ISO/DIS 25122:2026(en)
ISO/TC 47
Secretariat: JISC
Date: 2025-12-04
Ethylene and propylene for industrial use —Determination of traces of carbon monoxide and carbon dioxide —Gas chromatographic method
© ISO 2026
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Contents
Foreword
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Ethylene and Propylene for Industrial Use — Determination of Traces of Carbon Monoxide and Carbon Dioxide —Gas Chromatographic Method
1.0 Scope
This document specifies the gas chromatographic (GC) method for the determination of traces of carbon monoxide and carbon dioxide in ethylene and propylene for industrial use.
The method is applicable to ethylene and propylene having carbon monoxide and carbon dioxide concentrations greater than 0,5 mL/m3.
2.0 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 7382, Ethylene for industrial use — Sampling in the liquid and the gaseous phase
ISO 8563, Propylene and butadiene for industrial use — Sampling in the liquid phase
3.0 Terms and definitions
No terms and definitions need to be defined in this document.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
4.0 Principle
Under the conditions specified in this document, gaseous (or liquid vaporized) sample is introduced into the packed column by carrier gas through a gas sampling device. Carbon monoxide and carbon dioxide are separated from other components and converted into methane through a column of hydrogenation catalyst, which allows the use of a hydrogen flame ionization detector to make the final determination.
The reaction principles of converting carbon monoxide and carbon dioxide into methane are as follows:
The peak area of each impurity component is recorded and the quantification is carried out by external standard method.
5.0 Reagents
WARNING—The following gases are high-pressure compressed or highly flammable, which shall be paid attention to safe when used.
5.1 Nitrogen
Carrier gas and auxiliary gas, with a minimum purity of 99,999 % (volume fraction), dried and purified by silica gel and 5A molecular sieve.
5.1.1 Hydrogen
Combustion gas and reaction gas, with a minimum purity of 99,99 % (volume fraction), dried and purified by silica gel and 5A molecular sieve.
5.1.2 Air
Dried and purified, preferably by using silica gel and a 5A molecular sieve.
5.1.3 Gas standard
Gases with a known content of carbon monoxide and carbon dioxide, preferably close to that in the sample to be tested, and a base of nitrogen, helium or ethylene. These may be purchased from the market with certificates or be self-prepared. If self-prepared, the base gas shall be checked in advance under the conditions specified in this document. There shall be no peak outflow of impurities at the components to be measured, otherwise it shall be corrected.
6.0 Apparatus
6.1 Gas Chromatography
Any gas chromatograph equipped with a hydrogen flame ionization detector (FID) and operated according to suitable conditions may be used. The peak height produced by the instrument for impurities at the concentrations of 0,5 mL/m3 shall be at least twice greater than the height of the background noise. This document recommends two alternative operating conditions. Among them, system of condition 1 consists of one valve and two columns, the schematic diagram of device connection is shown in Figure 1, while system of condition 2 consists of two valves and three columns and the schematic diagram of the device connection is shown in Figure 2. Other sampling and blowback devices that meet the separation and quantification effects of this document may also be used.
Under condition 1, the existing of oxygen may interfere with the determination of carbon monoxide. Under condition 2, additional analytical column 2 enables effective separation between oxygen and carbon monoxide and eliminates the interference of oxygen.
Key
1 sample loop
2 sample in
3 vent
4 carrier gas 1 in
5 carrier gas 2 in
6 damping
7 pre-column
8 analytical column 1
9 methanizer
10 hydrogen in
11 FID
Figure 1 — Schematic diagram for condition 1 (sampling and back flushing state)
Key
1 sample loop
2 sample in
3 vent
4 carrier gas 1 in
5 carrier gas 2 in
6 damping
7 pre-column
8 analytical column 1
9 analytical column 2
10 methanizer
11 hydrogen in
12 FID
Figure 2 — Schematic diagram for condition 2 (sampling and back flushing state)
6.1.1 Column
The chromatographic columns and typical operating conditions recommended by this document are shown in Table 1. The typical chromatograms are shown in Figure 3 and Figure 4. Other columns and operating conditions that can provide equivalent separation and adequate limit of detection may also be used.
Table 1 — Columns and typical operating conditions for the determination of carbon monoxide and carbon dioxide
Operating conditions | Condition 1 | Condition 2 | |
Pre-column | Packing | Porapak Q packed column, 0,150 mm~0,180 mm (80 mesh~100 mesh) | Porapak Q packed column, 0,150 mm~0,180 mm (80 mesh~100 mesh) |
Length, m | 1,8 | 1,8 | |
Inner diameter, mm | 2 | 2 | |
Analytical column 1 | Packing | Porapak Q packed column, 0,150 mm~0,180 mm (80 mesh~100 mesh) | Porapak Q packed column, 0,150 mm~0,180 mm (80 mesh~100 mesh) |
Length, m | 1,8 | 1,0 | |
Inner diameter, mm | 2 | 2 | |
Analytical column 2 | Packing | — | Molecular sieve 13X packed column, 0,180 mm~0,250 mm (60 mesh~80 mesh) |
Length, m | — | 1,8 | |
Inner diameter, mm | — | 2 | |
Flow rate of carrier gas (N2), mL/min | 20 | ||
Column temperature, °C | 50 | ||
Column temperature holding time, min | 6 | 10 | |
Detector (FID) temperature, °C | 250 | ||
Flow rate of hydrogen, mL/min | 30 | ||
Flow rate of air, mL/min | 400 | ||
Valve box temperature, °C | 100 | ||
Injection volume, mL | 2,0 | ||
Ten-way valve backflush time, min | 2,2~2,3 | 2,7~2,9 | |
Six-way valve backflush time, min | — | 2,5 (on)/5,0 (off) | |
Key
1 carbon monoxide
2 methane
3 carbon dioxide
Figure 3 — Typical chromatogram of condition 1
Key
1 carbon dioxide
2 methane
3 carbon monoxide
Figure 4 — Typical chromatogram of condition 2
6.1.2 Methanizer
The methanizer is a device that converts carbon monoxide and carbon dioxide into methane by catalytic hydrogenation, which consists of a nickel catalytic hydrogenation column and a heating device. The recommended operating temperature is 350~400 °C and suitable hydrogen flow rate is needed to ensure that carbon monoxide and carbon dioxide are fully converted to methane.
6.1.3 Data processing equipment
Chromatographic workstation.
7.0 Sampling
Sampling shall be in accordance with ISO 7382 or ISO 8563.
8.0 Preparation of Apparatus
Install and age the column in the chromatograph according to the instrument operating instructions. Adjust the instrument to the operating conditions shown in Table 1 and start the measurement after the instrument is stable. The switching time of valve shall be properly adjusted according to the actual conditions of the instrument.
9.0 Calibration
9.1 Inject 2 mL of gas standard into the chromatograph with the gas injection valve under the specified conditions for measurement. Repeat the measurement twice and record the peak area of carbon monoxide and carbon dioxide. The difference in peak area between the two repeated measurements shall not be greater than 5 % of their mean value. Calculate the average peak area of the two measurements.
9.2 After the carbon dioxide flows out, switch the ten-way valve to backflush ethylene or propylene as soon as possible.
10.0 Procedure
10.1 Inject 2 mL of tested sample into the chromatograph with the gas injection valve under the same conditions as the gas standard determination. Repeat the measurement twice and record the peak area of carbon monoxide and carbon dioxide.
10.2 When injecting liquid propylene, a flash steam device or other suitable sample vaporization method shall be used to ensure that liquid propylene is completely vaporized. Prior sample introduction into the vaporizing device, ensure adequate sample pressure well above the vapour pressure of propylene to avoid gassing out the dissolved gases of high boiling points like carbon monoxide and carbon dioxide. In order to eliminate the interference of oxygen and carbon dioxide in the air, the system shall be fully replaced by sample when sampling and injecting.
11.0 Calculation
The content φi of carbon monoxide and carbon dioxide, in milliliters per cubic meter (mL/m3), is calculated, using Formula (1):
(1)
where
φs,i is content of carbon monoxide and carbon dioxide in the gas standard, mL/m3;
Ai is peak areas of carbon monoxide and carbon dioxide in the tested sample;
As,i is peak areas of carbon monoxide and carbon dioxide in the gas standard.
12.0 Reporting
Report the arithmetic mean of two repeated measurements as the analysis result to the nearest 0,1 mL/m3.
13.0 Precision
13.1 Repeatability (r)
The difference between two independent test results, obtained by the same operator with the same apparatus under constant operating conditions on identical test material would, in the long run, in the normal and correct operation of the test method, exceed the values given in Table 2 in only one case in twenty.
13.1.1 Reproducibility (R)
The difference between two independent test results, obtained by different operators working in different laboratories on identical test material would, in the long run, in the normal and correct operation of the test method, exceed the values given in Table 2 in only one case in twenty.
Table 2 — Precision statements a
Component | Repeatability b (r), mL/m3 | Reproducibility b (R), mL/m3 |
CO | 0,009 7x+0,032 | 0,107x0,651 |
CO2 | 0,021 7x+0,004 4 | 0,168x0,207 |
a Precision data is obtained for gaseous ethylene and propylene, and may not completely represent the analytical precision for liquefied matrix. b X is the average of the two results being compared. | ||
14.0 Quality Assurance
14.1 A quality control (QC) sample of known content of carbon monoxide and carbon dioxide shall be analysed periodically to ensure the accuracy of the results.
14.2 The QC sample shall be stable and representative with respect to the sample being analysed, which can be purchased with certificates or be self-prepared in 5.4.
15.0 Test report
The test report shall include the following information:
a) all information necessary for the complete identification of the sample;
b) a reference to this International Standard, i.e. ISO 25122;
c) the result of the test;
d) a statement of any experimental conditions which are regarded as optional;
e) ny deviation, by agreement or otherwise, from the procedure specified;
f) the date of the test.
