ASTM D2597-94(1999)
(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
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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An American National Standard
Designation: D 2597 – 94 (Reapproved 1999)
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 D 2597; 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 (ϵ) 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 fraction, when present in the
n-Butane and 2,2-Dimethylpropane 0.01–100.0
Isopentane 0.01–15.0
sample, is 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
GPA Standard 2177 Analysis of Demethanized Hydrocar-
physical properties) of these fractions. Since this test method makes no
bon Liquid Mixtures Containing Nitrogen and Carbon
provision for determining physical properties, the physical properties
Dioxide by Gas Chromatography
needed can be determined by an extended analysis or agreed to by the
contracting parties.
3. Summary of Test Method
1.3 The values stated in SI units are to be regarded as the
3.1 Components to be determined in a demethanized hydro-
standard. The values given in parentheses are for information
carbon liquid mixture are physically separated by gas chroma-
only.
tography and compared to calibration data obtained under
1.4 This standard does not purport to address all of the
identical operating conditions.Afixed volume of sample in the
safety concerns, if any, associated with its use. It is the
liquid phase is isolated in a suitable sample inlet system and
responsibility of the user of this standard to establish appro-
entered onto the chromatographic column.
priate safety and health practices and determine the applica-
3.1.1 Components nitrogen/air through n-hexane are indi-
bility of regulatory limitations prior to use. For specific hazard
vidually separated with the carrier flow in the forward direc-
statements see Annex A3.
tion.The numerous heavy end components are grouped into an
irregular shape peak by reversing direction of carrier gas
2. Referenced Documents
throughthecolumnbymeansofaswitchingvalveimmediately
2.1 ASTM Standards:
following the elution of normal hexane. (See Fig. 1.) Samples
D 3700 PracticeforContainingHydrocarbonFluidSamples
that contain no heptanes plus fraction are analyzed until the
Using a Floating Piston Cylinder
final component has eluted with no reverse of carrier flow.
2.2 Other Standard:
3.1.2 An alternative to the single column backflush method
istheuseofaprecutcolumnwhichisbackflushedtoobtainthe
heptanes plus as a single peak at the beginning of the
This test method is under the jurisdiction of Committee D-2 on Petroleum
chromatogram. Two advantages of the alternate method are as
Products and Lubricants and is the direct responsibility of Subcommittee D02.H on
follows:(1)betterprecisioninmeasuringtheC plusportionof
Liquefied Petroleum Gas.
Current edition approved July 15, 1994. Published September 1994. Originally
published as D 2597 – 67T. Last previous edition D 2597 – 88.
2 3
Annual Book of ASTM Standards, Vol 05.02. Available from Gas Processors Assn., 6526 E. 60th St., Tulsa, OK 74145.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
D 2597 – 94 (1999)
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
the carrier gas stream ahead of the chromatographic column so
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
that delivered by the liquid sample valve in accordance with
FIG. 1 Chromatogram of Demethanized Hydrocarbon Liquid
5.1.2. (See Section 6 for further explanation of instrument
Mixture (Frontal Carrier Gas Flow ThroughN-Hexane, Reverse
Grouping Heptanes Plus) linearity check procedures.)
5.1.4 Chromatographic Columns:
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
detector to the recorder when using manual calculation meth-
4. Significance and Use
ods. The attenuation between steps shall be accurate to
4.1 The component distribution of hydrocarbon liquid mix-
60.5 %.
tures is often required as a specification analysis for these
5.1.6 Temperature Control—The chromatographic col-
materials.Wide use of these hydrocarbon mixtures as chemical
umn(s) and the detector shall be maintained at their respective
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
deflection of at least 0.5 mv for 1 mol % of n-butane in a
1.0-µL sample.
5.1.2 SampleInletSystem,Liquid—Aliquid sampling valve
shall be provided, capable of entrapping a fixed volume of
sample at a pressure at least 200 psi (1379 kPa) above the
FIG. 2 Chromatogram of Demethanized Hydrocarbon Liquid
vapor pressure of the sample at valve temperature, and intro-
Mixture (Precut Column Grouping Heptanes Plus, Frontal Carrier
ducing this fixed volume into the carrier gas stream ahead of Gas Flow Remaining Components)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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D 2597 – 94 (1999)
temperatures, constant to 60.3°C during the course of the
sample and corresponding reference standard runs.
5.2 Carrier Gas—Pressure-reducing and control devices to
give repeatable flow rates.
5.3 Recorder—Astrip chart recorder with a full-scale range
of 1 mv shall be required when using manual calculation
FIG. 3 Repressuring System and Chromatographic Valving with
methods.Amaximum pen response time of 1 s and a minimum
Floating Piston Cylinder
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)
for securing, containing, and transferring samples into a liquid
are required if the chromatogram is to be interpreted using
sample valve. (See Fig. 4 and Fig. 5.)
manual methods to obtain areas.
NOTE 5—Caution: This container is acceptable when the displacement
NOTE 2—A strip chart recorder is recommended for monitoring the
liquid does not appreciably affect the composition of the sample of
progress of the analysis if an electronic digital integrator without plotting
interest. Specifically, components such as CO or aromatic hydrocarbons
capability is in service.
are partially soluble in many displacement liquids and thus can compro-
5.4 Electronic Digital Integrator—Astrongly preferred and
mise the final analysis. This caution is of the utmost importance and
should be investigated prior to utilizing this technique.
recommended device for determining peak areas. This device
offers the highest degree of precision and operator conve-
6. Calibration
nience.
6.1 In conjunction with a calibration on any specific chro-
NOTE 3—Caution: Electronic digital integrators are able to integrate
matography, the linear range of the components of interest
peak areas by means of several different methods employing various
shall be determined. The linearity is established for any new
correction adjustments. The operator should be well versed in integrator
chromatograph and reestablished whenever the instrument has
operation, preventing improper handling and manipulation of data—
ultimately resulting in false information. undergone a major change (that is, replaced detectors, in-
creased sample size, switched column size, or dramatically
5.5 Ball and Disk Integrator—An alternative device in the
modified run parameters).
absence of an electronic digital integrator for determining peak
6.1.1 The preferred and more exacting procedure is to
areas. This device gives more precise areas than manual
prepareresponsecurves.Theprocedurefordevelopingthedata
methods and saves operator time in interpreting the chromato-
necessary to construct these response curves for all compo-
gram.
nents nitrogen through n-pentane is set forth in Annex A2.
5.6 Manometer—Well type, equipped with an accurately
6.1.2 A second procedure utilizes gravimetrically con-
graduated and easily readable scale covering the range from 0
structed standards of a higher concentration than is contained
to 900 mm of mercury. The manometer is required in order to
charge partial pressure samples of pure hydrocarbons when
determining response curves for linearity checks when using
the gas sampling valve.
5.7 VacuumPump—Shallhavethecapabilityofproducinga
vacuum of 0.1 mm of mercury absolute or less. Required for
linearity checks when using the gas sampling valve.
5.8 Sample Filter—An optional device to protect the liquid
sampling valve from scoring due to the presence of foreign
contaminates such as metal shavings, dirt, and so forth, in a
natural gas liquid (NGL) sample. The filter can be of a small
total volume, or an in-line type design and contain a
replaceable/disposable element.
NOTE 4—Caution: A filter can introduce error if not handled properly.
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 Piston Cylinder—A strongly preferred and
recommended device suitable for securing, containing, and
transferring samples into a liquid sample valve and which
preserves the integrity of the sample. (See Fig. 3 and Test
Method D 3700.)
5.9.2 Double-Valve Displacement Cylinder—An alternate
FIG. 4 Repressuring System and Chromatographic Valving with
device used in the absence of a floating piston cylinder suitable Double-Valve Displacement Cylinder
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
D 2597 – 94 (1999)
second (or third) gravimetrically determined standard (either
purity or blend) can then be run, using the originally obtained
response factors, which contain a concentration of individual
components exceeding the expected amounts in the unknowns.
When both (or all three) runs match their respective standards
within the precision guidelines allowed in Section 10, then the
instrument can be considered linear within that range.
NOTE 6—This test method omits the need of a gas sample valve on the
chromatographic instrument. However, several accurate primary NGL
standards are required and the exact point at which nonlinearity occurs is
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