1、Designation: D 1945 03Standard Test Method forAnalysis of Natural Gas by Gas Chromatography1This standard is issued under the fixed designation D 1945; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A nu
2、mber in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the determination of the chemi-cal composition of natural gases and similar gaseous mixtureswithin the range of
3、 composition shown in Table 1. This testmethod may be abbreviated for the analysis of lean naturalgases containing negligible amounts of hexanes and higherhydrocarbons, or for the determination of one or more compo-nents, as required.1.2 The values stated in SI units are to be regarded as thestandar
4、d. The values given in parentheses are for informationonly.1.3 This standard 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-bi
5、lity of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 2597 Test Method for Analysis of Demethanized Hydro-carbon Liquid Mixtures Containing Nitrogen and CarbonDioxide by Gas Chromatography2D 3588 Practice for Calculating Heat Value, Compressibil-ity Factor, and Rela
6、tive Density (Specific Gravity) ofGaseous Fuels3E 260 Practice for Packed Column Gas Chromatography43. Summary of Test Method3.1 Components in a representative sample are physicallyseparated by gas chromatography (GC) and compared tocalibration data obtained under identical operating conditionsfrom
7、a reference standard mixture of known composition. Thenumerous heavy-end components of a sample can be groupedinto irregular peaks by reversing the direction of the carrier gasthrough the column at such time as to group the heavy endseither as C5and heavier, C6and heavier, or C7and heavier. Thecompo
8、sition of the sample is calculated by comparing eitherthe peak heights, or the peak areas, or both, with the corre-sponding values obtained with the reference standard.4. Significance and Use4.1 This test method is of significance for providing data forcalculating physical properties of the sample,
9、such as heatingvalue and relative density, or for monitoring the concentrationsof one or more of the components in a mixture.5. Apparatus5.1 DetectorThe detector shall be a thermal-conductivitytype, or its equivalent in sensitivity and stability. The thermalconductivity detector must be sufficiently
10、 sensitive to producea signal of at least 0.5 mV for 1 mol % n-butane in a 0.25-mLsample.5.2 Recording InstrumentsEither strip-chart recorders orelectronic integrators, or both, are used to display the separatedcomponents. Although a strip-chart recorder is not requiredwhen using electronic integrat
11、ion, it is highly desirable forevaluation of instrument performance.5.2.1 The recorder shall be a strip-chart recorder with afull-range scale of 5 mV or less (1 mV preferred). The width ofthe chart shall be not less than 150 mm. A maximum penresponse time of2s(1spreferred) and a minimum chart speedo
12、f 10 mm/min shall be required. Faster speeds up to 100mm/min are desirable if the chromatogram is to be interpretedusing manual methods to obtain areas.1This test method is under the jurisdiction of ASTM Committee D03 on GaseousFuels and is the direct responsibility of Subcommittee D03.07 on Analysi
13、s ofChemical Composition of Gaseous Fuels.Current edition approved May 10, 2003. Published July 2003. Originallyapproved in 1962. Last previous edition approved in 2001 as D194596(2001).2Annual Book of ASTM Standards, Vol 05.02.3Annual Book of ASTM Standards, Vol 05.05.4Annual Book of ASTM Standards
14、 Vol 14.02.TABLE 1 Natural Gas Components and Range ofComposition CoveredComponent Mol %Helium 0.01 to 10Hydrogen 0.01 to 10Oxygen 0.01 to 20Nitrogen 0.01 to 100Carbon dioxide 0.01 to 20Methane 0.01 to 100Ethane 0.01 to 100Hydrogen sulfide 0.3 to 30Propane 0.01 to 100Isobutane 0.01 to 10n-Butane 0.
15、01 to 10Neopentane 0.01 to 2Isopentane 0.01 to 2n-Pentane 0.01 to 2Hexane isomers 0.01 to 2Heptanes+ 0.01 to 11*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.5.2.2 Ele
16、ctronic or Computing IntegratorsProof of sepa-ration and response equivalent to that for a recorder is requiredfor displays other than by chart recorder. Baseline trackingwith tangent skim peak detection is recommended.5.3 AttenuatorIf the chromatogram is to be interpretedusing manual methods, an at
17、tenuator must be used with thedetector output signal to maintain maximum peaks within therecorder chart range. The attenuator must be accurate to within0.5 % between the attenuator range steps.5.4 Sample Inlet System:5.4.1 The sample inlet system shall be constructed ofmaterials that are inert and n
18、onadsorptive with respect to thecomponents in the sample. The preferred material of construc-tion is stainless steel. Copper, brass, and other copper-bearingalloys are unacceptable. The sample inlet system from thecylinder valve to the GC column inlet must be maintained at atemperature constant to 6
19、1C.5.4.2 Provision must be made to introduce into the carriergas ahead of the analyzing column a gas-phase sample that hasbeen entrapped in a fixed volume loop or tubular section. Thefixed loop or section shall be so constructed that the totalvolume, including dead space, shall not normally exceed 0
20、5mL at 1 atm. If increased accuracy of the hexanes and heavierportions of the analysis is required, a larger sample size may beused (see Test Method D 2597). The sample volume must bereproducible such that successive runs agree within 1 % oneach component. A flowing sample inlet system is acceptabl
21、eas long as viscosity effects are accounted for.NOTE 1The sample size limitation of 0.5 mL or smaller is selectedrelative to linearity of detector response, and efficiency of columnseparation. Larger samples may be used to determine low-quantitycomponents to increase measurement accuracy.5.4.3 An op
22、tional manifold arrangement for enteringvacuum samples is shown in Fig. 1.5.5 Column Temperature Control:5.5.1 IsothermalWhen isothermal operation is used,maintain the analyzer columns at a temperature constant to0.3C during the course of the sample run and correspondingreference run.5.5.2 Temperatu
23、re ProgrammingTemperature program-ming may be used, as feasible. The oven temperature shall notexceed the recommended temperature limit for the materials inthe column.5.6 Detector Temperature ControlMaintain the detectortemperature at a temperature constant to 0.3C during thecourse of the sample run
24、 and the corresponding reference run.The detector temperature shall be equal to or greater than themaximum column temperature.5.7 Carrier Gas ControlsThe instrument shall beequipped with suitable facilities to provide a flow of carrier gasthrough the analyzer and detector at a flow rate that is cons
25、tantto 1 % throughout the analysis of the sample and the referencestandard. The purity of the carrier gas may be improved byflowing the carrier gas through selective filters prior to its entryinto the chromatograph.5.8 Columns:5.8.1 The columns shall be constructed of materials that areinert and non
26、adsorptive with respect to the components in thesample. The preferred material of construction is stainlesssteel. Copper and copper-bearing alloys are unacceptable.5.8.2 An adsorption-type column and a partition-type col-umn may be used to make the analysis.NOTE 2See Practice E 260.5.8.2.1 Adsorptio
27、n ColumnThis column must completelyseparate oxygen, nitrogen, and methane. A 13X molecularsieve 80/100 mesh is recommended for direct injection. A 5Acolumn can be used if a pre-cut column is present to removeinterfering hydrocarbons. If a recorder is used, the recorder penmust return to the baseline
28、 between each successive peak. Theresolution (R) must be 1.5 or greater as calculated in thefollowing equation:R1,2! 5x22 x1y21 y13 2, (1)where x1,x2are the retention times and y1,y2are the peakwidths. Fig. 2 illustrates the calculation for resolution. Fig. 3 isa chromatogram obtained with an adsorp
29、tion column.FIG. 1 Suggested Manifold Arrangement for Entering Vacuum SamplesD19450325.8.2.2 Partition ColumnThis column must separateethane through pentanes, and carbon dioxide. If a recorder isused, the recorder pen must return to the base line betweeneach peak for propane and succeeding peaks, an
30、d to base linewithin 2 % of full-scale deflection for components eluted aheadof propane, with measurements being at the attenuation of thepeak. Separation of carbon dioxide must be sufficient so that a0.25-mL sample containing 0.1-mol % carbon dioxide willproduce a clearly measurable response. The r
31、esolution (R)must be 1.5 or greater as calculated in the above equation. Theseparation should be completed within 40 min, includingreversal of flow after n-pentane to yield a group response forhexanes and heavier components. Figs. 4-6 are examples ofchromatograms obtained on some of the suitable par
32、titioncolumns.5.8.3 GeneralOther column packing materials that pro-vide satisfactory separation of components of interest may beused (see Fig. 7). In multicolumn applications, it is preferred touse front-end backflush of the heavy ends.NOTE 3The chromatograms in Figs. 3-8 are only illustrations ofty
33、pical separations. The operating conditions, including columns, are alsotypical and are subject to optimization by competent personnel.5.9 DrierUnless water is known not to interfere in theanalysis, a drier must be provided in the sample enteringsystem, ahead of the sample valve. The drier must remo
34、vemoisture without removing selective components to be deter-mined in the analysis.NOTE 4See A2.2 for preparation of a suitable drier.FIG. 2 Calculation for ResolutionFIG. 3 Separation Column for Oxygen, Nitrogen, and Methane (See Annex A2)D19450335.10 ValvesValves or sample splitters, or both, are
35、re-quired to permit switching, backflushing, or for simultaneousanalysis.5.11 ManometerMay be either U-tube type or well typeequipped with an accurately graduated and easily read scalecovering the range 0 to 900 mm (36 in.) of mercury or larger.The U-tube type is useful, since it permits filling the
36、 sampleloop with up to two atmospheres of sample pressure, thusextending the range of all components. The well type inher-ently offers better precision and is preferred when calibratingwith pure components. Samples with up to one atmosphere ofpressure can be entered. With either type manometer the m
37、mscale can be read more accurately than the inch scale. Cautionshould be used handling mercury because of its toxic nature.Avoid contact with the skin as much as possible. Washthoroughly after contact.FIG. 4 Chromatogram of Natural Gas (BMEE Column) (See Annex A2)FIG. 5 Chromatogram of Natural Gas (
38、Silicone 200/500 Column) (See Annex A2)D19450345.12 Vacuum PumpMust have the capability of producinga vacuum of 1 mm of mercury absolute or less.6. Preparation of Apparatus6.1 Linearity CheckTo establish linearity of response forthe thermal conductivity detector, it is necessary to completethe follo
39、wing procedure:6.1.1 The major component of interest (methane for naturalgas) is charged to the chromatograph by way of the fixed-sizesample loop at partial pressure increments of 13 kPa (100 mmHg) from 13 to 100 kPa (100 to 760 mm Hg) or the prevailingatmospheric pressure.FIG. 6 Chromatogram of Nat
40、ural Gas (See Annex A2)FIG. 7 Chromatogram of Natural Gas (Multi-Column Application) (See Annex A2)D19450356.1.2 The integrated peak responses for the area generated ateach of the pressure increments are plotted versus their partialpressure (see Fig. 9).6.1.3 The plotted results should yield a strai
41、ght line. Aperfectly linear response would display a straight line at a 45angle using the logarithmic values.6.1.4 Any curved line indicates the fixed volume sampleloop is too large. A smaller loop size should replace the fixedvolume loop and 6.1.1 through 6.1.4 should be repeated (seeFig. 9).6.1.5
42、The linearity over the range of interest must be knownfor each component. It is useful to construct a table noting theresponse factor deviation in changing concentration. (See Table2 and Table 3).6.1.6 It should be noted that nitrogen, methane, and ethaneexhibit less than 1 % compressibility at atmo
43、spheric pressure.Other natural gas components do exhibit a significant com-pressibility at pressures less than atmospheric.6.1.7 Most components that have vapor pressures of lessthan 100 kPa (15 psia) cannot be used as a pure gas for alinearity study because they will not exhibit sufficient vaporpre
44、ssure for a manometer reading to 100 kPa (760 mm Hg).For these components, a mixture with nitrogen or methane canbe used to establish a partial pressure that can extend the totalpressure to 100 kPa (760 mm Hg). Using Table 4 for vaporpressures at 38C (100F), calculate the maximum pressure towhich a
45、given component can be blended with nitrogen asfollows:B 5 100 3 V!/i (2)P 5 i 3 M!/100 (3)where:B = blend pressure, max, kPa (mm Hg);V = vapor pressure, kPa (mm Hg);i = mol %;P = partial pressure, kPa (mm Hg); andM = manometer pressure, kPa (mm Hg).6.2 . Procedure for Linearity Check:6.2.1 Connect
46、the pure-component source to the sample-entry system. Evacuate the sample-entry system and observethe manometer for leaks. (See Fig. 1 for a suggested manifoldarrangement.) The sample-entry system must be vacuum tight.6.2.2 Carefully open the needle valve to admit the purecomponent up to 13 kPa (100
47、 mm Hg) of partial pressure.6.2.3 Record the exact partial pressure and actuate thesample valve to place the sample onto the column. Record thepeak area of the pure component.6.2.4 Repeat 6.2.3 for 26, 39, 52, 65, 78, and 91 kPa (200,300, 400, 500, 600, and 700 mm Hg) on the manometer,recording the
48、peak area obtained for sample analysis at each ofthese pressures.6.2.5 Plot the area data (x axis) versus the partial pressures(y axis) on a linear graph as shown in Fig. 9.6.2.6 An alternative method is to obtain a blend of all thecomponents and charge the sample loop at partial pressure overthe ra
49、nge of interest. If a gas blender is available, the mixturecan be diluted with methane thereby giving response curves forall the components. (WarningIf it is not possible to obtaininformation on the linearity of the available gas chromatographdetector for all of the test gas components, then as a minimumrequirement the linearity data must be obtained for any gasFIG. 8 Separation of Helium and HydrogenD1945036component that exceeds a concentration of 5 mol%. Chromato-graphs are not truly linear over wide concentration ranges andlinearity should be establi
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