1、Designation: D 2597 94 (Reapproved 2004)An American National StandardStandard Test Method forAnalysis of Demethanized Hydrocarbon Liquid MixturesContaining Nitrogen and Carbon Dioxide by GasChromatography1This standard is issued under the fixed designation D 2597; the number immediately following th
2、e designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers
3、 the analysis of demethanizedliquid hydrocarbon streams containing nitrogen/air and carbondioxide, and purity products, such as an ethane/propane mixthat fall within the compositional ranges listed in Table 1. Thistest method is limited to mixtures containing less than 5 mol %of heptanes and heavier
4、 fractions.1.2 The heptanes and heavier fractions, when present in thesample, are analyzed by either (1) reverse flow of carrier gasafter n-hexane and peak grouping or (2) precut column to eluteheptanes and heavier first as a single peak. For purity mixeswithout heptanes and heavier, no reverse of c
5、arrier flow isrequired.NOTE 1Caution: In the case of unknown samples with a relativelylarge C6plus or C7plus fraction and where precise results are important,it is desirable to determine the molecular weight (or other pertinentphysical properties) of these fractions. Since this test method makes nop
6、rovision for determining physical properties, the physical propertiesneeded can be determined by an extended analysis or agreed to by thecontracting parties.1.3 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.4 This standard
7、does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For specific hazardstatements se
8、e Annex A3.2. Referenced Documents2.1 ASTM Standards:2D 3700 Practice for Obtaining LPG Samples Using a Float-ing Piston Cylinder2.2 GPA Standard:3GPA Standard 2177 Analysis of Demethanized Hydrocar-bon Liquid Mixtures Containing Nitrogen and CarbonDioxide by Gas Chromatography3. Summary of Test Met
9、hod3.1 Components to be determined in a demethanized hydro-carbon liquid mixture are physically separated by gas chroma-tography and compared with calibration data obtained underidentical operating conditions. A fixed volume of sample in theliquid phase is isolated in a suitable sample inlet system
10、andentered onto the chromatographic column.3.1.1 Components nitrogen/air through n-hexane are indi-vidually separated with the carrier flow in the forward direc-tion. The numerous heavy end components are grouped into anirregular shape peak by reversing direction of carrier gasthrough the column by
11、means of a switching valve immediatelyfollowing the elution of normal hexane. (See Fig. 1.) Samplesthat contain no heptanes plus fraction are analyzed until thefinal component has eluted with no reverse of carrier flow.1This test method is under the jurisdiction of Committee D02 on PetroleumProducts
12、 and Lubricants and is the direct responsibility of Subcommittee D02.H0 onLiquefied Petroleum Gas.Current edition approved May 1, 2004. Published May 2004. Originallyapproved in 1967. Last previous edition approved in 1999 as D 2597 94 (1999).2For referenced ASTM standards, visit the ASTM website, w
13、ww.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from Gas Processors Association (GPA), 6526 E. 60th St., Tulsa, OK74145.TABLE 1 Components and Compositiona
14、l Ranges AllowedComponentsConcentration Range,Mol %Nitrogen 0.015.0Carbon Dioxide 0.015.0Methane 0.015.0Ethane 0.0195.0Propane 0.01100.0Isobutane 0.01100.0n-Butane and 2,2-Dimethylpropane 0.01100.0Isopentane 0.0115.0n-Pentane 0.0115.02,2-Dimethylbutane 0.010.52,3-Dimethylbutane and 2-Methylpentane3-
15、Methylpentane and Cyclopentane 0.0115.0n-HexaneHeptanes and Heavier 0.015.01Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.2 An alternative to the single column backflush methodis the use of a precut column which is backflushed t
16、o obtain theheptanes plus as a single peak at the beginning of thechromatogram. Two advantages of the alternate method are asfollows: (1) better precision in measuring the C7plus portion ofthe sample and (2) reduction in analysis time over the singlecolumn approach by approximately 40 %.3.2 The chro
17、matogram is interpreted by comparing the areasof component peaks obtained from the unknown sample withcorresponding areas obtained from a run of a selected referencestandard. Any component in the unknown suspected to beoutside the linearity range of the detector, with reference to theknown amount of
18、 that component in the reference standard,must be determined by a response curve. Peak height methodof integration can be used only if the chromatograph isoperating in the linear range for all components analyzed.Linearity must be proved by peak height for all componentswhen using peak height method
19、. (See Section 6 for furtherexplanation of instrument linearity check procedures.)4. Significance and Use4.1 The component distribution of hydrocarbon liquid mix-tures is often required as a specification analysis for thesematerials. Wide use of these hydrocarbon mixtures as chemicalfeedstocks or as
20、 fuel require precise compositional data toensure uniform quality of the reaction product. In addition,custody transfer of these products is often made on the basis ofcomponent analyses of liquid mixtures.4.2 The component distribution data of hydrocarbon mix-tures can be used to calculate physical
21、properties, such asspecific gravity, vapor pressure, molecular weight, and otherimportant properties. Precision and accuracy of compositionaldata are extremely important when these data are used tocalculate physical properties of these products.5. Apparatus5.1 Any gas chromatograph can be used that
22、meets thefollowing specifications.5.1.1 DetectorThe detector shall be a thermal-conductivity type. It must be sufficiently sensitive to produce adeflection of at least 0.5 mv for 1 mol % of n-butane in a1.0-L sample.5.1.2 Sample Inlet System, LiquidA liquid sampling valveshall be provided, capable o
23、f entrapping a fixed volume ofsample at a pressure at least 1379 kPa (200 psi) above thevapor pressure of the sample at valve temperature, and intro-ducing this fixed volume into the carrier gas stream ahead ofthe analyzing column. The fixed sample volume should notexceed 1.0 L and should be reprodu
24、cible such that successiveruns agree within 62 % on each component peak area. Theliquid sampling valve is mounted exterior of any type heatedcompartment and thus can operate at laboratory ambientconditions.5.1.3 Sample Inlet System, Gas (Instrument Linearity)Provision is to be made to introduce a ga
25、s phase sample intothe carrier gas stream ahead of the chromatographic column sothat linearity of the instrument can be estimated from responsecurves. The fixed volume loop in the gas sample valve shall besized to deliver a total molar volume approximately equal tothat delivered by the liquid sample
26、 valve in accordance with5.1.2. (See Section 6 for further explanation of instrumentlinearity check procedures.)5.1.4 Chromatographic Columns:5.1.4.1 Column No. 1A partition column shall be pro-vided capable of separating nitrogen/air, carbon dioxide, andthe hydrocarbons methane through normal hexan
27、e. (See Fig. 1and Fig. 2.) Separation of carbon dioxide shall be sufficient sothat a 1-L sample containing 0.01 mol % carbon dioxide willproduce a measurable peak on the chromatogram. (The silicone200/500 column, containing a 27 to 30 weight % liquid phaseload, has proven satisfactory for this type
28、of analysis.)5.1.4.2 Column No. 2A partition column similar to Col-umn No. 1. It shall be of the same diameter as Column No. 1.The column shall be of an appropriate length to clearly separatethe heptanes plus fraction from the hexanes and lightercomponents.5.1.5 AttenuatorA multistep device shall be
29、 included inthe detector output circuitry to attenuate the signal from theFIG. 1 Chromatogram of Demethanized Hydrocarbon LiquidMixture (Frontal Carrier Gas Flow Through N-Hexane, ReverseGrouping Heptanes Plus)FIG. 2 Chromatogram of Demethanized Hydrocarbon LiquidMixture (Precut Column Grouping Hept
30、anes Plus, Frontal CarrierGas Flow Remaining Components)D 2597 94 (2004)2detector to the recorder when using manual calculation meth-ods. The attenuation between steps shall be accurate to60.5 %.5.1.6 Temperature ControlThe chromatographic col-umn(s) and the detector shall be maintained at their res
31、pectivetemperatures, constant to 60.3C during the course of thesample and corresponding reference standard runs.5.2 Carrier GasPressure-reducing and control devices togive repeatable flow rates.5.3 RecorderA strip chart recorder with a full-scale rangeof 1 mv shall be required when using manual calc
32、ulationmethods. A maximum pen response time of 1 s and a minimumchart speed of 1 cm/min (0.5 in./min accepted) shall berequired. Faster speeds up to 10 cm/min (3 in./min accepted)are required if the chromatogram is to be interpreted usingmanual methods to obtain areas.NOTE 2A strip chart recorder is
33、 recommended for monitoring theprogress of the analysis if an electronic digital integrator without plottingcapability is in service.5.4 Electronic Digital IntegratorA strongly preferred andrecommended device for determining peak areas. This deviceoffers the highest degree of precision and operator
34、conve-nience.NOTE 3Caution: Electronic digital integrators are able to integratepeak areas by means of several different methods employing variouscorrection adjustments. The operator should be well versed in integratoroperation, preventing improper handling and manipulation of dataultimately resulti
35、ng in false information.5.5 Ball and Disk IntegratorAn alternative device in theabsence of an electronic digital integrator for determining peakareas. This device gives more precise areas than manualmethods and saves operator time in interpreting the chromato-gram.5.6 ManometerWell type, equipped wi
36、th an accuratelygraduated and easily readable scale covering the range from 0to 900 mm Hg. The manometer is required in order to chargepartial pressure samples of pure hydrocarbons when determin-ing response curves for linearity checks when using the gassampling valve.5.7 Vacuum PumpShall have the c
37、apability of producing avacuum of 0.1 mm Hg absolute or less. Required for linearitychecks when using the gas sampling valve.5.8 Sample FilterAn optional device to protect the liquidsampling valve from scoring due to the presence of foreigncontaminates, such as metal shavings, dirt, and so forth, in
38、 anatural gas liquid (NGL) sample. The filter can be of a smalltotal volume, or an in-line type design and contain areplaceable/disposable element.NOTE 4Caution: A filter can introduce error if not handled properly.The filter should be clean and free of any residual product from previoussamples so t
39、hat a buildup of heavy end hydrocarbon components does notresult. (Can be accomplished by a heating/cooling process or inert gaspurge, etc.) The filter element should be 15-m size or larger so that duringthe purging process, NGL is not flashed, preventing fractionation andbubble formation.5.9 Sample
40、 Containers:5.9.1 Floating Piston CylinderA strongly preferred andrecommended device suitable for securing, containing, andtransferring samples into a liquid sample valve and thatpreserves the integrity of the sample. (See Fig. 3 and TestMethod D 3700.)5.9.2 Double-Valve Displacement CylinderAn alte
41、rnatedevice used in the absence of a floating piston cylinder suitablefor securing, containing, and transferring samples into a liquidsample valve. (See Fig. 4 and Fig. 5.)NOTE 5Caution: This container is acceptable when the displacementliquid does not appreciably affect the composition of the sampl
42、e ofinterest. Specifically, components such as CO2or aromatic hydrocarbonsare partially soluble in many displacement liquids and thus can compro-mise the final analysis. This caution is of the utmost importance andshould be investigated prior to utilizing this technique.6. Calibration6.1 In conjunct
43、ion with a calibration on any specific chro-matography, the linear range of the components of interestshall be determined. The linearity is established for any newchromatograph and reestablished whenever the instrument hasundergone a major change (that is, replaced detectors, in-creased sample size,
44、 switched column size, or dramaticallymodified run parameters).6.1.1 The preferred and more exacting procedure is toprepare response curves. The procedure for developing the datanecessary to construct these response curves for all compo-nents nitrogen through n-pentane is set forth in Annex A2.6.1.2
45、 A second procedure utilizes gravimetrically con-structed standards of a higher concentration than is containedin the unknown. A set of response factors are first determinedfor all components by means of a blend mix. (See 6.3.) Asecond (or third) gravimetrically determined standard (eitherpurity or
46、blend) can then be run, using the originally obtainedresponse factors, which contain a concentration of individualcomponents exceeding the expected amounts in the unknowns.When both (or all three) runs match their respective standardswithin the precision guidelines allowed in Section 10, then theins
47、trument can be considered linear within that range.NOTE 6This test method omits the need of a gas sample valve on thechromatographic instrument. However, several accurate primary NGLstandards are required and the exact point at which nonlinearity occurs isnot determined.6.2 For routine analysis usin
48、g this procedure, it is intendedthat calibration be accomplished by use of a selected referencestandard containing known amounts of all components ofinterest. It is recommended that the reference standard compo-sition be similar to the one shown in Table 2, or closelyresemble the composition of expe
49、cted unknowns. This ap-proach is valid for all components that lie within the provenlinear range for a specific gas chromatograph.NOTE 7Check the reference standard for validity when received andFIG. 3 Repressuring System and Chromatographic Valving withFloating Piston CylinderD 2597 94 (2004)3periodically thereafter. Annex A1 details one procedure for making thevalidity check.6.3 Using the selected liquid reference standard, obtain achromatogram as outlined in Section 7.6.3.1 Determine peak areas (or peak heights) from thechromatogram for a
