U.S. patent application number 17/181532 was filed with the patent office on 2021-06-17 for water vapor harvesting materials and devices.
The applicant listed for this patent is KING ABDULLAH UNIVERSITY OF SCIENCE AND TECHNOLOGY. Invention is credited to Renyuan LI, Yifeng SHI, Peng WANG, Mengchun WU.
Application Number | 20210178321 17/181532 |
Document ID | / |
Family ID | 1000005419734 |
Filed Date | 2021-06-17 |
United States Patent
Application |
20210178321 |
Kind Code |
A1 |
WANG; Peng ; et al. |
June 17, 2021 |
WATER VAPOR HARVESTING MATERIALS AND DEVICES
Abstract
An atmospheric water harvesting material includes a deliquescent
salt, a photothermal agent, and a polymeric hydrogel matrix
containing the deliquescent salt and photothermal agent.
Inventors: |
WANG; Peng; (Thuwal, SA)
; LI; Renyuan; (Thuwal, SA) ; SHI; Yifeng;
(Thuwal, SA) ; WU; Mengchun; (Thuwal, SA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KING ABDULLAH UNIVERSITY OF SCIENCE AND TECHNOLOGY |
Thuwal |
|
SA |
|
|
Family ID: |
1000005419734 |
Appl. No.: |
17/181532 |
Filed: |
February 22, 2021 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
17049421 |
Oct 21, 2020 |
10960347 |
|
|
PCT/IB2019/052726 |
Apr 3, 2019 |
|
|
|
17181532 |
|
|
|
|
62795691 |
Jan 23, 2019 |
|
|
|
62672865 |
May 17, 2018 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 2257/80 20130101;
B01J 20/0296 20130101; C08J 3/075 20130101; B01D 53/28 20130101;
E03B 3/28 20130101; B01J 20/0229 20130101; B01J 20/0288 20130101;
B01D 5/0057 20130101; B01D 2253/25 20130101; B01D 2253/202
20130101; B01J 20/321 20130101; B01J 20/3208 20130101; B01J 20/046
20130101; B01J 20/0244 20130101; B01J 20/0237 20130101; B01D 53/261
20130101; B01D 2253/112 20130101; B01J 20/28026 20130101; C08J
2333/26 20130101; B01D 53/06 20130101; B01J 20/0222 20130101; B01J
20/0225 20130101; B01D 2259/40098 20130101 |
International
Class: |
B01D 53/28 20060101
B01D053/28; C08J 3/075 20060101 C08J003/075; B01J 20/02 20060101
B01J020/02; B01J 20/04 20060101 B01J020/04; B01J 20/32 20060101
B01J020/32; B01D 5/00 20060101 B01D005/00; B01D 53/26 20060101
B01D053/26; E03B 3/28 20060101 E03B003/28; B01D 53/06 20060101
B01D053/06; B01J 20/28 20060101 B01J020/28 |
Claims
1-20. (canceled)
21. A method for generating water from water vapor, the method
comprising: absorbing water vapor by an atmospheric water
harvesting material arranged on an outer surface of a cylinder,
wherein the atmospheric water harvesting material comprises a
deliquescent salt, a photothermal agent, and a polymeric hydrogel
matrix containing the deliquescent salt and photothermal agent;
rotating the cylinder so that a portion of the atmospheric water
harvesting material that has absorbed the water vapor is facing a
condensation chamber, which is arranged above the cylinder and has
a light-admitting upper surface; exposing the portion of the
atmospheric water harvesting material facing the condensation
chamber to solar energy passing through the light-admitting upper
surface; releasing, due to the solar energy, the water vapor from
the portion of the atmospheric water harvesting material facing the
condensation chamber into the condensation chamber; and condensing,
in the condensation chamber, the released water vapor into water,
wherein the condensed water is pure water or the water vapor is
released exclusively due to the solar energy.
22. The method of claim 21, wherein when the portion of the
atmospheric water harvesting material is facing a condensation
chamber, a second portion of the atmospheric water harvesting
material is not directly exposed to the solar energy, the method
further comprising: absorbing water vapor by the second portion of
the atmospheric water harvesting material.
23. The method of claim 21, wherein the atmospheric water
harvesting material does not change phase from hydrophilic to
hydrophobic while releasing the water vapor.
24. The method of claim 21, wherein the condensed water is pure
water.
25. The method of claim 21, wherein the water vapor is released
exclusively due to the solar energy.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application No. 62/672,865, filed on May 17, 2018, entitled
"MATERIALS FOR SOLAR-ASSISTED ATMOSPHERIC WATER HARVESTING FOR
FRESH WATER PRODUCTION," and U.S. Provisional Patent Application
No. 62/795,691, filed on Jan. 23, 2019, entitled "A SORPTION-BASED
CONTINUOUS ATMOSPHERIC WATER GENERATOR (AWG) DEVICE," the
disclosures of which are incorporated herein by reference in their
entirety.
BACKGROUND
Technical Field
[0002] Embodiments of the subject matter disclosed herein generally
relate to a device, materials, and method for harvesting
atmospheric water vapor using a polymeric hydrogel that includes a
deliquescent salt and a photothermal agent.
Discussion of the Background
[0003] Water is essential for life on this planet. Many regions of
the world, however, do not have ready access to water. Further,
even regions that have access to water, the available water may not
be suitable for human consumption. For example, the available water
may be salinated water from the ocean, which contains too much
sodium for consumption in the amounts required to sustain human
life.
[0004] One readily-available source of water is the Earth's
atmosphere, which is accessible almost anywhere on Earth and holds
approximately 12,900 billion tons of fresh water. Thus, there has
been considerable research into capturing atmospheric water vapor
to provide clean water for arid regions, land-locked regions, and
remote communities. The most promising conventional atmospheric
water harvesting devices employ a water sorbent to capture
atmospheric water vapor and solar energy to release the captured
atmospheric water vapor for consumption. The use of solar energy to
release the captured atmospheric water is advantageous because the
device does not require an external power source to desorb the
captured atmospheric water from the water sorbent.
[0005] In order to be cost-effective and encourage wide-spread
adoption, an atmospheric water harvesting device should include a
water sorbent capable of adsorbing large amounts of water from the
air, even in relatively low humidity conditions, and capable of
releasing the adsorbed water under relatively low temperatures.
Conventional desiccants, such as silica gel, zeolite, activated
alumina, typically have wide water vapor sorption window, but to
efficiently release the captured water, they require high
temperatures (>160.degree. C.), which are typically beyond what
simple solar photothermal based heating devices are capable of
offering.
[0006] Document [1] discloses solid super desiccants formed from a
sodium polyacrylate powder with a lithium chloride solution. The
desiccants can be regenerated, i.e., the absorbed water can be
released, at temperatures less than 80.degree. C. Although Document
[1] does not disclose how much lower than 80.degree. C. the
desiccants can be regenerated, heating the super desiccants to
approximately 80.degree. C. using solar radiation would require
very strong sun rays. Thus, the solution disclosed in Document [1]
can produce water only under limited environmental conditions.
[0007] Document [2] discloses a hydrogel composite desiccant
composed of porous Poly(N-isopropylacrylamide) impregnated by
hygroscopic salt in the form of calcium chloride (CaCl.sub.2).
Specifically, the calcium chloride is impregnated in a
thermo-responsive polymer matrix-double network Al-alginate/PNIPPAm
hydrogel. The hydrogel composite desiccant is a thermo-responsive
polymer, which is a temperature-induced phase transfer material.
When the temperature is low, the polymer exhibits hydrophilic
wetting behavior in which water can be absorbed into the crosslink
structure. When the temperature is higher than certain value (known
as the lower critical solution temperature, LOST), the polymer
converts into hydrophobic wetting behavior in which the polymer
chain will shrink and extrude water.
[0008] Because PNIPAAm is an electrostatically crosslinked
hydrogel, the ion strength (i.e., concentration of salt solution)
of infiltrated solution will significantly influence its
phase-conversion property, which appears to be the reason why
Document [2] discloses that very limited salt can be loaded into
the hydrogel.
[0009] One problem with the hydrogel disclosed in Document [2] is
that it requires a heat source that is sufficient to raise the
temperature of the hydrogel so that it converts to a hydrophobic
phase. This typically involves a heat source that burns fossil
fuels, thus requiring additional fossil fuel energy input to
convert water vapor into water.
[0010] Another problem with the hydrogel disclosed in Document [2]
relates to its water release process. When the temperature is
higher than LOST, the polymer chain/crosslink will shrink due to
the conversion of hydrophilicity to hydrophobicity. Thus, water is
"left behind" at its original position. This process will lead to a
serious salt wash out and the hygroscopic, as well as other
impurities precipitated from the hydrogel, will contaminate the
collected water. Further, the wash out of salt will lead to a
decrease of water sorption property of sorbent, and accordingly,
requires occasional addition of salt to the hydrogel to maintain
its water absorption properties.
[0011] Thus, there is a need for an atmospheric water harvesting
material that is able to absorb large amounts of atmospheric water
vapor and to safely desorb the atmospheric water vapor under
relatively low temperatures without requiring a fossil fuel heating
source and/or that can produce pure water instead of salt
contaminated water.
SUMMARY
[0012] According to an embodiment, there is an atmospheric water
harvesting material, which includes a deliquescent salt, a
photothermal agent, and a polymeric hydrogel matrix containing the
deliquescent salt and photothermal agent.
[0013] According to another embodiment, there is a method for
forming an atmospheric water harvesting material. A polymeric
hydrogel matrix comprising a photothermal agent is formed. The
polymeric hydrogel matrix comprising the photothermal agent is then
freeze-dried. The freeze-dried polymeric hydrogel matrix comprising
the photothermal agent is immersed in a solution containing
deliquescent salt to form a polymeric hydrogel matrix comprising
the photothermal agent and the deliquescent salt. The polymeric
hydrogel matrix comprising the photothermal agent and the
deliquescent salt is then dried.
[0014] According to a further embodiment, there is an atmospheric
water harvesting device, which includes a condensation chamber
having a light admitting upper surface and a water outlet. The
device also includes an atmospheric water harvesting chamber,
arranged below the condensation chamber, containing an atmospheric
water harvesting material and having a bottom surface with an
opening to accept ambient air and an upper surface having an
opening to allow atmospheric water captured from the ambient air by
the atmospheric water harvesting material to pass into the
condensation chamber due to heat generated from solar energy
impinging on the light admitting upper surface of the condensation
chamber.
[0015] According to another embodiment, there is a method for
generating water from water vapor. Water vapor is absorbed by an
atmospheric water harvesting material arranged on an outer surface
of a cylinder. The atmospheric water harvesting material includes a
deliquescent salt, a photothermal agent, and a polymeric hydrogel
matrix containing the deliquescent salt and photothermal agent. The
cylinder is rotated so that a portion of the atmospheric water
harvesting material that has absorbed the water vapor is facing a
condensation chamber, which is arranged above the cylinder and has
a light-admitting upper surface. The portion of the atmospheric
water harvesting material facing the condensation chamber is
exposed to solar energy passing through the light-admitting upper
surface. The water vapor from the portion of the atmospheric water
harvesting material facing the condensation chamber is released
into the condensation chamber due to the solar energy. The released
water vapor is condensed into water in the condensation chamber.
The condensed water is pure water or the water vapor is released
exclusively due to the solar energy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate one or more
embodiments and, together with the description, explain these
embodiments. In the drawings:
[0017] FIG. 1 is a diagram of an atmospheric water harvesting
material according to embodiments;
[0018] FIG. 2 is a flow diagram of a method for making an
atmospheric water harvesting material according to embodiments;
[0019] FIGS. 3A-3E are diagrams of the making of an atmospheric
water harvesting material according to embodiments;
[0020] FIG. 4 is a diagram of an atmospheric water harvesting
device according to embodiments; and
[0021] FIG. 5 is a flow diagram of a method of generating water
from water vapor according to embodiments.
DETAILED DESCRIPTION
[0022] The following description of the exemplary embodiments
refers to the accompanying drawings. The same reference numbers in
different drawings identify the same or similar elements. The
following detailed description does not limit the invention.
Instead, the scope of the invention is defined by the appended
claims. The following embodiments are discussed, for simplicity,
with regard to the terminology and structure of atmospheric water
harvesting for production of water. It should be recognized,
however, that the embodiments can also be employed in connection
other uses of atmospheric water harvesting, including
dehumidification, desiccant-assisted cooling, etc.
[0023] Reference throughout the specification to "one embodiment"
or "an embodiment" means that a particular feature, structure or
characteristic described in connection with an embodiment is
included in at least one embodiment of the subject matter
disclosed. Thus, the appearance of the phrases "in one embodiment"
or "in an embodiment" in various places throughout the
specification is not necessarily referring to the same embodiment.
Further, the particular features, structures or characteristics may
be combined in any suitable manner in one or more embodiments.
[0024] FIG. 1 is a diagram illustrating an atmospheric water
harvesting material 100. The atmospheric water harvesting material
includes a deliquescent salt 110, a photothermal agent 120, and a
polymeric hydrogel matrix 130 containing the deliquescent salt 110
and photothermal agent 120. The deliquescent salt 110 is in a
liquid phase but is held in a solid form in the polymeric hydrogel
matrix 130. The polymeric hydrogel matrix 130 comprises a
cross-linked and flexible hydrogel network. Those skilled in the
art will appreciate that a photothermal agent is one that produces
thermal energy in the form of heat due to photoexcitation of the
agent.
[0025] The disclosed atmospheric water harvesting material is
particularly advantageous because it is not sensitive to the ion
strength of infiltrated solution, which allows it to hold more
hygroscopic salt and thus exhibits a higher water capacity compared
to conventional materials, such as those disclosed in Document [2].
Specifically, the disclosed atmospheric water harvesting material
releases water while exhibiting a hydrophilic phase and does not
require conversion to a hydrophobic phase that can exhibit salt
wash out. Thus, compared to the material disclosed in Document [2],
the disclosed atmospheric water harvesting material shows better
durability, as well as the ability to produce pure water instead of
water contaminated by salt that requires further treatment.
Accordingly, the disclosed atmospheric water harvesting material
can produce potable water (i.e., distilled water) from atmospheric
water vapor without requiring additional, complicated
post-treatment.
[0026] The inclusion of a photothermal agent in the atmospheric
water harvesting material allows the atmospheric water harvesting
material to generate heat under natural sunlight, which causes the
atmospheric water harvesting material to heat up and evaporate out
the absorbed water vapor. Thus, the disclosed atmospheric water
harvesting material can release water exclusively due to solar
energy (i.e., it is self-heating) and does not require electricity
or other heat sources that may require consumption of fossil
fuels.
[0027] In the illustrated embodiment, the deliquescent salt 110 is
calcium chloride (CaCl.sub.2). However, the deliquescent salt 110
can be one or more of the following:
TABLE-US-00001 Chemical formula IUPAC Name Chloride salt LiCl
Lithium chloride MgCl.sub.2 Magnesium chloride ZnCl.sub.2 Zinc
chloride FeCl.sub.3 Iron (III) chloride Nitrate salt
Zn(NO.sub.3).sub.2 Zinc nitrate Cu(NO.sub.3).sub.2 Copper (II)
nitrate Ni(NO.sub.3).sub.2 Nickel (II) nitrate Mn(NO.sub.3).sub.2
Manganese (II) nitrate
[0028] In the illustrated embodiment, the photothermal agent 120
comprises carbon nanotubes (CNTs). However, the photothermal agent
120 can be one or more of the following:
TABLE-US-00002 Material Composition Carbon black Carbon material
Graphite Graphene Graphene oxide (GO) Reduced Graphene oxide (rGO)
MXene (i.e., Ti.sub.3C.sub.2, Ti.sub.3CN, Ti.sub.4N.sub.3, 2-D
structured Metal carbide, metal Mo.sub.2TiC.sub.2, etc.) nitride
Black phosphorous Phosphorous Black titanium oxide Titanium oxide
Nanorods Metal (i.e., Al, Ag, Au, etc.) Nanoparticles Metal (i.e.,
Al, Ag, Au, etc.) Nanowire Metal (i.e., Al, Ag, Au, etc.) Ferrous
ferric oxide Iron oxide polypyrrole polymer dopamine polymer Metal
oxides CuO, MnO.sub.2, CuCr.sub.2O.sub.4, Fe.sub.2O.sub.3,
Fe.sub.3O.sub.4, etc.
[0029] In the illustrated embodiment, the polymeric hydrogel matrix
130 is a poly(acrylamide) (PAM) hydrogel. However, the polymeric
hydrogel matrix 130 can be comprised of one or more of the
following polymers:
TABLE-US-00003 Polymer Abbreviation Poly(acrylic acid) PAA
Poly(vinyl pyrrolidone) PVP Poly(acrylamide) PAM Poly(ethylene
oxide) PEO Poly(vinyl methyl ether) PVME Poly(vinyl alcohol) PVA
Hydroxypropylcellulose HPC Hydroxyethylcellulose HEC
Poly(2-hydroxyethyl vinyl ether) PHEVE Poly(N-isopropylacrylamide)
PNIPAM
[0030] A method of making an atmospheric water harvesting material
will now be described in connection with the flowchart of FIG. 2
and the diagrams of FIGS. 3A-3E. Although this method is described
with calcium chloride as the deliquescent salt, carbon nanotubes as
the photothermal agent, and poly(acrylamide) (PAM) hydrogel as the
hydrogel matrix, this method can employ any of the deliquescent
salts, photothermal agents, and hydrogel matrices described
above.
[0031] Initially, a polymeric hydrogel matrix comprising a
photothermal agent is formed (step 210). Specifically, the carbon
nanotubes are initially pretreated by dispersing, for example, 6.0
g of carbon nanotubes having a size of, for example, 6-9 nm.times.5
.mu.m, in a mixture of, for example, 70% nitric acid (60 mL) and
97% sulfuric acid (180 mL). The dispersion was then refluxed for 4
hours at 70.degree. C. followed by 2 hours of sonication. The
as-treated dispersion can then be filtrated and thoroughly washed
by deionized water before insertion into the hydrogel matrix. The
hydrogel matrix is formed by dissolving, for example, 1.0 gram of
acrylamide (AM) in, for example, 5 ml of the carbon nanotube
dispersion with a specified amount of carbon nanotubes added (e.g.,
2.5, 1.25, 0.5, 0.375, 0.25, 0.125, 0.05, 0.025 mg). The
acrylamide-carbon nanotube dispersion is then purged with nitrogen
to eliminate dissolved oxygen. The results of this is illustrated
in FIG. 3A, which illustrates acrylamide 310 and carbon nanotubes
320 suspended in deionized water 305.
[0032] An initiator, for example 5.00 mg of potassium
peroxydisulfate (KPS), and a hydrogelling agent, for example 0.38
mg of N,N'-Methylenebis(acrylamide) (MBAA), are added into the
acrylamide-carbon nanotube dispersion. A hydrogelling accelerator,
for example, 25 .mu.L of tetramethylethylenediamine (TEMED) is then
added and the mixture is allowed to settle overnight at a
temperature of, for example, 22.degree. C. The resulting
poly(acrylamide) (PAM)-carbon nanotube hydrogel matrix 322 is
illustrated in FIG. 3B, in which the hydrogel is labeled as element
325 and the poly(acrylamide) is labeled as element 330.
[0033] The polymeric hydrogel matrix comprising the photothermal
agent is then freeze-dried to make the hydrogel into a microporous
hydrogel (step 220). The polymeric hydrogel matrix can be
freeze-dried at, for example, -80.degree. C. The resulting
microporous hydrogel is illustrated in FIG. 3C.
[0034] The freeze-dried polymeric hydrogel matrix comprising the
photothermal agent is then immersed in a solution containing
deliquescent salt to form a polymeric hydrogel matrix comprising
the photothermal agent and the deliquescent salt (step 230). For
example, the freeze-dried hydrogel can be immersed in, for example,
10 ml of a calcium chloride solution for, for example, 24 hours.
The drying can occur under ambient conditions, for example, 60%
relative humidity and 22.degree. C. Experiments were performed
using calcium chloride concentrations of 0.1, 0.2, 0.3, 0.4, 0.5,
and 0.6 g/mL for 24 hours under ambient condition, for example, 60%
relative humidity and 22.degree. C. Based on experimentation, the
highest loading of calcium chloride and the highest water vapor
sorption capacity occurred with a calcium chloride concentration of
0.4 g/mL. The resulting hydrogel is illustrated in FIG. 3D, in
which the calcium chloride is not visible because it is suspended
in the solution.
[0035] Finally, the polymeric hydrogel matrix comprising the
photothermal agent and the deliquescent salt is dried (step 240).
For example, the poly(acrylamide)-carbon nanotube-calcium chloride
hydrogel can be dried at 80.degree. C. in a blast oven for three
days. The resulting hydrogel, which is referred to herein as an
atmospheric water harvesting material, is illustrated in FIG. 3E,
in which the calcium chloride is labeled as element 335.
[0036] The disclosed atmospheric water harvesting material can be
employed in any type of water harvesting device, one example of
which is illustrated in FIG. 4. The atmospheric water harvesting
device 400 includes a condensation chamber 405 having a
light-admitting upper surface 410 and a water outlet 415. The
atmospheric water harvesting device 400 also includes an
atmospheric water harvesting chamber 420, arranged below the
condensation chamber 405, containing an atmospheric water
harvesting material 425 and having a bottom surface 430 with an
opening 435 to accept ambient air 440 and an upper surface 445
having an opening 450 to allow atmospheric water 455 captured from
the ambient air 440 by the atmospheric water harvesting material
425 to pass into the condensation chamber 405 due to heat generated
from solar energy 460 impinging on the light-admitting upper
surface 410 of the condensation chamber 405. As illustrated, the
condensation chamber 405 includes a sloped water collector 465 for
moving collected water to the water outlet 415. Further, the
light-admitting surface 410 of the condensation chamber 405 should
be made of a material that has minimal effect on the incoming solar
energy 460, such as, for example, quartz.
[0037] The atmospheric water harvesting chamber 420 comprises a
cylinder 470 having an outer surface on which the atmospheric water
harvesting material 425 is arranged. The atmospheric water
harvesting chamber 420 also includes a frame 475 surrounding the
cylinder 470. The cylinder 470 includes a spindle 480 to which a
motor (not illustrated) is attached. It should be recognized that
the atmospheric water harvesting device 400 can include elements in
addition to those that are illustrated, such as bearings on the
spindle, washers, bolts, nuts, etc.
[0038] The cylinder 470 can be comprised of a material, such as
acrylic. The interior of the cylinder 470 can be empty or can be
filled. The side surfaces of the cylinder (i.e., the surface
visible in FIG. 4) can include holes. Thus, when there is solar
energy 460 impinging upon the cylinder 470, the upper part of the
cylinder 470 will be warmer than the lower part. Due to heating of
the atmospheric water harvesting material 425 with the aid of the
photothermal agent, water vapor is released from the cylinder 470
into the condensation chamber 405. The water vapor will attach to
the upper surface 410 and/or the side walls of the condensation
chamber and water droplets will fall onto sloped water collector
465 and exit the condensation chamber 405 via the water outlet 415.
At the same time, the atmospheric water harvesting material 425 in
the lower part of the cylinder 470 will not be heated enough to
release water vapor, and thus will continue to absorb water vapor
from the atmosphere. In order to assist with the condensation of
the water vapor, the side walls of the condensation chamber 405 can
be made of metal, such as copper.
[0039] Thus, as will be appreciated, the motor spins the cylinder
470 so that the atmospheric water harvesting material 425 in the
upper part, from which water vapor has been released, is rotated to
face the bottom surface 430 of the atmospheric water harvesting
chamber 420 so that it can absorb water vapor from the ambient air
440 and the atmospheric water harvesting material 425 in the lower
part, which has absorbed water vapor from the ambient air 440, is
rotated so that it faces the opening 450 in the atmospheric water
harvesting chamber 420 so that it can be exposed to the solar
energy 460 and heated to release the absorbed water vapor into the
condensation chamber 405.
[0040] By attached a motor to the cylinder 470, the atmospheric
water harvesting device 400 can be continuously operated so that it
can continuously absorb water vapor from the ambient air 440 and
discharge water vapor into the condensation chamber 405. The
cylinder 470 can be rotated at a speed of, for example, 00.5, 0.75,
1.5, or 4 revolutions per hour. This is particularly advantageous
because water vapor can be continuously absorbed and desorbed
without further human intervention, thus making it practical for a
number of implementations outside of a pure industrial
implementation, such as in residential use.
[0041] A method for generating water from water vapor using the
atmospheric water harvesting device 400 illustrated in FIG. 4 will
now be described in connection with the flow diagram of FIG. 5.
Initially, water vapor is absorbed by the atmospheric water
harvesting material 425 arranged on an outer surface of a cylinder
470 (step 510). The atmospheric water harvesting material 425
comprises a deliquescent salt 110, a photothermal agent 120, and a
polymeric hydrogel matrix 130 containing the deliquescent salt 110
and photothermal agent 120. The cylinder 470 is rotated so that a
portion of the atmospheric water harvesting material 425 that has
absorbed the water vapor is facing a condensation chamber 405,
which is arranged above the cylinder 470 and has a light-admitting
upper surface 410 (step 520). The portion of the atmospheric water
harvesting material 425 facing the condensation chamber 405 is
exposed to solar energy passing through the light-admitting upper
surface 410 (step 530). The solar energy causes the water vapor to
be released from the portion of the atmospheric water harvesting
material 425 facing the condensation chamber 405 into the
condensation chamber 405 (step 540). The released water vapor is
condensed into water in the condensation chamber 405 (step 550).
The condensed water is pure water or the water vapor is released
exclusively due to the solar energy.
[0042] When the portion of the atmospheric water harvesting
material 425 is facing a condensation chamber 405 a second portion
of the atmospheric water harvesting material 425 is not directly
exposed to the solar energy and the second portion of the
atmospheric water harvesting material absorbs water vapor.
Accordingly, the atmospheric water harvesting device 400 can be
continuously operated so that it can continuously absorb water
vapor from the ambient air 440 and discharge water vapor into the
condensation chamber 405. Further, the atmospheric water harvesting
material does not change phase from hydrophilic to hydrophobic
while releasing the water vapor.
[0043] A number of experiments were conducted on the atmospheric
water harvesting material comprising the poly(acrylamide)-carbon
nanotube-calcium chloride hydrogel (hereinafter "PAM-CNT-CaCl.sub.2
hydrogel"), as well as a poly(acrylamide)-carbon nanotube hydrogel
(hereinafter "PAM-CNT hydrogel"), poly(acrylamide)-calcium chloride
hydrogel (hereinafter "PAM-CaCl.sub.2 hydrogel"), and a
poly(acrylamide) hydrogel (hereinafter "PAM hydrogel").
[0044] With regard to composition of the atmospheric water
harvesting material, experiments were conducted with different
concentrations of carbon nanotubes (i.e., with 2.5, 1.25, 0.5,
0.375, 0.25, 0.125, 0.05, and 0.025 mg) and with different
concentrations of calcium chloride (i.e., 0.1, 0.2, 0.3, 0.4, 0.5,
and 0.6 g/mL). The experiments demonstrated that the structure
rigidity of the hydrogel is strongly dependent on the amount of the
polymer in the hydrogel, which can be modulated by changing the
amount of acrylamide monomer in the synthesis process. The amount
of the acrylamide monomer precursor was optimized to be 20 wt %
based on the following facts and the cost consideration. First, the
acrylamide monomer of 20 wt % is the threshold at which the PAM
hydrogel exhibits a standalone solid form and has a sufficient
structural stability. If the acrylamide monomer concentration is
lower than 20%, the product is sticky and thick liquid-like.
Second, increasing acrylamide monomer concentration to above 20 wt
% does not lead to any noticeable benefit of enhanced water
sorption and release.
[0045] Because the atmospheric water harvesting material is
designed to release water by being exposed to solar energy, the
light absorbance of the PAM hydrogel without carbon nanotubes and
with carbon nanotubes were evaluated. The PAM hydrogel without
carbon nanotubes strongly absorbs near-infrared light at wavelength
above 1400 nm, which is due to the light absorption by the water
molecules inside the hydrogel. Adding the carbon nanotubes
increased the light absorption from 240 to 1400 nm. Experiments
demonstrated that a small amount of carbon nanotubes in the
hydrogel (i.e., at a ppm level) leads to a large increase in light
absorbance. Experiments demonstrated that 99% of the incident light
was absorbed when the carbon nanotube loading amount was only 0.083
wt .Salinity.. In one embodiment, the carbon nanotube loading in
the PAM hydrogel can be set to be 0.42.Salinity., where almost 100%
of the incident light will be absorbed.
[0046] The water vapor sorption behavior of the calcium chloride
was evaluated both by itself and when incorporated into the PAM-CNT
hydrogel. The experiments demonstrated that the white solid salt
was fully liquidized to a colorless transparent solution after the
calcium chloride salt was exposed in 60% relative humidity
conditions and that after water sorption, the PAM-CNT-CaCl.sub.2
hydrogel significantly expanded but still in a solid form like a
soft rubber.
[0047] The water sorption behaviors of the PAM-CNT-CaCl.sub.2
hydrogel was investigated and compared under dynamic and static
humidity scenarios. A constant temperature of 25.degree. C. was set
and kept throughout the water sorption process for all samples. A
temperature of 25.degree. C. was selected because it is a typical
in arid areas at night when water vapor sorption takes place. All
samples for water sorption assessment were first dried prior
testing. In the dynamic scenario, the hydrogels were kept in a flow
with a step-wise increasing humidity for certain period of time and
in the static scenario the relative humidity was unchanged
throughout the water sorption process.
[0048] The dynamic relative humidity test was first applied to PAM
hydrogels and PAM-CNT hydrogels. Both exhibited a similar water
sorption characteristic, with the water vapor sorption slightly
higher for the dried PAM hydrogel than for the dried PAM-CNT
hydrogel in the low humidity range (<40%) and no obvious
difference in high relative humidity range. However, there was no
significant difference in high humidity range. The static relative
humidity test indicated that the PAM hydrogel and the PAM-CNT
hydrogel both gradually approached water uptake value near to its
saturation capacity within 400 min, and the final weight change due
to water sorption are 32 wt % and 38 wt % water in 80% relative
humidity, respectively.
[0049] Further relative humidity experiments were performed using a
PAM-CaCl.sub.2 hydrogel and a PAM-CNT-CaCl.sub.2 hydrogel. Both of
these exhibited a similar relative humidity-dependent water vapor
sorption trend in dynamic water sorption measurement. Specifically,
for both, the water sorption started at a very low humidity of 5%,
and then gradually increased with the increase of humidity, with
much higher water sorption amounts than the hydrogels without
calcium chloride loading under otherwise the same condition. With a
relative humidity of 10, 35, 60 and 80%, the water sorption amounts
at the end of the experiment were respectively 6, 72, 116, 203% for
the PAM-CaCl.sub.2 hydrogel, and were respectively 5, 69, 110, 173%
for the PAM-CNT-CaCl.sub.2 hydrogel. The amount of water sorbed by
the PAM-CaCl.sub.2 hydrogel and the PAM-CNT-CaCl.sub.2 hydrogel at
80% humidity were 6.3 and 4.5 times the weight of the respective
hydrogels before loading with calcium chloride, which clearly
demonstrates the effectiveness of calcium chloride in water
sorption.
[0050] The water sorption property of the hydrogels with calcium
chloride loading is very similar to that of pure calcium chloride
crystal, with only slight difference in specific sorption amount,
indicating that calcium chloride is primarily responsible for the
water sorption of PAM-CNT-CaCl.sub.2 hydrogel. Because the phase
diagram of water-calcium chloride has been well studied and can be
easily found in literature, it is believed that this can be used to
explain the water sorption behavior of the disclosed
PAM-CNT-CaCl.sub.2 hydrogel. The calcium chloride contains two
primary stages in connection with the water sorption process. In
the first stage, anhydrous calcium chloride crystal captures water
molecules through hydration reaction and forms hydrates. After the
calcium chloride sorbs enough water and forms CaCl.sub.2.6H.sub.2O,
it is then dissolved in the sorbed water as more water is sorbed.
The vapor pressure of a saturated calcium chloride aqueous solution
at 25.degree. C. is 0.9 kPa, equivalent to a humidity of 26%. In
other words, the water sorption by calcium chloride at a relative
humidity less than 26% is attributed to its increase of the
hydration water, and that occurring at a relative humidity greater
than 26% leads to a dilution of the calcium chloride aqueous
solution, i.e., deliquescence. It should be noted that the value
26% relative humidity value as a critical point can be varied with
the ambient temperature.
[0051] Theoretically, the water sorption amount in the first stage
for pure anhydrous calcium chloride is 97% ending as
CaCl.sub.2.6H.sub.2O. However, the last two water crystals are
difficult to remove at a temperature lower than 160.degree. C. In
the experiments, the samples were pre-dried at 80.degree. C.
because this is a reasonable temperature that can be achieved by
photothermal heating under regular and non-concentrated sunlight.
Consequently, after drying process at 80.degree. C., the calcium
chloride in the disclosed PAM-CNT-CaCl.sub.2 hydrogel was mainly a
mixture of CaCl.sub.2.4H.sub.2O and CaCl.sub.2.2H.sub.2O, which was
confirmed by x-ray diffraction analysis and phase diagram. Because,
in the experiments, 4 grams of calcium chloride was loaded into 1
gram of PAM-CNT hydrogel (4/5 of overall weight), the loading ratio
of calcium chloride was 80%. The overall weight change contributed
by hydration reaction should be insignificant during water sorption
process, i.e., less than 30%, which is small portion of the final
water sorption amount. This analysis indicates that most of the
water sorption for the hydrogel material is contributed by
deliquesce of the calcium chloride aqueous solution. The amount of
water sorbed during deliquescent stage is highly dependent on
humidity of the surroundings. Therefore, the sorption continuously
increases with the increase of humidity, which gives calcium
chloride a broad sorption window.
[0052] Derivative weight change based on the results obtained from
the static relative humidity test was employed to investigate the
water sorption kinetics of calcium chloride, PAM-CaCl.sub.2
hydrogel, and PAM-CNT-CaCl.sub.2 hydrogel. All three samples
exhibited a small sorption rate at a relative humidity of 10% in
the first 200 mins, and the sorption rate quickly decreases to near
zero after 200 min, implying a quick but small water uptake at a
relative humidity of 10%. When the relative humidity was less than
10%, PAM-CaCl.sub.2 hydrogel and a PAM-CNT-CaCl.sub.2 hydrogel
share similar sorption trends to that of calcium chloride, but with
much higher sorption rates, which might be due to the porous
structure of the hydrogels. During the period of the static
relative humidity test (i.e., 1,000 min), the PAM-CaCl.sub.2
hydrogel and the PAM-CNT-CaCl.sub.2 hydrogel reached their
saturation states at the definite relative humidity of 10, 35 and
60%, indicated by their sorption rate at the end of the test being
quite close to zero. However, at a relative humidity of 35, 60 and
80%, pristine calcium chloride salt failed to reach its saturation
state within 1,000 min, which might be attributed to its liquid
characteristic after deliquescence. Presumably, water sorption only
occurs and is controlled by boundary layer at the air on the
calcium chloride solution interface.
[0053] By comparing the results of three batches of the samples all
together, the following conclusions can be made: (1) the water
sorption performance of PAM-CaCl.sub.2 hydrogel and
PAM-CNT-CaCl.sub.2 hydrogel are mainly contributed by calcium
chloride; (2) the hydrogel substrate does not suppress the overall
water sorption performance; and (3) the hydrogel platform not only
provides physical stability of the atmospheric water harvesting
device but also enhances the water sorption kinetics, leading to a
faster vapor sorption rate than pristine calcium chloride salt.
[0054] In an atmospheric water harvesting device, water is released
under the help of sunlight via photothermal effect to increase the
temperature of the sorbent. Accordingly, the water release
performance of the hydrogels was investigated using a simulated
sunlight source in lab. PAM-CaCl.sub.2 hydrogel and
PAM-CNT-CaCl.sub.2 hydrogel samples were first stored at room
temperature in air with a relative humidity of 60% for 36 hours to
ensure a full water sorption. The water content of these two
water-saturated hydrogels was 53.7% for the PAM-CaCl.sub.2 hydrogel
and 54.5% for the PAM-CNT-CaCl.sub.2 hydrogel. 5.0 g of the
water-saturated hydrogels were exposed under a simulated sunlight
with an intensity of 1 kW/m.sup.2 for water releasing. The surface
temperature of the PAM-CaCl.sub.2 hydrogel only increased to
35.degree. C. under the light illumination for 50 mins, and then
slowly increased to approximately 42.degree. C. after 275 mins. The
temperature increase is mainly attributed to the light sorption by
water in this case, as discussed above. The surface temperature of
the hydrogel is determined by its energy balance. In the initial
stage of 50 mins light illumination, there was a relatively fast
water release, which takes away a large amount of heat and thus
leads to a low temperature of the hydrogel. The water evaporation
rate then gradually decreases because the salt concentration in the
residual water inside the hydrogel keeps increasing during this
process due to the loss of water. As a result, the heat consumption
by the water evaporation decreases, moving the balance to a higher
equilibrium temperature. At the end of the experiment, the
temperature of the PAM-CaCl.sub.2 hydrogel reached 42.degree. C.
and 25% of the total weight of the hydrogel was lost to the
released water. This suggests that only less than half of the water
inside the PAM-CaCl.sub.2 hydrogel was able to be released.
[0055] Regarding the disclosed PAM-CNT-CaCl.sub.2 hydrogel, its
surface temperature jumped to 50.degree. C. initially at 25 mins,
which is 15.degree. C. higher than that of the PAM-CaCl.sub.2
hydrogel. This comparison convincingly demonstrates the great
photothermal effect of the carbon nanotubes in the hydrogel. It
should be noted that, due to its higher temperature, the
PAM-CNT-CaCl.sub.2 hydrogel had a much higher evaporation rate than
the PAM-CaCl.sub.2 hydrogel. The water evaporation rate then
gradually decreased along with the increase of the surface
temperature. The temperature recorded in the end was 75.degree. C.
and the weight change % was .about.53% at the end of 270 min for
the PAM-CNT-CaCl.sub.2 hydrogel, indicating almost all (>97%)
sorbed water inside the PAM-CNT-CaCl.sub.2 hydrogel was released.
With most of the available water being released from the hydrogel,
the heat loss via convection, radiation, and conduction are the
major energy consumption to balance the constant solar input, and
therefore the hydrogel temperature profile exhibits a plateau in
the last stage from 180 min to 270 min.
[0056] The temperature and weight variation time course of the
PAM-CNT-CaCl.sub.2 hydrogel irradiated with simulated sunlight with
varied light intensity was also evaluated. The temperature observed
at 270 min under 0.6, 0.8 and 1.0 kW/m2 sunlight illumination was
55, 66 and 75.degree. C., respectively. The corresponding weight
change of the samples was 44, 49 and 53%, respectively,
corresponding to 80, 89 and 97% release of the sorbed water. This
demonstrates that most of the sorbed water can still be efficiently
released under weakened sunlight. These photothermal-assisted water
release experiments indicate that the disclosed PAM-CNT-CaCl.sub.2
hydrogel has a great potential as an efficient atmospheric water
harvesting device working within a wide range of relative humidity
and sunlight conditions.
[0057] A cycling test was performed to evaluate the stability of
the disclosed PAM-CNT-CaCl.sub.2 hydrogel. Water sorption was
conducted by letting 2.5 g of the dried hydrogel sit in an open air
with a relative humidity of 60% at 22.degree. C. for 36 hours in
the dark, followed by one sun irradiation for 5 hours. The whole
cycle was repeated for 10 times. This experiment showed that the
water sorption and release performances of the PAM-CNT-CaCl.sub.2
hydrogel exhibited no degradation after 10 cycles, indicating its
long-term operational stability.
[0058] In conclusion, the disclosed PAM-CNT-CaCl.sub.2 hydrogel
possesses outstanding water sorption capability, which is similar
to calcium chloride, and its flexible solid form makes it an
effective atmospheric water harvesting device. Due to the fact that
the working relative humidity range of the disclosed
PAM-CNT-CaCl.sub.2 hydrogel covers most of arid deserts, almost all
islands, and inland remote regions, the atmospheric water
harvesting device based on the hydrogel are low cost, versatile,
deployable, and thus suitable for delivering much needed fresh
water therein. Additionally, the disclosed PAM-CNT-CaCl.sub.2
hydrogel only requires solar energy to release the captured water
vapor and the released water is pure water that does not contain
hygroscopic or other impurities.
[0059] The disclosed embodiments provide an atmospheric water
harvesting material, method of producing an atmospheric water
harvesting material, and an atmospheric water harvesting device. It
should be understood that this description is not intended to limit
the invention. On the contrary, the exemplary embodiments are
intended to cover alternatives, modifications and equivalents,
which are included in the spirit and scope of the invention as
defined by the appended claims. Further, in the detailed
description of the exemplary embodiments, numerous specific details
are set forth in order to provide a comprehensive understanding of
the claimed invention. However, one skilled in the art would
understand that various embodiments may be practiced without such
specific details.
[0060] Although the features and elements of the present exemplary
embodiments are described in the embodiments in particular
combinations, each feature or element can be used alone without the
other features and elements of the embodiments or in various
combinations with or without other features and elements disclosed
herein.
[0061] This written description uses examples of the subject matter
disclosed to enable any person skilled in the art to practice the
same, including making and using any devices or systems and
performing any incorporated methods. The patentable scope of the
subject matter is defined by the claims, and may include other
examples that occur to those skilled in the art. Such other
examples are intended to be within the scope of the claims.
CITED DOCUMENTS
[0062] [1] Yang et al., Development of Solid Super Desiccants Based
on a Polymeric Superabsorbent Hydrogel Composite, RSC Adv., 2015,5,
59583-59590.
[0063] [2] Cui et al., Fast Superabsorbent Thermo-Responsive
Hydrogel Composite Desiccant with Low Regeneration Temperature
(2018).
* * * * *