CA2278084C - Scale inhibitor for an aqueous system - Google Patents

Abstract

This invention relates to a composition and a method for inhibiting the formation of scale, particularly complex scale; in an aqueous system where more than one type of scale is present. The scale typically present in the aqueous system includes silica, silicates, and carbonates. The scale inhibiting composition comprises (1) 2-phosphonobutane- 1,2.4- tricarboxylic acid and salts thereof, and (2) a water soluble polymer(s) of allyloxybenzenesulfonate monomer.

Description

SCALE INHI$ITOR FOIL AN AQUEOUS SYSTEM
_ . _ FIELD OF THE INVENTION
s This invention relates to a composition and a method for inhibiting the formation of scale, particularly complex scale, in an aqueous system where more than one type of scale is present. The, scale typically present in the aqueous system includes silica, silicates, and carbonates. The scale inhibiting composition comprises (1) 2-phosphonobutane-1,2.4-tricarboxylic acid and salts thereof, and (2) a water soluble polymers) of i o allyloxybenzenesulfonate monomer.
BACKGROUND OF THE INVENTION
"Silica" deposits are not pure silica, but a complex mixture of polymeric silica, calcium silicate, magnesium silicate, calcium carbonate, and smaller amounts of other i s inorganic compounds. In most of the aqueous systems, where there is a need to inhibit silica or silicate scale, there is also a need for the simultaneous inhibition of the calcium carbonate scale, and the need to disperse silt arid the bulk water precipitation of silica, silicates and carbonates.
Some of the most difficult deposits encountered in cooling, reverse osmosis, 2 o mining and geothermal water systems are those comprised of silica. The temperature and pH of the water affects silica precipitation and deposit formation. The pH of geothermal brines is generally 4.0 to 6.0 and the brine temperature is generally about 100°C to 2I0°C.
The temperature of cooling water is generally about 30°C to 80°C
and the pH is generally about 6.0 to 9Ø Cooling water is also exposed to cathodic microenvirorunents within 2 s corrosion cells on the metallic heat transfer surfaces where the pH is about 9.0 to 9.5 and higher.
Several methods are used to prevent or inhibit silica deposits. The simplest method involves keeping silica, calcium and magnesium below the critical concentration levels necessary for the precipitation of silicates. The critical concentrations suggested by the 3 o water treatment industry are: (1 ) at pH < 7.5, silica (as SiO~< 200 ppm;
and (2) at pH >
7.5, silica (as SiO~) <100 ppm. If magnesium is present then (expressing Mg as ppm CaCO~ and Si as ppm SiO~, the recommended concentrations are (I) at pH < ?.5 (Mg x Si) is < 40,000, and (2) at pH > 7.5 (Mg x Si) is < 20,000.
Various chemical treatment methods have been developed that inhibit silica/silicate and other scale/dcposits. Anionic polymers, cationic polymers, organic phosphonates, s boric acid, and its sodium salts are described in the patent literature. Of particular interest is U.S. Patent 5,078,879 which discloses a method for controlling silica/silicate deposition in a aqueous system with an admixture of 2-phosphonobutane-1,2,4-tricarboxylic acid and a water soluble polymers based on acrylic and sulfonic monomers, but not on the allyloxybenzcnesulfonate monomer..
to Scale inhibitors uc needed which will inhibit multiple scales very c~ciently in an economical way. Currently the most effective silica/silicate antiscalant is an acrylic TM TM
terpolymer from Rohm&Haas sold under the trade name ACUMER 5000 . ACUMER
TM
5000 is disclosed in U.S. Patent 5,277,823. The exact composition of ACUMER
5000 is not disclosed, but the above mentioned patent gives strong indication that the polymer is consists of selection of monomers such as AMPS, acrylic, malefic and others but not allyloxybenzenesulfonate monomer. This low molecular weight, water soluble polymer is as excellent antiscalant, but it is expensive. 'Thus there is a need for antiscalanis that have TM
equal or improved effectiveness, but which are less expensive than ACUMER
5000.
U.S. Patent 4,915,845 discloses the use ofwater soluble polymers of 2 o allyloxybenzcneslufoaate monomer and their use in aqueous systems in dispersing particulate matter, particularly drilling mud. Although the above mentioned polymer is also claimed as an inhibitor for the mineral scale in an aqueous systems but not specifically for the inhibition of silica and silicates and not in an admixture with other inhibitors.
~s SUMMARY OF )<NNVENTION
This invention relates to a scale inhibitor composition and a method for inhibiting the formation of scale, particularly complex scale, in an aqueous system where more than one type of scale is present. The scale typically present is silica (SiO,, silicates (e.g.

MgSi03), and carbonates (e.g.CaCO,), and the complex scale is a mixture thereof. The scale inhibiting treatment composition comprises:
(I) 2-phosphonobutane-1,2,4-tricarboxylic acid; and (2) a water soluble polymer that consists of allyloxybenzenesulfonate s monomer and one monomer from the selection of several acrylic or substituted acrylic monomers.
?he scale inhibiting treatment composition not only inhibits scale and complex scale formation very efficiently, but it does so very economically. The composition works as TM
effectively or more effectively thaw ACtJMER 5000, and is less expensive to use.
io BEST MODE AND OTHER MODES
It is known that 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) is a well known scale inhibitor. For purposes of this invention, 2-phosphonobutane-1,2,4-tricarboxyIie acid (PBTC) shall also include salts thereof. PBCT is disclosed in may U.S.
is Patents, for instance U.S. Patents 4,432,879 and 5,078,879, which are hereby incorporated into this specification by reference. The water soluble copolymers of an acrylic or substituted acrylic monomer and allyloxybenzeneslufonate monomer used in the invention are disclosed in the U.S. Patent 4,892,898 and 4,915,845 which are hereby incorporated into this specification. These copolymers have a weight average molecular weight of about Zo 1,000 to 5,000,000, preferably fi~om 1,000 to 250,000.
The acrylic/substituted acrylic monomer preferably used is selected from the group consisting of acrylic acid, methacrylic acid, alkyl and hydroxyalkyl substituted acrylic acid, and the alkali metal, alkaline earth metal, and ammonium salts thereof.
The water soluble copolymers comprise at least 1 mole percent of the allyloxybenzeneslufonate zs monomer, preferably from 2 to 15 mole percent. The molar ratio of the alIyloxybenzcnesulfonate monomer to acrylic monomer in the water soluble copolymer typically ranges from about 1:99 to 20:80, preferably 2:98 to 15:85. The water soluble copolymers may be prepared by any number of conventional means well known to those skilled in the art including, for instance, bulls, emulsion, suspension, precipitation, or solution polymerization.
The weight ratio of the 2-phosphonobutane tricarboxylic acid to water soluble copolymer in the scale inhibitor is from 20:1 to 1:20, preferably 1:2 to 2:1.
s The scale inhibitors are used by adding to an aqueous system such as;
cooling water, boiler water, reverse osmosis and geothermal/mining water, in amounts from 0.1 to 1000 ppm, but preferably from 1.0 to 100.0 ppm.
Other components may be added to the scale inhibitor composition, such as corrosion inhibitors, surfactants, or agents that inhibit microbiological growth..
so ABBREVIATIONS
The following abbreviations arc used in the Examples:
TM
is ACUMER 5000 - acrylic/sulfonic nonionic terpoIymer available from Rohm&Ha,as CRABS - a copolymer of allyloxybenzenesulfonate and acrylidsubstituted acrylic monomer, along the lines of the ao copolymers disclosed in U.S. Patents 4,432,879 and 5,078,879, and which is available from Alco Chemical.
PBTC - 2-phosphonobutanc-1,2,4.tricarboxylic acid available from Bayer as Bayhibit AM.
TF - aatiscalant within the scope of the invention consisting of 15 PBTC (50% actives), 28 % CRABS (40% actives), and 57 deionized (Dn water.

EXAMPLES
The examples which follow will illustrate specific embodiments of the invention:
These examples along with the written description will enable one skilled in the art to practice the invention. It is contemplated that many equivalent embodiments of the s invention will be operable besides those specifically disclosed. All parts are by weight of solids and all temperatures are in degrees centigrade unless otherwise specified.
TM
In these examples, ACLTMER 5000, CAABS, and PBTC, and TF were evaluated as antiscalants for various deposits. The efficacy of the additives was tested using the following tests: (1) Magnesium Silicate Shaker Test, (2) Silica Shaker Test (pH 8.5), and io (3) Calcium Carbonate Shaker Test.
Tests based oa the Magnesium Silicate Shaker Test In this test, the concentration of each reactant (MgClz, NazSiO,) was 600 ppm as MgSiO,. The pH of the test solution was about 10.2 at the start and about 9.5 at the end of i5 the test. The pH of the test water simulates the high pH of a cathodic site on the corroding metal. The turbidity, measured in FTU units with a DR 2000 spectrophotometer, was used for the comparison of antiscalants. A turbidity of 10 FTU units or less was taken as a measure of a clear solution. The concentration of an antiscaIant required to maintain a such clear solution was then used as a measure of an antiscalant cfftcacy. The efficacy of zo an antisealant is inversely proportional to the minimum concentration of an antiscalant required to maintain a clear test solution.
Procedure To a 125 ml conical plastic flask measure 5.0 ml of MgCI= solution (24.0 g of z s MgCl:.6HZ0 per liter of DI water) and the desired amount of an antiscalant. Add 90.0 ml of 80°C to 81 °C warm DI water and immediately add 5.0 ml of NazSiOy solution (15.1 g of Na,.Si43 per liter of DI water) and immediately put covered flask on the shaker for 30 minutes at 250 rpm. After 30 minutes take the flask out and cool at room temperature for s 30 minutes, then shake the flask until a uniform dispersion of the precipitated flocks is obtained (2-5 seconds) and measure the turbidity of such uniform sample in FTU
units using DR 2000 spectrophotometer. The dosage of additive to maintain a clear solution was determined. The lower this dosage the better the additive. The results of these experiments are shown in Table I
TABLE I (MgSiO, SHAKER TES'I~
Test conditions:
io Mg = 600 ppm as MgSi03; NazSiO, = 600 ppm as MgSiO~; pH = 10.2-9.5.
Shaker time = 30 minutes at 250 rpm and 60-63°C.
ADDITIVE MINIMUM PPM REQUIRED

PBTC (50"/n) 300 The results in Table I indicate that the Test Formulation (TF) performed better than PBTC
TM
and about the same as ACUMER 500 and CAABS in the Magnesium Silicate Shaker Test.
Tests based on the Silica (pH-8.5) Shaker Test zo In this test the concentration of CaCIz.ZHZO was 600 ppm as CaSi03 and the concentration of Na~Si03 was 1800 ppm as CaSiO~. The pH of the test water was adjusted to 8.5 to simulate the conditions of bulk cooling water and conditions in other applications (e.g. mining, geothermal). The minimum concentration of each antiscalant required to maintain a clear test solution was determined visually. The etf cacy of an antiscalant is 2s inversely proportional, to the (minimum) concentration of an antiscalant required to maintain a clear test solution.

Procedure To a 125 mi conical plastic flask, measure 90.0 ml of NaiSiO, solution (4.2 g of NazSiO, dissolved in 2 liters of DI water and pH adjusted to 8.5 with diluted HCl). Into each flask add desired amount of an aatiscalant solution (pH 8.5). Add 10 ml CaCIZ
s solution (7.6 g of CaC12.2Hz0 per liter of DI water). Put each covered flask on the shaker at 60°-63°C and 250 rpm for 5 hours. After 5 hours cool the flask at the roam temperature for about 30 minutes and visually determine the presence or lack of flocks in the test solution. The minimum ppm of additive solids required to maintain a clear solution is determined. A lower dosage of additive would be a better inhibitor. Results of these i o experiments are shown in Table II.
TASt,~ a SILICA SHAKER TEST (p8 8.5) is Test Conditions:
Ca = 600 ppm as CaSiO,, NazSiOj. =1800 ppm as CaSiO" pH = 8.5 Shaker Time = 4-5 hours at 250 rpm and 60-63°C
ADDITIVE MINIMUM OF PPM REQUIRED

ACtJMER 5000250 PBTC, SO% 50 9s zo The results in Table II indicate that the Test Formulation (TF) performed much better than TM
ACUMER 500 and CAABS and not quite as good as PHTC and in the Silicate Shaker Test.
CaCO, Shaker Test In this test, the test water was prepared in the 125 ml glass shaker flask by mixing 90.0 ml of DI water with 5.0 ml of calcium chloride stock solution (12.5 g CaCI=.2H~0/liter) plus less than 1.0 ml of antiscalant solution, and 5,0 ml of carbonate stock solution (3.45 g NazCO, plus 5.46 g NaHCO~ per liter). The calcium concentration of the resulting test water was 425 ppm as CaC03, had an alkalinity of 325 ppm as CaCO~, and an initial pH of about 9. 1. The covered flasks were the put on the shaker for 16-18 hours at 250 rpm and 50°C. After 16-18 hours the contents of flasks were filtrated through s #5 Whatman filter paper and the filtrate was titrated with EDTA solution to determine its calcium content. The amount of the calcium in the filtrate expressed as a percent fraction of its initial concentration is % calcium inhibition. Higher % inhibition corresponds to the higher efficacy of an antiscalant. Results of these experiments are shown in Table III.
i o Table III (CaCO, Shaker Test) Test conditions:
Ca = 425 ppm as CaCO,; total alkalinity = 325 ppm as CaC03; pH = 9.1.
is Shaker Time =16-18 hours at Z50 rpm and 50°C
PPM OF % G AS C8C0~
ADDITIVE ( ADDIT'IVE INHIBTfION

ACUMER 5000 25 34.1 ~ 5.1 CAABS 25 53.9 t 9.7 PHTC, 50% 25 95.8 ~ 0.6 TF 25 90.9 ~ 2.4 The results in Table III indicate that the Test Formulation (TF) performed much better than TM
2 o ACLJMER 5000 and CAABS and similar to PBTC in the Calcium Shaker Test.
a

Claims (5)

1. A process for inhibiting complex scale in an aqueous system, which comprises, adding to said aqueous system an effective scale inhibiting amount of a scale inhibiting composition comprising:
(a) 2-phosphonobutane-1,2,4-tricarboxylic acid, and (b) a copolymer of (1) one or more allyloxybenzenesulfonate monomers, and (2) one or more water soluble acrylic monomers, substituted acrylic monomers, or mixtures thereof, where the mole ratio of (1) to (2) is from 1:99 to 20:80, and such that the weight ratio of (a) to (b) is from 9:1 to 1:9.

2. The process of claim 1 wherein an effective scale inhibiting amount of the scale inhibiting composition is from 0.1 to 1000 ppm.

3. The process of claim 2 wherein said aqueous system is selected from the group consisting of a cooling water system, a boiling water system, and a geothermal water system, a reverse osmosis system, and a mining water system.

4. The process of claim 3 wherein the weight ratio of (a) to (b) is from 2:1 to 1:2.

5. The process of claim 4 wherein an effective scale inhibiting amount of the scale inhibiting composition is from 0.1 to 100 ppm.