1、Designation: D1946 90 (Reapproved 2011)Standard 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.1. Scope1.1 This practice covers the determination of the chemicalcomposition of reformed gases and similar gaseous mixturescontaining
3、the following components: hydrogen, oxygen, ni-trogen, 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 standard does not purport to address all of thesaf
4、ety 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 Documents2.1 ASTM Standards:2E260 Practice for Packed Column
5、 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 a reference standardmixture of known composition. T
6、he 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 the chemical composition can beused to calculate phys
7、ical properties of the gas, such as heating(calorific) value and relative density. Combustion characteris-tics, products of combustion, toxicity, and interchangeabilitywith other fuel gases may also be inferred from the chemicalcomposition.5. Apparatus5.1 DetectorThe detector shall be a thermal cond
8、uctivitytype 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 recorders orelectronic integrators, or both, are used t
9、o display the separatedcomponents. Although a strip chart recorder is not requiredwhen using electronic integration, it 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).
10、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 or Comp
11、uting 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 within
12、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 material
13、 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 be re
14、producible such that successiveruns of the same sample agree within the limits of repeatabilityfor the concentration range as specified in 11.1.1.1This practice is under the jurisdiction of ASTM Committee D03 on GaseousFuels and is the direct responsibility of Subcommittee D03.07 on Analysis ofChemi
15、cal Composition of Gaseous Fuels.Current edition approved Nov. 1, 2011. Published December 2011. Originallyapproved in 1962. Last previous edition approved in 2006 as D1946 90 (2006).DOI: 10.1520/D1946-90R11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Custome
16、r 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, PA 19428-2959, United States.5.4.3 If the instrument is calibrated
17、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 maintained
18、 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 Detecto
19、r 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 shall b
20、e 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 filters
21、before its entryinto the chromatograph.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 construction is stainlesssteel. Copper and copper-bearing alloys are unacceptable.5.8.2 Either
22、 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 completelyseparate hydrogen, oxygen, nitrogen, methane, and carbonmonoxide. If a recorder is us
23、ed, 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 adsorp-tion column.(1) Because of similarities in thermal conductivities, he-lium shoul
24、d 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 carrier gas mixture of 8.5 % hydrogen and91.5 % helium will avoid the problem of re
25、versing 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 argon or nitrogen for the carrier gas.(4) Another technique for isolating the hydrog
26、en 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.Column: 2-m by 6-mm inside diameter Type 133molecular sieves, 14 to
27、 30 meshFlow rate: 60-mL helium/minSample size: 0.5 mLTemperature: 35CFIG. 1 Chromatogram of Reformed Gas on Molecular Sieve ColumnD1946 90 (2011)25.8.2.2 Partition ColumnThis column must separate eth-ane, carbon dioxide, and ethylene. If a recorder is used, therecorder pen must return to the baseli
28、ne 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 materials, operated eitherisothermally or with temperature programming, or both, maybe us
29、ed 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 the components, except oxygen (Note2), that are to be determined in the unknown samp
30、le. 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 mol % from, the fraction of thecorresponding component in the unknown. The composi
31、tion 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 calibratefor oxygen by an alternative method.6.2 PreparationA reference standard
32、may be prepared 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
33、be measuredprecisely, 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 oxygenColumn: 1.2 m by 6.35 mm Temperature: 40CPorapak Q, 50 to 80 mesh Flow
34、rate: 50-mL helium/minCurrent setting: 225 mA Sample size: 0.5 mLFIG. 2 Chromatogram of Reformed Gas on Porapak Q ColumnD1946 90 (2011)3plus 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 permissib
35、le 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 133 molecu-lar sieves, 14 to 30 mesh, that have been dried 12 h or more at300 to 350C. Pack a s
36、econd 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 of theoven in the chromatograph.NOTE 4Variations in column material, dimensions, and mesh sizes ofpacking are permissible if the columns produce separati
37、ons 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 ChromatographPlace the proper column and samplevolume in operation for the desire
38、d 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 allow the instrument to stabilize.Check the stability by making repeat runs on t
39、he 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 0.2 and0.5 mL. Sufficient accuracy can be obtained for the determi-nation of all
40、 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 mL is permissible. However, components whoseconcentrations are in excess of 5 % should not be analyzed byusing sampl
41、e 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 unknownmixture at atmospheric pressure into the chromatograph andobtain a response
42、 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 sample ofair, either at an accurately measured reduced pressure, or airfreshly dil
43、uted 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 molecular sieves have become contaminated.If this occurs, replace or regenerate
44、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 through the Porapak Qcolumn. Introduce a sample of the reference standard and thena sample of the unknown mixture. Obtain responses similar tothat shown
45、 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 isolation valves may be used to make theentire analysis with a single injection if t
46、he 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 exaggerated. The expressed numericalvalue of any component in the sample should n
47、ot 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 correspondingcomponents in the sample and reference standard, and calcu-late the mole
48、 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 samesensitivity as with A, andS = mole percent of the component in the reference sta
49、n-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 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 sievescolumn.9.4 If air has been analyzed at reduced pressure to calibratefor oxygen,
