Water softener abstract
Salt composition and method for regenerating spent water softener
cation exchange resins, to remove or prevent the accumulation of
iron in its various forms, insolubles, and oily deposits. The dry
composition comprises from about 10 ppm to about 400 ppm of an alkylated
diphenyl oxide disulfonate surfactant, from about 500 ppm to about
8000 ppm of sodium citrate, and as the remainder of the composition
sodium chloride. The composition is preferably provided and used
in the form of compacted products. The method for regenerating the
spent cation exchange resin bed comprises the step of contacting
the resin bed with an aqueous brine solution containing from about
25 to about 1200 ppm sodium citrate and from about 0.5 to about
60 ppm of alkylated diphenyl oxide disulfonate surfactant. The method
is conveniently practiced by dissolving the composition first set
forth above in the water of a conventional brine tank, using known
Water softener claims
What is claimed is:
1. A composition for regenerating hardness cation exchange resins,
A. from about 10 ppm to about 400 ppm of an alkylated diphenyl
oxide disulfonate surfactant;
B. from about 500 ppm to about 8000 ppm of an alkali metal citrate;
C. as the remainder of the composition, sodium chloride.
2. The composition of claim 1 wherein said surfactant is selected
from: ##STR3## and mixtures thereof.
3. The composition of claim 1 comprising about 75 ppm of said
surfactant and about 770 ppm of sodium citrate.
4. The composition of claim 3 wherein said surfactant is selected
from: ##STR4## and mixtures thereof.
5. A method for regenerating the spent hardness cation exchange
resin bed of a water softener, comprising the step of contacting
said resin bed with an aqueous brine solution containing from about
25 to about 1200 ppm of sodium citrate and from about 0.5 to about
60 ppm of an alkylated diphenyl oxide disulfonate surfactant.
Water softener description
The present invention relates to salt compositions for regenerating
cation exchange resin beds in water softeners, particularly salt
compositions containing ingredients for continuously inhibiting
resin fouling by iron, insolubles, oils, and other contaminants
commonly found in water supplies.
Water softening systems are used in households and by industry
to replace hardness cations such as calcium and magnesium with sodium
ions by passing an incoming water supply through a bed of cationic
exchange resin beads or particles. When the ion exchange resin bed
periodically becomes saturated with ions removed from the incoming
water, and depleted of sodium ions, it is recharged by passing a
brine solution consisting essentially of sodium chloride through
the resin bed. This replenishes the bed with sodium ions and removes
the calcium, magnesium, or other ions previously removed from the
The exchange capacity of an ion exchange resin bed deteriorates
as impurities in the incoming water collect in the resin bed and
are not removed by the recharging process. Sooner or later, depending
on the level of maintenance of the resin bed and the characteristics
of the water supply being softened, the resin becomes "fouled",
meaning that the resin bed's capacity to soften water has diminished
so much that the resin must be specially treated to restore its
The presence of iron in the incoming water supply is the most common
cause of resin fouling. Iron can exist in the water supply as clear
water iron, red water iron, bacterial iron, colloidal iron, or tannate
Clear water iron is iron in the divalent (ferrous), soluble state.
Clear water iron is not visible when the water is drawn, but when
the water is allowed to stand for a prolonged period the ferrous
ions are oxidized by air to become ferric or trivalent ions, which
settle as a precipitate of ferric hydroxide. The iron may also oxidize
after having been exchanged into a resin bed, which will prevent
it from being removed by regeneration.
Red water iron is already oxidized to the ferric state when it
reaches the water softener. Water containing red water iron is cloudy
and orange when drawn. This form of iron may be filtered by the
resin bed or may be passed and be present in the softened water.
Bacterial iron is a third troublesome form of iron, and is caused
by iron crenothrix bacteria which feed on the iron in the water
supply. These bacteria thrive in water softener resin beds supplied
with ample iron, and the resulting biomass clouds the water system,
creates a bad taste and odor in the softened water, and occasionally
releases large, unsightly masses of rust colored material.
Colloidal iron is similar to red water iron, but is composed of
particles too small to settle. Colloidal iron will normally pass
directly through a water softener.
Finally, tannate iron, which is quite similar in appearance to
colloidal iron, is ferric iron complexed and held in solution by
tannates or other naturally occurring soil ingredients. This final
form of iron usually passes through a water softening resin bed.
Iron present in any of the previously discussed forms can foul
the resin bed. Oxidation of ferrous iron captured by the resin beads
can crack them, thereby physically degrading the resin bed as well.
The iron problem is well known in the softening art, and attempts
have been made to remove iron in all its forms from water softening
resin beds. Other chelating compounds for sequestering iron are
listed in column 2 lines 47 through 53 of U.S. Pat. No. 3454503
issued to Blankenhorn et al. on July 8 1969. Among the iron chelating
materials disclosed therein is citric acid. U.S. Pat. No. 2769787
issued to Diamond on Nov. 6 1956 also discloses a method for regenerating
cation exchange resins fouled by iron by adding to the brine regeneration
medium any of a variety of organic acids, particularly citric acid.
Citric acid is used commercially in water softening salt compositions,
and does remove iron from the system, but citric acid or the mineral
acids suggested in some other references can accelerate damage to
metal or plastic materials found within a water softener if they
are used regularly to recharge the system.
U.S. Pat. Nos. 4071446 and 4116860 respectively issued to
Kunin on Jan. 31 1978 and Sept. 26 1978 disclose compositions
for regenerating resin beds, comprising a major proportion of an
alkali metal chloride, a minor proportion of an alkali metal carbonate,
and as the remainder an alkali metal carboxylate chelating agent.
Among the many carboxylates disclosed in these references are sodium
and potassium citrates. The resins disclosed therein, further characterized
in U.S. Pat. No. 4083782 are weak acid cation exchange resins
adapted to exchange sodium or potassium ions for hydrogen cations,
thereby reducing the acidity of the incoming water. No disclosures
of the iron problem or the present solution to that problem are
made in the Kunin patents. Furthermore, Kunin suggests extremely
high concentrations of sodium citrate (5 to 15 per cent of the exemplary
Oily materials and insoluble particulate matter (which can include
precipitated ferric iron) in the water supply also foul cation exchange
resins. The particulate matter is bound to the resin beads by the
hydrophobic oily matter, and then defies removal when the resin
bed is backwashed or otherwise treated with aqueous solutions. The
insolubles bound to the resin beads limit the contact area exposed
to incoming water, thus fouling the resin bed. U.S. Pat. No. 3216932
issued to Heiss et al. on Nov. 9 1965 discloses a composition
consisting predominantly of salt, and containing minor proportions
of (1) a dialkali metal sulfonate of an alkylated diphenyl ether;
(2) a dialkali metal sulfonate of dinaphthylmethane; and (3) an
aqueous mineral acid. The mineral acid can generate fumes which
attack metal and plastic components of the water softener, and the
surfactant is used at a higher level than is desirable for economic
reasons. Heiss also teaches away from the use of sequestering agents.
(See column 1 lines 54-63).
Hofheins, "Cleaning Methods for Fouled Cation Exchange Resins",
Water Technology, Feb. 1983 pages 21-25 33 and 41 discusses how
to clean resins fouled by various contaminants, particularly iron,
by occasional treatment with sodium hydrosulfite, hydrochloric acid,
or polyphosphate or organophosphorus sequestering compounds. This
article also recommends the removal of fats, oils, and the like
by contacting the resin bed with caustic solutions, which are not
suitable for household use.
Another class of products, for restoring resin beds which are so
fouled that regeneration would be pointless without pretreatment,
also employs surfactants. These materials are not adapted for regular
use in a water softener. The patents disclosing products of this
type include U.S. Pat. No. 3748285 issued to Wiltsey on July
24 1973. Another patent, which discloses the use of a surfactant
in a special process for removing entrapped air from a water softener,
is U.S. Pat. No. 3299617 issued to Dunklin on Jan. 24 1967.
Here again, the composition is not intended to regenerate the resin
bed, but is used for a special purpose.
The prior art known to the inventors does not suggest combining
a sequestering agent with a surfactant, particularly in the context
of a resin regenerating composition for regular use to maintain
the cleanliness of the resin, comprising salt, a sequestering agent,
and a surfactant.
The art also has not recognized the special characteristics required
of a surfactant for use in a salt composition intended for routinely
regenerating cation exchange resin beds. Surfactants for this purpose
must be anionic, as cationic surfactants would bind to the resin
exchange sites and nonionic surfactants are not soluble in brine.
The candidate surfactant must be safe for human consumption at low
levels in drinking water, as minute quantities of the regenerating
composition might be carried into the treated water supply. The
surfactant must be low foaming at the normal level of use, to prevent
the introduction of air into the softener. The surfactant must be
soluble in saturated brine (which few surfactants are). It must
be compatible with hard water, so no insoluble precipitates are
formed. Finally, the surfactant must be sufficiently inexpensive
to be economically justifiable and must be stable at the high temperatures
encountered when compacting granulated salt to form products such
SUMMARY OF THE INVENTION
The inventors have discovered water softening regeneration salt
compositions combining low levels of alkylated diphenyl oxide disulfonate
surfactants with an alkali metal citrate, preferably sodium citrate,
as a sequestering agent. Regular use of such compositions to regenerate
water softener resin beds can increase the softening capacity of
resin beds already in service and can protect cationic exchange
resin beds against deterioration due to the accumulation of iron,
other insolubles, oily and fatty deposits, and other impurities
derived from the water supply.
Furthermore, the inventors have discovered that the same treatment
increases the brine generating capacity of the system for each regeneration
cycle, reduces the deleterious caking and bridging of salt pellets
in the portion of the water softening salt which is intended to
be above the level of water in the brine tank, and solubilizes or
prevents formation of scum in the brine tank, even if iron is present
in the water supply or in the salt.
Sodium citrate provides much of the sequestering ability of citric
acid, but (unlike citric acid) does not tend to cause acid fumes
in the water softener or otherwise accelerate deterioration of the
metal or plastic parts therein.
The preferred alkylated diphenyl oxide disulfonate surfactants
have the following formula: ##STR1## wherein X is an alkali metal
ion, preferably a sodium ion, R.sup.1 is an aliphatic moiety having
from 6 to 16 carbon atoms, preferably an n-decyl moiety, and R.sup.2
is selected from hydrogen and R.sup.1 and preferably is hydrogen
or an n-decyl moiety.
Surprisingly, the inventors have found that combinations of the
citrate and surfactant work better than either ingredient taken
The preferred compositions for use herein comprise from about 10
parts per million (ppm) to about 400 ppm, and preferably about 75
ppm, of an alkylated diphenyl oxide disulfonate surfactant; from
about 500 ppm to about 8000 ppm, and preferably about 770 ppm,
of sodium citrate (which is equivalent to 880 ppm of sodium citrate
dihydrate); and as the remainder sodium chloride. (The inventors
do not, however, exclude other ingredients which do not detract
appreciably from the utility of the compositions disclosed herein.)
Another aspect of the invention is a method for regenerating the
spent cation exchange resin bed of a water softener, comprising
the step of contacting the resin bed with an aqueous solution containing
from about 50000 to about 150000 ppm of sodium chloride, from
about 25 to about 1200 ppm of sodium citrate, and from about 0.5
to about 60 ppm of an alkylated diphenyl oxide sulfonate surfactant.
This method can be employed routinely to regenerate the resin bed
of a water softener, rather than waiting until the resin bed becomes
fouled before taking more extreme measures. Also, attention to the
condition of the resin bed is not deferred until failure of the
system, meaning that the supply of soft water need not be interrupted
while service for the water softener is sought.
DESCRIPTION OF PREFERRED EMBODIMENT
The surfactants useful herein, represented by formula I above,
are commercially available under the trademark DOWFAX from the Dow
Chemical Company, Midland, Mich. The preferred commercially available
surfactant for use herein is DOWFAX 3B2 which is a mixture of the
following two species: ##STR2## The inventors contemplate that either
of these species or any mixture thereof is useful herein as a surfactant.
The commercial material is approximately 45% of the surfactant dissolved
Sodium citrate is available from a wide variety of commercial sources,
and the preferred material is provided as granules of sodium citrate
dihydrate which pass through a 20 mesh screen and are substantially
retained on a 70 mesh screen. In the preferred embodiment, the particle
size distribution of the sodium citrate dihydrate feedstock is similar
to the particle size distribution of the sodium chloride feedstock.
The granular sodium chloride feedstock preferred herein is that
which has conventionally been compacted for use as water softening
Although an individual consumer could practice the method invention
taught herein by purchasing the individual components and dissolving
them in water to form a brine, in the preferred mode of practicing
the invention, the components of the composition are compacted to
provide a unitary composition. To pelletize the composition the
sodium citrate, sodium chloride, and surfactant feedstocks are mixed
together homogeneously and passed through conventional compacting
The following examples are provided to illustrate the invention
and its practice. The scope of the invention is not limited by these
examples, and is defined in the claims concluding this specification.
The following laboratory procedure was employed to measure the
effect of the improved salt composition on the exchange capacity
of fouled resins.
1. Water softener simulators, approximately 1/45 the size of a
full scale unit, were modeled after a residential water softener.
These simulators consisted of upright 1000 ml soil test cylinders
167/8 inches (429 mm) tall, having an inside diameter of 23/4 inches
(60 mm), plugged at the top by a rubber stopper penetrated by two
glass tubes. The center tube extended to the bottom of the cylinder
and was fitted with a fine-mesh screen to prevent resin from washing
out. The lower end of the side tube was flush with the bottom of
the stopper. Influent water could be directed down the center tube
(upflow) for backwashing the resin or through the side tube (downflow)
to simulate the brine, rinse and service cycles of a softener.
2. Approximately 200 ml of glass beads were placed at the bottom
of the cylinders before adding exactly 500 ml. of packed-down resin
beads collected from residential water softeners. (The beads were
measured by placing a graduated cylinder containing resin beads
on a vibrating table until settling was complete, then resin beads
were added or removed to provide exactly 500 ml). The remaining
space was filled with water and the stopper was tightly secured
to close the system.
3. The resin was backwashed with 2500 ml. of deionized water. The
flow rate was adjusted to obtain 50% expansion of the resin bed.
4. The resins were regenerated with 802 g. of 10% sodium chloride
solution (10 pounds (4.5 kg) per cubic foot (28 liters) of resin)
containing test additives or no additives (control). The brining
flow rate was 50 ml./min.
5. After brining, the resin was rinsed slowly with 1500 ml. of
deionized water at 130 ml./min., followed by a fast rinse consisting
of 1160 ml. of deionized water at 300 ml./min.
6. Effluents from the brine and rinse cycles were collected in
one gallon glass jars for subsequent analysis.
7. The resin was then exhausted with 12 liters of synthetic hard
water at a flow of 70 ml./min. ("Exhausted" means that
the influent hardness was equal to the effluent hardness). The synthetic
hard water was deionized water to which CaCl.sub.2 and FeSO.sub.4
were added and allowed to stand overnight to provide 200 grains
of hardness per gal. (expressed as CaCO.sub.3), (equivalent to 684
milliequivalents (meq.) of hardness per ml. of water) and 30 ppm
8. Steps 4 through 8 were repeated for 3-4 complete cycles.
9. On the final exhausting step, incremental samples of the effluent
water (soft water) were continuously taken and the cumulative volume
of water through the simulator was recorded with each sample.
10. The samples were analyzed for hardness and results were plotted
against the cumulative volume measurements. The "breakpoint"
was determined from this graph, and was arbitrarily chosen as the
point on the curve where the water hardness of the effluent water
was equal to one-half the hardness of the influent water.
11. The resin was then quantitatively recovered from each simulator
and dried to constant weight at 140.degree. C.