Note: Descriptions are shown in the official language in which they were submitted.
7~
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PROCESS FOR THE PREPARATION OF ION EXCHANGE
RESINS USING SEEDED POI.YMERIZATION TECHNOLOGY
The present invention relates to ion exchange
resin particles, and in particular, to those particles
that are prepared using seeded polymerization technology.
Ion exchange resins are typically prepared by
providing functional groups which have the capacity for
ion exchange to crosslinked copolymer particles or
beads. The copolymer beads provide a strong, insoluble
and rigid substrate for carrying the ion exchange
functional groups. Thus, the durability and hydraulic
characteristics of the ion exchange resin are generally
limited by those characteristics of the copolymer from
which it is derived.
Typically, ion exchange copolymers are prepared
using a batch process whereby monomer droplets are
formed and suspended in an aqueous phase, and polymerized.
Unfortunately, such a process can provide a wide distri-
bution of bead particle sizes. Thus, it becomes neces-
sary to mechanically screen the beads and/or ion exchange
resin particles in order to obtain a desirable product
r t
~"';j~'iY
~ 32,637-F -1-
.
7706D~
having a relatively uniform or narrow distribution of
bead size.
In a batch seeded process, for example, a
lightly crosslinked copolymer seed can be s~lellad irl
the presence of a monomer mix containiny an initia-tor
and a crosslinker. The imbibed monomer mixture is
polymerized in situ by a standard suspension pol~meri-
zation process. Such particles have very high physical
strengths. The copolymer particles are then function-
alized by chemically treating the insoluble, crosslinkedbead in order to attach an ion exchange group thereto.
Although the batch seeded process provides
the skilled artisan with a means for preparing relatively
highly uniformly sized particles, the particles so
prepared can exhibit several disadvantages. For example,
an ion exchange resin which is prepared using the batch
seeded process may not provide sufficient ion exchange
properties, or bed operation time before breakthrough
may be very short. In addition, if such ion exchange
resins are stirred in relatively pure water, a cloudy
aqueous suspension may be observed to form. It is
believed that insoluble organic materials which leach
out of the resin particle provide this undesirable
contamination of the water. Thus, the resin particles
which have highly desirable physical characteristics
are not acceptable for use in applications such as
water treatment.
In view of the deficiencies of the prior art,
it would be highly desirable to provide ion exchange
resin particles having relatively uniform particle
sizes, good physical characteristics, good ion exchange
32,637-F -2-
i4
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proper-ties, and a minimal amount of leachable organic
specles .
This invention is a seed process for prepariny
improved crosslinked copolymer particles capable of
being functionalized to provide ion exchange copolymer
particles having a high capability of wi-thstanding
osmotic shock during use, which process comprises:
(a) forming an agitated a~ueous suspension
of polymerized, lightly crosslinked seed
particles, and
(b) contacting said suspended seed particles
with a monomer or monomer mixture
comprising a minor amount of the total
crosslinking monomer which is employed
in order to ultimately produce a seed
swollen by imbibition of said monomer or
monomer mixture and polyvinyl cross-
. linking monomer, and
(c) contacting the suspended swollen seeds
with a suspending agent in an amount
sufficient to provide suspension of said
swollen seeds, prevent substantial
agglomeration of swollen seeds, and also
allow further imbibation of ~onomer, and
(d) subjecting the suspended swollen seeds
to polymerization conditions to the
extent that at least subs-tantial polymer-
ization of imbibed monomers occurs, and
(e) substantially stopping the polymerization
reaction and contacting the partially
polymerized particles wi-th a second
monomer or monomer mixture comprising a
32,637-F -3-
~77~
--4--
major amount of the total crosslinking
monomer which is employed, and
(f) subjecting the further imbibed swollen
seed to polymerization conditions in
order to provide a copolymer bead.
In another aspect, this invention is a seed
process for preparing improved crosslinked copol~mer
particles capable of being functionalized to provide
ion exchange copolymer particles having a high capabllity
of withstanding osmotic shock during use, which process
comprises:
(a) forming an agitated aqueous suspension
of polymerized, lightly crosslinked seed
particles, and
(b) contacting said suspended seed par-ticles
with a monomer or monomer mixture
comprising a minor amolmt of -the total
polyvinyl crosslinking monomer which is
employed in order to ultimately produce
a seed swollen by imbibition of said
monomer or monomer mixture and cross-
linking monomer, and
(c) contacting the suspended s~ollen seeds
with a suspendin~ agent in an amount
sufficient to provide suspension of said
swollen seeds, prevent substantial
agglomeration of swollen seeds, and also
allow further imbibition o~ monomer, and
(d) subjecting the suspended swollen seeds
to polymerization conditions to the
extent that at leas-t substantial polymer-
ization of imbibed monomers occurs, and
: 32,637-F -4-
-' .
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~77~)6~
(e) contacting the partially polymerized
particles with a second monomer or
monomer mixture comprising a major
amount of the total crosslinking monomer
which is employed, while controlling the
rate of addition of the monomer mixture
and polymerization condi-tions .such tha-t
the monomer mixture can be imbibe~ into
the swollen seed which is under polymer-
ization conditions and polymerization
continued to provide a compolymer bead.
The copolymer particles prepared via the
process of this invention can be functionalized to
provide ion exchange resin beads, which resin beads
have good osmotic shock and mechanical resistances to
breaking. That is, for example, functionalized copolymer
particles prepared via the process of this invention
possess crush strengths (i.e., mechanical load reguired
to break individual resin beads) of at least 500 g/bead
crush strength and a resis-tance to osmotic shock such
that when said particles are contacted with 10 cycles
of alternating trea-tments with 8 molar sodium hydroxide
and 8 molar hydrochloric acid, separated by backwashings
with deionized water, fewer than about 15 percent by
number of the particles are broken. One full cycle o
said treatment comprises ~a) immersing a quantity of
beads into 8 M HCl for one minute, (b) washing with
deionized water until the wash water is neutral,
(c) immersing the beads in 8 M NaOH for one minute and
(d) washing the beads with deionized water until khe
wash water is neutral. All references to alternating
treatments with 8 M HCl and 8 M NaOH contained herein
refer to repeating cycles of this test. The resistance
to osmotic shock of the beads is measured by the mlmber
32,637-F 5-
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.
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of beads which remain unbroken after 10 cycles of the
test. Typically, at least 85 percent of the function-
alized beads of this invention will remain unbroken
after 10 cycles of the osmotic shock test. Ion exchanye
resins can be either anionic or cationic in nature.
Such ion exchange resins are use~ul for a wide varie-ty
of applications known in the art. Of particular interest
is the treatment of aqueous fluids in ordex to obtain
highly pure water.
The monoethylenically unsaturated monomers
useful herein are those commonly employed in the produc-
tion of ion exchange resins. Examples of suitable mono-
mers are disclosed in US 4,419,245. Reference is made
to Polymer Processes, edited by Calvin E. Schildknecht,
published in 1956 by Interscience Publishers, Inc.,
New York, Chapter III, "Polymerization in Suspension"
by E. Trommsdoff and C. E. Schildknecht, pp. 69-109
for purposes of illus-tration. In Table II on pp. 78-81
of Schildknecht are listed diverse kinds of monomers
which can be employed in the practice of thls invention.
Styrene is the most preferred monomer.
Suitable crosslinking monomers are preferably
those polyethylenically unsaturated monomers including
those listed in U.S. Paten-t No. ~,419,245. The preferred
polyethylenically unsatura-ted monomer is divinylbenzene.
The crosslinked seed particles useful in this
invention are those which are lightly crosslinked in
order to achieve the degree of swelling required to
32,637-F -6-
~L~t77~6~
--7--
produce the final copolymer products of the desired
size. Preferably, the seed particles are spheroidal
beads derived from polymerized monoethylenically unsa-t-
urated monomer(s) and a crosslinking agen-t -therefor.
The crosslinking agen-t is preferably a polyethylenicall~
unsaturated monomer. Generally, the amount o~ cross-
linking agent in the seed can range from about 0.1 to
about 3 weight percent, based on the weight of total
monomer used in preparing the seed.
Typically, the amounts of each of the mono-
and polyethylenically unsaturated monomers most advan-
tageously employed in the preparation of the seed and
seeded bead depend on a variety of factors including
the type of each monomer employed and the desired size
of the seed, seeded bead and resulting ion exchange
bead. In addition, the amount and type of the mono-
and polyethylenically unsaturated monomers employed in
preparing the seeded bead from the seed bead (i.e., those
monomers imbibed by the seed bead) most advantageously
employed herein will also vary depending on the size
(i.e., diameter) and composition (i.e., the amount and
type of monomers) of the seed bead. In general, the
seed and seeded beads are advantageously prepared using
amounts of the mono- and polyethylenic monomers such
that the seeded beads can be converted in~o ion exchange
resin beads via techni~ues such as sulfonation, chloro-
methylation, amination, and the like. The resulting
functionalized beads when completely saturated with
water preferably have a particle size of 0.3 mm to
1.O mm and exhibit improved integrity (i.e., spheroidal
character) and increased resistance to osmotic shock
when compared to a conventionally prepared copolymer
bead functionalized usiny similar conditions.
32,637-F -7-
36
--8--
The size of the seed can vary. Typically,
the size varies from 100 ~m to 600 ~Im, preferably from
about 200 ~m to about 400 ~Im. The seed is generally
swelled from about 1.5 to about 2.2 times its original
diameter. It is imbibed with monomer to about 3 to
about 10 times its original ~leight.
Polymerization initia-tors useful herein
include those initiators useful in the preparation of
the seed bead. Preferably! the aqueous suspension of
seed particles is contacted with the initiator along
with the first monomer mixture comprising the minor
amount of polyvinyl crosslinking monomer. Preferably,
the initiator is a conventional chemical initiator
useful as a free radical generator in the polymerization
of ethylenically unsaturated monomers. Representative
of such initiators are W radiation and chemical
initiators including azo compounds such as azobisiso-
butyronitrile; peroxygen compounds such as benzoyl
peroxide, t-butyl peroctoate, t~butyl perbenzoate and
isopropylpercarbonate; and the like. Several catalysts
are disclosed in U.S. Patent Nos. 4,192,921; 4,246,386;
and 4,283,499. The initiator is employed in an amount
sufficient to cause the copolymerization of the monomeric
components in the monomer mixture. Such amount will
generally vary depending on a variety of factors
including the type of initiator employed, reaction
temperature, the composition of -the seed bead and the
type and proportion of monomers in the monomer mixture
imbibed thereby. Generally, the initiator is employed
in amounts from 0.02 to 1, preferably from 0.05 to 0.5,
weight percent based on the total weight of the monomer
mixture.
32,637-F -8-
~L~770~i~
_9_
The seed beads are advantageously suspended,
using relatively high agita-tion rates, in a sui-table
suspending medium such as water or other aqueous liguid.
Suspending agents are most preferably added af-ter the
first monomer mixture has been allowe~ to imbibe into
the seed. Suspending agents useful herein are those
materials which assist in maintaining a more uniform
dispersion of the swollen seed beads in the aqueous
liquid. Although the suspending agents most advan-
tageously employed herein are dependent on the type andamount of monomers employed in preparing the swollen
seed bead, in general, suspending agents conventionally
employed hereto in the suspension polymerization of
mono- and polyethylenically unsaturated monomers are
advantageously employed. Representative of such suspending
agents are gelatin, polyvinyl alcohol, sodillm, dodecyl
sulfonate, sodium methacr~late, magnesium silicate,
sodium cellulose glycolate, hydroxyethylcellulose,
methylcelluloses and the like. Suitable suspending
agents are disclosed in U.S. Patent No. 4,419,245. The
amount of the suspending agent employed is dependent on
a variety of factors and is advantageously that amount
which prevents agglomeration of the swollen seed beads
but does not prevent further imbibition of monomers.
Typically, from 0.05 to l.0 weight percent, o~ the
suspending agent, based on the weight of the aqueous
phase is advantageously employed.
While the amount of the suspending medium
advantageously employed herein, will vary depending on
the type and amount of the suspending agent and swollen
bead, in general, the suspending medium is employed in
amounts from 30 to 70, preferably from 40 to 60, weight
32,637-F -9-
~770~ -
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percent based on the weight of the swollen seed beads,
i.e., the wei~ht of the seed bead and monomer mixture.
The process of this invention involves t~lO
critical stages in the preparation of -the copolymer
bead. The first s-tage involves suspending the seed
under conditions such that imbibition of monomers which
are contacted with the seed can occur. That is, upon
contacting the seed bead with the monomer mixture, -the
seed bead swells, which swelling is believed to be due
generally to the absorption of monomer mixture by the
seed bead. The monomer can be added continuously or
batchwise. The initiator can be added to the medium or
added along with the monomer. The seed bead can be
suspended during imbibition using suitable agitation
conditions.
It is preferable in the first stage of the
preparation that for reasons of mechanical strength of
the final resin bead, the monomer mixture includes a
minor amount of the crosslinking agent which is employed.
That is, 1 to 15, preferably 1 to 10, most preferably
1 to 5, weight percent of the total amount of cross-
linking agent which is employed is added in the first
stage.
The temperature employed to polymerize the
imbibed monomers in the first stage can vary depending
upon the choice of initiator. Polymerization is generally
conducted at temperatures between 50C and 100C, pre-
ferably between 60C and 90c, most preferably 8~C.
32,637-F -10-
~Z7~7~i4
In one aspect of this invention, before the
second stage of process is commenced, it is necessary
to remove the reaction mixture from a state of polymer~
ization conditions. In addition, it is highly desirable
that polymerization conditions be cease~ before -total
polymerization has occured. If desired, polymerization
of imbibed monomer can be substantially comple-ted.
This typically occurs when the seeded, swollen bead
reaches its gel point. Advantageously, polymerization
in the first stage should continue until 40 to 80 per-
cent monomer conversion to polymer. This typically
means lowering the temperature of the reaction mixture
such that the second mixture of monomers can be con-
tacted and imbibed into the swollen seeds without
significant latex formation. If desired, the second
stage monomer mixture can include a suitable amount of
initiator.
The second stage of the polymerization process
is commenced after the second monomer mixture has been
contacted with the partially polymerized bead. This is
believed necessary in order to allow the second monomer
mixture to be imbibed into said bead. The second stage
monomer mixture includes a major amount of -the cross-
linking agent which is employed. That is, 85 to 99,
preferably 90 to 99, most preferably 95 to 99, weight
percent of the total amount of crosslinking agent which
is employed is added in the second stage. The reaction
mi~ture is subjected to polymerization conditions until
essentially total polymerization of the monomer has been
achieved. The polymerization reaction is th~n finished,
for example, by raising the reactor temperature.
32,637~
1277
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In another aspect of this invention, the second
stage of the process involves a continuous feed of the
second monomer mixture to the suspended swollen, partiall~
polymerized seeds. I-t is not necessary to remove the
reaction mixture from a state o~ polymeriza-tion conditio~s.
That is, by controlling the feed rate of the addition of
the second monomer mixture, the suspension conditions,
the rate of reaction, and the like, it is possible to
continuously imbibe the second stage monomer mixture into
the swollen bead, which is subjected to polymerization
conditions where the imbibed monomers continue to undergo
polymerization.
The amount of various monomeric components in
the first stage monomer mix can range from 0.5 to 5
weight percent crosslinking agents, and from 95 to 99.5
weight percent monethylenically unsaturated monomer(s).
The amount of various monomeric components in the second
stage monomer mix can range from 5 to 20 weight percent
crosslinking agent, and from 80 to 95 weight percent
monoethylenically unsaturated monomer(s). The amount of
second stage monomer mixture relative to the first stage
monomer mixture can range from 50 to 80 weight percent
based on the total weight of the monomer mixtures, subject
to the limitation that the amount of crosslinking agen-t
e~ployed in the second stage mixture is a major amount
based on the total amount of crosslinking agent which is
employed. That is, the amount of crosslinking monomer
employed in preparing the final resin is 2 to 18, pre
ferably 5 to 15 percen-t based on the total amount of
organic material (i.e., seed plus polymerizable monomer).
32,637-F -12-
l3
The time periods over which each of the two
(i.e., first or second) polymerization stages occur can
vary as long as the desired species are obtained in each
case. For example, the first stage monomer mixture can
be added to the seed suspension either batchwise or
continuously and subjec-ted -to polymerization con~i~ions
over a period ranging from 2 to 8 hours. The second
stage monomer mixture is added either batchwise or con-
tinuously, preferably over a period ranging from 3 to 5
hours. If batch addition is employed, the imbibition is
preferably carried out at 20C to 50C and is allowed to
occur, preferably with suitable mixing, for a period of 1
to 3 hours. The polymerization conditions are maintained
in the second stage polymerization step for 8 to 14
1~ hours. Finishing the reaction is performed for 1 to 3
hours, preferably at temperatures from 90C to 120C.
Following polymerization, the resulting seeded
beads are recovered from the reaction media using con-
ventional techniques, such as filtration, and the
recovered beads are washed and dried. Functional groups
are provided to the beads using known technlques. That
is, copolymer beads are converted to anion and cation
exchange beads. Beads can be fractionated lnto various
size ranges using techniques such as screening.
The following examples are presented to further
illustrate ~ut not limit the scope of this invention~
Example 1
Into a 1-gallon (3.79 x 10 3 m3) stainless
steel reactor equipped with an agitator were'loaded 875
grams (g) deionized water, 130 g of 0.3 percent cross-
linked styrene/divinylbenzene copolymer seed of -50~70
32,637-F -13-
~ ~77a~6~
-14-
mesh (from 210 ~Im to 297 ~lm) particle size with agi-tation,
and 300 g of monomer I, comprising styrene and 1.3 percent
active divinylbenzene, 0.05 percent active t-but~llper-
octoate (TBP0) and 0.16 active percent t-butylperbenzoate
(TBPB) based on monomer I. After 30 to 60 minu~es of
swelling time, 325 g of an aqueous solution of 6 g ye:La~in
and 0.3 g sodium lauryl sulfate stabilizers, and 3.3 g
sodium dichromate latex inhibitor was added. The reactor
temperature was raised to and maintained at 80C for 4 -to
- 10 6 hours. The reactor mass was cooled to 40C, and 860 g
of monomer II con-taining styrene and 14.5 percent active
divinylbenzene was added to reactor and after 60 to 120
minutes of swelling time~ the reactor mass was heated to
85C, 95C, and 110C for 12, 1.5, and 1.5 hours each,
successivel~.
The copolymer, thus, made after appropriate
screening was checked for crosslink density and then
converted into a strong acid cation e~change resin.
Fifty grams of the copolymer thus obtained was sulfonated
to a cation exchange resin. The resin after appropriate
washing was tested for capacity, crush strength, osmotic
shock resistance, and water quality. A mixture of 50 ml
each of resin and water was vigorously stirred magnetically
for 30 minutes and the aqueous layer examined for clari-ty.
Example 2
Into a reactor as described in Example 1 was
charged 850 g deionized water, 215 g of 0.3 percent
crosslinked styrene/divinylbenzene copolymer seed of
-50-~60 mesh (from 2.10 ~m to 297 ~m) particle size with
agitation, and 215 g of monomer I containing styrene and
1.7 percent active divinylbenzene, 0.036 active percent
TBPO and 0.05 percent active TBPB. After 30 to 60 minutes
32,637-F -14-
7C3~
~15-
of swelling time, 325 g o~ an aqueous solution of the
previously described stabilizers and latex inhibitor WclS
added. The reac-tor was sealed, purged with nitrogen and
the temperature of the mixture ~las raised to 80C, 95C
and 110C for 8, 1.5 and 1.5 hours, respectively. '~he
reaction mixture was cooled to ~0C, and 995 g o~ monomer
II containing styrene and 13.9 percent divinylbenzene,
0.015 percent TBPO and 0.05 percent TBPB was added to the
reactor. The mixture was allowed 60 to 120 minutes
swelling time. The reaction mixture was heated at 85C,
95C and 110C for 10, 1.5 and 1.5 hours, respectively.
The copolymer beads were isolated and converted to strong
acid cation exchange resins.
Example 3
Into a 20 gallon (75.7 x 10 3 m3) stainless
steel reactor equipped with an agitator were charged 70
lbs. (31.75 kg) of deionized water and with stirring,
13.3 lbs. (6.03 kg) of 0.3 percent divinylbenzene cross-
linked polystyrene seed of -50+60 mesh (from 210 ~m to
297 ~m). Also charged was 20 lbs. (9.07 kg) of monomer I
containing styrene, 1.44 percent active divinylbenzene,
0.26 percent active TBPO and 0.22 percent TBPB. After 30
to 60 minutes of imbibing time, 20 lbs. (9.07 kg) of an
a~ueous solution of 228 g gelatin and 20 g sodium lauryl
sulfate suspending agent, and 11.5 g sodium dichromate
latex inhibitor was added to the mixture. The reactor
was purged with nitrogen and the reaction mixture was
heated to 80C. After 90 to 120 minutes at 80C to the
reaction mixture was added 66.7 lbs. (30.25 kg) of monomer
II containing styrene and 15 percent active divinyl-
benzene, over a 5 hour period, while polymerization
conditions were continued. The reactor was maintained at
80C for an additional 5 to 7 hours. At that time the
32~637-F -15-
~Z~7V6
--16~
reactor mixture temperature was raised to 95C and 110C
for 1.5 and 1.5 hours, respectively. The copolymer beads
were isolated and conver-ted to strong acid cation exchange
reslns.
Exam~ e 4
Copolymer particles were prepared employlng the
procedures generally described in Example Mos. 1-3.
These samples were compared to beads prepared using a
conventional methods of preparation as follows:
Into a l-gallon (3.79 x 10 3 m3) stainless
steel reactor equipped with an agitator were loaded 875 g
of water and 375 g of 0.3 percent crosslinked s-tyrene/-
divinylbenzene copolymer seed of -40~45 mesh (from 354 ~m
to 420 ~m) particle si~e with agitation. To the suspended
seed particles were added 875 g of monomer mix containing
15.6 percent active divinylbenzene, 0.036 percent active
TBPO, and 0.05 percent active TBPB. The monomer was
allowed to imbibe for 30 to 60 minutes and then 375 g of
an aqueous solution containing a suspending agent and an
aqueous phase inhibitor was added. The reaction mixture
was then heated to and maintained at 80C for 8 hours,
and the temperature raised to 95C and 110C for 90
minutes each, respectively. The copolymer beads were
isolated and converted -to strong acid cation exchange
resins.
Properties of the various sulfonated samples
of this invention exhibit excellent osmotic shock
properties (i.e., greater than 95 unbroken bea~s after
10 cycles of alternate treatments with 8 M ~Cl and 8 M
NaOH, separated by backwashings with deionized water).
In addition, when 50 ml of beads aFe placed in 50 ml
32,637-F -16- -
- ~, . , ~ .
~L~7~ 4
deionized water and agitated for 30 minutes, heads of
this invention yield clear solutions, whereas such a tes-t
performed using the beads prepared using the previousl~
described conven-tional procedure yield cloudy solutions.
Exa~
Into a 1 gallon (3.79 x 10 3 m3) stainless
steel reactor, equipped with an agitator, were loaded
750 g deionized water, 215 g of 0.3 percent crosslinked
styrene/divinylbenzene copolymer seed of -50+60 mesh
(from 210 ~m to 297 ~m) particle size with agitation and
215 g of monomer I, containing styrene and 1.7 percent
active divinylbenzene, 0.075 percent active TBPO and 0.25
percent active TBP~. After 30-60 minutes of swelling
time, 325 g of an aqueous solution of stabilizer and
latex inhibitor was added. The reactor temperature was
raised to and maintained at 80C for 6 hours. The
reactor mass was cooled to 40C and 640 g of monomer II
containing styrene and ~.8 percent active divinylbenzene
was added to the reactor. After 60 to 90 minutes of
swelling time, the reactor mass was heated to 85, 95
and 110C for 10, 1.5 and 1.5 hours, each successively.
The copolymers thus made, after appropriate washin~ and
drying, were checked for toluene swell crosslink density
and converted to both anion and cation resins,
respectively.
.
32,637-F -17-
