Note: Descriptions are shown in the official language in which they were submitted.
2167612
R- 1026
METHOD OF CONTROLLING FLUORIDE
SCALE FORMATION IN AQUEOUS SYSTEMS
FIELD OF THE INVENTION
The present invention relates to the treatment of water to inhibit the
formation of scale. More particularly, the present invention relates to the
use of an alkyl epoxy carboxylate to inhibit fluoride salt scale formation in
aqueous systems.
BACKGROUND OF THE INVENTION
In an aqueous system such as a steel casting process, molten
steel is shaped as it passes through a mold. This mold is coated with
powder to prevent the adherence of steel to the sides. Many mold pow-
ders contain fluoride salts which dissolve in the spray water used to cool
the hot molten slab. These fluoride-containing solutions are splashed on
the inside of the enclosure which houses the spray nozzle banks (the
spray chamber) and on the outside of the spray nozzles in such a continu-
ous caster spray water system. Subsequently, fluorides are deposited in
and around the spray nozzles and the piping immediately preceding the
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nozzles, particularly in areas of decreased spray water flow and high radi-
ant heat. Water to the spray nozzles is from the cooling tower at a pH of
about 8. Dissolution of mold powders decreases the pH to about 4.
It would be advantageous to prevent the formation of scale in and
around the spray nozzles and chambers, thereby enhancing spray water
cooling efficiency by increasing water flow and maintaining the spray
pattern, reducing the potential for a breakout which poses serious safety
concerns, and reducing production downtime. Such objectives are ac-
complished by the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The method of the present invention comprises treating industrial
waters with an alkyl epoxy carboxylate (hereinafter Polymer A) of the
general formula:
R R
I I
HO --t-i -i -O~H
0 = C C = 0
1 1
0 0
1 1
M M
where n ranges from about 2 to 50, preferably 2 to 25, M is hydrogen or a
water soluble cation such as Na+, NH4+ or K+ and R is hydrogen, C1_4
alkyl or C1_4 substituted alkyl (preferably R is hydrogen).
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A method of preparing an alkyl epoxy carboxylate similar to that
employed as a scale control agent in the present invention is described in
U.S. Pat. No. 4,654,159, issued March 31, 1987 to Bush et al. The Bush
et al. patent describes ether hydroxypolycarboxylate prepared from epoxy
succinates by treatment with an alkaline calcium compound. The
polyepoxysuccinic acid of a specific molecular weight distribution is
described in Bush et al. as a useful detergent builder due to its ability to
act
as a sequestering agent. The sequestering agent of Bush et al. complexes
with hardness cations in water supplies which aids in detergent processes
by preventing the cations from adversely effecting the detergents.
In the present invention, the alkyt epoxy carboxylate is added to
aqueous systems at substoichiometric levels to inhibit fluoride-containing
salt scale formation. The method of the present invention provides effec-
tive deposition inhibition in waters having relatively high Langelier satura-
tion indexes. The method of the present invention provides such control
at relatively low active treatment levels without the use of phosphates or
phosphonates.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention pertains to a novel method of inhibiting the
formation of fluoride salt scale such as calcium fluoride scale from aque-
ous systems. Specifically, the method of the present invention comprises
adding to an aqueous system an alkyl epoxy carboxylate (or polyepoxy-
succinic acid) of the general formula:
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R R
HO -t- i - i - O}-nH
O= C C= O
0 0
M M
where n ranges from about 2 to 50, preferably 2 to 25, M is hydrogen or a
water soluble cation such as Na+, NH4+ or K+ and R is hydrogen, C1_4
alkyl or C1_4 substituted alkyl (preferably R is hydrogen).
The polyepoxysuccinic acid material employed in the present in-
vention can be obtained by the polymerization of epoxysuccinate in the
presence of calcium hydroxide or other alkaline calcium salts. The
general reaction can be represented as follows:
Ca(OH)2/H20 R R
0 HO-{-C -C -O}-õH
R-C C- R O= C C O
0=C C=0 O O
0 O M M
M M
CA 02167612 2006-01-04
A complete description of a method of preparing such a polyepoxy-
succinic acid of a specific molecular weight distribution is included in U.S.
Pat. No. 4,654,159, issued March 31, 1987.
5 The treatment levels of alkyl epoxy carboxylate added to an aque-
ous system can range from about 25 parts per billion up to about 500 parts
per million. The preferred treatment levels range from about 50 ppm up to
about 100 ppm. The concentration of alkyl epoxy carboxylate necessary to
provide effective calcium fluoride control will, of course, vary from system
to system. The treatment level wi!l vary, in part, with changes in tempera-
tures, pH, and LSI. However, in all cases, the concentration of alkyl epoxy
carboxylate added to an aqueous water system in accordance with the
present invention is at substoichiometric concentrations. That is, the con-
centration of alkyl epoxy carboxylate is much lower than the concentration
of the scale forming material in the system to be treated.
The treatment of the present invention may be added to a circulating
aqueous system such as a once-through cooling system, a recirculating
system such as cooling tower where the water is reused or a static/stagnant
system such as a stand-by service system. The treatment of the present
invention is effective at inhibiting the formation of scale in systems where
the water is in motion as well as systems where the water is static or
stagnant.
The present invention will now be further described with reference
to a number of specific examples which are to be regarded solely as
illustrative and not as restricting the scope of the present invention.
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Laboratory experiments were conducted with solutions of pH, Ca2+
and F- levels typical of those in spray water systems and those encoun-
tered under more aggravated process upset conditions. Plant water was
obtained and spiked with additional calcium and fluoride to resemble con-
ditions at the spray nozzles. The concentration of the soluble Ca2+ and
calcium inhibition were determined relative to a control under the same
conditions. Static beaker and dynamic recirculated tests were conducted.
In the static beaker tests, several sets of varying calcium and fluoride
levels were evaluated.
Static Beaker Tests
Condition I: (Synthetic Water)
600 ppm Ca2+ as CaCO3, 75 ppm F', 500 ppm Mg2+ as CaCO3, 250
ppm S042-, pH=7, Temperature=50 C, time=18 hours.
Condition II: (Pre-clarifier Plant Water)
Spiked to 621 ppm Ca2+ as CaCO3, 253 ppm F-, pH=8, temperature=30 C,
time=4 hours.
Calcium fluoride inhibition efficacy results of a commercially
available phosphonate and Polymer A under Condition I are found in
Table I. Table I shows the relative ability of phosphonate and an alkyl
epoxy carboxylate (Polymer A) to inhibit calcium fluoride using synthetic
test water as described in Condition I.
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TABLE I
Static Beaker Tests - Condition I
Sample ppm, actives % Inhibition
Polymer A 1 28
5 32
33
10 Phosphonate 1 16
5 17
10 17
As shown, the polyepoxysuccinic acid polymer is more effective
than the phosphonate under these conditions. Calcium levels in these
systems are not typically this elevated. However, this result reflects the
calcium tolerance and superior inhibition of Polymer A relative to a
phosphonate under process upset conditions.
Calcium fluoride efficacy of phosphonate and Polymer A under
Condition II with pre-clarifier water received from the field is summarized
in Table II. In Table II, experiments were conducted with pre-clarifier
plant water spiked to elevate the calcium and fluoride levels. Note that
these particular test conditions are relatively severe and that Polymer A
continued to outperform the phosphonate. Similar results were achieved
atapHof4.
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TABLE II
Static Beaker Tests - Condition II
Sample ppm, actives % Inhibition
Polymer A 5 21
32
25 82
10 75 89
Phosphonate 5 9
10 8
12.5 11
25 2
75 3
Dynamic recirculation tests were conducted to duplicate the nozzle
environment, with radiant heat generated from the slab. In these tests,
pre-clarifier (or "scale pit") plant water was circulated over a metal sleeve
heated to 205 +/- 5 C. Bulk water temperature was maintained at 21 C.
Tests were conducted for 4 hours. Results are summarized in Table III.
Table III shows the ability of Polymer A relative to phosphonate and
AA/AHPSE (acrylic acid/allyl hydroxypropyl sulfonate ether sodium salt
copolymer) to maintain calcium in solution in scale pit waters of two
compositions where CaF2 is expected to precipitate. As shown, Polymer
A provided significant benefit over phosphonate and AA/AHPSE.
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TABLE III
Percent Soluble Calcium Retained in Scale Pit Water Solutions
by Selected Inhibitors After Four Hours in a Dynamic Test
Scale Pit Water Composition
Percent Soluble
ppm Ca++ ppm F- Bulk Water Calcium Retained in
as CaCO3 as Fluoride pH Temperature Treatment Solution atT=4 hours
138 118 6.8 70 F Control 75
0.5 ppm phosphonate 85
0.5 ppm Polymer A 95
99 135 7.6 70 F Control 40
5 ppm AA/AHPSE 65
4 ppm Polymer A 88 @ T=220 min
While this invention has been described with respect to particular
embodiments thereof, it is apparent that numerous other forms and modi-
fications of this invention will be obvious to those skilled in the art. The
appended claims and this invention generally should be construed to
cover all such obvious forms and modifications which are within the true
spirit and scope of the present invention.
