U.S. patent application number 09/855311 was filed with the patent office on 2001-11-22 for filtration and purification system for ph neutral solutions.
This patent application is currently assigned to Millipore Corporation. Invention is credited to Bruening, Ronald L., Deane, Edward, DiLeo, Anthony J., Parekh, Bipin S..
Application Number | 20010042715 09/855311 |
Document ID | / |
Family ID | 23510253 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010042715 |
Kind Code |
A1 |
Parekh, Bipin S. ; et
al. |
November 22, 2001 |
Filtration and purification system for pH neutral solutions
Abstract
The invention pertains to a method for removing metallic ions
and/or particulate material from a pH neutral solution using
particle-removing membranes (e.g., ultra high molecular weight
polyethylene) having immobilized ligands that possess the capacity
and high equilibrium binding constants for ion removal. The method
is particularly useful for simultaneously filtering/purifying
deionized water.
Inventors: |
Parekh, Bipin S.;
(Chelmsford, MA) ; DiLeo, Anthony J.; (Westford,
MA) ; Deane, Edward; (Newton Junction, NH) ;
Bruening, Ronald L.; (Springville, UT) |
Correspondence
Address: |
Alice O. Carroll, Esq.
HAMILTON, BROOK, SMITH & REYNOLDS, P.C.
Two Militia Drive
Lexington
MA
02421-4799
US
|
Assignee: |
Millipore Corporation
|
Family ID: |
23510253 |
Appl. No.: |
09/855311 |
Filed: |
May 14, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09855311 |
May 14, 2001 |
|
|
|
09382748 |
Aug 25, 1999 |
|
|
|
Current U.S.
Class: |
210/638 ;
210/321.77; 210/490; 210/502.1; 210/651; 210/688 |
Current CPC
Class: |
B01D 2323/30 20130101;
B01J 45/00 20130101; C02F 1/44 20130101; B01D 61/14 20130101; B01D
67/0093 20130101; Y10S 210/90 20130101; C02F 2101/20 20130101; B01D
61/00 20130101; C02F 1/683 20130101 |
Class at
Publication: |
210/638 ;
210/321.77; 210/490; 210/502.1; 210/651; 210/688 |
International
Class: |
B01D 063/00 |
Claims
What is claimed is:
1. A process for removing metallic ions and optionally particulate
material from a pH neutral solution, comprising contacting said
solution with a composition suitable for removing metallic ions and
optional particulate material contained in said solution and
recovering a purified and filtered solution essentially depleted of
metallic ions and optional particulate material; wherein the
composition comprises a membrane ligand combination represented by
the formula:M-B-Lwherein M is a membrane or composite membrane
having a hydrophilic or partially hydrophilic surface and
containing polar functional groups; L is a ligand having an
affinity for metallic ions and containing a functional group
reactive with an activated polar group from the membrane; and B is
a covalent linkage formed by the reaction between the activated
polar group and the functional group of the ligand.
2. The method according to claim 1 wherein L is a ligand selected
from the group consisting of amine-containing hydrocarbons; sulfur
and nitrogen-containing hydrocarbons; sulfur-containing
hydrocarbons; crowns and cryptands; aminoalkylphosphoric
acid-containing hydrocarbons; proton-ionizable macrocycles;
pyridine-containing hydrocarbons; polytetraalkylammonium and
polytrialkylamine-containing hydrocarbons; thiol and/or
thioetheraralkyl nitrogen-containing hydrocarbons; sulfur and
electron withdrawing group-containing hydrocarbons;
hydroxypyridinone; and oxygen donor macrocycles.
3. The method according to claim 2 wherein B is a covalent linkage
selected from the group consisting of amide (NHCO), ester (COO),
thioester (COS), carbonyl (CO), ether (O), thioether (S), sulfonate
(SO.sub.3), and sulfonamide (SO.sub.2NH) linkages.
4. The method according to claim 3 wherein M is a membrane selected
from the group consisting of polyamides and cellulosics.
5. The method according to claim 4 wherein said membrane is a
polyamide comprising nylon.
6. The method according to claim 4 wherein said membrane is a
cellulosic selected from the group consisting of cellulose,
regenerated cellulose, cellulose acetate and nitrocellulose.
7. The method according to claim 3 wherein M is a composite
membrane comprising a membrane substrate formed of a first polymer,
said substrate being directly coated on its entire surface with a
second polymer by a precipitated crystal technique and having a
hydrophilic surface.
8. The method according to claim 7 wherein said first polymer is a
polymer or copolymer of a member selected from the group consisting
of fluorinated polymers, polyolefins, polystyrenes, polysulfones,
polyesters, polyacrylates, polycarbonates, vinyl polymers and
polyacrylonitriles.
9. The method according to claim 8 wherein said second polymer is a
perfluorinated polyether.
10. The method according to claim 3 wherein M is a composite
membrane comprising a membrane substrate formed of a first polymer,
said substrate being directly coated on its entire surface with a
cross-linked second polymer formed from a monomer polymerized in
situ and cross-linked in situ on said substrate and having a
hydrophilic surface.
11. The method according to claim 10 wherein said first polymer is
a polymer or copolymer of a member selected from the group
consisting of fluorinated polymers, polyolefins, polystyrenes,
polysulfones, polyesters, polyacrylates, polycarbonates, vinyl
polymers and polyacrylonitriles.
12. The method according to claim 11 wherein said second polymer is
formed from a polymerizable monomer selected from the group
consisting of acrylates, methacrylates, ethacrylates, acrylic acid,
acrylamides, methacrylamides, ethacrylamides and mixtures
thereof.
13. The method according to claim 12 wherein B is an amide
linkage.
14. The method according to claim 3 wherein B is a sulfonamide
linkage.
15. The method according to claim 1 wherein said composition is
contained in a contacting device for holding said composition,
wherein said contacting device includes means for flowing a source
solution and a receiving solution past said composition.
16. The method according to claim 15 wherein said contacting device
comprises cartridge means.
17. A device for removing metallic ions and optional particulate
material from a pH neutral solution, comprising: a membrane ligand
combination represented by the formula:M-B-Lwherein M is a membrane
or composite membrane having a hydrophilic surface and containing
polar functional groups; L is any ligand having an affinity for
metallic ions and containing a functional grouping reactive with an
activated polar group from the membrane; and B is a covalent
linkage formed by the reaction between the activated polar group
and the functional group of the ligand; and a housing therefor.
18. The device of claim 17 wherein the device is in the form of a
cartridge.
19. The device of claim 18 wherein the membrane ligand combination
is housed in the cartridge in a pleated configuration.
Description
RELATED APPLICATION
[0001] This application is a continuation of U.S. application Ser.
No. 09/382,748 filed Aug. 25, 1999, the entire teachings of which
are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] Liquids, such as aqueous and organic liquids, are purified
to remove unwanted ions by passing the liquid through a packed
column of ion exchange resin beads. In order to improve efficiency
of ion removal and rate of processing the liquid, small particle
size ion exchange resin beads and high flow rates are desirable.
While smaller particle size resin beads improve efficiency in a
packed column, they also effect a decrease in the fluid flow rate
which, in turn, renders the optimization of the purification
process utilizing the beads difficult. A common undesirable
phenomenon when using a packed column of beads is the phenomenon of
channeling wherein the liquid being purified passes only through a
portion of the bed while rendering the remainder of the bed
underutilized.
[0003] A significant problem associated with incorporating ion
exchange resin particles into a polymer matrix is that the resin
particles are swellable in aqueous liquids. Thus, when a composite
material comprising a polymer binder and the ion exchange resin
particles is contacted with water, in the case of a porous membrane
composite, the porosity of the composite is significantly reduced
thereby significantly reducing the flow rate of the liquid through
the porous composite.
[0004] Ultrahigh molecular weight polyethylene is a desirable
material since it exhibits good chemical resistance to a wide
variety of reagents and therefore provides wide flexibility as a
material for uses in processes involving contact with these
reagents such as in purification processes.
[0005] Accordingly, it would be desirable to provide membranes
having ion removal capacity which have high ion capture
(efficiency) characteristics, have a high ion removal capacity per
unit area and permit maintenance of desirable flow rate per unit
area through the membrane when it is wet in aqueous solution. In
addition, it would be desirable to provide such membranes which are
useful in efficiently processing high volumes of pH neutral
liquid.
SUMMARY OF THE INVENTION
[0006] This invention pertains to a method for removing selected
ions (e.g., metallic ions) and particulate material from pH neutral
aqueous and organic solutions using particle-removing membranes
(e.g., ultra high molecular weight polyethylene) having immobilized
ligand groups that possess the capacity and high equilibrium
binding constants for ion removal. The method is particularly
useful for simultaneously filtering/purifying deionized (DI)
water.
[0007] According to the method of the invention, metallic ions and
particulate material are simultaneously removed from a pH neutral
aqueous solution by contacting the aqueous solution, which is
contaminated with metallic ions and particulate material, with a
composition suitable for removing metallic ions and particulate
material contained in said solution, then recovering a purified and
filtered solution essentially depleted of metallic ions and
particulate material. Compositions useful for purifying and
filtering comprise an ion-binding ligand bound to a membrane,
having an affinity for metallic ions and having an ability to
remove particulate material contained in said solution. The
membrane ligand combination is represented by the formula:
M-B-L
[0008] wherein M is a membrane or composite membrane derivatized to
have a hydrophilic surface and containing polar functional groups;
L is a ligand (e.g., macrocycle or other similar chelating ligand)
having an affinity for metallic ions and containing a functional
group reactive with an activated polar group from the membrane; and
B is the covalent linkage formed by the reaction between the
activated polar group and the functional group of the ligand. In a
preferred embodiment, the membrane will comprise a plurality of
different ligands that are ion specific. In another embodiment, M
is capable of removing particulate material contained in the
solution.
[0009] The filtration/purification methods of this invention have
several advantages. The fluid to be processed can flow through a
membrane structure and react with the ligand that is immobilized on
the membrane inner surface with very small mass transfer
resistance. This allows the fluid to be processed through membranes
at relatively high throughputs with no loss in ligand-ion
complexing efficiency. The particle retention properties of
membranes have been combined with ligand technology in one system
to remove both ions and particles from fluids.
[0010] The invention further pertains to filtration/purification
devices comprising membranes or composite membranes with
immobilized ligand groups. The ligand immobilized membranes have
been fabricated into devices that enable high flow rates and low
pressure drops. These engineering requirements may not as easily be
met with bead technology.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The foregoing and other objects, features and advantages of
the invention will be apparent from the following more particular
description of preferred embodiments of the invention, as
illustrated in the accompanying drawings in which like reference
characters refer to the same parts throughout the different views.
The drawings are not necessarily to scale, emphasis instead being
placed upon illustrating the principles of the invention.
[0012] FIG. 1 is a schematic view of a process for
filtering/purifying a pH neutral aqueous solution aqueous acid
utilizing the membrane of this invention.
[0013] FIG. 2 is a graphic illustration of the effectiveness of a
pleated cartridge device containing a copper immobilized ligand.
Copper feed at 100 ppb (diamonds); data curve (circles); model
curve (squares).
DETAILED DESCRIPTION OF THE INVENTION
[0014] The invention pertains to methods and devices for removing
metallic ions and particulate material from a pH neutral aqueous
solution such as, but not limited to, deionized water and buffered
aqueous solutions. The method uniquely purifies and filters out
metallic ions and particulates from pH neutral aqueous solutions by
using a combination of ligands that have an affinity for metallic
ions of interest and membranes that are capable of filtering out
particulate material present in the pH neutral aqueous solution.
These impurities can be simultaneously removed using membranes or
composite membranes (i.e., surface modified) having ion-binding
ligands immobilized thereon. The ligands possess ion complexing
capacity and high equilibrium binding constants for ion removal.
Metal recovery from aqueous and organic waste solutions, represent
a real need in modem technology. Metal ions and particulate
material are typically present at low concentrations in solutions.
Hence, there is a real need for a process to efficiently purify and
filter pH neutral aqueous solutions for their reuse or disposal.
The present invention accomplishes this separation effectively and
efficiently by the use of ligands bonded to membranes in accordance
with the present invention. It has been found that the membranes of
this invention are capable of rapidly and essentially completely
removing metals and particulates from pH neutral solutions to
specification levels of about 10 to 50 parts per trillion (ppt).
The term "pH neutral solutions" as used herein is intended to
embrace water (e.g., deionized water; (DI) and DI water containing
very low (ppb) concentrations of NaCl), buffered aqueous solutions,
having a pH range of from about 6 to about 8, with pH about 6.5 to
about 7.5 being preferred.
[0015] It should be understood from the discussion herein that the
membrane can be used to simultaneously remove metallic ions and
particulate material. However, it is not essential that both events
occur. For example, a membrane can be chosen such that the pore
size is sufficiently large to allow particulates to flow through.
Thus, it is contemplated that the ion-binding ligand membrane and
devices can be used to remove metallic ions, or to remove both
metallic ions and particulates.
[0016] The methods of this invention can be used in a variety of
industrial applications including, but are not limited to,
analytical, catalysis, chemical and petrochemical, environmental,
food and beverages, metallurgical processes, microelectronics,
pharmaceutical/life science, and power generation. Many of these
industrial applications contaminate pH neutral solutions with
metallic ions, such as heavy metals, and particulates. In fresh
aqueous solutions the sources of particles and ions can come from
manufacturing equipment, processes, raw materials and containers.
During use the contaminants are added from plumbing and the wafer
cleaning operations. The particles are usually sub-micron colloidal
types. Use of the invention can eliminate or reduce environmental
considerations associated with disposal of contaminated waste
waters.
[0017] The general method for simultaneously removing metallic ions
and particulate material from pH neutral aqueous solutions
comprises contacting the aqueous solution, which is contaminated
with metallic ions and particulate material, with a composition
suitable for simultaneously removing metallic ions and particulate
material contained in said solution, then recovering a purified and
filtered solution essentially depleted of metallic ions and
particulate material. Compositions useful for purifying and
filtering comprise an ion-binding membrane ligand combination
represented by the formula:
M-B-L
[0018] wherein M is any membrane or composite membrane derivatized
to have a hydrophilic surface and containing polar functional
groups, wherein M is capable of removing particulate material
contained in said solution; L is a ligand having an affinity for
metallic ions and containing a functional group reactive with an
activated polar group from the membrane; and B is a covalent
linkage formed by the reaction between the activated polar group
and the functional group of the ligand. Representative B linkages
are selected from the group consisting of amide (NHCO), ester
(COO), thioester (COS), carbonyl (CO), ether (O), thioether (S),
sulfonate (SO.sub.3) and sulfonamide (SO.sub.2NH).
[0019] In a preferred embodiment, the membrane will comprise a
plurality of different ligands that are ion specific. The exact
ligands chosen and the ratio of ion specific ligands relative to
each other will depend upon the ions to be removed from the pH
neutral aqueous solution and the desired lifetime of the
filtration/purification lifetime. For new neutral water
applications the only requirement for proper ion removal is a
ligand with an interaction constant high enough to remove the ion
efficiently to the desired level. For instance, low ppb and low ppt
levels for most ions are equivalent to 10.sup.-10 to 10.sup.-8 and
10.sup.-9 to 10.sup.11 Molar, respectively. Hence, an effective
interaction constant of .gtoreq.10.sup.6-10.sup.8 and preferably
.gtoreq.10.sup.9 to 10.sup.11 is sufficient to perform the removal
to ppt or sub ppb levels, with at least significant and preferably
near quantitative use of the ligand capacity, along with rapid
kinetics of interaction to deal with the low levels involved. The
Table is exemplary of accomplishing the goal. The specific removal
of target ions by a ligand is unaffected by other ligands. Ion
removal is stoichiometric.
[0020] The composite membranes with immobilized ligand groups are
particularly useful for removing trace metal ions from high purity
water. The water to be purified flows through the membrane
structure and the trace metals react with the ligand (immobilized
on the membrane inner surface) at high mass transfer rates.
Therefore, the fluid can be processed through the membranes at
relatively high throughputs with no loss in ligand-ion complexing
efficiency. The residence time of water through the membrane is of
the order of a fraction of a second, far less than minutes required
for the ion exchange column operation. The ligand immobilized
membranes have been fabricated into devices that enable high flow
rates and low pressure drops. These engineering requirements are
not easily met with ion exchange bead technology. The particle
retention properties of membranes have been combined with ligand
technology in one system to remove both ions and particles from
water and other pH neutral solutions.
[0021] To achieve the removal of multiple ions from DI water,
several ligands are immobilized onto one membrane/device. Each
ligand is designed to remove a specific class of ions. For the DI
water purification, ligands SL 420, SL 415 and SL 407 (commercially
available from IBC, Advanced Technologies, Inc., American Fork,
Utah) are immobilized on the same membrane device to remove ions
listed in the following Table. As shown in the Table, these ligands
have binding constants that are suitable for removing ions to ppt
levels.
1TABLE LogK Values for DI Water Purifier Ligands Element LogK
Ligand Cu.sup.++ 16 SL 420.sup.1 Ni.sup.+- 13.5 SL 420.sup.1
Zn.sup.-+ 9.5 SL 420.sup.1 Co.sup.++ 11 SL 420.sup.1 Fe.sup.++ 8 SL
420.sup.1 Ag.sup.++ 6.5 SL 420.sup.1 Mn.sup.++ 6 SL 415.sup.2
Fe.sup.+++ 18 SL 415.sup.2 Al.sup.+++ 16 SL 415.sup.2 Ca.sup.++ 7
SL 407.sup.3 Na.sup.+ 5.5 SL 407.sup.3 Pb >8 SL 437.sup.4
.sup.1U.S. patent application No. 09/202,731 .sup.2U.S. Pat. No.
5,182,251 .sup.3U.S. Pat. Nos. 4,943,375 (particles), 5,547,760
(membrane) and 4,960,882 .sup.4U.S. Pat. No. 5,393,892
[0022] According to the methods of the invention, high purity water
is contacted with a microporous ligand membrane device to effect
simultaneous removal of metal ions (such as those provided in the
Table above) and particulates. The purified water is recovered or
recycled for further use, such as for cleaning/rinsing silicon
wafers following the chemical wet etch processes, or for any other
process where it is desirable to have highly purified water or
aqueous solutions. The purified DI water can be monitored
continuously or periodically for the presence of undesired metal
ions to determine if the membrane device should be replaced. The
purifier can be used in a recirculation system shown in FIG. 1 or
in a once-through (one pass) flow configuration in which the water
continuously flows through the device and purified. As shown in
FIG. 1, container 10 contains DI water and silicon wafers. The
water is pumped by means of pump 12 through conduits 14 and 16 into
contact with the membrane purifier/filter 22, which functions to
remove ions and particles in the water. The purified water then is
recycled through conduit 24 back to container 10 (40 liters size)
for reuse. The water is continuously recirculated through the
purifier until bath concentration reaches low equilibrium ion
levels. In this flow mode, the solution has many chances to pass
through the purifier and be purified.
[0023] In a once-through (one pass) flow mode, the water flows
through the purifier continuously. The ions and particles are
removed by the ligand device. The purified water is then directed
to the rinsing and cleaning equipment. In this application, the
water has only one chance to interact with the ligands on the
membrane, thus the removal of ions must occur to equilibrium levels
instantaneously as the residence time in the membrane is less than
one second. The high inner surface area of the ligand membranes
provides greater access to ions for binding to the ligand sites.
The high binding constants create stronger interactions between
ions and ligands that allow ions removal to ppt levels in one pass
through the purifier.
[0024] The filtration/purification process of the invention can be
carried out in any manner that provides for bringing the ions and
particulate material to be removed from the pH neutral solution
into contact with the ligands affixed to the membrane. The
preferred embodiment disclosed herein involves carrying out the
process by bringing the pH neutral solution into contact with a
composition of matter of the invention. Contact is preferably made
in a contacting device comprising a housing, such as a cartridge,
containing the composition of matter of the invention by causing
the pH neutral solution to flow through the housing (e.g.,
cartridge) and thus come in contact with the composition of the
invention. The contacting device can include means for flowing a
source solution and a receiving solution past said ligand-membrane
composition. Preferably, the membrane configuration is a pleated
membrane, although other membrane configurations, such as flat
sheet, stacked disk or hollow fibers may be used. However, various
contact apparatus may be used instead of cartridges. The selected
ion or ions complex with the composition and the filtered and
purified pH neutral solution can be reused.
[0025] An advantage of the ligand membrane and cartridges
containing the same is that they can be regenerated by removal of
bound ions from the ligand. A cleaning method has been developed to
remove all contaminants from the device so it would not contribute
any significant extractables to the processing fluids. Effective
cleaning is a key factor responsible for the superior performance
of the ligand/membrane device, especially for applications that
require sub-ppb level of cleanliness. This can be accomplished by
contacting the membrane with an acid solution (e.g., from about 6M
to about 12M hydrochloric acid) under conditions sufficient to
remove the ions from the membrane. The ions can be collected and
recovered using known techniques. Preferably, the cleaning chemical
should be extremely clean (sub-ppb impurity) and should be strong
enough to remove all metals bound to the ligand. For example,
Megabit grade HCl (from about 6M to about 12M ) is preferred
(Ashland Chemical Co., Columbus, Ohio).
[0026] Compositions useful in the present invention comprise
ion-binding ligands that are covalently bonded to a membrane
through an amide, ester, thioester, carbonyl or other suitable bond
and have been described in detail in U.S. Pat. Nos. 5,547,760,
5,618,433 and U.S. Ser. No. 08/745,026; the entire teachings of
which are incorporated herein by reference. Membranes that are
inherently hydrophilic, or partially hydrophilic, and contain
moieties appropriate for making these bonds are preferred. Such
membranes include polyamides, such as nylon, and cellulosic
materials, such as cellulose, regenerated cellulose, cellulose
acetate, and nitrocellulose. If the membrane used does not contain
reactive groups it may be modified or derivatized appropriately.
Composite membranes are also useful. A composite membrane comprises
a porous polymer membrane substrate and an insoluble, cross-linked
coating deposited thereon. Representative suitable polymers forming
the membrane substrate include fluorinated polymers including poly
(tetrafluoroethylene) ("TEFLON"), polyvinylidene fluoride (PVDF),
and the like; polyolefins such as polyethylene, ultra-high
molecular weight polyethylene (UPE), polypropylene,
polymethylpentene, and the like; polystyrene or substituted
polystyrenes; polysulfones such as polysulfone, polyethersulfone,
and the like; polyesters including polyethylene terephthalate,
polybutylene terephthalate, and the like; polyacrylates and
polycarbonates; polyethers such as perfluorinated polyethers; and
vinyl polymers such as polyvinyl chloride and polyacrylonitriles.
Copolymers can also be used for forming the polymer membrane
substrate, such as copolymers of butadiene and styrene, fluorinated
ethylene-propylene copolymer, ethylene-chlorotrifluoroethylen- e
copolymer, and the like. The preferred membrane is hydrophilic
ultrahigh molecular weight polyethylene containing carboxylic
groups, such as those described in U.S. Pat. Nos. 4,618,533,
5,618,433 and 5,547,760.
[0027] With composite membranes, the substrate membrane material is
not thought to affect that performance of the derivatized membrane
and it is limited in composition only by its ability to be coated,
or have deposited on its surface, an insoluble polymer layer that
contains the appropriate reactive group. This provides a
hydrophilic layer which interacts well with water or other aqueous
solutions. The end result is that when the ligand is attached to
the surface of either a hydrophilic membrane or a composite
membrane having a hydrophilic surface, the basic characteristics of
any given ligand molecule are not changed by the process of
attaching it to the surface or by the nature of the surface
itself.
[0028] The coating of the composite membrane comprises a
polymerized cross-linked monomer, such as acrylates, methacrylates,
ethacrylates, acrylic acid, acrylamides, methacrylamides,
ethacrylamides and mixtures thereof. Representative suitable
polymerizable monomers include hydroxyalkyl acrylates or
methacrylates including 1-hydroxyprop-2-yl acrylate and
2-hydroxyprop-1-yl acrylate, hydroxypropylmethacrylate,
2,3-dihydroxypropyl acrylate, hydroxyethylacrylate, hydroxyethyl
methacrylate, and the like, and mixtures thereof. Other
polymerizable monomers that can be utilized include acrylic acid,
2-N,N-dimethylaminoethyl methacrylate, sulfoethylmethacrylate and
the like, acrylamides, methacrylamides, ethacrylamides, and the
like. Other types of hydrophilic coatings that can be used within
the scope of the invention include epoxy functional groups such as
glycidyl acrylate and methacrylate, primary amines such as
aminoethyl methacrylates, and benzyl derivatives such as vinyl
benzyl chloride, vinyl benzyl amine, and p-hydroxyvinyl
benzene.
[0029] The basic consideration in selecting a composite membrane is
that the coating placed on the membrane substrate is the
determining factor in defining the chemistry used to covalently
attach the ligand. For example, a composite membrane displaying a
carboxylic acid functional group can form an amide bond with a
pendant amine group from the ligand, one of the most stable methods
of ligand immobilization. The composite polymers referenced above
can be prepared with carboxylic acid active groups that can be
readily converted to amides upon reaction with an amine group on a
ligand. However, any of the other organic species which are
reactive toward an acid chloride could be used to attach an organic
ligand to the surface. Additional examples of such groups would be
esters, thioesters, Grignard reagents, and the like. If the
reactive group on the surface is a sulfonic acid, then an analogous
procedure using a sulfonyl chloride would yield results similar to
those obtained with carboxylic acid functionalities. One such
polymer containing sulfonic acid reactive groups is available under
the tradename NAFION.RTM. from DuPont as described above.
Preferably, suitable ligands contain an ester or carboxyl group and
an amine to form an amide linkage.
[0030] The composite membrane comprises a membrane substrate formed
of a first polymer and having coated thereon a second polymer
having a hydrophilic surface. The second polymer can be coated onto
the first polymer by a precipitated crystal technique.
Alternatively, the surface of the first polymer is coated with a
cross-linked second polymer formed from a monomer polymerized in
situ and cross-linked in situ on the substrate. In one embodiment,
the coating of composite membranes also comprises a precipitated
crystal system, such as that involving the material known under the
trademark NAFION.RTM.. NAFION.RTM. is a sulfonic acid or sodium
sulfonate of a perfluorinated polyether. In another embodiment, the
preferred coating is commercially available as ETCHGUARD.RTM.
(Millipore Corporation); U.S. Pat. No. 4,618,533.
[0031] Ligands which may be adapted to contain --NH.sub.2, --OH,
--SH, --MgX moieties that are reactive so as to form a covalent
bond with membrane attached functionalities are described in U.S.
Pat. Nos. 5,618,433, 5,547,760 and 5,078,978. The ligand can be
selected from the group consisting of amine-containing hydrocarbons
(e.g., U.S. Pat. No. 4,952,321), sulfur and nitrogen-containing
hydrocarbons (e.g., U.S. Pat. Nos. 5,071,819 and 5,084,430),
sulfur-containing hydrocarbons (e.g., U.S. Pat. Nos. 4,959,153 and
5,039,419), crowns and cryptands (e.g., U.S. Pat. Nos. 4,943,375
and 5,179,213), aminoalkylphosphoric acid-containing hydrocarbons
(e.g., U.S. Pat. No. 5,182,251), polyalkylene-polyamine-poly-
carboxylic acid-containing hydrocarbons, proton-ionizable
macrocycles (e.g., U.S. Pat. No. 4,960,882), pyridine-containing
hydrocarbons (e.g., U.S. Pat. No. 5,078,978), polyetraalkylammonium
and polytrialkylamine-containing hydrocarbons (e.g., U.S. Pat. No.
5,244,856), thiol and/or thioetheraralkyl nitrogen-containing
hydrocarbons (e.g., U.S. Pat. No. 5,173,470), sulfur and electron
withdrawing groups containing hydrocarbons (e.g., U.S. Pat. No.
5,190,661), hydroxypyridinone, hydroxypyridinone on a polyamine or
other carrier (e.g., U.S. Ser. No. 09/330,543), and macrocyclic
polyether cryptands. The ligands are capable of selectively
complexing ions such as either certain alkali, alkaline earth,
noble metal, other transition metal, and post transition metal ions
when contacted with solutions thereof when admixed with other ions.
Examples of ligands that can be used for the above-identified
application have been previously described in U.S. Pat. No.
5,618,433 and in U.S. application Ser. Nos. 09/330,543 and
09/330,477, entitled "Polymeric Membranes Functionalized with
Polyhydroxypyridinone Ligands" and "Particulate Solid Supports
Functionalized with Polyhydroxypyridinone Ligands", respectively,
both filed on Jun. 11, 1999, for removal of iron (SuperLig
435.RTM.; IBC Corp.); entire teachings are incorporated herein by
reference, such as U.S. application Ser. No. 09/202,731 for removal
of copper (SuperLig 420.RTM.; IBC Corp.); SuperLig 415 .RTM. for
Mn(II), Fe(III) and Al(III); SuperLig 40.RTM. for removal of
calcium and sodium, both described in U.S. Pat. Nos. 4,943,375 and
5,547,760; and SuperLig 437.RTM. for lead removal described in U.S.
Pat. No. 5,393,892 (See Table above.).
[0032] The compositions of the present invention may be prepared by
any suitable method wherein the macrocycle ligands can be
covalently bonded to a membrane containing reactive functional
groups. See U.S. Pat. No. 5,618,433, issued Apr. 8, 1997, the
entire teachings of which are incorporated herein by reference. For
example, immobilization of the ligand onto the membrane is carried
out in a two step procedure: [1] activation and [2] coupling. The
activation procedure involves reaction of carboxylic acid groups on
membranes with 1-Ethyl-3-(3-Dimethylaminopro- pyl) carbodiimide
Hydrochloride (EDAC) in either water or IPA/water medium to produce
a reactive intermediate compound. In the coupling step this
reactive intermediate compound reacts with the amine group on the
linker arm attached to the ligand, producing the ligand immobilized
membrane surface. The immobilization procedure can be carried out
for multiple ligands that are immobilized one at a time (in
series), or for multiple ligands co-immobilized simultaneously. In
a preferred embodiment, the membrane is an ultrahigh molecular
weight polyethylene having a hydrophilic coating, the ligand is
covalently attached thereto via amide bonds. The hydrophilic
coating is available under the trademark, ETCHGUARD.RTM. (Millipore
Corp., U.S. Pat. No. 4,618,533).
[0033] The membrane/ligand compositions that are useful for
carrying out the present invention will be apparent to those
skilled in the art by the following examples each of which utilizes
a composite membrane prepared according to U.S. Pat. No. 4,618,533
and containing carboxylic acid groups or sulfonic acid groups. One
objective of the membrane or composite membrane itself is to filter
out particulate material, if present, in the pH neutral solution.
For this purpose, the membranes should have a microporous or
ultraporous structure. Microporous pore sizes typically range from
about 0.005 to about 10 microns. Ultraporous pore sizes are smaller
than microporous pore sizes, typically ranging from about 0.0001 to
about 0.005 microns. The ligands may be attached to the upstream
outer surface of the membrane, the downstream outer surface of the
membrane, the inner porous surface of the membrane or any
combination of these surfaces. Preferably, the entire surface of
the membrane, including the pores, contain ligands.
[0034] The following examples illustrate the present invention and
are not intended to be limiting in any way. All references cited
herein are incorporated by reference in their entirety.
EXAMPLES
Example 1
Multiple Ligand Immobilization in Series
[0035] This example illustrates sequentially immobilizing three
ligands (SL 415, SL 420 and SL 407; IBC Advanced Technologies,
Inc., American Fork, Utah) on one cartridge containing a pleated
membrane of hydrophilic polyethylene (10,000 cm.sup.2 surface area)
(ETCHGUARD.RTM.; Millipore Corp.). An SL 415 ligand was first
immobilized to the membrane. A cartridge was activated using 15 gms
of EDAC dissolved in 1.2 liters of DI water for 15 minutes,
followed by an additional 15 gms of EDAC in the same solution for
10 or more minutes. In the coupling step, the activated cartridge
was then contacted with 59 gms of the SL 415 macrocycle ligand
solution in one liter DI water. The coupling was effective with or
without decanting the activation solution, the coupling reaction
contact time can be several hours or up to an overnight duration.
The cartridge was washed with DI water to prepare for the second
ligand attachment. A membrane coupon was processed with the
cartridge to determine the ligand capacity. The Fe capacity was
0.091 .mu.mole/cm.sup.2.
[0036] In the second step, ligand SL 407 (e.g., capable of removing
nickel, cobalt, zinc and copper) was immobilized to the membrane.
As in the above procedure, the cartridge now containing the ligand
SL 415 was activated with EDAC (two steps, 15 gms EDAC in 1.2 liter
DI water each and 15 mins. and 10 mins. activation time,
respectively). The activated cartridge was then coupled using 20
gms of SL 407 in one liter DI water. The cartridge was washed with
DI water to prepare it for the third ligand attachment. A membrane
coupon was processed with the cartridge to determine the ligand
capacity. The Na capacity was 0.3 .mu.mole/cm.sup.2.
[0037] The third ligand SL 420 was immobilized following the same
procedures described above of activation and coupling. The
activation medium was 1.2 liters of 75% IPA and 25% DI water. The
SL 420 ligand was prepared by dissolving 30 gms of the ligand in
one liter of 75% IPA (790 ml) and 25% DI water (210 ml). After the
coupling reaction, the cartridge was washed with a mixture of 75%
IPA (790 ml) and 25% DI water (210 ml). A membrane coupon was
processed with the cartridge to determine the macrocycle ligand
capacity. The Cu capacity measured was 0.034 .mu.mole/cm.sup.2.
Example 2
Multiple Ligands Co-immobilized Simultaneously
[0038] This example illustrates immobilizing three ligands (SL 415,
SL 420 and SL 407; IBC Advanced Technologies, Inc.) on one
cartridge containing a pleated membrane of hydrophilic polyethylene
(10,000 cm.sup.2 surface area) (ETCHGUARD.RTM.; Millipore Corp.).
An SL 415 ligand was first immobilized to the membrane. A cartridge
was activated using 15 gms of EDAC dissolved in 1.2 liters of DI
water for 15 minutes, followed by additional 15 gms of EDAC in the
same solution for 20 more minutes. In the coupling step, the
activated cartridge is then contacted with 50 gms of the SL 415
macrocycle ligand solution in one liter DI water. The coupling was
effective with or without decanting the activation solution, the
coupling reaction contact time can be several hours or up to an
overnight duration. The cartridge was washed with DI water to
prepare for attaching two more ligands simultaneously. Two membrane
coupons were processed with the cartridge to determine the ligand
capacity. The Fe capacity measured was 0.0.15 and 0.22
.mu.mole/cm.sup.2.
[0039] In the second step, the ligands 407 and 420 were attached to
the cartridge membrane in one step. The cartridge with the SL 415
ligand already attached was activated using 15 gms of EDAC
dissolved in 1.2 liters of DI water for 15 minutes, followed by an
additional 15 gms of EDAC in the same solution for 10 more minutes.
In the coupling step, the activated cartridge was then contacted
with a solution containing 20 gms of SL 407 and 30 gms of SL 420
dissolved in a mixture of 900 ml methanol and 400 ml DI water. The
procedure also worked if methanol was substituted with isopropyl
alcohol. Two membrane coupons were processed with the cartridge to
determine the ligand capacity. The measured capacity for Na (SL
407) was 0.11 and 0.096 .mu.mole/cm.sup.2, and 0.35 and 0.29
.mu.mole/cm.sup.2 for Cu (SL 420).
Example 3
Purification of Water
[0040] This example illustrates the use of a ligand membrane device
of this invention to purify Cu containing water solutions in a
one-pass flow mode. The solution flowed through a pleated cartridge
device made with the Cu-ligand (SL 420)-immobilized membrane
(hydrophilic polyethylene). The device membrane area is about
10,000 cm.sup.2 and the ligand capacity 0.4 .mu.mol/cm.sup.2 (SL
420). The incoming feed concentration was maintained at about 100
ppb Cu and the solution flow rate at 1 gpm. The purifier product
(effluent) was monitored for Cu concentration to determine the
breakthrough. The experimental results are plotted in FIG. 2 as the
product Cu concentration (ppb) versus the total volume throughput
(expressed as ppb* liters), a product of the total volume (liters)
processed and the incoming feed concentration (ppb). The data show
that the purifier removes the incoming feed Cu from 100-145 ppb
levels (Feed curve in the figure) to less than detection levels
(<0.02 ppb, Data curve) continuously until the breakthrough
capacity is reached at about 130000 ppb* liters throughput. The
performance is as predicted (Model curve) by the engineering design
model (see below) developed to custom design chemical purifiers for
specific applications and to predict their performance from knowing
the process parameters such as liquid flow rate, incoming ion
contamination, purifier size, and the macrocycle ligand membrane
ion capacity. The breakthrough capacity and the tolerable effluent
concentration for a given application typically govern a device
lifetime.
[0041] Performance Model 1 C cu = VC 0 ( H + ) 2 / A V ( H + ) 2 /
A + Kq 0 - KVC 0 / A
[0042] Where:
[0043] C.sub.cu=equilibrium copper concentration (mol/l )
[0044] V=volume (liters)
[0045] C.sub.o=initial Cu concentration (mol/liter)
[0046] H+=hydrogen ion concentration (mol/l)
[0047] K=equilibrium binding constant (mol/l)
[0048] q.sub.o=membrane capacity (mole/cm.sup.2)
[0049] A=cartridge area (Cm.sup.2)
Example 4
Device Cleaning
[0050] The membrane device was cleaned using 2-4 liters of 100%
isopropyl alcohol (IPA) to remove organics, followed by a deionized
(DI) water flush to remove IPA. The device was then cleaned with
concentrated hydrochloric acid, HCl, 6 molar (e.g., for copper
ligand) to 12 molar (e.g., for iron ligand) concentration. The
device was static soaked in 1.2 liters of acid for 1-2 hours,
followed by an additional 8 liters of acid flowed through the
device at 30-50 ml/min flow rate. The device was drained to remove
all acids. The device was then flushed with the ultrahigh purity
deionized water to remove all traces of residual acid. This
cleaning procedure was very effective in producing clean devices of
extremely low extractables.
[0051] While this invention has been particularly shown and
described with references to preferred embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
spirit and scope of the invention as defined by the appended
claims.
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