NB/SH/T 0879-2014 Determination of boiling range distribution of residual-containing oil samples — High-temperature gas chromatography

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

• Standard number: NB/SH/T 0879—2014
• Chinese title: Determination of boiling range distribution of residual-containing oil samples — High-temperature gas chromatography
• English title: Standard test method for boiling point distribution of samples with residues by high temperature gas chromatography
• Replacement relationship: not provided in the available source (no mention of replacing any old standard)
• Adoption relationship: modified adoption by redrafting method of ASTM D7169-11
• Main differences from ASTM D7169-11:
  • The standard title is changed to "Determination of boiling range distribution of residual-containing oil samples — High-temperature gas chromatography"
  • Clause 2 "Normative references" adopts corresponding national standards and industry standards
  • Added chromatographic conditions for injection with column 35 °C (see Table 1)
  • Added boiling range distribution data for external standard reference oil HTSD (see Table 2)
• Publication/implementation: published on 2014-06-29, implemented on 2014-11-01
• Issuing authority: National Energy Administration
• Drafting organization: Sinopec Research Institute of Petroleum Processing
• Main drafter: Jin Ke

2. Scope of application and non-applicability

Applicable:

• Determination of boiling range distribution and cut point intervals of crude oil and residual oil by high-temperature gas chromatography
• Determination of residue content (or sample recovery) by external standard method
• Applicable to boiling range distribution of crude oil and residual oil (such as atmospheric residue and vacuum residue)
• Applicable to boiling range distribution of other residual-containing oil samples that cannot completely flow out of the chromatographic system
• Can determine boiling range distribution up to a temperature of 720 °C (equivalent to the temperature at which n-C100 flows out)

Not applicable:

• With a thin liquid film capillary column, in the presence of a large amount of carbon disulfide, components C4~C5 cannot be completely separated; not applicable to determination of boiling range distribution corresponding to this range
• During the elution of carbon disulfide, the detector response to hydrocarbons is affected, resulting in inaccurate quantitative determination of the boiling range distribution in the interval C4~C5
• Not applicable to determination of oil samples containing complex compounds such as polyesters and polyolefins

Supplementary notes:

• By injecting only the solvent to subtract from the sample, and correcting according to the quenching factor for this interval, the net chromatographic area occupied by carbon disulfide can be roughly determined
• To obtain a more accurate boiling point curve for the temperature interval C4~C5, an independent high-resolution chromatographic system may be used (see Appendix A)

3. Method principle

In this gas chromatographic method, both the inlet and the capillary column use programmed temperature. A flame ionization detector is used as the sensor to convert mass into an electronic signal. The data acquisition system acquires the signal in slice mode and uses chromatography software to accumulate the signal. The retention time calibration standard is measured to obtain the curve of retention time versus boiling point. The reference oil solution is used to determine the detector response factor (the source text here has source-text extraction noise, suspected to be "detector response factor"). Because the reference oil can completely flow out under the chromatographic conditions in this standard. Solvent injection is performed, and the resulting signal is subtracted from the blank and sample chromatographic results. Finally, the sample solution is injected and the response factor is applied to calculate the sample recovery and, after converting the sample retention time to temperature, calculate the boiling range distribution within the recovered amount.

4. Reagents and materials (purity / preparation)

• 8.1 Carbon disulfide (CS2): purity greater than 99%, used as solvent to dilute samples and standards. Warning: flammable, toxic liquid.
• 8.2 Synthetic wax 655 or synthetic wax 1000: used as a component of the calibration mixture for retention time determination. Since the first compound of these synthetic waxes is n-C22, the n-alkane mixture in clause 8.3 should be supplemented so as to cover the entire range C5~C100 in the sample.
• 8.3 Alkanes: prepare a retention time calibration mixture using n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentadecane, n-hexadecane, n-heptadecane, n-octadecane, n-nonadecane, n-eicosane, and n-tetracontane.
  • 8.3.1 The purity of these compounds should be 99% or higher.
• 8.4 Retention time calibration standard: composed of synthetic wax (P655 or P1000) and an alkane mixture. An additional alkane mixture of C5~C20 needs to be added. Preparation steps:
  • 8.4.1 Carefully pipette 20 mL CS2 into a 50 mL round-bottom flask.
  • 8.4.2 Prepare the alkane mixture listed in clause 8.3: weigh 500 mg of each compound into a 20 mL glass bottle, additionally add 500 mg n-dodecane and about 20 mg n-tetracontane. Store this mixture at 4 °C; when in use, add a certain amount of synthetic wax 655 to prepare the retention time calibration standard.
  • 8.4.3 Weigh about 25 mg synthetic wax 655 into the container of 8.4.1, and add about 10 mg 8.4.2 of the prepared alkane mixture. Under a fume hood, heat with an infrared lamp (about 200 W) for 20 min or until the solution becomes clear. Keep the mixture at a distance of about 15~20 cm from the infrared lamp. Operate carefully to avoid igniting CS2.
  • 8.4.4 Transfer 2 mL of the final mixture into a 2 mL autosampler vial and seal tightly. This solution can be stored at 4 °C for about one week.
• 8.5 Detector relative response factor test mixture:
  • 8.5.1 Prepare an n-alkane solution containing n-decane, n-tetradecane, n-octadecane, n-eicosane, n-octacosane, n-dotriacontane, n-tetracontane, and n-pentacontane.
  • 8.5.2 Weigh about 100 mg of each n-alkane into a 50 mL volumetric flask, accurate to 0.1 mg. Mix thoroughly and add CS2 to the mark. Ensure the alkanes are completely dissolved. Record the amount of each n-alkane.
  • 8.5.3 Record the reagent purity of each n-alkane.
  • 8.5.4 Transfer the mixture separately into two 2 mL sample bottles. Inject 0.1 μL~0.2 μL.
• 8.6 Reference oil (5010, HTSD): used to determine sample recovery; the detector response factor must be determined. Use the reference oil as the external standard.
• 8.7 Gases:
  • 8.7.1 Nitrogen: 99.999%, total impurities not exceeding 10 mL/m³, used as detector makeup gas. Warning: high-pressure compressed gas.
  • 8.7.2 Hydrogen: 99.999%, total impurities not exceeding 10 mL/m³, used as detector fuel gas. Warning: flammable under high pressure.
  • 8.7.3 Air: 99.999%, total impurities not exceeding 10 mL/m³, used as FID detector combustion-supporting gas. Warning: high-pressure compressed gas, supports combustion.
  • 8.7.4 Helium: 99.999%, used as carrier gas. The O2 content in helium is not greater than 5 mL/m³. Total impurities should not exceed 10 mL/m³. Warning: high-pressure compressed gas.

5. Instruments and equipment

• 6.1 Gas chromatograph: requires a cryogenic valve to cool the column oven below ambient temperature, and operate according to the conditions in Table 1. Includes:
  • 6.1.1 Flame ionization detector (FID): temperature at least 5~10 °C higher than the maximum column temperature. Use a jet with an orifice of 0.45 mm to delay jet blockage caused by column bleed. The linear range should be 0.005 C/g and 10⁷ (the source text here has source-text extraction noise, requires confirmation).
  • 6.1.2 Inlet: a programmed temperature inlet with a glass liner or a cold on-column inlet may be used. The inlet can be programmed from 50 °C to the final column oven temperature. At any time during the analysis, the inlet temperature must be higher than the column oven temperature. The liner needs to be replaced frequently or part of the column needs to be cut off.
• 6.2 Carrier gas purification system: use gas purifiers to remove trace oxygen, moisture, and other impurities from the carrier gas. The purification system should include a hydrocarbon adsorption trap and an oxygen adsorption trap. A suitable visual indicator should follow to observe the remaining capacity of the oxygen trap.
• 6.3 Data system: a detector digital signal data acquisition system composed of a computer and software is recommended. The acquisition frequency is about 10 Hz, equivalent to a slice width of 0.1 s.
• 6.4 Integrator: a digital signal integrator may also be used to obtain the chromatogram.
• 6.5 Autosampler: an autosampler must be used. Repeatability of small-volume injection (0.1 μL–0.2 μL) must be ensured. Use a syringe with a needle size of 23–26 and a capacity of 5 μL~10 μL.
• 6.6 Carrier gas control: the gas chromatograph is operated under constant flow conditions. The difference between the initial flow rate and the final flow rate during the oven temperature program is not greater than 1%. Electronic flow control is strongly recommended.

6. Recommended operating conditions

Table 1 Chromatographic operating conditions:

ᵃ Recommended operating conditions for crude oil. ᵇ Operating conditions for crude oil and residual oil.

Other conditions:

• 9.3 Detector temperature: at least 5~10 °C higher than the maximum column temperature
• 9.4 Selection of initial column oven temperature:
  • 9.4.1 Crude oil sample: may contain methane, C2, C3 and C4 hydrocarbons, which elute together with C5. Even at an initial temperature of -20 °C, C5 and C6 are partially separated from CS2.
  • 9.4.2 Residual oil and high initial boiling point (IBP) samples: for samples with an initial boiling point of 100 °C or higher, set the initial column oven temperature to 35 °C~40 °C. If the light hydrocarbon tail cannot be separated from the solvent, proceed according to 9.4.1. If the user does not know the sample type, all samples can be determined at an initial temperature of -20 °C.
• 7.7 Column flow rate: with helium as carrier gas, set the column flow rate to 20 mL/min

7. Sampling and sample preparation

• 10.1 Sampling shall be carried out in accordance with GB/T 4756. Crude oil samples shall be stored at 4 °C or lower until determination. Before the determination procedure, first take out a small portion (about 10 mL) of the sample. Samples are allowed to be weighed at room temperature.
• 10.2 Samples that are solid or semi-solid at room temperature need to be heated to 60 °C so that they can be poured into the weighing container.
• 10.3 Weigh 0.2 g~0.25 g of sample, to the nearest 0.1 mg. Add 10 mL CS2. Record the mass to the nearest 0.1 mg.
• 10.4 Store all prepared solutions at 4 °C. Minimize the waiting time between preparing the sample and analyzing it. Samples may be stored in autosampler vials.
• 10.5 When a sample needs to be determined multiple times, prepare multiple identical sample vials. Do not run the same sample vial twice; use different sample vials containing the same solution for the determinations.
• 11 Preparation of response factor standard: Weigh 0.2 g~0.25 g of reference oil (see 8.6), to the nearest 0.1 mg. Add 10 mL CS2, and record the solvent mass to the nearest 0.1 mg. If not used immediately, store the solution at 4 °C.

8. Analytical procedure

• 9 Preparation of the gas chromatograph:
  • 9.1 Table 1 gives the conditions used to obtain the precision data 1.
  • 9.2 Column installation: install the column using graphite ferrules and check for leaks with an electronic leak detector.
  • 9.3 Detector temperature: at least 5~10 °C higher than the maximum column temperature.
  • 9.4 Selection of initial column oven temperature (see Section 6).
• 12 Preparation of equipment and data system:
  • 12.1 After installing the column and checking for leaks, prepare the gas chromatograph according to the conditions in Table 1.
  • 12.2 Set the data acquisition system acquisition frequency to 10 Hz (0.1 s slice width). Keep the data acquisition frequency constant for all samples, standards and solvent. The different chromatographic data acquired in one sequence may differ by 5~10 slices, which does not affect the calculation.
  • 12.3 Organize and save the acquired data files, and edit the sample injection sequence of the gas chromatograph.
• 13 System performance check:
  • 13.1 Column resolution: inject 0.1 μL–0.2 μL retention time calibration standard. Calculate the resolution according to equation (1), R = 1.699(t_C50) / (W_C50 + W_C52) (the original equation source-text extraction is incomplete, requires confirmation against the source standard). Ensure that the resolution R is between 1.8–4.0.
  • 13.2 Peak asymmetry test for column overload: select any alkane between C12–C24 in the chromatogram. Calculate the asymmetry according to equation (2) s = (a+b)/2a. Ensure that s is between 0.8–1.2.
  • 13.3 Determination of detector relative response factors: inject 0.1 μL–0.2 μL detector relative response factor test mixture. Calculate the relative response factor F of each alkane relative to n-eicosane according to equation (3). F should be between 0.95–1.05.
• 14 Analysis sequence:
  • 14.1 Set the sample analysis sequence.
  • 14.2 Blank run: perform a blank run at the beginning of each sequence and after column aging. Perform more than two blanks until a stable plateau is shown with no residual material eluting. An acceptable blank run should have a stable plateau at the maximum column oven temperature. The baseline should show no signs of residue or residual sample elution, and there should be no ghost peaks.
  • 14.3 Retention time calibration standard: insert 8.4 prepared standard. After the analysis is completed, repeat the analysis of this sample to verify column stability. Identify all carbon numbers up to C100.
  • 14.4 Standard response factor: insert the reference oil sample vial prepared in 8.5. Determine twice consecutively. Repeat the determination of the response factor standard once every 8 samples. The change in response factor shall not be greater than 2%.
  • 14.5 Sample determination: insert the sample prepared in 10.3. Inject the sample twice consecutively and overlay the chromatograms for observation; the change in retention time of compounds shall not be greater than 3 s and the signal magnitudes shall be similar.
  • 14.6 Additional blank run: perform a blank run after injecting each sample to confirm that there is no carryover from the preceding sample.
• 15 Inspection of acquired data:
  • 15.1 Check all chromatographic data; the signal magnitude should be similar to the chromatographic data of the calibration mixture and reference oil.
  • 15.2 Confirmation of retention times of the chromatographic calibration mixture: the retention time of each alkane in the two injections shall not differ by more than 3 s. The chromatograms of the C5~C6 components and the solvent peak should be the same as the inset in Figure B.2. The peaks should not be split or tailing.
  • 15.3 Sample chromatogram: the chromatograms of the two determinations can be overlaid. The retention times of the two runs shall not differ by more than 3 s.
  • 15.3.1 A quality control check (QC) sample should be analyzed once per sequence. Determine once after every ten samples.
  • 15.4 Baseline or blank run: there is no obvious difference between the blank signal and the sample analysis. The baseline gradually rises to the isothermal segment of the chromatogram; ensure that after the gradual change there is a baseline plateau. If the blank baseline exceeds the sample signal at the tail end, the sample signal cannot be used. If at the end of the sample run it exceeds the blank baseline by 10%, it also cannot be used.
  • 15.4.1 Determination of quenching interval: select the time when the solvent peak begins to elute, and record the time when the solvent peak has completely eluted.
  • 15.4.2 Determination of solvent response value: overlay the solvent chromatograms to confirm similarity. The difference in total area between solvent peaks shall not be greater than 3% each time.
  • 15.5 External standard chromatographic response factor: check the external standard chromatogram obtained by injecting the reference oil. The boiling range distribution results of the reference oil should be consistent with the values listed in Table 2. If consistent data are not obtained, correct the chromatographic error (see 16.1.7).

9. Qualitative and quantitative determination and calculation formulas

• 16.1 Zeroing of the reference oil chromatogram:
  • 16.1.1 Ensure that the first 5 slices in the data system do not contain eluting sample or solvent.
  • 16.1.2 Before calculation, calculate the average slice area of 5 slices and subtract it from each slice. Set negative numbers to zero.
  • 16.1.3 Similarly complete the zero value calculation of the blank baseline.
  • 16.1.4 Subtract the blank baseline from the reference oil chromatographic result. Set negative numbers to zero.
  • 16.1.5 Determination of the reference oil elution end time point: determine the sample chromatographic elution end point according to the method in NB/SH/T 0829.
  • 16.1.6 Determination of the reference oil chromatographic area: sum all slices from the solvent elution end time point to the sample elution end point as the standard area A_smp.
  • 16.1.7 Calculation of the reference oil boiling range distribution: calculate according to the method in NB/SH/T 0829. The data should be consistent with Table 2.
• 16.2 Zeroing of the sample chromatogram: same as 16.1.2.
• 16.3 Subtraction of the blank baseline from the sample: same as 16.1.4.
• 16.4 Quenching correction: for crude oil samples, the quenching factor is used to correct the weakening of the FID response value caused by CS2 eluting together with the sample. In the interlaboratory study, the factor used was 1.93. Samples that do not contain components co-eluting with the solvent (such as residual oil or reference oil) do not require quenching correction.
  • 16.4.1 Determination of quenching interval: select the time when the solvent peak begins to elute, and determine the time when it has completely eluted.
  • 16.4.2 Determine the number of slices in the quenching interval.
  • 16.4.3 Correct for response attenuation by multiplying each slice in this interval by the quenching factor (QF).
• 16.5 Determination of final elution time of the sample: Determine the time when the column oven reaches the isothermal interval of the temperature program (baseline inflection point), called the final elution time (FET).
• 16.6 Determination of sample area: Sum all slice values from 0 to the final elution time to obtain the net sample area A_sMWP.
• 16.7 Calculation of response factor (RF): Equation (4) RF = (M_smp / (M_srp + M_susmp)) × (A_smp / ...) (original equation source-text extraction incomplete, requires confirmation against the source standard)
  • A_smp: Net area of the reference oil after baseline subtraction and solvent peak deletion
  • M_susTp: Amount of solvent dissolving the reference oil (g)
  • M_srp: Amount of reference oil in the response factor solution (g)
• 16.8 Calculation of recovery: Equation (5)~(8) (original equation source-text extraction incomplete, requires confirmation against the source standard)
  • 16.8.1 Determine whether the recovery (RC) is below the recovery threshold (R_t). If less than or equal to the threshold, use the measured percent recovery. If greater than the threshold, set the recovery to 100%. If the recovery is greater than 102%, repeat the analysis or check the chromatographic system.
• 16.9 Determination of boiling range distribution:
  • 16.9.1 Multiply the percent recovery by the area of each slice of the sample, then divide by the total sample area to obtain the slice value expressed as a percentage.
  • 16.9.2 Sum the slices to obtain 0.5%, 1%, 2%, etc. percent recoveries. Use interpolation to calculate the corresponding actual slice values.
  • 16.9.3 Stop the calculation when the sum of slice values is closest to equal to the entire integrated percent yield.
  • 16.9.4 Convert retention time to boiling point according to the algorithm of method NB/SH/T 0829. Use the boiling point temperatures listed in Table 3.
• 16.10 Calculation of cut point range:
  • 16.10.1 Find the two slices corresponding to the two temperatures that define the cut point range.
  • 16.10.2 Use the calibration curve to convert the temperature range to a time range.
  • 16.10.3 Multiply by 60 and divide by the slice width in seconds to convert the time range to a slice number range.
  • 16.10.4 Sum the corrected slices to equal the mass percentage of the cut.
  • 16.10.5 Equation (9) ERc = ((RC - Rc-1%) / (TRc - TRc-1%)) × (T - TRc-1%) + Rc-1%
  • 16.10.5.1 For T > FET, this equation is not recommended.

10. Precision

• 18.1 Precision: Obtained statistically from the results of determinations of five selected crude oils and five residual oils within a laboratory. The precision results shown in Table 4 to Table 6 apply only to the temperature intervals listed in the tables. Extended ranges not listed require additional study. 95% confidence level.
  • 18.1.1 Repeatability: The difference between two results obtained by the same operator using the same apparatus on the same test sample shall not exceed the values listed in Table 4 (residual oil), Table 5 (crude oil), and Table 6 (cut interval).
  • 18.1.2 Reproducibility: The difference between two single and independent test results obtained by different operators in different laboratories on the same test sample shall not exceed the values listed in Table 4 (residual oil), Table 5 (crude oil), and Table 6 (cut interval).
• 18.2 Bias: Since the boiling range distribution is defined only in this test method, the bias of this method has not been determined.

Table 4 Repeatability and reproducibility of residual oil (shall not be extrapolated):

Table 5 Repeatability and reproducibility of crude oil (shall not be extrapolated):

Table 6 Repeatability and reproducibility of cut intervals (X is the mass yield of the cut, shall not be extrapolated):

11. Report

Report temperatures at intervals of every 1% from 1% to the integer range of recovery, accurate to 0.5 °C. Report the initial boiling point (IBP). Report the selected cut intervals.

12. Referenced documents

• GB/T 4756 Standard practice for manual sampling of petroleum liquids (GB/T 1884-1998, eqv ISO 3170:1988)
• GB/T 17280 Standard test method for distillation of crude oil 15- theoretical plate distillation column
• NB/SH/T 0829 boiling point range 174 °C~700 °C Determination of boiling range distribution of petroleum fractions by gas chromatography
• ASTM D7169-11 (modified adoption)
• References:
  • [1] ASTM D6729 100m Determination of individual hydrocarbons in spark-ignition engine fuels by capillary high-resolution gas chromatography
  • [2] ASTM D6730 100m Determination of individual hydrocarbons in spark-ignition engine fuels by capillary (with precolumn) high-resolution gas chromatography

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