ASTM D2597-94(2004)
(Test Method)Standard Test Method for Analysis of Demethanized Hydrocarbon Liquid Mixtures Containing Nitrogen and Carbon Dioxide by Gas Chromatography
Standard Test Method for Analysis of Demethanized Hydrocarbon Liquid Mixtures Containing Nitrogen and Carbon Dioxide by Gas Chromatography
SIGNIFICANCE AND USE
The component distribution of hydrocarbon liquid mixtures is often required as a specification analysis for these materials. Wide use of these hydrocarbon mixtures as chemical feedstocks or as fuel require precise compositional data to ensure uniform quality of the reaction product. In addition, custody transfer of these products is often made on the basis of component analyses of liquid mixtures.
The component distribution data of hydrocarbon mixtures can be used to calculate physical properties, such as specific gravity, vapor pressure, molecular weight, and other important properties. Precision and accuracy of compositional data are extremely important when these data are used to calculate physical properties of these products.
SCOPE
1.1 This test method covers the analysis of demethanized liquid hydrocarbon streams containing nitrogen/air and carbon dioxide, and purity products such as an ethane/ propane mix that fall within the compositional ranges listed in Table 1. This test method is limited to mixtures containing less than 5 mol % of heptanes and heavier fractions.
1.2 The heptanes and heavier fraction, when present in the sample, is analyzed by either ( ) reverse flow of carrier gas after -hexane and peak grouping or ( ) precut column to elute heptanes and heavier first as a single peak. For purity mixes without heptanes and heavier no reverse of carrier flow is required. Note 1-In the case of unknown samples with a relatively large C plus or C plus fraction and where precise results are important, it is desirable to determine the molecular weight (or other pertinent physical properties) of these fractions. Since this test method makes no provision for determining physical properties, the physical properties needed can be determined by an extended analysis or agreed to by the contracting parties.
1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.4 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 and health practices and determine the applicability of regulatory limitations prior to use. For specific hazard statements see Annex A3.
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Standards Content (Sample)
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Designation: D2597 – 94 (Reapproved 2004)
Standard Test Method for
Analysis of Demethanized Hydrocarbon Liquid Mixtures
Containing Nitrogen and Carbon Dioxide by Gas
Chromatography
This standard is issued under the fixed designation D2597; 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.
TABLE 1 Components and Compositional Ranges Allowed
1. Scope
Concentration Range,
1.1 This test method covers the analysis of demethanized
Components
Mol %
liquid hydrocarbon streams containing nitrogen/air and carbon
Nitrogen 0.01–5.0
dioxide, and purity products, such as an ethane/propane mix
Carbon Dioxide 0.01–5.0
that fall within the compositional ranges listed in Table 1. This
Methane 0.01–5.0
Ethane 0.01–95.0
test method is limited to mixtures containing less than 5 mol %
Propane 0.01–100.0
of heptanes and heavier fractions.
Isobutane 0.01–100.0
1.2 The heptanes and heavier fractions, when present in the
n-Butane and 2,2-Dimethylpropane 0.01–100.0
Isopentane 0.01–15.0
sample, are analyzed by either (1) reverse flow of carrier gas
n-Pentane 0.01–15.0
after n-hexane and peak grouping or (2) precut column to elute
2,2-Dimethylbutane 0.01–0.5
heptanes and heavier first as a single peak. For purity mixes
2,3-Dimethylbutane and 2-Methylpentane
3-Methylpentane and Cyclopentane 0.01–15.0
without heptanes and heavier, no reverse of carrier flow is
n-Hexane
required.
Heptanes and Heavier 0.01–5.0
NOTE 1—Caution: In the case of unknown samples with a relatively
large C plus or C plus fraction and where precise results are important,
6 7
it is desirable to determine the molecular weight (or other pertinent
physical properties) of these fractions. Since this test method makes no D3700 Practice for Obtaining LPG Samples Using a Float-
provision for determining physical properties, the physical properties
ing Piston Cylinder
needed can be determined by an extended analysis or agreed to by the
2.2 GPA Standard:
contracting parties.
GPA Standard 2177 Analysis of Demethanized Hydrocar-
1.3 The values stated in SI units are to be regarded as the
bon Liquid Mixtures Containing Nitrogen and Carbon
standard. The values given in parentheses are for information
Dioxide by Gas Chromatography
only.
3. Summary of Test Method
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 3.1 Components to be determined in a demethanized hydro-
responsibility of the user of this standard to establish appro-
carbon liquid mixture are physically separated by gas chroma-
priate safety and health practices and determine the applica- tography and compared with calibration data obtained under
bility of regulatory limitations prior to use. For specific hazard identical operating conditions.Afixed volume of sample in the
statements see Annex A3. liquid phase is isolated in a suitable sample inlet system and
entered onto the chromatographic column.
2. Referenced Documents
3.1.1 Components nitrogen/air through n-hexane are indi-
2.1 ASTM Standards: vidually separated with the carrier flow in the forward direc-
tion.The numerous heavy end components are grouped into an
irregular shape peak by reversing direction of carrier gas
This test method is under the jurisdiction of ASTM Committee D02 on throughthecolumnbymeansofaswitchingvalveimmediately
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
following the elution of normal hexane. (See Fig. 1.) Samples
D02.H0 on Liquefied Petroleum Gas.
that contain no heptanes plus fraction are analyzed until the
Current edition approved May 1, 2004. Published May 2004. Originally
final component has eluted with no reverse of carrier flow.
approved in 1967. Last previous edition approved in 1999 as D2597 – 94 (1999).
DOI: 10.1520/D2597-94R04.
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
Standards volume information, refer to the standard’s Document Summary page on Available from Gas ProcessorsAssociation (GPA), 6526 E. 60th St.,Tulsa, OK
the ASTM website. 74145.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D2597 – 94 (2004)
5.1.2 Sample Inlet System, Liquid—Aliquid sampling valve
shall be provided, capable of entrapping a fixed volume of
sample at a pressure at least 1379 kPa (200 psi) above the
vapor pressure of the sample at valve temperature, and intro-
ducing this fixed volume into the carrier gas stream ahead of
the analyzing column. The fixed sample volume should not
exceed 1.0 µLand should be reproducible such that successive
runs agree within 62 % on each component peak area. The
liquid sampling valve is mounted exterior of any type heated
compartment and thus can operate at laboratory ambient
conditions.
5.1.3 Sample Inlet System, Gas (Instrument Linearity)—
Provision is to be made to introduce a gas phase sample into
FIG. 1 Chromatogram of Demethanized Hydrocarbon Liquid
the carrier gas stream ahead of the chromatographic column so
Mixture (Frontal Carrier Gas Flow ThroughN-Hexane, Reverse
Grouping Heptanes Plus) that linearity of the instrument can be estimated from response
curves. The fixed volume loop in the gas sample valve shall be
sized to deliver a total molar volume approximately equal to
3.1.2 An alternative to the single column backflush method
that delivered by the liquid sample valve in accordance with
istheuseofaprecutcolumnwhichisbackflushedtoobtainthe
5.1.2. (See Section 6 for further explanation of instrument
heptanes plus as a single peak at the beginning of the
linearity check procedures.)
chromatogram. Two advantages of the alternate method are as
5.1.4 Chromatographic Columns:
follows:(1)betterprecisioninmeasuringtheC plusportionof
5.1.4.1 Column No. 1—A partition column shall be pro-
the sample and (2) reduction in analysis time over the single
vided capable of separating nitrogen/air, carbon dioxide, and
column approach by approximately 40 %.
the hydrocarbons methane through normal hexane. (See Fig. 1
3.2 Thechromatogramisinterpretedbycomparingtheareas
and Fig. 2.) Separation of carbon dioxide shall be sufficient so
of component peaks obtained from the unknown sample with
that a 1-µL sample containing 0.01 mol % carbon dioxide will
correspondingareasobtainedfromarunofaselectedreference
produceameasurablepeakonthechromatogram.(Thesilicone
standard. Any component in the unknown suspected to be
200/500 column, containing a 27 to 30 weight % liquid phase
outside the linearity range of the detector, with reference to the
load, has proven satisfactory for this type of analysis.)
known amount of that component in the reference standard,
5.1.4.2 Column No. 2—A partition column similar to Col-
must be determined by a response curve. Peak height method
umn No. 1. It shall be of the same diameter as Column No. 1.
of integration can be used only if the chromatograph is
Thecolumnshallbeofanappropriatelengthtoclearlyseparate
operating in the linear range for all components analyzed.
the heptanes plus fraction from the hexanes and lighter
Linearity must be proved by peak height for all components
components.
when using peak height method. (See Section 6 for further
5.1.5 Attenuator—A multistep device shall be included in
explanation of instrument linearity check procedures.)
the detector output circuitry to attenuate the signal from the
4. Significance and Use
4.1 The component distribution of hydrocarbon liquid mix-
tures is often required as a specification analysis for these
materials.Wide use of these hydrocarbon mixtures as chemical
feedstocks or as fuel require precise compositional data to
ensure uniform quality of the reaction product. In addition,
custody transfer of these products is often made on the basis of
component analyses of liquid mixtures.
4.2 The component distribution data of hydrocarbon mix-
tures can be used to calculate physical properties, such as
specific gravity, vapor pressure, molecular weight, and other
important properties. Precision and accuracy of compositional
data are extremely important when these data are used to
calculate physical properties of these products.
5. Apparatus
5.1 Any gas chromatograph can be used that meets the
following specifications.
5.1.1 Detector—The detector shall be a thermal-
conductivity type. It must be sufficiently sensitive to produce a
FIG. 2 Chromatogram of Demethanized Hydrocarbon Liquid
deflection of at least 0.5 mv for 1 mol % of n-butane in a
Mixture (Precut Column Grouping Heptanes Plus, Frontal Carrier
1.0-µL sample. Gas Flow Remaining Components)
D2597 – 94 (2004)
detector to the recorder when using manual calculation meth- transferring samples into a liquid sample valve and that
ods. The attenuation between steps shall be accurate to preserves the integrity of the sample. (See Fig. 3 and Test
60.5 %. Method D3700.)
5.1.6 Temperature Control—The chromatographic col- 5.9.2 Double-Valve Displacement Cylinder—An alternate
umn(s) and the detector shall be maintained at their respective device used in the absence of a floating piston cylinder suitable
temperatures, constant to 60.3°C during the course of the for securing, containing, and transferring samples into a liquid
sample and corresponding reference standard runs. sample valve. (See Fig. 4 and Fig. 5.)
5.2 Carrier Gas—Pressure-reducing and control devices to
NOTE 5—Caution: This container is acceptable when the displacement
give repeatable flow rates.
liquid does not appreciably affect the composition of the sample of
5.3 Recorder—Astrip chart recorder with a full-scale range
interest. Specifically, components such as CO or aromatic hydrocarbons
of 1 mv shall be required when using manual calculation
are partially soluble in many displacement liquids and thus can compro-
mise the final analysis. This caution is of the utmost importance and
methods.Amaximum pen response time of 1 s and a minimum
should be investigated prior to utilizing this technique.
chart speed of 1 cm/min (0.5 in./min accepted) shall be
required. Faster speeds up to 10 cm/min (3 in./min accepted)
6. Calibration
are required if the chromatogram is to be interpreted using
6.1 In conjunction with a calibration on any specific chro-
manual methods to obtain areas.
matography, the linear range of the components of interest
NOTE 2—A strip chart recorder is recommended for monitoring the
shall be determined. The linearity is established for any new
progress of the analysis if an electronic digital integrator without plotting
chromatograph and reestablished whenever the instrument has
capability is in service.
undergone a major change (that is, replaced detectors, in-
5.4 Electronic Digital Integrator—Astrongly preferred and
creased sample size, switched column size, or dramatically
recommended device for determining peak areas. This device
modified run parameters).
offers the highest degree of precision and operator conve-
6.1.1 The preferred and more exacting procedure is to
nience.
prepareresponsecurves.Theprocedurefordevelopingthedata
necessary to construct these response curves for all compo-
NOTE 3—Caution: Electronic digital integrators are able to integrate
nents nitrogen through n-pentane is set forth in Annex A2.
peak areas by means of several different methods employing various
correction adjustments. The operator should be well versed in integrator 6.1.2 A second procedure utilizes gravimetrically con-
operation, preventing improper handling and manipulation of data—
structed standards of a higher concentration than is contained
ultimately resulting in false information.
in the unknown. A set of response factors are first determined
for all components by means of a blend mix. (See 6.3.) A
5.5 Ball and Disk Integrator—An alternative device in the
second (or third) gravimetrically determined standard (either
absence of an electronic digital integrator for determining peak
purity or blend) can then be run, using the originally obtained
areas. This device gives more precise areas than manual
response factors, which contain a concentration of individual
methods and saves operator time in interpreting the chromato-
components exceeding the expected amounts in the unknowns.
gram.
When both (or all three) runs match their respective standards
5.6 Manometer—Well type, equipped with an accurately
within the precision guidelines allowed in Section 10, then the
graduated and easily readable scale covering the range from 0
instrument can be considered linear within that range.
to 900 mm Hg. The manometer is required in order to charge
partial pressure samples of pure hydrocarbons when determin-
NOTE 6—This test method omits the need of a gas sample valve on the
ing response curves for linearity checks when using the gas
chromatographic instrument. However, several accurate primary NGL
sampling valve. standards are required and the exact point at which nonlinearity occurs is
not determined.
5.7 VacuumPump—Shallhavethecapabilityofproducinga
vacuum of 0.1 mm Hg absolute or less. Required for linearity
6.2 For routine analysis using this procedure, it is intended
checks when using the gas sampling valve.
that calibration be accomplished by use of a selected reference
5.8 Sample Filter—An optional device to protect the liquid
standard containing known amounts of all components of
sampling valve from scoring due to the presence of foreign
interest. It is recommended that the reference standard compo-
contaminates, such as metal shavings, dirt, and so forth, in a
sition be similar to the one shown in Table 2, or closely
natural gas liquid (NGL) sample. The filter can be of a small
resemble the composition of expected unknowns. This ap-
total volume, or an in-line type design and contain a
proach is valid for all components that lie within the proven
replaceable/disposable element.
linear range for a specific gas chromatograph.
NOTE 4—Caution: A filter can introduce error if not handled properly.
NOTE 7—Check the reference standard for validity when received and
The filter should be clean and free of any residual product from previous
samples so that a buildup of heavy end hydrocarbon components does not
result. (Can be accomplished by a heating/cooling process or inert gas
purge,etc.)Thefilterelementshouldbe15-µmsizeorlargersothatduring
the purging process, NGL is not flashed, preventing fractionation and
bubble formation.
5.9 Sample Containers:
5.9.1 Floating Pis
...
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