ASTM D5160-95(1998)
(Guide)Standard Guide for Gas-Phase Adsorption Testing of Activated Carbon
Standard Guide for Gas-Phase Adsorption Testing of Activated Carbon
SCOPE
1.1 This guide covers the evaluation of activated carbons for gas-phase adsorption. It presents a procedure for determining the dynamic adsorption capacity, o, and critical bed depth, c, for an activated carbon used to remove a specific adsorbate from a gas stream under conditions chosen by the user.
1.2 The values stated in SI units are to be regarded as the standard.
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. Specific hazards statements are given in Section 8.
General Information
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Standards Content (Sample)
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Designation: D 5160 – 95 (Reapproved 1998)
Standard Guide for
Gas-Phase Adsorption Testing of Activated Carbon
This standard is issued under the fixed designation D 5160; 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.
1. Scope pressure, and relative humidity set by the user. The time to
breakthrough of a specified concentration of adsorbate is
1.1 This guide covers the evaluation of activated carbons for
measured. The measurement is repeated using the same con-
gas-phase adsorption. It presents a procedure for determining
ditions but varying the amount of carbon in the bed. For many
the dynamic adsorption capacity, N , and critical bed depth, d
o
practical systems, a plot of breakthrough time versus amount of
c, for an activated carbon used to remove a specific adsorbate
carbon is linear. The slope and x-intercept of this line can be
from a gas stream under conditions chosen by the user.
used to calculate the dynamic capacity, N (expressed as grams
1.2 The values stated in SI units are to be regarded as the o
adsorbate/grams carbon or grams adsorbate/cm carbon) and
standard.
critical bed depth, d , characteristic of the activated carbon
1.3 This standard does not purport to address all of the c
under the conditions used in the test.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
5. Significance and Use
priate safety and health practices and determine the applica-
5.1 Activated carbon is used extensively for removing gases
bility of regulatory limitations prior to use. Specific hazards
and vapors from air or other gas streams. The physical and
statements are given in Section 8.
chemical characteristics of an activated carbon can strongly
2. Referenced Documents influence its suitability for a given application. The procedure
in this guide allows the evaluation of the dynamic adsorption
2.1 ASTM Standards:
characteristics of an activated carbon for a particular adsorbate
D 2652 Terminology Relating to Activated Carbon
under conditions chosen by the user. It is necessary that the
D 2854 Test Method for Apparent Density of Activated
user choose test conditions that are meaningful for the appli-
Carbon
cation (see Section 9).
D 2867 Test Method for Moisture in Activated Carbon
5.2 This guide can also be used to evaluate activated
D 3467 Test Method for Carbon Tetrachloride Activity of
carbons that have been impregnated with materials to enhance
Activated Carbon
their effectiveness at removing gases otherwise poorly ad-
E 300 Practice for Sampling Industrial Chemicals
sorbed on activated carbon.
3. Terminology 5.3 The procedure given in this guide is not generally
applicable for evaluation of carbons used as catalysts for such
3.1 Definitions:
purposes as decomposition of low levels of ozone or oxidation
3.1.1 breakthrough—the appearance in the effluent of a
of SO to SO .
specified concentration of an adsorbate of interest. 2 3
5.4 The procedure given in this guide can be applied to
3.1.2 Other terms relating to this guide are defined in
reactivated or regenerated activated carbons.
Terminology D 2652.
5.5 Fig. 1 shows the adsorbate concentration profile in an
4. Summary of Guide
activated carbon bed at breakthrough. The bed has a zone at the
inlet in which the adsorbate concentration is equal to the
4.1 An activated carbon bed that contains a known amount
influent concentration. In this region the carbon is at equilib-
of carbon is challenged with an adsorbate in a gas stream under
rium with adsorbate. The adsorbate concentration in the
conditions of flow rate, adsorbate concentration, temperature,
remainder of the bed drops until at the outlet it is equal to the
breakthrough concentration. The shorter the length of this mass
transfer zone (adsorption zone), the more effectively the carbon
This guide is under the jurisdiction of ASTM Committee D-28 on Activated
in the bed is utilized. A bed whose depth is less than the length
Carbon and is the direct responsibility of Subcommittee D28.04 on Gas Phase
Evaluation Tests.
of this zone will show immediate appearance of adsorbate in
Current edition approved Sept. 10, 1995. Published November 1995. Originally
the effluent (breakpoint).
published as D 5160 – 91. Last previous edition D 5160 – 91.
2 5.6 From the standpoint of best carbon utilization it is
Annual Book of ASTM Standards, Vol 15.01.
Annual Book of ASTM Standards, Vol 15.05. desirable to choose a carbon which will give as short a mass
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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 5160
by heavier screens may be used. Commercially available
spunbonded polyester nonwovens having both high strength
and very low pressure drop may also be used as very
convenient supports for tests in small tubes.
NOTE 1—A test fixture in which the bed is held in place at both top and
bottom requires less skill to obtain reproducible results. An 8.8 cm
diameter aluminum fixture with a perforated plate that screws down onto
the bed from above has been used successfully at bed depths from 1 to 3.5
cm. A diagram of this fixture is shown in Fig. 2.
6.1.1 Flow should be downward through the sample to
avoid disturbing the bed. For tests on small amounts of carbon,
a ground glass outer joint at the top of the tube allows easy
connection and disconnection from the challenge gas without
disturbing the bed. It is very easy to disturb the packing of a
small bed. Preferably these should not be moved after loading.
6.1.2 The length of the sample tube must be several times
greater than the critical bed depth of the activated carbon under
FIG. 1 Concentration Profile of an Activated Carbon Bed at
the test conditions chosen.
Breakthrough
6.2 Fill Device—For small beds the sample tube can be
loaded using the vibration feed device described in Test
transfer zone as possible under use conditions. However, in
Method D 2854. The bottom of the delivery funnel should have
many applications, high adsorptive capacity is more important
the same diameter as the sample tube. It is desirable to allow
than a short mass transfer zone. In almost every application,
the carbon to fall at least 10 cm from the bottom of the delivery
bed pressure drop is also a primary consideration.
funnel to the top of the bed. For larger beds, the best packing
5.7 In a few situations such as respiratory protection against
is obtained when the carbon falls through a loading column
low levels of extremely toxic gases such as radioactive methyl
which contains screens to evenly distribute the carbon across
iodide, a short mass transfer zone (that is, high adsorption rate
the bed. The column should have the same cross section as the
coefficient) is more important than ultimate capacity. In other
bed.
cases such as solvent recovery, a high dynamic capacity is
more important.
7. Hazards
5.8 Although the design of adsorber beds is beyond the
7.1 Carbons containing toxic or radioactive adsorbates
scope of this guide, the following points should be considered.
should be disposed of in accordance with applicable federal,
The bed diameter should be as large as possible in order to
state, and local regulations.
lower the pressure drop and to maximize the amount of carbon
7.2 Certain gases and vapors have very high heats of
in the bed. Subject to pressure drop constraints, the deepest
reaction as they chemisorb on a carbon surface. At high
possible carbon bed should be used. All else being equal, the
use of smaller particle size carbon will shorten the mass
transfer zone and improve bed efficiency at the expense of
British patent 606,867.
higher pressure drop. If pressure drop considerations are
critical, some particle morphologies offer less resistance to
flow than others.
5.9 The two parameters obtained by the procedure in this
guide can be used as an aid in selecting an activated carbon and
in sizing the adsorption bed in which this carbon will be used.
The best carbon for most applications should have a high
dynamic capacity for the adsorbate N coupled with a short
o
mass transfer zone (small d ) when evaluated under the
c
operating conditions anticipated for the adsorber.
6. Apparatus
6.1 Sample Tube—This is often a vertically supported
cylindrical glass tube with diameter at least twelve times the
diameter of the largest carbon particles present or 16 times the
mean diameter. The lower end of the tube must have a flat
support for the carbon bed. Care should be taken to ensure
uniformity of flow profile across the bed. The support should
contribute as little as possible to the total pressure drop of the
bed. For this reason, fritted glass supports are often undesir-
FIG. 2 Test Fixture for Gas-Phase Adsorption Testing of Activated
able. Fine mesh stainless steel screens supported if necessary Carbon
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D 5160
concentrations, enough heat can be liberated to cause ignition
of the carbon bed if oxygen is present. An example is
chemisorption of high concentrations of phosphine or arsine on
whetlerized carbon.
7.3 Another hazard is encountered when large quantities of
easily oxidizable substances such as hydrazines are adsorbed
on carbon from an inert gas stream. When these carbons are
exposed to air, they often ignite as oxidation rapidly takes
place. The same materials adsorbed in low concentrations from
an air stream cause no problems since the oxidation occurs
slowly during the adsorption process.
7.4 Adsorption of high concentrations of strong oxidizers
such as ozone (formation of ozonides), fluorine, hydrogen
peroxide, or nitric acid vapors can result in ignition or
explosion of the carbon bed.
8. Selection and Preparation of Activated Carbon
8.1 A representative sample should be obtained and pre-
pared for testing in accordance with Practice E 300.
8.2 The particle size distribution of the activated carbon
must be considered if several different carbons are to be
compared using this procedure. All other things being equal, an
activated carbon consisting of smaller particles will possess a
higher adsorption rate and hence a smaller critical bed depth,
d , than one consisting of larger particles. Therefore, carbons
c
that have different particle sizes should not be compared
against each other using critical bed depth. However, the
dynamic capacities, N , calculated using this guide are directly
FIG. 3 Time to Breakthrough Versus Volume of Carbon
o
comparable regardless of particle size distribution. For many
applications, the dynamic capacity is more important than the
correlate as closely as possible.
critical bed depth.
9.2 Temperature affects the capacity of the activated carbon
8.3 Since pre-adsorbed water can strongly affect adsorption
through its effects on the adsorption isotherm and on diffusion
of both organic vapors and reactive gases, the water content of
rates. This is usually not a large effect over narrow ranges of
each carbon sample tested should be determined using Test 5
temperature for fairly non-volatile organic vapors (1). It can
Method D 2867. Impregnated carbons are often sold containing
be much more significant for chemisorption.
up to about 20 % by weight water to increase their capacity for
9.3 The relative humidity (RH) of the challenge strongly
reactive gases.
affects the capacity and adsorption rate of the activated carbon
8.4 The carbon tetrachloride activity (CTA) determined by
(see Fig. 4). The RH of the challenge entering the carbon bed
Test Method D 3467 is often used to qualify activated carbons
is the important parameter and should be carefully controlled
for a particular use. It should be realized that these activities
especially at high relative humidities. As mentioned in 8.3,
are a measure of the total micropore volume of an activated
pre-adsorbed water also strongly influences the adsorption
carbon sample. They say nothing about the distribution of
characteristics of the activated carbon. The strong dependence
micropore area among pores of various sizes. At low adsorbate
of RH on temperature at high RH values requires good
concentrations, the smallest micropores are most effective.
temperature control at the bed when working at high RH.
Therefore, a carbon with many small pores may have a higher
Generally, physical adsorption of organic vapors on dry new
capacity for a low concentration adsorbate than a carbon with
carbon shows little RH dependence unless the challenge RH is
greater total micropore volume (higher activity) but fewer very
higher than about 65 %. Chemisorption or catalytic activity is
small pores. Fig. 3 shows a situation in which high activity is
usually much more sensitive to RH.
not favorable. The 57.9 % CTA carbon in this figure is
9.4 Accelerated Tests—At low adsorbate concentrations
specially activated to have a high proportion of very small
these tests can require considerable time. Therefore, attempts
micropores.
are often made to accelerate the tests.
9.4.1 The most common way to accelerate this test is to
9. Selection of Test Conditions
increase the concentration of adsorbate in the gas stream. Since
9.1 The user of this guide must decide under what experi-
this increases the driving force for adsorption, the dynamic
mental conditions to evaluate the activated carbon. The pre-
capacity of the carbon for the adsorbate N will be higher than
o
ferred procedure is to use the same adsorbate concentration and
same gas stream velocity as will be encountered in the
application. Other factors such as relative humidity, tempera- 5
The boldface numbers in parentheses refer to a list of references at the end of
ture, pressure, and breakthrough concentration should also the text.
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 5160
FIG. 5 Time to Breakthrough Versus Bed Residence Time
FIG. 4 Effect of Test Relative Humidity on the 1 % Breakthrough
Time as a Function of Challenge Concentration V
t~s! 5 0.06
S D
Q
The almost linear characteristic implies a dyna
...
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