ASTM D4222-03(2015)e1

Standard Test Method for Determination of Nitrogen Adsorption and Desorption Isotherms of Catalysts and Catalyst Carriers by Static Volumetric Measurements

SIGNIFICANCE AND USE
5.1 The test method has two main functions: first, it provides data useful for establishing the pore size distribution of catalyst materials, which in turn may influence their performance; and second, it serves as a laboratory test which may be used to study porosity changes that may occur during the manufacture and evaluation of catalysts.
SCOPE
1.1 This test method covers the determination of nitrogen adsorption and desorption isotherms of catalysts and catalyst carriers at the boiling point of liquid nitrogen.2 A static volumetric measuring system is used to obtain sufficient equilibrium adsorption points on each branch of the isotherm to adequately define the adsorption and desorption branches of the isotherm. Thirty points evenly spread over the isotherm is considered to be the minimum number of points that will adequately define the isotherm.  
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 31-Mar-2015
• ICS: 17.060 - Measurement of volume, mass, density, viscosity
• ICS: 71.040.30 - Chemical reagents
• Technical Committee: D32 - Catalysts
• Drafting Committee: D32.01 - Physical-Chemical Properties

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
´1
Designation: D4222 − 03 (Reapproved 2015)
Standard Test Method for
Determination of Nitrogen Adsorption and Desorption
Isotherms of Catalysts and Catalyst Carriers by Static
Volumetric Measurements
This standard is issued under the fixed designation D4222; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Eq 10 in subsection 12.4.7 was corrected editorially in August 2015.
1. Scope E691Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method
1.1 This test method covers the determination of nitrogen
adsorption and desorption isotherms of catalysts and catalyst
3. Terminology
carriers at the boiling point of liquid nitrogen. A static
3.1 Definitions—See Terminology D3766.
volumetric measuring system is used to obtain sufficient
equilibriumadsorptionpointsoneachbranchoftheisothermto
3.2 Symbols:
adequately define the adsorption and desorption branches of
the isotherm. Thirty points evenly spread over the isotherm is
PH = initial helium pressure, torr.
considered to be the minimum number of points that will
PH = helium pressure after equilibration, torr.
adequately define the isotherm.
TH = temperature of manifold at initial helium pressure,
1.2 The values stated in SI units are to be regarded as the
°C.
standard. The values given in parentheses are for information
TH = temperature of manifold after equilibration, °C.
only.
P = initial N pressure, torr.
1 2
T = manifold temperature at initial N pressure, K.
1.3 This standard does not purport to address all of the 1 2
T' = manifold temperature at initial N pressure, °C.
1 2
safety concerns, if any, associated with its use. It is the
P = pressure after equilibration, torr.
responsibility of the user of this standard to establish appro-
T = manifold temperature after equilibrrium, K.
priate safety and health practices and determine the applica-
T' = manifold temperature after equilibrium, °C.
bility of regulatory limitations prior to use.
P = initial N pressure during desorption, torr.
3 2
T = manifold temperature at initial N pressure, K.
3 2
2. Referenced Documents
T' = manifold temperature at initial N pressure, °C.
3 2
2.1 ASTM Standards: P = pressure after equilibration during desorption, torr.
D3663Test Method for Surface Area of Catalysts and T = manifold temperature after equilibration, K.
T' = manifold temperature after equilibration, °C.
Catalyst Carriers
P = liquid nitrogen vapor pressure, torr.
D3766Terminology Relating to Catalysts and Catalysis 0
T = liquid nitrogen temperature, K.
s
E177Practice for Use of the Terms Precision and Bias in
X = relative pressure, P /P .
2(4) 0
ASTM Test Methods
V = volume of manifold, cm .
d
E456Terminology Relating to Quality and Statistics
V = the dead-space volume factor, cm (STP)/torr.
s
W = mass of sample, g.
s
W = tare of sample tube, g.
ThistestisunderthejurisdictionofASTMCommitteeD32onCatalystsandis
W' = sample mass + tare of tube after degassing, g.
the direct responsibility of Subcommittee D32.01 on Physical-Chemical Properties.
W = sample mass + tare of tube after adsorption, g.
Current edition approved April 1, 2015. Published August 2015. Originally
V = volume of nitrogen in the dead-space, cm (STP).
approved in 1983. Last previous edition approved in 2008 as D4222–03 (2008). ds
V = see 12.4.3.
DOI: 10.1520/D4222-03R15.
Adamson,A. W., Physical Chemistry of Surfaces, 3rd ed., John Wiley & Sons,
V = see 12.4.4.
New York, NY, 1976, p. 532.
V = see 12.4.5.
t
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
V = see 12.4.7.
ad
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
V = see 12.5.
de
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
D4222 − 03 (2015)
6.1.1 Distribution Manifold, having a (V ), known to the
d
nearest 0.05 cm . This volume is defined as the volume
between the stopcocks or valves and includes the pressure
gauge.
6.1.2 Vacuum System, capable of attaining pressures below
-4
10 torr (1 torr = 133.3 Pa). This will include a vacuum gauge
(not shown in Fig. 1). Access to the distribution manifold is
through the valve V.
6.1.3 Pressure Sensing Devices or Pressure Transducers,
capable of measurements with a sensitivity of at least 0.1 torr,
FIG. 1 Schematic Diagram of Adsorption Apparatus
in the range from 0 to 1000 torr (1 torr = 133.3 Pa).
6.1.4 Value (H), from the helium supply to the distribution
manifold.
6.1.5 Valve (N), from the nitrogen supply to the distribution
4. Summary of Test Method
manifold.
6.1.6 The connection between the sample tube and the S
4.1 Thesampleisheatedandevacuatedtoremoveadsorbed
valve can be a standard-taper glass joint, a glass-to-glass seal,
vapors from the surface.The nitrogen adsorption branch of the
or a compression fitting.
isotherm is determined by evacuating the sample, cooling the
3 3
sample to the boiling point of liquid nitrogen (;77.3 K), and
6.2 Sample Tubes, with volumes from 5 cm to 100 cm
subsequently adding stepwise, known amounts of nitrogen gas
depending on the application.
to the sample in such amounts that the form of the adsorption
6.3 Heating Mantles or Small Furnaces.
isotherm is adequately defined and the saturation pressure of
6.4 Dewar Flasks.
nitrogen is reached. Each additional dose of nitrogen is
introduced to the sample only after the foregoing dose of 10−7
6.5 Laboratory Balance, with 0.1-mg ( kg) sensitivity.
nitrogen has reached adsorption equilibrium with the sample.
6.6 Thermometer or Thermocouple, for measuring the tem-
By definition, equilibrium is reached if the change in gas
perature of the distribution manifold [T' (i)or T' (i)] in °C.
1 2
pressure is no greater than 0.1 torr/5 min interval. The
6.6.1 The manifold may be thermostated at a particular
desorption isotherm is determined by desorbing nitrogen from
temperature, a few degrees above ambient, to obviate the
the saturated sample in a stepwise mode with the same
necessity of recording this temperature at each reading.
precautions taken to ensure desorption equilibration as applied
under adsorption conditions. It is essential that the experimen- 6.7 Thermometer, for measuring the temperature of the
tal points be distributed over the isotherm in such a manner as liquidnitrogenbath(T (i))inKelvin.Preferably,thisthermom-
s
tocorrectlyidentifyanddefinetheisotherm.Iftheadditionsor eter will be a nitrogen vapor-pressure-thermometer, often
withdrawals of nitrogen are too large, the temporarily too-high referred to in a commercial instrument as a pressure saturation
nitrogengaspressureduringadsorptionortoo-lowgaspressure tube, that gives P directly and has greater precision, or a
during desorption, may result in so-called scanning effects resistance thermometer from which P values may be derived.
within the hysteresis loop of the adsorption-desorption
NOTE1—Apressuretransducermaybeplacedbetweenthesampletube
branches of the isotherm. The occurrence of scanning may
and the manifold to monitor equilibrium pressure, but this is not a
result in too-high equilibrium values for the adsorption iso-
requirement of the system.
therm and too-low values for the desorption isotherm.
7. Reagents
5. Significance and Use 7.1 Helium Gas—A cylinder of helium gas at least 99 %
pure.
5.1 The test method has two main functions: first, it pro-
vides data useful for establishing the pore size distribution of 7.2 Liquid Nitrogen , of such purity that P is not more than
catalyst materials, which in turn may influence their perfor- 20 torr above barometric pressure. A fresh daily supply is
mance; and second, it serves as a laboratory test which may be recommended.
used to study porosity changes that may occur during the
7.3 Nitrogen Gas—A cylinder of nitrogen gas at least
manufacture and evaluation of catalysts.
99.999 % pure.
6. Apparatus 8. Procedure-Sample Preparation and Degassing
6.1 Ageneric schematic diagram of the minimum apparatus 8.1 Selectasampletubeofthedesiredsize.Tominimizethe
requirement is shown in Fig. 1.Acommercial instrument may dead-space, a 5-cm sample tube is preferred for samples not
be used and may be constructed of glass or of metal. The exceeding about 1 g. However, to avoid boiling when degas-
specific commercial apparatus chosen may have a different sing is started, a 25-cm sample tube may be preferred for
configuration than that shown in Fig. 1 and may require finely powdered catalysts. A small glass-wool plug or fritted
modification of the sequence of valve operation and of the disk placed in the neck of the sample tube above the liquid
calculations and equations used. It should have the following nitrogen level, will eliminate the possibility of any small
features as a minimum: catalyst particles entering the vacuum system.
´1
D4222 − 03 (2015)
tion and desorption, if more convenient, as long as adequate degassing
8.2 Fill the sample tube with nitrogen or helium at atmo-
precedesit.Inthatcase,replacetheliquidnitrogenbathafter10.14before
sphericpressure,afterremovingairbyevacuation.Thismaybe
proceeding with 9.3 – 9.9. Then, remove the Dewar flask before carrying
done on the adsorption unit or on a separate piece of equip-
out 10.15 and 10.16.
ment.
9.3 PlaceaDewarflaskofliquidnitrogenaroundthesample
8.3 Remove the sample tube from the system, cap, and
and adjust the liquid level to a fixed point on the sample tube.
weigh. Record the mass as W .
Maintain this level throughout the test.
8.4 Place the catalyst sample, whose approximate mass is
NOTE 5—Some modern commercial instruments do not require manual
known,intothesampletube.Choosethesamplesizetoprovide
maintenance or readjusting of the level of liquid nitrogen during the
an estimated total sample surface area of approximately 20 m
analysis. Follow the manufacturer’s recommendations for operating the
particular instrument used.
or greater.
8.5 Attachthesampletubetotheapparatus.Ifothersamples 9.4 Zero the pressure gauge.
are to be run, attach them at this time to the other ports.
9.5 Admit the helium gas into the system to a pressure of
8.6 Open the S valve. 600 to 900 torr by carefully opening the H valve. Record this
pressure as P , and the manifold temperature as T .
H1 H1
8.7 Slowlyopenthe Vvalve,monitoringtherateofpressure
decreasetoavoidtoohigharate,whichmightleadtoexcessive
9.6 Open the S valve to admit helium to the sample.
fluidization of powdered samples.
9.7 After about 5 min of equilibration, readjust the liquid
8.8 Install a heating mantle or furnace around each sample
nitrogenlevel,andrecordthepressureas P andthemanifold
H2
and raise the temperature to about 300°C (573 K).
temperature as T .
H2
NOTE 2—Take special precautions if the moisture content exceeds
9.8 Repeat 9.5 – 9.7 for each sample on the manifold.
approximately5%to avoid bumping of powdered catalyst and to avoid
9.9 Open the S valve; then slowly open the V valve to
surfacearealossbyself-steaming.Itisrecommendedthattheheatingrate
not exceed 100 K/h under these circumstances.
remove the helium gas.
−3
8.9 Continue degassing at about 300°C (573 K) for a
9.10 Close the S valve when a pressure below 10 torr has
-3
minimumof3h,atapressurenottoexceed10 torr.Overnight
been attained.
degassing is permissible.
10. Procedure-Nitrogen Adsorption
NOTE 3—Certain materials will decompose at 300°C (for example,
alumina hydrates) or will sinter (for example, platinum black). Lower
10.1 Admit nitrogen gas, and record the pressure as P (1)
degassing temperatures are permissible for such materials; however, the
(torr) and the temperature as T (1) (°C). It is desirable, but not
degassing temperature should be specified when reporting the results.
necessary, to choose P (1) such that the first equilibrium
8.10 Remove the heating mantle, and allow the sample to
adsorption pressure, P (1), will be about 40 torr equivalent to
cool.
P (1)/ P (1) of about 0.05.
2 o
8.11 Close the S valve.
10.2 Open the S valve to admit nitrogen to the catalyst.
8.12 It is permissible to exercise the option of preliminary
10.3 Allow sufficient time for equilibration, readjusting the
degassing on an external unit. In such a case, follow the
liquid nitrogen level to the marking on the sample tube as
proceduresof8.4–8.10andthenrepeatontheadsorptionunit,
necessary. Equilibrium shall be considered as attained when
except that the degassing time in 8.9 should not exceed 1 h.
the pressure change is no more than 0.1 torr in 5 min. If the
8.13 If it is desired to weigh the sample after preliminary
pressure becomes less than the value which gives the desired
degassing on an external unit, back-fill with the same gas used
relative pressure P /P , admit more nitrogen gas and allow the
2 0
in 8.2 to above atmospheric pressure. Close the S valve.
system to reequilibrate.
8.14 Detach the sample tube from the apparatus, recap with
10.4 Record the equilibrium pressure as P (1) and the
the stopper used previously, and weigh. Record the mass as
manifold temperature as T' .
W' .
10.5 Record the liquid nitrogen temperature [ T (1)] or the
s
8.15 Remove the backfilled gas by evacuation to less than
−3 nitrogen vapor pressure [ P (1)].
10 torr at room temperature.
10.6 Close the S valve and then admit nitrogen gas to
9. Procedure-Dead-Space Determination
increasethepressurebyasuitableamount,dependinguponthe
sample’sadsorptivecapacity.Recordthepressureas P (2),and
9.1 From this point on, each sample being tested for
nitrogen adsorption must be run on an individual basis. Thus, the manifold temperature as T' (2).
9.2through11.4mustbecarriedoutseparatelyforeachtubein
10.7 Open the S valve to admit the new increment of
test.
nitrogen to the catalyst.
9.2 Thedead-spaceisthequantityofgaswithinthecharged
10.8 Allow sufficient time for equilibration, readjusting the
sample tube, including the S valve, when the tube is immersed
liquidnitrogenlevelasnecessary.Thecriterionforequilibrium
in liquid nitrogen to the proper depth.
is defined in 10.3. If the pressure becomes less than the value
NOTE 4—The dead-space may be determined after the nitrogen adsorp- that gives the desired relative pressure P /P , an additional
2 0
´1
D4222 − 03 (2015)
known amount of gas should be admitted to the manifold and marking on the sample tube as necess
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1
Designation: D4222 − 03 (Reapproved 2008) D4222 − 03 (Reapproved 2015)
Standard Test Method for
Determination of Nitrogen Adsorption and Desorption
Isotherms of Catalysts and Catalyst Carriers by Static
Volumetric Measurements
This standard is issued under the fixed designation D4222; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Eq 10 in subsection 12.4.7 was corrected editorially in August 2015.
1. Scope
1.1 This test method covers the determination of nitrogen adsorption and desorption isotherms of catalysts and catalyst carriers
at the boiling point of liquid nitrogen. A static volumetric measuring system is used to obtain sufficient equilibrium adsorption
points on each branch of the isotherm to adequately define the adsorption and desorption branches of the isotherm. Thirty points
evenly spread over the isotherm is considered to be the minimum number of points that will adequately define the isotherm.
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D3663 Test Method for Surface Area of Catalysts and Catalyst Carriers
D3766 Terminology Relating to Catalysts and Catalysis
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E456 Terminology Relating to Quality and Statistics
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Terminology
3.1 Definitions—See Terminology D3766.
3.2 Symbols:
PH = initial helium pressure, torr.
PH = helium pressure after equilibration, torr.
TH = temperature of manifold at initial helium pressure, °C.
TH = temperature of manifold after equilibration, °C.
P = initial N pressure, torr.
1 2
T = manifold temperature at initial N pressure, K.
1 2
T' = manifold temperature at initial N pressure, °C.
1 2
P = pressure after equilibration, torr.
T = manifold temperature after equilibrrium, K.
T' = manifold temperature after equilibrium, °C.
This test is under the jurisdiction of ASTM Committee D32 on Catalysts and is the direct responsibility of Subcommittee D32.01 on Physical-Chemical Properties.
Current edition approved April 1, 2008April 1, 2015. Published April 2008August 2015. Originally approved in 1983. Last previous edition approved in 20032008 as
D4222D4222 – 03 (2008).–03. DOI: 10.1520/D4222-03R08.10.1520/D4222-03R15.
Adamson, A. W., Physical Chemistry of Surfaces, 3rd ed., John Wiley & Sons, New York, NY, 1976, p. 532.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
D4222 − 03 (2015)
FIG. 1 Schematic Diagram of Adsorption Apparatus
P = initial N pressure during desorption, torr.
3 2
T = manifold temperature at initial N pressure, K.
3 2
T' = manifold temperature at initial N pressure, °C.
3 2
P = pressure after equilibration during desorption, torr.
T = manifold temperature after equilibration, K.
T' = manifold temperature after equilibration, °C.
P = liquid nitrogen vapor pressure, torr.
T = liquid nitrogen temperature, K.
s
X = relative pressure, P /P .
2(4) 0
V = volume of manifold, cm .
d
V = the dead-space volume factor, cm (STP)/torr.
s
W = mass of sample, g.
s
W = tare of sample tube, g.
W' = sample mass + tare of tube after degassing, g.
W = sample mass + tare of tube after adsorption, g.
V = volume of nitrogen in the dead-space, cm (STP).
ds
V = see 12.4.3.
V = see 12.4.4.
V = see 12.4.5.
t
V = see 12.4.7.
ad
V = see 12.5.
de
4. Summary of Test Method
4.1 The sample is heated and evacuated to remove adsorbed vapors from the surface. The nitrogen adsorption branch of the
isotherm is determined by evacuating the sample, cooling the sample to the boiling point of liquid nitrogen (;77.3 K), and
subsequently adding stepwise, known amounts of nitrogen gas to the sample in such amounts that the form of the adsorption
isotherm is adequately defined and the saturation pressure of nitrogen is reached. Each additional dose of nitrogen is introduced
to the sample only after the foregoing dose of nitrogen has reached adsorption equilibrium with the sample. By definition,
equilibrium is reached if the change in gas pressure is no greater than 0.1 torr/5 min interval. The desorption isotherm is determined
by desorbing nitrogen from the saturated sample in a stepwise mode with the same precautions taken to ensure desorption
equilibration as applied under adsorption conditions. It is essential that the experimental points be distributed over the isotherm
in such a manner as to correctly identify and define the isotherm. If the additions or withdrawals of nitrogen are too large, the
temporarily too-high nitrogen gas pressure during adsorption or too-low gas pressure during desorption, may result in so-called
scanning effects within the hysteresis loop of the adsorption-desorption branches of the isotherm. The occurrence of scanning may
result in too-high equilibrium values for the adsorption isotherm and too-low values for the desorption isotherm.
5. Significance and Use
5.1 The test method has two main functions: first, it provides data useful for establishing the pore size distribution of catalyst
materials, which in turn may influence their performance; and second, it serves as a laboratory test which may be used to study
porosity changes that may occur during the manufacture and evaluation of catalysts.
6. Apparatus
6.1 A generic schematic diagram of the minimum apparatus requirement is shown in Fig. 1. A commercial instrument may be
used and may be constructed of glass or of metal. The specific commercial apparatus chosen may have a different configuration
than that shown in Fig. 1 and may require modification of the sequence of valve operation and of the calculations and equations
used. It should have the following features as a minimum:
6.1.1 Distribution Manifold, having a (V ), known to the nearest 0.05 cm . This volume is defined as the volume between the
d
stopcocks or valves and includes the pressure gage.gauge.
´1
D4222 − 03 (2015)
-4
6.1.2 Vacuum System, capable of attaining pressures below 10 torr (1 torr = 133.3 Pa). This will include a vacuum gagegauge
(not shown in Fig. 1). Access to the distribution manifold is through 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 = 133.3 Pa).
6.1.4 Value (H), from the helium supply to the distribution manifold.
6.1.5 Valve (N), from the nitrogen supply to the distribution manifold.
6.1.6 The connection between the sample tube and the S valve can be a standard-taper glass joint, a glass-to-glass seal, or a
compression fitting.
3 3
6.2 Sample Tubes, with volumes from 5 cm to 100 cm depending on the application.
6.3 Heating Mantles or Small Furnaces.
6.4 Dewar Flasks.
10−7
6.5 Laboratory Balance, with 0.1-mg ( kg) sensitivity.
6.6 Thermometer or Thermocouple, for measuring the temperature of the distribution manifold [T' (i) or T' (i)] in °C.
1 2
6.6.1 The manifold may be thermostated at a particular temperature, a few degrees above ambient, to obviate the necessity of
recording this temperature at each reading.
6.7 Thermometer, for measuring the temperature of the liquid nitrogen bath (T (i)) in Kelvin. Preferably, this thermometer will
s
be a nitrogen vapor-pressure-thermometer, often referred to in a commercial instrument as a pressure saturation tube, that gives
P directly and has greater precision, or a resistance thermometer from which P values may be derived.
0 0
NOTE 1—A pressure transducer may be placed between the sample tube and the manifold to monitor equilibrium pressure, but this is not a requirement
of the system.
7. Reagents
7.1 Helium Gas—A cylinder of helium gas at least 99 % pure.
7.2 Liquid Nitrogen , of such purity that P is not more than 20 torr above barometric pressure. A fresh daily supply is
recommended.
7.3 Nitrogen Gas—A cylinder of nitrogen gas at least 99.999 % pure.
8. Procedure-Sample Preparation and Degassing
8.1 Select a sample tube of the desired size. To minimize the dead-space, a 5-cm sample tube is preferred for samples not
exceeding about 1 g. However, to avoid boiling when degassing is started, a 25-cm sample tube may be preferred for finely
powdered catalysts. A small glass-wool plug or fritted disk placed in the neck of the sample tube above the liquid nitrogen level,
will eliminate the possibility of any small catalyst particles entering the vacuum system.
8.2 Fill the sample tube with nitrogen or helium at atmospheric pressure, after removing air by evacuation. This may be done
on the adsorption unit or on a separate piece of equipment.
8.3 Remove the sample tube from the system, cap, and weigh. Record the mass as W .
8.4 Place the catalyst sample, whose approximate mass is known, into the sample tube. Choose the sample size to provide an
estimated total sample surface area of approximately 20 m or greater.
8.5 Attach the sample tube to the apparatus. If other samples are to be run, attach them at this time to the other ports.
8.6 Open the S valve.
8.7 Slowly open the V valve, monitoring the rate of pressure decrease to avoid too high a rate, which might lead to excessive
fluidization of powdered samples.
8.8 Install a heating mantle or furnace around each sample and raise the temperature to about 300°C (573 K).
NOTE 2—Take special precautions if the moisture content exceeds approximately 5 % to avoid bumping of powdered catalyst and to avoid surface area
loss by self-steaming. It is recommended that the heating rate not exceed 100 K/h under these circumstances.
-3
8.9 Continue degassing at about 300°C (573 K) for a minimum of 3 h, at a pressure not to exceed 10 torr. Overnight degassing
is permissible.
NOTE 3—Certain materials will decompose at 300°C (for example, alumina hydrates) or will sinter (for example, platinum black). Lower degassing
temperatures are permissible for such materials; however, the degassing temperature should be specified when reporting the results.
8.10 Remove the heating mantle, and allow the sample to cool.
8.11 Close the S valve.
´1
D4222 − 03 (2015)
8.12 It is permissible to exercise the option of preliminary degassing on an external unit. In such a case, follow the procedures
of 8.4 – 8.10 and then repeat on the adsorption unit, except that the degassing time in 8.9 should not exceed 1 h.
8.13 If it is desired to weigh the sample after preliminary degassing on an external unit, back-fill with the same gas used in 8.2
to above atmospheric pressure. Close the S valve.
8.14 Detach the sample tube from the apparatus, recap with the stopper used previously, and weigh. Record the mass as W' .
−3
8.15 Remove the backfilled gas by evacuation to less than 10 torr at room temperature.
9. Procedure-Dead-Space Determination
9.1 From this point on, each sample being tested for nitrogen adsorption must be run on an individual basis. Thus, 9.2 through
11.4 must be carried out separately for each tube in test.
9.2 The dead-space is the quantity of gas within the charged sample tube, including the S valve, when the tube is immersed in
liquid nitrogen to the proper depth.
NOTE 4—The dead-space may be determined after the nitrogen adsorption and desorption, if more convenient, as long as adequate degassing precedes
it. In that case, replace the liquid nitrogen bath after 10.14 before proceeding with 9.3 – 9.9. Then, remove the Dewar flask before carrying out 10.15
and 10.16.
9.3 Place a Dewar flask of liquid nitrogen around the sample and adjust the liquid level to a fixed point on the sample tube.
Maintain this level throughout the test.
NOTE 5—Some modern commercial instruments do not require manual maintenance or readjusting of the level of liquid nitrogen during the analysis.
Follow the manufacturer’s recommendations for operating the particular instrument used.
9.4 Zero the pressure gage.gauge.
9.5 Admit the helium gas into the system to a pressure of 600 to 900 torr by carefully opening the H valve. Record this pressure
as P , and the manifold temperature as T .
H1 H1
9.6 Open the S valve to admit helium to the sample.
and the manifold
9.7 After about 5 min of equilibration, readjust the liquid nitrogen level, and record the pressure as P
H2
temperature as T .
H2
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 to remove the helium gas.
−3
9.10 Close the S valve when a pressure below 10 torr has been attained.
10. Procedure-Nitrogen Adsorption
10.1 Admit nitrogen gas, and record the pressure as P (1) (torr) and the temperature as T (1) (°C). It is desirable, but not
1 1
necessary, to choose P (1) such that the first equilibrium adsorption pressure, P (1), will be about 40 torr equivalent to P (1)/ P (1)
1 2 2 o
of about 0.05.
10.2 Open the S valve to admit nitrogen to the catalyst.
10.3 Allow sufficient time for equilibration, readjusting the liquid nitrogen level to the marking on the sample tube as necessary.
Equilibrium shall be considered as attained when the pressure change is no more than 0.1 torr in 5 min. If the pressure becomes
less than the value which gives the desired relative pressure P /P , admit more nitrogen gas and allow the system to reequilibrate.
2 0
10.4 Record the equilibrium pressure as P (1) and the manifold temperature as T' .
2 2
10.5 Record the liquid nitrogen temperature [ T (1)] or the nitrogen vapor pressure [ P (1)].
s 0
10.6 Close the S valve and then admit nitrogen ga
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