U.S. patent application number 14/407362 was filed with the patent office on 2015-06-11 for composite polyamide membrane with carboxylic acid functionality.
The applicant listed for this patent is DOW GLOBAL TECHNOLOGIES LLC. Invention is credited to Tina L. Arrowood, Anand S. Badami, Robert C. Cieslinski, Bruce B. Gerhart, David D. Hawn, Steven D. Jons, Mou Paul, Martin H. Peery, XiaoHua sam Qiu, Mark A. Rickard, Steven Rosenberg, Abhishek Roy, Ian A. Tomlinson, Cheng Li Zu.
Application Number | 20150157990 14/407362 |
Document ID | / |
Family ID | 48790674 |
Filed Date | 2015-06-11 |
United States Patent
Application |
20150157990 |
Kind Code |
A1 |
Roy; Abhishek ; et
al. |
June 11, 2015 |
COMPOSITE POLYAMIDE MEMBRANE WITH CARBOXYLIC ACID FUNCTIONALITY
Abstract
A thin film composite polyamide membrane including a porous
support and a thin film polyamide layer which is a reaction product
of m-phenylene diamine (mPD) and trimesoyl chloride (TMC), wherein
the membrane is characterized by the thin film polyamide layer
having a dissociated carboxylic acid content of at least 0.18
moles/kg at pH 9.5, and wherein pyrolysis of the thin film
polyamide layer at 650 C results in a ratio of responses from a
flame ionization detector for fragments produced at 212 m/z and 237
m/z of less than 2.8.
Inventors: |
Roy; Abhishek; (Edina,
MN) ; Arrowood; Tina L.; (Elko New Market, MN)
; Badami; Anand S.; (Midland, MI) ; Cieslinski;
Robert C.; (Midland, MI) ; Gerhart; Bruce B.;
(Midland, MI) ; Hawn; David D.; (Midland, MI)
; Jons; Steven D.; (Eden Prairie, MN) ; Paul;
Mou; (Edina, MN) ; Peery; Martin H.;
(Bloomington, MN) ; Qiu; XiaoHua sam; (Midland,
MI) ; Rickard; Mark A.; (Midland, MI) ;
Rosenberg; Steven; (Shorewood, MN) ; Tomlinson; Ian
A.; (Midland, MI) ; Zu; Cheng Li; (Midland,
MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DOW GLOBAL TECHNOLOGIES LLC |
Midland |
MI |
US |
|
|
Family ID: |
48790674 |
Appl. No.: |
14/407362 |
Filed: |
July 3, 2013 |
PCT Filed: |
July 3, 2013 |
PCT NO: |
PCT/US2013/049182 |
371 Date: |
December 11, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61673462 |
Jul 19, 2012 |
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61673467 |
Jul 19, 2012 |
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61673466 |
Jul 19, 2012 |
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61673456 |
Jul 19, 2012 |
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61673453 |
Jul 19, 2012 |
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61674634 |
Jul 23, 2012 |
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61675412 |
Jul 25, 2012 |
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61775814 |
Mar 11, 2013 |
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61775777 |
Mar 11, 2013 |
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Current U.S.
Class: |
210/490 ;
427/244 |
Current CPC
Class: |
B01D 69/10 20130101;
B01D 61/025 20130101; B01D 67/0002 20130101; B01D 2323/40 20130101;
B01D 2323/00 20130101; B01D 67/0006 20130101; B01D 69/12 20130101;
B01D 71/56 20130101; B01D 69/125 20130101; B01D 2323/38 20130101;
B01D 2325/20 20130101 |
International
Class: |
B01D 71/56 20060101
B01D071/56; B01D 69/12 20060101 B01D069/12 |
Claims
1. A thin film composite polyamide membrane comprising a porous
support and a thin film polyamide layer comprising a reaction
product of m-phenylene diamine (mPD) and trimesoyl chloride (TMC),
wherein the membrane is characterized by the thin film polyamide
layer having a dissociated carboxylic acid content of at least 0.18
moles/kg at pH 9.5, and wherein pyrolysis of the thin film
polyamide layer at 650.degree. C. results in a ratio of responses
from a flame ionization detector for fragments produced at 212 m/z
and 237 m/z of less than 2.8.
2. The membrane of claim 1 wherein the polyamide layer has a
dissociated carboxylate content of at least 0.3 moles/kg at pH
9.5.
3. The membrane of claim 1 wherein pyrolysis of the thin film
polyamide layer at 650.degree. C. results in a ratio of responses
from a flame ionization detector for fragments produced at of 212
m/z and 237 m/z of less than 2.6.
4. The membrane of claim 1 characterized by the thin film polyamide
layer having a dissociated carboxylic acid content of at least 0.18
moles/kg at pH 9.5, and wherein the ATR IR of a thin film polyamide
layer results in a COOH C.dbd.O stretch/Amide C.dbd.O stretch
absorbance ratio of less than 0.1.
5. A method for making a thin film composite membrane by applying a
polar solution of m-phenylene diamine and a non-polar solution
comprising trimesoyl chloride to a surface of a porous support to
form a thin film polyamide layer, wherein the non-polar solution
further comprises: i) an acyl halide reactant comprising at least
one acyl halide moiety and at least one carboxylic acid moiety, and
ii) tri-hydrocarbyl phosphate compound.
6. The method of claim 5 wherein the non-polar solution comprises a
tri-hydrocarbyl phosphate compound in a molar ratio to trimesoyl
chloride of at least 0.5:1.
7. The method of claim 5 wherein the non-polar solution comprises
at least 0.15 wt % of the acyl halide reactant.
8. The method of claim 5 wherein the acyl halide reactant comprises
mono-hydrolyzed trimesoyl chloride.
Description
FIELD
[0001] The present invention is directed toward thin film composite
membranes along with methods for making and using the same.
INTRODUCTION
[0002] Composite polyamide membranes are used in a variety of fluid
separations. One class includes a porous support with a "thin film"
polyamide layer. These membranes are commonly referred to as "thin
film composite" (TFC) membranes. The thin film polyamide layer may
be formed by an interfacial polycondensation reaction between
polyfunctional amine (e.g. m-phenylenediamine) and polyfunctional
acyl halide (e.g. trimesoyl chloride) monomers which are
sequentially coated upon the support from immiscible solutions, see
for example U.S. Pat. No. 4,277,344 to Cadotte. WO 2010/120326
describes the use of trimesoyl chloride in combination with its
mono and di-hydrolyzed counterparts. Additional constituents have
also been added to the coating solution to improve membrane
performance. For example, U.S. Pat. No. 6,878,278 to Mickols
describes the addition of a tri-hydrocarbyl phosphate compound to
the acyl halide coating solution.
[0003] The incorporation of carboxylic acid functional groups into
the polyamide layer imparts the layer with a more negative charge
and this is believed to improve the rejection of certain solutes
(e.g. NaCl, nitrate) along with providing the membrane with
improved resistance to certain foulants (e.g. humic acid). A
portion of the acyl halide groups of the polyfunctional acyl halide
monomer inevitably become hydrolyzed during interfacial
polymerization (e.g. via reaction with water present in the
atmosphere or with water present in the amine coating solution).
The overall carboxylic acid content ("dissociated carboxylate
content") of the polyamide layer can be further increased by
utilizing acyl halide monomers including carboxylic acid functional
groups. See for example WO 2010/120326. Other approaches which may
increase the carboxylic acid content of the polyamide layer involve
post-treatment with a chlorinating agent (see for example: U.S.
Pat. No. 4,277,344, U.S. Pat. No. 4,761,234, U.S. Pat. No.
5,051,178 and U.S. Pat. No. 5,876,602) or the post-application of
charged coatings. Unfortunately, post-treatment steps add to the
cost and complexity of membrane preparation. Moreover,
post-chlorination can compromise long term membrane
performance.
SUMMARY
[0004] In one embodiment, the invention includes a thin film
composite polyamide membrane including a porous support and a thin
film polyamide layer which is a reaction product of m-phenylene
diamine (mPD) and trimesoyl chloride (TMC), wherein the membrane is
characterized by the thin film polyamide layer having a dissociated
carboxylic acid content of at least 0.18 moles/kg at pH 9.5, and
wherein pyrolysis of the thin film polyamide layer at 650.degree.
C. results in a ratio of responses from a flame ionization detector
for fragments produced at 212 m/z and 237 m/z of less than 2.8. In
another embodiment, the invention includes a method for making a
thin film composite membrane by applying a polar solution of
m-phenylene diamine and a non-polar solution comprising trimesoyl
chloride to a surface of a porous support to form a thin film
polyamide layer, wherein the non-polar solution further comprises:
i) an acyl halide reactant comprising at least one acyl halide
moiety and at least one carboxylic acid moiety, and ii)
tri-hydrocarbyl phosphate compound. Many additional embodiments are
described.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a plot of pyrolysis GC-MS response (a) for a
representative thin film polyamide layer as a function of
temperature (b) corresponding to a representative thin film
polyamide layer.
DETAILED DESCRIPTION
[0006] The invention includes thin film composite membranes and
methods for making and using the same. The invention is not
particularly limited to a specific type, construction or shape of
composite membrane or application. For example, the present
invention is applicable to flat sheet, tubular and hollow fiber
polyamide membranes useful in a variety of applications including
forward osmosis (FO), reverse osmosis (RO) and nano filtration
(NF). RO composite membranes are relatively impermeable to
virtually all dissolved salts and typically reject more than about
95% of salts having monovalent ions such as sodium chloride. RO
composite membranes also typically reject more than about 95% of
inorganic molecules as well as organic molecules with molecular
weights greater than approximately 100 Daltons. NF composite
membranes are more permeable than RO composite membranes and
typically reject less than about 95% of salts having monovalent
ions while rejecting more than about 50% (and often more than 90%)
of salts having divalent ions--depending upon the species of
divalent ion. NF composite membranes also typically reject
particles in the nanometer range as well as organic molecules
having molecular weights greater than approximately 200 to 500
Daltons.
[0007] The subject method involves forming a thin film polyamide
layer upon a porous support. The porous support is not particularly
limited and preferably includes a polymeric material having pore
sizes which are of sufficient size to permit essentially
unrestricted passage of permeate but not large enough so as to
interfere with the bridging over of a thin film polyamide layer
formed thereon. For example, the pore size of the support
preferably ranges from about 0.001 to 0.5 .mu.m. Non-limiting
examples of porous supports include those made of: polysulfone,
polyether sulfone, polyimide, polyamide, polyetherimide,
polyacrylonitrile, poly(methyl methacrylate), polyethylene,
polypropylene, and various halogenated polymers such as
polyvinylidene fluoride.
[0008] The thin film polyamide layer is prepared by an interfacial
polycondensation reaction between m-phenylene diamine (mPD) and
trimesoyl chloride (TMC) on the surface of the porous support as
described in U.S. Pat. No. 4,277,344 and U.S. Pat. No. 6,878,278.
The term "polyamide" refers to a polymer in which amide linkages
(--C(O)NH--) occur along the molecular chain. mPD and TMC may be
applied to the porous support by way of a coating step from
solution, wherein mPD is preferably coated from an aqueous-based or
polar coating solution and TMC is coated from an organic-based or
non-polar coating solution. The polar coating solution preferably
contains from about 0.1 to about 20 weight percent and more
preferably from about 0.5 to about 6 weight percent of mPD. The
non-polar solution preferably contains from about 0.1 to 10 weight
percent and more preferably from 0.3 to 3 weight percent of TMC.
Once brought into contact with one another, the monomers react at
their surface interface to form a polyamide layer or film. This
layer, often referred to as a polyamide "discriminating layer" or
"thin film layer," provides the composite membrane with its
principal means for separating solute (e.g. salts) from solvent
(e.g. aqueous feed). The reaction time of the monomers may be less
than one second but contact times typically range from about 1 to
60 seconds, after which excess liquid may be optionally removed by
way of an air knife, water bath(s), dryer or the like. The removal
of the excess solution can be achieved by drying at elevated
temperatures, e.g. from about 40.degree. C. to about 120.degree.
C., although air drying at ambient temperatures may be used.
Although the coating steps need not follow a specific order, mPD is
preferably coated first followed by TMC. Coating can be
accomplished by spraying, film coating, rolling or through the use
of a dip tank among other coating techniques.
[0009] The interfacial polymerization is conducted in the presence
of an acyl halide reactant. The reactant may be coated from a
separate coating solution or in some embodiments, combined and
coated from the aforementioned non-polar coating solution. The acyl
halide reactant includes at least one acyl halide moiety and at
least one carboxylic acid moiety (or salt thereof). Non-limiting
examples of acyl halide reactants include mono and di-hydrolyzed
counterparts of the polyfunctional acyl halide monomers described
below along with the mono, di and tri-hydrolyzed counterparts of
the tetraacyl halide monomers described below. Preferred acyl
halide reactants include mono-hydrolyzed trimesoyl chloride (mhTMC)
i.e. 1-carboxy-3,5-dichloroformyl benzene and the mono-hydrolyzed
isophthaloyl chloride (mhIPC). Additional examples include that
represented by Formula (I):
##STR00001##
[0010] wherein X is a halogen (preferably chlorine) and n is an
integer from 1 to 10. Representative species include:
4-(chlorocarbonyl) butanoic acid; 5-(chlorocarbonyl) pentanoic
acid; 6-(chlorocarbonyl) hexanoic acid; 7-(chlorocarbonyl)
heptanoic acid; 8-(chlorocarbonyl) octanoic acid;
9-(chlorocarbonyl) nonanoic acid and 10-(chlorocarbonyl) decanoic
acid. While the acyl halide and carboxylic acid groups are shown in
terminal positions, one or both may be located at alternative
positions along the aliphatic chain. While not shown in Formula
(I), the aliphatic reactant may include additional carboxylic acid
and acyl halide groups. Additionally, corresponding aromatic
species may used including 3-carboxybenzoyl chloride and
4-carboxybenzoyl chloride.
[0011] Non-limiting polyfunctional acyl halide monomers that may be
hydrolyzed to form the subject reactant include: terephthalic acid
chloride, isophthalic acid chloride, biphenyl dicarboxylic acid
chloride, and naphthalene dicarboxylic acid dichloride.
Non-limiting examples of aliphatics include adipoyl chloride,
malonyl chloride, glutaryl chloride, and sebacoyl chloride.
Non-limiting examples of alicyclic polyfunctional acyl halides
include: cyclopropane tri carboxylic acid chloride, cyclopentane
tri carboxylic acid chloride, cyclohexane tri carboxylic acid
chloride, cyclopentane dicarboxylic acid chloride, cyclobutane
dicarboxylic acid chloride, cyclohexane dicarboxylic acid chloride,
and tetrahydrofuran dicarboxylic acid chloride. Representative
polyfunctional acyl halide monomers also include a tetraacyl halide
monomers as represented by Formula (II):
##STR00002##
[0012] wherein A is selected from: oxygen (--O--), carbon (--C--),
silicon (--Si--), sulfur (--S--) and nitrogen (--N--) which may be
unsubstituted or substituted, e.g. with alkyl groups of 1-4 carbon
atoms; or a carbonyl group (--C(O)--). X is the same or different
and is selected from a halogen. In a preferred embodiment, each X
is chlorine. In another preferred embodiment, A is an unsubstituted
carbon, i.e. the subject monomer is 5,5'-methylene diisophthaloyl
dichloride.
[0013] The acyl halide reactant and TMC are preferably coated from
a common non-polar coating solution having a total acyl halide
content of at least 0.10 wt % (e.g. 0.10 to 5 wt %). As used
herein, the term "acyl halide content" refers to the concentration
of compounds including at least one acyl halide moiety, as measured
by weight and common dilution practices. The concentration of the
acyl halide reactant in the coating solution is preferably at least
0.001 wt % and in some embodiments at least 0.005, 0.01, 0.02, 0.04
or 0.07 wt %. A preferred upper limit for this reactant is 0.25 wt
%, 0.15 wt %, 0.010 wt % and in some embodiments, equal to or less
than 0.08 wt %. The coating solution may be applied to the porous
support as part of a continuous or batch coating operation.
Suitable non-polar solvents are those which are capable of
dissolving the acyl halide reactants and which are immiscible with
water, e.g. hexane, cyclohexane, heptane and halogenated
hydrocarbons such as the FREON series. Preferred solvents include
those which pose little threat to the ozone layer and which are
sufficiently safe in terms of flashpoints and flammability to
undergo routine processing without taking special precautions. A
preferred solvent is ISOPAR.TM. available from Exxon Chemical
Company. The coating solution may optionally include additional
materials including co-solvents, phase transfer agents,
solubilizing agents and complexing agents wherein individual
additives may serve multiple functions. Representative co-solvents
include: benzene, toluene, xylene, mesitylene, ethyl benzene,
diethylene glycol dimethyl ether, cyclohexanone, ethyl acetate,
butyl carbitol.TM. acetate, methyl laurate and acetone. In one
embodiment, the non-polar coating solution utilized to coat the
polyfunctional acyl halide includes from 4 to 100 wt % mesitylene
as a co-solvent along with a solvent such as an isoparaffin.
[0014] In another embodiment, the subject method includes the step
of conducting the interfacial polymerization in the presence of a
tri-hydrocarbyl phosphate compound. The means of applying the
tri-hydrocarbyl phosphate compound to the porous support are not
particularly limited, e.g. the tri-hydrocarbyl phosphate compound
may be included in one or both of the aforementioned coating
solutions or may be coated from a separate coating solution before
or during the interfacial polymerization. In a preferred
embodiment, the tri-hydrocarbyl phosphate compound is added to the
non-polar coating solution used to apply TMC to the porous
support.
[0015] In preferred embodiments, the tri-hydrocarbyl phosphate
compound is present during the interfacial polymerization in a
molar ratio with TMC of at least 0.1:1, 0.5:1, 1:1, 1.1:1, 1.2:1,
1.5:1 or 2:1. Preferred ranges of molar ratios (tri-hydrocarbyl
phosphate compound to TMC) include: 1:1 to 5:1, 1.2:1 to 4:1, 1.5:
to 3:1 and 2:1 to 3:1.
[0016] Representative examples of applicable tri-hydrocarbyl
phosphate compounds are described in U.S. Pat. No. 6,878,278. A
preferred class of such compounds includes those represented by
Formula (III):
##STR00003##
[0017] wherein "P" is phosphorous, "O" is oxygen and R.sub.1,
R.sub.2 and R.sub.3 are independently selected from hydrogen and
hydrocarbyl groups comprising from 1 to 10 carbon atoms, with the
proviso that no more than one of R.sub.1, R.sub.2 and R.sub.3 are
hydrogen. R.sub.1, R.sub.2 and R.sub.3 are preferably independently
selected from aliphatic and aromatic groups. Applicable aliphatic
groups include both branched and unbranched species, e.g. methyl,
ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, 2-pentyl,
3-pentyl. Applicable cyclic groups include cyclopentyl and
cyclohexyl. Applicable aromatic groups include phenyl and naphthyl
groups. Cyclo and aromatic groups may be linked to the phosphorous
atom by way of an aliphatic linking group, e.g., methyl, ethyl,
etc. The aforementioned aliphatic and aromatic groups may be
unsubstituted or substituted (e.g., substituted with methyl, ethyl,
propyl, hydroxyl, amide, ether, sulfone, carbonyl, ester, cyanide,
nitrile, isocyanate, urethane, beta-hydroxy ester, etc); however,
unsubstituted alkyl groups having from 3 to 10 carbon atoms are
preferred. Specific examples of tri-hydrocarbyl phosphate compounds
include: tripropyl phosphate, tributyl phosphate, tripentyl
phosphate, trihexyl phosphate, triphenyl phosphate, propyl biphenyl
phosphate, dibutyl phenyl phosphate, butyl diethyl phosphate,
dibutyl hydrogen phosphate, butyl heptyl hydrogen phosphate and
butyl heptyl hexyl phosphate.
[0018] In a preferred embodiment, the thin film polyamide layer is
characterized by having a dissociated carboxylate content of at
least 0.18, 0.20, 0.22, 0.3, and in some embodiments at least 0.4
moles/kg of polyamide at pH 9.5 as measured by the Rutherford
Backscattering measurement technique described below in the Example
section. While not used in the present experiments, the carboxylic
acid content of TFC polyamide membranes (moles/kg of polyamide) can
also be determined using the measured polyamide mass per unit area
and the moles of carboxylic acids groups per unit area, such as by
complexation and quantification methods also described in the
Example section.
[0019] In another preferred embodiment, pyrolysis of the thin film
polyamide layer at 650.degree. C. results in a ratio of responses
from a flame ionization detector for fragments produced at 212 m/z
and 237 m/z of less than 2.8, and more preferably less than 2.6.
The fragments produced at 212 and 237 m/z are represented by
Formula IV and V, respectively.
##STR00004##
This ratio of fragments is believed to be indicative of polymer
structures that provide improved flux, salt passage or integrity
(particularly for membranes having relatively high carboxylic acid
content, e.g. a dissociated carboxylate content of at least 0.18,
0.20, 0.22, 0.3, and in some embodiments at least 0.4 moles/kg of
polyamide at pH 9.5). With reference to FIG. 1, investigation has
shown that dimer fragment 212 m/z forms predominantly during
pyrolysis temperatures below 500.degree. C. whereas dimer fragment
237 m/z predominantly forms at pyrolysis temperatures above
500.degree. C. This indicates that dimer fragment 212 originates
from end groups where only single bound cleavage prevails and that
dimer fragment 237 originates substantially from the bulk material
where multiple bond cleavages and reduction occurs. Thus, the ratio
of dimer fragment 212 to 237 can be used as a measure of relative
conversion.
[0020] A preferred pyrolysis methodology is conducted using gas
chromatography mass spectrometry with mass spectral detection, e.g.
a Frontier Lab 2020iD pyrolyzer mounted on an Agilent 7890 GC with
detection using a LECO time of flight (TruTOF) mass spectrometer.
Peak area detection is made using a flame ionization detector
(FID). Pyrolysis is conducted by dropping the polyamide sample cup
into pyrolysis oven set at 650.degree. C. for 6 seconds in single
shot mode. Separation is performed using a 30 M.times.0 25mm id
column from Varian (FactorFour VF-5MS CP8946) with a 1 um 5% phenyl
methyl silicone internal phase. Component identification is made by
matching the relative retention times of the fragment peaks to that
of the same analysis performed with a LECO time of flight mass
spectrometer (or optionally by matching mass spectra to a NIST
database or references from literature). Membrane samples are
weighed into Frontier Labs silica lined stainless steel cups using
a Mettler E20 micro-balance capable of measuring to 0.001 mg.
Sample weight targets were 200 ug +/-50 ug. Gas chromatograph
conditions are as follows: Agilent 6890 GC (SN: CN10605069), with a
30 M.times.0.25 mm, 1 .mu.m 5% dimethyl polysiloxane phase (Varian
FactorFour VF-5MS CP8946); injection port 320.degree. C., Detector
port: 320.degree. C., Split injector flow ratio of 50:1, GC Oven
conditions: 40.degree. C. to 100.degree. C. at 6.degree. C. per min
, 100.degree. C. to 320.degree. C. at 30.degree. C./min,
320.degree. C. for 8 min; Helium carrier gas with constant flow of
0.6 mL/min providing a back pressure of 5.0 psi. LECO TruTOF Mass
Spectrometer Parameters are as follows: electron ionization source
(positive EI mode), Scan Rate of 20 scans per second, Scan range:
14-400 m/z; Detector voltage=3200 (400V above tune voltage); MS
acquisition delay=1 min; Emission Voltage--70V. The peak area of
the fragment 212 m/z and fragment 237 m/z are normalized to the
sample weight. The normalized peak areas are used to determine the
ratio of fragments 212 m/z to 237 m/z. Further the normalize peak
area of fragment 212 m/z is divided by the sum of the normalized
peak areas for all other fragments providing a fraction of the m/z
212 fragment relative to the polyamide and is commonly noted as a
percent composition by multiplying by 100. Preferably this value is
less than 12%.
[0021] In another preferred embodiment, the thin film polyamide
layer is characterized by having an ATR IR carboxylic acid carbonyl
stretch/amide carbonyl stretch (here in referred to as COOH/amide)
of less than 0.1 and more preferably 0.08. The measurement is
believed to be indicative of polymer structures that provide
improved flux, salt passage or integrity (particularly for
membranes having relatively high carboxylic acid content). A
preferred ATR IR methodology is conducted by first isolating the
polyamide layer from the porous support by first delaminating from
the backing sheet. The delaminated membrane is immersed in a
solvent suitable to dissolve the porous support (e.g. dimethyl
formamide). After dissolving the porous support, the insoluble
polyamide is collected by filtration, washed 2 times
dimethylformamide, 2 times with DI water, and 2 times with methanol
then dried in a vacuum oven at 50 .degree. C. for 20 hours.
Infrared spectra of delaminated polyamide layer was acquired with a
Perkin Elmer Spectrum One FT-IR and Universal ATR Sampling
Accessory at a nominal resolution of 4 cm.sup.-1 and 16 scans
(approximate acquisition time of 90 seconds). The Universal ATR
Sampling Accessory was equipped with a single bounce diamond/ZnSe
crystal. The carboxylic acid peak height was measured at 1706
cm.sup.- with a single-point baseline at 1765 cm.sup.-1. The amide
peak height was measured at 1656 cm.sup.- with a single-point
baseline at 1765 cm.sup.-.
[0022] In yet another preferred embodiment, the subject membranes
have an isoelectric point (IEP) of less than or equal to 4.3, 4.2,
4.1, 4, 3.8, 3.6 or in some embodiments 3.5, as measured using a
standard zeta-potential measurement method as described below.
[0023] In another preferred embodiment, the subject membranes have
improved flux as compared with comparable membranes prepared
without the subject acyl halide reactants, e.g. when tested with an
aqueous salt solution (2000 ppm NaCl) at 150 psi, 25.degree. C. and
pH 8. In another embodiment, the subject membranes also maintain
comparable NaCl passage values, e.g. less than 1% when tested using
an aqueous solution of 2000ppm NaCl at 150 psi, 25.degree. C. and
pH 8. In another embodiment, the subject membranes have a NaCl
passage value less than 5% when tested such conditions.
[0024] In another preferred embodiment, the subject composite
membrane is not subject to post-treatment with a chlorinating
agent.
[0025] While post application coatings may be used in combination
with the present invention, in many preferred embodiments, no such
coating is used, i.e. no coating of polyacrylic acid or polyvinyl
acetate.
EXAMPLES
[0026] Sample membranes were prepared using a pilot scale membrane
manufacturing line. Polysulfone supports were casts from 16.5 wt %
solutions in dimethylformamide (DMF) and subsequently soaked in an
aqueous solution of 3.5 wt % meta-phenylene diamine (mPD). The
resulting support was then pulled through a reaction table at
constant speed while a thin, uniform layer of a non-polar coating
solution was applied. The non-polar coating solution included a
isoparaffinic solvent (ISOPAR L), a combination of trimesoyl acid
chloride (TMC) and 1-carboxy-3,5-dichloroformyl benzene (mhTMC) in
varying ratios while maintaining the total acid chloride content at
0.26 wt %, and tributyl phosphate (TBP) in a constant
stoichiometric molar ratio of 1.1:1 with TMC. Excess non-polar
solution was removed and the resulting composite membrane was
passed through water rinse tanks and drying ovens. Coupons of the
sample membranes were then subject to standard testing using an
aqueous salt solution (2000 ppm NaCl) at 150 psi, 25.degree. C. and
pH 8. The dissociated carboxylate content, isoelectric point (IEP),
dimer fragment ratio (212 m/z:237 m/z) and carboxylic acid/amide
(COOH:Amide) ratios for the sample membranes were also determined
(as per the methodologies described herein). The results are
summarized in Table 1. A second set of similar membranes were
prepared without TBP and the results are summarized in Table 2.
Standard deviations for flux and NaCl passage are provided in
parenthesis. A third set of membranes were prepared in a manner the
same as the first set with the exception that
1-carboxy-3,5-dichloroformyl benzene (mhTMC) was replaced with
3-(chlorocarboynyl)benzoic acid, i.e. "mono hydrolyzed isophthaloyl
chloride" or "mhIPC". The dissociated carboxylate content and dimer
fragment ratio (212 m/z : 237 m/z) ratios for the sample membranes
were also determined (as per the methodologies described herein).
The results are summarized in Table 3.
TABLE-US-00001 TABLE 1 Dissociated Sample mhTMC FLUX NaCl
Carboxylate 212 m/z:237 m/z Isoelectic COOH/ No. (wt %) (GFD)
Passage (%) (moles/kg) ratio % 212 Pt. (IEP) Amide 1-1 0 46.90 0.86
0.156 1.9 9.4 4.26 0.064 (1.81) (0.074) 1-2 0.0065 45.75 0.49 0.188
2.2 10.0 4.11 0.065 (1.05) (0.037) 1-3 0.013 44.09 0.42 0.229 2.5
11.5 3.94 0.073 (0.91) (0.063) 1-4 0.026 43.65 0.37 0.303 2.6 14.7
3.76 0.097 (2.06) (0.037) 1-5 0.052 48.61 0.43 0.442 3.1 16.0 3.72
0.084 (1.33) (0.029) 1-6 0.078 53.58 0.75 0.556 3.1 16.6 3.5 0.100
(1.37) (0.062) 1-7 0.104 49.47 4.51 0.874 -- -- 3.36 0.148 (1.93)
(0.263)
TABLE-US-00002 TABLE 2 Dissociated Sample mhTMC FLUX NaCl
Carboxylate 212 m/z:237 m/z % Isoelectic COOH/ No. (wt %) (GFD)
Passage (%) (moles/kg) ratio 212 Pt. (IEP) Amide 2-1 0 13.64 1.10
0.17 3.0 13.1 4.02 0.111 (0.63) (0.036) 2-2 0.0065 10.14 1.18 0.239
3.0 14.7 3.94 0.139 (0.91) (0.039) 2-3 0.013 11.02 1.41 0.321 3.2
13.7 3.98 0.137 (0.50) (0.058) 2-4 0.019 13.55 0.99 0.356 3.3 15.6
3.87 0.162 (0.52) (0.134) 2-5 0.026 8.95 1.81 0.428 3.4 16.8 3.92
0.175 (0.50) (0.061)
TABLE-US-00003 TABLE 3 NaCl Flux Passage Dissociated Sample mhIPC
FLUX NaCl (Standard (Standard Carboxylate 212 m/z:237 m/z No. (wt
%) (GFD) Passage (%) Deviations) Deviations) (moles/kg) ratio 3-1
0.0065 43.58 0.61% 3.51 0.058 0.114 1.53 3-2 0.0261 43.17 0.52%
4.73 0.067 0.139 1.62 3-3 0.039 41.6 0.63% 1.89 0.09 0.161 1.89 3-4
0.052 28.8 0.66% 0.48 0.1 0.203 1.71 3-5 0.078 41.76 1.57% 0.69
0.178 0.203 2.13
The "dissociated carboxylate content" of the polyamide layer of the
sample membranes was determined by silver titration and a
Rutherford Backscattering measurement as described below.
[0027] (i) Samples membranes (1 inch.times.6 inch) were boiled for
30 minutes in deionized water (800 mL), then placed in a 50/50 w/w
solution of methanol and water (800 mL) to soak overnight. Next, 1
inch.times.1 inch size sample of these membranes were immersed in a
20 mL 1.times.10.sup.-4 M AgNO.sub.3 solution with pH adjusted to
9.5 for 30 minutes. Vessels containing silver ions were wrapped in
tape and to limit light exposure. After soaking with the silver ion
solution, the unbound silver was removed by soaking the membranes
in 2 clean 20 mL aliquots of dry methanol for 5 minutes each.
Finally, the membranes were allowed to dry in a nitrogen atmosphere
for a minimum of 30 minutes.
[0028] (ii) Rutherford Backscattering (RBS) Measurement: Membrane
samples were mounted on a thermally and electrically conductive
double sided tape, which was in turn mounted to a silicon wafer
acting as a heat sink The tape used was Chromerics Thermattach T410
or a 3M copper tape. RBS measurements were obtained with a Van de
Graff accelerator (High Voltage Engineering Corp., Burlington,
Mass.); A 2 MeV He room temperature beam with a diameter of 3 mm
was used at an incident angle of 22.5.degree., exit angle of
52.5.degree., scattering angle of 150.degree., and 40 nanoamps
(nAmps) beam current. Membrane samples were mounted onto a movable
sample stage which is continually moved during measurements. This
movement allows ion fluence to remain under 3.times.10.sup.14
He.sup.+/cm.sup.2.
[0029] (iii) Data Analysis: Analysis of the spectra obtained from
RBS was carried out using SIMNRA.RTM., a commercially available
simulation program. A description of its use to derive the
elemental composition from RBS analysis of RO/NF membranes has been
described by.; Coronell, et. al. J. of Membrane Sci. 2006, 282,
71-81 and Environmental Science & Technology 2008, 42(14),
5260-5266. Data in tables were obtained using the SIMNRA.RTM.
simulation program to fit a two layer system, a thick polysulfone
layer beneath a thin polyamide layer, and fitting a three-layer
system (polysulfone, polyamide, and surface coating) can use the
same approach. The atom fraction composition of the two layers
(polysulfone before adding the polyamide layer, and the surface of
final TFC polyamide layer) was measured first by XPS to provide
bounds to the fit values. As XPS cannot measure hydrogen, an H/C
ratio from the proposed molecular formulas of the polymers were
used, 0.667 for polysulfone and a range of 0.60-0.67 was used for
polyamide. Although the polyamides titrated with silver nitrate
only introduces a small amount of silver, the scattering cross
section for silver is substantially higher than the other low
atomic number elements (C, H, N, O, S) and the size of the peak is
disproportionately large to the others despite being present at
much lower concentration thus providing good sensitivity. The
concentration of silver was determined using the two layer modeling
approach in SIMNRA.RTM. by fixing the composition of the
polysulfone and fitting the silver peak while maintaining a narrow
window of composition for the polyamide layer (layer 2, ranges
predetermined using XPS). From the simulation, a molar
concentration for the elements in the polyamide layer (carbon,
hydrogen, nitrogen, oxygen and silver) was determined The silver
concentration is a direct reflection of the carboxylate molar
concentration available for binding silver at the pH of the testing
conditions.
[0030] The moles of carboxylic acids groups per unit area of
membrane is indicative of the number of interactions seen by a
species passing through the membrane, and a larger number will thus
favorably impact salt passage. This value may be calculated by
multiplying the measured carboxylate content by a measured
thickness and by the polyamide density. Alternatively, the
carboxylate number per unit area of membrane (moles/m2) may be
determined more directly by methods that measure the total
complexed metal within a known area. Approaches using both Uranyl
acetate and toluidine blue O dye are described in: Tiraferri, et.
al., Journal of Membrane Science, 2012, 389, 499-508. An approach
to determine the complexed cation (sodium or potassium) content in
membranes by polymer ashing is described in (Wei Xie, et al.,
Polymer, Volume 53, Issue 7, 22 March 2012, Pages 1581-1592).
[0031] A preferred method to determine the dissocated carboxylate
number at pH 9.5 per unit area of membrane for a thin film
polyamide membrane is as follows. A membrane sample is boiled for
30 minutes in deionized water, then placed in a 50 wt % solution of
methanol in water to soak overnight. Next, the membrane sample is
immersed in a 1-10.sup.-4 M AgNO.sub.3 solution with pH adjusted to
9.5 with NaOH for 30 minutes. After soaking in the silver ion
solution, the unbound silver is removed by soaking the membranes
twice in dry methanol for 30 minutes. The amount of silver per unit
area is preferably determined by ashing, as described by Wei, and
redissolving for measurement by ICP. Preferably, the dissocated
carboxylate number at pH 9.5 per square meter of membrane is
greater than 6.times.10.sup.-5, 8.times.10.sup.-5,
1.times.10.sup.-4, 1.2.times.10.sup.-4, 1.5.times.10.sup.-4,
2.times.10.sup.-4, or even 3.times.10.sup.-4 moles/m.sup.2.
[0032] The isoelectric point for the sample membranes was
determined using a standard Zeta-Potential technique with a quartz
cell by electrophoretic light scattering (ELS) using Desal Nano HS
instrument. Membrane samples (2 inch.times.1 inch) were first
boiled for 20 minutes in DI water, then rinsed well with room
temperature DI water and stored at room temperature in a fresh DI
solution overnight. The samples were then loading as per reference:
2008 "User's Manual for the Delsa.TM. Nano Submicron Particle Size
and Zeta Potential," and the "Pre-Course Reading" for the same
instrument presented by Beckmann Coulter. The pH titration was done
over a range from pH 10 to pH 2 and isoelectric point was
determined at the pH where the zeta potential became zero.
[0033] Many embodiments of the invention have been described and in
some instances certain embodiments, selections, ranges,
constituents, or other features have been characterized as being
"preferred." Characterizations of "preferred" features should in no
way be interpreted as deeming such features as being required,
essential or critical to the invention. The entire subject matter
of each of the aforementioned US patent documents is incorporated
herein by reference.
* * * * *