Designation:D6228–98
Standard Test Method for
Determination of Sulfur Compounds in Natural Gas and Gaous Fuels by Gas Chromatography and Flame Photometric Detection1
This standard is issued under thefixed designation D6228;the number immediately following the designation indicates the year of original adoption or,in the ca of revision,the year of last revision.A number in parenthes indicates the year of last reapproval.A superscript epsilon(e)indicates an editorial change since the last revision or reapproval.
1.Scope
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1.1This test method provides for the determination of individual volatile sulfur-containing compounds in gaous fuels by gas chromatography(GC)withflame photometric detection(FPD).The detection range for sulfur compounds is from20to20000picograms(pg)of sulfur.This is equivalent to0.02to20mg/m3or0.014to14ppmv of sulfur bad upon the analysis of a1-mL sample.
1.2This test method describes a GC-FPD method using a specific capillary GC column.Other GC-FPD methods,with differences in GC column and equipment tup and operation, may be ud as alternative methods for sulfur compound analysis with different range and precision,provided that appropriate paration of the sulfur compounds of interest can be achieved.
1.3This test method does not intend to identify all indi-vidual sulfur species.Total sulfur content of samples can be estimated from the total of the individual compounds deter-mined.Unknown compounds are calculated as monosulfur-containing compounds.
1.4The values stated in SI units are to be regarded as standard.The values stated in inch-pound units are for infor-mation only.
1.5This standard does not purport to address all the safety concerns,if any,associated with its u.It is the responsibility of the ur of this standard to establish appropriate safety and health practices a
nd determine the applicability of regulatory limitations prior to u.
2.Referenced Documents
2.1ASTM Standards:
D1072Test Method for Total Sulfur in Fuel Gas2
D1265Practice for Sampling Liquefied Petroleum(LP) Gas–Manual Method3
D1945Test Method for Analysis of Natural Gas by Gas Chromatography2
D3609Practice for Calibration Techniques Using Perme-ation Tubes4
D4468Test Method for Total Sulfur in Gaous Fuels by Hydrogenolysis and Rateometric Colorimetry2
D4626Practice for Calculation of Gas Chromatographic Respon Factors5
D5287Practice for Automatic Sampling of Gaous Fuels2 D5504Test Method for Determination of Sulfur Com-pounds in Natural Gas and Gaous Fuels by Gas Chro-matography and Chemilumines
cence Detection2
E840Practice for Using Flame Photometric Detectors in Gas Chromatography6
2.2EP A Standards:
EPA–15Determination of Hydrogen Sulfide,Carbonyl Sul-fide and Carbon Disulfide Emissions from Stationary Sources,40CFR,Chapter1,Part60,Appendix A
EPA–16Semicontinuous Determination of Sulfur Emis-sions from Stationary Sources,40CFR,Chapter1,Part 60,Appendix A
3.Terminology
3.1Abbreviations:
3.1.1A common abbreviation of a hydrocarbon compound is to designate the number of carbon atoms in the compound.
A prefix is ud to indicate the carbon chain form,while a subscript suffix denotes the number of carbon atoms,for example,normal decane=n-C10,isotetradecane=i-C14.
3.1.2Sulfur compounds commonly are referred to by their initials,chemical or formula,for example,methyl mercaptan= MeSH,dimethyl sulfide=DMS,carbonyl sulfide=COS, di-t-butyl trisulfide=DtB-TS,and tetrahydothiophene=THT or thiophane.
1This test method is under the jurisdiction of ASTM Committee D-3on Gaous Fuels and is the direct responsibility of Subcommittee D03.05on Determination of Special Constituents of Gaous Fuels.
Current edition approved March10,1998.Published May1998. 2Annual Book of ASTM Standards,V ol05.05.
3Annual Book of ASTM Standards,V ol05.01.
4Annual Book of ASTM Standards,V ol11.03.
5Annual Book of ASTM Standards,V ol05.02.
6Annual Book of ASTM Standards,V ol14.02. 1
Copyright©ASTM International,100Barr Harbor Drive,PO Box C700,West Conshohocken,PA19428-2959,United States.
青年责任4.Summary of Test Method
4.1Sulfur analysis ideally is performed on-site to eliminate potential sample deterioration during storage.The reactive nature of sulfur components may po problems both in sampling and analysis.Samples should be collected and stored in containers that are nonreactive to sulfur compounds,such as Tedlar 7bags.Sample containers should be filled and purged at least three times to ensure reprentative sampling.Laboratory equipment also must be inert,well conditioned,and passivated with a gas containing the sulfur compounds of interest to ensure reliable results.Frequent calibration and daily verifica-tion of calibration curve using stable standards are required.Samples should be analyzed within 24h of collection to minimize sample deterioration.If the stability of analyzed sulfur components is proved experimentally,the time between collection and analysis may be lengthened.
4.2A 1-mL sample of the fuel gas is injected into a gas chromatograph where it is pasd through a 6
0-m,0.53-mm inside diameter (ID),thick film,methyl silicone liquid pha,open tubular partitioning column,or a similar column capable of parating sulfur components.
4.3Flame Photometric Detectors —When combusted in a hydrogen-rich flame,sulfur compounds emit light energy characteristic to all sulfur species.The light is detected by a photomultiplier tube (PMT).The PMT respon is proportional to the concentration or the amount of sulfur.All sulfur compounds including sulfur odorants can be detected by this technique.
4.4Other Detectors —This test method is written primarily for the flame photometric detector.The same gas chromato-graphic (GC)method can be ud with other sulfur-specific detectors provided they have sufficient nsitivity and lectiv-ity to all sulfur compounds of interest in the required measure-ment range.
4.5Other GC Test Methods —The GC test methods using sulfur chemiluminescence,reductive rateometric,and electro-chemical detectors are available or under development.
5.Significance and U
5.1Many sources of natural gas and petroleum gas contain varying amounts and types of sulfur co
mpounds,which are odorous,corrosive to equipment,and can inhibit or destroy catalysts ud in gas processing.Their accurate measurement is esntial to gas processing,operation,and utilization.
5.2Small amounts,typically,1to 4ppmv of sulfur odorant compounds,are added to natural gas and liquefied petroleum (LP)gas for safety purpos.Some odorant compounds can be reactive and may be oxidized,forming more stable com-pounds having lower odor thresholds.The gaous fuels are analyzed for sulfur odorants to help ensure appropriate odorant levels for safety.
5.3This test method offers a technique to determine indi-vidual sulfur species in gaous fuel and the total sulfur content by calculation.Gas chromatography is ud commonly and extensively to determine other components in gaous fuels
including fixed gas and organic components (e Test Method D 1945).This test method dictates the u of a specific GC technique with one of the more common detectors for mea-surement.
6.Apparatus
6.1Chromatograph —Any gas chromatograph that has the following performance characteristics can be ud.
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6.1.1Sample Inlet System —Gas samples are introduced to the gas chromatograph using an automated or manually oper-ated stainless steel gas sampling valve enclod in a heated valve oven,which must be capable of operating continuously at a temperature of 50°C above the temperature at which the gas was sampled.TFE-fluorocarbon tubing made of fluorinated ethylene propylene (FEP),316stainless steel tubing,or other tubing made of nonpermeable,nonsorbing,and nonreactive materials,as short as possible and heat traced at the same temperature,should be ud for transferring the sample from a sample container to the gas-sampling valve.A 1.0-mL sam-pling loop made of nonreactive materials,such as deactivated fud silica or 316stainless steel is ud to avoid possible decomposition of reactive sulfur species.Other size fixed-volume sampling loops may be ud for different concentration ranges.A 1-to 2-m ction of deactivated precolumn attached to the front of the analytical column is recommended.The precolumn is connected directly to the gas sampling valve for on-column injection.The inlet system must be well condi-tioned and evaluated frequently for compatibility with trace quantities of reactive sulfur compounds,such as tert -butyl mercaptan.
6.1.2Digital Pressure Transmitter —A calibrated stainless steel pressure/vacuum transducer with a digital readout may be equipped to allow sampling at different pressures to generate calibration curves.
6.1.3Column Temperature Programmer —The chromato-graph must be capable of linear programmed temperature operation over a range from 30to 200°C,in programmed rate ttings of 0.1to 30°C/min.The programming rate must be sufficiently reproducible to obtain retention time repeatability of 0.05min (3s).
6.1.4Carrier and Detector Gas Control —Constant flow control of carrier and detector gas is critical to optimum and consistent analytical performance.Control is best provided by the u of pressure regulators and fixed flow restrictors.The gas flow rate is measured by any appropriate means and the required gas flow indicated by the u of a pressure gage.Mass flow controllers,capable of maintaining gas flow constant to 61%at the required flow rates also can be ud.The supply pressure of the gas delivered to the gas chromatograph must be at least 69kPa (10psi)greater than the regulated gas at the instrument to compensate for the system back pressure.In general,a supply pressure of 552kPa (80psig)will be satisfactory.
6.1.5Detector —A flame photometric detector calibrated in the sulfur-specific mode is ud for this test method.Other detectors as mentioned in 4.4will not be covered in this test method.This detector may be obtained from various manufac-turers;however,there are variations in design.The puld flame photometric detector (PFPD)is one of the new FPD
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designs.The pressure andflow rate of the hydrogen and air gas ud in the detector may be different.The lection of which detector to u should be bad on its performance for the intended application.The detector should be t according to the manufacturer’s specifications and tuned to the best performance of nsitivity and lectivity as needed.
6.1.5.1When sulfur-containing compounds are burned in a hydrogen-richflame,they quantitatively produce a S2*species in an excited state(Eq1and Eq2).The light emitted from this species is detected by a photomultiplier tube(PMT)(Eq3).A 393-nm bandpass opticalfilter normally is ud to enhance the lectivity of detection.The lectivity normally is about104to 1by mass of sulfur to mass of carbon.
RS1O2→n CO21SO2(1)
2SO214H2→4H2O1S2*(2)
S2*→S21h n(3) where:
h n=emitted light energy.
6.1.5.2The intensity of light is not linear with the sulfur concentration but is proportional approximately to the square of the sulfur concentration.The relationship between the FPD respon(R D)and the sulfur concentration(S)is given by Eq 4and Eq5.The n-factor usually is less than2.0.
R D a@S#n(4)
Log@S#a1/n Log R(5) where:
n=exponential factor(1.7to2.0).
6.1.5.3The linear calibration curve can be made using a log-log plot.Some instruments u an electronic linearizer to produce a signal with direct linear respon.The dynamic range of this linear relationship is about13103.
6.2Column—A60-by0.53-m ID fud silica open tubular column containing a5-µmfilm thickness of bonded methyl silicone liquid pha is ud.The column shall provide adequate retention and resolution characteristics under the experimental conditions described in
7.3.Other columns, which can provide equivalent paration can be ud,as well.
6.3Data Acquisition:
6.3.1Recorder—A0-to1-mV range recording potentiom-eter or equivalent,with a full-scale respon time of2s or less can be ud.
6.3.2Integrator—The u of an electronic integrating de-vice or computer is recommended.The device and software must have the following capabilities:
6.3.2.1Graphic prentation of the chromatogram.
6.3.2.2Digital display of chromatographic peak areas.
6.3.2.3Identification of peaks by retention time or relative retention time,or both.
7.Reagents and Materials
7.1Sulfur Permeation Tube Standards—Gaous standards generated from individual or a combination of certified perme-ation tubes at a constant temperature andflow rate shall be ud for all calibrations.Each permeation tube will be weighed to the nearest0.1mg on a periodic basis after the permeation rate has equilibrated and remains constant.The standard concen-tration is calculated by mass loss and dilution gasflow rate. Impurities permeated from each tube must be detected,mea-sured,and accounted for in the mass loss,if they are prent above a level of0.1%of the permeated sulfur species.See Practice D3609.
7.2Compresd Cylinder Gas Standards—As an alterna-tive,blended gaous sulfur standards may be ud if a means to ensure accuracy and stability of the mixture is available. The mixtures can be a source of error if their stability during storage cannot be guaranteed.
N OTE1—Warning:Sulfur compounds may beflammable and harmful or fatal if ingested or inhaled.
7.3Carrier Gas—Helium or nitrogen of high purity (99.999%min purity)(Warning—See Note2).Additional purification is recommended by the u of molecular sieves or other suitable agents to remove water,oxygen,and hydrocar-bons.Available pressure must be sufficient to ensure a constant carrier gasflow rate(e6.1.4).
N OTE2—Warning:Helium and nitrogen ud are compresd gas under high pressure.
7.4Hydrogen—Hydrogen of high purity(99.999%min purity)is ud as fuel for theflame photometric detector(FPD) (Warning—See Note3).
N OTE3—Warning:Hydrogen is an extremelyflammable gas under high pressure.
7.5Air—High-purity(99.999%min purity)compresd air is ud as the oxidant for theflame photometric detector(FPD) (Warning—See Note4).
N OTE4—Warning:Compresd air is a gas under high pressure that supports combustion.
8.Preparation of Apparatus and Calibration
河车丸8.1Chromatograph—Place in rvice in accordance with the manufacturer’s instructions.Typical operating conditions are shown in Table1.
8.2FPD—Place the detector in rvice in accordance with the manufacturer’s instructions.Hydrogen and airflows are critical and must be adjusted properly in accordance with the instruction furnished by the manufacturer.With the FPDflame ignited,monitor the signal to verify compliance with the signa
l noi and drift specified by the manufacturer.The FPDflame should be maintained to give consistent and optimum nsitiv-ity for the detection range.
8.2.1Sample Injection—A sample loop of1.0mL of suit-able size for sample injection may be ud for performance check.A linear calibration curve may be determined by using standards of varying concentrations or by injecting a single TABLE1Gas Chromatographic Operating Parameters Gas Sample Loop: 1.0mL at120°C
Injection Type:On-column
Carrier Gas:He at11.0mL/min or at aflow rate allowing CH4
elutes at approximately2.1min
Column Oven:30°C hold1.5min,15°C/min to200°C,hold8min,or
as needed
Detector:H2/air ratio specified by manufacturer,250°C,20
mL/min,helium makeup
gas
calibration standard at different pressures from 13.3to 133kPa (100to 1000torr).If the latter method is ud,the concentra-tion of sulfur component for calibration is calculated using the following equation.
S n 5~P s /P o !3C n
(6)
where:
S n =calculated concentration of the sulfur compound in
the sampled gas on mole or volume basis,
P s =sampling pressure as absolute,
P o =laboratory ambient pressure as absolute,and
C n =concentration of the sulfur compound in the calibra-tion standard.
8.2.2Detector Respon Calibration —Analyze the calibra-tion gas and obtain the chromatograms and peak areas.Determine the linear range of detector respon using sample injection techniques illustrated in 8.2.1.A log/log plot or a linearized plot may be constructed with the linear correlation factor calculated.Calculate the relative sulfur respon factor of each sulfur compound at ambient pressure by:
鲁迅的杂文集F n 5~S n /A n !3L n
(7)
where:
F n =sulfur respon factor of compound,
S n =concentration of the sulfur compound in the sampled
gas on mole or volume basis,
A n =peak area of the sulfur compound measured,and L n =moles of sulfur in the compound.Example:
Assume 1.0ppmv of dimethyl sulfide (DMS)injected with a 1.0-mL sample loop.
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1-ppmv DMS =62.13/22.41=2.772mg/m 3(from Table 2). 1.0mL of 1-ppmv DMS =2772-pg DMS =2772351.61%=1430-pg S.If the peak area of DMS respon is 15850counts,the respon factor F n (S /peak)is 1430/1585031=9.023102(pg sulfur/unit area).The respon factor (F n )of 1.0-mL injection =1.0/1585031=63310–6(ppmv DMS/unit area).
All mono -sulfur compounds should have approximately the same respon factor.The respon factor (F n )of each sulfur compound should be within 10%of F n for dimethyl sulfide.The day-to-day variation of F n should not be greater than 5%.
The detector should be maintained and flow rates readjusted to optimize the detector performance if F n exceeds this limitation.Table 2lists common sulfur compounds found in gaous fuel and their pr
operties for calculation.
8.2.3Interferences —There are two types of interferences that must be minimized for reliable quantitation.
8.2.3.1Hydrocarbon Quenching —Hydrocarbons produce a quenching effect on sulfur detection as a result of the formation of a large amount of carbon dioxide in the flame suppressing the formation of SO 2.The quenching can be minimized by optimizing the chromatographic conditions to parate the sulfur components of interest from large hydrocarbons prent in the sample matrix.A flame ionization detector (FID)or thermal conductivity detector (TCD)can be ud to identify the prence of interfering hydrocarbons.Sample dilution or in-jection of a smaller volume of sample may be ud to alleviate the quenching effect if sulfur concentration is significantly higher than the method detection limit.
8.2.3.2Self-Quenching —In other cas,the rever of the reaction shown in Eq 3produces lf-quenching.This aris when the emitted light is reabsorbed before reaching the photomultiplier.It occurs when a very large concentration of any sulfur species is prent in the flame above and beyond the linearity range of the detector.It often generates an M-shape peak with the inverted signa
l at a component’s peak apex,which mistakenly can be identified as two clo eluting compounds.Sample dilution or smaller sample injection may eliminate this effect.
8.3Chromatography —A chromatogram of typical natural gas analysis is illustrated in Fig.1(relative respon versus retention time).The retention times of lected sulfur compo-nents are listed for reference (Table 3).They may vary considerably depending on the chromatographic conditions.The eluting quence and spread of sulfur peaks and their peak shape should remain the same.Adequate resolution defined as baline paration of adjacent peaks shall be achieved.The baline paration of two peaks is defined as the FPD signal of the first compound returns to a point at least below 5%of the smallest peak of two.
9.Procedure
9.1Sampling and Preparation of Sample Aliquots :
9.1.1Gas Samples —Samples should be supplied to the laboratory in specially conditioned high-pressure sample con-tainers or in Tedlar 7bags at atmospheric pressure.The sample must be analyzed as soon as possible,preferably within 24h of sampling.
9.2Instrument Setup —Set up the GC-FPD in accordance with the chromatograph operating parameters listed in Table 1.9.3Instrument Performance —Analyze lected standards to verify the chromatographic performance (e 8.3),retention times (Table 3),and the respon factors (e 8.2.2).The calibration made at the beginning and the end of each run or ries of runs within 24-h period shall not exceed 65%.9.4External Standard Calibration —At least twice a day or as frequently as necessary,analyze the calibration standard mix to verify the calibration curve determined in 8.2.1and 8.2.2and determine the standard respon factors for the sample analysis.
TABLE 2Physical Properties of Common Sulfur Compounds
Compound
Relative Molecular Mass (Molecular Weight)
%5
Boiling Point,
°C
Vapor Pressure kPa at 37.78°C
H 2S 34.0894.09–COS 60.0853.37–MeSH 48.1166.65 6.2214EtSH 62.1351.6135.0112DMS 62.1351.6137.3103CS 276.1484.iPrSH 76.1642.1052.661TBM 90.1935.5564.041nPrSH 76.1642.1067.035MES 76.1642.1067.036THT 88.1736.37120 4.6di-EtS 90.1935.DMDS 94.2068.di-Et-DS 122.25
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9.5Sample Analysis —Evacuate and purge the lines from the sample container through the sample loop in the gas chromato-graph.Inject 1.0mL with a gas sampling valve as in 8.2.1.If the sample size exceeds the linear range of the detector,reduce the sample size using a smaller loop or lower sampling pressure.Run the analysis in accordance with the conditions specified in Table 1.Obtain the chromatographic data by means of a potentiometric record (graphic),digital integrator,or computer-bad chromatographic data system.Examine the graphic display or digital data for any errors,for ex
ample,over-range component data,and repeat the injection and analysis,if necessary.The difference between corresponding peak areas of repeated runs should not exceed 5%.
9.6Compound Identification —Sulfur compounds are iden-tified by their retention times established during calibration.All compounds without matching standards are identified as indi-vidual unknowns.
10.Calculation
10.1Determine the chromatographic peak area of each component and u the respon factor (Eq 7)obtained from the calibration run to calculate the amount of each sulfur compound prent corrected for injection pressure.The amount of each unknown sulfur compound is calculated using the respon factor of the clost adjacent identified compound,unless that compound shows abnormal peak shape.
C n 5~A n /F n !~P o /P s !/L n
(8)
where:
C n =concentration of the sulfur compound in the gas on
mole or volume basis,
A n =peak area of the sulfur compound measured,F n =sulfur respon factor of compound,P o =laboratory ambient pressure,P s =sampling pressure,and
L n =moles of sulfur in the compound.
11.Report
11.1Report the identification and concentration of each individual sulfur compound in ppmv.Report the sum of all sulfur components detected to the nearest ppmv or pg as total sulfur.
12.Precision and Bias
12.1Precision —The precision of this test method is deter-mined bad on a sulfur standard mix in methane,which is stable during the testing period.The statistical examination of the laboratory test results is as
follows:
FIG.1Chromatogram of a Composite Odorized Natural Gas
TABLE 3Retention Times of Various Sulfur Components
RT ,min Compound RT ,min Compound RT ,min Compound 2.09methane 5.50CS 211.23M-iPr-DS 2.20ethane 5.80iPrSH 11.62DEDS 2.45H 2S 6.45TBM 11.74M-nPr-DS 2.55COS 6.70nPrSH 11.90M-tB-DS 2.65propane 6.80MES
12.35DMTS 3.00i -butane 7.80thiophene 12.87E-nPr-DS 3.40n -butane 8.25DES 12.98DiPr-DS 3.52MeSH 9.00DMDS
13.50iPr-tB-DS 4.50i -pentane 9.42M -thiophenes 13.65iPr-nPr-DS 4.75EtSH
9.95THT 14.35DtB-DS 4.90n -pentane 10.37MEDS
14.55DEt-TS 5.10
DMS
11.00
C 27thiophenes
17.15
DtB-TS
