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to provide full physical adsorption
characterizations of activated carbons
and other sorbent materials. This robust
and rugged instrument allows the
activated carbon industry to solve prior
refractory questions for clients. Also,
GAED solves modern and classical
problems and guides new R&D product
developments more cost effectively,
compared to existing test methods.
An archival record of how GAED
works and some applications is available
(1). The most recent publication
points out GAED’s use to reveal markets
available for a particular AC or
new material (2). The AC industry is in
the process of transforming from an art
to a science and GAED and other testing
methods facilitate this important
transformation.
STRATEGY FOR ANSWERING QUESTIONS
GAED strategy is to use a standardized
set of test parameters on field samples
and known commercial
benchmark AC samples. GAED measurements
along with ASTM and other
needed laboratory methods satisfy the
lab part. Professional knowledge about
different AC products and applications
coupled with lab, results in a useful
flexible problem solving strategy.
CHARACTERISTIC CURVES AND USES
It is important to clean the test sample
before the GAED test is performed.
When comparing a group of samples
one should provide dry samples to the
GAED laboratory. Some field samples in
the testing group may have more moisture
and volatile matter. The GAED provides
these values as a measure of
cleanliness. It is important to know the
cleanliness of purchased AC. Do not
pay for excess water on the carbon.
After samples are thermally cleaned
they are challenged with 1,1,1,2-Tetrafluoroethane
(TFE) gas at 240˚C. This
gas was chosen because it is difficult to
be adsorbed by AC (at 240˚C only the
highest adsorption energy sites are able
to capture TFE from the mobile gas
stream), its low cost, available worldwide,
non-toxic, and friendly to the environment.
After the high adsorption
energy pore volume is determined at
240˚C the temperature program lowers
the sample temperature hot to cold
slowly reaching a quasi-equilibrium
state before starting the next incremental
temperature lowering. Physical adsorption
is a function of temperature,
the lower the temperature the better
the adsorption capacity, weight of TFE
picked up. Lowering the temperature
until -20˚C avoids TFE condensation
on the sample. Condensation on the
sample is a false positive for adsorption.
This resulting hot to cold curve is
called the adsorption Characteristic
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Curve; it is characteristic of the sample
when it is run thru the standard GAED
test parameters. At the lowest temperature
the temperature program is reversed,
cold to hot, to obtain the
desorption Characteristic Curve. AC
does not demonstrate any hysterias, i.e.
the adsorption and desorption curves
are the same. Other physical adsorbents
do show hysterias.
From the graphical Characteristic
Curves in Figure 1 polynomial equations
are derived, see Table 5. These equations