WO2002034681A2

WO2002034681A2 - Method for inhibiting the deposition of silica and silicate compounds in water systems

Info

Publication number: WO2002034681A2
Application number: PCT/US2001/042556
Authority: WO
Inventors: Zahid Amjad
Original assignee: Noveon Ip Holdings Corp.
Priority date: 2000-10-23
Filing date: 2001-10-09
Publication date: 2002-05-02
Also published as: AU2001297009A1; WO2002034681A3

Abstract

A method of inhibiting the deposition of silica and silicate compounds on surfaces in water systems by treating the water with an effective amount of an EO/PO block polymer, either alone or in combination with, e.g., an (meth)acrylic or maleic homo-copolymer.

Description

METHOD FOR INHIBITING THE DEPOSITION OF SILICA AND SILICATE COMPOUNDS IN WATER SYSTEMS

Background of the Invention

The present invention relates to a method for inhibiting the formation and deposition of silica and silicate compounds in water systems with certain EO/PO block copolymers, i.e., ethylene oxide-propylene oxide block copolymers, either alone or in combination with acrylic acid copolymers. In many parts of the world, including Western United States, Mexico and

Southeast Asia, the efficient use of water in cooling towers, boilers, geothermal applications, and reverse osmosis applications such as sugar concentration and enhanced oil recovery operations, is limited by the solubility of silica. Water supplies in these areas can have silica levels of from 30 to 120 parts per million (ppm). Water treatment operations with waters containing high silica levels are limited because the solubility of silica at about 150 ppm can be exceeded when minerals are concentrated during processing. This can result in the precipitation and deposition of amorphous silica and silicates with consequential loss of equipment efficiency.

The accumulation of silica on internal surfaces of water treatment equipment, such as boilers, cooling, and purification systems, reduces heat transfer and fluid flow through heat exchange tubes and membranes. Soluble silica is mainly composed of silicic acid and silicates, in proportions that depend on pH. Insoluble, amorphous silica originates from base-catalyzed condensation polymerization of soluble silica to produce nominally Si0₂. The reactions can be expressed as follow:

Si OrT + HO^~ ** (HO)₃Si-0^~ + other silicates

OH OH

I I

HO - Si - O - Si - O ^'

(OH)₃SiO" + Si(OH)₄ I I „

0 0 Silica"

I I

HO - Si - O - Si - O^"

I I

O^' O^" The primary insoluble particle is smaller than 0.1 μm and comprises a core of Si0₂ with a surface of silanol groups (Si-OH). The polymerization rate is also pH dependent, with a maximum at about 8.0 to 8.5. However, group II metals, especially Ca, Mg, and Fe are almost always present with silica, and they can influence the rate of scale development.

5 With Mg, for example, highly insoluble "magnesium silicate" can form, especially at pH>8. This scale actually comprises silica particles with magnesium polysilicates on the particle surfaces. The removal of silica scale once it is formed is very difficult and costly. With high silica water, therefore, cooling and reverse osmosis (RO) systems typically operate at low water-use efficiency to assure that the solubility of silica is not

I o exceeded. Under these conditions, RO systems must limit their pure water recovery rate and cooling systems must limit water recycling. In both cases, water discharge volumes are large.

Various additives have been employed to inhibit silica depositions. For example, several compositions based upon acrylic acid copolymers have been taught in various

15 U.S. patents. U.S. Patent No. 4,71 1 ,725, to Amick, et al., teaches acrylic acid copolymerized with acrylamido alkyl or aryl sulfonate, and substituted acrylamide. U.S. Patent No. 5,510,059 to Amjad teaches acrylic acid copolymerized with dimethyl- diallylammonium chloride and acrylamide. U.S. Patent No. 4,328, 106, to Harrar, et al., teaches inhibiting silica scaling and precipitation by injecting low concentrations of

20 cationic nitrogen containing compounds, such as polymeric amines, polymeric imines, and quaternary ammonium compounds. U.S. Patent No. 4,584,104, to Dubin, teaches inhibiting amorphous silica scale formulation by treating industrial waters with a boron compound which dissolves in or hydrolyzes in the industrial waters to give the orthoborate ion. U.S. Patent No. 5,271 ,847, to Chen, et al., teaches controlling the

25 deposition of silica by the use of a water soluble graft copolymer of acrylic acid and a polyalkylene glycol ether. U.S. Patent No. 5,271 ,862, to Freese, teaches inhibiting the deposition of silica and silicate compounds by adding a composition consisting of a hydroxyphosphono-acetic acid and a copolymer of acrylic acid and allyl hydroxypropyl sulfonate ether. U.S. Patent No. 5,658,465 to Nicholas, et al., teaches the use of

JO 2-ethyloχazoline as a silica polymerization inhibitor. EO/PO polymers are known for use as surfactants and are commercially available from BASF Corporation as Pluronic® and Tetronic® surfactants. They have also been evaluated for their ability as silica inhibitors in U.S. Patent No. 4,532,047 to Dubin and have been found to be ineffective.

Summary of the Invention

The present invention is the result of the discovery that certain EO/PO block polymers are effective at inhibiting the formation of silica and silicate compounds in water systems. They can be used alone or in combination with other water treating agents, such as phosphoric acids and their salts, phosphonic acids and their salts, metal chelating agents, corrosion inhibitors, oxygen scavengers, homo- and copolymers of acrylic acid, homo- and copolymers of maleic acid or anhydride, or acrylic acid/ maleic acid based polymers.

The EO/PO block polymers are employed in an effective amount, which will vary depending upon the makeup of the water that is being treated, but the amount will usually be in the range of about 0.5 to about 500 ppm.

Detailed Description of the Invention

The present invention is directed to EO/PO block polymers for inhibiting deposition of silica and silicate compounds in water systems. The EO/PO block polymers can be used either alone or in combination with acrylic acid copolymers.

EO/PO block polymers are block copolymers of ethylene -oxide (EO) and propylene-oxide (PO), as well as copolymers of EO and PO from ethylene diamine, and are available in a variety of formulas and from a variety of sources, including the Tetronic® and Pluronic® polymers from BASF, the Monolan® polymers from Akcros

Chemicals, the Antarox® polymers from Rhone-Poulenc, the Hartpo® polymers from Huntsman Corporation, the Marcol® polymers from PPG Industries, as well as other sources. The following formulas are representative of EO/PO block copolymers: e n

-H ϋ - I L U ; C li > 0 I L » : H O - { 1- C l O ^- ll

(H where x and x^" are approximately 5 to 20 (preferably 6 to 15), y is approximately 40 to 90 (preferably 50 to 70) and the polymer has a molecular weight (weight average or MWvv) of approximately 1 , 100 to 9,000 (preferably 3,000 to 6,000). These are made by the controlled addition of propylene oxide to the two hydroxyl groups of propylene glycol to form a hydrophobe, then ethylene oxide is added to sandwich the hydrophobe between hydrophylic groups. The polyoxyethylene or hydrophilic group will comprise 20 to 80% by weight of the molecule while the molecular weight of the polyoxypropylene or hydrophobe will be between about 950 and 4,000. These are available commercially as Pluronic® R surfactants.

^CH3 CH₃

0-(CHCH₂0)_x-(CH₂CH₂0)_y-(CH2CHO) -H

(II) where x plus x' equals at least 20 (usually 20 to 40, preferably 25 to 36), y is at least 20 (usually 20 to 35, preferably 22 to 32), and the molecular weight (MWw) is about 2,000 to about 5,000 (preferably 3,000 to 4,000). These are made by adding ethylene oxide to ethylene glycol to form a hydrophile of a designated molecular weight. Propylene oxide is then added to obtain hydrophobic blocks on the outside of the molecule. The polyoxyethylene or hydrophile group will comprise 10% to 80% by weight, while the hydrophobe or polyoxypropylene will have a molecular weight of about 1 ,000 to 3,100. These are commercially available as Pluronic® R surfactants.

H-(OCH₂CH₂) _"-(OCHCH₂)_λ (CH₂CHO) -(CH₂CH₂0)_v-H

/

N-CH.-CH.-N

H-(OCH₂CH₂)_v..-(OCHCH₂) «

CH, CH,

(III)

where x, x\ x", and x"" are about 1 to 21 and y, y y^", and y"' are about 7 to 114, and the molecular weight is about 1,650 to about 25,000. These are made by the sequential addition of propylene oxide and ethylene oxide to ethylenediamine. The tetra-functional structure provides four alkylene oxide chains. The polyoxyethylene or hydrophile group will comprise 10% to 80% by weight, while the hydrophobe or polyoxypropylene will have a molecular weight of about 500 to 7,000. These are commercially available as Tetronic® surfactants. CH₃ CH,

H-(OCHCH₂\ «-(OCH₂CH₂V (CH₂CH₂0\-(CH₂CHO)_v -H

N-CH.-CH.-N

CH, CII,

(IV) where x, x\ x", and x¹¹' are about 1 to 21 and y, y\ y", and y"' are about 7 to 1 14, and the molecular weight is about 1 ,650 to about 25,000. These are made by the sequential addition of ethylene oxide and propylene oxide. The polyoxyethylene or hydrophile group will comprise 10% to 80% by weight, while the hydrophobe or polyoxypropylene

5 will have a molecular weight of about 2, 100 to 6,700. These are commercially available as Tetronic® R surfactants.

The EO/PO polymers in accordance with the present invention can be employed per se, in an amount of between about 1 ppm (parts per million) up to about 250 ppm, although the range 5 to 75 ppm is preferred, and 15 to 50 ppm being further preferred,

] o for the inhibition of silica and silicate formation and/or deposition of silica and/or silicate compounds, or in combination with other water treating agents, such as phosphoric acids and their salts, scale inhibitors, corrosion inhibitors, oxygen scavengers, homo- and copolymers of acrylic acid, homo- and co-polymers of maleic acid or anhydride, and acrylic acid/maleic acid based polymers. Although combinations with copolymers of

15 acrylic acid are preferred.

Although any of the known (meth)acrylic acid copolymers known for use in water treatment can be employed in combination with the EO/PO block copolymers of the present invention, the preferred copolymers are terpolymers of acrylic acid, 2-acrylamido-2-methylpropane sulfonic acid, and styrene sulfonic acid. The methods of

20 preparing and examples of (meth)acrylic acid copolymers and terpolymers are disclosed, for example, in US Patent Nos. 3,646,099; 4,301,266; 4,314,004: 5,277,823; and 5,547,612, which disclosures are incorporated herein by reference, but are not considered limiting as to the scope of (meth)acrylic copolymers that can be employed..

The additives were evaluated for their ability to stabilize remarkably high levels

25 of soluble silica in water, based on the yellow silicomolybdic acid test for soluble silica set forth in R. . Her, "The Chemistry of Silica;¹ 1979, John Wiley, New York, page 95. The test measures the ability of a polymer to inhibit the polymerization of silica in a solution containing soluble silica (sodium silicate), calcium ion (Ca^~ ), magnesium ion (Mg~⁺) and chloride ion (CD at pH 7 and at 40°C. To perform this test, three aqueous

30 stock solutions were prepared comprising 0.20M Na₂Si0₃, a combination of 0.2M CaCl₂ and 0.2M MgCl₂, and 1 ,000 ppm of additive, in accordance with the present invention. A 200 mL test solution was prepared which contained 0 to 70.0 mL of the additive solution, 10.0 mL of Na₂Si0₃ solution, and 5.0 mL of the CaCL/MgCL solution, with the volume adjusted to 200 mL with distilled water and the pH adjusted to 7.0. The resulting test solution contains the following concentrations: 600 ppm soluble silica as Si0₂, 200 ppm Ca, 120 pm Mg, and 0 to 350 ppm of additive. The test solution is placed in a 225 mL wide mouth polyethylene jar containing a 2-hole rubber stopper. One opening is used for a pH probe and the second for sampling. The test solution was stirred with a magnetic stir bar while heated at 40°C in a circulating bath. The pH was maintained at 7.0±0.1. A 3 to 5 mL sample was periodically removed and passed through a 0.22 μm filter. A 2.00 mL sample of the filtrate was diluted to 25 L with distilled water. The contents of one pillow of Molybdate Reagent for high range silica is added (Hach Co., Loveland, Colo., see Hach Water Analysis Handbook, 1989, p. 546) and the mixture stirred for 10 min. This was followed by one pillow of Acid Reagent for high range silica. The absorbance of the sample was measured at 450 nm. The reduction in soluble silica is based on the decrease in absorbance relative to the absorption obtained for the test solution immediately following its preparation.

The decline in soluble silica is measured with time, specifically at 0, 5 and 20 hr. The yellow compound formed between the molybdate reagent and monomeric silicic acid/silicate forms quantitatively, and the color intensity, as measured by absorbance at 450 nm, is proportional to the amount of soluble silica present in the test solution. Absorbance is measured with a spectrophotometer.

The invention can best be understood by reference to the following examples, in which the invention is presented in greater detail. The examples are not, however, to be construed to limit the invention herein in any manner, the scope of which is defined in the appended claims. Examples

Table I EO/PO Block Polymers

Table II Ingredients

Table III Comparative Examples

As can be seen from the data presented in Table 1, the Pluronic® and Tetronic® EO/PO block copolymers provide excellent silica polymerization inhibition. This can be contrasted to the data presented in the comparison examples presented in Table 3, where the performance of prior art silica inhibitors, e.g., boric acid, ethanolamines, hydroxy compounds, and vinyl polymers, which can be used for comparison, is presented. Blend Example

A blend of equal parts (based upon the solids) of Pluronic F-68 and Good-Rite K-798 was made by putting the Pluronic in water, mixing the aqueous blend, and then adding the Good-Rite K-798 to provide a mixture having 31 to 35% solids. The blend was compared with commercially available silica inhibitors on an equal actives basis to show their effectiveness at inhibiting the deposition of silica. The silica solution was a mixture of 560 milligrams per liter (mg/L) of Si0₂, 200 mg/L of Ca, 120 mg/L of Mg, all at 40°C, and a pH of 7.0. The results are recorded in Table IV and show that even at a lower dosage, and at 22 hours, a blend employing the block copolymers of the present invention is effective at inhibiting the deposition of silica.

Table IV

As can be appreciated, the silica inhibitors of the present invention can be used in any water systems where high silica levels are a problem. Examples would include water in cooling towers, boilers, reverse osmosis applications, geothermal applications where the water undergoes controlled temperature reduction, where an aqueous sugar (or concentrate is being evaporated during sugar production), or a drilling fluid is used to enhance oil recovery.

The additives of the present invention have excellent performance as a silica inhibitor, either alone or in combination with known water treatment additives. The precise effective dosages at which they are employed will vary depending upon the makeup of the water that is being treated. An effective dosage for an effective combination of additives for water treatment will usually be in the range of 0.5 to

500 ppm, with the dosage in the range of 1 to 100 ppm being preferred since the higher the dose, the higher will be the cost, with 5 to 50 ppm being another preferred range. These dosages are typical for water treatment additives. The additives of the present invention are excellent threshold silicate precipitation inhibitors, but they also can be designed to stabilize, disperse, and solubilize silica and silicates. Further, the additives of the present invention could be combined with a variety of other water treatment chemicals or compositions, including surfactants, phosphonates and their salts, substituted phosphonates and their salts, other phosphonic acids and their salts, phosphoric acids, metal chelating agents, oxygen scavengers, and other scale inhibiting agents. Thus, the additives of the present invention are useful in a wide variety of aqueous systems, including, but not limited to, cooling water systems, boiler water systems, desalination systems, gas scrubber water systems, blast furnace water systems, reverse osmosis water systems, evaporator systems, paper manufacturing systems, mining systems, geothermal applications and the like.

The foregoing embodiments of the present invention have been presented for the purposes of illustration and description. These descriptions and embodiments are not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above disclosure. The embodiments were chosen and described in order to best explain the principle of the invention and its practical applications to thereby enable others skilled in the art to best utilize the invention in its various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the invention be defined by the following claims.

Claims

What 1 claim is:

1. A method for controlling silica or silicate scale formation in an aqueous systems comprising adding to said system an effective amount of scale inhibitor comprising an EO/PO block polymer composition.

2. The method of claim 1 wherein the EO/PO block polymer composition is selected from the following formulas:

A)

CH₃

ΗO-(CH₂CH₂0)_x-(CH₂CHO)_v-(CH₂CH₂OVH

where x and x¹ are approximately 5 to 20 and y is approximately 40 to 90 and the polymer has a molecular weight of approximately 1 ,100 to 9,000;

B)

CH₃ CH,

0-(CHCH₂0) -(CH₂CH₂0)_v-(CH₂CHO\-H

where x plus x' equals at least 20, y is at least 20, and the molecular weight (MW ) is about 2,000 to about 5,000;

C)

CH, CH,

H-(OC

(CH₂CH0)v-(CH₂CH₂0χ-H

N-CH,-CH,-N

HCH₂V (CH₂CHOV(CH₂CHiθχ.-H

CH^ CH,

where x, x\ x", and x-"" are about 1 to 21 and y, y\ y", and y¹" are about 7 to 1 14, and the molecular weight is about 1 ,650 to about 25,000; and

D)

H- OCHCH₂V-(OCH₂CH₂V (CH₂CH₂0\-(CH₂CHO)_v-H

H-(OCHCH₂\.-(OCH₂CH₂V (C H₂C H₂OX-(C H₂C HO\ .- H

where x,

and x^'" are about 1 to 21 and y, y^", y", and y"" are about 7 to 1 14, and the molecular weight is about 1 ,650 to about 25,000.

3. The method of claim 1 wherein the EO/PO block copolymer is present in an amount of between about 1.0 and 250 ppm.

4. The method of claim 1 wherein the EO/PO block copolymer is present in an amount of between about 5.0 and 75 ppm.

5. The method of claim 1 wherein the EO/PO block copolymer is present in an amount of between about 15 and 50 ppm.

6. The method of claim 1 wherein the EO/PO block copolymer has a molecular weight of 2,000.

7. The method of claim 1 wherein the EO/PO block copolymer has a molecular weight of 12,600.

8. The method of claim 1 wherein the EO/PO block copolymer has a molecular weight of 14,600.

9. The method of claim 1 wherein the EO/PO block copolymer has a molecular weight of 8,400.

10. The method of claim 1 wherein the EO/PO block copolymer has a molecular weight of 2,500.

1 1. The method of claim 1 wherein the EO/PO block copolymer is derived from ethylene diamine and has a molecular weight of 2,500.

12. The method of claim 1 wherein said polymer is combined with an effective amount of an homo- or copolymer costabilizer containing acrylic acid and/or maleic acid wherebv mineral scale is inhibited in the water svstem.

13. The method of claim 1 wherein said polymer or copolymer are combined with an effective amount of poly-maleic acid or anhydride costabilizer whereby mineral scales are inhibited in the water system.

14. The method of claim 1 wherein said polymer or copolymer are combined with an effective amount of corrosion inhibitor whereby corrosion inhibition is provided in the water system.

15. The method of claim 1 wherein said polymer or copolymer are combined with an effective amount of a phosphonate whereby mineral scale inhibition and coiTOsion inhibition are provided in the water system.

16. The method of claim 1 wherein said polymer or copolymer are combined with effective amounts of polymer costabilizer s, metal chelating agents, oxygen scavengers, suspending aids, and corrosion inhibitors whereby dispersion of suspended matter and mineral scale, stabilization of metal ions, and corrosion inhibition are provided in the water system.

17. A method for controlling silica or silicate scale formation in an aqueous systems comprising adding to said system an effective amount of scale inhibitor comprising a blend of.

A) a water soluble terpolymer of (meth)acrylic acid or maleic acid or salts thereof of having a weight average molecular weight of from about 1 ,000 to about 25,000 where the terpolymer is formed from: 1) from about 30 to about 80 weight percent of (meth)acrylic or maleic acid, and

2) from about greater than 1 1 to about 40 weight percent of a (meth)acrylamido methylpropane sulfonic acid or styrene sulfonic acid; and/or

3) from about 3 to about 30 weight percent of styrene sulfonic acid, and B) an ethylene oxide/propylene oxide block copolymer selected from the group consisting of:

1)

where x and x" are approximately 5 to 20 and y is approximately 40 to 90 and the polymer has a molecular weight of approximately 1 , 100 to 9,000; 2)

^{C H}3 CH₃

0-(CHCH₂OX-(CH₂CH₂OX.-(CH₂CHOX-H

where x plus x' equals at least 20, y is at least 20, and the molecular weight

is about 2,000 to about 5,000;

3)

CH₃ CH,

H-(OCH₂CH₂)_v"-(OCHCH₂X (CH₂CHOX-(CH₂CH₂0\ -H

N-CH.-CH-N

H-(OCH CH₂χ.-(OCHCH₂X" (CH₂CH0X-(CH₂CH₂0X-H

CH₃ CH₃

where x, x", x", and x^""^" are about 1 to 21 and y, y\ y'\ and y^'" are about 7 to 1 14, and the molecular weight is about 1 ,650 to about 25,000; and 4)

CH, CH,

H-(0CHCH₂χ »-(OCH₂CH₂χ. (CH₂CH₂0) -(CH₂CH0)_y-H

\ /

N-CH₂-CH₂-N

/ \

H-(OCHCH₂)_v~(OCH₂CH₂V (CH₂CH₂0) -(CH₂CH0X-H

CH, "3

where x, x\ x", and x'" are about 1 to 21 and y, y\ y", and y"^"' are about 7 to 114, and the molecular weight is about 1 ,650 to about 25,000.

18. A method for controlling silica or silicate scale formation in an aqueous systems comprising adding to said system an effective amount of scale inhibitor comprising a blend of: A) a water soluble copolymer of (meth)acrylic acid or maleic acid or salts thereof having a weight average molecular weight of from about 1 ,000 to about 25,000, and

B) an ethylene oxide/propylene oxide block copolymer selected from the group consisting of; 1)

CH₃

-H0-(CH₂CΗ₂0X-(CH₂CH0X-(CH₂CH₂0χ-H

where x and x¹ are approximately 5 to 20 and y is approximately 40 to 90 and the polymer has a molecular weight of approximatelv 1,100 to 9,000: CΉ₃ CH₃

0-(CHCH₂0),-(CH₂CH₂0)_y-(CH₂CH0X-H

where x plus x' equals at least 20, y is at least 20, and the molecular weight (MWw) is about 2,000 to about 5,000;

3)

H-(OCH₂CH₂X "-

X-(CH₂CH₂0X -H

N-CHTCH_J-N

H-(0CH CH₂)_v >.-(OCHCH₂X» (CH₂CH0X-(CH₂CH₂0)_v.-H

CH₃ CH,

where x, x', x", and x'" are about 1 to 21 and y, y\ y", and y"' are about 7 to 1 14, and the molecular weight is about 1,650 to about 25,000; and

4)

CH, CH₃

H-(OCHCH₂)_v..-(OCH₂CH₂V (CH₂CH₂0 V(C H₂CHO\ - H

H-(0CHCH₂)_y-(0CH₂CH₂X» (CH₂CH₂0X-(CH₂CH0)_v-H

CH, CH₃

where x, x\ x", and x'" are about 1 to 21 and y, y\ y", and y"' are about 7 to 114, and the molecular weight is about 1,650 to about 25,000.