1、Designation: D 1946 90 (Reapproved 2006)Standard Practice forAnalysis of Reformed Gas by Gas Chromatography1This standard is issued under the fixed designation D 1946; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of las
2、t 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 practice covers the determination of the chemicalcomposition of reformed gases and similar gaseous mixturescontaini
3、ng the following components: hydrogen, oxygen, ni-trogen, carbon monoxide, carbon dioxide, methane, ethane,and ethylene.1.2 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-pr
4、iate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 260 Practice for Packed Column Gas Chromatography3. Summary of Practice3.1 Components in a sample of reformed gas are physicallyseparated by gas chrom
5、atography and compared to correspond-ing components of a reference standard separated underidentical operating conditions, using a reference standardmixture of known composition. The composition of the re-formed gas is calculated by comparison of either the peakheight or area response of each compon
6、ent with the corre-sponding value of that component in the reference standard.4. Significance and Use4.1 The information about the chemical composition can beused to calculate physical properties of the gas, such as heating(calorific) value and relative density. Combustion characteris-tics, products
7、 of combustion, toxicity, and interchangeabilitywith other fuel gases may also be inferred from the chemicalcomposition.5. Apparatus5.1 DetectorThe detector shall be a thermal conductivitytype or its equivalent in stability and sensitivity. The thermalconductivity detector must be sufficiently sensi
8、tive to producea signal of at least 0.5 mV for 1 mol % methane in a 0.5-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 integration, it
9、is highly desirable forevaluation of instrument performance.5.2.1 The recorder, when used, shall be a strip chart recorderwith a full-range scale of 5 mV or less (1 mV preferred). Thewidth of the chart shall be not less than 150 mm. A maximumpen response time of2s(1spreferred) and a minimum chartspe
10、ed of 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.5.2.2 Electronic or Computing IntegratorsProof of sepa-ration and response equivalent to that for the recorder isrequired for displays other tha
11、n by chart recorder.5.3 AttenuatorIf manual methods are used to interpret thechromatogram, an attenuator must be used with the detectoroutput signal to keep the peak maxima within the range of therecorder chart. The attenuator must be accurate to within 0.5 %between the attenuator range steps.5.4 Sa
12、mple Inlet System:5.4.1 The sample inlet system must be constructed ofmaterials that are inert and nonadsorptive with respect to thecomponents in the sample. The preferred material of construc-tion is stainless steel. Copper and copper-bearing alloys areunacceptable.5.4.2 Provision must be made to i
13、ntroduce into the carriergas ahead of the analyzing column a gas-phase sample that hasbeen entrapped in either a fixed volume loop or tubular section.The injected volume must be reproducible such that successiveruns of the same sample agree within the limits of repeatabilityfor the concentration ran
14、ge as specified in 11.1.1.5.4.3 If the instrument is calibrated with pure components,the inlet system shall be equipped to introduce a sample at lessthan atmospheric pressure. The pressure-sensing device mustbe accurate to 0.1 kPa (1 mm Hg).1This practice is under the jurisdiction of ASTM Committee
15、D03 on GaseousFuels and is the direct responsibility of Subcommittee D03.07 on Analysis ofChemical Composition of Gaseous Fuels.Current edition approved June 1, 2006. Published June 2006. Originallyapproved in 1962. Last previous edition approved in 2000 as D 1946 90 (2000).2For referenced ASTM stan
16、dards, visit the ASTM website, www.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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken,
17、PA 19428-2959, United States.5.5 Column Temperature Control:5.5.1 IsothermalWhen isothermal operation is used, theanalytical columns shall be maintained at a temperature con-stant to 0.3C during the course of the sample run and thecorresponding reference run.5.5.2 Temperature ProgrammingTemperature
18、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 ControlThe detector tempera-ture shall be maintained at a temperature constant to 0.3Cduring the course of the sample run and the corr
19、espondingreference run. The detector temperature shall be equal to, orgreater than, the maximum column temperature.5.7 Carrier GasThe instrument shall be equipped withsuitable facilities to provide flow of carrier gas through theanalyzer and detector at a flow rate that is constant to 1 %throughout
20、the analysis of the sample and the referencestandard. The purity of the carrier gas may be improved byflowing the carrier gas through selective filters before its entryinto the chromatograph.5.8 Columns:5.8.1 The columns shall be constructed of materials that areinert and nonadsorptive with respect
21、to the components in thesample. The preferred material of construction is stainlesssteel. Copper and copper-bearing alloys are unacceptable.5.8.2 Either an adsorption-type column or a partition-typecolumn, or both, may be used to make the analysis.NOTE 1See Practice E 260 for general gas chromatogra
22、phy proce-dures.5.8.2.1 Adsorption ColumnThis column must completelyseparate hydrogen, oxygen, nitrogen, methane, and carbonmonoxide. If a recorder is used, the recorder pen must return tothe baseline between each successive peak. Equivalent proof ofseparation is required for displays other than by
23、chart recorder.Fig. 1 is an example chromatogram obtained with an adsorp-tion column.(1) Because of similarities in thermal conductivities, he-lium should not be used as the carrier gas for hydrogen whenhydrogen is less than 1 % of the sample. Either argon ornitrogen carrier gas is suitable for both
24、 percent and parts permillion quantities of hydrogen.(2) The use of a carrier gas mixture of 8.5 % hydrogen and91.5 % helium will avoid the problem of reversing polarities ofhydrogen responses as the concentration of hydrogen in thesample is increased.(3) The precision of measurement of hydrogen can
25、 beincreased by using a separate injection for hydrogen, usingeither argon or nitrogen for the carrier gas.(4) Another technique for isolating the hydrogen in asample is to use a palladium transfer tube at the end of theadsorption column; this will permit only hydrogen to betransferred to a stream o
26、f argon or nitrogen carrier gas foranalysis in a second thermal conductivity detector.5.8.2.2 Partition ColumnThis column must separateethane, carbon dioxide, and ethylene. If a recorder is used, therecorder pen must return to the baseline between each succes-sive peak. Equivalent proof of separatio
27、n is required fordisplays other than by chart recorder. Fig. 2 is an examplechromatogram obtained with a partition column.Column: 2-m by 6-mm inside diameter Type 133molecular sieves, 14 to 30 meshFlow rate: 60-mL helium/minSample size: 0.5 mLTemperature: 35CFIG. 1 Chromatogram of Reformed Gas on Mo
28、lecular Sieve ColumnD 1946 90 (2006)25.8.3 GeneralThose column materials, operated eitherisothermally or with temperature programming, or both, maybe used if they provide satisfactory separation of components.6. Reference Standards6.1 Moisture-free mixtures of known composition are re-quired for com
29、parison with the test sample. They must containknown percentages of the components, except oxygen (Note2), that are to be determined in the unknown sample. Allcomponents in the reference standard must be homogeneous inthe vapor state at the time of use. The fraction of a componentin the reference st
30、andard should not be less than one half of,nor differ by more than 10 mol % from, the fraction of thecorresponding component in the unknown. The composition ofthe reference standard must be known to within 0.01 mol % forany component.NOTE 2Unless the reference standard is stored in a container that
31、hasbeen tested and proved for inertness to oxygen, it is preferable to calibratefor oxygen by an alternative method.6.2 PreparationA reference standard may be prepared byblending pure components. Diluted dry air is a suitablestandard for oxygen and nitrogen.NOTE 3A mixture containing approximately 1
32、 % of oxygen can beprepared by pressurizing a container of dry air at atmospheric pressure to20 atm (2.03 MPa) with pure helium. This pressure need not be measuredprecisely, as the fraction of nitrogen in the mixture such prepared must bedetermined by comparison to nitrogen in the reference standard
33、. Thefraction of nitrogen is multiplied by 0.280 to obtain the fraction of oxygenplus argon. Argon elutes with oxygen in the molecular sieves column. Donot rely on oxygen standards that have been prepared for more than a fewdays. It is permissible to use a response factor for oxygen that is relative
34、to a stable component.Column: 1.2 m by 6.35 mm Temperature: 40CPorapak Q, 50 to 80 mesh Flow rate: 50-mL helium/minCurrent setting: 225 mA Sample size: 0.5 mLFIG. 2 Chromatogram of Reformed Gas on Porapak Q ColumnD 1946 90 (2006)37. Preparation of Apparatus7.1 Column PreparationPack a 2- to 3-m colu
35、mn (6-mminside diameter stainless steel tubing) with Type 133 molecu-lar sieves, 14 to 30 mesh, that have been dried 12 h or more at300 to 350C. Pack a second column (1 m by 6 mm) withPorapak Q, 50 to 80 mesh, that has been dried 12 h or more atabout 150C. Shape the columns to fit the configuration
36、of theoven in the chromatograph.NOTE 4Variations in column material, dimensions, and mesh sizes ofpacking are permissible if the columns produce separations equivalent tothose shown in Fig. 1 and Fig. 2. Better performance may be obtained byusing a 2.1-mm stainless steel tubing with corresponding sm
37、aller meshpacking materials and substituting Haysep Q for Porapak Q.7.2 ChromatographPlace the proper column and samplevolume in operation for the desired run in accordance with 8.1and 8.2. For isothermal operation, the column should bemaintained at a temperature between 30 and 45C. Whenappropriate,
38、 column temperatures may be increased.Adjust theoperating conditions and allow the instrument to stabilize.Check the stability by making repeat runs on the referencestandard to obtain reproducible peak heights as described in5.4.2 for corresponding components.8. Procedure8.1 Sample VolumeThe sample
39、introduced into the chro-matographic column should have a volume between 0.2 and0.5 mL. Sufficient accuracy can be obtained for the determi-nation of all but the very minor components with this samplesize. When increased sensitivity is required for the determina-tion of components present in low con
40、centrations, a samplesize of up to 5 mL is permissible. However, components whoseconcentrations are in excess of 5 % should not be analyzed byusing sample volumes greater than 0.5 mL.8.2 Chromatograms:8.2.1 Adsorption Column (Fig. 1)Obtain a steady baselineon the recorder with a constant carrier gas
41、 flowrate appropriateto the column diameter. Introduce a sample of the unknownmixture at atmospheric pressure into the chromatograph andobtain a response similar to that of Fig. 1 of the componentshydrogen, oxygen, nitrogen, methane, and carbon monoxide,which elute in that order. Repeat with a sampl
42、e of the referencestandard. If oxygen is present in the mixture, run a sample ofair, either at an accurately measured reduced pressure, or airfreshly diluted with helium, so that the partial pressure ofoxygen is approximately equal to that of the oxygen in themixture being analyzed.NOTE 5The peak fo
43、r carbon monoxide can appear between those ofnitrogen and methane if the molecular sieves have become contaminated.If this occurs, replace or regenerate the column packing by heating inaccordance with 7.1.8.2.2 Partition Column (Fig. 2)Establish a steady base-line with the helium carrier gas flowing
44、 through the Porapak Qcolumn. Introduce a sample of the reference standard and thena sample of the unknown mixture. Obtain responses similar tothat shown in Fig. 2 for carbon dioxide, ethane, and ethylene.8.2.3 All chromatograms for manual measurement shouldbe run at a sensitivity setting that permi
45、ts maximum peakheight to be recorded for each component.8.2.4 Column isolation valves may be used to make theentire analysis with a single injection if the separationsspecified in 5.8.2.1 and 5.8.2.2 are produced.9. Calculation9.1 The number of significant digits retained for the quan-titative value
46、 of each component shall be such that accuracy isneither sacrificed nor exaggerated. The expressed numericalvalue of any component in the sample should not be presumedto be more accurate than the corresponding certified value ofthat component in the calibration standard.9.2 Manual MeasurementMeasure
47、 the response of eachcomponent, convert to the same sensitivity for correspondingcomponents in the sample and reference standard, and calcu-late the mole percent of each component in the sample asfollows:C 5 A/B!S! (1)where:C = mole percent of the component in the sample,A = response of the componen
48、t in the sample,B = response of the component in the standard at the samesensitivity as with A, andS = mole percent of the component in the reference stan-dard.9.3 If a helium-diluted air mixture was run for oxygencalibration, calculate the fraction of oxygen in the mixturefrom the fraction of the n
49、itrogen and the composition of thediluted air. Calculate the fraction of nitrogen in the mixture inaccordance with 9.1, using the nitrogen response of thereference standard for comparison. Air composition values of78.1 % nitrogen and 21.9 % oxygen should be used, as argon(0.9 % in air) elutes with oxygen on the molecular sievescolumn.9.4 If air has been analyzed at reduced pressure to calibratefor oxygen, correct the equation for pressure as follows:C 5 A/B!S!Pa/Pb! (2)where:Pa= absolute pressure at which air was analyzed andPb= barometric pressur
