Abstrict A desiccant composition and a method for making the desiccant composition.
The dessicant composition includes an absorbent such as calcium
chloride or lithium chloride which is impregnated onto a highly
porous support such as activated carbon that has well controlled
porosity characteristics. The material is particularly useful for
absorbing high levels of water.
Claims What is claimed is:
1. A composite desiccant, comprising a porous support material
and an absorbent selected from the group consisting of calcium chloride,
lithium chloride, lithium bromide, magnesium chloride, calcium nitrate,
potassium fluoride and combinations thereof impregnated onto said
porous support material wherein said porous support material has
a pore volume of at least about 0.8 cc/g and an average pore size
of from about 1 to about 20 nanometers and wherein said composite
desiccant has a pore volume that is at least about 50 percent of
said pore volume of said porous support.
2. A composite desiccant as recited in claim 1 wherein said porous
support material has a pore volume of at least about 1 cc/g.
3. A composite desiccant as recited in claim 1 wherein said porous
support material has a pore volume of from about 1.5 cc/g to about
2.0 cc/g.
4. A composite desiccant as recited in claim 1 wherein said porous
support comprises activated carbon.
5. A composite desiccant as recited in claim 1 wherein said porous
support comprises silica.
6. A composite desiccant as recited in claim 1 wherein said absorbent
comprises calcium chloride.
7. A composite desiccant as recited in claim 1 wherein said composite
desiccant has a pore volume that is at least about 66 percent of
said pore volume of said porous support.
8. A composite desiccant as recited in claim 1 wherein said composite
desiccant comprises from about 20 to about 80 weight percent of
said absorbent.
9. A composite desiccant as recited in claim 1 wherein said composite
desiccant comprises from about 40 to about 60 weight percent of
said absorbent.
10. A composite desiccant as recited in claim 1 wherein said composite
desiccant is capable of absorbing at least about 1 gram of water
for every gram of said composite desiccant.
11. A composite desiccant as recited in claim 1 wherein said absorbent
comprises lithium chloride.
12. A composite desiccant, comprising a porous silica support material
and an absorbent salt selected from the group consisting of calcium
chloride, lithium chloride, lithium bromide, magnesium chloride,
calcium nitrate, potassium fluoride and combinations thereof impregnated
onto said porous silica support and wherein said composite desiccant
comprises from about 20 to about 80 weight percent of said absorbent
salt.
13. A composite desiccant as recited in claim 12 wherein said
composite desiccant comprises from about 40 to about 60 weight percent
of said absorbent salt.
14. A composite desiccant as recited in claim 12 wherein said
absorbent salt comprises calcium chloride.
15. A composite desiccant as recited in claim 12 wherein said
composite desiccant has a pore volume of at least about 1.0 cc/g.
16. A composite desiccant as recited in claim 12 wherein said
composite desiccant is capable of absorbing at least about 1 gram
of water per gram of said composite desiccant.
17. A composite desiccant as recited in claim 12 wherein said
absorbent salt comprises lithium chloride.
18. A composite desiccant as recited in claim 12 wherein said
porous silica support has a pore volume of at least about 0.8 cc/g.
19. A composite desiccant as recited in claim 12 wherein said
porous silica support has an average pore size of from about 1 to
about 20 nanometers.
20. A composite desiccant as recited in claim 12 wherein said
composite desiccant has a pore volume of at least about 50 percent
of the pore volume of said porous support.
21. A composite desiccant comprising activated carbon, said activated
carbon having an average pore size of from about 1 to about 20 nanometers
and a pore volume of at least about 0.8 cc/g and an absorbent salt
impregnated on said activated carbon and wherein said composite
desiccant comprises from about 20 to about 80 weight percent of
said absorbent salt.
22. A composite desiccant as recited in claim 21 wherein said
absorbent salt is selected from the group consisting of calcium
chloride, lithium chloride, lithium bromide, magnesium chloride,
calcium nitrate, potassium fluoride and combinations thereof.
23. A composite desiccant as recited in claim 21 wherein said
composite desiccant comprises from about 40 to about 60 weight percent
of said absorbent salt.
24. A composite desiccant composition as recited in claim 21 wherein
said activated carbon is in the form of activated carbon pellets.
25. A composite desiccant, comprising a porous support material
and an absorbent selected from the group consisting of calcium chloride,
lithium chloride, lithium bromide, magnesium chloride, calcium nitrate,
potassium fluoride and combinations thereof impregnated onto said
porous support material wherein said porous support material has
a pore volume of at least about 0.8 cc/g and an average pore size
of from about 1 to about 20 nanometers and wherein said composite
desiccant comprises from about 20 to about 80 weight percent of
said absorbent.
26. A composite desiccant as recited in claim 25 wherein said
porous support material has a pore volume of at least about 1 cc/g.
27. A composite desiccant as recited in claim 25 wherein said
porous support material has a pore volume of from about 1.5 cc/g
to about 2.0 cc/g.
28. A composite desiccant as recited in claim 25 wherein said
porous support comprises activated carbon.
29. A composite desiccant as recited in claim 25 wherein said
porous support comprises silica.
30. A composite desiccant as recited in claim 25 wherein said
absorbent comprises calcium chloride.
31. A composite desiccant as recited in claim 25 wherein said
composite desiccant has a pore volume that is at least about 66%
of said pore volume of said porous support.
32. A composite desiccant as recited in claim 25 wherein said
composite desiccant comprises from about 40 to about 60 weight percent
of said absorbent.
33. A composite desiccant as recited in claim 25 wherein said
composite desiccant is capable of absorbing at least about 1 gram
of water for every gram of said composite desiccant.
34. A composite desiccant as recited in claim 25 wherein said
absorbent comprises lithium chloride.
35. A composite desiccant, comprising a porous silica support material
and an absorbent salt selected from the group consisting of calcium
chloride, lithium chloride, lithium bromide, magnesium chloride,
calcium nitrate, potassium fluoride and combinations thereof impregnated
onto said porous silica support and wherein said composite desiccant
has a pore volume of at least about 50 percent of the pore volume
of said porous support.
36. A composite desiccant as recited in claim 35 wherein said
composite desiccant comprises from about 40 to about 60 weight percent
of said absorbent salt.
37. A composite desiccant as recited in claim 35 wherein said
absorbent comprises calcium chloride.
38. A composite desiccant as recited in claim 35 wherein said
composite desiccant has a pore volume of at least about 1.0 cc/g.
39. A composite desiccant as recited in claim 35 wherein said
composite desiccant is capable of absorbing at least about 1 gram
of water per gram of said composite desiccant.
40. A composite desiccant as recited in claim 35 wherein said
absorbent comprises lithium chloride.
41. A composite desiccant as recited in claim 35 wherein said
silica support has a pore volume of at least about 0.8 cc/g.
42. A composite desiccant as recited in claim 35 wherein said
silica support has an average pore size of from about 1 to about
20 nanometers.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to desiccant compositions, methods
for producing desiccant compositions and applications of desiccant
compositions. More specifically, the present invention is directed
to a composite desiccant composition having a high affinity for
water wherein the desiccant includes an absorbent deposited onto
a porous, high surface area support.
2. Description of Related Art
Desiccants are materials that are capable of capturing and retaining
water in the form of a liquid or a vapor. Desiccants can operate
by two fundamental mechanisms referred to as absorption and adsorption.
Absorption occurs when a substance (e.g., water vapor) penetrates
the inner structure of another (the absorbent). Absorbents for water
include salts such as calcium chloride (CaCl.sub.2) and lithium
chloride (LiCl). Adsorption occurs when a substance (e.g., water
vapor) is attracted and held onto the surface of another (the adsorbent).
Adsorbents for water vapor include highly porous hydrophilic materials
such as activated carbon and silica gel.
Examples of such materials can be found in the prior art. For example,
U.S. Pat. No. 4402717 by Izumo et al. discloses an apparatus for
removing moisture and odors from air. The apparatus includes a cylindrical
honeycomb structure fabricated from paper through which the moist
air flows. An adsorbent such as activated carbon is incorporated
into the paper during the papermaking process to deodorize the air.
The paper is also impregnated with an absorbent salt such as lithium
chloride by dipping the paper into a salt solution and drying.
U.S. Pat. No. 5135548 by Golden et al. discloses an oxygen selective
desiccant. A carbon molecular sieve is impregnated with absorbent
salts or inorganic oxides for the simultaneous removal of water
and oxygen from air to produce nitrogen gas. The carbon molecular
sieve is impregnated with the absorbent such that the volume of
solvent utilized is roughly equivalent to the pore volume of the
materials to be impregnated, resulting in a loading of absorbent
on the carbon molecular sieve of about 5 to 10 weight percent.
Japanese Patent Publication No. JP59228935 by Hiroyasu et al. discloses
a fibrous active carbon filament which is impregnated with a dehumidifying
agent such a lithium chloride, lithium bromide or calcium chloride
to form a dehumidifying element. The filaments are wound or woven
onto a support structure to form the dehumidifying element. The
amount of dehumidifying agent added to the carbon fiber is 0.5 to
90 weight percent. The agent is added by immersing the filament
into a salt solution and drying the filament.
For many applications, there is a need to absorb relatively large
quantities of water using only a small volume of desiccant. There
is also a need for a desiccant that can absorb the water at a fast
rate. For example, cooling devices that utilize a sorption cycle
for cooling with water as a refrigerant require that large quantities
of water vapor be removed from the system very quickly and stored
in a small volume.
SUMMARY OF THE INVENTION
One aspect of the present invention is directed to a composition
of matter that is a desiccant composition. The desiccant composition
preferably includes a porous support material and an absorbent dispersed
on the porous support material wherein the porous support material
has a pore volume of at least about 0.8 cc/g and an average pore
size of from about 1 to about 20 nanometers.
The porous support can include a material such as activated carbon
or silica. In one embodiment, the desiccant composition includes
a porous silica support material and an absorbent salt dispersed
on the porous silica support.
Another aspect of the present invention is directed to a method
for forming a desiccant composition, comprising the steps of providing
a porous support material having a pore volume of at least about
0.8 cc/g, contacting the porous support material with a flowable
medium comprising an absorbent for a time sufficient to substantially
fill porosity in the porous support material and then drying the
porous support material to remove liquid from the flowable medium
and form a desiccant composition comprising the absorbent dispersed
on the porous support. The desiccant composition preferably has
a pore volume of at least about 0.4 cc/g.
According to another aspect of the present invention a method is
provided for absorbing water vapor by contacting the water vapor
with a desiccant composition comprising an absorbent dispersed on
a porous support for a time sufficient to absorb at least about
0.4 gram of water per gram of desiccant.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to desiccant compositions, methods
for producing desiccant compositions and applications of desiccant
compositions. The desiccant compositions of the present invention
are composite desiccants that include an absorbent, such as a salt,
which is dispersed onto a porous support material that has a high
pore volume and a controlled pore size. The resulting desiccant
has a high affinity for water and is useful in a number of applications
that require the absorption of high levels of water. It is a particular
advantage of the present invention that a relatively large quantity
of water vapor can be absorbed in a relatively small volume of the
desiccant. As used herein, the terms absorb, absorption or the like
refer to the retention of the water by the desiccant, regardless
of the actual mechanism by which the water is retained.
The desiccant according to the present invention includes a porous
support material. The porous support material preferably has a high
pore volume, and therefore a high surface area, to accommodate the
absorption of large amounts of liquid by the desiccant. The pore
volume, expressed as a volume per unit mass, can be measured by
a nitrogen condensation method. Alternatively, the pore volume can
be measured gravimetrically by wicking a wetting fluid into the
pores and measuring the change in mass. Support materials having
a low pore volume are not capable of forming desiccants that can
accommodate the absorption of large quantities of water. For example,
carbon molecular sieves, as described in U.S. Pat. No. 5135548
by Golden et al., have a pore volume of about 0.2 cc/g or less and
are not able to retain large quantities of water.
The pore volume of the porous support according to the present
invention is preferably at least about 0.8 cc/g, more preferably
at least about 1 cc/g and even more preferably at least about 1.5
cc/g, such as at least about 2 cc/g. In one embodiment, the pore
volume of the support material is from about 1.5 cc/g to about 2
cc/g. As is discussed above, support materials having a pore volume
of less than about 0.8 cc/g will not effectively retain large amounts
of water. Porous support materials having pore volumes in excess
of about 8 cc/g may be useful for some applications, however the
structural integrity of the support is typically too low for most
applications.
In order to accommodate high levels of liquid such as water, it
is also important to control the average pore size and pore size
distribution of the support material. As used herein, the pore size
refers to the pore diameter. The average pore size is preferably
at least about 1 nanometer, such as in the range of from about 1
to about 20 nanometers. The pore size distribution is such that
there are very few pores having a size of less than about 0.5 nanometers.
Pore size can be measured, for example, by nitrogen adsorption.
In addition, the porous support material should be substantially
non-reactive to the absorbent which is dispersed onto the porous
support surface to form the desiccant. That is, the porous support
material should not react with the absorbent in a manner to reduce
or eliminate the water absorption properties of the absorbent.
The support material can be selected from virtually any material
having the above identified properties. Preferably, the support
material is hydrophilic. Particularly preferred materials include
activated carbon and silica. A suitable activated carbon is available
under the tradename "NUCHAR BAX 1500" from Westvaco Corp.
A suitable silica material is available under the tradename "AEROSIL
TS 100" from DeGussa Corp. The preferred support material will
depend upon the application of the desiccant composition. For example,
some support materials have a lower heat of adsorption than others.
This represents the amount of heat generated when the desiccant
absorbs water. This can be important where the heat generated upon
adsorption of the water vapor needs to be minimized. For example,
when the desiccant composition is utilized in a sorption cooling
device, the heat generated by sorption of the water vapor should
be minimized.
The porous support material can come in a variety of shapes and
sizes selected for a particular application. In one embodiment,
the porous support is provided in the form of small activated carbon
pellets having a size in the range of from about 0.5 to 2 millimeters.
The size of the pellets can be selected to influence the rate at
which water is absorbed wherein larger pellets will absorb water
at a slower rate due to the increased path length that the water
vapor travels. In another embodiment, the porous support is silica
having a size of from about 0.25 to 0.5 millimeters.
According to the present invention, an absorbent is dispersed onto
the surface of the porous support. The absorbent is preferably an
absorbent salt known in the art and can be selected, for example,
from calcium chloride (CaCl.sub.2), lithium chloride (LiCl), lithium
bromide (LiBr), magnesium chloride (MgCl.sub.2), calcium nitrate
(Ca(NO.sub.3).sub.2) and potassium fluoride (KF). Other absorbents
can include phosphorous pentoxide (P.sub.2 O.sub.5), magnesium perchlorate
(Mg(ClO.sub.4).sub.2), barium oxide (BaO), calcium oxide (CaO),
calcium sulfate (CaSO.sub.4), aluminum oxide (Al.sub.2 O.sub.3),
calcium bromide (CaBr.sub.2), barium perchlorate (Ba(ClO.sub.4).sub.2)
and copper sulfate (CuSO.sub.4). Combinations of two or more of
these salts can also be used and the particularly preferred absorbent
will depend upon the application of the desiccant.
The desiccant composition according to the present invention can
be formed by contacting the porous support material with a liquid
solution comprising the absorbent. For example, the porous support
can be contacted with a predetermined amount of liquid solution
that is sufficient to fill the porosity of the porous support with
the solution without substantial excess. The solution is typically
aqueous-based, however non-aqueous solutions such as ethanol solutions
can be used for wicking into hydrophobic porous support materials.
Preferably, the solution is a saturated solution of the absorbent
salt. In a preferred embodiment, the solution includes sufficient
absorbent to provide a desiccant composition comprising from about
20 weight percent to about 80 weight percent of the absorbent, more
preferably from about 40 weight percent to about 60 weight percent
of the absorbent, and even more preferably from about 45 to about
55 weight percent of the absorbent.
Thus, the available pore volume for a given amount of porous support
material is calculated and the porous support material is then contacted
with a volume of the solution approximately equal to the pore volume.
The entire solution wicks into the porosity, leaving virtually no
excess solution filling the channels between support particles or
on the outer surface.
Alternatively, the porous support can be contacted with a solution
of the absorbent for a calculated amount of time so that the porosity
is substantially filled without excess solution residing on the
support surface.
The porous support is then dried to remove the solvent. For example,
the porous support coated with the salt solution can be dried at
an elevated temperature (e.g., about 200.degree. C.) for a sufficient
period of time to drive off the solvent and crystallize the absorbent
salt.
The amount of absorbent dispersed onto the porous support is carefully
controlled to ensure maximum water sorption properties. For example,
after impregnation of the absorbent, it is preferred that the pore
volume of the desiccant is at least about 50 percent of the pore
volume of the porous support, and even more preferably at least
about 66 percent of the pore volume of the porous support. That
is, it is preferred that if the pore volume of the porous support
is about 1.5 cc/g, then the pore volume of the desiccant is preferably
no less than about 0.75 cc/g, more preferably no less than about
1.0 cc/g. Such high pore volumes can be realized even at high absorbent
loadings such as 40 to 60 weight percent.
The desiccant composition according to the present invention is
preferably capable of absorbing at least about 100 percent of its
weight in water, more preferably at least about 150 percent of its
weight in water and even more preferably at least about 200 percent
of its weight in water. The amount of water that can be absorbed
will also be influenced by the relative humidity and temperature,
as is illustrated in the examples below.
The desiccant composition of the present invention is useful in
a number of applications. In many applications the desiccant is
used in the form of a packed bed. The relative density of the packed
bed will partially control the rate of water absorption into the
bed.
The desiccant composition of the present invention can also be
regenerated for multiple uses by heating the desiccant to remove
water.
EXAMPLES
The following examples illustrate various embodiments of the present
invention. In each of Examples 1-15 the absorbent was calcium chloride
(CaCl.sub.2). A solution of calcium chloride (CaCl.sub.2) was prepared
by adding a water-soluble, anhydrous calcium chloride salt (Alfa
Aesar, Ward Hill, Mass.) to deionized water to form a salt solution
and contacting the porous support with the solution in a manner
such that the solution was wicked into the porous support structure.
In Examples 16-19 lithium chloride (LiCl) was the absorbent salt
and the samples were prepared in a similar manner.
In all examples using activated carbon as a porous support material,
activated carbon pellets (BAX 1500 Westvaco Corp.) were used. The
particles had a mean particle diameter, as-received, of about 2.2
mm and consisted of cylindrical pellets measuring from about 2 mm
to 4 mm in length. To obtain reduced particle sizes in the following
examples, the as-received carbon was ground and sieved. The resulting
mean particle size was determined by sieving. The measured BET surface
area of the as-received activated carbon was 2178 m.sup.2 /g, the
pore volume was about 1.5 cc/g and the average pore diameter was
about 27 .ANG..
For the following examples that utilized silica as a porous support
material, AEROSIL TS 100 (DeGussa Corp.) was utilized. The porous
silica had a pore volume of about 8 cc/g.
For Examples 1 to 7 and 17 the available pore volume in the porous
support was calculated and the amount of deionized water used was
equal to the available pore volume. For Examples 8 to 12 and 16
the volume of water was calculated as the amount needed to dissolve
the available calcium chloride. The solubility of calcium chloride
at room temperature is about 0.75 g/ml and the solubility of lithium
chloride at room temperature is about 0.63 g/ml.
BET theory was used to calculate surface area for the samples.
The nitrogen adsorption isotherm for each sample was measured using
5 points distributed between a relative pressure of 0.05 and 0.25.
The samples were outgased at 150.degree. C. and 0.01 torr for 3
hours prior to measurement.
Example 1
0.34 grams of anhydrous calcium chloride was added to 11 ml of
deionized water at room temperature and the salt was allowed to
dissolve. 6.5 grams of activated carbon having a mean particle size
of about 150 .mu.m and previously dried at 130.degree. C. for 3
hours was then added to the solution and stirred until all of the
solution was adsorbed into the activated carbon. The sample was
then placed in a convection oven at 200.degree. C. for 18 hours
to dry the calcium chloride. The resulting desiccant composition
included 5 weight percent calcium chloride.
Example 2
1.15 grams of calcium chloride was added to 11 ml of deionized
water at room temperature and allowed to dissolve. 6.5 grams of
activated carbon having a mean particle size of about 150 .mu.m
and previously dried at 130.degree. C. for 3 hours was then added
to the solution and stirred until all of the solution was adsorbed
into the activated carbon. The sample was then placed in a convection
oven at 200.degree. C. for 18 hours to dry the calcium chloride.
The resulting desiccant composition included 15 weight percent calcium
chloride and the BET surface area was 1793 m.sup.2 /g.
Example 3
2.3 grams of calcium chloride was added to 11 ml of deionized water
at room temperature and the salt was allowed to dissolve. 6.5 grams
of activated carbon having a mean particle size of about 150 .mu.m
and previously dried at 130.degree. C. for 3 hours was then added
to the solution and stirred until all of the solution was adsorbed
into the activated carbon. The sample was then placed in a convection
oven at 200.degree. C. for 18 hours. The resulting desiccant composition
included 26 weight percent calcium chloride and the BET surface
area was 1047 m.sup.2 /g.
Example 4
0.67 grams of calcium chloride was added to 10 ml of deionized
water at room temperature and the salt was allowed to dissolve.
6 grams of activated carbon having a mean particle size of about
250 .mu.m and previously dried at 130.degree. C. for 3 hours was
then added to the solution and stirred until all of the solution
was adsorbed into the activated carbon. The sample was then placed
in a convection oven at 200.degree. C. for 18 hours. The resulting
desiccant composition included 10 weight percent calcium chloride.
Example 5
1.1 grams of calcium chloride was added to 10 ml of deionized water
at room temperature and the salt was allowed to dissolve. 6 grams
of activated carbon having a mean particle size of about 250 .mu.m
and previously dried at 130.degree. C. for 3 hours was then added
to the solution and stirred until all of the solution was adsorbed
into the activated carbon. The sample was then placed in a convection
oven at 200.degree. C. for 18 hours. The resulting desiccant composition
included 15.5 weight percent calcium chloride.
Example 6
2.6 grams of calcium chloride was added to 10 ml of deionized water
at room temperature and the salt was allowed to dissolve. 6 grams
of activated carbon having a mean particle size of about 250 .mu.m
and previously dried at 130.degree. C. for 3 hours was then added
to the solution and stirred until all of the solution was adsorbed
into the activated carbon. The sample was then placed in a convection
oven at 200.degree. C. for 18 hours. The resulting desiccant composition
included 30 weight percent calcium chloride and the BET surface
area was 663 m.sup.2 /g.
Example 7
227 grams of calcium chloride was added to 386 ml of deionized
water at room temperature and the salt was allowed to dissolve.
227 grams of activated carbon having a mean particle size of about
1.3 mm was then added to the solution and stirred until all of the
solution was adsorbed into the activated carbon. The sample was
then placed in a convection oven at 200.degree. C. for 18 hours
to dry the calcium chloride. The resulting desiccant composition
included 50 weight percent calcium chloride and the BET surface
area was 353 m.sup.2 /g.
Example 8
227 grams of calcium chloride was added to 303 ml of deionized
water at room temperature and the salt was allowed to dissolve.
227 grams of activated carbon having a mean particle size of about
1.3 mm was then added to the solution and stirred until all of the
solution was adsorbed into the activated carbon. The sample was
then placed in a convection oven at 200.degree. C. for 18 hours
to dry the calcium chloride. The resulting desiccant composition
included 50 weight percent calcium chloride and the BET surface
area was 119 m.sup.2 /g.
Example 9
227 grams of calcium chloride was added to 303 ml of deionized
water at room temperature and the salt was allowed to dissolve.
227 grams of activated carbon having a mean particle size of about
1.3 mm was added to the solution and stirred until all of the solution
was adsorbed into the activated carbon. The sample was then placed
in a convection oven at 200.degree. C. for 18 hours. The resulting
desiccant included 50 weight percent calcium chloride. The BET surface
area was 70 m.sup.2 /g. After the sample was dry it was ground,
sieved and separated into 3 sample groups having mean particle sizes
of about 1 mm (Example 9a), 250 .mu.m (Example 9b) and 150 .mu.m
(Example 9c).
Example 10
100 grams of calcium chloride was added to 134 ml of room temperature
deionized water and the salt was allowed to dissolve. 100 grams
of activated carbon having a mean particle size of about 1.3 mm
was added to the solution and stirred until all of the solution
was adsorbed into activated carbon. The sample was then placed in
a convection oven at 200.degree. C. for 18 hours. The resulting
desiccant composition included a 50 weight percent calcium chloride
and the BET surface area was 70 m.sup.2 /g.
Example 11
50 grams of calcium chloride was added to 67 ml of deionized water
at room temperature and the salt was allowed to dissolve. 50 grams
of activated carbon having a mean particle size of about 2 to 3
mm and previously dried in 130.degree. C. convection oven for 3
hours was added to the solution and stirred until all of the solution
was adsorbed into the activated carbon. The sample was then placed
in a convection oven at 200.degree. C. for 18 hours. The resulting
desiccant composition included 50 weight percent calcium chloride.
TABLE I Mean Particle Size of BET Surface Example CaCl.sub.2 (wt.
%) Support Area (m.sup.2 /g) 1 5 150 .mu.m N/A 2 15 150 .mu.m 1793
3 26 150 .mu.m 1122 4 10 250 .mu.m 663 5 15 250 .mu.m 663 6 30 250
.mu.m 663 7 50 1.3 mm 353 8 50 1.3 mm 119 9.sup.1 50 1.3 mm 70 10
50 1.3 mm 70 11 50 2-3 mm N/A .sup.1 before sieving
Water adsorption was used to measure the capacity of the samples
to adsorb water at 6 different relative humidities. Using salt solutions,
6 different environments of a specific relative humidity were created
in containers. The containers were sealed, allowed to reach equilibrium
and then approximately 1 g of each sample was placed in the containers.
To measure water adsorption at temperatures greater than 25.degree.
C., containers were placed in a convection oven at 60.degree. C.
and 100.degree. C. Samples were weighed every 24 hours until capacitance
was reached and weight percent gained calculated.
The results of these test for Examples 1-11 are illustrated in
Table II. The level of absorption generally increased with increased
amounts of absorbent dispersed on the porous support. Compare Examples
1 2 and 3 (increased levels of absorbent at a mean particle size
of 150 .mu.m) and compare Examples 4 5 and 6 (increased levels
of absorbent at a mean particle size of 250 .mu.m).
TABLE II Weight % gained (grams water per grams desiccant) Relative
Humidity 6% 16% 29% 53% 84% Example 1 6 6 12 24 79 Example 2 17
17 29 42 96 Example 3 34 33 48 30 88 Example 4 13 11 19 28 69 Example
5 17 17 26 36 69 Example 6 31 32 44 51 76 Example 9a 32 30 46 59
102 Example 9b 44 43 61 76 126 Example 9c 42 41 59 73 116 Example
10 61 37 76 93 144 Example 11 51 44 78 98 170
For Example 9a, the effect of temperature on adsorption was measured.
Table III illustrates the absorption at 60.degree. C. and Table
IV illustrates the absorption at 100.degree. C.
TABLE III Weight % gained (grams water per grams desiccant) Relative
Humidity Example 6% 10% 16% 50% 75% 80% Example 9a 28 22 38 53 113
99
TABLE IV Weight % gained (grams water per grams desiccant) Relative
Humidity Example 7% 9% 46% 74% 76% Example 9a 22 48 61 110 102
Example 13
This example utilizes 2 separate wicking steps to increase the
amount of calcium chloride dispersed on the activated carbon support.
In Step 1 12.665 grams of calcium chloride was added to 17 ml of
deionized water at room temperature and the salt was allowed to
dissolve. 10 grams of activated carbon having a mean particle size
of about 1.3 mm and previously dried at 130.degree. C. in a convection
oven for 3 hours was added to this first solution and stirred until
all of the solution was adsorbed into the activated carbon. The
sample was then placed in a convection oven of 200.degree. C. for
18 hours.
In Step 2 a second solution was prepared. 2.335 grams of calcium
chloride was added to 3.13 ml of deionized water at room temperature
and the salt was allowed to dissolve. The sample from Step 1 was
added to the second wicking solution and was stirred until all of
the solution was adsorbed into the activated carbon. The sample
was then placed in a convection oven at 200.degree. C. for 18 hours.
The resulting desiccant composition included 60 weight percent calcium
chloride.
Example 14
10 grams of calcium chloride was added to 100 ml of deionized water
at room temperature and the salt was allowed to dissolve. 10 grams
of hydrophilic silica aerogel was added to the solution and stirred
until all of the solution was adsorbed into the hydrophilic silica
aerogel. The sample was then placed in a convection oven at 200.degree.
C. for 18 hours to dry the calcium chloride. The resulting desiccant
composition included 50 weight percent calcium chloride.
Example 15
10 grams of calcium chloride was added to 10 ml of deionized water
at room temperature and the salt was allowed to dissolve. The solution
was then stirred into 100 ml of ethanol. 10 grams of hydrophobic
silica aerogel, was added to the solution and stirred until all
of the solution was adsorbed into the hydrophobic silica aerogel.
The sample was then placed in a convection oven at 200.degree. C.
for 18 hours to dry the calcium chloride. The resulting desiccant
composition included 50 weight percent calcium chloride.
Example 16
6 grams of lithium chloride was added to 10 ml of deionized water
at room temperature and the salt was allowed to dissolve. 10 grams
of activated carbon pellets 2 to 4 mm in length and previously dried
at 130.degree. C. for 3 hours was added to the solution and stirred
until all of the solution was adsorbed into the activated carbon.
The sample was then placed in a convection oven of 200.degree. C.
for 18 hours. The resulting desiccant composition included about
38 weight percent lithium chloride.
Example 17
10 grams of lithium chloride was added to 17 ml of deionized water
at room temperature and the salt was allowed to dissolve. 10 grams
of activated carbon pellets 2 to 4 mm in length and previously dried
at 130.degree. C. for 3 hours was added to the solution and stirred
until all of the solution was adsorbed into the activated carbon.
The sample was then placed in a convection oven at 200.degree. C.
for 18 hours. The resulting desiccant composition included 50 weight
percent lithium chloride.
Example 18
10 grams of lithium chloride was added to 17 ml of deionized water
at room temperature and the salt was allowed to dissolve. 10 grams
of activated carbon pellets 2 to 4 mm in length and previously dried
at 130.degree. C. for 3 hours was added to the solution and stirred
until all of the solution was adsorbed into the activated carbon.
The sample was then placed in a convection oven at 200.degree. C.
for 18 hours.
A second solution was prepared by adding 5 grams of lithium chloride
to 8 ml of deionized water at room temperature and allowing the
salt to dissolve. Preparation of the sample was completed by mixing
the sample from step 1 above with the second solution and stirring
until all of the solution was adsorbed into the activated carbon.
The sample was then placed in a convection oven of 200.degree. C.
for 18 hours. The resulting desiccant composition included 60 weight
percent lithium chloride.
Example 19
10 grams of lithium chloride was added to 17 ml of deionized water
at room temperature and the salt was allowed to dissolve. 10 grams
of activated carbon previously dried at 130.degree. C. for 3 hours
was added to the solution and stirred until all of the solution
was adsorbed into the activated carbon. The sample was then dried
at 200.degree. C. for 18 hours.
A second solution was prepared by adding 7.6 grams of lithium chloride
to 12 ml of deionized water at room temperature and the salt was
allowed to dissolve. Preparation of the sample was completed by
mixing the sample from step 1 into the second solution and stirring
until all of the solution was adsorbed into the activated carbon.
The sample was then dried at 200.degree. C. for 18 hours.
A third solution was prepared by adding 2.4 grams of lithium chloride
to 3.8 ml of deionized water at room temperature and the salt was
allowed to dissolve. Preparation of the sample was completed by
mixing the step 1 sample, while stirring, into the second wicking
solution and stirred until all of the solution was adsorbed into
the activated carbon pores. The sample was then dried at 200.degree.
C. for 18 hours. The resulting desiccant composition included about
67 weight percent lithium chloride.
For Examples 16-19 utilizing lithium chloride as an absorbent,
the samples were tested for water absorption at different humidity
levels. Using salt solutions, 6 different environments of a specific
relative humidity were created in containers. The containers were
sealed, allowed to reach equilibrium and then approximately 1 g
of each sample was placed in the containers. The result are illustrated
in Table V. The desiccant compositions were able to absorb up to
almost 3 times their weight in water in a high humidity environment.
TABLE V Weight % gained (grams water per grams desiccant) Weight
% Relative Humidity Example LiCl 6% 16% 29% 53% 84% 16 38 wt % 25
40 61 122 17 50 wt % 36 64 81 116 194 18 60 wt % 35 78 101 138 225
19 67 wt % 47 100 115 168 294
While various embodiments of the present invention have been described
in detail, it is apparent that modifications and adaptations of
those embodiments will occur to those skilled in the art. However,
it is to be expressly understood that such modifications and adaptations
are within the spirit and scope of the present invention. |