1、Designation: D4051 10 (Reapproved 2015)Standard Practice forPreparation of Low-Pressure Gas Blends1This standard is issued under the fixed designation D4051; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision
2、. 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 a laboratory procedure for thepreparation of low-pressure multicomponent gas blends. Thetechnique is applicabl
3、e to the blending of components atpercent levels and can be extended to lower concentrations byperforming dilutions of a previously prepared base blend. Themaximum blend pressure obtainable is dependent upon therange of the manometer used, but ordinarily is about 101 kPa(760 mm Hg). Components must
4、not be condensable at themaximum blend pressure.1.2 The possible presence of small leaks in the manifoldblending system will preclude applicability of the method toblends containing part per million concentrations of oxygen ornitrogen.1.3 This practice is restricted to those compounds that donot rea
5、ct with each other, the manifold, or the blend cylinder.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bilit
6、y of regulatory limitations prior to use.2. Summary of Practice2.1 Through the use of a blending manifold, the blendcomponents are combined based upon partial pressure. Com-ponents are added in order of ascending vapor pressure; that is,components of lowest vapor pressure are added first, with theex
7、ception that components at concentrations of 5 % or lesswould usually be added first. Compressibility factors areapplied to the component partial pressures to convert themfrom ideal to real gas. The real partial pressures, which areproportional to gas volumes, are normalized to give molpercent compo
8、sition of the blend.3. Significance and Use3.1 The laboratory preparation of gas blends of knowncomposition is required to provide primary standards for thecalibration of chromatographic and other types of analyticalinstrumentation.4. Apparatus4.1 Blending ManifoldConstruct manifold as shown inFig.
9、1. Details of construction are not critical; that is, glass,pipe, or tubing with welded or compression fittings may beused. The manifold must be leak free and arranged forconvenience of operation. More than one feedstock connectionpoint may be included if desired. Connections to the pump andmanomete
10、r shall follow accepted vacuum practice. Valves shallhave large enough apertures to permit adequate pumping in areasonable length of time.4.1.1 The finished manifold shall have a leak rate no greaterthan 1 mm Hg/h (0.133 kPah).4.2 Gauge, a well-type manometer such as the MeriamModel 30EB25 (see Note
11、 1).NOTE 1A high-vacuum gauge of the McLeod Manostat type pressuretransducer or a 0 bar to 2 bar (absolute) gauge may be included in themanifold system to determine how well the system has been evacuated.4.2.1 Alternatively, an electronic pressure gauge may beused in place of a manometer.4.3 Pump, h
12、igh-vacuum, two-stage, capable of pumpingdown to a pressure of 1.33 104kPa (0.1 m).5. Reagents and Materials5.1 Blend Components, high-purity, as required dependingon the composition of the proposed blend.5.2 Nitrogen, high purity, as required, for purging and forbalance gas, where applicable.6. Pro
13、cedure6.1 Connect the blend cylinder to the manifold at position A(see Fig. 1 for valve and position designations). Open valves 1,2, 3, and 6 and evacuate the manifold system thoroughly.Valves 4 and 5 are closed.NOTE 2AMcLeod Manostat type gauge may be used at various timesduring the procedure to de
14、termine how well the system has beenevacuated and to indicate if there are leaks present. Otherwise, a steady1This practice is under the jurisdiction of ASTM Committee D02 on PetroleumProducts, Liquid Fuels, and Lubricants and is the direct responsibility of Subcom-mittee D02.04.0A on Preparation of
15、 Standard Hydrocarbon Blends.Current edition approved Oct. 1, 2015. Published December 2015. Originallyapproved in 1981. Last previous edition approved in 2010 as D4051 10. DOI:10.1520/D4051-10R15.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. Uni
16、ted States1state condition of the manometer or electronic pressure gauge reading canbe taken as an indication that an acceptable vacuum has been attained.6.1.1 When a good vacuum less than 0.01 kPa (0.1 mm Hg)is reached, connect one or more blend component cylinders tothe manifold at positions B or
17、C, or both. Close valve 2 andopen valves 4 and 5, thereby evacuating the connecting linesup to the blend component cylinder valves. When a goodvacuum is again reached, close valves 4 and 5 and open theblend component cylinder valves. Ensure that the pressure ofany blend component delivered to valves
18、 4 and 5 does notexceed 200 kPa (1500 mm Hg). Record the initial pressurereadings from both sides of the manometer.6.1.2 The first component to be added will either have thelowest vapor pressure or will be present in the final blend at aconcentration of 5 % or less. Assume that the first componentfe
19、edstock is connected to manifold valve 4. Close valve 1 andopen valve 2. While carefully watching the manometer orelectronic pressure gauge reading, slowly open valve 4. Allowthe blend gas component to flow into the blend manifold untilthe desired precalculated manometer reading is reached (see7.1).
20、 Close valve 4 and be sure that the pressure remainsconstant. If using a manometer, tap it lightly to be certain thecorrect reading is obtained. Record the reading of both sides ofthe manometer and then close valve 3. Open valve 1 and waituntil the manifold is thoroughly evacuated.6.1.3 If the manif
21、old includes only one feedstock connec-tion point it will be necessary at this time to remove the firstfeedstock cylinder, connect the second, and evacuate the lineback to the feedstock cylinder valve. Assume this to be thecase; value 4 will, therefore, always be used as the feedstockcontrol valve.6
22、.1.4 When manifold evacuation is complete, close valve 1and 4. Open the feedstock cylinder valve and then slowly openvalve 4, allowing the second blend gas to flow into themanifold. Carefully watch the manometer or electronic pres-sure gauge.NOTE 3All additions should be made slowly to avoid tempera
23、turechanges.6.1.5 When the pressure in the manifold is several pascalshigher than the previous reading and is still slowly rising,slowly begin to open valve 3 so as to admit the component tothe sample cylinder. Valve 4 will remain partially open.Continue to open valve 3 while controlling the flow th
24、roughvalve 4 until the next desired pressure level is reached, alwaysmaintaining a higher pressure in the manifold than that in thecylinder. Close valve 4, allow the pressure to equilibrate, andrecord the manometer reading from both sides. Close valve 3.When additional components are to be included
25、in the blend,repeat the procedures outlined above for each component.6.1.6 When all components have been added, and valve 3 isclosed, evacuate the manifold, close valve 2 and disconnect theblend cylinder from the manifold at position A. To shut downthe apparatus, close the feedstock cylinder valve a
26、nd openvalve 4 to evacuate the connection. Close valve 4, remove thefeedstock cylinder, close valve 1, and by using valve 2 or 4,slowly admit air into the system until it is at atmosphericpressure.6.2 The blend must be mixed before it is used. This can beaccomplished in several ways, one of which is
27、 to causeconvection currents to occur within the cylinder. This mayconveniently be done by heating one end of the cylinder witheither a hot air gun or by running hot water over one end of itfor about an hour. Never use a flame to heat the cylinder.Blends containing hydrogen or helium are very diffic
28、ult to mix.Therefore, it is necessary to periodically alternate heating offirst one end of the cylinder and then the other for severalhours.6.3 To prepare a blend containing components at the partsper million level, it is necessary to make an initial blend ofthose components at higher concentrations
29、 and then to makesuccessive dilutions until the final desired concentration levelFIG. 1 Manifold SystemD4051 10 (2015)2is reached. For example, if a blend is desired that contains64 ppm, butane in nitrogen, the initial blend would be made tocontain 4 % butane in nitrogen.After mixing, a second blend
30、 isprepared by combining 4 % of the initial blend and 96 %nitrogen.After mixing this blend, the final blend is prepared bycombining 4 % of the second blend and 96 % nitrogen. Thisprocedure will provide manometer readings that are largeenough to be accurately read.7. Preblending Calculations7.1 In or
31、der to make blends of components at specific levels,it is necessary to calculate before hand the desired manometerreadings required to achieve these levels. Calculate thesepartial pressures as follows:LN5 LE2N %1003PT2(1)where:LN= desired manometer reading on the side connected tothe manifold for co
32、mponent N, kPa (mm Hg),LE= expected manometer reading on the same side be-fore component N is added, kPa (mm Hg),N% = desired percentage of component N, andPT= expected total absolute pressure of blend, 202 kPa(1520 mm Hg)For the first component to be added, LEis equal to the initialmanometer readin
33、g of the side connected to the manifold. Foreach component thereafter, LEis equal to the calculated LNofthe component to be added just previous to it.NOTE 4Compressibility factors may be included in preblendingcalculations but their usage will not significantly change the calculatedvalues. Compressi
34、bility factors are, however, utilized in the final-blendcalculations.8. Blend Cylinder Preparation8.1 It is advisable to equip the cylinder with a compoundgauge capable of indicating pressures from vacuum up to agauge pressure of 200 kPa (15 psi). The volume of the blendcylinder is not critical; how
35、ever, a size of 112 L to 2 L, orlarger, is satisfactory.8.2 The interior of the cylinder must be dry and free ofvolatile substances. Thorough cleaning of the interior may berequired if the cylinder had previously been used to contain gasmixtures having heavier components or components that wouldhave
36、 absorbed on the walls.8.3 Purge the cylinder several times with air from a low-pressure source and then pull a partial vacuum on it for at least15 min. Close the cylinder valve while the cylinder is stillunder vacuum.9. Calculation9.1 Calculate the partial pressure of each component asfollows:PN5 L
37、B2 LA!1RA2 RB! (2)where:PN= partial pressure of component N, kPa (mm Hg),LB= manometer reading on the side connected to themanifold, before component addition, kPa (mm Hg),LA= manometer reading on the side connected to themanifold, after component addition, kPa (mm Hg),RA= manometer reading on the s
38、ide not connected to themanifold, after component addition, kPa (mm Hg), andRB= manometer reading on the side not connected to themanifold, before component addition, kPa (mm Hg).For the first component added, LBand RBare equal to theinitial readings taken. For each component added thereafter, LBand
39、 RBare equal to LAand RAof the component just previouslyadded.NOTE 5If a well-type manometer is used, calculations will be differentfrom those shown above since only one manometer reading is taken withthe addition of each compound.9.2 Calculate the mol percent composition as follows:Mol % of compone
40、nt N (3)5PN/FN! 3100(PN/FN!1PO/FO!1PQ/FQ!#where:PN,PO,PQ= partial pressure of components N,O,Q, etc.,kPa, (mm Hg) as calculated above, andFN,FO,FQ= compressibility factor of each compound.Table 1 lists compressibility factors for a number of com-monly occurring compounds from ASTM DS 4A.NOTE 6This c
41、alculation is not rigorous in that the calculation ofcompressibility does not allow for binary interactions. The errors howeverare small by comparison with those associated with the pressure measure-ments.10. Precision and Bias10.1 Precision and bias for preparation of gas blends cannotbe determined
42、 since the result merely states whether there isconformance to the criteria for success specified in the proce-dure.10.2 The maximum systematic error introduced by use ofthis procedure is dependent largely upon the precision of theequipment used and the care exercised in its use. This error canbe es
43、timated by taking into account such error sources as thereadability and accuracy of the pressure measuring device,temperature variations during blend preparation, and whethercompressibility factors are known for all blend components.For example, a component having a partial pressure in theblend of 1
44、.07 kPa (8 mm Hg) whose compressibility factor isunknown, measured by means of a manometer readable to 0.07kPa (60.5 mm Hg) could be subject to an error of as much as612 % relative at constant temperature, in the worst case.S0.5/8!18/0.95! 2 8/1!#8D3100 5 12% (4)As component concentration increases,
45、 the error becomessmaller.D4051 10 (2015)311. Keywords11.1 analytical standard; low-pressure gas blendsASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that d
46、etermination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved
47、 or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel
48、that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprin
49、ts (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ 1 Compressibility Factor of the Real Gas at 15.6 C (60 F) and 1 Atm Z=PV/RT (Data from ASTM DS 4A Except as Noted)NOTE 1Values in parentheses are e
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