1、Designation: D1946 90 (Reapproved 2015)1Standard Practice forAnalysis of Reformed Gas by Gas Chromatography1This standard is issued under the fixed designation D1946; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、 revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTESection 5 updated editorially in December 2015.1. Scope1.1 This practice covers the determination of the chemicalcomposition of r
3、eformed gases and similar gaseous mixturescontaining the following components: hydrogen, oxygen,nitrogen, carbon monoxide, carbon dioxide, methane, ethane,and ethylene.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This
4、 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-bility of regulatory limitations prior to use.2. Referenced Documents
5、2.1 ASTM Standards:2E260 Practice for Packed Column Gas Chromatography3. Summary of Practice3.1 Components in a sample of reformed gas are physicallyseparated by gas chromatography and compared to correspond-ing components of a reference standard separated underidentical operating conditions, using
6、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 component with the corre-sponding value of that component in the reference standard.4. Significance and Use4.1 The information about th
7、e chemical composition can beused to calculate physical properties of the gas, such as heating(calorific) value and relative density. Combustioncharacteristics, products of combustion, toxicity, and inter-changeability with other fuel gases may also be inferred fromthe chemical composition.5. Appara
8、tus5.1 DetectorThe detector shall be a thermal conductivitytype or its equivalent in stability and sensitivity. The thermalconductivity detector must be sufficiently sensitive to producea signal of at least 0.5 mV for 1 mol % methane in a 0.5-mLsample.5.2 Recording InstrumentsEither strip chart reco
9、rders orelectronic integrators, or both, are used to display the separatedcomponents. It is highly desirable to evaluate the performanceof strip chart recorders or electronic integrators5.2.1 The recorder, when used, shall be a strip chart recorderwith a full-range scale of 5 mV or less (1 mV prefer
10、red). Thewidth of the chart shall be not less than 150 mm. A maximumpen response time of2s(1spreferred) and a minimum chartspeed 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 o
11、r Computing IntegratorsProof of sepa-ration and response equivalent to that for the recorder isrequired for displays other than 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 w
12、ithin the range of therecorder chart. The attenuator must be accurate to within 0.5 %between the attenuator range steps.5.4 Sample 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 ma
13、terial of construc-tion is stainless steel. Copper and copper-bearing alloys areunacceptable.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 either a fixed volume loop or tubular section.The injected volume must
14、 be reproducible such that successive1This practice is under the jurisdiction of ASTM Committee D03 on GaseousFuels and is the direct responsibility of Subcommittee D03.07 on Analysis ofChemical Composition of Gaseous Fuels.Current edition approved Nov. 1, 2015. Published December 2015. Originallyap
15、proved in 1962. Last previous edition approved in 2011 as D1946 90 (2011).DOI: 10.1520/D1946-90R15.2For referenced ASTM standards, 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 Doc
16、ument Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1runs of the same sample agree within the limits of repeatabilityfor the concentration range as specified in 11.1.1.5.4.3 If the instrument is calibr
17、ated 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).5.5 Column Temperature Control:5.5.1 IsothermalWhen isothermal operation is used, theanalytical columns shall be maint
18、ained at a temperature con-stant to 0.3C during the course of the sample run and thecorresponding reference run.5.5.2 Temperature ProgrammingTemperature program-ming may be used, as feasible. The oven temperature shall notexceed the recommended temperature limit for the materials inthe column.5.6 De
19、tector Temperature ControlThe detector tempera-ture shall be maintained at a temperature constant to 0.3Cduring the course of the sample run and the correspondingreference run. The detector temperature shall be equal to, orgreater than, the maximum column temperature.5.7 Carrier GasThe instrument sh
20、all be equipped withsuitable facilities to provide flow of carrier gas through theanalyzer and detector at a flow rate that is constant to 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 fil
21、ters before its entryinto the chromatograph. Refer to 5.8.2.1(1) through (4) for theappropriate selection of carrier gases.5.8 Columns:5.8.1 The columns shall be constructed of materials that areinert and nonadsorptive with respect to the components in thesample. The preferred material of constructi
22、on 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 E260 for general gas chromatography proce-dures.5.8.2.1 Adsorption ColumnThis column must completelys
23、eparate 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 chart recorder.Fig. 1 is an example chromatogram obtained with an ads
24、orp-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 percent and parts permillion quantities of hydrogen.(2) The use of a
25、 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 beincreased by using a separate injection for hydrogen, usingeither
26、argon or nitrogen for the carrier gas.Column: 2-m by 6-mm inside diameter Type 13molecular sieves, 14 to 30 meshFlow rate: 60-mL helium/minSample size: 0.5 mLTemperature: 35CFIG. 1 Chromatogram of Reformed Gas on Molecular Sieve ColumnD1946 90 (2015)12(4) Another technique for isolating the hydrogen
27、 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 of argon or nitrogen carrier gas foranalysis in a second thermal conductivity detector.5.8.2.2 Partition ColumnThis column must separateethane, carbon dioxi
28、de, and ethylene. If a recorder is used, therecorder pen must return to the baseline between each succes-sive peak. Equivalent proof of separation is required fordisplays other than by chart recorder. Fig. 2 is an examplechromatogram obtained with a partition column.5.8.3 GeneralThose column materia
29、ls, 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 comparison with the test sample. They must containknown percentages of th
30、e 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 standard should not be less than one half of,nor differ by more than 10
31、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 hasbeen tested and proved for inertness to oxygen, it is preferable to
32、 calibrateColumn: 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 ColumnD1946 90 (2015)13for oxygen by an alternative method.6.2 PreparationA reference standard may be pre
33、pared byblending pure components. Diluted dry air is a suitablestandard for oxygen and nitrogen.NOTE 3A mixture containing approximately 1 % 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 measure
34、dprecisely, as the fraction of nitrogen in the mixture such prepared must bedetermined by comparison to nitrogen in the reference standard. 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 o
35、n oxygen standards that have been prepared for more than a fewdays. It is permissible to use a response factor for oxygen that is relativeto a stable component.7. Preparation of Apparatus7.1 Column PreparationPack a 2- to 3-m column (6-mminside diameter stainless steel tubing) with Type 13 molecular
36、sieves, 14 to 30 mesh, that have been dried 12 h or more at 300to 350C. Pack a second column (1 m by 6 mm) with PorapakQ, 50 to 80 mesh, that has been dried 12 h or more at about150C. Shape the columns to fit the configuration of the ovenin the chromatograph.NOTE 4Variations in column material, dime
37、nsions, 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 smaller meshpacking materials and substituting Haysep Q for Porapak Q.7.2 C
38、hromatographPlace 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, column temperatures may be increased.Adjust theoperating conditions and
39、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 introduced into the chro-matographic column should have a volume between
40、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 concentrations, a samplesize of up to 5 mLis permissible. However, component
41、s 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 flowrate appropriateto the column diameter. Introduce a sample of the unk
42、nownmixture 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 sample of the referencestandard. If oxygen is present in the mixture, run a sam
43、ple 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 for carbon monoxide can appear between those ofnitrogen and methane if the m
44、olecular 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 baselinewith the helium carrier gas flowing through the Porapak Qcolumn. Introduce a sample of the reference standard a
45、nd 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 permits maximum peakheight to be recorded for each component.8.2.4 Column isolati
46、on 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 of each component shall be such that accuracy isneither sacrificed nor exag
47、gerated. 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 the response of eachcomponent, convert to the same sensitivity for correspo
48、ndingcomponents 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 component in the sample,B = response of the component in the standard at the samesen
49、sitivity as with A, andS = mole percent of the component in the referencestandard.9.3 If a helium-diluted air mixture was run for oxygencalibration, calculate the fraction of oxygen in the mixturefrom the fraction of the nitrogen 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 sie
