U.S. patent application number 10/098928 was filed with the patent office on 2003-06-12 for heat and moisture exchange device.
This patent application is currently assigned to Dais Analytic Corporation. Invention is credited to Ehrenberg, Scott G., Serpico, Joseph M..
Application Number | 20030106680 10/098928 |
Document ID | / |
Family ID | 26957431 |
Filed Date | 2003-06-12 |
United States Patent
Application |
20030106680 |
Kind Code |
A1 |
Serpico, Joseph M. ; et
al. |
June 12, 2003 |
Heat and moisture exchange device
Abstract
A unitary humidity exchange cell (HUX) is disclosed that
includes at least one composite membrane, disposed between at least
one first chamber for flow of the first fluid therethrough and at
least one second chamber for flow of the second fluid therethrough.
The composite membrane include an at least partially sulfonated
humidity-conducting polymer comprising residues derived from at
least one arylvinyl monomer; and a reinforcing substrate bonded
thereto. The product finds utility in a variety of physical and
chemical processes and products whereby moisture or other highly
polar liquid or gas transfer, exchange removal or delivery is
important. A notable application is the Membrane Energy Recovery
Ventilator (MERV) in which both heat and moisture is transferred
between two air streams, one intake and one exhaust, from an
air-conditioned building.
Inventors: |
Serpico, Joseph M.; (Palm
Harbor, FL) ; Ehrenberg, Scott G.; (New Port Richey,
FL) |
Correspondence
Address: |
HESLIN ROTHENBERG FARLEY & MESITI PC
5 COLUMBIA CIRCLE
ALBANY
NY
12203
US
|
Assignee: |
Dais Analytic Corporation
11552 Prosperous Drive
Odessa
FL
33556-3452
|
Family ID: |
26957431 |
Appl. No.: |
10/098928 |
Filed: |
March 13, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60275459 |
Mar 13, 2001 |
|
|
|
60327746 |
Oct 9, 2001 |
|
|
|
Current U.S.
Class: |
165/166 ;
165/905 |
Current CPC
Class: |
Y02P 20/124 20151101;
F28F 21/065 20130101; B01D 71/28 20130101; B01D 71/80 20130101;
B01D 53/268 20130101; B01D 69/10 20130101; B01D 63/082 20130101;
B01D 71/82 20130101; F24F 3/147 20130101; F24F 2003/1435 20130101;
B01D 2325/48 20130101; Y02P 20/10 20151101; F28D 21/0015
20130101 |
Class at
Publication: |
165/166 ;
165/905 |
International
Class: |
F28F 003/00 |
Claims
What is claimed is:
1. A cell for transferring heat and moisture between a first fluid
and a second fluid, said cell comprising: at least one composite
membrane, disposed between at least one first chamber for flow of
the first fluid therethrough and at least one second chamber for
flow of the second fluid therethrough; whereby heat and moisture is
transferable between the first fluid and second fluid via the
composite membrane.
2. A cell according to claim 1, wherein said composite membrane
comprises: an at least partially sulfonated humidity-conducting
polymer comprising residues derived from at least one arylvinyl
monomer; and a reinforcing substrate bonded thereto.
3. A cell according to claim 2, additionally comprising at least
one spacer disposed on a surface of the composite membrane
4. A cell according to claim 3, wherein said at least one spacer
comprises a dimension normal to the surface of the composite
membrane corresponding to a height of the first chamber.
5. A cell according to claim 3, wherein a longitudinal axis of the
at least one spacer is oriented parallel to a direction of flow of
the first fluid in the first chamber.
6. A cell according to claim 5, wherein the direction of flow of
the first fluid in the first chamber is orthogonal to a direction
of flow of the second fluid in the second chamber.
7. A cell according to claim 5, wherein the direction of flow of
the first fluid in the first chamber is opposite to a direction of
flow of the second fluid in the second chamber.
8. A cell according to claim 3, wherein the at least one spacer
comprises a plurality of synthetic polymer ribs.
9. A cell according to claim 3, wherein the at least one spacer
comprises an adhesive composition.
10. A cell according to claim 3, wherein the at least one spacer
comprises a corrugated sheet.
11. A cell according to claim 2, wherein said at least one
composite membrane comprises a plurality of composite membranes,
and said at least one first chamber and said at least one second
chamber comprises a plurality of alternating first chambers and
second chambers, each separated by a composite membrane.
12. A cell according to claim 2, wherein said reinforcing substrate
comprises a nonwoven fabric.
13. A cell according to claim 2, wherein said reinforcing substrate
comprises a microporous film.
14. A cell according to claim 2, wherein said reinforcing substrate
comprises at least one synthetic fiber.
15. A cell according to claim 14, wherein said at least one
synthetic fiber comprises at least one polyolefin.
16. A cell according to claim 2, wherein the humidity-conducting
polymer additionally comprises an additive selected from the group
of antioxidants, biocides, flame retardants, uv stabilizers,
hydrophilic plasticizers, and mixtures thereof.
17. A cell according to claim 2, wherein the humidity-conducting
polymer comprises at least one antioxidant, at least one biocide,
and at least one flame retardant.
18. A cell according to claim 2, wherein the humidity-conducting
polymer is crosslinked using a peroxide initiator and an
organometallic enolate coupling agent.
19. A cell according to claim 18, wherein the peroxide initiator is
1,1-di-(tert-butylperoxy)-3,3,5-trimethylcyclohexane and the
organometallic enolate coupling agent is aluminum
acetoacetonate.
20. A cell according to claim 18, wherein the peroxide initiator is
2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional
applications 60/275,459, filed Mar. 13, 2001, and 60/327,746, filed
Oct. 9, 2001.
FIELD OF THE INVENTION
[0002] The invention relates to devices and apparatus for transfer
of heat and water between fluids, via a composite polymer
membrane.
BACKGROUND OF THE INVENTION
[0003] A unitary humidity exchange cell (or HUX), as the name
implies, is an element of a device that is capable of transferring
water or other highly polar liquid or gas from one side of the cell
to the other by action of a difference in some quantity or gradient
across said cell. A key operational characteristic of the HUX cell
is that a difference of some intensive or extensive property of the
system (relative to the surrounding) leads to a gradient change of
said property to effect mass transfer of water or some other highly
polar liquid or gas from one side of the membrane to the other with
or without an accompanying flow of electrons, protons, ions or
molecules other than said water or other highly polar liquid or
gas. It is under the influence of this property that exchange in
liquid water or some other highly polar liquid or gas occurs across
the permaselective membrane. This transfer of water or some other
highly polar liquid or gas may or may not be accompanied by
evaporation of said water or other highly polar liquid or gas into
(or from) the stream by the absorption of heat or adiabatically or
by some other thermodynamic means; for example the condensation or
evaporation of liquid water or some other highly polar liquid or
gas or the simple diffusion of water or some other highly polar
liquid or gas into a pure liquid stream. A finite gradient across
the membrane must exist in some quantity; examples are vapor
pressure, osmotic or hydrostatic pressure, chemical,
thermochemical, electrochemical, magnetochemical potential, as well
as thermal (temperature or heat content), electric,
electromagnetic, thermoelectric, or electrothermal potential
difference. There must be at least two streams, one supplied to
each surface of said membrane by some means either as a liquid or
vapor flow each of which differs in at least one identical property
of the system. The system attempts to reach a thermodynamic
equilibrium by transporting water or some other highly polar liquid
or gas from one stream to the other. The orientation of the streams
to one another is considered arbitrary for the invention; these may
be counter flow, coflow, crossflow, mixed flow or any other
geometric arrangement of one or more streams. Water or some other
highly polar liquid or gas transport (e.g. hydrodynamic,
electrohydrodynamic, magnetohydrodynamic, diffusion, migration, or
convection) occurs until the imposed gradient can no longer meet
the physicochemical constraints of the system required to sustain
the motion. In many cases, the exchange of water or some other
highly polar liquid or gas between the streams is slow, but this
may be due to some other limiting factor, such as, boundary layer
effects, concentration polarization, hydrostatic pressure lag or
gravity, surface tension effects, and convective or frictional
effects. However, once these engineering design or system effects
are minimized, inevitably, the exchange or transport of water or
some other highly polar liquid or gas is rate-limiting if the
permeability of the membrane to water or some other highly polar
liquid or gas is poor. Hence, an important object of the invention
is that hydrophilic polymer membrane has high permeability to water
or some other highly polar liquid or gas; more than necessary for
most applications. The hydrophilic polymer membrane (or
formulation) must be mechanically supported and there must be means
to supply the two streams to said surfaces. A second object of the
invention is that the three sub-elements be fabricated as one unit
by conventional means at low cost. This requires that the
hydrophilic polymer wet the support, achieve intimate contact and
demonstrate exceptional adhesion to it. Therefore, a third object
of the invention is that the support be a polyolefin or blend
thereof such that one component of said hydrophilic polymer is
similar in chemical structure to one component of the support.
[0004] HUX cell design is general in that water (liquid or vapor)
or other highly polar material (liquid or vapor) can be transferred
between any two fluids. Examples of applications are
per-vaporation, humidification and dehumidification of fuel cell
streams in stacks and devices, drying gases at pressure, tertiary
oil recovery, process control for chemical manufacture of chemicals
for which water is a reactant, isolation of minerals from mining
fluids, industrial separation of oil-water emulsions,
microfiltration and ultrafiltration of colloidal suspensions and
biological or organic macromolecules for purification, maintaining
water content of methanol in direct methanol fuel cells, reverse
osmosis for isolation of fresh water from brine, electrolysis
cells, dialysis, electro-dialysis, piezo-dialysis, electro-osmosis
and chloro-alkali cells.
SUMMARY OF THE INVENTION
[0005] The present invention relates to cells for transferring heat
and moisture between a first fluid and a second fluid. Such a cell
comprises at least one composite membrane, disposed between at
least one first chamber for flow of the first fluid therethrough
and at least one second chamber for flow of the second fluid
therethrough; whereby heat and moisture is transferable between the
first fluid and second fluid via the composite membrane. The
composite membrane may comprise an at least partially sulfonated
humidity-conducting polymer comprising residues derived from at
least one arylvinyl monomer; and a reinforcing substrate bonded
thereto. The cell may additionally include at least one spacer
disposed on a surface of the composite membrane. The spacer(s) may
have a dimension normal to the surface of the composite membrane
corresponding to a height of the first chamber; the longitudinal
axis of the at least one spacer may be oriented parallel to a
direction of flow of the first fluid in the first chamber. The
direction of flow of the first fluid in the first chamber may be
orthogonal to a direction of flow of the second fluid in the second
chamber, or it may be opposite to it. In some embodiments, a
plurality of synthetic polymer ribs are used as spacers; in others,
the spacer is merely a bead of an adhesive composition; in still
others, the spacer is a corrugated sheet composed of paper or
plastic. The invention also relates to cell containing a plurality
of composite membranes, and a plurality of alternating first
chambers and second chambers, each separated by a composite
membrane. The reinforcing substrate of the composite membrane may
be a nonwoven fabric, composed of synthetic fibers, particularly
one or more polyolefins. The humidity-conducting polymer of the
composite membrane may include an additive selected from the group
of antioxidants, biocides, flame retardants, uv stabilizers,
hydrophilic plasticizers, and mixtures thereof, particularly,
antioxidant(s), biocide(s), and flame retardant(s). The
humidity-conducting polymer may be crosslinked using a peroxide
initiator and an organometallic enolate coupling agent,
particularly, 1,1-di-(tert-butylperoxy)-3,3,5-trimethylcyclohexane
and aluminum acetoacetonate, or
2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 and aluminum
acetoacetonate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 shows a composite membrane for use in a humidity
exchange cell according to present invention.
[0007] FIG. 2 is a partially exploded view of a humidity exchange
cell according to the present invention.
[0008] FIG. 3 is a graph showing high heat and water transfer using
a humidity exchange cell according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0009] FIG. 1 shows a single composite membrane 10 for use in a
humidity exchange cell according to the present invention. The
membrane includes a continuous film of a humidity-conducting
polymer 12 bonded to a reinforcing substrate 14 in the form of a
cross-laid mesh or netting. Reinforcing substrate 14 strengthens
the membrane so it can be handled, and allows the membrane to
withstand pressure differentials without deflecting. As shown in
FIG. 1, there are spacers, ribs or ridges 16 adhered to the surface
of membrane 10 and running in one direction. The other side of the
membrane is a smooth surface of humidity-conducting polymer 12. The
height of spacer 16 sets the layer-to-layer spacing. Air channels
in the humidity exchange cell are formed by spacers 16 when they
rest against the smooth surface of the membrane that is placed on
top of it.
[0010] The humidity-conducting polymer may be an at least partially
sulfonated copolymer comprising residues derived from at least one
arylvinyl monomer. Accordingly, the polymer includes repeating
units of formula III, derived from an arylvinyl monomer, in
addition to one or both of the repeating units of formulas I and
II, derived from olefin monomers. 1
[0011] wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4 are chosen
independently from the group consisting of hydrogen, nitrile,
phenyl and lower alkyl; R.sup.5 is hydrogen, chlorine or lower
alkyl; R.sup.6 is hydrogen or methyl; R.sup.7 is --COOH,
--SO.sub.3H, --P(O)(OR.sup.8)OH, --R.sup.9--COOH,
--R.sup.9--SO.sub.3H, --R.sup.9--P(O)(OR.sup.8)OH; R.sup.8 is
hydrogen or lower alkyl, R.sup.9 is lower alkylene; Ar is phenyl;
and m, n, p, and q are zero or integers from 50 to 10,000.
[0012] The humidity-conducting polymer may be a block, graft or
statistical copolymer derived from arylvinyl monomers. Some
suitable polymers are described in U.S. Pat. Nos. 5,468,574;
5,679,482; and 6,110,616; the disclosure of each of these is
incorporated by reference herein in its entirety. Block and graft
copolymers contain relatively long segments made up of a
homopolymer derived from one of the comonomers. In contrast, the
term "statistical" is used herein to refer to polymers that do not
contain long segments made up of homopolymer, and to distinguish
these from block and graft copolymers. Preferably, the statistical
polymers do not contain more than 15 percent of the total amount of
arylvinyl monomer in blocks of arylvinyl monomer of more than 3
units. More preferably, the statistical polymers are not
characterized by a high degree of either isotacticity or
syndiotacticity. This means that in the carbon-13 NMR spectrum of
the statistical polymer the peak areas corresponding to the main
chain methylene and methine carbons representing either meso diad
sequences or racemic diad sequences should not exceed 75 percent of
the total peak area of the main chain methylene and methine
carbons.
[0013] A statistical copolymer is a well-defined term of art (see
G. Odian, Principles of Polymerization, 1991), and the use of the
term herein is consistent with the commonly understood usage.
Statistical copolymers are derived from the simultaneous
polymerization of two monomers and have a distribution of the two
monomer units along the copolymer chain that follows Bernoullian
(zero-order Markov), or first or second order Markov statistics.
The polymerization may be initiated by free radical, anionic,
cationic or coordinatively unsaturated (e.g., Ziegler-Natta
catalysts) species. According to Ring et al., (Pure Appl. Chem.,
57, 1427, 1985), statistical copolymers are the result of
elementary processes leading to the formation of a statistical
sequence of monomeric units (that) do not necessarily proceed with
equal probability. These processes can lead to various types of
sequence distributions comprising those in which the arrangement of
monomeric units tends toward alternation, tends toward clustering
of like units, or exhibits no ordering tendency at all. Bernoullian
statistics is essentially the statistics of coin tossing;
copolymers formed via Bernoullian processes have the two monomers
distributed randomly and are referred to as random polymers. For
example, it is possible in a free radical copolymerization for the
active end, in the case of one embodiment, a styryl or butadienyl
radical, to have essentially no selectivity for styrene vs.
butadiene. If so, the statistics will be Bernoullian, and the
copolymer obtained will be random. More often than not, there will
be a tendency for the propagating chain end to have some
selectivity for one monomer or the other. In rare cases block
copolymers can be derived from the simultaneous copolymerization of
two monomers when the preference of the propagating chain ends for
adding the opposite monomers is very low. The resulting polymer
would be categorized as a block copolymer for the purposes of the
present invention.
[0014] Statistical copolymers generally display a single glass
transition temperature. Block and graft copolymers typically
display multiple glass transitions, due to the presence of multiple
phases. Statistical copolymers are, therefore, distinguishable from
block and graft copolymers on this basis. The single glass
transition temperature reflects homogeneity at the molecular level.
An additional consequence of this homogeneity is that statistical
copolymers, such as those of styrene and butadiene, when viewed by
electron microscopy, display a single phase morphology with no
microphase separation. In contrast, block and graft copolymers of
styrene/butadiene, for example, are characterized by two glass
transition temperatures and separation into styrene-rich domains
and butadiene-rich domains. It should be noted that membranes of
the invention which are produced from statistical copolymers
originally having a single glass transition temperature and a
single phase morphology do not necessarily exhibit a single phase
morphology or a single glass transition temperature after
sulfonation because of chemical changes in the polymer effected by
the sulfonation, in combination with the physical changes effected
by the casting processes of the invention.
[0015] The humidity-conducting polymers for use in the humidity
exchange cells of the present invention are derived from the
polymerization of arylvinyl monomers and which, therefore, contain
pendant aryl or aromatic moieties. Arylvinyl monomers are defined
herein as monomers that contain a vinyl group substituted with an
aryl, haloaryl or alkyl-substituted aryl group. An example of a
monomer containing a vinyl group substituted with an aryl is
styrene, an example of a monomer containing a vinyl group
substituted with a haloaryl group is chlorostyrene, and examples of
monomers containing a vinyl group substituted with an
alkyl-substituted aryl group are p-octylstyrene and vinyl toluene.
One or more arylvinyl monomers may be copolymerized with olefin
comonomers to produce a polymer which may be sulfonated; the
resulting sulfonated copolymers may be used to form the membranes
of the present invention.
[0016] Suitable arylvinyl monomers that can be employed to prepare
the polymers for sulfonation include, for example, styrene, vinyl
toluene, .alpha.-methylstyrene, t-butyl styrene, chlorostyrene and
all isomers of these compounds. Particularly suitable such monomers
include styrene and lower alkyl- or halogen-substituted derivatives
thereof. Preferred monomers include styrene, .alpha.-methyl
styrene, the lower alkyl- (C.sub.1-C.sub.4) or phenyl-ring
substituted derivatives of styrene, such as for example, ortho-,
meta-, and para-methylstyrene, the ring halogenated styrenes,
para-vinyl toluene or mixtures thereof, and the like. A more
preferred arylvinyl monomer is styrene. Residues derived from vinyl
toluene and chlorostyrene may be less readily sulfonated than those
from styrene; therefore, it may be desirable to include utilize
vinyl toluene and chlorostyrene along with arylvinyl monomers that
result in residues that may be more readily sulfonated, such as
styrene or .alpha.-methyl styrene, rather than as the sole
arylvinyl component of the polymer. The aryl or aromatic moieties
may be sulfonated at one or more positions on the aromatic rings to
yield polymer chains having pendant aryl sulfonate groups.
[0017] Humidity-conducting polymers may also include residues
derived from at least one olefin monomer, in addition to those
derived from at least one arylvinyl monomer. Preferred olefin
monomers include monoolefins, such as .alpha.-olefins and strained
ring olefins, and diolefin monomers such as butadiene and isoprene.
.alpha.-Olefins include ethylene and C.sub.3-10 olefins having
ethylenic unsaturation in the .alpha.- or 1-position, such as
ethylene, propylene, butylene, and isobutylene. Suitable
.alpha.-olefins include for example, .alpha.-olefins containing
from 3 to about 20, preferably from 3 to about 12, more preferably
from 3 to about 8 carbon atoms. Particularly suitable are ethylene,
propylene, butene-1,4-methyl-1-pentene, 1-hexene or 1-octene or
ethylene in combination with one or more of propylene, 1-butene,
4-methyl-1-pentene, 1-hexene or 1-octene. These .alpha.-olefins do
not contain an aromatic moiety. Preferred monoolefin monomers are
ethylene, propylene, 1-butene, 2-butene, 1- pentene,
4-methyl-1-pentene, 1-hexene, and 1-octene. Preferred strained ring
olefins are the various isomeric vinyl-ring substituted derivatives
of cyclohexene and substituted cyclohexenes, norbornene and
C.sub.1-10 alkyl or C.sub.6-10 aryl substituted norbornenes,
including 5-ethylidene-2-norbornene. Especially suitable are 1-,
3-, and 4-vinylcyclohexene, norbornene and
5-ethylidene-2-norbornene. Simple linear non-branched
.alpha.-olefins including, for example, .alpha.-olefins containing
from 3 to about 20 carbon atoms such as propylene,
butene-1,4-methyl-1-pentene, hexene-1 or octene-1 are not examples
of strained ring olefins. Preferred statistical arylvinyl polymers
are ethylene/styrene, ethylene/propylene/styrene,
ethylene/styrene/norbornene, and
ethylene/propylene/styrene/norbornene copolymers.
[0018] The polymer may also contain residues derived from other
comonomers, for example, acrylate monomers. In addition, copolymers
derived from diolefins, for example, butadiene and isoprene
copolymers may contain residual unsaturation. These are typically
hydrogenated, or reduced, prior to being sulfonated. The sulfonated
copolymers may be blended with other sulfonated copolymers or with
conventional polymers in order to form composite membranes for use
in the present invention.
[0019] A humidity-conducting polymer for use in a humidity exchange
cell of the present invention typically contains at least 20 weight
% of residues derived from styrene. More preferably, the copolymer
contains from 20 to 50 weight % styrene, and most preferably, about
45 weight % styrene. The range of weight average molecular weight
(M.sub.W) of the polymer of the invention is from about 20,000
grams/mole to about 1,000,000 grams/mole, and preferably from about
50,000 grams/mole to 900,000 grams/mole. The sulfonated polymer
used for the membranes of the present invention are preferably
water-insoluble. Water-insoluble is defined as having a solubility
of less than 0.5 grams of polymer in 100 grams of water at
100.degree. C. Suitable humidity-conducting polymers include
sulfonated, block styrene-ethylene-butylene-styrene copolymers,
sulfonated, reduced, statistical styrene-butadiene copolymers and
sulfonated statistical styrene-ethylene copolymers. Statistical
styrene-butadiene copolymers may be obtained from Goodyear; block
styrene-ethylene-butylene-styrene copolymers may be obtained from
Shell and statistical ethylene-styrene copolymers (ethylene styrene
interpolymers (ESI)) may be obtained from Dow Chemical. The Dow ESI
polymers include the pseudo-random interpolymers as described in
EP-A-0,416,815 by James C. Stevens et al. and U.S. Pat. No.
5,703,187 by Francis J. Timmers, both of which are incorporated
herein by reference in their entirety.
[0020] Where diolefins are used as comonomers, the unsaturated
residues in the copolymer membranes of the invention are may
selectively hydrogenated prior to sulfonation of aromatic groups
derived from the styrene residues. The amount of unsaturation
remaining after hydrogenation is less than 5 percent of the
starting level of unsaturation, and preferably less than 3 percent
of the original. Statistical copolymers of styrene and butadiene,
also known as styrene-butadiene rubber, or SBR may be used. The
copolymer may be hydrogenated by methods known in the art, such as
hydrogen gas in the presence of catalysts such as Raney Nickel, and
platinum or palladium metals. The diimide reduction described in
the examples may also be employed to produce materials that are
useful as ion-conducting membranes. Hydrogenated statistical
copolymers of styrene and butadiene are also commercially
available. Oxidation of residual unsaturated sites in the polymer
at levels greater than 5 percent unsaturation leads to degradation
of the polymer and shortens the useful life of the membrane under
operating conditions.
[0021] The hydrogenation level may be determined by the method of
Parker et al. An FTIR spectrum of a hydrogenated styrene butadiene
copolymer is analyzed by measuring the heights of the peaks at 963
cm.sup.-1 and 1493 cm.sup.-1, corresponding to the absorbance of
.dbd.CH and --CH.sub.2, respectively. The percent hydrogenation is
calculated using the following equation:
% hydrogenation=-15.71.times.+99.4
[0022] where x=the ratio of the peak height at 963 cm.sup.-1 to the
peak height at 1493 cm.sup.-1
[0023] A sulfonation process for styrene copolymers is described in
U.S. Pat. Nos. 5,468,574, 5,679,482, and 6,110,616. The preferred
level of sulfonic acid functionality ranges from about one
functional group per five aromatic rings (20 mol %) to about four
functional groups per five aromatic rings (80 mol %), such that the
equivalent weight of the resulting sulfonated polymer is from about
100 grams/sulfonate equivalent to about 1000 grams/sulfonate
equivalent. For example, for a copolymer of 45 weight percent
styrene, the preferred range is between one sulfonic acid group per
five styrene units (20 mol %, equivalent weight=1200
grams/equivalent) to about four sulfonic acid group per five
styrene units (80 mol %, equivalent weight=300 grams/equivalent).
Equivalent weight may be further limited to 400-700, and even
further limited to 520-690. For a copolymer of 30 weight percent
styrene, the preferred range is between one sulfonic acid group per
four styrene units (25 mol %, equivalent weight=1400
grams/equivalent) to four sulfonic acid groups per five styrene
units (80 mol %, equivalent weight=430 grams/equivalent). The
sulfonation level of the polymer may be controlled by the
stoichiometric ratio of the sulfonating agent, acetyl sulfate, to
the styrene content of the polymer. For example, addition of 1.0
equivalents of acetyl sulfate yields a polymer of 32 mol %
sulfonation and 1.4 equivalents yields 44 mol % sulfonation.
[0024] The HUX membrane is a hydrocarbon hydrophilic polymer that
possesses a low equivalent weight, from 1000 down to 100,
preferably 700 down to 300 and most preferably 690 down to 380.
Partially sulfonated styrene-olefin copolymers are generally
preferred. Specifically, styrene-ethylene and styrene-hydrogenated
butadiene, isoprene or equivalent olefinic copolymers that possess
a random, alternating, segmented or statistical in monomer
distribution along the chain are preferred. Pseudo-random is a
subclass of statistical; a weighted change in the monomer
incorporation that skews the distribution from a random arrangement
(i.e. Bernoullian) is defined as statistical. Linear arrangements
have been described here, but branched or grafted including star
arrangements of monomers are possible as well. In addition, block
copolymers of styrene and hydrogenated butadiene, isoprene, or
equivalent olefin can be employed. The block architecture can be
diblock, triblock, graft-block, multi-arm starblock, multiblock,
segmented or tapered block.
[0025] The HUX support material is preferably, but not limited to,
a polyolefin, spaced-member, fiber netting. Fiber extrusion
followed by melt bonding is a common method to prepare the netting,
however, other methods can be used by themselves or in combination.
These include injection molding, compression molding, fiber
extrusion with solvent bonding, spin bonding, and ultrasonic
welding.
[0026] Suitable materials for the reinforcing substrate include
woven, nonwoven, knit and cross-laid fabrics; in the context of the
present invention, the term `fabrics` is defined as including
meshes and nettings. Microporous films may also be used. The fabric
of a reinforcing substrate may be composed of synthetic fibers or
filaments, glass yarns, non-corroding metal fibers, such as nickel
fibers, or carbon fibers. The fibers, filaments or yarns should be
ones to which the water-conducting polymer film adheres strongly.
Suitable synthetic fibers include polyolefins, particularly
polyethylene or polypropylene, and polyesters. The fibers may have
organic or inorganic sizing agents or coupling agents applied,
including polyvinylalcohol, starches, oil, polyvinylmethylether,
acrylic, polyester, vinylsilane, aminosilane, titanate, and
zirconate. Silicone-based lubricants are sometimes employed for
greater tear strength. A microporous film may be composed of any
synthetic polymer to which the humidity-conducting polymer adheres.
In particular, the films may have a polyolefin composition, and
more particularly, polyethylene. Films having a fluoropolymer
composition may also be used. A composite membrane for use in a
humidity exchange cell according to the present invention may be
prepared by impregnating the substrate with a humidity-conducting
polymer. This may be done by any of several known methods. These
methods include direct coating, wherein a solution of the
humidity-conducting polymer in a suitable solvent, such as a lower
alcohol, in particular, methanol or propanol. The benefit of direct
coating is that it reduces the number of sub-assemblies and parts
and, thus, reduces costs. Low cost fabrication is an object of the
invention. Indirect coating methods, such as solution casting, may
also be used.
[0027] Sequential buildup facilitates the manufacturing of the
overall composite; coating is typically continued until a
homogenous sheet is formed when reinforcement may or may not be
completely coated. Formulations that readily wet the substrate are
available at low cost and produce composites without holes or other
defects are preferred. Alternatively, the water-conducting polymer
may be applied to the reinforcing substrate by hot roll laminating
it with reinforcing substrate, thus eliminating the need for
multiple coating passes. The water-conducting polymer film may also
contain a ceramic filler, if desired. Finally, a composite membrane
composed of nonwoven fabric may be manufactured by adding
staple-pulped fiber to solution of the water conducting polymer,
and coating on a release substrate.
[0028] The humidity-conducting polymer may contain one or more
additives, including crosslinking agents, flame retardants
(suppressants and synergists), biocides (mildewicides, fungicides,
anti-mold agents, antiviral agents, bacteriocides, anti-parasitic
agents, and insecticides.), plasticizers, uv stabilizers (uv
absorbers, and light stabilizers), antioxidants (primary or
secondary) and thermal stabilizers. Any one compound may impart one
or more characteristic enhancements. The basic requirements are
that (a) the additive is miscible with the hydrophilic polymer, (b)
it does not compromise the mechanical strength or integrity of the
membrane in the cell, (c) it not reduce the performance (e.g.
moisture transfer effectiveness) or lifetime of the cell in the
application. Therefore, these are objects (a, b, c) of the
invention. Although not an object, it is desirable that the
additive, retain the activity and efficacy of said characteristic
when present with the polymer in the formulation.
[0029] For biocides, our principal concern is mold and mildew
growth because of the potentially low, local pH of these sulfonated
hydrophilic polymers. However, resistance to other possible
biological agents such as fungus, bacteria, viruses, parasites,
insects or protozoa is desirable. Any biologicals that reduce the
available surface area of the membrane for transfer of moisture
from the stream must be prevented. Compatible chemical agents are
10,10'-oxybisphenoxarsine available from Rohm and Haas in a liquid
or resin carrier under the tradname Vinyzene. An arsenic-free
alternative is 4-chloro-3,5-dimethyl phenol an organic chemical
available from Aldrich. These can be used effectively at loadings
up to 5.0 phr. However, Dow Chemical's fungicide AMICAL 48 and
bactericide BIOPAN BP PLUS, both toxic metal-free are
preferred.
[0030] Flame retardancy is important insofar as additives can
reduce the tendency of the cell to catch fire, spread a fire and to
reduce smoke emissions. For pure liquid streams the threat of fire
does not present itself, except for air/water or some other highly
polar gas vapor streams at low humidity. For these applications, a
non-halogen flame retardant (basically a flame inhibitor) is
typically used for polyolefins. This is available from Unitex
chemical under the tradename Uniplex FRX 44-94S. Bromine-containing
retardants, Uniplex BAP-755 (brominated alkyl phosphate) and
Uniplex FRP-64 (poly (2,6-dibromophenylene oxide)) are also viable.
For high performance, the polymeric, flame retardant is desirable
but it requires a synergist, for which the high
phosphorous-containing FRX 44-94S is suitable. However, Great Lakes
Chemicals' tetrabromobisphenol A is preferred for polymer
solubility.
[0031] Organophosphates serve as hydrophilic plasticizers that
function by increasing the water or some other highly polar liquid
retention of the membrane in HUX cell in the application
environment. The increased water or some other highly polar liquid
content may improve performance by increasing membrane permeability
as well as reduce flammability, since substantially more water or
some other highly polar liquid must evaporate before flames may
spread to the cell. In the process, the evaporation of water or
some other highly polar liquid suppresses smoke. Also, these can
potentially function as synergists for bromine-containing flame
retardants. These are trialkyl phosphates, such as trimethyl
phosphate, triethyl phosphate, tripropyl phosphate and tris(2-ethyl
hexyl) phosphate.
[0032] Antioxidants (and thermal stabilizers) can increase shelf
life of HUX cells by circumventing the auto-oxidation of the
hydrophilic polymer during storage. However, a more important
advantage is the ability to reduce oxidation of the sulfonated
hydrophilic polymer in the HUX cell during operation since at low
humidity the polymer is continuously subject to the transfer of
heat and thus, will see temperatures as high as 37.degree. C.
Oxidation of organic impurities may result and reduce performance
this be minimized with the use of antioxidants. These are basically
hindered phenols of high molecular weight and include:
stearyl-3-(3',5'-di-tert-butyl-4-hydroxyphenyl) propionate (BNX
1076) and tetrakis[methylene-3
(3',5'-di-tert-butyl4-hydroxyphenyl)propionate] methane (BNX 1010)
both available from Mayo Corp. and poly(phenol-formaldehyde)
novalac resin (HRJ-12700) available from Schenectady International.
Peroxide decomposers add benefit as synergists to hindered phenols,
these are aryl phosphites; such as Tris(2,4-ditert-butylphenyl)
phosphite (Benafos 1680). UV stabilizers are important for outdoor
applications; these are light absorbers with a broad absorption
range of which benzotriazoles are preferred. Ciba's Tinuvin 384-2
(Benzene propionic acid (3-2H-benzotriazol-2-yl)-5-(1,1-di--
methylethyl-4)-hydroxy, C7-C9-branched and linear alkyl esters) is
suitable because of good thermal and environmental stability.
Hindered amine light stabilizers (HALS) may be suitable. However,
free amines form salts that may reduce water or some other highly
polar liquid transport, these are less preferred. Therefore,
nitroso-alkyl and specifically nitroso-alkyl ethers containing HALS
are preferred for these polymers to maximize their effectiveness as
stabilizers.
[0033] Further improvements in mechanical strength and integrity
especially at saturation (dehydration or hydration), or when one
(separation, dehydration, hydration) or both sides (osmosis,
filtration or dialysis) of the membrane are in contact with liquid
water or some other highly polar liquid can be obtained through the
formation of crosslinks between the polymer chains in the membrane.
There are principally two types of crosslinking approaches: (a)
crosslinks through carbon-containing groups and (b) crosslinks
through sulfur-containing groups.
[0034] The first approach (or Type I) is small molecule coupling of
two chains through polymeric chain radicals. The polymeric chain
radicals are created by reaction of olefinic (or styrenic) units
with primary radicals (formed from the thermal decomposition of
peroxides, or created by scission and/or ionization of the olefinic
units by UV, e-beam, gamma-ray, high energy particles. The
polymeric chain radicals form bonds to maleimide by addition to
double bonds or by radical coupling. Reaction of two such chains
with the single molecule forms a crosslink.
N,N'-1,3-Phenylene-dimaleimide is a preferred example. Peroxide
initiators are benzoyl peroxide,
1,1-Di-(tert-butylperoxy)-3,3,5-trimethy- lcyclohexane, and
2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3.
[0035] The high levels of initiator (if below the solubility limit
in the polymer) required for the achievement of a dense
interconnected network of chains likely leads to primary radical
termination of low mobility polymeric chain radicals. Also,
cross-linking agents that form stable chain radicals consume
initiator without formation of the polymeric chain radicals
necessary for the dense network. Co-agent radicals must be of
similar reactivity to polymer chain radicals for coupling of
adjacent polymer chains. More important, however, is that a
substantial concentration of polymeric chain radicals are formed.
Initiators are chosen that decompose to highly reactive radicals at
moderate temperatures with a very high rate of initiation. The
degree of crosslinking necessary to form a `tight` interconnected
network of chains depends on a large variety of factors. The
initiator type: functionality, primary radical reactivity,
initiation efficiency, coupling or crosslinking agent type;
crosslinking mechanism, specific interaction with polymer,
microstructure of the polymer; reactivity of polymer radical,
mobility and concentration of radicals which is controlled for the
most part by temperature and/or where applicable the light
intensity for photoinitiation or photosensitization.
[0036] Organometallic crosslinking agents of the enolate-type also
fare well when used in conjunction with the more reactive alkyl
peroxides as initiators. The more stable benzoyl and isobutyrl
peroxide radicals tend to have low initiation efficiencies for
crosslinking but if high concentrations of initiator can be
achieved by increasing solubility in the polymer then these can be
suitable. Organometallic agents of chelated metals that possess
multiple stable oxidation states are promising, such as metal
diketonates or derivatives thereof. Aluminum acetoacetonate is a
preferred example. Provided the metals are redox-active in the
chelated state, these can potentially catalyze decomposition of
peroxides or serve as photoactivators or sensitizers for
photoinitiators. Useful peroxide initiators are benzoyl peroxide,
1,1-Di-(tert-butylperoxy)-3,3,5-trimethy- lcyclohexane, and
2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3. These can crosslink in
conjunction with other agents or alone with heat, ultraviolet,
visible light, e-beam, high energy particle bombardment, such,
alpha particles, ionizing radiation such as gamma rays and by
electric discharge such as plasma.
[0037] The list includes but is not limited to: initiators;
1,1-Di-(tert-butylperoxy)-3,3,5-trimethylcyclohexane,
2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, tert-butyl peroxide,
dicumyl peroxide, methyl ethyl ketone peroxide,
meta-chloroperoxybenzoic acid, benzoyl peroxide; crosslinking
agents (includes coupling agents); aluminum acetylacetonate,
cobalt(III) acetylacetonate, cobalt(II) acetylacetonate, nickel
ketene acetals, N,N'-1,3-phenylene-dimaleimide, divinyl sulfone,
trispropargyl benzene, divinyl benzene, vinyl triethoxy silane,
hexamethyldisilazane, trimethylolpropane trivinyl ether,
trimethylolpropane trimethacrylate, trimethyolpropane allyl ether,
triallyl cyanurate, and triallyl phosphate.
[0038] The second approach (or Type II) is sulfonamide
crosslinking. The reaction of sulfonyl-imidazole or equivalent with
aromatic amines results in sulfonamide linkage between styrene
units. The reaction of a styrene sulfonic acid unit of the polymer
chain with 1,1'-carbonyl diimidazole forms styrene sulfonyl
imidazole. The imidazole molecule is a good leaving group so even
moderate nucleophiles such as, aromatic diamines displace them. A
suitable aromatic diamine is 4-aminophenylsulfone.
[0039] The principal advantage of both types of crosslinking
schemes is that the crosslinking agents may be added to a solution
of the polymer, mixed in, and cast normally. Subsequently the HUX
cell may be dried in an oven to remove residual solvent, heated in
an oven, or exposed to radiation. It is an object of the invention
that the additives be simply incorporated into the formulation.
[0040] FIG. 2 is a partially exploded view of a humidity exchange
cell or ventilator core 20 including a composite membrane 10, a
first chamber 22 for containing a first fluid, a second chamber 24
for containing a second fluid and a number of spacers or ribs 16
which are adhered to membrane 10. Cell 20 includes a series of
alternating first and second chambers. A cap 26 may be used to
enclose the topmost and/or bottommost chambers.
[0041] The membranes 10 are stacked one on top of another to form
ventilator core 20 as shown in FIG. 2. The orientation of the each
layer is rotated by 90 degrees as it is put down into the core.
This forms the cross-flow pattern for the exchange of heat and
moisture within the core. Not shown, but fully realizable, is a
counter-flow arrangement of the layers. Here the layers would be in
a single orientation, with no rotation, in the core. A complex
manifold would be designed to route gas streams to every other
layer in the stack. These manifolds would be placed on opposite
sides of the core. The non-manifold sides of the core could be
sealed to the external environment if necessary.
[0042] Spacer 16, as shown in FIGS. 1 and 2, is configured as a
series of ribs, typically adhered to the humidity-conducting
polymer surface. These ribs may have a synthetic polymer
composition, particularly, PVC, and may be rectangular or circular
in cross-section. In other embodiments (not shown), spacer 16 may
be a corrugated paper or plastic sheet. In some embodiments, spacer
16 may be a series of adhesive beads. The adhesive may be a
hot-melt, cold-melt, or solid adhesive; it may be either
thermoplastic or thermosetting. The HUX cell may possess certain
specific sub-elements to be effective as a mass (i.e. moisture)
exchanger. The basic sub-elements are as follows: (a) a hydrocarbon
hydrophilic polymer membrane formulated to be highly permeable to
water or some other highly polar liquid or gas, (b) a support
matrix to impart mechanical integrity to the membrane and to
maintain planarity during operation and (c) a manifold for the
distribution of a fluid across the face of the membrane. The
disclosed HUX cell is of unitary design in that it incorporates all
three sub-elements into a complete cell structure that can be
fabricated as a single unit. The device can be built up of this
structure by simple stacking and securing the cells in an
enclosure.
EXAMPLES
[0043] A cross-flow sensible and latent heat exchanger was
constructed. The membranes in the exchanger were made by laminating
a nylon non-woven reinforcement to a layer of a sulfonated
styrene-olefin polymer. The membranes were stacked on top of one
another using a PVC spacer with an applied adhesive. The PVC
spacers were oriented at 90 degrees to each other on alternating
layers. Every other layer in the core had the same flow direction:
1, 3, 5, 7 etc. had the same flow direction while 2, 4, 6, 8, etc.
had a flow direction that was oriented 90 degrees. The edges of
each layer in the core were sealed with double-sided adhesive tape.
The cross-flow exchanger was placed in a test apparatus where the
flow rate, temperature, and moisture of two airflows could be
controlled. One air flow had approximately a 90.degree. F.
temperature at a relative humidity of 55% of saturation. The other
airflow was held at 70.degree. F. and a relative humidity of 50% of
saturation. The exchange of sensible and latent heat between the
two airflows at different airflow rates was monitored. The data in
graph form is shown in FIG. 3. The airflow is expressed is
normalized as a function of the square feet of membrane area. This
allows us to compare exchangers of various materials and exchangers
against each other using the exchange area within the exchanger.
The graph shows that over 70% total effectiveness for this type of
exchanger can be achieved using sulfonated styrene-olefin polymer
membranes.
* * * * *