Note: Descriptions are shown in the official language in which they were submitted.
CA 02333448 2000-11-24
WO 99/62630 PCT/US99/10989
POROUS PELLET ADSORBENTS FABRICATED FROM NANOCRYSTALS
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is broadly concerned with pelletized finely divided
adsorbents selected from the group consisting of metal oxides, metal
hydroxides, and
mixtures thereof, and methods of forming such pellets. The pellets are
preferably
formed by pressing the finely divided metal adsorbents at pressures of from
about 50
psi to about 6000 psi to yield self-sustaining bodies which retain at least
about 25% of
the surface area/unit mass and total pore volume of the starting metal
adsorbents prior
to pressing thereof. In use, target compound(s) are contacted with adsorbent
pellets of
the invention to destructively adsorb or chemisorb the target compound(s).
2. Description of the Prior Art
There is mounting concern about air quality, particularly the quality of
indoor
air. In most cases, indoor air is of worse quality than outdoor air. The
removal of
gaseous contaminants from air can be achieved by the application of a variety
of
principles. These include adsorption, catalytic transformation, and
absorption. Among
these adsorption is the most widely applied method. In adsorption, gases,
vapors, or
liquids come into contact with the surface of the adsorbent and adhere to it
to some
degree. This adsorption can be the result of residual physical forces (Van der
Waal's
forces) or chemical binding to the surface where the adsorbed molecule binds
stronger
to the adsorbing surface. Although adsorption can occur on a variety of solid
surfaces,
only a few materials have adsorptive characteristics sufficiently favorable
for air
cleaning. These include activated carbons, zeolites, molecular sieves, silica
gel, and
activated alumina.
Activated carbon has been the most commonly used in dealing with purification
of air. The highest quality activated carbon is made from coconut shells and
has a
surface area/unit mass of about 600-900 m2/g. However, activated carbon does
not
strongly adsorb air pollutants and the adsorbed material can be released over
time with
continued air flow. Moreover, activated carbon is difficult to clean up.
Another tool for indoor air purification is an electrostatic filter.
Electrostatic
filters work well at removing particulates from the indoor air. However,
electrostatic
filters are inadequate at removing many chemical vapors from the air, and
there are
CA 02333448 2000-11-24
WO 99/62630 PCTIUS99/10989
2
numerous chemical vapor air pollutants which are of concern. The most
prevalent of
these include formaldehyde, acetaldehyde, methanol, methylene chloride, carbon
tetrachloride, carbon monoxide, dimethyl amine, toluene, benzene, sulfur
dioxide,
acetonitrile, nitrosoamine, and nitrogen dioxide.
Nanocrystals make up a high surface area form of matter that can serve as
another adsorbent which can be used for removing pollutants such as
chlorocarbons,
acid gases, military warfare agents, and insecticides from the air. The unique
chemical
reactivity of nanocrystals allows the destructive adsorption and chemisorption
of toxic
substances and are a substantial advance in air purification. However,
nanocrystals are
a very fine dust which take up large volumes of space and are conducive to
electrostaticity, thus making them difficult to handle and at times
inconvenient.
There is a need for an adsorbent compound capable of strongly adsorbing air
pollutants which does not release those pollutants over time. Furthermore,
this
adsorbent compound must be easy to handle and be of decreased volume compared
to
nanocrystal adsorbents.
SUMMARY OF THE INVENTION
The present invention overcomes these problems and provides adsorbent pellet
bodies and methods for adsorbing a wide variety of target compounds using such
pellet
bodies. To this end, the invention contemplates the use of adsorbent pellets
which are
formed by pressing finely divided adsorbents. Adsorbent reactions using the
inventions
can be carried out over a wide range of temperatures, but preferably the
temperature is
such that the target compounds are in gaseous form.
In more detail, the adsorbent pellets of the invention are formed by pressing
or
agglomerating a quantity of finely divided adsorbent powder selected from the
group
consisting of metal hydroxides, metal oxides, and mixtures thereof. More
preferably,
the powder is an oxide or hydroxide of Mg, Ca, Ti, Zr, Fe, V, Mn, Ni, Cu, Al,
or Zn.
Metal oxides are the most preferred adsorbent powder with MgO and CaO being
particularly preferred. While conventionally prepared powders can be used to
form the
pellets, the preferred powders are prepared by aerogel techniques from
Utamapanya et
al., Chem. Mater., 3:175-181(1991). The starting powders should advantageously
have
an average crystallite size of up to about 20 nm, and more preferably from
about 3 to
9 nm. The pellets of this invention are formed by pressing the adsorbent
powder at a
pressure of from about 50 psi to about 6000 psi, more preferably from about
500 psi to
about 5000 psi, and most preferably at about 2000 psi. While pressures are
typically
CA 02333448 2000-11-24
WO 99/62630 PCT/US99/10989
3
applied to the powder by way of an automatic or hydraulic press, one skilled
in the art
will appreciate that the pellets can be formed by any pressure-applying or
other
agglomerating means (e.g., centrifugal or vibratory agglomerators).
Furthermore, a
binder or filler can be mixed with the adsorbent powder and the pellets can be
formed
by pressing the mixtiire by hand. Agglomerating or agglomerated as used
hereinafter
includes pressing together of the adsorbent powder as well as pressed-together
adsorbent powder. Agglomerating also includes the spraying, adhering,
centrifugation,
vibration or pressing of the adsorbent powder (either alone or in a mixture)
to form a
body, which may optionally be formed around a core material other than the
adsorbent
powder. To give but one example, the adsorbent powders of the invention can be
embedded in or supported on a porous substrate such as a filtration media.
If a metal oxide pellet is desired, the corresponding metal hydroxide should
be
thermally converted (i.e., "activated" at 500 C, overnight in a vacuum) to the
metal
oxide form. Activation can be carried out either on the metal hydroxide powder
or on
the finished metal hydroxide pellet. However, it is preferred that the metal
hydroxide
first be pressed into a pellet followed by thermal conversion to a metal oxide
pellet.
The pellets of the invention should retain at least about 25% of the multi-
point
surface area/unit mass of the metal hydroxide or metal oxide (whichever was
used to
form the pellet) particles prior to pressing together thereof. More
preferably, the multi-
point surface area/unit mass of the pellets will be at least about 50%, and
most
preferably at least about 90%, of the multi-point surface area/unit mass of
the starting
metal oxide or metal hydroxide particles prior to pressing. In another
embodiment, the
pellets retain at least about 25% of the total pore volume of the metal
hydroxide or
metal oxide particles prior to pressing thereof, more preferably, at least
about 50%, and
most preferably at least about 90% thereof. In the most preferred forms, the
pellets of
this invention will retain the above percentages of both the multi-point
surface area/unit
mass and the total pore volume.
In terms of pore radius, the preferred pelletized adsorbents should have an
average pore radius of at least about 45 A, more preferably from about 50 A to
about
100 A, and most preferably from about 60 A to about 75 A. The pellets of this
invention
normally have a density of from about.2 to about 2.0 g/cm3, more preferably
from about
.3 to about 1.0 g/cm3, and most preferably from about .4 to about .7 g/cm3.
The
minimum surface-to-surface dimension of the pellets (e.g., diameter in the
case of
spherical or elongated pellet bodies) of this invention is at least about 1
mm, more
preferably from about 10-20 mm.
CA 02333448 2000-11-24
WO 99/62630 PCT/US99/10989
4
Broadly speaking, the use of the pelletized adsorbents in accordance with the
invention is carried out by contacting the adsorbent powders with a target
compound
in fluid (i.e., liquid or gaseous) form. Preferable contacting systems include
any type
of flow reactor which allows a fluid stream containing the target compound to
be
circulated through a mass of pellets. Another suitable contacting system
includes
forming a membrane which contains the pelletized adsorbents and using the
membrane
to filter the target compound from a gas or liquid. The contacting step can
take place
over a wide range of temperatures and pressures; however, it is preferable
that the
temperature be such that the conveying stream and target compound are in a
gaseous
form.
A wide variety of target compounds can be adsorbed using the techniques of the
invention. These target compounds broadly include any compounds which can be
adsorbed, either destructively adsorbed or chemisorbed, by the starting metal
hydroxide
or metal oxide powder. More particularly, these target compounds may be
selected
from the group consisting of acids, alcohols, aldehydes, compounds containing
an atom
of P, S, N, Se or Te, hydrocarbon compounds (e.g., both halogenated and non-
halogenated hydrocarbons), and toxic metal compounds.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a graph depicting the adsorption of acetaldehyde on pelletized AP-
MgO compared to adsorption of acetaldehydes on powder AP-MgO;
Fig. 2 is a graph illustrating the adsorption of acetaldehyde onto powder AP-
MgO in comparison to the adsorption of acetaldehyde onto activated carbon;
Fig. 3 is a graph illustrating the adsorption of acetaldehyde onto powder AP-
MgO, powder CP-MgO, and powder CM-MgO;
Fig. 4 is a graph depicting the adsorption of acetaldehyde onto powder AP-MgO
after exposure to air for varying lengths of time versus the adsorption of
acetaldehyde
onto activated carbon exposed to air for varying lengths of time;
. Fig. 5 is a graph comparing the adsorption of propionaldehyde onto powder AP-
MgO under atmospheric pressure of air with the adsorption of propionaldehyde
onto
commercial samples of activated carbon under atmospheric pressure of air;
Fig. 6 is a graph comparing the adsorption of dimethylamine onto powder AP-
MgO under atmospheric pressure of air with the adsorption of dimethylamine
onto
activated carbon under atmospheric pressure of air;
CA 02333448 2007-08-16
Fig. 7 is a graph illustrating the adsorption of ammonia onto powder AP-MgO
both with and without exposure to air and comparing this adsorption to
adsorption of
ammonia onto activated carbon both with and without exposure to air; and
Fig. 8 is a graph which depicts the adsorption of methanol onto powder AP-
5 MgO under one atmosphere pressure of air compared to the adsorption of
methanol onto
activated at one atmosphere pressure of air.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following examples set forth preferred methods in accordance with the
invention. It is to be understood, however, that these examples are provided
by way of
illustration and nothing therein should be taken as a limitation upon the
overall scope
of the invention. In these examples, "AP-MgO" and "AP-CaO" refer to the
respective
aerogel (or autoclave) prepared oxides. "CP-MgO" and "CP-CaO" refer to the
respective oxides produced by conventional techniques. "CM-MgO" and "CM-CaO"
refer to the respective commercially available oxides.
Example 1
In this example, adsorbent AP-Mg(OH)2 pellets were prepared and their surface
characteristics were determined. These characteristics were compared to the
characteristics of AP-Mg(OH), in its powder form.
Materials and Methods
1. Preparation ofAP-Mg(O1I)2 Powder (no activation)
Highly divided nanocrystalline Mg(OH), samples were prepared by the
autoclave treatment described by Utamapanya et al., Chem. Mater., 3:175-181
(1991 ).
In this procedure, 10% by weight magnesium
methoxide in methanol solution was prepared and 83% by weight toluene solvent -
v, as
added. The solution was then hydrolyzed by addition of 0.75% by weight water
dropwise while the solution was stirred and covered with aluminum foil to
avoid
evaporation. To insure completion of the reaction, the mixiure was stirred
ovemight.
This produced a gel which was treated in an autoclave using a glass lined 600
ml
capacity Parr miniature reactor. The gel solution was placed within the
reactor and
flushed for 10 minutes with nitrogen gas, whereupon the reactor was closed and
pressurized to 100 psi using the nitrogen gas. The reactor was then heated up
to -" 65 C
over a-1 hour period at a heating rate of l C!min. The temperature was then
al i, ed
CA 02333448 2007-08-16
6
to equilibrate at 265 C for 10 minutes (final reactor pressure was about 700
psi). At
this point, the reactor was vented to release the pressure and vent the
solvent. Finally,
the reactor was flushed with nitrogen gas for 10 minutes.
2. Preparation ofAP-Mg(OH)2 Pellets
The AP-Mg(OH)2 powder prepared as set forth above was ground, using a
mortar and pestle, to remove any clumped powder. A portion of the powder was
then
placed in a small hydraulic press to make spherical 12 mm diameter pellets.
Pressures
ranging from 1000 psi to 10,000 psi were applied to form the pellets. The
resulting
pellets were crushed through sieves to form smaller pellets in order to
facilitate the
measuring of the surface characteristics (the sieve size was 0.25-1.168 mm ).
A second portion of the AP-Mg(OH)2 powder was pelletized using a Stokes
automatic press. The actual pressure applied is not known because the Stokes
press did
not have a gauge. However, the actual pressure applied to prepare the pellets
is
reproducible by controlling the movement of the upper punch on the pelletizer
which
has a scale. Low compression is just enough pressure to allow the sample to be
handled
without crumbling. High compression is the maximum compression that can be
used
without jatnming the machine or causing pellets to crack as they are ejected.
Medium
is the setting approximately half way between low and high.
3. Determination of Surface arealunit mass of AP-Mg(Offi; Powder and Pellets
The surface area/unit mass and total pore volume were measured for the powder
prepared above, as well as for the resultant pellets which were press-formed.
Similar surface area/unit mass measurements were performed using 70 mg
samples of magnesium hydroxide from each preparative procedure. Specifically,
the
powder samples were heated to a temperature of 120 C under dynamic vacuum
(about
1 x 10-2 Torr), held for 10 minutes, and then allowed to cool. Both the
Brunauer-
Emmett-Teller (BET) one-point and multi-point gas absorption methods were
employed using N2 adsorption at liquid N, temperature to measure the surface
areai unit
mass. The BET surface area measurement techniques are described in
Introducrion to
Powder Surface Area, Lowell, S., John Wiley & Sons: New York (1979).
4. Determination of Total Pore Volume of AP-Mg(OH);
The total pore volume was determined by the Barrett, Joyner. and Halcrda
(BJH) method. The sample was placed in a closed glass cell connected to a
manit-Old
CA 02333448 2007-08-16
7
filled with nitrogen gas. The sample cell was immersed in liquid nitrogen
until the
pressure above the sample was the same as ambient pressure at which time the
pores
were assumed to be filled with liquid nitrogen. The pressure above the sample
was then
reduced to 95% of ambient pressure and the volume of nitrogen gas released
from the
sample was measured by the BET machine. This desorption process was carried
out at
90%, 85%, 80%, and so on down to 5% of ambient pressure. At each interval, the
volume of nitrogen gas released from the sample is measured and used to derive
the
total pore volume. The BET total pore volume measurement techniques are
described
in the Quantachrome NOVA 2200 Gas Sorption Analyzer's User's Manual (Version
4.01).
Results and Discussion
1. Comparison of Characteristics of Powder AP-Mg(Off); vs. Pelletized AP-
Mg(OH);
a. Pellets Formed by Small Hydraulic Press
The surface area/unit mass for the multiple BET decreased from 346 m=/g for
the powder to 4.16 m'/g for the 10,000 psi pellets. The same was seen for the
single
point BET surface area/unit mass, which went from 635 mZ/g for the powder to
8.29
m2/g for the 10,000 psi pellets. The total pore volume also decreased from
0.956 cc/g
for the powder to 0.01217 cc/g for the 10,000 psi pellets. The average pore
radius was
affected very little with change in the pressure. There was however a
significant change
in the isotherm curves, which indicates a change in pore shape. The powder
sample
(before pelletization) looked almost identical to the sample subjected to a
pressure of
1,000 psi. The results are illustrated in Table 1.
CA 02333448 2000-11-24
WO 99/62630 PCT/US99/10989
8
Table 1. Surface area/unit mass and pore size distribution of magnesium
hydroxide in
powder and pellet form, prepared using the hydraulic press.
Multi- Avg.
Applied point % Multi- Single Total pore % Total pore Pore
Pressure S.A. point point S.A. volume Pore radius Shape
Form (psi) (mZ/g) S.A.b (m2/g) (cc/g) Volume` (A) Typed
Powder None 346 -- 635 0.956 -- 55.2 E
Pellet' 1,000 289 83.5 534 0.802 83.9 55.6 A, E
Pellet 2,000 235 67.9 458 0.629 65.8 53.5 A, E
Pellet 4,000 116 33.5 254 0.311 32.5 53.5 A
Pellet 5,000 80.3 23.2 165 0.216 22.6 53.8 A
Pellet 10,000 4.16 1.2 8.29 0.0122 1.3 58.4 D
'Pe11et size is 0.250-1.168 mm.
bPercent of multi-point surface area/un it mass retained by pellet when
compared to multi-point surface area/unit mass
of the powder
`Percent of total pore volume retained by pellet when compared to total pore
volume of the powder
Pore shape type abbreviation are as follows: A - Cylindrical pores, open at
both ends; D - Tapered or wedged-
shaped pores with narrow necks opened at one or both ends; and E - Bottleneck
pores
Table 1 demonstrates that the surface characteristics change a great deal
depending on formation pressure. It is noted that in going from the powder to
the pellet
compressed at 1,000 psi, the surface area/unit mass and pore size changed only
a little;
therefore, these pellets can be used in any type of flow reactor. In
conclusion, it was
found that the 1,000 psi pellets of AP-Mg(OH)2 worked ideally by eliminating
the
problem caused by electrostatic forces, without losing a significant amount of
surface
area/unit mass or pore volume.
b. Pellets Formed by Stokes Automatic Press
Referring to Table 2, it can again be seen that pelletization did not
significantly
decrease the surface areas/unit mass and porosities of the AP-Mg(OH)2. In some
instances the surface area/unit mass was even higher than that of the powder.
The
pellets made with low compression were very brittle and, after activation
(heating at
500 C under vacuum), they turned into powder. The medium compression pellets
were
much better, and only a small amount of powder was present after activation.
The
pellets formed by high compression were sturdy and did not break or form
powder upon
CA 02333448 2000-11-24
WO 99/62630 PCT/US99/10989
9
activation. Therefore, the medium and high compression pellets are ideal.
Because the
Stokes press did not include a pressure gauge, the exact value of the pressure
used in
the high compression test is not known. However, in comparing the pellet
characteristics of Table 2 with those of Table 1, the higli compression is
likely around
2000 psi.
Table 2. Surface area/unit mass and pore size distribution of magnesium
hydroxide in
a powder and pellet form, prepared using the Stokes press.
% Single Total % Average
Relative Multi- Multi- point pore Total pore Pore
Com- point S.A. point S.A. volume Pore radius Shape
Form pression (m2/g) S.A.' (mZ/g) (cc/g) Volume (A) Type`
Powder None 386 -- 692 1.038 -- 53.8 E
Pellet Low 440 114.0 699 1.090 105.0 49.5 A, E
Pellet Medium 346 89.6 679 0.944 90.9 54.6 A, E
Pellet High 300 77.7 606 0.794 76.5 53.0 A, E
Percent of multi-point surface area/unit mass retained by pellet wllen
compared to multi-point surface
area/unit mass of the powder
bPercent of total pore volume retained by pellet when compared to total pore
volume of the powder
`Pore shape type abbreviation are as follows: A - Cylindrical pores, open at
both ends; D - Tapered or
wedged-shaped pores with narrow necks opened at one or both ends; and E -
Bottleneck pores
Example 2
In this example, adsorbent AP-MgO pellets (one sample activated in its pellet
form and one sample activated in its powder form) were prepared from AP-
Mg(OH)2
powder and their physical characteristics were determined. These
characteristics were
compared to the characteristics of AP-MgO in its powder form. The purpose of
this test
was to determine whether the AP-MgO pellets would maintain substantially the
same
surface characteristics when activated in its pellet form as when activated in
the powder
form. It is preferable to pelletize the hydroxide first, and then activate the
pellets, which
converts the pellets to the oxide.
CA 02333448 2007-08-16
Materials and Methods
1. Preparation ofAP-Mg(OH)2 Powder (no activation) andAP-MgO Powder (with
activation)
Highly divided nanocrystalline Mg(OH)2 samples were prepared by the
5 autoclave treatment described by Utamapanya et al., Chem. Mater., 3:175-
181(1991).
[n this procedure, 10% by weight magnesium
methoxide in methanol solution was prepared and 83% by weight toluene solvent
was
added. The solution was then hydrolyzed by addition of 0.75% by weight water
dropwise while the solution was stirred and covered with aluminum foil to
avoid
10 evaporation. To insure completion of the reaction, the mixture was stirred
overnight.
This produced a gel which was treated in an autoclave using a glass lined 600
ml
capacity Parr miniature reactor. The gel solution was placed within the
reactor and
flushed for 10 minutes with nitrogen gas, whereupon the reactor was closed and
pressurized to 100 psi using the nitrogen gas. The reactor was then heated up
to 265 C
over a 4 hour period at a heating rate of 1 C/min. The temperature was then
allowed
to equilibrate at 265 C for 10 minutes (final reactor pressure was about 700
psi). At
this point, the reactor was vented to release the pressure and vent the
solvent. Finally,
the reactor was flushed with nitrogen gas for 10 minutes.
The Mg(OH)2 powder was then divided into two parts - one part for
pelletization
followed by activation, and one part for activation followed by pelletization.
The
Mg(OH), particles of the latter sample was then thermally converted to MgO.
This was
accomplished by heating the Mg(OH), under dynamic vacuum (10'Z Tonr)
conditions
at an ascending temperature rate to a maximum temperature of 500 C which was
held
for 6 hours. Further details about the MgO preparation can be found in PCT
Publication
WO 95/27679,
2. Preparation ofAP-Mg(OH)2 Pellets and AP-MgO Pellets
Magnesium hydroxide powder and magnesium oxide powder (as prepared
above) were each separately ground, using a mortar and a pestle, to remove any
clumped powder. A portion of each powder was separately pelletized using the
Stokes
automatic press resulting in AP-Mg(OH)2 pellets and AP-MgO pellets. The actual
pressure applied is unknown because the Stokes press did not have a gauge.
However,
the actual pressure applied to prepare the pellets is reproducible by
controlling the
movement of the upper punch on the pelletizer which has a scale. Low
compression is
just enough pressure to allow the sample to be handled without crumbling. High
CA 02333448 2000-11-24
WO 99/62630 PCTIUS99/10989
11
compression is the maximum compression that can be used without jamming the
machine or causing pellets to crack as they are ejected. Medium is the setting
approximately half way between low and high.
3. Activation ofAP-Mg(OH), Pellets to AP-MgO Pellets
The AP-Mg(OH)2 pellets were thermally converted to AP-MgO pellets in the
same manner in which the AP-Mg(OH)2 powder was activated as described above.
4. Determination of Surface area/unit mass and Total Pore Volume ofAP-MgO
The surface area/unit mass and total pore volume were measured for the pellets
which were activated after pelletization as well as for the pellets which were
activated
before pelletization. These measurements were made in the same manner as
described
in Example 1.
Results And Discussion
A. Comparison of Characteristics o f AP-MgO Pellets Activated Before Pelletiza-
tion vs. AP-MgO Pellets Activated After Pelletization
The results of this test are set forth in Tables 3 and 4 below. In comparing
the
results, it is observed that the pellets made out of the magnesium hydroxide
and
subsequently activated possessed higher surface area/unit mass and larger
porosity than
the pellets which were activated as a powder and then pelletized.
Table 3. Surface area/unit mass and pore size distribution of magnesium oxide
prepared
by activation of hydroxide pellets
Multi- % Single Total % Average Pore
Relative point Multi- point pore Total pore Shape
Form Com- S.A. Point S.A. volume Pore radius Type`
pression (m2/g) S.A.' (mZ/g) (cc/g) Volumeb (A)
Powder None 221 -- 334 0.682 -- 61.9 E
Pellet Low 222 100.0 340 0.715 104.8 64.5 A, E
Pellet Medium 214 96.8 328 0.684 100.3 63.9 A, E
Pellet High 214 96.8 330 0.677 99.3 63.4 A, E
'Percent of multi-point surface area/unit mass retained by pellet when
compared to multi-point surface
area/unit mass of the powder
CA 02333448 2000-11-24
WO 99/62630 PCTIUS99/10989
12
bPercent of total pore volume retained by pellet when compared to total pore
volume of the powder
'Wre shape type abbreviation are as follows: A - Cylindrical pores, open at
both ends; D - Tapered or
wedged-shaped pores with narrow necks opened at one or both ends; and E -
Bottleneck pores
Table 4. Surface area/unit mass and pore size distribution of magnesium oxide
activated as a powder and then pressed into pellets
Multi- % Single Total % Avg.
Relative point Multi- point pore Total pore Pore
Com- S.A. point S.A. volume Pore radius Shape
Form pression (mZ/g) S.A.3 (m'-/g) (cc/g) Volumeb (A) Type
Powder None 221 -- 334 0.682 -- 61.9 E
Pellet Low 210 95.0 324 0.676 99.1 64.3 A. E
Pellet Medium 205 92.8 321 0.657 96.3 64.1 A, E
Pellet High 199 90.0 316 0.613 89.9 61.6 A, E
'Percent of multi-point surface area/unit mass retained by pellet when
compared to multi-point surface
area/unit mass of the powder
bPercent of total pore volume retained by pellet when compared to total pore
volume of the powder
Pore shape type abbreviation are as follows: A - Cylindrical pores, open at
both ends; D - Tapered or
wedged-shaped pores with narrow necks opened at one or both ends; and E -
Bottleneck pores
Example 3
In this test, surface and pore characteristics of conventionally prepared MgO
and
CaO and aerogel prepared MgO and CaO were compared. Some samples were pressed
before activation (i.e., metal hydroxide was pressed into pellets and the
pellets were
activated) and some were pressed after activation (i.e., metal hydroxide
powder was
activated and the obtained oxide was pressed into pellet form). The samples
were
pressed with a Stokes press as described above. The aerogel powders were
prepared as
previously described. The conventional powders were prepared by hydrating
99.99%
ultrapure metal oxide with excess distilled deionized water, heating it under
a nitrogen
flow forming metal hydroxide, removing the excess of water in the microwave,
and
treating the metal hydroxide under dynamic vacuum at the same conditions used
in
preparing the aerogel metal oxide as in the previous examples. The surface
characteristics were determined by the procedures described in Example 1. The
results
are illustrated in Table 5 below.
CA 02333448 2000-11-24
WO 99/62630 PCT/US99/10989
13
Table 5. Results of pelletization studies (Activation = 500 C vacuum
dehydration)
Multi-Point Single Point Total Pore
Surface Area Surface Area Volume
Sample Description W/g) (m2/g) (cc/g)
CP-MgO Pressed Before Activation
Powder 235 241 0.438
Medium Compression 309 298 0.295
High Compression 275 271 0.275
CP-MgO Pressed After Activation
Powder 235 241 0.438
Medium Compression 255 251 0.287
High Compression 241 235 0.311
AP-MgO Pressed Before Activation
Powder 343 120 0.681
Low Compression 351 133 0.676
Medium Compression 337 135 0.657
High Compression 341 128 0.613
AP-MgO Pressed After Activation
Powder 343 120 0.681
Low Compression 335 137 0.676
Medium Compression 331 134 0.657
High Compression 326 141 0.613
CP-CaO Pressed Before Activation
Powder 133 128 0.233
Medium Compression 93 91 0.154
High Compression 80 77 0.144
CP-CaO Pressed After Activation
Powder 133 128 0.233
Medium Compression 105 102 0.173
High Compression 132 130 0.212
AP-CaO Pressed Before Activation
Powder 129 0.198
Low Compression 137 0.220
Medium Compression 144 0.231
High Compression 135 0.222
AP-CaO Pressed After Activation
Powder 129 0.198
Low Compression 141 0.234
Medium Compression 141 0.228
High Compression 146 0.244
The data from Table 5 provides further evidence that a higher surface
area/unit
mass is obtained when the hydroxide is activated in pellet form. This is
beneficial, as
storage of pelletized, rather than powder, hydroxide is more convenient due to
its lower
CA 02333448 2000-11-24
WO 99/62630 PCT/US99/10989
14
volume. The total pore volume shows the same trend for MgO; however, for CaO
it is
opposite. The difference is small, so most likely the shorter exposure time
will be the
main factor in choosing a preparation method. Overall the pelletizing is very
beneficial
as it preserves surface area/unit mass, decreases the volume, and minimizes
the static
nature of the powder, making it easier to handle the adsorbent.
Example 4
1. Adsorption ofAcetaldehyde by MgO pellets
In this test, the adsorptive abilities of MgO pellets were compared to that of
MgO powder. AP-Mg(OH)z powder was prepared and thermally activated to AP-MgO
powder as described above. MgO pellets (pressed at 4000 psi and activated
after
pelletization) were also prepared as described above. The adsorption
conditions and
procedure followed were the same for the pellet as for the powder. Each sample
was
placed in the U-tube of a conventional Recirculating Reactor. The reactor
contained a
circulation pump which continually passed the gaseous acetaldehyde over and
through
the adsorbents. Samples were taken at set time intervals and the pollutant
content was
analyzed. The contacting step was carried out for about 24 hours. For some
experiments, air was added to the acetaldehyde vapor.
2. Results and Conclusions
Fig. 1 graphically illustrates the adsorption of acetaldehyde on powder and
pelletized samples of AP-MgO. Over a period of twenty hours, the efficiency of
adsorption on the two samples was very similar. The adsorption on the
pelletized
samples evolved considerable amounts of heat just as in the adsorption on the
powder
samples. Furthermore, the adsorption on both the pellets and the powder caused
the
sample color to change to dark orange. This further indicates that the
pelletized AP-
MgO has retained the surface characteristics and thus the adsorptive abilities
of powder
AP-MgO.
Example 5
This test, in combination with the results from Example 4, illustrates the
superior adsorptive abilities of AP-MgO pellets in comparison to activated
carbon, a
prior art adsorbent. As demonstrated in Example 4, pelletized AP-MgO has
adsorptive
abilities very similar to powder AP-MgO. This Example illustrates that powder
AP-
MgO is substantially superior to activated carbon in its adsorptive abilities.
Therefore,
CA 02333448 2000-11-24
WO 99/62630 PCT/US99/10989
pelletized AP-MgO is also substantially superior to activated carbon in its
adsorptive
abilities. The adsorption conditions and procedures followed were identical to
those
described in Example 4.
The results are shown graphically in Fig. 2. The powder AP-MgO adsorbed
5 substantially more acetaldehyde than the activated carbon, particularly at
the twenty
hour point. As already demonstrated, the pelletized AP-MgO has surface
characteristics
and adsorptive abilities comparable to the powder AP-MgO. Therefore, the
pelletized
AP-MgO has the adsorptive qualities of the powder AP-MgO as well as the
reduced
volume and greater ease of handling not found in the powder AP-MgO. It follows
that
10 the results of the following examples will be applicable to the AP-MgO
pellets as well
as to the AP-MgO powder.
Example 6
The ability ofpowder AP-MgO, CP-MgO, and CM-MgO to adsorb acetaldehyde
15 was analyzed in the absence of air. Each sample was placed in the U-tube of
a
conventional Recirculating Reactor. The reactor contained a circulation pump
which
continually passed the gaseous acetaidehyde over and through the adsorbents.
Samples
were taken at set time intervals and the pollutant content was analyzed. The
contacting
step was carried out for about 20 hours.
The results of this experiment are depicted in Figure 3. One mole of AP-MgO
adsorbed one mole of acetaldehyde at room temperature over a short period of
time.
The adsorption was exothermic with a considerable amount of heat being
evolved. The
color of the solid sample changed dramatically from a whitish-gray before
adsorption
to a dark orange after adsorption. While adsorption was rapid and vigorous
onto the
AP-MgO and CP-MgO samples, it was barely observable on the CM-MgO sample
where no heat or color changes were observed.
Example 7
This series of tests was conducted to determine the effect of air exposure on
the
adsorptive abilities of powder AP-MgO in comparison to activated carbon. The
following categories of samples were analyzed: fresh samples of AP-MgO and
commercial activated carbon; AP-MgO and commercial activated carbon samples
exposed to air for 24 hours; AP-MgO and commercial activated carbon samples
exposed to air for ten (10) days; and AP-MgO and commercial activated carbon
stored
in an oven under air (60 C) for ten (10) days. The adsorptive procedure
followed was
identical to that set forth in Example 6.
CA 02333448 2000-11-24
WO 99/62630 PCTIUS99/10989
16
The results (Fig. 4) demonstrate that the different environments have only a
slight effect on the adsorption process. Furthermore, in each instance, the AP-
MgO
adsorbed substantially more acetaldehyde than did the activated carbon.
Example 8
An experiment was conducted to determine the ability of powder AP-MgO to
adsorb organic species other than acetaldehyde. This ability was compared to
the
adsorptive ability of three commercially available samples of activated
carbon. The
molar ratio of adsorbent to propionaldehyde was 10:1. The adsorption
conditions and
procedures followed were as described in Example 4 except that gaseous
propionaldehyde was recirculated over and through the adsorbents under
atmospheric
pressure of air for about 20 hours. As set forth in Figure 5, the AP-MgO
adsorbed more
propionaidehyde than any of the activated carbon samples. As shown in Example
4,
pelletized AP-MgO will achieve substantially the same results.
Example 9
An experiment was conducted to determine the ability of powder AP-MgO to
adsorb dimethylamine compared with the ability of activated carbon to adsorb
dimethylamine. The molar ratio of adsorbent to dimethylamine was 10:1. The
adsorption conditions and procedures followed were as described in Example 8
except
that gaseous dimethylamine was recirculated over and through the adsorbents
under
atmospheric pressure of air for about 20 hours. As set forth in Figure 6, the
AP-MgO
adsorbed more dimethylamine than the activated carbon samples. Pelletized AP-
MgO
will achieve substantially the same results as the powder AP-MgO.
Example 10
An experiment was conducted to determine the ability of powder AP-MgO to
adsorb ammonia compared with the ability of activated carbon to adsorb
ammonia. The
molar ratio of adsorbent to ammonia was 10:1. The adsorption conditions and
procedures followed were as described in Example 8 except that gaseous ammonia
was
recirculated over and through the adsorbents for about 20 hours both under air
and in
the absence of air. As set forth in Figure 7, the AP-MgO adsorbed more ammonia
than
the activated carbon samples. While the ammonia was adsorbed in lesser amounts
than
the aldehydes, it was adsorbed at a rapid rate. Pelletized AP-MgO will achieve
substantially the same results as the powder AP-MgO.
CA 02333448 2000-11-24
WO 99/62630 PCT/US99/10989
17
Example 11
An experiment was conducted to determine the ability of powder AP-MgO to
adsorb methanol as compared to the ability of activated carbon to adsorb
methanol. The
molar ratio of adsorbent to methanol was 10:1. The adsorption conditions and
procedures followed were as described in Example 8 except that gaseous
methanol was
recirculated over and through the adsorbents for about 20 hours under air. As
set forth
in Figure 8, the AP-MgO adsorbed substantially more methanol than the
activated
carbon samples adsorbed. While the methanol was adsorbed in lesser amounts
than the
aldehydes, it was adsorbed at a rapid rate. Pelletized AP-MgO will achieve
substantially the same results as the powder AP-MgO.
Example 12
Production of Pellet Using a Disk Granulator
The metal hydroxide powder is granulated in a Colton Mode1561 Rotary Wet
Granulator to generate spherical particles of about 10 mm in diameter. These
particles
are granulated through an addition of small amounts of water. The minimum
amount
of water is used to start the growth of granules.
Granules of the hydroxide after some drying in air or inert atmosphere are
activated to oxides, which regenerates the high surface area. This is
accomplished by
heating the Mg(OH)Z under dynamic vacuum (10-z Torr) conditions at an
ascending
temperature rate to a maximum temperature of 500 C which is held for 6 hrs.
Example 13
Production of Metal Oxide Powder-Enhanced HEPA Filter Using Spray Granulation
A mark 20 HEPA from Natural Solutions is impregnated using high surface area
metal oxides. Metal oxides can be applied to the filter substrate by spraying
metal oxide
or hydroxide mixed with water, or other solvent. In this technique, water or
solvent
droplets adhere to the filter substrate, forming a porous layer of powder
bound to the
filter. In case water is used and there is significant conversion from oxide
to hydroxide,
the filter has to be activated. Processing under vacuum to reactivate the
oxide may be
used.
