1、Designation: D 4780 95 (Reapproved 2007)Standard Test Method forDetermination of Low Surface Area of Catalysts byMultipoint Krypton Adsorption1This standard is issued under the fixed designation D 4780; the number immediately following the designation indicates the year oforiginal adoption or, in th
2、e case of revision, 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 test method covers the determination of the specificsurface area of catalysts an
3、d catalyst carriers in the range from0.05 to 10 m2/g. A volumetric measuring system is used toobtain at least three data points which fall within the linear BETregion.1.2 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.3 This
4、 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 limitations prior to use.2. Referenced Documents
5、2.1 ASTM Standards:2D 3663 Test Method for Surface Area of Catalysts andCatalyst CarriersD 3766 Terminology Relating to Catalysts and CatalysisE 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 456 Terminology Relating to Quality and StatisticsE 691 Practice for Conducting a
6、n Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 DefinitionsConsult Terminology D 3766.3.2 Symbols:PH1= initial helium pressure, torr.PH2= helium pressure after equilibration, torr.TH1= temperature of manifold at initial heliumpressure, C.TH2= temperature of manifo
7、ld after equilibration,C.P1= initial Kr pressure, torr.T81= manifold temperature at initial Kr pressure,K.T1= manifold temperature at initial Kr pressure,C.P2= Kr pressure after equilibration, torr.T82= manifold temperature at P2,K.T2= manifold temperature at P2, C.Po,N= liquid nitrogen vapor pressu
8、re, torr.Po,krypton= calculated krypton vapor pressure, torr.T8s= liquid nitrogen temperature, K.X = relative pressure, P2/Po,krypton.Vd= volume of manifold, cm3.Vs= the apparent dead-space volume, cm3.Ws= weight of sample, g.W1= tare weight of sample tube, g.W2= weight of sample plus tare weight of
9、 tube, g.Vds= volume of krypton in the dead space, cm.3V1= See 11.3.5.V2= See 11.3.6.Vt= See 11.3.7.Va= See 11.3.9.Vm= See 11.6.4. Summary of Test Method4.1 A catalyst sample is degassed by heating in vacuum toremove absorbed vapors from the surface. The quantity ofkrypton adsorbed at various low pr
10、essure levels is determinedby measuring pressure differentials after introduction of a fixedvolume of krypton to the sample at liquid nitrogen temperature.The specific surface area is then calculated from the sampleweight and adsorption data using the BET equation.5. Significance and Use5.1 This tes
11、t method has been found useful for the determi-nation of the specific surface area of catalysts and catalystcarriers in the range from 0.05 to 10 m2/g for materials1This test method is under the jurisdiction of ASTM Committee D32 onCatalysts and is the direct responsibility of Subcommittee D32.01 on
12、 Physical-Chemical Properties.Current edition approved Sept. 1, 2007. Published October 2007. Originallyapproved in 1988. Last previous edition approved in 2001 as D 478095(2001).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org.
13、 For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.specification, manufacturing control, and research and devel-opment
14、 in the evaluation of catalysts. The determination ofsurface area of catalysts and catalyst carriers above 10 m2/g isaddressed in Test Method D 3663.6. Apparatus6.1 Aschematic diagram of the apparatus is shown in Fig. 1.It may be constructed of glass or of metal and may operatemanually or automatica
15、lly. It has the following features:6.1.1 Vacuum System, capable of attaining pressures below10-4torr (1 torr = 133.3 Pa). This will include a vacuum gage(not shown in Fig. 1). Access to the distribution manifold isthrough the valve V.6.1.2 Distribution Manifold, having a volume between 5and 40 cm3(V
16、d) known to the nearest 0.01 cm3. This volume isdefined as the volume between the stopcocks or valves and itincludes the volume within the pressure gage.6.1.3 Constant Volume Gages, capable of measuring 1 to 10torr to the nearest 0.001 torr and 0 to 1000 torr to the nearesttorr (1 torr = 133.3 Pa).6
17、.1.4 Valve (H), from the helium supply to the distributionmanifold.6.1.5 Valve (K), from the krypton supply to the distributionmanifold.6.1.6 Sample Tube(s), with volume between 5 cm3and 25cm3, depending on the application. The sample tube(s) may beconnected to the distribution manifold with standar
18、d taperjoints, glass-to-glass seals, or compression fittings.NOTE 1Modern commercial instruments may employ simple tubeswith volumes outside of this range, and may be capable of testing multiplesamples simultaneously rather than separately as stated in 9.1.6.1.7 Dewar Flask(s) for immersion of the s
19、ample tube(s)in liquid nitrogen. The nitrogen level should be fixed at aconstant height by means of an automatic level controller ormanually refilled to a predetermined mark on the sampletube(s) about 30 to 50 mm below the distribution manifoldconnectors.6.1.8 Thermometer for measuring the temperatu
20、re of thedistribution manifold (T1(i)orT2(i) in degrees Celsius. (Al-ternatively, the distribution manifold may be thermostatted afew degrees above ambient to obviate the necessity of record-ing this temperature.)6.1.9 Heating Mantle(s) or Small Furnace(s) for eachsample tube to allow outgassing sam
21、ples at elevated tempera-tures.6.1.10 Laboratory Balance with 0.1 mg (107kg) sensitiv-ity.6.1.11 Thermometer for measuring the temperature of theliquid nitrogen bath (T8s(i) in kelvins. This will preferably bea nitrogen vapor-pressure-thermometer that gives Po,Ndirectlyand has greater precision, or
22、a resistance thermometer fromwhich Po,Nvalues may be derived.7. Reagents7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the American Ch
23、emical Society,where such specifications are available.3Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.7.2 Helium Gas, at least 99.9 % pure.7.3 Krypton Gas, at least 99.9 %
24、pure.7.4 Liquid Nitrogen, of such purity that the saturation vaporpressure Po,Nis not more than 20 torr above barometricpressure. A fresh daily supply is recommended.8. ProcedureSample Preparation and Degassing8.1 Select a sample tube of the desired size. A 5 cm3tube ispreferred for small samples to
25、 minimize dead space. However,larger tubes may be required for larger samples or for finelypowdered samples, to avoid boiling when degassing is started.8.2 Evacuate the sample tube and then fill to atmosphericpressure with helium. This may be done on the surface areaunit, or on a separate piece of e
26、quipment.8.3 Remove the sample tube, cap, and weigh. Record theweight as W1.8.4 Place the sample, whose weight is known approxi-mately, into the sample tube. If possible, choose the samplesize to provide an estimated total surface area of 1 to 5 m2.8.5 Attach the sample tube to the apparatus. If oth
27、er samplesare to be run, attach them at this time to the other ports.8.6 Open the S valves where there are samples.8.7 Slowly open the V valve, monitoring the rate of pressuredecrease to avoid too high a rate, which might lead to excessivefluidization of powdered samples.8.7.1 If a diffusion pump is
28、 used, it may be necessary toclose the V valve system periodically to protect the diffusionpump fluid from exposure to pressures above 0.1 torr forperiods of more than 30 s. Close the valve off for 2 min eachtime.8.8 Install a heating mantle or furnace around each sampleand raise the temperature to
29、about 300C (573 K). (WarningTake special precautions if the moisture content exceedsapproximately 5 % to avoid “bumping” of powdered catalyst,3Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted b
30、y the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,MD.FIG. 1 Schematic Diagram of Surface Area ApparatusD 4780 95 (2007)2and to
31、avoid surface area loss by self-steaming. It is recom-mended that the heating rate not exceed 100 K/h under thesecircumstances.)8.9 Continue degassing at about 300C (573 K) for aminimum of 3 h, at a pressure not to exceed 103torr.Overnight degassing is permissible.NOTE 2Certain materials decompose o
32、r sinter at 300C. Lowerdegassing temperatures are permissible for such materials; however, thedegassing temperature should be specified when reporting the results.8.10 Remove the heating mantles, and allow the samples tocool.8.11 Close the S valves.8.12 It is permissible to exercise the option of pr
33、eliminarydegassing on an external unit. In such a case, follow theprocedures of 8.4-8.11 and then repeat on the adsorption unit,except that the degassing on the adsorption unit can be at roomtemperature and need not exceed 1 h.8.13 If it is desired to weigh the sample after preliminarydegassing on a
34、n external unit, backfill with helium to slightlyabove atmospheric pressure. Close the S valve.8.13.1 Detach the sample tube from the apparatus, recapwith the stopper used previously, and weigh. Record the weightas W2.8.13.2 Reattach the sample tube to the apparatus. Removethe backfilled gas by evac
35、uation to less than 103torr at roomtemperature. This should normally take 5 to 10 min.9. ProcedureDead-Space Determination9.1 From this point on, each sample being tested for kryptonadsorption shall be run on an individual basis. Thus, 9.1-10.12shall be carried out separately for each tube in test.9
36、.2 The dead space is the void volume of the chargedsample tube, including the volume within the S valve, when thetube is immersed in liquid nitrogen to the proper depth.9.3 Place a Dewar flask of liquid nitrogen around the sampleand adjust the liquid level to a fixed point on the sample tube.Maintai
37、n this level through the test.9.4 Zero the pressure gage, if needed.9.5 Admit the helium gas into the system to a pressure of600 to 900 torr by carefully opening the H valve. Record thispressure, PH1, and the manifold temperature, TH1.9.6 Open the S valve to admit helium to the sample.9.7 After abou
38、t 5 min of equilibration, readjust the liquidnitrogen level (if needed), and record the pressure, PH2andmanifold temperature, TH2.9.8 Repeat 9.5-9.7 for each sample cell attached to themanifold.9.9 Open all S valves, then slowly open the V valve toremove the helium gas.9.10 Close the S valve when a
39、pressure below 103torr hasbeen attained. This should normally take 5 to 10 min.10. ProcedureKrypton Adsorption10.1 Close the V valve.10.2 Admit krypton gas by opening the K valve and recordpressure as P1(1) and temperature as T1(1). (It is desirable tochoose P1(1) such that P2(1)/Po(1) is about 0.05
40、.)10.3 Open the S valve to admit krypton to the sample.10.4 Allow sufficient time for equilibration, readjusting theliquid nitrogen level periodically if needed. Equilibrium shallbe considered as attained when the pressure changes by nomore than 0.001 torr in 5 min.10.5 Record the equilibrium pressu
41、re, P2(1), and manifoldtemperature, T2(1).10.6 Record the liquid nitrogen temperature T8s(1) or thenitrogen vapor pressure Po,N(1).10.7 Close the S valve.10.8 Repeat 10.2-10.7 until there are at least three points inthe linear BET region (P2/Po,krypton= 0.05 to 0.30). Designatethe pressures, manifol
42、d temperatures, liquid nitrogen bathtemperatures or nitrogen vapor pressures as P1(i), P2(i), T1(i),T2(i), T8s(i), and Po,N(i) respectively for each i8th iteration (i=2ton, where n is the total number of points).NOTE 3The quantity of krypton gas admitted at each adsorption pointin step 10.2 depends
43、on the manifold volume, possible dosing system,dead space, and sample surface area. It is recommended that small kryptondoses be used initially to ensure that at least three equilibration points areobtained in the linear BET region.10.9 Open the S valve, slowly open the V valve, remove theDewar flas
44、k, and allow the sample tube to warm to roomtemperature.10.10 When frost has disappeared from the sample tube,wipe it dry.10.11 Backfill the sample tube with helium to atmosphericpressure or slightly above. Close the S valve.10.12 Detach the sample tube from the apparatus, recapwith the stopper used
45、 previously, and weigh. Record the weightas W2. If the sample was previously weighed followingdegassing, this step may be omitted.11. Calculation11.1 Calculate the weight of sample Wsas follows:Ws5 W2 W1(1)11.2 Calculate the dead space Vsas follows:Vs5T8sVdPH23FPH1TH11 273.22PH2TH21 273.2G(2)11.3 Fo
46、r each point, i = 1, 2 ., n, calculate the following:11.3.1 If Po,N(i) is not measured directly, the values of T8s(i)can be converted to Po,N(i) by the following equation for 76#T8s(i) # 80:In Po,Ni!/2549.78! 5 Ax 1 Bx 3/2 1 Cx31 Dx6#/1x! (3)where:X = (1Ts/126.2),A = 6.09676,B = 1.1367,C = 1.04072,
47、andD = 1.93306 (1).411.3.2 Saturation vapor pressure of krypton Po,krypton(i):Po,kryptoni! 5 exp 1.919 In Po,Ni! 2 11.82 (4)NOTE 4The above calculation of Po,krypton(i) is based on the use of the4The boldface numbers in parentheses refer to a list of references at the end ofthis standard.D 4780 95 (
48、2007)3Clausius-Clapeyron equation to extrapolate the vapor pressure of liquidkrypton to liquid nitrogen temperature (2, 3). Other methods have beenreported in the literature or are used on commercially available instru-mentation. These methods are acceptable, but should be identified in thereport.11
49、.3.3 X i! 5 relative pressure 5 P2i!/Po,kryptoni!11.3.4 Manifold temperature in:T81i! 5 T1i! 1 273.2 (5)T82i! 5 T2i! 1 273.211.3.5 The krypton volume in the manifold (and dosingsystem) before equilibration (cm3STP):V1i! 5 Vd3P1i!T1i!3273.2760(6)11.3.6 The krypton volume in the manifold (and dosingsystem) after equilibration (cm3STP):V2i! 5 Vd3P2i!T2i!3273.2760(7)See 6.1.2 for Vd.11.3.7 Total inventory of krypton in the system (cm3STP):Vti! 5 Vti 1! 1 V1i! V2i1! (8)Vt0! 5 011.3.8 Volume of krypton in the dead space (cm3STP):Vds
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