ASTM D4824-94(1999)

Standard Test Method for Determination of Catalyst Acidity by Ammonia Chemisorption

SCOPE
1.1 This test method covers the determination of acidity of catalysts and catalyst carriers by ammonia chemisorption. A volumetric measuring system is used to obtain the amount of chemisorbed ammonia.
1.2 This standard does not purport to address all of the safety problems, 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: 09-Oct-1999
• ICS: 71.040.30 - Chemical reagents
• Technical Committee: D32 - Catalysts
• Drafting Committee: D32.01 - Physical-Chemical Properties

Relations

• Replaced By: ASTM D4824-03 - Standard Test Method for Determination of Catalyst Acidity by Ammonia Chemisorption
• Effective Date: 01-Oct-2003

Standards Content (Sample)

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: D 4824 – 94 (Reapproved 1999)
Standard Test Method for
Determination of Catalyst Acidity by Ammonia
Chemisorption
This standard is issued under the fixed designation D 4824; 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 (e) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
This test method involves the measurement of total catalyst acidity by chemisorption of ammonia
in a static volumetric system. Acidity is a very important parameter in determining catalyst activity
and selectivity in many commercial reactions. Zeolite based catalysts used in the petroleum industry
for catalytic cracking are a prime example. This test method describes a simple procedure employing
inexpensive equipment that could readily be assembled in most laboratories.
1. Scope
W 5 tare weight of sample tube, g.
W 5 sample plus tare weight of tube, g.
1.1 This test method covers the determination of acidity of 2
P 5 initial ammonia pressure corrected to standard tem-
catalysts and catalyst carriers by ammonia chemisorption. A 1T
perature, torr.
volumetric measuring system is used to obtain the amount of
P 5 final ammonia pressure corrected to standard tem-
2T
chemisorbed ammonia.
perature, torr.
1.2 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
4. Summary of Test Method
responsibility of the user of this standard to establish appro-
4.1 A sample is degassed by heating in a vacuum to remove
priate safety and health practices and determine the applica-
adsorbed vapors from the surface. The sample is then exposed
bility of regulatory limitations prior to use.
to an excess of gaseous ammonia and the excess ammonia is
2. Referenced Documents removed by freezing it into a trap cooled with liquid nitrogen.
The chemisorbed ammonia is calculated as the difference
2.1 ASTM Standards:
between the volume of ammonia before exposure and the
D 3766 Terminology Relating to Catalysts and Catalysis
volume recovered in the liquid nitrogen trap.
E 691 Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method
5. Significance and Use
3. Terminology 5.1 This test method can be used to determine the acidity of
catalysts and catalyst carriers by ammonia chemisorption for
3.1 Definitions—Consult Terminology D 3766.
materials specifications, manufacturing control, and research
3.2 Symbols:
and development in the evaluation of catalysts.
6. Apparatus
V 5 calibrated expansion volume, cm .
k
T 5 temperature of V at initial ammonia pressure, K.
1 k 6.1 A schematic diagram of one type of apparatus is shown
T 5 temperature of V at final ammonia pressure, K.
2 k in Fig. 1. It may be constructed of glass or metal and may
P 5 initial ammonia pressure, torr.
operate manually or automatically. It has the following fea-
P 5 final ammonia pressure, torr.
tures:
W 5 weight of sample, g.
s
6.1.1 Vacuum System capable of attaining and maintaining
−4
pressures below 10 torr (0.01 Pa) in the absence of catalyst.
6.1.2 Expansion Vessel having a volume between 300 to
3 3
500 cm (V ) known to the nearest 0.01 cm (Note 1). This
k
This test method is under the jurisdiction of ASTM Committee D-32 on
volume is defined as the volume between stopcocks V and V
Catalysts and is the direct responsibility of Subcommittee D32.01 on Physical-
7 8
Chemical Properties.
and includes the pressure gage and ammonia bulb.
Current edition approved Jan. 15, 1994. Published March 1994. Originally
NOTE 1—An expansion vessel of smaller volume is recommended for
published as D 4824 – 88. Last previous edition D 4824 – 93.
Annual Book of ASTM Standards, Vol 05.03. materials of low surface area or smaller sample size.
Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 4824
FIG. 1 Apparatus
NOTE 2—Take special precautions if the moisture content exceeds
6.1.3 Constant Volume Gage capable of measuring 0 to 250
−1
approximately 5 % to avoid “bumping’’ of powdered sample. It is
torr to the nearest 10 torr (10 Pa).
recommended that the heating rate not exceed 100 K/h under these
6.1.4 Vacuum Gage capable of measuring 0 to 1000 torr to
circumstances.
−3
the nearest 10 torr (0.1 Pa).
8.6 Continue degassing at 673 K for a minimum of 3 h, at
6.1.5 Valve, (V ) from ammonia supply to the expansion
−3
volume. a pressure not to exceed 10 torr (0.1 Pa) Pa. Overnight
degassing is permissible.
6.1.6 Sample Tubes, with volume between 5 and 25 cm .
The sample tube(s) may be connected to the apparatus with
NOTE 3—Certain materials will decompose at 673 K or will sinter.
standard taper joints, glass-to-glass seals, or compression
Lower degassing temperatures are permissible for such materials; how-
fittings.
ever, the degassing temperature should be specified when reporting the
6.1.7 Dewar Flask(s), for immersion of ammonia (freeze- results.
back bulb) in liquid nitrogen.
8.7 After outgassing, lower the sample temperature to 448
6.1.8 Thermometer or Thermocouple, for measuring the
K.
temperature of the expansion volume, V . Alternatively, the
k
8.8 Close stopcock V to isolate the samples from the
expansion volume may
...