SH/T 0614-1995 Determination of composition of industrial propane and butane (gas chromatography)

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

• Standard number: SH/T 0614-95
• Chinese full title: Determination of composition of industrial propane and butane (gas chromatography)
• English name: not provided in the available source
• Replacement relationship: not provided in the available source
• Adoption relationship: This standard is equivalent to the international standard ISO 7911:1988 "Analysis of commercial propane and butane (gas chromatography)".
• Approval/implementation: approved by China Petrochemical Corporation 1995-06-15, implemented on 1995-10-01.
• Custody/drafting: technical custody by the Research Institute of Petroleum Processing; drafting by the Second Petrochemical Plant of Tianjin Petrochemical Company; main drafters Li Hui and An Liqin.

2. Scope of application and non-applicability

• This standard specifies a method for the determination of the composition of industrial propane and butane by gas chromatography.
• It is applicable to the determination of propane, butane and their hydrocarbons, but does not include hydrocarbon components at concentrations below 0.1%(m/m).
• It is also applicable to the determination of various hydrocarbon components and their mixtures in liquefied petroleum gas (including saturated and unsaturated C, C, C, and C hydrocarbons). (The source-text extraction at this point in the original is doubtful, the carbon number labeling is unclear, requires confirmation against the source standard (source-text extraction))
• It is not applicable to "on-line" chromatography. (The original "not applicable to 'on-line' chromatography i A-" is source-text extraction noise, requires confirmation against the source standard (source-text extraction))

3. Method principle

The sample is carried into the chromatographic column by the carrier gas, separated into the corresponding components within the column, detected by a thermal conductivity or flame ionization detector, and its chromatogram is recorded. The components are identified qualitatively using relative retention values, and the content of each component is calculated by the area normalization method.

4. Reagents and materials (purity / preparation)

4.1 Reagents

• 4.1.1 Chromatographic stationary liquid
  • 4.1.1.1 Dibutyl maleate
  • 4.1.1.2 β,β′-oxydipropionitrile (the original source-text extraction is "R.r 9`oxydipropionitrile", requires confirmation against the source standard (source-text extraction))
  • 4.1.1.3 Sebaconitrile
• 4.1.2 6201 chromatographic support or other red support, sieve the fraction of 180～250 μm (see GB 6005).
• 4.1.3 n-Pentane or chloroform: analytical reagent.
• 4.1.4 Dichloromethane, toluene or diethyl ether: analytical reagent.

4.2 Materials

• 4.2.1 Hydrogen, helium: purity greater than "" (the original number is missing, requires confirmation against the source standard (source-text extraction)).
• 4.2.2 Standard gas: pure gases such as 1-butene, isobutene, cis-2-butene, isopentane, etc., or a gas mixture with known accurate components.

4.3 Preparation of stationary phase (7.1)

According to the liquid phase loading (see Table 1), first pour in the stationary liquid and add an appropriate solvent to dissolve it. Make the resulting solution volume slightly larger than the volume of the support, add the support while stirring, then gently stir and evaporate to remove the solvent.

5. Instruments and equipment

• 6.1 Injection device:
  • 6.1.1 Gas sampling valve: the volume of the quantitative tube is not greater than 0.5 mL.
  • 6.1.2 Sampling tube: 2 mL.
  • 6.1.3 Aluminum foil sampling bag: 2 L.
  • 6.1.4 Stainless steel capillary: inner diameter 0.2 mm, length 2～4 m.
  • 6.1.5 Liquid sampling valve: quantitative tube volume 0.5～1 μL (the original source-text extraction is "KL", requires confirmation against the source standard (source-text extraction)).
• 6.2 Chromatographic column: the chromatographic column and its operating conditions are shown in Table 1.
• 6.3 Detector: can be a thermal conductivity detector (hot wire type or thermistor type) or a flame ionization detector. The peak height produced for a hydrocarbon component at a content of 0.1%(m/m) should be greater than twice the noise. If an electronic integrator is used, when analyzing samples, it should be able to measure a signal at a component concentration of 0.1%(m/m), and the repeatability should not be greater than 20% (relative). Check the response linearity of the instrument by injecting a series of standard gas mixtures with a relatively large concentration variation but with known concentrations, or by injecting a mixture of multiple pure gases with known different partial pressures.
• 6.4 Recorder: 0～1 mV or 0～5 mV, full-scale response time less than 1 s.
• 6.5 Integrator or data processor.
• 6.6 Porous metal filter: if a liquid sampling valve (6.1.5) is used, it is recommended to install a suitable porous metal filter before the sampling valve to prevent solid particles from entering the sampling valve; the filter should be placed exactly after the outlet valve of the sampling bottle or cylinder.

6. Recommended operating conditions

Table 1 Chromatographic column and operating conditions

Note: The column length, column inner diameter and column tube material can be selected by the operator when they can satisfy the resolution requirement of 7.4.

9.1 Test conditions

• 9.1.1 Vaporization chamber temperature: 40±5℃ or a suitable temperature selected by the operator.
• 9.1.2 Column temperature: as shown in Table 1 or a suitable temperature that can achieve good separation.
• 9.1.3 Carrier gas flow rate: 30 mL/min or the flow rate required to achieve good resolution (7.4). Note: When hydrogen is used as the carrier gas, special safety precautions should be taken; the gas path system must be guaranteed to be leak-free, and hydrogen must be discharged outdoors.
• 9.1.4 Detector temperature:
  • The thermistor-type thermal conductivity detector should be operated between 40～50℃.
  • The hot wire-type thermal conductivity detector should be operated between 100～150℃.
  • The flame ionization detector should be operated between 100～150℃.

7.3 Aging of the chromatographic column

Before use, the chromatographic column should be purged with carrier gas for 5 h at a temperature slightly higher than the column temperature (below the maximum operating temperature of the stationary liquid).

7.4 Resolution of components

Between propane and propylene in industrial propane, and between propylene and isobutane in industrial butane, a resolution of formula (1) should be achieved. See Figure 1.

$$R = \frac{2(d'{A} - d'{B})}{W_A + W_B} \geq 1.5 \quad \cdots\cdots\cdots\cdots(1)$$

Where: A and B—— represent propane and propylene or propylene and isobutane components respectively; R—— the resolution of peak A and peak B; d'_A and d'_B—— are the adjusted retention times of components A and B respectively, expressed as distances on the chart, mm; W_A and W_B—— represent the peak widths of components A and B respectively.

Adoption notes:

1. ISO 7941 the solvents are n-pentane, toluene or dichloromethane; this standard recommends the use of chloroform and diethyl ether.
2. The length of the sebaconitrile column is increased by 3 m compared with ISO 7941.
3. The column temperature of the sebaconitrile column, ISO 7941 specifies 20±1℃, this standard recommends the use of 20～40℃.

7. Sampling and sample preparation

• 8 Sampling: sampling is carried out in accordance with GB/T 13290.
• 7.2 Packing of the chromatographic column: clean and dry the inside of the chromatographic column tube, plug a small amount of glass wool at one end, connect it to a vacuum pump for suction, slowly add the stationary phase from the other end while continuously tapping the column gently, until the column is packed tightly and uniformly. The connection between the two chromatographic columns is packed with the same stationary phase.

8. Analysis procedure

9.2 Calibration

9.2.1 Qualitative analysis

The components can be identified by passing a standard reference mixture or several pure hydrocarbons through the column, or by comparing with the typical chromatograms of Figure 2, Figure 3, Figure 4 and the relative retention values shown in Table 2 (see 4.4.3), thereby identifying the components qualitatively.

Table 2 Relative retention values

Note on adoption: This retention value was obtained from a large number of tests and is consistent with the typical chromatogram of ISO 7941. The retention values in ISO 7941 are not consistent with their own typical chromatograms.

9.2.2 Quantitative analysis

The calculation method is the normalization method. Table 3 gives the peak area correction factors used. These values are only a guide or approximation; laboratories with experience in preparing calibration gas mixtures should determine the correction factors themselves.

9.3 Determination

9.3.1 Liquid injection

Place the sampling bottle or gas cylinder upright so that the outlet valve is at the bottom. Using a non-plasticized transparent armored or pressure-resistant tube (the tube should be "grounded"), connect the valve to the injector through a metal filter (6.6) (see Figure 5). Install a pressure reducing valve downstream of the injection device vent system to avoid any vaporization upstream when the flow rate reaches equilibrium. Open the outlet valve and control the flow through the transparent tube so that the liquid completely fills the transparent tube. Inject the sample into the column and close the outlet valve.

9.3.2 Gas injection

• 9.3.2.1 Connect a sampling tube of specification 2 mL (see Figure 6) to the sample source or to a larger sampling cylinder containing the liquid phase of the sample. Open the valve of the 2 mL sampling tube until liquid appears at the outlet, close the outlet valve, and after about 10 min (to reach equilibrium), close the inlet valve, close the sample source, and disconnect the 2 mL sampling tube. Completely vaporize the sample in a 2 L empty aluminum foil sampling bag, mix the sample thoroughly (if necessary, place in water at 50～70℃ to fully vaporize), connect the aluminum foil sampling bag to the injection valve, control the flow rate to 20 mL/min, and then inject the sample into the chromatographic column.
• 9.3.2.2 Place a stainless steel capillary of inner diameter 0.2 mm and length 2～4 m in a constant-temperature water bath at 50～70℃. Connect one end of the capillary to the bottom outlet of the sampling cylinder and the other end directly to the injection valve. Open the outlet valve of the sampling cylinder, control the flow rate to 20 mL/min, and then inject the sample into the chromatographic column.

9.4 Chromatogram

9.4.1 Typical chromatogram

Figure 2, Figure 3, and Figure 4 represent typical chromatograms of industrial propane, butane, and a reference mixture containing liquefied petroleum gas components.

9.4.2 Qualitative analysis

For industrial propane, use a dibutyl maleate + β,β′-oxydipropionitrile column. For industrial butane, use a dibutyl maleate column. When determining both propane and butane, use a sebaconitrile column.

• 9.4.2.1 Identification of components: compare with a reference mixture, or use relative retention times (see 9.2.1) to identify components.
• 9.4.2.2 Interferences: Under the conditions recommended in this standard, the following pairs of components cannot be separated:
  • Air and methane (using dibutyl maleate column, dibutyl maleate + β,β′-oxydipropionitrile tandem column, sebaconitrile column).
  • Ethane and ethylene (using dibutyl maleate column, dibutyl maleate + β,β′-oxydipropionitrile tandem column, sebaconitrile column).
  • 1--butene and isobutylene (using dibutyl maleate column, dibutyl maleate + β,β′-oxydipropionitrile tandem column).

9.4.3 Quantitative analysis

• 9.4.3.1 Using a recorder: measure each peak height and half-height width (see 7.4), and calculate their product to obtain the recorded peak area for each peak. Correct all recorded peak areas to the same attenuation to plot the peak areas.
• 9.4.3.2 Using an integrator or computer: record the reading response value for each peak and use it in place of the peak area in the calculation (see 10).

9. Qualitative and quantitative analysis and calculation formulas

10 Expression of results

Calculate the concentration of each component in the sample using the following formula.

Thermal conductivity detector

The mass percentage X_i %(m/m) of component i in the sample is calculated according to formula (2):

$$X_i = \frac{f_i \cdot A_i}{\sum (f_i \cdot A_i)} \times 100 \quad \cdots\cdots\cdots\cdots(2)$$

Where: A_i—— peak area of component i; f_i—— mass correction factor of component i, see Table 3; n—— number of components in the mixture.

The mole percentage X_i %(mol) of component i in the sample is calculated according to formula (3):

$$X_i = \frac{f'_i \cdot A_i}{\sum (f'_i \cdot A_i)} \times 100 \quad \cdots\cdots\cdots\cdots(3)$$

Where: A_i—— peak area of component i; f'_i—— mole correction factor of component i, see Table 3; n—— number of components in the mixture.

The calculation results are rounded to two decimal places.

Flame ionization detector

The mass percentage X_i %(m/m) of component i in the sample is calculated according to formula (4):

$$X_i = \frac{f_i \cdot A_i}{\sum (f_i \cdot A_i)} \times 100 \quad \cdots\cdots\cdots\cdots(4)$$

Where: A_i—— peak area of component i; f_i—— mass correction factor of component i, see Table 3; n—— number of components in the mixture.

The mole percentage X_i %(mol) of component i in the sample is calculated according to formula (5):

$$X_i = \frac{A_i / n_{Ci}}{\sum (A_i / n_{Ci})} \times 100 \quad \cdots\cdots\cdots\cdots(5)$$

Where: A_i—— peak area of component i; n_{Ci}——effective carbon number in component i; n—— number of components in the mixture.

The calculation results are rounded to two decimal places.

Note on adoption: The formula in ISO 7941 is incorrect; upon consulting the literature, this formula should add ×100.

Table 3 Relative correction factors of components

(Note: Some values in Table 3 are misaligned due to source-text extraction typesetting; the above has been organized according to row-column correspondence and requires confirmation against the source standard (source-text extraction))

10. Precision

Judge the reliability of test results according to the following provisions (95% confidence level).

11.1 Repeatability

For the same operator, using the same instrument, on the same sample under the same operating conditions, with normal and correct operating methods, the difference between two results obtained from repeated determinations shall not exceed the value shown in Table 4.

11.2 Reproducibility

For different operators, using different instruments, on the same sample under the same operating conditions, with normal and correct operating methods, the difference between the two results obtained by each shall not exceed the values shown in Table 4.

Table 4 Repeatability and Reproducibility

Note: Component concentration ranges are expressed in mass percent; precision data are expressed in mass percent (absolute value).

11. Report

12 Test report: The report shall include the following contents:

• a. All information about the test sample: batch number, date, sampling location, etc.;
• b. Test results, with results reported to two decimal places;
• c. Abnormal phenomena observed during the test.

12. Referenced documents

• GB 6005 Test sieves — Metal wire woven mesh, perforated plates and electroformed sheets — Basic dimensions of sieve openings
• GB/T 13290 Propylene and butadiene for industrial use — Liquid sampling method
• ISO 7911:1988 Analysis of commercial propane and butane (gas chromatography method) (equivalent adoption)

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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