U.S. patent application number 09/378957 was filed with the patent office on 2001-08-09 for method for reducing metal ion concentration in brine solution.
Invention is credited to FOUST, DONALD FRANKLIN, FYVIE, THOMAS JOSEPH, SILVA, JAMES MANIO.
Application Number | 20010011645 09/378957 |
Document ID | / |
Family ID | 23495236 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010011645 |
Kind Code |
A1 |
SILVA, JAMES MANIO ; et
al. |
August 9, 2001 |
METHOD FOR REDUCING METAL ION CONCENTRATION IN BRINE SOLUTION
Abstract
This invention relates to a method for removing impurities from
a brine solution, the brine solution comprising a water soluble
chelating agent, the method comprising the steps of: a) adjusting
the pH of the brine solution to a pH of from about 2 to about 4; b)
passing the brine solution through a first functionalized resin;
the first functionalized resin having functional groups capable of
removing multivalent metal cations from the brine solution; c)
adjusting the pH of the brine solution to a pH of from about 9 to
about 11.5; and d) passing the brine solution through a second
functionalized resin; the second functionalized resin having
functional groups capable of removing alkaline earth metal cations
from the brine solution.
Inventors: |
SILVA, JAMES MANIO; (CLIFTON
PARK, NY) ; FOUST, DONALD FRANKLIN; (GLENVILLE,
NY) ; FYVIE, THOMAS JOSEPH; (SCHENECTADY,
NY) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY
CRD PATENT DOCKET ROOM 4A59
P O BOX 8
BUILDING K 1 SALAMONE
SCHENECTADY
NY
12301
US
|
Family ID: |
23495236 |
Appl. No.: |
09/378957 |
Filed: |
August 23, 1999 |
Current U.S.
Class: |
210/669 ;
210/687; 210/688 |
Current CPC
Class: |
C01D 3/145 20130101 |
Class at
Publication: |
210/669 ;
210/687; 210/688 |
International
Class: |
B01D 015/00 |
Claims
What is claimed is:
1. A method for removing impurities from a brine solution, the
brine solution comprising a water soluble metal chelating agent,
the method comprising the steps of: a) adjusting the pH of the
brine solution to a pH of from about 2 to about 4; b) passing the
brine solution through a first functionalized resin; the first
functionalized resin having functional groups capable of removing
multivalent metal cations from the brine solution; c) adjusting the
pH of the brine solution to a pH of from about 9 to about 11.5;and
d) passing the brine solution through a second functionalized
resin; the second functionalized resin having functional groups
capable of removing alkaline earth metal cations from the brine
solution.
2. The method of claim 1, further comprising the step of
pretreating the brine solution in a primary brine treatment stage,
prior to step a).
3. The method of claim 1, wherein the first functionalized resin
removes iron, nickel, chromium, aluminum or mixtures thereof.
4. The method of claim 1, wherein the second functionalized resin
removes calcium, magnesium, barium, strontium or mixtures
thereof.
5. The method of claim 1, further comprising the step of e)
recovering the brine solution.
6. The method of claim 1, wherein the first functionalized resin is
an imino diacetic acid functionalized ion exchange resin.
7. The method of claim 1, wherein the second functionalized resin
is an amino methyl phosphonic acid functionalized ion exchange
resin.
8. The method of claim 1, wherein the brine solution in step d) is
passed through the second functionalized resin at a space velocity
of from about 1 to about 15 bed volumes per hour.
9. The method of claim 8, wherein the temperature of the brine
solution is from about 20.degree. C. to about 90.degree. C.
10. The method of claim 1, wherein the brine solution in step b) is
passed through the first functionalized resin at a space velocity
of from about 1 to about 30 bed volumes per hour.
11. The method of claim 9, wherein the temperature of the brine
solution is from about 20.degree. C. to about 80.degree. C.
12. The method of claim 10, wherein the temperature of the brine
solution is about 60.degree. C.
13. The method of claim 1, wherein the brine solution in step b) is
passed through the first functionalized resin at a space velocity
of from about 1 to about 15 bed volumes per hour, and the brine
solution in step d) is passed through the second functionalized
resin at a space velocity of from about 4 to about 8 bed volumes
per hour.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a method for reducing the
concentration of multivalent metal cations in a brine solution
containing a metal chelating agent. In particular, this invention
relates to a method for reducing the concentration of multivalent
metal cations in a brine solution involving the use of a membrane
electrolyzer. The brine solution is a product of a condensation
polymer manufacturing process and contains a water-soluble
chelating agent, such as sodium gluconate.
BACKGROUND OF THE INVENTION
[0002] The manufacture of condensation polymers often produces a
brine solution as a by-product. For example, a brine solution is
produced in the manufacture of polycarbonate resins through the
reaction of phosgene with at least one bisphenol compound in an
organic solvent in the presence of aqueous sodium hydroxide. A
common example is the reaction of bisphenol A with phosgene in
dichloromethane in the presence of aqueous sodium hydroxide to
produce bisphenol A polycarbonate and sodium chloride solution.
[0003] To reduce production costs and avoid environmental
pollution, such brine solutions are often recycled to a
chlor-alkali plant for electrolysis to produce chlorine gas, sodium
hydroxide solution, and hydrogen gas. The electrolysis cells in
such chlor-alkali plants frequently comprise an anode compartment
and a cathode compartment with an appropriate separator in between
the two compartments. The purpose of the separator is to separate
the anolyte solution and the chlorine gas evolved at the anode from
the catholyte solution and the hydrogen gas evolved at the cathode,
within the electrolysis cell. The separator may be at least
partially porous to water. The types of separators used in
electrolysis cells include diaphragms and membranes.
[0004] During membrane electrolysis cell operation, the ion
exchange membrane separator may gradually become plugged by the
accumulation of solid material, retarding the passage of water and
dissolved species from anolyte solution to catholyte solution.
Separator plugging decreases the efficiency of cell operation and
lowers the production rate of products arising from electrolysis.
When plugging reaches a critical point, the separator must be
replaced, often before its expected lifetime is reached. To achieve
most economical electrolysis cell operation, it is necessary that
the cell separator have as long a lifetime as possible.
[0005] Brine solutions arising as by-products from condensation
polymer manufacture often contain both organic and inorganic
contaminants. Organic contaminants may include residual solvent,
catalyst, and aqueous-soluble organic species such as monomer and
low molecular weight oligomer. Inorganic contaminants may include
multivalent alkaline earth and transition metal cations,
particularly iron, calcium, and magnesium. When brine solution
containing one or more such contaminants is electrolyzed, both
organic species and metal species may precipitate on the surface of
and within an electrolysis cell separator to cause plugging. To
achieve maximum lifetime of a separator in an electrolysis cell,
the concentration of contaminating organic species and multivalent
metal cations must be reduced to as low a level as economically
possible in the feed-brine solution.
[0006] In order to lower the concentrations of organic and
inorganic contaminants to levels suitable for feeding the brine to
membrane electrolytic cells, primary and secondary brine treatment
are often employed. In primary brine treatment, the brine pH is
elevated to above about 10 in the presence of a molar excess of
carbonate ion in order to precipitate alkaline earth and transition
metals as their carbonates and/or hydroxides, followed by a
filtering or settling process such as clarification. This is
followed by acidification and stripping of the brine to remove
carbonate ion as well as organic contaminants such as organic
solvents and dissolved catalysts. Additional treatment such as
adsorption may be utilized as necessary to remove organic species
such as monomer and low molecular weight oligomer from the
brine.
[0007] In secondary brine treatment, the brine pH is adjusted to
about 8-11 and the brine is treated in a chelating ion exchange
resin such as aminomethylphosphonic acid-functionalized polystyrene
resin (AMP resin) or iminodiacetic acid-functionalized polystyrene
resin (IDA resin). These resins are both chelating cation exchange
resins and are commonly used in the chlor-alkali industry for
secondary brine treatment, particularly AMP resin. This treatment
normally reduces the concentration of alkaline earth metal ions
such as calcium and magnesium to levels that are acceptable for use
in membrane electrolyzers. Typical membrane electrolyzers require
that the combined calcium plus magnesium concentration in the brine
be less than 20 ppb.
[0008] This combined primary and secondary brine treatment
procedure may be effective for reducing impurity concentrations in
brine solutions to levels specified for membrane electrolyzers. The
concentration of alkaline earth metals is particularly important
for membrane electrolyzer operation (20 ppb combined calcium and
magnesium). However, it has been found that when a brine solution
which results from a condensation polymer manufacturing process,
such as a polycarbonate manufacturing process, is treated by
primary and secondary brine treatment, the concentration of
alkaline earth metal cations in the treated brine exceeds the
tolerable level and the membrane electrolyzer separator becomes
plugged at an unexpectedly rapid rate, resulting in premature
failure.
[0009] After careful experimentation it has been discovered that
the cause of rapid membrane separator plugging during electrolysis
of such brine solution is the precipitation of alkaline earth metal
hydroxide species, primarily derived from residual calcium and
magnesium in the feed-brine, on the surface of and within the
electrolysis cell membrane separator. Analysis has revealed that
there is still a very low concentration of alkaline earth metal
cations present in electrolyzer feed brine even after primary and
secondary brine treatment. Without being bound by any theory, the
cause of this problem is believed to be the presence of a
water-soluble chelating agent in the brine solution. The chelating
agent apparently retains some fraction of the transition metal
cations as water-soluble complexes so that these complexed cations
are not precipitated as salts during primary brine treatment. These
complexed transition metal cations are more strongly bound to the
ion exchange resin than alkaline earth metal cations in secondary
brine treatment. Therefore, during ion exchange treatment
(secondary brine treatment) they displace alkaline earth metal
cations from the ion exchange resin into the brine solution. These
displaced alkaline earth metal cations then exit the ion exchange
column with the brine and cause precipitation on an inside the
membrane separator in the electrolytic cell. The chelating agent is
typically a sugar acid such as gluconate anion.
[0010] Gluconate anion is often added in the form of sodium
gluconate in condensation polymer manufacturing processes to form
water-soluble complexes with a fraction of the multivalent
transition metal cations such as iron (III), nickel (II), and
chromium (III). Complexation beneficially hinders transition metal
salts from precipitating in the manufacturing equipment and from
contaminating the polymer product. With iron (III), for example,
gluconate anion forms an iron-gluconate complex, thereby
solubilizing iron in the brine solution so that the polymer product
is produced substantially free of iron contamination. However, when
the brine solution undergoes primary brine treatment, the fraction
of a transition metal species such as iron (III) that exists as a
gluconate complex remains strongly chelated and thus remains in
solution through the end of primary brine treatment. These
transition metal gluconate complexes such as iron (III) gluconate
are much more strongly bound to both AMP and IDA resins than are
alkaline earth metal cations. Therefore, when brine that contains
iron (III) gluconate enters a bed of chelating ion exchange resin,
alkaline earth metal cations are displaced from the resin and are
dissolved in the brine, typically as gluconate complexes. Under
these conditions, it is not possible to achieve the 20 ppb alkaline
earth metal cation specification for brine leaving secondary brine
treatment. When brine containing metal-gluconate complexes such as
an alkaline earth metal-gluconate complex enters a membrane
electrolytic cell, the gluconate is substantially destroyed by
oxidation by chlorine, and at least a portion of the alkaline earth
metals precipitates on the surface of and inside the membrane. The
precipitated alkaline earth metal species gradually plug the
membrane and force lower production rates from the electrochemical
cell and lead to premature membrane failure.
[0011] Methods for removing metal cations from an aqueous solution
have been reported. Removal of multivalent metal cations from an
aqueous solution using a chelating ion exchange resin is known. For
example, Yokota et al. (U.S. Pat. No. 4,119,508) employ a chelating
ion exchange resin to remove calcium and magnesium cations from a
brine solution in the absence of a water-soluble metal chelating
agent. Kelly (U.S. Pat. No. 4,450,057) utilizes AMBERLITE.RTM.
IRC-718 chelating ion exchange resin (Rohm and Haas Company) to
remove aluminum (III) from brine at pH 2 to 3 in the absence of a
water-soluble metal chelating agent. Courduvelis et al. (U.S. Pat.
No. 4,303,704) utilize AMBERLITE.RTM. IRC-718 resin at either
acidic or alkaline pH to recover and reuse very high concentrations
of copper or nickel ions from non-brine aqueous solutions derived
from an electroless plating process and containing chelating agents
such as alkanolamines. However, these methods do not address
achieving membrane electrolyzer specification levels of alkaline
earth metal cations in brine solutions derived from a condensation
polymer manufacturing process and containing a water-soluble metal
chelating agent.
[0012] Commonly owned copending application 09/177,588 discloses a
method for increasing the life-time of a preferably diaphragm
separator in an electrolysis cell for electrolyzing brine solution
containing a water-soluble metal chelating agent.
[0013] Diaphragm separators are often composed substantially of a
porous asbestos or polytetrafluoroethylene. In contrast, membrane
separators often comprise a substantially non-porous polymeric film
ion exchange resin which selectively passes alkali metal cations
such as sodium, but not anions, from the anolyte solution to the
catholyte solution, and which substantially retards back-migration
of hydroxide anions from the catholyte solution to the anolyte
solution.
[0014] There is thus a need for a method which will substantially
reduce the concentration of multivalent metal cations, particularly
alkaline earth metal cations, in brine solution derived from a
condensation polymer manufacturing process and containing a
water-soluble metal chelating agent. Such a method provides a means
to retard the decrease of the lifetime of an electrolysis cell
separator, such as a membrane, by reducing the rate of
precipitation of metal species on the surface of and inside the
separator, thereby increasing the separator lifetime. It would
further be desirable to replace asbestos diaphragms with membrane
separators. Asbestos poses health and environmental issues.
Further, the supply of asbestos in the future is uncertain.
Commercially available non-asbestos diaphragm materials not only
permit the elimination of asbestos, a hazardous material, but also
have the potential for cost savings from lower electrical usage and
longer diaphragm life. Establishing a process that purifies
condensation polymer manufacturing brine that contains soluble
chelating agents to membrane electrolyzer specifications enables
use of membrane electrolyzers for conversion of such brines to
chlorine and caustic soda.
SUMMARY OF THE INVENTION
[0015] In one aspect, the invention relates to a method for
removing impurities from a brine solution, the brine solution
comprising a water soluble chelating agent, the method comprising
the steps of:
[0016] a) adjusting the pH of the brine solution to a pH of from
about 2 to about 4;
[0017] b) passing the brine solution through a first functionalized
resin; the first functionalized resin having functional groups
capable of removing multivalent metal cations from the brine
solution;
[0018] c) adjusting the pH of the brine solution to a pH of from
about 9 to about 11.5; and
[0019] d) passing the brine solution through a second
functionalized resin, the second functionalized resin having
functional groups capable of removing alkaline earth metal cations
from the brine solution.
[0020] The invention further provides a method to increase the
lifetime of a membrane separator in an electrolysis cell for
electrolyzing brine solution containing a water-soluble metal
chelating agent. It is preferable to pretreat the brine solution in
a primary brine treatment stage.
DETAILED DESCRIPTION OF THE INVENTION
[0021] The present invention may be understood more readily by
reference to the following detailed description of preferred
embodiments of the invention and the examples included therein.
[0022] Before the present methods are disclosed and described, it
is to be understood that this invention is not limited to specific
methods or to particular formulations, as such may, of course,
vary. It is also to be understood that the terminology used herein
is for the purpose of describing particular embodiments only and is
not intended to be limiting.
[0023] In the specification and claims which follow, reference will
be made to a number of terms which shall be defined to have the
following meanings:
[0024] The singular forms "a", "an" and "the" include plural
referents unless the context clearly dictates otherwise.
[0025] A "brine solution" is herein defined as an aqueous solution
of an alkali metal halide, including but not limited to, sodium
chloride, potassium chloride or a mixture thereof.
[0026] A "raw brine solution" is a brine solution which has not
been treated or purified. "Optional" or "optionally" means that the
subsequently described event or circumstance may or may not occur,
and that the description includes instances where the event occurs
and instances where it does not.
[0027] The raw brine solution as contemplated in the present
invention may be obtained as a by-product of a manufacturing
process, such as a condensation polymer manufacturing process.
Condensation manufacturing process that may produce brine as a
by-product include, but are not limited to, condensation processes
that produce polycarbonates, polyesters, polyarylates, polyamides,
polyamideimides, polyetherimides, polyethersulfones,
polyetherketones, polyetheretherketones, polyarylene sulfides,
polyarylene sulfidesulfones, and the like.
[0028] In a polycarbonate production process, for instance, aqueous
sodium chloride arises as a by-product when at least one bisphenol
is reacted in an organic solvent with phosgene or a carbonate
precursor such as an oligomeric carbonate chloroformate in the
presence of an aqueous alkaline earth metal hydroxide, such as
aqueous sodium hydroxide to produce a polycarbonate. Representative
polycarbonate and polycarbonate copolymers that can be made by such
a process include, but are not limited to, bisphenol A
polycarbonate; 3, 3', 5, 5'-tetramethyl bisphenol A polycarbonate;
3, 3', 5, 5'-tetrabromo bisphenol A polycarbonate, and mixtures
thereof.
[0029] Before recycling to an electrolysis cell, the concentration
of the alkali metal halide in the brine solution, for instance
sodium chloride, may be increased to obtain the most efficient
operation of the cell. The sodium chloride concentration, for
instance, may be increased by the addition of make-up salt. Make-up
salt is sodium chloride obtained, for example, from natural ground
deposits or from evaporation of sea water.
[0030] In the brine solution which is subjected to purification,
the amount of sodium chloride in solution ranges from a
concentration of about 50 grams per liter of solution to about that
concentration at which the solution is saturated with sodium
chloride at a given temperature. Preferably, the sodium chloride
concentration ranges from about 100 to about 320 grams per liter of
solution, more preferably from about 180 to about 315 grams per
liter of solution.
[0031] Typically, the brine solution by-product is separated from
the condensation polymer product and, after various treatment steps
to increase the concentration of sodium chloride and to remove
contaminants, is recycled to an electrolysis cell to produce
chlorine gas, sodium hydroxide solution, and hydrogen gas. Suitable
electrolysis cells may comprise an anode compartment and a cathode
compartment with an appropriate separator between the two
compartments to separate the anolyte solution and the chlorine gas
evolved at the anode from the catholyte solution and the hydrogen
gas evolved at the cathode within the cell. Optionally, the
separator may be at least partially porous to water. Commonly,
membrane separators are used to the separate the anode compartment
and the cathode compartment.
[0032] Membrane separators may comprise an ion exchange resin which
selectively passes alkali metal cations, but not anions, from the
anolyte solution to the catholyte solution and which substantially
retards back-migration of hydroxide anions from the catholyte
solution to the anolyte solution.
[0033] During operation of a membrane electrolysis cell, solid
species may gradually accumulate on the surface of and within the
membrane. This causes a general performance decline, in which the
current efficiency decreases and the cell voltage increases,
resulting in increased power consumption per unit chlorine
production. The effects of impurities on membrane cells are
documented in a report published by DuPont, "Effect of Impurities
on Membrane for Chloralkali Production", James T. Keating, E. I.
DuPont de Nemours and Company, Wilmington, Del., USA. Details of
the chloralkali process are given by L. C. Curlin, T.V . Bommaraju,
and C. B. Hansson in "Alkali and Chlorine Products: Chlorine and
Sodium Hydroxide", Kirk-Othmer Encyclopedia of Chemical Technology,
fourth edition, vol. 1, pp. 938-1025 (1991).
[0034] To maximize membrane lifetime and efficiency of electrolysis
cell operation, the brine solution before electrolysis is subjected
to purification steps to remove contaminants. Contaminants include
both those from the polymer manufacturing process and those from
make-up salt, which is often added to brine that is recycled from
the polymer manufacturing process. Typical contaminants include
phenolic species, organic catalyst and solvent residues, and metal
species such as alkaline earth and transition metal cations.
Purification steps to remove contaminants include one or more steps
of addition of carbonate and hydroxide ion to precipitate metals,
clarification, filtration, volatiles stripping, contact with an
adsorbent to remove polar organic impurities, and treatments such
as ion exchange to reduce the concentration of multivalent metal
cations.
[0035] Alkaline earth metal cations that are often present in the
raw brine solution include calcium and magnesium. The calcium and
magnesium concentrations in the raw brine solution may each
independently be in the range of about 0.005 parts per million
(ppm) to about 2000 ppm, preferably in the range of about 0.005 ppm
to about 400 ppm, and more preferably in the range of about 0.005
ppm to about 10 ppm. For maximum membrane lifetime and efficiency
of electrolysis cell operation the sum of the concentrations of
both calcium and magnesium in the purified electrolyzer feed brine
solution is most preferably in the range of less than about 20
ppb.
[0036] Multivalent cations, such as transition metal cations, that
are often present in the raw brine solution include iron, chromium,
and nickel. The iron, chromium, and nickel concentrations in the
brine solution prior to the purification process of the invention
may each independently be in the range of about 0.001 ppm to 100
ppm, preferably in the range of about 0.001 ppm to about 10 ppm,
and more preferably in the range of about 0.001 ppm to about 2 ppm.
For maximum membrane lifetime and efficiency of electrolysis cell
operation and in order to achieve membrane specification levels of
alkali metal cation levels in the membrane electrolyzer feed brine,
the concentration of iron and chromium in the purified brine
solution are most preferably each independently in the range of
about 0.001 ppm to about 0.1 ppm and the concentration of nickel in
the purified brine is most preferably below about 10 parts per
billion (ppb). In particular, it was found that the presence of
iron in the feed brine precludes achieving membrane specification
levels of alkaline earth metal cations in the purified brine and
causes fouling of membranes in electrolyzers.
[0037] Brine solutions, as contemplated in the present invention,
contain a water-soluble metal chelating agent which may form
water-soluble complexes with multivalent metal cations,
particularly transition metal cations. Typical water-soluble
chelating agents include N, N, N', N'-ethylenediarnine-tetraacetic
acid (EDTA), nitrilotriacetic acid (NTA), gluconic acid, and all of
their sodium salts. Sodium gluconate is particularly preferred in
the brine solutions of this invention. The preferred concentration
of water-soluble metal chelating agent in the brine solution prior
to the purification process of the invention is in the range of
about 10 ppm to about 2000 ppm, and the more preferred
concentration is in the range of about 50 ppm to about 1200
ppm.
[0038] In general membrane separators are more sensitive to
contaminants than diaphragm separators. Impurities which affect
membrane cell performance and which may be present in the brine
from a condensation polymerization process include, but are not
limited to, calcium, magnesium, strontium, barium, nickel, mercury,
aluminum, iron, and silica.
[0039] Impurities have different effects on the membrane and
different amounts of the various impurities may be present before
the system is fouled. For instance, calcium and magnesium at about
20 parts per billion (ppb) will begin precipitating in the membrane
as hydroxides. Strontium at about 500 ppb will begin precipitating
in the membrane. Barium at about 1 part per million (ppm) will
begin precipitating in the membrane. Sodium sulfate at
concentrations of about 10 grams/liter result in a decline in the
efficiency of the cell.
[0040] As mentioned, the brine solution comprises a water soluble
metal chelating agent, such as sodium gluconate. Water soluble
metal chelating agents, such as sodium gluconate, exhibit a strong
affinity for trivalent cations, such as ferric, chromium, and
aluminum ions, and a modest affinity for divalent cations, such as
calcium and magnesium. A process that removes multivalent cations
from a gluconate containing stream must, therefore, overcome this
interaction.
[0041] Complex metal-gluconate equilibria determine the composition
of a stream that contains multivalent metal ions such as iron or
calcium. These equilibria are strongly affected by the pH of the
brine solution. For example, the iron-gluconate interaction is very
strong under all alkaline conditions, from a pH of about 8 up to 35
wt % NaOH solutions. However, the interaction is relatively weak
under acidic conditions. For example, at pH 2.5, rather than being
complexed with gluconate, about 30% of the iron exists as free
ferric ion
[0042] It has been discovered that by modifying the secondary brine
treatment process, membrane specification levels of alkaline earth
metals in brines that are byproducts of condensation polymerization
manufacturing operations may be achieved. Specifically, it has been
discovered that if transition metals are first removed, the ion
exchange process for alkaline earth metal removal is able to
achieve membrane specification levels of alkaline metal
concentration in the brine.
[0043] Prior to the modified secondary brine treatment process, as
contemplated in the instant invention, the raw brine solution, from
a condensation polymerization reaction, for instance, preferably
undergoes primary brine treatment. Primary brine treatment helps to
minimize the impurities in the brine solution before secondary
brine treatment.
[0044] As mentioned, in primary brine treatment, the brine pH is
elevated to above about 10 in the presence of a molar excess of
carbonate ion in order to precipitate alkaline earth and transition
metals as their carbonates and/or hydroxides, followed by a
filtering and/or settling process such as clarification. This is
followed by acidification and stripping of the brine to remove
carbonate ion as well as volatile organic contaminants such as
organic solvents and dissolved catalysts. Additional treatment such
as adsorption may be utilized as necessary to remove organic
species such as monomer and low molecular weight oligomer from the
brine.
[0045] In the present invention, the adjustment of the pH to
produce some free ferric iron is utilized after primary brine
treatment. The removal of iron and other trivalent species in a
first stage is necessary to enable successful removal of divalent
alkaline earth metal cations in a second stage and thus achieve
membrane specification levels of alkaline earth metals in the
brine, which prevents fouling of the membrane.
[0046] In the present invention, a two stage process is employed,
preferably after primary brine treatment. In a first stage, the pH
of the brine solution is adjusted to a pH of from about 2 to about
4 and the brine solution is passed through a first functionalized
resin; the first functionalized resin having functional groups
capable of removing multivalent metal cations, including iron
cations, from the brine solution. In a second stage, the pH of the
brine solution is adjusted to a pH of from about 9 to about 11.5
and the brine solution is passed through a second functionalized
resin, the second functionalized resin having functional groups
capable of removing alkaline earth metal cations from the brine
solution.
[0047] In the first stage of the process of the present invention,
the pH of the gluconate-containing brine solution is adjusted from
its initial pH to a pH of from about 2 to about 4, more preferably
about 2.5 to about 3.5, even more preferably about 2.5. The initial
pH is typically weakly alkaline, pH 8-10, which is common for brine
storage after primary brine treatment. Typical means of adjusting
the pH to the desired range include addition to the brine solution
of a sufficient amount of at least one mineral acid. Hydrochloric
acid is particularly preferred in the application of the present
invention.
[0048] Following adjustment of the pH, the brine solution is then
intimately contacted with at least one resin bed comprising a first
functionalized resin. The first functionalized resin may be any
resin capable of removing multivalent metal cations, including but
not limited to, iron, nickel, aluminum or mixtures thereof.
[0049] Ion exchange resins suitable as the first functionalized
resin include, but are not limited to chelating ion exchange
resins. Chelating ion exchange resins that are effective for iron
removal include iminodiacetic acid functionalized resins (IDA) and
aminomethyl phosphonic acid (AMP) functionalized resins. Although
AMP functionalized resin has about 20% more iron capacity than IDA,
only about 13 to about 25% of the iron loaded onto AMP resin is
recovered during regeneration. For this reason, IDA functionalized
resins are preferred.
[0050] Commercially available IDA resins such as AMBERLITE IRC-718,
manufactured by Rohm & Haas Co. or LEWATIT TP207, manufactured
by Bayer, may be used in the first functionalized ion exchange
resin bed.
[0051] The first functionalized resins preferably have an ion
exchange capacity from about 0.1 milliequivalents of metal ion per
milliliter of resin to about 3 milliequivalents of metal ion per
milliliter of resin, and preferably from about 0.5 milliequivalents
of metal ion per milliliter of resin to about 1.5 milliequivalents
of metal ion per milliliter of resin.
[0052] Contact of the gluconate-containing brine solution in the
first functionalized ion exchange resin bed may be performed by
methods known in the art, such as batch, continuous, or
semi-continuous methods. In a preferred method, the brine solution
is passed through a column containing a bed of the first
functionalized ion exchange resin. Passage of brine through the
column may continue until the metal ion complexing capacity of the
resin bed is substantially exhausted as shown by an increase in the
concentration of contaminating metal ions in brine solution exiting
the column. When the metal ion complexing capacity of a resin bed
is exhausted, then a fresh resin bed is employed for treatment of
further brine solution. Exhausted ion exchange resin beds may be
regenerated according to methods known in the art. These include,
for example, acid treatment to strip cations from the resin bed
followed by base treatment to return the resin to the sodium form
prior to being placed back into service. Ion exchange processes are
described by C. Dickert in "Ion Exchange" Kirk-Othmer Encyclopedia
of Chemical Technology, fourth edition, vol. 14, pp. 760-770
(1995).
[0053] In the first stage, the brine is intimately contacted with
the first functionalized ion exchange resin bed in a continuous or
semi-continuous process and the flow rate of brine over the resin
bed ranges from about 1 resin bed volumes per hour to about 30
resin bed volumes per hour. More preferably, the flow rate in a
continuous process is in the range of about 8 resin bed volumes per
hour to about 25 resin bed volumes per hour. As used in the present
invention, a flow rate expressed as 10 resin bed volumes per hour
indicates, for example, that 5 gallons of the brine solution is
contacted with 0.5 gallons of a chelating ion exchange resin per
hour. The temperature for contacting the brine solution with the
ion exchange resin bed ranges from about 20.degree. C. to about
90.degree. C., more preferably from about 40.degree. C. to about
70.degree. C., even more preferably about 60.degree. C.
[0054] The brine solution recovered from treatment with the first
functionalized ion exchange resin contains a significantly reduced
concentration of multivalent metal cation contaminants. The amount
of multivalent metal cations that is removed depends, among other
factors, upon the initial metal cation concentrations, the pH to
which the brine solution is adjusted, and the volume of first
functionalized ion exchange resin with which the brine solution
comes into contact.
[0055] Typically, the concentrations of iron, chromium, and nickel
cations are each reduced to below their detection limits in the
brine solution following contact with the first functionalized ion
exchange resin. This is surprising in view of the strong
interaction between the metal cations and gluconate. Because of
this strong interaction, a fraction of multivalent metal cation
contaminants removed from the thus treated brine was present in the
form of water-soluble complexes with a metal chelating agent. In
particular, a substantial fraction of the iron removed as a
contaminant from the thus treated brine solution was initially
present in the form of a water-soluble gluconate complex.
[0056] After the passage of the brine from the first functionalized
resin, the pH of the brine solution is readjusted to a pH of from 9
to about 11.5. Typical means of adjusting the pH to the said range
include one or more steps of addition to the brine solution of a
sufficient amount of an alkali metal compound, such as an alkali
metal hydroxide.
[0057] Suitable alkali metal compounds which may be used to adjust
the pH in the brine solution include, but are not limited to,
sodium hydroxide, potassium hydroxide, lithium hydroxide or a
mixture thereof. Sodium hydroxide is preferred.
[0058] Following the adjustment of the brine solution to a pH of
from about 9 to about 11.5, preferably to about 10, the brine is
intimately contacted with a second functionalized ion exchange
resin bed in a batch, continuous, or semi-continuous process and
the flow rate of brine over the resin bed ranges from about 1 resin
bed volume per hour to about 25 resin bed volumes per hour, more
preferably between about 5 resin bed volumes per hour and about 15
resin bed volumes per hour. The brine is preferably passed through
the second functionalized ion exchange resin bed at a temperature
of from about 20.degree. C. to about 90.degree. C., preferably from
about 40.degree. C. to about 70.degree. C., even more preferably
about 60.degree. C.
[0059] The second functionalized ion exchange resin functions to
remove the "hardness" from the brine solution. As used herein,
"hardness" refers to alkaline earth metal cations, including but
not limited to cations of calcium, magnesium, barium, strontium or
mixtures thereof. The second functionalized resin may be any resin
capable of removing hardness. Amino methyl phosphonic acid
functionalized (AMP) ion exchange resins are preferred. Suitable
AMP resins include DUOLITE 467, manufactured by Rohm and Haas
company and LEWATIT OC 1060, manufactured by Bayer. It is necessary
to remove trivalent metal cations from the gluconate-containing
brine prior to introduction of the brine to the second
functionalized resin.
[0060] Although hardness is primarily removed in the second stage,
the first stage, comprising adjustment of the pH to from about 2 to
about 4 and passage of the brine solution through a first
functionalized resin, serves to protect the AMP resin from iron
contamination, as iron is essentially irreversibly adsorbed or ion
exchanged onto AMP resin.
[0061] Contact of the brine solution in the second functionalized
ion exchange resin bed may be performed by methods known in the
art, such as batch, continuous, or semi-continuous methods. In a
preferred method, the brine solution is passed through a column
containing a bed of the second functionalized ion exchange. Passage
of brine through the column may continue until the capacity of the
resin bed is substantially exhausted as shown by an increase in the
concentration of contaminating alkaline earth metal cations in the
brine solution exiting the column. When the metal ion complexing
capacity of a resin bed is exhausted, then a fresh resin bed is
employed for treatment of further brine solution. Exhausted ion
exchange resin beds may be regenerated according to methods known
in the art.
[0062] When brine solution from a polymer manufacturing process
treated by the method of the present invention is electrolyzed in
an electrolysis cell, the separator in such a cell exhibits a
significantly longer lifetime. The increased lifetime is due to the
decreased deposition on the surface of and within the separator of
solid species derived from contaminating multivalent metal cations
in the brine solution. In particular, a membrane separator in an
electrolysis cell exhibits a significantly longer lifetime using
brine treated by the method of the present invention.
[0063] This invention has been described in detail with particular
reference to preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention. In particular, although the
invention has been described in reference to a membrane
electrolyzer, the process as described may also be used in other
processes, for instance those utilizing a diaphragm for
separation.
EXAMPLES
[0064] The following examples are put forth so as to provide those
of ordinary skill in the art with a complete disclosure and
description of how the compositions of matter and methods claimed
herein are made and evaluated, and not intended to limit the scope
of what the inventors regard as their invention. Efforts have been
made to insure accuracy with respect to numbers (e.g., amounts,
temperatures, etc.) but some error and deviations should be
accounted for. Unless indicated otherwise, parts are by weight,
temperature is in .degree.C. or is at room temperature. In the
processes described, unless stated otherwise, the pressure is at or
near atmospheric.
Example 1
[0065] Brine was treated in two stages to achieve membrane
electrolyzer brine specification levels of hardness and heavy
metals. In the first stage, the brine was treated at low pH by an
iminodiacetic acid-functionalized chelating ion exchange resin (IDA
resin) to remove heavy metals. In the second stage, the brine was
treated at elevated pH with an aminomethyl phosphonic
acid-functionalized chelating ion exchange resin (AMP resin) to
remove hardness. The details of the two steps are given in Table
II. The brine contained 300 grams per liter (gpl) NaCl and 80 ppm
sodium gluconate. The crude and purified production brine
compositions are shown in Table I.
[0066] This example shows that the process of this invention may be
used to achieve membrane electrolyzer specification brine impurity
levels for hardness and heavy metals in the presence of 80 ppm
sodium gluconate.
1TABLE I Production Brine Composition Component Raw Brine Purified
Brine Specification Ca 0.6 ppm 11 ppb Ca + Mg Mg 0.2 ppm 7 ppb
<30 ppb Fe 0.3 ppm <0.07 ppm 0.5 ppm
[0067]
2TABLE II Brine Purification Conditions Step I Step II Resin Type
IDA-Functionalized AMP-Functionalized Polystyrene Polystyrene
(AMBERLITE IRC- (DUOLITE C-467) 718) Bed Volumes/hr 10 10 Feed pH
2.5-3.5 >11 Temperature 60.degree. C. 60.degree. C.
Example 2
[0068] This example shows that the process of this invention may be
used to achieve membrane specification brine impurity levels for
hardness and heavy metals in the presence of 350 ppm sodium
gluconate.
3TABLE III Production Brine Composition 300 gpl NaCl 350 ppm sodium
gluconate Component Crude Brine Purified Brine Specification Ca 2.8
ppm 6 ppb Ca + Mg Mg 10.2 ppm 0.4 ppb <30 ppb Fe .apprxeq.0.3
ppm <0.05 ppm 0.5 ppm
[0069]
4TABLE IV Brine Purification Conditions 300 gpl NaCl Step I Step II
Resin Type IDA-Functionalized AMP-Functionalized Polystyrene
Polystyrene (AMBERLITE IRC-718) (DUOLITE C-467) Space Velocity 10
10 (Bed Volume/hr) Feed pH 2.5-3.5 9-10 Temperature 60.degree. C.
60.degree. C.
Comparative Example 3
[0070] This example shows the necessity of removing iron before
removing hardness in gluconate-containing brines.
[0071] The feed brine contained 0.32 ppm iron, 2.0 ppm Ca, 0.81 ppm
Mg, and 390 ppm sodium gluconate. The brine contained 300 gpl
NaCl.
5 Feed pH 9-10 Feed Rate 3.3 bed volumes/hr Temperature 60.degree.
C.
[0072] In this case, only a single ion exchange step was performed
on the brine. An AMP type resin was used to treat the brine for
hardness removal without removing the iron and other heavy metals
first. The product hardness level was<10 ppm Mg and 50 ppb Ca,
which is above the membrane electrolyzer specification for calcium.
Without being bound by any theory, it is believed that the presence
of iron in the feed (as iron gluconate complex) interfered with the
ion exchange process for calcium by continuously displacing calcium
from the ion exchange resin.
Comparative Example 4
[0073] This example shows the necessity of removing iron before
removing hardness in gluconate-containing brines.
[0074] Feed Brine Composition:
[0075] 300 ppm sodium gluconate
[0076] 0.72 ppm Mg
[0077] 5.8 ppm Ca
[0078] 1.90 ppm Iron (Fe)
[0079] Feed pH 10.3
[0080] 60 degrees C
[0081] 50 gm resin (AMP resin)
[0082] 14 gm/min brine feed rate (12.6 bed volumes/hr)
[0083] The effluent composition is shown in Table V. This shows
that the ion exchange resin is unable to remove hardness to levels
required for membrane cell operation if the brine contains both
iron and gluconate. The higher effluent concentration of both Mg
and Ca (vs comparative example 3) is attributed to the higher level
of iron in this example (vs comparative example 3). This example
further shows that the iron was only partially removed under these
conditions.
6 TABLE V Hours Fe (ppm) Ca (ppm) Mg (ppb) 24 0.42 0.14 60 48 0.64
0.14 40 72 0.90 0.25 40 96 1.09 0.43 35 120 0.674 42.4
* * * * *