Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~26~2~
IMPROVED METHOD AND COMPOSITIONS FOR
CLEA~ING ORGANICALLY FOULED ANION
EXCHANGE RESINS
Field of The Invention:
The present invention pertains to an improved method and
composltlons for cleaning organically fouled anionlc exchange
resins.
Background: The fouling of anion resins-has posed a prob-
lem that has confronted ion exchange applications since their incep-
tion. Humic substances found in surface waters are high molecular
weight polyfunctional organic ac~ds (both carbo~ylic and phenolic)
formed ~rom the breakdo~n of plant and animal materials. In deminer~
alizer operations, the large organic molecules may coat the resin
bead, block~ng and/or entering the pores of an an~on exchange resln.
These organics are retained because of a high affinity for ~he ex-
change sites and hydrophobic interactions with ~he po1ymer backbone
ol~ the resin~
Since the diffusion rates of the organics within the res~n
are usually slower than those of inorganic ions9 not all of the bonds
linking the organic acids to the resin are broken during the regener-
ation cycle. This situation results 1n only partial regeneration of
the resin and excessive rinse times following regeneration. In
severe cases, the resin may become "-irreversibly" fouled. To allevi
ate these problems, out-of-service brine or brine/caustic cleaning
1,
~22~6~
has traditionally been performed. I~ has alsu been suggested that
sodium hypochlorite may also be used as such a cleaning treatment.
However, resin degradation may o:cur with use of such a strong oxi-
dizing agent. Other prior art cleansing compounds and methods are
disclosed ln U.Sq Patent 3,536,637 (Noll et al) and U.S. Patent
3~748,285 (Wiltsey).
Another approach has been suggested in U.S. Patent
4,1539761 (Marsh). Specifically, Marsh teaches the use of aqueous
solu~ions comprising hydrogen peroxide, ozone, or sodium peroxide.
To be sure9 ~he use of such compounds has proven ePfective insofar as
the resin cleaning function is ccncerned. However, as is well known,
hydrogen peroxide in aqueous solltion is extremely unstable~ More-
over, when concentrated and in d~,rect contact ~ith impurities, explo-
sion may occur. Simllar comment; can be made with respect to sodium
peroxide and ozone itself.
Accordingly, there remLins a need in the art for the provi-
sion of an effective anionic exc~ange resin cleaner ~hat ~s generally
as effect1ve as hydrogen peroxidl! ln its cleaning function and is
safe ~or commercial use and tran;port from manufacturer to customer
; 20 location.
Detailed Description
I have surprisingly found that organic foulants are effec-
tively cleansed from anionic exchange resins by the use of aqueous
solutions compr~sing a water soluble inorganic peroxide salt having a
peroxy containing anion selected from the group consisting of per-
borate, persulfate and percarbonate an~ons. The cation of the perox-
~de salt may be any cation which is non-oxidizable upon dilutlon of
water and which renders the peroxide salt water soluble. Exemplary
catlons include, but are not 11mited to, Na nd K.
~2~:6~
Preferred inorganic peroxide salts include sod~um per-
borate, sod~um persulfate and sodium percarbonate. At present5 sodi-
um perborate is most highly preferred for commercial use. Utiliza-
tion of these compounds allows the manufacturer to provide a dry,
stable product that is more safely transported to khe customer
location, in contrast to the suggested use of hydrogen peroxide made
by Marsh. Moreover, upon rece~pt of the dry product from the manu-
facturer, the end-user may simply add water to the product on an as
needed basis prior to cleansing of the fouled res~n thereby.
As the resln cleaning agents of the present ~nvention are
ideally suited for use in combination with the tra~itional use of
brine (NaCl), the brine may read~7y be incorporated into the dry,
stable compos~tion of the water soluble inorganlc peroxide salt. The
end user may then derive the benefit of improved anion resin cleans-
lS ~ng simply by adding water to the dry composition an~ contacting the
resin with the resulting aqueous composltion.
In many instances, it has been found desirable to mix the
water soluble peroxide salt directly wlth an inorganic chela~ing
agent such as tetrasodium pyrophosphate and pentasodium tripolyphos-
phate for the purpose of complexing ~ron wh;ch normally accompaniesorganic foulants.
The presently preferred composition comprises sodium per-
borate 90% (weight), tetrasodium pyrophospnate 5% (weight) and
sodium tetraborate 5% (weight) an inert lnorganic salt.
Exemplary sompositions, in accordance with the invention,
may comprise:
~2~2~
Compos~tion one: 5 - 99X (weight) sodium perborate,
remainder ~norgan~c chelating agent
Compos~ion ~wo: 80 - 95% sodium perborate
2.5 - 10% inert organic salt, such as sodium
tetraborate
2.5 - 10% inorganic chelating agent, with
the fore~oing percentages adding up to 100%
Composi~ion three: 5 - 99% (weight) sodlum perborate,
remainder NaC~.
Although the resin cleaning agents of the invention are
preferred for use in the cleansing of strong base anionic res~nsJ
they may also be employed ln the cleansing of weak base anion
exchange resins~
At the end user locat~on it is preferred to add water to
the dry water soluble peroxide salt composition and to add brlne and/
or caus~c to the extent necessary so that the resulting aqueous com-
position comprises abo~t 0.1 - abnu~. 30X (weigh~) peroxide salt,
about 1 - 5% caustic and, 0 - 30% brine, rPmainder water.
. ~
The invention will now be further described w~th reference
to a number of specific e~amples wh~ch are to be regarded solely as
illustrative and not as restricting the scope of the invention~
In order to demonstrate the efficacy of the resin cleaning
agents in accordance with the invention, effluent from a treated
6~
resin was analyzed to ascertain the Total Or~anic Carbon (TOC) con-
tent thereof. Samples treated in accordanc~ with the invention were
comparecl to control values. TOC content higher than control values
~ndicates efficacy of the cleaning agents.
TOC measurements were made by a ccmbustion/I.R.
spectroscopy method in which all of the organic carbon found in the
effluent is first converted to C02 which is then detected by I.R~
analysis.
Table I hereinbelow gives ~he results for materi als evalua-
~ed as cleaning agents ~n demineral k ed water three-hour static soak
tests ~n combination with caustic and brine. In each instance in
which a material in accordance with the invention was tested~ only a
1~ (weight) aqueous solution of each was used.
Table I
~ ~L~L_ts
Under Static Soak Condition!,
STRONG BASE RESIN
ProGedure - 50 grdms ~f a drainea~ fou7ed res~n were p7aced
in a 600 ml beaker. Each tested cleaning solution comprised a 1%
(weight) concentration of the cleaning agent along with 10% NaOl and
1% Na~H In demineralized waterD The thus treated resins were agi-
tated and then allowed to stand at room temperature over a three hour
period. The TOC of ~he resulting effluents was then determined in
accordance with the combustiontI.R. spectroscopy method outlined
above.
~_f2d ~
--6--
Treatment TO
.
Brine C~ustic Control 3240
NaC10
NaB03 4H20 (perborate) 3780
Table II gives the test results for two different fouled
strong base resins cleaned with sodium perborate in brine-caustic.
These data show an Increase in e~f~cacy with the sodium perborate
over bline caustic alone. The use of sodium perborate in brine-caus-
tic as an alternative to sodium hypochlorite was indicated by these
test re!,ults.
TABLE II
__
EYPLUATION OF SODIUM PERBORATE IN STATIC SOAK TESTS
(BRINE-CAUSTIC)
-
% Increase
Resin P~ (Same as resin tested in Table I).
1% NaCH 70
10% Na~l 2100
10% NaCl + 1% NaOH - Control 2521
lG% NaCl ~ 1% NaOH ~ 1% NaB03 4 H202950 17
lOg NaCl + 1% NaOH + 1% NaB03 4 H2032~C 29
10% NaCl ~ lX NaOH + 1% NaC10 3450 37
~2~Z620
TABLE I I
(Cont~nued)
X Increase
Res~n B TOC (ppm) In Efficacy
10% NaCl ~ 1% NaOH - Control 663
lG% NaCl ~ 1% NaOH ~ 0.2% NaB03 4 H20 765 15
10% NaCl + l~ NaOH + Q~4% NaBO3 4 H20 867 31
10% NaCl ~ 1% NaOH ~ 0.6% NaB03 4 H20 765 15
10% NaCl ~ 1% NaOH + 0.~ NaB03 4 H20 714 8
10% NaCl ~ 1% NaOH ~ 1.0~ NaB03 4 H20 816 23
Test Conditions
Par~ A - Three-hour stat1c soak test same as Table I.
Par~ B - Resin samples cleaned for one hour ln brine-caustic only9
drained and r~nsed two times with demineralized water.
Brlne-caustic or sodium perbora~e in brine caustic is then
added to the precondit~oned resin. The length of the
second static soak was one hour.
As Cleaning Agents for Weak Base Resin -
Beaker Tests
In accordance with the procedure reported above for Table
I, 50 grams of a weak base resln was ~ested for TOC effluent content
after wash~ng. Each of the noted clean~ng a~ents was present in a 1%
; aqueous solut~on. Results are repor~ed in Table III.
.iL-Cd;~2262(.)
Table III
Evaluat~on of Inor~an~c Compounds
As Cleaning A~qents For Weak
Base Res~n - Beaker Tests
% Increase
Sample Test Conditions TOC (ppm) In Eff~ ac~
_. ~ .
Brine-Caustic Control Brine-Caustic 160
Na2B407 Soak-3 hrs 181 13
TSP 176 10
10 NaC10 480 200
3rine-Caustic Oontrol - 94
TSP
NaBO 4 H 0 198 111
NaF 146 55
? 15 1% NaOH Control 1 hr. Gang Stirrer 219
NaBO 4 H O lX NaOH274 25
Room Temper~ture,
Na2B407 = sodium tetraborate (borax).
TSP = Na3P04) trisodium phosphate
NaC10 = sodium hypochlorite
NaB03 4 H20 = sodium perborate
NaF = sodium fluoride
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g
Resin Degradnt n Studies with Sodlum Perborate
Sodium perborate is an oxidizing agent. Upon dilution with
water, it forms hydrogen peroxide in situ. The potential for oxida-
t1ve degradation of a strong base anion resin or boron or borate up-
take on the resin due to the sodium perborate cleaning treatment was1nvestigated.
Fouled s~rong base resin was placed in the ~on exchange
column. 0.3% sodium perborate (as NaB03) in brine-caustic was
passed through the resin column at a flow rate of approxima~ely 22
lQ mls/min for 1.5 hour; at room temperature. Another resin sample was
treated similarly, e~cept heat was applied ~o the column such that
the effluent temper ture was maintained at 100F. These two sodium
perborate cleaned samples plus an "as received" sample were then
analyzed for absolu1e salt-splitting anion exchange capacity deter-
minations. ~The ab~olute salt-splittlng anion exchange capacity is
determ~ned followins an exhaustive cleaning procedure, and thus it
measures the active sites which are available in the absence of
fouling. Any permarent degradation of active exchange sites will be
expressed as a reduction in absolute salt-splitting capacity.) No
differences in the ~alt-splitting capacity were found for these
samples. Sodium pe!borate cleaning did not affect the absolute
salt-splitting anicn exchange capacity of the resin.
A fouled strong base resin sample was placed in the ion
exchange column, cleaned with 200 mls brine-caustic plus 0.4~ of
Formulation "A" ~as NaB03) (see Table IY), rinsed with demineral-
~zed water, regenerated with 200 mls of 4% NaOH and rinsed again with
dem~neral~zed water. The e~fluent solutions were sent for boron
analyses by the ICP method (inductively coupled plasma emission
spectroscopy). A materials balance utiliz~ng these data showed no
~2~ 6;~
-~o
uptake o~ ~oron in the resin. The sodium perborate was not rPta~ned
on the resin after regeneration.
Accordinglyg it appears tha~ there are no or only minimal
detrimental effects (oxidative degradation) on the salt-spl~tting
anion exchange capacity of a fouled strong base resln sample cleaned
with sod~um perborate.
Evaluation of Sodium Perborate Formulat~on
~ .. .... ~ , .
A fonmulation consisting of 90~ (weight) NaB03 4
H20 (sod~um perborate), 5% Na4P207 (tetrasodium pyro-
~O phosphate) and 5% Na2B407 ' 10 H20 (sod~um tetraborate),
was tested to determine the TOC content of effluent from a treated
res~n compared to the TOC content of a control standard in accordance
w~th the procedures expla~ned here~nabove. Results are reported in
Table IV.
3L~222626)
TABLE IV
EYALUATION OF SODIUM PERBORATE_FORMULATION BRINE-
CAUSTIC AND DEM.NERILIZED WATER STATIC AND GANG
STIRRER EEAKER TESTS
ROOM TEMPERATURE
% Increase
Resin ~e * Tes~ Conditions ToC ( ~ In Efficacy
1 Control Br~ne-Caust~c 630
0.8~ A Sta~ic Soak-3 hrs 790 25
0.8% ~ 8~ 3~`
0.8% A 740 17
2 Control Brine-Caustlc 690
0.8X A Gang Stirrer-l hr 840 2"
0.8% A 790 1
o.a~ A 740 7'
3 Control Brf ne-Caustic 850
0.8% A Gang St~rrer 2 hrs 900 H
4 Contro~ Brine-Caust~c 350
O~g A Gang St~rrer-2 hrs 750 214
*TOC values dete~mined by Combust~on/IR Spectroscopy me~hod.
Formulation "A" equals 90 weight % NaB03 ' 4H20, 5%
Na4P207, and 5% Na2B407; in aqueous solution concen-
trat~on 0.8X NaB03 4H20 as NaB03. This formulation is
presently preferred for use.
3l2
-12-
D~scuss~on
As Table I indicates, the sodium perborate cleaning agent
is comparable to sodium hypochlor~te in efflcacy as measured by the
TOC content of ~he ~ffluen~ ~rom washed resin samples.
Table II demonstrate~ that khe sodium perborate treatments
lncrease the cleans~ng efficacy of br~ne and caustic washing.
Insofar as weak bas~ anion resins are concerned, Table III
lndicates that the sodium perborate cleansing compos~tions of the
present invention are approxin.itely equal to sodium hypochlorite.
10 However, unlike those me~hods involving sodium hypochlorite, the
sodium perborate containing c eans~ng compos~tions are not, in any
significant amount retained on the resin, nor is there any s~gnlf~-
cant resin degradation occasioned by use of the sodium perborate
treatment of the invent~on.
Table IY indicates 1.ha~ the compositions presently pre-
ferred for use (Formulation ~ herein) increases brine and caus~ic
cleansing efficacy
It can thus be seen that the disclosed inven~ion carries
out ~he objects of the inven1.ion set forth above. In accord with the
20 patent statutes, the best mode has been set forth However, it will
be apparent to those skilled ~n the art that many other modificat~ons
can be made without departing from the invention herein disolosed and
descrlbed, ~he scope of the lnventlon being limited only by the scope
of the attaGhed claims.
