Download ASTM D1945 Standard Test Method For Analysis of Natural Gas by Gas Chromatography...
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D1945 − 14 (Reapproved 2019)
Standard Test Method for
Analysis of Natural Gas by Gas Chromatography1 This standard is issued under the fixed designation D1945; the number immediately following the designation indicates the year of original origin al adoption or, in the case of revis revision, ion, the year of last revision. revision. A number in paren parenthese thesess indicates the year of last reappr reapproval. oval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
calibration data obtained under identical operating conditions from a refer reference ence standard mixture of know known n compo composition. sition. The numerous heavy-end components of a sample can be grouped into irregular peaks by reversing the direction of the carrier gas through the column at such time as to group the heavy ends either as C5 and heavier, C6 and heavier, or C 7 and heavier. The composition of the sample is calculated by comparing either the peak heights, or the peak areas, or both, with the corresponding values obtained with the reference standard.
1. Sco Scope* pe* 1.1 This test method covers covers the determination determination of the chemical composition of natural gases and similar gaseous mixtures within the range of composition shown in Table 1. 1. This test method meth od may be abb abbrev reviate iated d for the ana analys lysis is of lea lean n nat natura urall gases gas es con contain taining ing neg neglig ligibl iblee amo amount untss of hex hexane aness and hig higher her hydr hy droc ocar arbo bons ns,, or fo forr th thee de dete term rmin inat atio ion n of on onee or mo more re components, as required. 1.2 Th 1.2 Thee va valu lues es sta stated ted in SI un units its are to be re rega gard rded ed as standard. No other units of measurement are included in this standard.
4. Signi Significanc ficancee and Use 4.1 This test method is of significance significance for providing providing data data for calculating physical properties of the sample, such as heating value and relative density, or for monitoring the concentrations of one or more of the components in a mixture.
1.3 This standar standard d doe doess not purport purport to add addre ress ss all of the safetyy co safet conc ncer erns ns,, if an anyy, as asso socia ciate ted d wi with th its us use. e. It is th thee responsibility of the user of this standard to establish appro priate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.4 This int intern ernati ationa onall sta standa ndard rd was dev develo eloped ped in acc accor or-dance with internationally recognized principles on standardizatio iza tion n es esta tabl blis ishe hed d in th thee De Decis cisio ion n on Pr Prin incip ciple less fo forr th thee Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
5. Appar Apparatus atus 5.1 Detector— The The detector shall be a thermal-conductivity type, or its equivalent in sensitivity and stability. The thermal conductivity detector must be sufficiently sensitive to produce a signal of at least 0.5 mV for 1 mol % n -butane in a 0.25-mL sample. 5.2 Recording Instruments— Either Either strip-chart recorders or electronic integrators, or both, are used to display the separated components. compo nents. Although Although a stripstrip-chart chart recorder is not required when whe n usi using ng elec electro tronic nic int integr egratio ation, n, it is hig highly hly des desira irable ble for evaluation of instrument performance.
2. Referenc Referenced ed Documents Documents 2.1 ASTM Standards:2 D2597 Test Method for Analysis of Demethanized HydroD2597 carbon Liquid Mixtures Containing Nitrogen and Carbon 3
Dioxide by Gas Chromatography Chromatography (Withdrawn (Withdrawn 2016) E260 E260 Practice Practice for Packed Column Gas Chromatography
5.2.1 5.2 .1 The recorder recorder shall be a str stripip-cha chart rt rec record order er wit with h a full-range scale of 5 mV or less (1 mV preferred). The width of thee ch th char artt sh shall all be no nott les lesss th than an 15 150 0 mm mm.. A maximu maximum m pe pen n response time of 2 s (1 s preferred) and a minimum chart speed of 10 mm mm/m /min in sh shal alll be re requ quir ired ed.. Fa Fast ster er sp spee eeds ds up to 100 10 0 mm ⁄m ⁄min in ar aree de desi sira rabl blee if th thee ch chro roma mato togr gram am is to be interpreted using manual methods to obtain areas. 5.2.2 Electronic or Computing Integrators— Proof of separation and response equivalent to that for a recorder is required for dis displa plays ys oth other er tha than n by cha chart rt rec record order er.. Bas Baselin elinee tra trackin cking g with tangent skim peak detection is recommended.
3. Summ Summary ary of Test Test Method 3.1 Compo Components nents in a repre representativ sentativee sample are physically separate separ ated d by ga gass ch chro roma mato togr grap aphy hy (G (GC) C) an and d co comp mpar ared ed to 1
This test method is under the jurisdiction of ASTM Committee D03 Committee D03 on on Gaseous Fuels and is the direct responsibility responsibility of Subco Subcommitte mmitteee D03.07 on Analysis of Chemical Composition of Gaseous Fuels. Current Curre nt editio edition n appro approved ved Dec. 1, 2019. Published Published Janua January ry 2020. Originally Originally approved in 1962. Last previous edition approved in 2014 as D1945 – 14. DOI: 10.1520/D1945-14R19. 2 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at
[email protected]. For Annual Book of ASTM Standards volume information, refer to the standard’s Document Summary page on the ASTM website. 3 The last app approve roved d vers version ion of this historica historicall sta standa ndard rd is refe referenc renced ed on
5.3 Attenuator— If I f the chromatog chromatogram ram is to be int interp erpret reted ed using manual methods, an attenuator must be used with the detector output signal to maintain maximum peaks within the recorder chart range. The attenuator must be accurate to within
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0.5 % between the attenuator range steps.
*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
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D1945 − 14 (2019) TABLE 1 Natural Gas Components and Range of Composition Covered Component Helium Hydrogen Oxygen Nitrogen Carbon dioxide Methane Ethane Hydrogen sulfide Propane Isobutane n -Butane Neopentane Isopentane n -Pentane Hexane isomers Heptanes+
5.4.3 An op 5.4.3 optio tiona nall ma manif nifold old arr arran angem gement ent fo forr en enter tering ing vacuum samples is shown in Fig. in Fig. 1. 1.
Mol %
5.5 Column Temperature Control: 5.5.1 Isothermal— When W hen is isot othe herm rmal al op oper erati ation on is us used ed,, maintain main tain the ana analyze lyzerr col column umnss at a temp temperat erature ure con constan stantt to 0.3 °C during the course of the sample run and corresponding reference run. 5.5.2 Temperature Programming— Temperatu emperature re progr programamming may be used, as feasible. The oven temperature shall not
0.01 to 10 0.01 to 10 0.01 to 20 0.01 to 100 0.01 to 20 0.01 to 100 0.01 to 100 0.3 to 30 0.01 to 100 0.01 to 10 0.01 to 10 0.01 to 2 0.01 to 2 0.01 to 2 0.01 to 2 0.01 to 1
exceed the recommended temperature limit for the materials in the column. 5.6 Detector Temperature Control— Maintain Maintain the detecto detectorr temperatur tempera turee at a temp tempera eratur turee con consta stant nt to 0.3 °C dur during ing the course of the sample run and the corresponding reference run. The detector temperature shall be equal to or greater than the maximum column temperature. 5.7 Car Thee ins instru trumen mentt sh shall all be Carrier rier Gas Con Contro trols— ls— Th equipped with suitable facilities to provide a flow of carrier gas through the analyzer and detector at a flow rate that is constant to 1 % throughout the analysis of the sample and the reference standard. The purity of the carrier gas may be improved by flowing the carrier gas through selective filters prior to its entry into the chrom chromatogra atograph. ph.
5.4 Sample Inlet System: 5.4. 5. 4.1 1 The sa samp mple le in inlet let sy syst stem em sh shall all be co cons nstr truc ucted ted of materials that are inert and nonadsorptive with respect to the components compo nents in the sample. The prefe preferred rred material of const construcruction is stainless steel. Copper, brass, and other copper-bearing alloys allo ys are una unacce cceptab ptable. le. The sam sample ple inl inlet et sys system tem fro from m the cylinder valve to the GC column inlet must be maintained at a temperature constant to 61 °C. 5.4.2 Provi Provision sion must be made to introduce introduce into the carrier gas ahead of the analyzing column column a gas-p gas-phase hase sample that has been entrapped in a fixed volume loop or tubular section. The fixed fix ed lo loop op or se secti ction on sh shal alll be so co cons nstru tructe cted d th that at th thee to total tal volume vol ume,, inc includ luding ing dea dead d spa space, ce, sha shall ll not nor normal mally ly exc exceed eed 0.5 mL at 100 kPa. If increased accuracy of the hexanes and heavier portions of the analysis is required, a larger sample size may be used (see Test Method D2597). D2597). The sample volume must be reproducible such that successive runs agree within 1 % on each componen component. t. A flow flowing ing sample inlet sys system tem is acceptable as long as viscosity effects are accounted for.
5.8 Columns: 5.8.1 The columns columns shall be constructed constructed of materials that are inert and nonadsorptive with respect to the components in the sample sam ple.. The pre prefer ferred red mate material rial of con constru structio ction n is sta stainle inless ss steel. Copper and copper-bearing alloys are unacceptable. 5.8.2 An adsorption-typ adsorption-typee column and a partiti partition-ty on-type pe column may be used to make the analysis. NOTE 2—See Practice E260 Practice E260..
NOTE 1—The sample size limitation of 0.5 mL or smaller is selected relativee to lin relativ linear earity ity of det detect ector or res respon ponse, se, and ef efffici icienc ency y of col column umn separa sep aratio tion. n. Lar Larger ger sam sample pless may be use used d to det determ ermine ine low low-qu -quant antity ity
5.8.2.1 Adsorption Column— This This column must completely separa sep arate te oxy oxygen gen,, nit nitrog rogen, en, and met methan hane. e. A 13X mol molecu ecular lar sieve 80/100 mesh is recommended for direct injection. A 5A column can be used if a pre-cut column is present to remove interfering hydrocarbons. If a recorder is used, the recorder pen must return to the baseline between each successive peak. The resolution resolu tion ( R) mu must st be 1. 1.5 5 or greater greater as ca calcu lculat lated ed in th thee
components to increase measurement accuracy.
following equation:
FIG. 1 Sugge Suggested sted Manifold Arrangemen Arrangementt for Enter Entering ing Vacuum Samples
2
D1945 − 14 (2019) R ~ 1, 2 ! 5
x 2 2 x 1 y 2 1 y 1
3 2,
5.11 Vacuum A ny type of vacuum gauge may be Vacuum Gauge— Any used which has a resolution of 0.14 kPa or better and covers the range of 0 to 120 kPa or larger.
(1)
where x 1 , x 2 are the retention times and y1 , y2 are the peak widths. Fig. widths. Fig. 2 illustrates 2 illustrates the calculation for resolution. Fig. resolution. Fig. 3 is 3 is a chromatogram obtained with an adsorption column. 5.8.2.2 Partition Column— This This column must separate ethane through pentanes and carbon dioxide. If a recorder is used, the recorder pen must return to the base line between each peak for propane and succeeding peaks, and to base line within 2 %
5.12 Vacuum Pump— Must Must have the capabil capability ity of produ producing cing a vacuum of 0.14 kPa absolute or less. 6. Preparat Preparation ion of Apparatus Apparatus 6.1 Linearity Check— To To establish linearity of response for the thermal conductivity detector, it is necessary to complete the following procedure: 6.1.1 The major component component of interest (methane (methane for natural gas) is charged to the chromatograph by way of the fixed-size sample loop at partial pressure increments of 13 kPa from 13 to 100 kPa or the prevailing atmospheric pressure. 6.1.2 The integrated peak responses for the area generated at each of the pressure increments are plotted versus their partial pressure (see Fig. (see Fig. 9). 9). 6.1. 6. 1.3 3 Th Thee pl plot otted ted re resu sults lts sh shou ould ld yi yiel eld d a st stra raig ight ht lin line. e. A perfectly linear response would display a straight line at a 45° angle using the logarithmic values. 6.1.4 6.1 .4 Any curved curved lin linee ind indicat icates es the fixed vol volume ume sample loop is too large. A smaller loop size should replace the fixed volume loop and and 6.1.1 through through 6.1.4 6.1.4 should be repeated (see Fig. 9). 9). 6.1.5 The linearity linearity over the range of interest interest must be known for each component. It is useful to construct a table noting the respon res ponse se fac factor tor dev deviati iation on in cha changi nging ng con concen centrat tration ion.. (Se (Seee Table 2 2 and and Table Table 3) 3). 6.1.6 It should be noted that nitrogen, nitrogen, methane, and ethane exhibit less than 1 % compressibility at atmospheric pressure. Other Oth er nat natura urall gas com compon ponent entss do exh exhibi ibitt a sig signifi nifican cantt com com-pressibility at pressures less than atmospheric. 6.1.7 6.1 .7 Mos Mostt com compon ponents ents that hav havee vap vapor or pre pressu ssures res of less than 100 kPa cannot be used as a pure gas for a linearity study because they will not exhibit sufficient vapor pressure for a vacuum gauge reading to 100 kPa. For these components, a mixture with nitrogen or methane can be used to establish a
of fu fullll-sca scale le defl deflect ection ion for com compon ponent entss elu eluted ted ahe ahead ad of propan pro pane, e, with measuremen measurements ts bei being ng at the atte attenua nuation tion of the peak. Separation of carbon dioxide must be sufficient so that a 0.25-m 0.2 5-mL L sam sample ple con contain taining ing 0.1 0.1-mo -moll % car carbon bon dio dioxid xidee will produc pro ducee a clea clearly rly mea measur surabl ablee res respon ponse. se. The res resolu olution tion ( R) must be 1.5 or greater as calculated in the above equation. The separa sep aration tion sho should uld be com complet pleted ed wit within hin 40 min min,, inc includ luding ing reversal of flow after n-pentane to yield a group response for hexanes and heavier components. Figs. 4-6 are examples of chroma chr omatog togram ramss obt obtain ained ed on som somee of the sui suitab table le par partiti tition on columns. 5.8.3 General— Other O ther col column umn pac packin king g mate material rialss tha thatt pro pro-vide satisfactory separation of components of interest may be used (see Fig. (see Fig. 7) 7). In multicolumn applications, it is preferred to use front-end backflush of the heavy ends. NOTE 3—The chrom chromatogra atograms ms in Figs. Figs. 3-8 are only illust illustration rationss of typical separations. The operating conditions, including columns, are also typical and are subject to optimization by competent personnel.
5.9 Drier— Unless U nless water is known not to interfere in the analy an alysis sis,, a dr drie ierr mu must st be pr prov ovid ided ed in th thee sa samp mple le en ente teri ring ng system, sys tem, ahead of the sample valve. valve. The drier must rem remove ove moisture without removing selective components to be determined in the analysis. NOTE 4—See 4—See A2.2 for A2.2 for preparation of a suitable drier.
5.10 Valves— Valv alves es or sam sample ple spl splitte itters, rs, or bot both, h, are required to permit switching, backflushing, or for simultaneous analysis.
FIG. 2 Calcul Calculation ation for Resoluti Resolution on
3
D1945 − 14 (2019)
FIG. 3 Separa Separation tion Column Column for Oxygen, Nitrogen, Nitrogen, and Methane (See Annex (See Annex A2) A2)
FIG. 4 Chrom Chromatogr atogram am of Natural Gas (BMEE Column) (See Annex (See Annex A2) A2)
partial pressure that can extend the total pressure to 100 kPa. Using Tabl Tablee 4 for vap vapor or pre pressu ssures res at 38 °C, calc calculat ulatee the maximum pressure to which a given component can be blended with nitrogen as follows: B 5 ~ 100 3 V ! / i
P 5 ~ i 3 M ! /100
(2 )
where: B = V = i = P =
(3 )
M = vacuu vacuum m gauge gauge press pressure, ure, kPa.
4
blend pressu pressure, re, max, kPa; vapor pressu pressure, re, kPa; mol %; mol partial press pressure, ure, kPa; and
D1945 − 14 (2019)
FIG. 5 Chrom Chromatogr atogram am of Natural Gas (Silicone 200/500 Column) Column) (See Annex (See Annex A2) A2)
FIG. 6 Chrom Chromatogr atogram am of Natural Gas (See Annex (See Annex A2) A2)
6.2 Procedure for Linearity Check: 6.2.1 6.2 .1 Con Connec nectt the pur pure-c e-comp ompone onent nt sou source rce to the sam samplepleentry system. Evacuate the sample-entry system and observe
6.2.2 Car 6.2.2 Carefu efully lly open the needle needle val valve ve to adm admit it the pure component up to 13 kPa of partial pressure.
the va the vacu cuum um ga gaug ugee fo forr le leak aks. s. (S (See ee Fig. Fig. 1 for a sug sugges gested ted manifo man ifold ld arr arrang angeme ement. nt.)) The sam sample ple-en -entry try sys system tem mus mustt be vacuum tight.
sample valve to place the sample onto the column. Record the peak area of the pure component.
6.2. 6. 2.3 3 Rec Recor ord d th thee ex exac actt pa part rtial ial pr press essur uree an and d ac actu tuate ate th thee
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D1945 − 14 (2019)
FIG. 7 Chrom Chromatogr atogram am of Natur Natural al Gas (Multi (Multi-Colu -Column mn Application) Application) (See Annex (See Annex A2) A2)
FIG. 8 Separat Separation ion of Helium and Hydrogen Hydrogen
6.2.4 Repeat 6.2.3 Repeat 6.2.3 for for 26, 39, 52, 65, 78, and 91 kPa on the vacuum gauge, recording the peak area obtained for sample analysis at each of these pressures. 6.2.5 6.2 .5 Plo Plott the area data ( x axis) axis) versus the partial pressures ( y axis) on a linear graph as shown in Fig. 9. 9.
6.2.6 An alternat 6.2.6 alternative ive method method is to obt obtain ain a ble blend nd of all the components and charge the sample loop at partial pressure over the range of interest. If a gas blender is available, the mixture can be diluted with methane thereby giving response curves for all the components. (Warning (Warning—If —If it is not possible to obtain 6
D1945 − 14 (2019)
FIG. 9 Linear Linearity ity of Detector Detector Response TABLE 2 Linearity Evaluation of Methane
TABLE 3 Linearity Evaluation for Nitrogen
S/B diff = (low mole % − high mole %) ⁄low mole % × 100
S/B diff = (low mole % − high mole %) ⁄low mole % × 100
B area
S mole %
S/B mole % ⁄area
223 119 392 242 610 272 261 785 320 280 494 912 299 145 504 317 987 328 336 489 056 351 120 721
51 56 61 66 71 76 81 85
2.2858e-07 2.3082e-07 2.3302e-07 2.3530e-07 2.3734e-07 2.3900e-07 2.4072e-07 2.4208e-07
S/B dif diff., f., % on low value −0.98 −0.95 −0.98 −0.87 −0.70 −0.72 −0.57
information on the linearity of the available gas chromatograph detector for all of the test gas components, then as a minimum requirement the linearity data must be obtained for any gas component that exceeds a concentration of 5 mol%. Chromatographs are not truly linear over wide concentration ranges and linearity should be established over the range of interest.)
B area
S mole %
S/B mole % ⁄area
5 879 836 29 137 066 57 452 364 84 953 192 111 491 232 137 268 784 162 852 288 187 232 496
1 5 10 15 20 25 30 35
1.7007e-07 1.7160e-07 1.7046e-07 1.7657e-07 1.7939e-07 1.8212e-07 1.8422e-07 1.8693e-07
S/B dif diff., f., % on low value −0.89 −1.43 −1.44 −1.60 −1.53 −1.15 −1.48
7. Referenc Referencee Standards
contain kno contain known wn per percen cents ts of the com compon ponent ents, s, exc except ept oxy oxygen gen (Note 5), 5), that are to be determined in the unknown sample. All components in the reference standard must be homogenous in thee va th vapo porr sta state te at th thee tim timee of us use. e. Th Thee co conc ncen entra tratio tion n of a component in the reference standard gas should not be less than one half nor more than twice the concentration of the corresponding component in the test gas.
7.1 Moistu Moisture-fr re-free ee gas mixtures of known composition composition are requ re quire ired d fo forr co comp mpar aris ison on wit with h th thee tes testt sam sampl ple. e. Th They ey mu must st
NOTE 5—Unles 5—Unlesss the refere reference nce standard is stored in a container that has been tested and proved for inertness to oxygen, it is preferable to calibrate
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D1945 − 14 (2019) TABLE 4 Vapor Pressure at 38 °C A Component Nitrogen Methane Carbon dioxide Ethane Hydrogen sulfide Propane Isobutane n -Butane Isopentane n -Pentane n -Hexane n -Heptane
8.2.2 Conne Connections ctions from the sample container container to the sample inlet of the instrument should be made with stainless steel or with wit h sho short rt pie pieces ces of TFE TFE-flu -fluoro orocar carbon bon.. Cop Copper per,, vin vinyl, yl, or rubber connections are not acceptable. Heated lines may be necessary for high hydrocarbon content samples.
kPa absolute >34 500 >34 500 >5 520 >5 520 2 720 1 300 501 356 141 108
8.3 Sample Introduction— The The size of the sample introduced to the chromatographic columns shall not exceed 0.5 mL. (This small sm all sa samp mple le si size ze is ne neces cessa sary ry to ob obtai tain n a lin linea earr de detec tecto torr response for methane.) Sufficient accuracy can be obtained for the determination of all but the minor constituents by the use of this sample size. When increased response is required for the determ det ermina ination tion of com compon ponent entss pre presen sentt in con concen centra tration tionss not exce ex ceed edin ing g 5 mo moll %, it is pe perm rmis issi sibl blee to us usee sa samp mple le an and d refe re fere renc ncee st stan anda dard rd vo volu lume mess no nott ex exce ceed edin ing g 5 mL. (A (Avo void id introduction of liquids into the sample system.) 8.3.1 Purging Method— Open Open the outlet valve of the sample cylinder and purge the sample through the inlet system and sample loop or tube. The amount of purging required must be established and verified for each instrument. The sample loop pressure should be near atmospheric. Close the cylinder valve and allow the pressure of the sample in the loop or tube to stabilize. Then immediately inject the contents of the loop or tube into the chromatographic column to avoid infiltration of contaminants.
34.2 11.2
A
The most rec recent ent data for the vap vapor or pre pressu ssures res listed are ava availa ilable ble from the Thermodynamics Thermodynamic s Researc Research h Center Center,, Texas A&M Univer University sity System, College Station, Statio n, TX 77843.
for oxygen by an alternative method.
7.2 Preparation— A reference standard may be prepared by blen bl endi ding ng pu pure re co comp mpon onen ents. ts. Di Dilu luted ted dr dry y air is a su suita itabl blee standard for oxygen and nitrogen (see 8.5.1 8.5.1)).4,5 8. Pro Procedu cedure re 8.1 Instrument Preparation— Place Place the proper column(s) in operation as needed for the desired run (as described in either 8.4,, 8.5 8.4 8.5,, or or 8.6 8.6)). Adjust the opera operating ting conditions conditions and allow the chromatogra chrom atograph ph to stabiliz stabilize. e. 8.1.1 For hexanes hexanes and higher, heat the sample loop.
8.3.2 Water Displacement— If I f the sample was obtained by water displacement, then water displacement may be used to purg pu rgee an and d fill the sam sampl plee lo loop op or tu tube be.. (Warning Warning—Some —Some components, compo nents, such as carbo carbon n dioxid dioxide, e, hydr hydrogen ogen sulfide, and hexanes hexan es and highe higherr hydr hydrocarb ocarbons, ons, may be partially or completely removed by the water.) 8.3.3 Evacuation Metho Evacuate the charg charging ing system, Method— d— Evacuate including the sample loop, and the sample line back to the valve on the sample cylinder, to less than 0.1 kPa absolute pressure. Close the valve to the vacuum source and carefully meter the fuel-gas sample from the sample cylinder until the sample loop is filled to the desire desired d pressure, as indicated on the vacuum gauge (see Fig. 1) 1). Inject the sample into the chromatograph.
NOTE 6—Most modern chromatographs have valve ovens that can be temperature controlled. temperature controlled. It is strongly recommended recommended in the absence of valve ovens to mount the gas sampling valve in the chromatograph oven and operate at the column temperature.
8.1.2 After the instrument has apparently apparently stabilized, make check runs on the reference standard to establish instrument repeatability. Two consecutive checks must agree within the repeata rep eatabil bility ity limits for the mol % amo amount unt present present of each component. Either the average of the two consecutive checks, or the latest check agreeing within the repeatability limits of the previous check on each component may be used as the refe re fere renc ncee sta stand ndar ard d fo forr all su subs bseq eque uent nt ru runs ns un until til th ther eree is a change in instrument operating conditions. Daily calibrations are recommended.
8.4 Partition Column Run for Ethane and Heavier Hydrocarbons and Carbon Dioxide— This This run is made using either helium or hydrogen as the carrier gas; if other than a thermal conductivity detector is used, select a suitable carrier gas for that detector. Select a sample size in accordance with 8.1 8.1.. Enter the sample, and backflush heavy components when appropriate. Obtain a corresponding response on the reference standard. 8.4.1 Methan Methanee may also be determ determined ined on this column if the column will separate the methane from nitrogen and oxygen (such as with silicone 200/500 as shown in Fig. 5) 5), and the sample size does not exceed 0.5 mL.
8.2 Sample Preparation— If If desired, hydrogen sulfide may be removed by at least two methods (see Annex A2.3 A2.3)). 8.2.1 Prepa Preparat ration ion and Int Intro roduc ductio tion n of Sam Sample— ple— Samples must be equilibrated in the laboratory at 10 to 30 °C above the sour so urce ce tem tempe pera ratu ture re of th thee fiel field d sam sampl plin ing. g. Th Thee hi high gher er th thee temperature the shorter the equilibration time (approximately 2 h fo forr sm smal alll sa samp mple le co cont ntai aine ners rs of 30 300 0 mL or les less) s).. Th This is analys ana lysis is met method hod ass assume umess field sam samplin pling g meth methods ods hav havee removed entrained liquids. If the hydrocarbon dewpoint of the sample is known to be lower than the lowest temperature to which the sample has been exposed, it is not necessary to heat the sample.
8.5 Adso Adsorpt rption ion Col Column umn Run for Oxy Oxygen gen,, Nit Nitro rogen gen,, and Methane— Make M ake th this is ru run n us usin ing g he heliu lium m or hy hydr drog ogen en as th thee carrier gas. The sample size must not exceed 0.5 mL for the dete de term rmin inati ation on of met metha hane ne.. En Ente terr th thee sa samp mple le an and d ob obtai tain n a response respo nse throu through gh methan methanee (Note 5) 5). Lik Likew ewise ise,, ob obta tain in a re re-sponse spo nse on the ref refere erence nce stan standar dard d for nitr nitroge ogen n and meth methane ane.. Obtai Ob tain n a re resp spon onse se on dr dry y ai airr fo forr ni nitr trog ogen en an and d ox oxyg ygen en,, if desi de sire red. d. Th Thee air mu must st be ei eith ther er en enter tered ed at an ac accu cura ratel tely y measured measur ed reduc reduced ed press pressure, ure, or from a helium helium-dilut -diluted ed mixtur mixture. e.
4 A suitable reference reference stand standard ard is avail available able from Scott Specialty Specialty Gases Inc., Plumsteadville, PA. 5 A ten-component ten-component reference standard traceable to the Natio National nal Instit Institute ute of Standards and Technology (NIST) is available from Institute of Gas Technology (IGT), 3424 S. State St., Chicago, IL 60616.
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D1945 − 14 (2019) approximately 1 % of oxyg oxygen en 8.5.1 A mixture containing approximately can be pr prep epar ared ed by pr pres essu suri rizi zing ng a co cont ntain ainer er of dr dry y air at atmospheric pressure to 2 MPa with pure helium. This pressure need ne ed no nott be me meas asur ured ed pr prec ecise isely ly,, as th thee co conc ncen entr trati ation on of nitrogen in the mixture thus prepared must be determined by comparison to nitrogen in the reference standard. The percent nitrogen is multiplied by 0.268 to obtain the mole percent of oxygen or by 0.280 to obtain the mole percent total of oxygen and argon. Do not rely on oxygen standards that have been
9.2.2 Hexanes and Heavier Components— Measure Measure the areas of the hexanes portion and the heptanes and heavier portion of the reverse-flow peak (see Annex (see Annex A1, A1, Fig. A1.1, A1.1, and X3.6 X3.6). ). Also measure the areas of both pentane peaks on the sample chroma chr omatog togram ram,, and adjust all mea measur sured ed are areas as to the same attenuation basis. 9.2.3 Calcula Calculate te corrected areas areas of the reverse flow peaks as follows: Corrected C 6 area 5 72/86 3 measured C 6 area
(6)
prepared for more a few It is permissible to use a response factor for than oxygen thatdays. is relative to a stable constituent.
Corrected C 7 and heavier area
(7)
5
8.6 Adsorption Adsorption Column Run for Helium and Hydr Hydrogen— ogen— Make this run using either nitrogen or argon as the carrier gas. Enter a 1 to 5 mL sample and record the response for helium, follow fol lowed ed by hyd hydrog rogen, en, which wil willl be jus justt ahe ahead ad of oxy oxygen gen (No Note te 5). Obt Obtain ain a cor corres respon pondin ding g res respon ponse se on a ref refere erence nce standar stan dard d con contain taining ing sui suitabl tablee con concen centra tration tionss of hel helium ium and hydrogen (see Fig. (see Fig. 8). 8).
where A = average molecular weight of the C 7 and heavier fraction. NOTE 7—The value of 98 is usually sufficiently accurate for use as the C7 and heavier fraction average molecular weight; the small amount of C 8 and heavier present is usually offset by the lighter methyl cyclopentane and cyclohexane cyclohexane that occur in this fractio fraction. n. A more accurate value for the molecular weight of C 7 and heavier can be obtained as described described in Annex A1.3.. A1.3
9. Calc Calculat ulation ion
9.2.4 Calcula Calculate te the concentration concentration of the two fractions fractions in the sample as follows:
9.1 The number of significant significant digits retained for the quantitative value of each component shall be such that accuracy is neither neit her sac sacrifi rificed ced or exa exagge ggerat rated. ed. The exp expres ressed sed num numeri erical cal value of any component in the sample should not be presumed to be more accurate than the corresponding certified value of that component in the calibration standard.
Moll % C6 Mo 3
3
(4 )
C = component component concen concentration tration in the the sample, sample, mol mol %; peak k height height of of compon component ent in in the samp sample, le, mm; mm; A = pea B = peak height of compone component nt in the standar standard, d, mm; and compon ponent ent concent concentrati ration on in the refe referen rence ce standard standard,, S = com mol %.
1nC5
6
! / ~ i C
5
~ mol% i C
5
1n C 5
! / ~ i C
(8 )
(9 )
!.
1 n C 5 area
5
1nC5
area! .
and heavier) shall then be used for calculating the final mole percentt value. percen 9.2.6 9.2 .6 Nor Normal malize ize the mol molee per percen centt val values ues by mul multip tiplyin lying g each value by 100 and dividing by the sum of the original values. The sum of the original values should not differ from 100.0 % by more than 1.0 %. 9.2.7 See sample calculations calculations in in Appendix X2. X2.
9.2.1.1 If air has been run at reduced pressure 9.2.1.1 pressure for oxygen oxygen or nitrogen calibration, or both, correct the equation for pressure as follows:
5
~ corrected C area!
9.2.4.1 9.2.4. 1 If the mol molee per percen centt of iC5 + n C5 has bee been n dete deterrmined by a separ separate ate run with a smaller sized sample, sample, this value need not be redetermined. 9.2.5 The entire reverse reverse flow area may be calculated in this manner as C6 and heavier, or as C 5 and heavier should the carrierr gas revers carrie reversal al be made after n -butane. The measured area should shoul d be corre corrected cted by using the average molecular weights of the ent entire ire rev revers erse-fl e-flow ow com compon ponents ents for the val value ue of A. The mole percent and area of the i C5 and n C5 reverse flow peak of an identically sized sample of reference standard (free of C 6
where:
C 5 S 3 ~ A / B ! 3 ~ P a / P b !
~ mol% i C
5
Mol% C 7 1 5 ~ corrected C 7 area!
9.2 External Standard Method: 9.2.1 Penta Pentanes nes an and d Lig Lighte hterr Co Compo mponen nents— ts— Mea Measur suree the heig he ight ht of eac each h co comp mpon onen entt pe peak ak fo forr pe pent ntan anes es an and d lig light hter er,, convert to the same attenuation for corresponding components in the sample and reference standard, and calculate the concentration of each component in the sample as follows: C 5 S 3 ~ A / B !
72/A 3 measured C 7 and heavier area
(5 )
where: pressure re at which which air air is run and and Pa = pressu truee baro barome metr tric ic pr pres essu sure re du duri ring ng th thee ru run, n, wit with h bo both th Pb = tru pressures being expressed in the same units.
10. Pre Precisi cision on
9.2.1. 9.2 .1.2 2 Use com compos positio ition n valu values es of 78. 78.1 1 % nit nitrog rogen en and 21.9 % oxygen for dry air, because argon elutes with oxygen
10.1 Precision— The The precision of this test method, as determined by the statistical examination of the interlaboratory test results, for gas samples of pipeline quality 38 MJ/m 3 is as follows: 10.1.1 Repeatability— The The difference between two succes-
on molecular thisatest method.sieves column under the normal conditions of
si sive ve re resu sults lts obtai ob taine ned d byoperating thee sa th same meconditions oper op erato atorr on with wi th thee sa th same me apparatus under constant identical test
9
D1945 − 14 (2019) materials should be considered suspect if they differ by more than the following amounts: Component, mol %
Repeatability
0 to 0.09 0.1 to 0.9 1.0 to 4.9 5.0 to 10 Over 10
0.01 0.04 0.07 0.08 0.10
11. Keywords 11.1 gas analysis; gas chromatography 11.1 chromatography;; natural gas compo compo-sition
10.1.2 Reproducibility— The The difference between two results obtain obt ained ed by dif differ ferent ent ope operat rators ors in dif differ ferent ent lab labora orator tories ies on identica iden ticall tes testt mate materia rials ls sho should uld be con consid sidere ered d sus suspec pectt if the they y differ by more than the following amounts: Component, mol %
Reproducibility
0 to 0.09 0.1 to 0.9 1.0 to 4.9 5.0 to 10 Over 10
0.02 0.07 0.10 0.12 0.15
ANNEXES (Mandatory Information) A1. SUPPLEMEN SUPPLEMENT TARY PROCEDURES PROCEDURES
A1.2.2 Enter a 1 to 5 mL sample sample into the partition column column and reverse the carrier gas flow after n-pentane is separated. Obtain a corresponding chromatogram of the reference standard. Measure the peak heights of ethane through n-pentane and an d th thee ar area eass of th thee pe pent ntan anee pe peak akss of th thee st stan anda dard rd.. Ma Make ke calculations on ethane and heavier components in the same manner man ner as for the com comple plete te ana analys lysis is meth method. od. Met Methan hanee and lighter may be expressed as the difference between 100 and the sum of the determined components.
A1.1 Analysis for Only Propane Propane and Heavier Components Components A1.1.1 This determinatio A1.1.1 determination n can be made in 10 to 15 min run timee by us tim using ing co colum lumn n co cond nditi ition onss to sep separ arate ate pr prop opan ane, e, isobutane, n-bu -butane, tane, isop isopentan entane, e, n-pe -penta ntane, ne, hex hexane anes, s, and heptanes, and heavier, but disregarding separation on ethane and lighter. A1.1.2 A1. 1.2 Use a 5 m bis bis-(2 -(2(2(2-meth methoxy oxyeth ethoxy oxy)) ethy ethyl)et l)ether her (BMEE) column column at about 30 °C, or a suitable length of another partition column that will separate propane through n -pentane in about 5 min. Enter a 1 to 5 mL sample into the column and
A1.3 Spec Special ial Analysis Analysis to Dete Determin rminee Hexan Hexanes es and Heavier
reverse the carrier gasomatog flowtogram after is separated. Obtain a cor corres respon pondin ding g chr chroma ram n -pentane on the ref refere erence nce sta standa ndard, rd, which can be accomplished in about 5 min run time, as there is no need to reverse the flow on the reference standard. Make calculations in the same manner as for the complete analysis method.
Components A1.3.1 A shor shortt partition column column can be used advantageous advantageously ly to separate heavy-end components and obtain a more detailed breakdown on composition of the reverse-flow fractions. This information provides quality data and a basis for calculating physic phy sical al pro proper perties ties suc such h as mol molecu ecular lar wei weight ght on the these se fra fracctions.
A1.1.3 A1. 1.3 A det determ ermina inatio tion n of pro propan pane, e, iso isobut butane ane,, n-butane, and pentanes and heavier can be made in about 5 min run time by reversing the carrier-gas flow after n -butane. However, it is neces ne cessa sary ry to kn know ow th thee av aver erag agee mo mole lecu cular lar we weig ight ht of th thee pentanes pentan es and heavie heavierr compo components. nents.
A1.2.1 A1.2. 1 In many cases, a single partition run using using a sample
A1.3.2 Fig. Fig. A1. A1.1 1 is a chromatogram that shows components that are separated by a 2 m BMEE column in 20 min. To make this determination, enter a 5 mL sample into the short column and reverse the carrier gas after the separation of n-heptane. Measure Measu re areas of all peaks eluted after n -pentane. Correct each peak area to the mol basis by dividing each peak area by the molecular weight of the component. A value of 120 may be
size in the order except of 1 to 5 mL will which be adequate all components methane, cannotfor bedetermining determined accu ac cura rate tely ly us usin ing g th this is si size ze sa samp mple le wi with th pe peak ak he heig ight ht measurements, because of its high concentration.
us used ed fo forr th thee peak. mole mo lecu cular lar we weig ight ht mole of th theepercent octa oc tane nes s an and heav he avier ier reverse-flow Calculate the of thed hexanes and hea heavie vierr com compon ponent entss by add adding ing the cor correc rected ted are areas as and dividing to make the total 100 %.
A1.2 Single-Run Analysis for Ethane and Heavier Heavier Components
10
D1945 − 14 (2019)
FIG. A1.1 Compo Compositio sition n of Hexanes and Heavier Fraction
PREPARA ARATION TION OF COLUMNS AND DRIER A2. PREP
A2.1 Preparation of Columns—See Practice E260 Practice E260..
sulfatee in the line ups sulfat upstre tream am of bot both h the chr chroma omatog tograp raph h and drying dry ing tub tube. e. Thi Thiss pro proced cedure ure will rem remove ove sma small ll amo amount untss of hydrogen sulfide while having but minimal effect on the carbon dioxide in the sample.
A2.2 Prepa —Fil illl a 10 mm di diam amet eter er by Preparat ration ion of Dri Drier er —F 100 mm length glass tube with granu granular lar phos phosphoru phoruss pentox pentoxide ide or magnes magnesium ium perch perchlorate lorate,, obser observing ving all prope properr safety precautions. Mount as required to dry the sample. Replace the drying agent after about one half of the material has become spent.
A2.4 Colu Column mn Arran Arrangemen gement t —For — For an anal alys yses es in wh whic ich h hexanes and heavier components are to be determined, Fig. A2.1 shows A2.1 shows an arrangement whereby columns can be quickly and an d eas easily ily ch chan ange ged d by th thee tu turn rn of a se selec lecto torr va valv lve. e. Two column col umnss are nec necess essary ary to det determ ermine ine all of the com compon ponent entss
A2.3 Remova Removall of Hydr Hydrogen ogen Sulfide: Sulfide: A2.3.1 For samples containing more more than about 300 300 ppm by mass hydrogen sulfide, remove the hydrogen sulfide by connecting a tube of sodium hydrate absorbent (Ascarite) ahead of the sample container during sampling, or ahead of the drying tube when entering the sample into the chromatograph. This proced pro cedure ure als also o rem remove ovess car carbon bon dioxide, dioxide, and the res results ults obtained will be on the acid-gas free basis.
covered this test method. However, short long column col umnss inpro provid vide e the flexibi flex ibility lity of thr three ee and partiti par tition on partition column col umn lengths, by using them either singly or in series. The connection between V 1 and V 2 in Fig. A2.1 should be as short as possible (20 mm is practical) to minimize dead space between the columns when used in series. If all columns are chosen to operate ope rate at the sam samee tem temper peratu ature, re, the then n sta stabili bilizati zation on time between changing columns will be minimized.
A2.3.2 Hydr A2.3.2 Hydrogen ogen sulfide sulfide may also be removed by connectconnecting a tube of pumice that has been impregnated with cupric
11
D1945 − 14 (2019)
FIG. A2.1 Colum Column n Arrangement Arrangement
APPENDIXES (Nonmandatory Information) X1. REFERENC REFERENCE E STANDARD STANDARD MIXTURE
X1.1 Prepara Preparation tion
dioxide. The pure components should be 99+ % pure. Methane shou sh ould ld be in a 1 L cy cyli lind nder er at 10 MP MPa) a) pr pres essu sure re.. Ru Run n a chro ch roma mato togr gram am of ea each ch co comp mpon onen entt to ch check eck on it itss gi give ven n composition.
X1.1.1 X1.1. 1 Gas mixtures of the follo following wing typical compositions compositions will suffice for use as reference standards for most analytical requirements requir ements (Note X1.1) X1.1): Component Helium Hydrogen Nitrogen Methane (maximum) Ethane Carbon dioxide Propane Isobutane n -Butane Neopentane Isopentane n -Pentane Hexanes+
Lean Gas, mol %
Rich Gas, mol %
1.0 3.0 4.0 85 6.0 1.0 4.0 2.0 2.0 0.5 0.5 0.5 0.1
0.5 0.5 0.5 74 10 10 1.0 7.0 3.0 3.0 1.0 1.0 1.0 0.2
X1.1.2 X1.1 .2.2 .2 Ev Evacu acuate ate th thee 20 L cy cylin linde derr fo forr se seve vera rall ho hour urs. s. Evacua Eva cuate te 100 mL Cyli Cylinde nderr A, an and d ob obtai tain n its tr true ue we weig ight ht.. Connect Conne ct Cylind Cylinder er A to a cylinder of pure n-pe -pentan ntanee wit with h a metal connection of calculated length to contain approximately the amount of n n-pentane to be added. Flush the connection with the n -pentane by loosening the fitting at the valve on Cylinder A. Tighten the fitting. Close the n-pentane cylinder valve and open Cylind Cylinder er A valv valvee to ad admi mitt th thee n-pe -penta ntane ne fro from m the connection conne ction and then close the valve on Cylind Cylinder er A . Disconnect and weigh Cylinder A to obtain the weight of n n -pentane added. X1.1.2.3 Similarly, X1.1.2.3 Similarly, add isopen isopentane, tane, n-butan -butane, e, isobu isobutane, tane, propane, ethane, and carbon dioxide, in that order, as desired, in the reference standard. Weigh Cylinder A after each addition to obtain the weight of the component added. Connect Cylinder A to th thee ev evac acua uate ted d 20 L cy cyli lind nder er wi with th as sh shor ortt a cl clea ean, n, small-diameter connector as possible. Open the valve on the 20 L cylinder, then open the valve on Cylinder A . This will result in the transfer of nearly all of the contents of Cylinder A into the 20 L cylinder. Close the cylinder valves, disconnect, and weigh Cylinder A to determine the weight of mixture that was
NOTE X1.1—If the mixture is stored under pressure, take care to ensure that the partial that partial pre pressu ssure re of any componen componentt doe doess not exceed its vap vapor or pressure at the temperature and pressure at which the sample is stored and used. use d. The lean mixture mixture has a cri cricon conden denthe therm rm at 15. 15.6 6 °C and the ric rich h mixture has a cricondentherm at 37.8 °C.
X1.1 X1 .1.2 .2 A us usef eful ul met metho hod d fo forr pr prep epar arati ation on of a re refe fere renc ncee standard by weight is as follows:4 X1.1.2.1 X1.1. 2.1 Obtain the following equipment equipment and materia material: l: Cylinder , 20 L Pressure Cylinders, two 100 mL ( A and B) Balance, 2000 g capacity, sensitivity of 10 mg. Puree Compo Pur Components nents, meth methane ane thr throug ough h n-pe -penta ntane, ne, and carb carbon on
not transferred to the 20 L cylinder. X1.1.2.4 X1.1.2 .4 Evacua Evacuate te and weigh 100 mL Cylind Cylinder er B. Then fill Cylinder B with with hel helium ium and hyd hydrog rogen en res respec pectiv tively ely to the pressu pre ssures res req requir uired ed to pro provid videe the des desired ired con concen centrat tration ionss of 12
D1945 − 14 (2019) these components in the final blend. (Helium and hydrogen are prepared and measured separately from the other components to prevent their pressures, while in the 100-mL cylinder, from causin cau sing g con conden densat sation ion of the hig higher her hyd hydroc rocarb arbons ons.) .) Weig eigh h Cylinder B after after each add additio ition n to obt obtain ain the wei weight ght of the component compo nent added added.. Conne Connect ct Cylind Cylinder er B to the 20 L cylinder with as short a clean, small-diameter connector as possible. Open the valve on the 20 L cylinder, then open the valve on Cylinder B , which will result in the transfer of nearly all of the
where: component nent concen concentration tration,, mol; mol; C = compo heightt of compo component nent in in blend; blend; A = peak heigh B = peak heigh heightt of pure compo component; nent; Pa = pre pressu ssure re at which which blend blend is run, run, kPa; kPa; Pb = press pressure ure at which which componen componentt is run, kPa; kPa; and V f = volum volumee fraction fraction of pure compon component. ent. NOTE X1.3—V f = 1.000 if the calibration component is free of impurities.
contents conten ts of Cyl Cylind inder er B into into th thee 20 L cy cylin linde derr. Clo Close se th thee cylinder valves, disconnect, and weigh Cylinder B to obtain the weight weig ht of the mix mixtur turee tha thatt was not tra transf nsferr erred ed to the 20 L cylinder.
X1.2.5.3 X1.2.5 .3 Normal Normalize ize values to 100.0 %. X1.3 Calibration using Relative Molar Response Response Values Values X1.3.1 Relativ Relativee response ratios can be deriv derived ed from linearity data and used for calculating response factors. This eliminate na tess th thee ne need ed fo forr a mu multi ltico comp mpon onen entt sta stand ndar ard d fo forr da daily ily calibration. The test method can be used on any gas chromatograph using a thermal conductivity or thermistor detector.
X1.1.2.5 Weigh a 1 L cylind X1.1.2.5 cylinder er containing pure methane methane at abou ab outt 10 MP MPaa pr pres essu sure re.. Tra rans nsfe ferr th thee me meth than anee to th thee 20 L cylinder until the pressure equalizes. Weigh the 1 L cylinder to determine the weight of methane transferred. X1.1.2.6 X1.1. 2.6 Thoro Thoroughly ughly mix the contents of the 20 L cylinder by heating at the bottom by a convenient means such as hot water or a heat lamp, and leaving the cylinder in a vertical position for at least 6 h. X1.1.2 X1. 1.2.7 .7 Use the weig weights hts and pur puritie itiess of all com compon ponent entss added add ed to calc calcula ulate te the wei weight ght com compos positio ition n of the mix mixtur ture. e. Convert the weight percent to mole percent.
X1.3.2 Obt X1.3.2 Obtain ain a ble blend nd tha thatt bra bracke ckets ts the exp expect ected ed con concen cen-tration the instrument will be analyzing. The major component (methane) is used as the balance gas and may fall below the expected expect ed concentration. concentration. This compo component nent is presen presentt in the daily calibra cali bratio tion n sta standa ndard rd and lin linear earity ity is ass assure ured d fro from m pre previo vious us tests. X1.3.3 X1. 3.3 Inject Inject the sam sample ple at red reduce uced d pre pressu ssures res usi using ng the apparatus in apparatus in Fig. Fig. 1 or 1 or using a mechanical gas blender. Obtain repeatable peak areas or height at 90, 75, 60, 45, 30, and 15 % of absolute pressure. For 100 kPa, the pressures used are 90 kPa, 75 kPa, 60 kPa, 45 kPa, 30 kPa, 15 kPa.
X1.2 Calibration with Pure Pure Components Components X1.2.1 X1.2. 1 Use helium carrier carrier gas to admit a sample volume of 0.25 to 0.5 mL into the adsorption column, providing methane at 50 kPa and nitrogen at 10 kPa absolute pressure. Run a sample of the standard mixture at 70 kPa pressure and obtain peaks for methane and nitrogen.
X1.3.4 Plot the area or height height (attenuated (attenuated at the same height as the reference component) versus concentration and calculate the slope of the line by the least squares method. Given the equation of the line as Y = a0 + a1 X where Y represents the area or height points and X the the concentration points. The line is assumed to intersect through the origin and a 0 = 0. The slope a1 can be calculated by:
NOTE X1.2—E X1.2—Each ach run mad madee thr throug oughou houtt thi thiss pro proced cedure ure sho should uld be repeated to ensure that peak heights are reproducible after correction for pressure differences to within 1 mm or 1 % of the mean value. All peaks should be recorded at an instrument attenuation that gives the maximum measurable peak height.
X1.2.2 Chang X1.2.2 Changee the carrier gas to argon or nitrogen nitrogen and, after the base line has stabilized, enter a sample of pure helium at 7 kPa absolute pressure, recording the peak at an attenuation that allows maximum peak height. Run a sample of the mixture at 70 kPa absolute pressure and obtain the helium peak.
a1 5
X1.2.4 X1.2. 4 Run the gas mixture at 70 kPa absolute absolute pressure. X1.2.5 Calculat X1.2.5 Calculatee the compo composition sition of the prepared gas mixture as follows: X1.2.5.1 X1.2. 5.1 Corre Correct ct peak height heightss of all pure components components and the respective components components in the blend to the same attenu attenuation ation
(X1.2)
X1.3.6 For daily calibration, a four four-comp -component onent standard standard is used containing nitrogen, methane, ethane, and propane. The fewer components eliminates dew point problems, reactivity, is more accurate and can be blended at a higher pressure. The referenced components’ response factors are calculated from the current reference factor and the Relative Molar Response
(Note X1.2). X1.2). X1.2.5.2 X1.2. 5.2 Calcula Calculate te the concen concentration tration of each component component as follows:
2
X1.3.5 Ratio the slopes of the referenced referenced components components (i) to the slopes of the reference components ( r ) present in the daily calibration standard. This gives the Relative Molar Response factor fac tor ( RMRi) for compone component nt ( i). The ref refere erence nce com compon ponent ent mustt be pre mus presen sentt in the sam samee ins instru trumen mental tal seq sequen uence ce (ex (excep ceptt Hexanes+) as the referenced components. For instance, propane pa ne ca can n be th thee re refe fere renc ncee co comp mpon onen entt fo forr th thee bu buta tane ness an and d pentanes if propane is separated on the same column in the same sequence as the butanes and pentanes. Ethane can be the reference refer ence component component for carbo carbon n dioxide if it elutes in the same sequence as carbon dioxide. The hexanes + peak can be referenced to propane or calculated as mentioned in the body of the standard.
X1.2.3 Switch to the partit X1.2.3 partition ion column with helium carrier gas, and run the gas mixture at 70 kPa absolute pressure. Then admit samples of pure ethane and propane at 10 kPa absolute pressure, and butanes, pentanes, and carbon dioxide at 5 kPa absolute pressure.
C 5 ~ 100V f !~ A / B !~ P b / P a !
( XY ~ ( Y !
(X1.1)
13
D1945 − 14 (2019) TABLE X1.1 Least Square Calculation for Slope of Iso-Butane
sum =
Area Y
Mole % X
XY
Y2
984 515 900 410 758 917 611 488 466 037 314 649 159 303
1 0.9 0.75 0.6 0.45 0.3 0.15
984 515 810 369 569 187.75 366 892.8 209 716.65 94 394.7 23 895.45
9.693e + 11 8.107e + 11 5.670e + 11 3.739e + 11 2.172e + 11 9.900e + 10 2.538e + 10
4 195 319
4.15
slope =
Response Factor ~ R ! 5
Relative Molar Response ~ RMRi ! 5 R iC
4
5 RMRic
Mole% ~ i ! /Area~ i ! (X1.4) Mole% ~ r ! /Area~ r !
3 R C
3
(X1.5)
operating conditions, all of the components will be affected equally and the calculated response factors will shift accordingly. See Table See Table X1.1 X1.1 and and Fig. Fig. X1.1 a X1.1 and nd Table Table X1.2. X1.2.
9.9594e-07
factor. Following is a description of the basic calculations, an example of deriving a Relative Molar Response factor (Fig. (Fig. X1.1), X1.1 ), and a table showing how response factors are calculated (Table X1.2) X1.2).
FIG. X1.1 Exampl Example e of Derivi Deriving ng a Relati Relative ve Molar Response Factor Factor
4
(X1. 3)
X1.3.7 Perio Periodic dic checks of the RMR relationship relationship is recom recom-mended men ded.. The rela relatio tionsh nship ip is ind indepe epende ndent nt of temp tempera erature ture,, sample size, and carrier gas flow rate. If changes occur in these
3 058 971.35 3. 3.071 452e + 12
^XY/ ^Y2
Mole% , Area
14
D1945 − 14 (2019) TABLE X1.2 Calculation of Response Factors Using Relative Molar Response Values Component
Nitrogen Methane Ethane Propane Carbon dioxide Isobutane n -Butane Neopentane Isopentane n -Pentane Hexanes+
Mole % in Reference Standard S
Response of Reference Standard B
Response Factor From Reference Standard S/B,K
5.08 82.15 8.75 4.02
2 685 885 36 642 384 6 328 524 3 552 767
1.8914E-6 2.2419E-6 1.3826E-6 1.1315E-6
Response Factor of Referenced Components (RMRi)x(Ki)
Relative MolarA Response from Slope /K i i RMRi
1.116 07c2 0.729 58c3 0.693 10c3 0.682 71c3 0.638 74c3 0.600 41c3 0.547 62c3
1.5429E-6 9.9594E-7 9.1142E-7 8.9776E-7 8.3994E-7 7.8953E-7 7.2012E-7
A
The Relative Molar Response is a constant that is calculated by dividing the slope of the referenced component by the component that is present in the reference standard. For example: RMRic
4
5
slopeic ic d / s K c d s slope 4
3
5
9.9594E 9.9594 E
2
7 1.1315E 1.1315E
2
6
5
0.72958 0.7 2958
X2. SAMPLE CALCULA CALCULATIONS (SEE SECTION 9 SECTION 9))
TABLE X2.1 Sample Calculations Component Helium Hydrogen Oxygen Nitrogen Methane Ethane Carbon dioxide Propane Isobutane n -Butane Neopentane Isopentane n -Pentane Hexanes+B A
Mol % in Reference Standard, S Standard, S
Response of Reference Standard, B Standard, B
Response Factor, S/B Factor, S/B
0.50 0.74 0.27 4.89 70.27 9.07 0.98 6.65 2.88 2.87 0.59 0.87 0.86
41.1 90.2 35.5 77.8 76.4 96.5 57.5 55.2 73.2 60.3 10.4 96.0 86.8
0.0122 0.0082 0.0076 0.0629 0.9198 0.0940 0.0170 0.1205 0.0393 0.0476 0.0567 0.0091 0.0099
Response for Sample,A A 12.6 1.5 2.1 75.6 90.4 79.0 21.2 20.6 11.0 15.0 0.1 24.0 20.5 72.1C
Percent C = (S × A) ⁄B 0.154 0.012 0.016 4.755 83.150 7.426 0.360 2.482 0.432 0.714 0.006 0.218 0.203 0.166D 100.094 %
The response for a constituent in the sample has been corrected to the same attenuation as for that constituent in the reference standard.
B
Average molecular weight of C6 + = 92. Average 92. Corrected C6 response = (original response of 92.1) × (72 ⁄92) = 72.1. D Mol % C6 + = (0.218 + 0.203) × (72.1) (72.1) ⁄(96.0 + 86.8) = 0.166. % iC 5 % nC 5 Areas iC Areas iC + + nC 5 C
15
Normalized, % 0.15 0.01 0.02 4.75 83.07 7.42 0.36 2.48 0.43 0.71 0.01 0.22 0.20 0.17 100.00 %
D1945 − 14 (2019) X3. PRECAUT PRECAUTIONS IONS FOR AVOIDING COMMON CAUSES CAUSES OF ERRORS ERRORS
X3.1 Hexa Hexane ne and Heav Heavier ier Content Content Change
X3.5.3 X3.5 .3 Be su sure re th that at th thee in inlet let dr drier ier is in go good od co cond nditi ition on.. Moisture on the column will enlarge the reverse flow peak.
X3.1.1 The amounts of heavy-end compounds compounds in natural gas are easily changed during handling and entering of samples to give seriously erroneous low or high values. Concentration of these components has been observed to occur in a number of cases cas es be beca caus usee of co colle llecti ction on of he heav avier ier co comp mpon onen ents ts in th thee sample loop during purging of the system. The surface effect of small diameter tubing acts as a separating column and must not be used in the sampling and entering system when components heavier than pentanes are to be determined. An accumulation of oily film in the sam sampli pling ng sys system tem gre greatly atly aggravat aggravates es thi thiss prob pr oble lem. m. Al Also so,, th thee ri rich cher er th thee ga gas, s, th thee wo wors rsee th thee pr prob oblem lem.. Periodically, check C6 and heavier repeatability of the apparatus by making several check runs on the same sample. It is helpful to retain a sample containing some hexanes and heavier for per period iodic ic che checki cking. ng. When enla enlarg rgeme ement nt of the hea heavy vy end peaks is noted, thoroughly clean the sampling valve and loop with acetone. acetone. Thi Thiss tro troubl ublee has bee been n exp experie erience nced d with some inlet systems even when clean and with the specified sample loop lo op si size. ze. Th This is co cont ntam amin inati ation on can be mi mini nimi mized zed by su such ch techniques as purging with inert gas, heating the sample loop, using a vacuum system, or other such effective means.
X3.5.4 Be sure the column is clean by occasionally occasionally giving giving it severall hours’ sweep of carrier gas in rever severa reverse se flow directi direction. on. A level baseline should be quickly attained in either flow direction if the column is clean. X3.5.5 Whe X3.5.5 When n the reverse reverse flow val valve ve is tur turned ned,, ther theree is a reversal of pressure conditions at the column ends that upsets the carrier gas flow. This flow should quickly return to the same flow rate and the baseline level out. If it does not, the cause may be a leak in the carrier gas system, faulty flow regulator, or an unbalanced condition of the column or plumbing. X3.6 Refere Reference nce Standard X3.6 X3 .6.1 .1 Ma Main intai tain n th thee re refe fere renc ncee st stan anda dard rd at +1 +15 5 °C or a temperature that is above the hydrocarbon dew point. If the reference standard should be exposed to lower temperatures, heat at the bottom for sever several al hours before removing a sample sample.. If in doubt about the composition, check the n-pent -pentane ane and isopen iso pentan tanee val values ues wit with h pur puree com compon ponent entss by the pro proced cedure ure prescribed in Annex in Annex A2. A2. X3.7 Measurem Measurements ents
X3.2 Acid Gas Content Content Change
X3.7.1 The baseline X3.7.1 baseline and top topss of pea peaks ks sho should uld be pla plainl inly y visible for making peak height measurements. Do not use a fixed fixe d zer zero o line as the baseline, baseline, but use the actu actual al obs observ erved ed baseline. On high sensitivity, this baseline may drift slightly without harm and it need not frequently be moved back to zero. A strip-chart recorder with an offset zero is desirable. The area of re reve vers rsee flo flow w pe peak ak ma may y be mea measu sure red d by pl plan anim imete eterr or geometric construction. The reverse flow area, and the pentanes peaks used for comparison, should be measured by the samee met sam method hod.. Tha Thatt is, use eith either er geo geomet metric ric con constru structio ction n or planimeter, but do not intermix. When a planimeter is used, carefully make several tracings and use the average. Check this average by a second group of tracings.
X3.2.1 The carbon dioxide and hydrogen sulfide contents of gas are easily altered during sampling and handling. If samples containing carbon dioxide or hydrogen sulfide, or both, are to be taken, use completely dry sample cylinders, connections, and lin lines, es, as moi moistu sture re wil willl sel selecti ectivel vely y abs absorb orb app apprec reciabl iablee amou am ount ntss of th thee ac acid id ga gase ses. s. If hy hydr drog ogen en is pr pres esen ent, t, us usee aluminum, stainless steel, or other materials inert to hydrogen sulfide for the cylinder, valves, lines, and connections. X3.3 Samp Sample le Dew Point Point X3.3.1 Nonrepresentative samples frequently occur because of con conden densati sation on of liq liquid uid.. Mai Mainta ntain in all sam sample pless abo above ve the hydrocarbon dew point. If cooled below this, heat 10 °C or more above the dew point for several hours before using. If the dew point is unknown, heat above the sampling temperature.
X3.8 Miscellaneo Miscellaneous us X3.8.1 Moistu X3.8.1 Moisture re in the carrier gas that would cause cause trouble on the reverse flow may be safeguarded against by installing a cartridge cartrid ge of molecular sieves ahead of the instru instrument. ment. Usually 1 m of 6 mm tubing packed with 30- to 60-mesh molecular sieves is adequate, if changed with each cylinder of carrier gas.
X3.4 Samp Sample le Inlet System System X3.4.1 Do not use rubber or plastic that may preferentially X3.4.1 preferentially adsorb ads orb sample componen components. ts. Keep the sys system tem sho short rt and the drier small to minimize the purging required. X3.5 Samp Sample le Size Repeatabili Repeatability ty
X3.8.2 Check the carrier gas flow system periodically X3.8.2 periodically for leaks with soap or leak detector solution.
X3.5.1 X3. 5.1 Vary Varying ing bac back k pre pressu ssures res on the sam sample ple loo loop p may impair sample size repeat repeatability ability..
X3.8.3 X3. 8.3 Use elec electri trical cal con contact tact cleaner cleaner on the atte attenua nuator tor if noisy contacts are indicated.
X3.5.2 Make it a practice to make all reverse X3.5.2 reverse flow determinations in the same carrier gas flow direction. All single-peak determinations and corresponding reference runs will then be made in the same carrier gas flow direction.
X3.8.4 Peaks with square X3.8.4 square tops with omission of small peaks peaks can be caused by a sluggish recorder. If this condition cannot be remedied by adjustment of the gain, check the electronics in the recorder.
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D1945 − 14 (2019) SUMMARY OF CHANGES Committ Comm ittee ee D0 D03 3 as id iden entifi tified ed th thee lo loca catio tion n of se selec lected ted ch chan ange gess to th this is st stan anda dard rd si sinc ncee th thee la last st iss issue ue (D1945–96(2010)) that may impact the use of this standard. was re rewr writ itten ten to all allow ow th thee us usee of an any y (1) Subsection 5.11 was vacuum gauge, includ including ing mercur mercury y manom manometers. eters. (2) Fig. 1 replaced. 1 replaced.
(3) References to pressure in mm Hg have been removed and replaced with the SI unit Pascal. (4) All non-SI units removed.
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