ASTM D4051-1999(2004) Standard Practice for Preparation of Low-Pressure Gas Blends《低压气体混合物的制备》.pdf

1、Designation: D 4051 99 (Reapproved 2004)An American National StandardStandard Practice forPreparation of Low-Pressure Gas Blends1This standard is issued under the fixed designation D 4051; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revi

2、sion, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 b

3、lends. Thetechnique is applicable 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

4、kPa(760 mm Hg). Components must 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 t

5、o those compounds that donot react 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

6、 and determine the applica-bility 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 pres

7、sure are added first, with theexception 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 nor

8、malized to give molpercent composition 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 ManifoldCon

9、struct manifold as shown inFig. 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. Con

10、nections to the pump andmanometer 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 kPa/h).4.2 Gage, open manometer, vacuum, or pre

11、ssure, consistingof a full-length U-tube mounted on a vertically adjustablemeter scale.NOTE 1A well-type manometer such as the Miriam Model 30EB25may be used in place of the U-tube manometer.NOTE 2A high-vacuum gage of the McLeod Manostat type pressuretransducer ora0to2bar(absolute) may be included

12、in the manifoldsystem to determine how well the system has been evacuated.4.2.1 Alternatively, an electronic pressure gage may be usedin place of a mercury manometer.4.3 Pump, high-vacuum, two-stage, capable of pumpingdown to a pressure of 1.33 3 104kPa (0.1 m).5. Reagents and Materials5.1 Blend Com

13、ponents, high-purity, as required dependingon the composition of the proposed blend.5.2 Mercury, reagent grade, triple distilled. (WarningMercury may be harmful if inhaled or swallowed.)5.3 Nitrogen, high purity, as required, for purging and forbalance gas, where applicable.1This practice is under t

14、he jurisdiction of ASTM Committee D02 on PetroleumProducts and Lubricants and is the direct responsibility of Subcommittee D02.04 onHydrocarbon Analysis.Current edition approved May 1, 2004. Published May 2004. Originallyapproved in 1981. Last previous edition approved in 1999 as D 4051 99.1Copyrigh

15、t ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6. Procedure6.1 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.Va

16、lves 4 and 5 are closed.NOTE 3A McLeod gage may be used at various times during theprocedure to determine how well the system has been evacuated and toindicate if there are leaks present. Otherwise, a steady state condition ofthe mercury in the manometer can be taken as an indication that anacceptab

17、le 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 C, or both. Close valve 2 andopen valves 4 and 5, thereby evacuating the connecting linesup to the blend component cylinder va

18、lves. 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 4 and 5 does notexceed 200 kPa (1500 mm Hg). Record the initial pressurereadings from both sides of the manometer.6.1.2 The f

19、irst 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 componentfeedstock is connected to manifold valve 4. Close valve 1 andopen valve 2. While carefully watching the mercury level in themano

20、meter, slowly open valve 4. Allow the blend gas compo-nent to flow into the blend manifold until the desired precal-culated manometer reading is reached (see 7.1). Close valve 4and be sure that the pressure remains constant. Tap themanometer lightly to be certain the correct reading is obtained.Reco

21、rd the reading of both sides of the manometer and thenclose valve 3. Open valve 1 and wait until the manifold isthoroughly evacuated.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 ev

22、acuate the lineback to the feedstock cylinder valve. Assume this to be thecase; value 4 will, therefore, always be used as the 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 ble

23、nd gas to flow into themanifold. Carefully watch the mercury level of the manometer.NOTE 4All additions should be made slowly to avoid temperaturechanges.6.1.5 When the pressure in the manifold is several pascals(or millimetres of mercury) higher than the previous readingand is still slowly rising,

24、slowly begin to open valve 3 so as toadmit the component to the sample cylinder. Valve 4 willremain partially open. Continue to open valve 3 while control-ling the flow through valve 4 until the next desired pressurelevel is reached, always maintaining a higher pressure in themanifold than that in t

25、he cylinder. Close valve 4, allow thepressure to equilibrate, and record the manometer reading fromboth sides. Close valve 3. When additional components are tobe included in the blend, repeat the procedures outlined abovefor each component.6.1.6 When all components have been added, and valve 3 isclo

26、sed, 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 and openvalve 4 to evacuate the connection. Close valve 4, remove thefeedstock cylinder, close valve 1, and by using valve 2 or 4,

27、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 to causeconvection currents to occur within the cylinder. This mayconveniently be done by heating one end of the cylinder withei

28、ther 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.FIG. 1 Manifold SystemD 4051 99 (2004)2Blends containing hydrogen or helium are very difficult to mix.Therefore, it is necessary to periodically alternate heating offirst one end of

29、 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 and then to makesuccessive dilutions until the final desired concentration levelis reache

30、d. 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 mixing, a second blend isprepared by combining 4 % of the initial blend and 96 %nitrogen. After mixing this blend, the final blend is prepared bycomb

31、ining 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 order to make blends of components at specific levels,it is necessary to calculate before hand the desired manometerreadings req

32、uired to achieve these levels. Calculate thesepartial pressures as follows:LN5 LE2N %1003 PT2(1)where:LN= desired manometer reading on the side connectedto 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 p

33、ercentage 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 reading of the side connected to the manifold. Foreach component thereafter, LEis equal to the calculated LNofthe component to be add

34、ed just previous to it.NOTE 5Compressibility factors may be included in preblendingcalculations but their usage will not significantly change the calculatedvalues. Compressibility factors are, however, utilized in the final-blendcalculations.8. Blend Cylinder Preparation8.1 It is advisable to equip

35、the cylinder with a compoundgage capable of indicating pressures from vacuum up to a gagepressure of 200 kPa (15 psi). The volume of the blend cylinderis not critical; however, a size of 112 to2L,orlarger,issatisfactory.8.2 The interior of the cylinder must be dry and free ofvolatile substances. Tho

36、rough cleaning of the interior may berequired if the cylinder had previously been used to contain gasmixtures having heavier components or components 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

37、 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 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, b

38、efore 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 side not connected to themanifold, after component addition, kPa (mm Hg),andRB= manometer reading on the side not connected to themanif

39、old, before component addition, kPa (mm Hg).For the first component added, LBand RBare equal to theinitial readings taken. For each component added thereafter, LBand RBare equal to LAand RAof the component just previouslyadded.NOTE 6If a well-type manometer is used, calculations will bedifferent fro

40、m those shown above since only one manometer reading istaken with the addition of each compound.9.2 Calculate the mol percent composition as follows: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 abo

41、ve, 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 7This calculation is not rigorous in that the calculation ofcompressibility does not allow for binary interactions. The errors howeverare

42、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 since the result merely states whether there isconformance to the criteria for success specified in the proce-dure.10.2 The maximu

43、m 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 estimated by taking into account such error sources as thereadability and accuracy of the pressure measuring device,temperature varia

44、tions during blend preparation, and whethercompressibility factors are known for all blend components.For example, a component having a partial pressure 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 b

45、e 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)D 4051 99 (2004)3As component concentration increases, the error becomessmaller.11. Keywords11.1 analytical standard; low-pressure gas blendsASTM International takes n

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47、sibility.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 or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed

48、to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the ad

49、dress shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (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).TABLE 1 Compressibility Factor of the Real Gas at 15.6C (60F) and 1 Atm Z=PV/RT (Data from ASTM DS 4A Except as Noted)NOTEValues in parentheses are estimated.Compound Z