1、Designation: D 4222 03Standard 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 designation indicates the ye
2、ar 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 determination of nitrogen
3、adsorption 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 desorption branches ofthe
4、 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 standard does not pur
5、port 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 ASTM Standards:3D
6、3663 Test Method for Surface Area of CatalystsD 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 Interlaboratory Study toDetermine the Pre
7、cision 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 equilibration, C.P1= initial N2pressur
8、e, 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 N2pressure during desorption, torr.T3= manifol
9、d 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 nitrogen vapor pressure, torr.Ts= liquid nitr
10、ogen 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 after adsorption, g.Vds= volume of nitrog
11、en 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 determined by evacuating the sample, c
12、ooling thesample to the boiling point of liquid nitrogen (;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 pressure ofnitrogen is reached. Each additional dose of nit
13、rogen is1This test is under the jurisdiction of ASTM Committee D32 on Catalysts and isthe direct responsibility of Subcommittee D32.01 on Physical-Chemical Properties.Current edition approved Oct. 1, 2003. Published October 2003. Originallyapproved in 1983. Last previous edition approved in 1998 as
14、D 422298.2Adamson, A. W., Physical Chemistry of Surfaces, 3rd ed., John Wiley 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 A generic schematic diagram of the minimum apparatusreq
15、uirement 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 thecalculations and e
16、quations 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 below10-4to
17、rr (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 torr = 13
18、3.3 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.6.2 Sample
19、 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) in C.6.6.1
20、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 a nitrogen
21、 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 1A pressure transducer may be placed between the sample tubeand the manifold to m
22、onitor 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 cylinder of
23、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 tube may b
24、e 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 atmo-sph
25、eric 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. Choose th
26、e sample size to providean estimated total sample surface area of approximately 20 m2or greater.8.5 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 the S valve.FIG. 1 Schematic Diagram of Adsorption ApparatusD42220328.7 Slo
27、wly 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 precautions if the moistu
28、re 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 not to exceed 10-3
29、torr. 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 when reporting the
30、 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 the degassing tim
31、e 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 previously, and
32、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 must be carried out
33、 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 more convenient, a
34、s 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 to a fixed point
35、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 used.9.4 Zero the pr
36、essure 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 the liquidnitroge
37、n 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-Nitrogen Adsorpt
38、ion10.1 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 the S valve to adm
39、it 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 less than the va
40、lue 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).10.6 Close the S val
41、ve 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 sufficient time for e
42、quilibration, 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 system allowed to co
43、me 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 minimum) toproperly
44、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 nitrogen adsorbedincre
45、ases 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 of25 torr. If P0(i) is not measured directly, use the equation in12.3.2.1 to determine a value from a recorded liquid nitro
46、gentemperature.10.12 If the desorption isotherm is to be measured, proceedto 11.1.D422203310.13 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 sample tube,wipe it dry.10.15 Back-fill the sample tube wit
47、h the same gas used in8.2 to about atmospheric pressure. Close the S valve.10.16 Detach the sample tube from the apparatus, recapwith the stopper used previously, and weigh. Record the massas W2.11. Procedure-Nitrogen Desorption11.1 Measurement of the true desorption isotherm requiresfirst saturatin
48、g the sample with nitrogen at a pressure that is atleast 0.995 of the measured value of P0. If the adsorptionbranch of the isotherm is not required, use the precedingprocedure to reach the saturation point. Much larger incre-ments in pressure may now be used but it is still necessary todetermine the
49、 P1values and the final P2value when close tothe value of P0so that the total amount of nitrogen added to thesystem and the volume of nitrogen adsorbed at saturation canbe calculated. It is not necessary to wait for equilibration afterdose if the adsorption isotherm is not desired. In this case,equilibration of the gas with the sample is only required at thefinal P2pressure. Record the liquid nitrogen temperatureTs(1) or the nitrogen vapor pressure P0(1).11.2 After the sample has been saturated, close the S valve.Open the V valve very slowly, and evacuat
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