1、Designation: D 4222 03 (Reapproved 2008)Standard Test Method forDetermination of Nitrogen Adsorption and DesorptionIsotherms of Catalysts and Catalyst Carriers by StaticVolumetric Measurements1This standard is issued under the fixed designation D 4222; the number immediately following the designatio
2、n indicates the year oforiginal adoption or, in the 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 determi
3、nation of nitrogenadsorption and desorption isotherms of catalysts and catalystcarriers at the boiling point of liquid nitrogen.2A staticvolumetric measuring system is used to obtain sufficientequilibrium adsorption points on each branch of the isotherm toadequately define the adsorption and desorpt
4、ion branches ofthe isotherm. Thirty points evenly spread over the isotherm isconsidered to be the minimum number of points that willadequately define the isotherm.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 sta
5、ndard 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 Documents2.1
6、ASTM Standards:3D 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 an In
7、terlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 DefinitionsSee Terminology D 3766.3.2 Symbols:PH1= initial helium pressure, torr.PH2= helium pressure after equilibration, torr.TH1= temperature of manifold at initial helium pressure,C.TH2= temperature of manifold after
8、 equilibration, C.P1= initial N2pressure, torr.T1= manifold temperature at initial N2pressure, K.T81= manifold temperature at initial N2pressure, C.P2= pressure after equilibration, torr.T2= manifold temperature after equilibrrium, K.T82= manifold temperature after equilibrium, C.P3= initial N2press
9、ure during desorption, torr.T3= manifold temperature at initial N2pressure, K.T83= manifold temperature at initial N2pressure, C.P4= pressure after equilibration during desorption, torr.T4= manifold temperature after equilibration, K.T84= manifold temperature after equilibration, C.P0= liquid nitrog
10、en vapor pressure, torr.Ts= liquid nitrogen temperature, K.X = relative pressure, P2(4)/P0.Vd= volume of manifold, cm3.Vs= the dead-space volume factor, cm3(STP)/torr.Ws= mass of sample, g.W1= tare of sample tube, g.W82= sample mass + tare of tube after degassing, g.W2= sample mass + tare of tube af
11、ter adsorption, g.Vds= volume of nitrogen in the dead-space, cm3(STP).V1= see 12.4.3.V2= see 12.4.4.Vt= see 12.4.5.Vad= see 12.4.7.Vde= see 12.5.4. Summary of Test Method4.1 The sample is heated and evacuated to remove adsorbedvapors from the surface. The nitrogen adsorption branch of theisotherm is
12、 determined by evacuating the sample, cooling the1This test is under the jurisdiction ofASTM Committee D32 on Catalysts and isthe direct responsibility of Subcommittee D32.01 on Physical-Chemical Properties.Current edition approved April 1, 2008. Published April 2008. Originallyapproved in 1983. Las
13、t previous edition approved in 2003 as D 422203.2Adamson, A. W., Physical Chemistry of Surfaces, 3rd ed., John Wiley 77.3 K), andsubsequently adding stepwise, known amounts of nitrogen gasto the sample in such amounts that the form of the adsorptionisotherm is adequately defined and the saturation p
14、ressure ofnitrogen is reached. Each additional dose of nitrogen isintroduced to the sample only after the foregoing dose ofnitrogen has reached adsorption equilibrium with the sample.By definition, equilibrium is reached if the change in gaspressure is no greater than 0.1 torr/5 min interval. Thedes
15、orption isotherm is determined by desorbing nitrogen fromthe saturated sample in a stepwise mode with the sameprecautions taken to ensure desorption equilibration as appliedunder adsorption conditions. It is essential that the experimen-tal points be distributed over the isotherm in such a manner as
16、to correctly identify and define the isotherm. If the additions orwithdrawals of nitrogen are too large, the temporarily too-highnitrogen gas pressure during adsorption or too-low gas pressureduring desorption, may result in so-called scanning effectswithin the hysteresis loop of the adsorption-deso
17、rptionbranches of the isotherm. The occurrence of scanning mayresult in too-high equilibrium values for the adsorption iso-therm and too-low values for the desorption isotherm.5. Significance and Use5.1 The test method has two main functions: first, it pro-vides data useful for establishing the pore
18、 size distribution ofcatalyst materials, which in turn may influence their perfor-mance; and second, it serves as a laboratory test which may beused to study porosity changes that may occur during themanufacture and evaluation of catalysts.6. Apparatus6.1 Ageneric schematic diagram of the minimum ap
19、paratusrequirement is shown in Fig. 1. A commercial instrument maybe used and may be constructed of glass or of metal. Thespecific commercial apparatus chosen may have a differentconfiguration than that shown in Fig. 1 and may requiremodification of the sequence of valve operation and of thecalculat
20、ions and equations used. It should have the followingfeatures as a minimum:6.1.1 Distribution Manifold, having a (Vd), known to thenearest 0.05 cm3. This volume is defined as the volumebetween the stopcocks or valves and includes the pressuregage.6.1.2 Vacuum System, capable of attaining pressures b
21、elow10-4torr (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.6.1.3 Pressure Sensing Devices or Pressure Transducers,capable of measurements with a sensitivity of at least 0.1 torr,in the range from 0 to 1000 torr (1
22、 torr = 133.3 Pa).6.1.4 Value (H), from the helium supply to the distributionmanifold.6.1.5 Valve (N), from the nitrogen supply to the distributionmanifold.6.1.6 The connection between the sample tube and the Svalve can be a standard-taper glass joint, a glass-to-glass seal,or a compression fitting.
23、6.2 Sample Tubes, with volumes from 5 cm3to 100 cm3depending on the application.6.3 Heating Mantles or Small Furnaces.6.4 Dewar Flasks.6.5 Laboratory Balance, with 0.1-mg (107kg) sensitivity.6.6 Thermometer or Thermocouple, for measuring the tem-perature of the distribution manifold T81(i)orT82(i) i
24、n C.6.6.1 The manifold may be thermostated at a particulartemperature, a few degrees above ambient, to obviate thenecessity of recording this temperature at each reading.6.7 Thermometer, for measuring the temperature of theliquid nitrogen bath (Ts(i) in Kelvin. Preferably, this ther-mometer will be
25、a nitrogen vapor-pressure-thermometer, oftenreferred to in a commercial instrument as a pressure saturationtube, that gives P0directly and has greater precision, or aresistance thermometer from which P0values may be derived.NOTE 1Apressure transducer may be placed between the sample tubeand the mani
26、fold to monitor equilibrium pressure, but this is not arequirement of the system.7. Reagents7.1 Helium GasA cylinder of helium gas at least 99 %pure.7.2 Liquid Nitrogen , of such purity that P0is not more than20 torr above barometric pressure. A fresh daily supply isrecommended.7.3 Nitrogen GasA cyl
27、inder of nitrogen gas at least99.999 % pure.8. Procedure-Sample Preparation and Degassing8.1 Select a sample tube of the desired size. To minimize thedead-space, a 5-cm3sample tube is preferred for samples notexceeding about 1 g. However, to avoid boiling when degas-sing is started, a 25-cm3sample t
28、ube may be preferred forfinely powdered catalysts. A small glass-wool plug or fritteddisk placed in the neck of the sample tube above the liquidnitrogen level, will eliminate the possibility of any smallcatalyst particles entering the vacuum system.8.2 Fill the sample tube with nitrogen or helium at
29、 atmo-spheric pressure, after removing air by evacuation.This may bedone on the adsorption unit or on a separate piece of equip-ment.8.3 Remove the sample tube from the system, cap, andweigh. Record the mass as W1.8.4 Place the catalyst sample, whose approximate mass isknown, into the sample tube. C
30、hoose the sample size to providean estimated total sample surface area of approximately 20 m2or greater.FIG. 1 Schematic Diagram of Adsorption ApparatusD 4222 03 (2008)28.5 Attach the sample tube to the apparatus. If other samplesare to be run, attach them at this time to the other ports.8.6 Open th
31、e S valve.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.8.8 Install a heating mantle or furnace around each sampleand raise the temperature to about 300C (573 K).NOTE 2Take special precauti
32、ons if the moisture content exceedsapproximately5%toavoid bumping of powdered catalyst and to avoidsurface area loss by self-steaming. It is recommended that the heating ratenot exceed 100 K/h under these circumstances.8.9 Continue degassing at about 300C (573 K) for aminimum of 3 h, at a pressure n
33、ot to exceed 10-3torr. Overnightdegassing is permissible.NOTE 3Certain materials will decompose at 300C (for example,alumina hydrates) or will sinter (for example, platinum black). Lowerdegassing temperatures are permissible for such materials; however, thedegassing temperature should be specified w
34、hen reporting the results.8.10 Remove the heating mantle, and allow the sample tocool.8.11 Close the S valve.8.12 It is permissible to exercise the option of preliminarydegassing on an external unit. In such a case, follow theprocedures of 8.4-8.10 and then repeat on the adsorption unit,except that
35、the degassing time in 8.9 should not exceed 1 h.8.13 If it is desired to weigh the sample after preliminarydegassing on an external unit, back-fill with the same gas usedin 8.2 to above atmospheric pressure. Close the S valve.8.14 Detach the sample tube from the apparatus, recap withthe stopper used
36、 previously, and weigh. Record the mass asW82.8.15 Remove the backfilled gas by evacuation to less than103torr at room temperature.9. Procedure-Dead-Space Determination9.1 From this point on, each sample being tested fornitrogen adsorption must be run on an individual basis. Thus,9.2 through 11.4 mu
37、st be carried out separately for each tube intest.9.2 The dead-space is the quantity of gas within the chargedsample tube, including the S valve, when the tube is immersedin liquid nitrogen to the proper depth.NOTE 4The dead-space may be determined after the nitrogen adsorp-tion and desorption, if m
38、ore convenient, as long as adequate degassingprecedes it. In that case, replace the liquid nitrogen bath after 10.14 beforeproceeding with 9.3-9.9. Then, remove the Dewar flask before carryingout 10.15 and 10.16.9.3 Place a Dewar flask of liquid nitrogen around the sampleand adjust the liquid level
39、to a fixed point on the sample tube.Maintain this level throughout the test.NOTE 5Some modern commercial instruments do not require manualmaintenance or readjusting of the level of liquid nitrogen during theanalysis. Follow the manufacturers recommendations for operating theparticular instrument use
40、d.9.4 Zero the pressure gage.9.5 Admit the helium gas into the system to a pressure of600 to 900 torr by carefully opening the H valve. Record thispressure as PH1, and the manifold temperature as TH1.9.6 Open the S valve to admit helium to the sample.9.7 After about 5 min of equilibration, readjust
41、the liquidnitrogen level, and record the pressure as PH2and the manifoldtemperature as TH2.9.8 Repeat 9.5-9.7 for each sample on the manifold.9.9 Open the S valve; then slowly open the V valve toremove the helium gas.9.10 Close the S valve when a pressure below 103torr hasbeen attained.10. Procedure
42、-Nitrogen Adsorption10.1 Admit nitrogen gas, and record the pressure as P1(1)(torr) and the temperature as T1(1) (C). It is desirable, but notnecessary, to choose P1(1) such that the first equilibriumadsorption pressure, P2(1), will be about 40 torr equivalent toP2(1)/Po(1) of about 0.05.10.2 Open t
43、he S valve to admit nitrogen to the catalyst.10.3 Allow sufficient time for equilibration, readjusting theliquid nitrogen level to the marking on the sample tube asnecessary. Equilibrium shall be considered as attained whenthe pressure change is no more than 0.1 torr in 5 min. If thepressure becomes
44、 less than the value which gives the desiredrelative pressure P2/P0, admit more nitrogen gas and allow thesystem to reequilibrate.10.4 Record the equilibrium pressure as P2(1) and themanifold temperature as T82.10.5 Record the liquid nitrogen temperature Ts(1) or thenitrogen vapor pressure P0(1).10.
45、6 Close the S valve and then admit nitrogen gas toincrease the pressure by a suitable amount, depending upon thesamples adsorptive capacity. Record the pressure as P1(2), andthe manifold temperature as T81(2).10.7 Open the S valve to admit the new increment ofnitrogen to the catalyst.10.8 Allow suff
46、icient time for equilibration, readjusting theliquid nitrogen level as necessary. The criterion for equilibriumis defined in 10.3. If the pressure becomes less than the valuethat gives the desired relative pressure P2/P0, an additionalknown amount of gas should be admitted to the manifold andthe sys
47、tem allowed to come to equilibrium.10.9 Record the equilibrium pressure as P2(2), and recordT82(2).10.10 Again record Ts(2) or P0(2).10.11 Repeat 10.6-10.10, increasing the pressure P1by asuitable amount above the previous pressure each time untilthere are sufficient data points, (30 points as a min
48、imum) toproperly define the isotherm up to a pressure that is at least0.995 of the determined P0value. As a guide, increasing P2byabout 25 torr for each equilibration point will usually providethe required number of points necessary to adequately definethe adsorption isotherm. If the amount of nitro
49、gen adsorbedincreases rapidly, which may occur for highly porous catalystswhen approaching the saturation pressure, it will be desirableto use an increment in P2smaller than the suggested value ofD 4222 03 (2008)325 torr. If P0(i) is not measured directly, use Eq 3 in 12.3.2.1to determine a value from a recorded liquid nitrogen tempera-ture.10.12 If the desorption isotherm is to be measured, proceedto 11.1.10.13 Slowly open the V valve, remove the Dewar flask, andallow the sample flask to come to room temperature.10.14 When frost has disappeared from the s
