ASTM D1945-14(2019)
(Test Method)Standard Test Method for Analysis of Natural Gas by Gas Chromatography
Standard Test Method for Analysis of Natural Gas by Gas Chromatography
SIGNIFICANCE AND USE
4.1 This test method is of significance for providing data for calculating physical properties of the sample, such as heating value and relative density, or for monitoring the concentrations of one or more of the components in a mixture.
SCOPE
1.1 This test method covers the determination of the chemical composition of natural gases and similar gaseous mixtures within the range of composition shown in Table 1. This test method may be abbreviated for the analysis of lean natural gases containing negligible amounts of hexanes and higher hydrocarbons, or for the determination of one or more components, as required.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D1945 − 14 (Reapproved 2019)
Standard Test Method for
Analysis of Natural Gas by Gas Chromatography
This standard is issued under the fixed designation D1945; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* calibration data obtained under identical operating conditions
from a reference standard mixture of known composition. The
1.1 This test method covers the determination of the chemi-
numerous heavy-end components of a sample can be grouped
cal composition of natural gases and similar gaseous mixtures
into irregular peaks by reversing the direction of the carrier gas
within the range of composition shown in Table 1. This test
through the column at such time as to group the heavy ends
method may be abbreviated for the analysis of lean natural
either as C and heavier, C and heavier, or C and heavier. The
5 6 7
gases containing negligible amounts of hexanes and higher
composition of the sample is calculated by comparing either
hydrocarbons, or for the determination of one or more
the peak heights, or the peak areas, or both, with the corre-
components, as required.
sponding values obtained with the reference standard.
1.2 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
4. Significance and Use
standard.
4.1 This test method is of significance for providing data for
1.3 This standard does not purport to address all of the
calculating physical properties of the sample, such as heating
safety concerns, if any, associated with its use. It is the
value and relative density, or for monitoring the concentrations
responsibility of the user of this standard to establish appro-
of one or more of the components in a mixture.
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
5. Apparatus
1.4 This international standard was developed in accor-
5.1 Detector—The detector shall be a thermal-conductivity
dance with internationally recognized principles on standard-
type, or its equivalent in sensitivity and stability. The thermal
ization established in the Decision on Principles for the
conductivity detector must be sufficiently sensitive to produce
Development of International Standards, Guides and Recom-
a signal of at least 0.5 mV for 1 mol % n-butane in a 0.25-mL
mendations issued by the World Trade Organization Technical
sample.
Barriers to Trade (TBT) Committee.
5.2 Recording Instruments—Either strip-chart recorders or
2. Referenced Documents
electronic integrators, or both, are used to display the separated
2.1 ASTM Standards:
components. Although a strip-chart recorder is not required
D2597 Test Method for Analysis of Demethanized Hydro-
when using electronic integration, it is highly desirable for
carbon Liquid Mixtures Containing Nitrogen and Carbon
evaluation of instrument performance.
Dioxide by Gas Chromatography (Withdrawn 2016)
5.2.1 The recorder shall be a strip-chart recorder with a
E260 Practice for Packed Column Gas Chromatography
full-range scale of 5 mV or less (1 mV preferred). The width of
the chart shall be not less than 150 mm. A maximum pen
3. Summary of Test Method
response time of 2 s (1 s preferred) and a minimum chart speed
3.1 Components in a representative sample are physically
of 10 mm/min shall be required. Faster speeds up to 100 mm-
separated by gas chromatography (GC) and compared to
⁄min are desirable if the chromatogram is to be interpreted
using manual methods to obtain areas.
This test method is under the jurisdiction of ASTM Committee D03 on Gaseous
5.2.2 Electronic or Computing Integrators—Proof of sepa-
Fuels and is the direct responsibility of Subcommittee D03.06.01 on Analysis of
ration and response equivalent to that for a recorder is required
Major Constituents by Gas Chromatography.
for displays other than by chart recorder. Baseline tracking
Current edition approved Dec. 1, 2019. Published January 2020. Originally
approved in 1962. Last previous edition approved in 2014 as D1945 – 14. DOI:
with tangent skim peak detection is recommended.
10.1520/D1945-14R19.
5.3 Attenuator—If the chromatogram is to be interpreted
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
using manual methods, an attenuator must be used with the
Standards volume information, refer to the standard’s Document Summary page on
detector output signal to maintain maximum peaks within the
the ASTM website.
3 recorder chart range. The attenuator must be accurate to within
The last approved version of this historical standard is referenced on
www.astm.org. 0.5 % between the attenuator range steps.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D1945 − 14 (2019)
TABLE 1 Natural Gas Components and Range of
5.4.3 An optional manifold arrangement for entering
Composition Covered
vacuum samples is shown in Fig. 1.
Component Mol %
5.5 Column Temperature Control:
Helium 0.01 to 10
5.5.1 Isothermal—When isothermal operation is used,
Hydrogen 0.01 to 10
maintain the analyzer columns at a temperature constant to
Oxygen 0.01 to 20
Nitrogen 0.01 to 100
0.3 °C during the course of the sample run and corresponding
Carbon dioxide 0.01 to 20
reference run.
Methane 0.01 to 100
Ethane 0.01 to 100 5.5.2 Temperature Programming—Temperature program-
Hydrogen sulfide 0.3 to 30
ming may be used, as feasible. The oven temperature shall not
Propane 0.01 to 100
exceed the recommended temperature limit for the materials in
Isobutane 0.01 to 10
n-Butane 0.01 to 10 the column.
Neopentane 0.01 to 2
5.6 Detector Temperature Control—Maintain the detector
Isopentane 0.01 to 2
n-Pentane 0.01 to 2 temperature at a temperature constant to 0.3 °C during the
Hexane isomers 0.01 to 2
course of the sample run and the corresponding reference run.
Heptanes+ 0.01 to 1
The detector temperature shall be equal to or greater than the
maximum column temperature.
5.7 Carrier Gas Controls—The instrument shall be
5.4 Sample Inlet System:
equipped with suitable facilities to provide a flow of carrier gas
5.4.1 The sample inlet system shall be constructed of
through the analyzer and detector at a flow rate that is constant
materials that are inert and nonadsorptive with respect to the
to 1 % throughout the analysis of the sample and the reference
components in the sample. The preferred material of construc-
standard. The purity of the carrier gas may be improved by
tion is stainless steel. Copper, brass, and other copper-bearing
flowing the carrier gas through selective filters prior to its entry
alloys are unacceptable. The sample inlet system from the
into the chromatograph.
cylinder valve to the GC column inlet must be maintained at a
5.8 Columns:
temperature constant to 61 °C.
5.8.1 The columns shall be constructed of materials that are
5.4.2 Provision must be made to introduce into the carrier
inert and nonadsorptive with respect to the components in the
gas ahead of the analyzing column a gas-phase sample that has
sample. The preferred material of construction is stainless
been entrapped in a fixed volume loop or tubular section. The
steel. Copper and copper-bearing alloys are unacceptable.
fixed loop or section shall be so constructed that the total
5.8.2 An adsorption-type column and a partition-type col-
volume, including dead space, shall not normally exceed
umn may be used to make the analysis.
0.5 mL at 100 kPa. If increased accuracy of the hexanes and
NOTE 2—See Practice E260.
heavier portions of the analysis is required, a larger sample size
5.8.2.1 Adsorption Column—This column must completely
may be used (see Test Method D2597). The sample volume
separate oxygen, nitrogen, and methane. A 13X molecular
must be reproducible such that successive runs agree within
sieve 80/100 mesh is recommended for direct injection. A 5A
1 % on each component. A flowing sample inlet system is
column can be used if a pre-cut column is present to remove
acceptable as long as viscosity effects are accounted for.
interfering hydrocarbons. If a recorder is used, the recorder pen
NOTE 1—The sample size limitation of 0.5 mL or smaller is selected
must return to the baseline between each successive peak. The
relative to linearity of detector response, and efficiency of column
resolution (R) must be 1.5 or greater as calculated in the
separation. Larger samples may be used to determine low-quantity
components to increase measurement accuracy. following equation:
FIG. 1 Suggested Manifold Arrangement for Entering Vacuum Samples
D1945 − 14 (2019)
x 2 x 5.11 Vacuum Gauge—Any type of vacuum gauge may be
2 1
R~1,2! 5 × 2, (1)
y 1y used which has a resolution of 0.14 kPa or better and covers the
2 1
range of 0 to 120 kPa or larger.
where x , x are the retention times and y , y are the peak
1 2 1 2
5.12 Vacuum Pump—Must have the capability of producing
widths. Fig. 2 illustrates the calculation for resolution. Fig. 3 is
a vacuum of 0.14 kPa absolute or less.
a chromatogram obtained with an adsorption column.
5.8.2.2 Partition Column—This column must separate eth-
6. Preparation of Apparatus
ane through pentanes and carbon dioxide. If a recorder is used,
the recorder pen must return to the base line between each peak
6.1 Linearity Check—To establish linearity of response for
for propane and succeeding peaks, and to base line within 2 %
the thermal conductivity detector, it is necessary to complete
of full-scale deflection for components eluted ahead of
the following procedure:
propane, with measurements being at the attenuation of the
6.1.1 The major component of interest (methane for natural
peak. Separation of carbon dioxide must be sufficient so that a
gas) is charged to the chromatograph by way of the fixed-size
0.25-mL sample containing 0.1-mol % carbon dioxide will
sample loop at partial pressure increments of 13 kPa from 13
produce a clearly measurable response. The resolution (R)
to 100 kPa or the prevailing atmospheric pressure.
must be 1.5 or greater as calculated in the above equation. The
6.1.2 The integrated peak responses for the area generated at
separation should be completed within 40 min, including
each of the pressure increments are plotted versus their partial
reversal of flow after n-pentane to yield a group response for
pressure (see Fig. 9).
hexanes and heavier components. Figs. 4-6 are examples of
6.1.3 The plotted results should yield a straight line. A
chromatograms obtained on some of the suitable partition
perfectly linear response would display a straight line at a 45°
columns.
angle using the logarithmic values.
5.8.3 General—Other column packing materials that pro-
6.1.4 Any curved line indicates the fixed volume sample
vide satisfactory separation of components of interest may be
loop is too large. A smaller loop size should replace the fixed
used (see Fig. 7). In multicolumn applications, it is preferred to
volume loop and 6.1.1 through 6.1.4 should be repeated (see
use front-end backflush of the heavy ends.
Fig. 9).
6.1.5 The linearity over the range of interest must be known
NOTE 3—The chromatograms in Figs. 3-8 are only illustrations of
for each component. It is useful to construct a table noting the
typical separations. The operating conditions, including columns, are also
typical and are subject to optimization by competent personnel.
response factor deviation in changing concentration. (See
Table 2 and Table 3).
5.9 Drier—Unless water is known not to interfere in the
6.1.6 It should be noted that nitrogen, methane, and ethane
analysis, a drier must be provided in the sample entering
exhibit less than 1 % compressibility at atmospheric pressure.
system, ahead of the sample valve. The drier must remove
Other natural gas components do exhibit a significant com-
moisture without removing selective components to be deter-
pressibility at pressures less than atmospheric.
mined in the analysis.
6.1.7 Most components that have vapor pressures of less
NOTE 4—See A2.2 for preparation of a suitable drier.
than 100 kPa cannot be used as a pure gas for a linearity study
5.10 Valves—Valves or sample splitters, or both, are re- because they will not exhibit sufficient vapor pressure for a
quired to permit switching, backflushing, or for simultaneous vacuum gauge reading to 100 kPa. For these components, a
analysis. mixture with nitrogen or methane can be used to establish a
FIG. 2 Calculation for Resolution
D1945 − 14 (2019)
FIG. 3 Separation Column for Oxygen, Nitrogen, and Methane (See Annex A2)
FIG. 4 Chromatogram of Natural Gas (BMEE Column) (See Annex A2)
partial pressure that can extend the total pressure to 100 kPa. where:
Using Table 4 for vapor pressures at 38 °C, calculate the
B = blend pressure, max, kPa;
maximum pressure to which a given component can be blended
V = vapor pressure, kPa;
with nitrogen as follows: i = mol %;
P = partial pressure, kPa; and
B 5 100 × V /i (2)
~ !
M = vacuum gauge pressure, kPa.
P 5 ~i × M!/100 (3)
D1945 − 14 (2019)
FIG. 5 Chromatogram of Natural Gas (Silicone 200/500 Column) (See Annex A2)
FIG. 6 Chromatogram of Natural Gas (See Annex A2)
6.2 Procedure for Linearity Check: 6.2.2 Carefully open the needle valve to admit the pure
6.2.1 Connect the pure-component source to the sample- component up to 13 kPa of partial pressure.
entry system. Evacuate the sample-entry system and observe
6.2.3 Record the exact partial pressure and actuate the
the vacuum gauge for leaks. (See Fig. 1 for a suggested
sample valve to place the sample onto the column. Record the
manifold arrangement.) The sample-entry system must be
peak area of the pure component.
vacuum tight.
D1945 − 14 (2019)
FIG. 7 Chromatogram of Natural Gas (Multi-Column Application) (See Annex A2)
FIG. 8 Separation of Helium and Hydrogen
6.2.4 Repeat 6.2.3 for 26, 39, 52, 65, 78, and 91 kPa on the 6.2.6 An alternative method is to obtain a blend of all the
vacuum gauge, recording the peak area obtained for sample components and charge the
...
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