no correction is needed for the integral value of the A region.
• 9.6.6 If TMS is used as an internal standard, subtract from the total integral value of the B region the integral contribution of the TMS peak (which is 0.0ppm in the hydrogen spectrum).
• 9.6.7 Use the corrected integral values of the A region and the B region, together with clauses 10.1 and 10.2, to calculate the aromatic hydrogen content of the sample.

Procedure B—— uses a pulsed Fourier transform (FT) NMR spectrometer to determine ¹H NMR:

• 9.7.1 Use a pipette to transfer a homogeneous sample into a NMR sample tube matched to the pulsed Fourier transform spectrometer, usually a capped NMR sample tube with an outer diameter of 5mm or 10mm.
• 9.7.2 Add deuterated chloroform to the NMR sample tube to produce a final oil solution with a concentration in the solvent of up to 5% (volume fraction). The concentration of oil in the solvent should be optimized for the spectrometer when used, but its maximum should not exceed the above value. Carefully check to ensure the final solution is homogeneous and free of undissolved particles.
• 9.7.3 Using the instrument conditions shown in Table 2, acquire data and plot the pulsed Fourier transform ¹H NMR spectrum. If TMS is used as an internal standard, assign the chemical shift value of this peak as 0.0ppm.
• 9.7.4 Figure 1 shows an acceptable pulsed Fourier ¹H spectrum of a heavy distillate oil sample dissolved in deuterated chloroform (heavy distillate oil sample 80MHz ¹H NMR spectrum).
• 9.7.5 Integrate two chemical shift regions, from 5.0ppm–10.0ppm (A region) and from -0.5ppm–5ppm (B region). See Appendix A for suggested integration procedures.
• 9.7.6 Subtract from the total integral value of the A region the integral contribution of the residual chloroform solvent peak (which is 7.25ppm in the ¹H spectrum); if the residual chloroform peak is not obvious or if carbon tetrachloride is used as the solvent, no correction is needed for the integral value of the A region.
• 9.7.7 If TMS is used as an internal standard, subtract from the total integral value of the B region the integral contribution of the TMS peak (which is 0.0ppm in the ¹H spectrum).
• 9.7.8 Use the corrected integral values of the A region and the B region, together with clauses 10.1 and 10.2, to calculate the aromatic hydrogen content of the sample.

Procedure C—— uses a pulsed Fourier transform (FT) NMR spectrometer to determine ¹³C NMR:

• 9.8.1 Use a pipette to transfer a homogeneous sample into a NMR sample tube matched to the pulsed Fourier transform spectrometer, usually a capped NMR sample tube with an outer diameter of 5mm or 10mm.
• 9.8.2 If a relaxation reagent is used, weigh 10mg 2,4- chromium acetylacetonate per milliliter of final solution and add it directly to the sample tube containing the sample. Note: The use of a relaxation reagent is recommended but not mandatory (see clause A.4.3). If no relaxation reagent is used, the instrument setting for "delay time" (see ASTM E386) must be increased by a considerably longer time than when a relaxation reagent is added. In this case, if the long delay time shown in Table 2 is not used, erroneous results will be obtained.
• 9.8.3 Add deuterated chloroform to the NMR sample tube to produce a final oil solution with a concentration in the solvent of up to 50% (volume fraction) and a coal-derived liquid solution of up to 30% (volume fraction). The concentration of oil in the solvent should be optimized for the spectrometer when used, but its maximum should not exceed the above value. Carefully check to ensure the final solution is homogeneous and free of undissolved particles.
• 9.8.4 Acquire data using the instrument conditions shown in Table 2, and plot the pulsed Fourier transform ¹³C NMR spectrum. If TMS is used as an internal standard, assign the chemical shift value of this peak as 0.0ppm.
• 9.8.5 Figure 2 shows an acceptable pulsed Fourier ¹³C spectrum of a heavy distillate oil sample dissolved in deuterated chloroform containing a relaxation reagent (heavy distillate oil sample 100MHz ¹³C NMR spectrum).
• 9.8.6 Integrate two chemical shift regions, from 100ppm–170ppm (A region) and from -10ppm–70ppm (B region). See Appendix A for suggested integration procedures.
• 9.8.7 If TMS is used as an internal standard, subtract from the total integral value the integral contribution of the TMS peak (which is 0.0ppm in the ¹³C spectrum).
• 9.8.8 Use the corrected integral values of the A region and the B region, together with clauses 10.1 and 10.3, to calculate the aromatic carbon content of the sample.

9. Qualitative and Quantitative Determination and Calculation Formulas

• 10.1 Calculate the aromatic hydrogen content or aromatic carbon content of the sample: aromatic hydrogen content or aromatic carbon content = [A/(A+B)]×100%
  • A: integral value of the aromatic hydrogen or aromatic carbon portion in the spectrum
  • B: integral value of the aliphatic hydrogen or aliphatic carbon portion in the spectrum
• 10.2 Aromatic hydrogen content: A is the corrected integral value of the A region (from 5.0ppm–10.0ppm), and B is the corrected integral value of the B region (from -0.5ppm–5.0ppm). The result is expressed as the mole fraction of aromatic hydrogen atoms or %H(Ar).
• 10.3 Aromatic carbon content: A is the integral value of the A region (from 100ppm–170ppm), and B is the corrected integral value of the B region (from -10ppm–70ppm). The result is expressed as the mole fraction of aromatic carbon atoms or %C(Ar).
• 3.1 Definition of aromatic carbon content: mole fraction of aromatic carbon atoms or percentage of aromatic carbon atoms in total carbon atoms, see formula (1): aromatic carbon content (%) = 100×(aromatic carbon atoms/total carbon atoms). Note: For example, the aromatic carbon content of toluene is 100×(6/7)% or 85.7% (mole fraction) aromatic carbon atoms.
• 3.2 Definition of aromatic hydrogen content: mole fraction of aromatic hydrogen atoms or percentage of aromatic hydrogen atoms in total hydrogen atoms, see formula (2): aromatic hydrogen content (%) = 100×(aromatic hydrogen atoms/total hydrogen atoms). Note: For example, the aromatic hydrogen content of toluene is 100×(5/8)% or 62.5% (mole fraction) aromatic hydrogen atoms.

10. Precision

• 12.1 The precision of this test method depends on the aromatic content of the sample.
• 12.2 Within the ranges 1%H(Ar)~78%H(Ar) and 8%C(Ar)~93%C(Ar), five oils were tested by twelve cooperating laboratories, namely one lubricating oil, one heavy distillate oil, two aromatic distillate oils, and one anthracene oil. The precision of this method obtained from statistical examination of interlaboratory test results (95% confidence level) is as follows:
• 12.2.1 Repeatability: The difference between two results obtained by the same operator using the same instrument on the same sample for repeated determinations shall not exceed the following values:
  • Aromatic hydrogen content (%H(Ar)): 0.32X
  • Aromatic carbon content (%C(Ar)): 0.59X (requires confirmation against the source standard (source-text extraction): the number at this place in the original text is unclear in the source text, suspected to be 0.59X)
  • X refers to the average of two repeated determination results of aromatic hydrogen content or aromatic carbon content.
• 12.2.2 Reproducibility: The difference between two results obtained by different operators in different laboratories using different instruments on the same sample shall not exceed the following values:
  • Aromatic hydrogen content (%H(Ar)): 0.49X (requires confirmation against the source standard (source-text extraction): the number at this place in the original text is unclear in the source text, suspected to be 0.49X)
  • Aromatic carbon content (%C(Ar)): 1.37X (requires confirmation against the source standard (source-text extraction): the number at this place in the original text is unclear in the source text, suspected to be 1.37X)
  • X refers to the average of two determination results of aromatic hydrogen content or aromatic carbon content.
• 12.3 Bias: Because there is no acceptable reference method for determining oils consisting of unknown mixtures of various aromatic compounds, or it can be calculated from known concentrations of different molecular structures, no bias of method NMR relative to known or calculated values has been observed, and the bias cannot be determined.

11. Report

• 11.1 Report the mole fraction of aromatic hydrogen atoms and/or the mole fraction of aromatic carbon atoms of the sample, with the result retained to one decimal place.

12. Referenced Documents

• GB/T 4756 Manual sampling method for petroleum liquids (GB/T 4756-1998, eqv ISO 3170:1988)
• SH/T 0729 Calculation method for carbon distribution and structural group composition of petroleum fractions (n-d-M method)
• ASTM E386 Practical method for the expression of high-resolution nuclear magnetic resonance spectral data
• ASTM D5292-99 (2004) (modified adoption of the source standard)

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