1、Designation: D4051 10Standard 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. A number in pare
2、ntheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice covers a laboratory procedure for thepreparation of low-pressure multicomponent gas blends. Thetechnique is applicable to the blending
3、 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 not be condensabl
4、e 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 react with each othe
5、r, 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-bility of regulatory l
6、imitations 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 theexception that comp
7、onents 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 composition of the ble
8、nd.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. 1. Details of con
9、struction 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 andmanometer shall follow ac
10、cepted 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 kPa/h).4.2 Gauge, a well-type manometer such as the MeriamModel 30EB25 (see Note 1).NOTE 1A high
11、-vacuum gauge of the McLeod Manostat type pressuretransducer ora0to2bar(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, high-vacuum, two-stage, cap
12、able of pumpingdown to a pressure of 1.33 3 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. Procedure6.1 Connect the bl
13、end 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.1This practice is under the jurisdiction of ASTM Committee D02 on PetroleumProducts and Lubricants and is the di
14、rect responsibility of Subcommittee D02.04.0Aon Preparation of Standard Hydrocarbon Blends.Current edition approved May 1, 2010. Published July 2010. Originally approvedin 1981. Last previous edition approved in 2004 as D405199(2004). DOI:10.1520/D4051-10.1*A Summary of Changes section appears at th
15、e end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.NOTE 2A McLeod Manostat type gauge may be used at various timesduring the procedure to determine how well the system has beenevacuated and to indicate if there are
16、 leaks present. Otherwise, a steadystate 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 man
17、ifold at positions B or 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 compo
18、nent delivered to valves 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 th
19、at the first componentfeedstock 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 read
20、ing is reached (see7.1). 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 evac
21、uated.6.1.3 If the manifold 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
22、feedstockcontrol valve.6.1.4 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
23、 slowly to avoid temperaturechanges.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
24、 controlling the flow throughvalve 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 compon
25、ents are to be included 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 fe
26、edstock cylinder valve and 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 sever
27、al ways, one of which is 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 o
28、r helium are very difficult to mix.Therefore, it is necessary to periodically alternate heating offirst one end of the cylinder and then the other for severalhours.FIG. 1 Manifold SystemD4051 1026.3 To prepare a blend containing components at the partsper million level, it is necessary to make an in
29、itial blend ofthose components at higher concentrations and then to makesuccessive dilutions until the final desired concentration levelis reached. For example, if a blend is desired that contains 64ppm, butane in nitrogen, the initial blend would be made tocontain 4 % butane in nitrogen. After mixi
30、ng, a second blend 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 Ca
31、lculations7.1 In order 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 %1003 PT2(1)where:LN= desired manometer reading on the side connectedto
32、 the manifold for component N, kPa (mm Hg),LE= expected manometer reading on the same sidebefore 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 initi
33、almanometer reading 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 calculate
34、dvalues. Compressibility 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
35、 not critical; however, a size of 112 to 2 L, or larger,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 component
36、s that wouldhave 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
37、 asfollows:PN5 LB2 LA! 1 RA2 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= manomete
38、r reading on the side 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
39、thereafter, LBand RBare equal to LAand RAof the component just previouslyadded.NOTE 5If a well-type manometer is used, calculations will bedifferent from those shown above since only one manometer reading istaken with the addition of each compound.9.2 Calculate the mol percent composition as follows
40、:Mol % of component N5PN/FN! 3 100(PN/FN! 1 PO/FO! 1 PQ/FQ!#(3)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 AS
41、TM DS 4A.NOTE 6This calculation 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 blend
42、s cannotbe determined 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
43、. This error canbe estimated 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 pres
44、sure in theblend of 1.07 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! 8/1!#8D3 100 5 12 % (4)As component co
45、ncentration increases, the error becomessmaller.11. Keywords11.1 analytical standard; low-pressure gas blendsD4051 103SUMMARY OF CHANGESSubcommittee D02.04 has identified the location of selected changes to this standard since the last issue(D405199(2004) that may impact the use of this standard.(1)
46、 Revised 4.2 and incorporated original Note 1. Renumberedall notes.(2) Revised 4.2.1.(3) Deleted original 5.2.(4) Revised Note 2.(5) Revised 6.1.2.(6) Revised 6.1.4.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this
47、 standard. Users of this standard are expressly advised that determination 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
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