CA1270258A - Sulfate-containing polymers as scale inhibitors - Google Patents

Abstract

ABSTRACT OF THE INVENTION
A novel, water-soluble, sulfated vinyl monomer is presented; which may be used to provide scale-inhibiting agents which are particularly effective against phosphate scale, and which comprise vinyl alkylolamide sulfate or vinyl alkylolanilide sulfate, polymerized with an alkenyl compound, such as acrylic acid or the like.

Description

~27~58 FIELD OF THE INVENTION
This invention relates generally to chemical agents for inhibiting the deposit of mineral scale in industrial water systems and like equipment. The invention relates more particularly to chemical agents which act to inhibit the formation of calcium phosphate scale and similar deposits in cooling water systems. In one specific aspect, the present invention relates to a novel, water-soluble, sulfated vinyl monomer.
BACKGROUND OF THE INVENTION
Water is caused to flow through various types of piping and heat exchanger systems for extracting heat fLom turbine steam, chemical processes, and numerous o-ther operations. Common to all of these applications is the exposure of comparatively cool, flowing water to a comparatively hot metal surface; and this combination of factors promotes the precipitation or deposit of various salt matrices, depending upon the mineral content of the cooling water. The resultant scale interferes with efficient heat transfer, leading ultimately to destructive overheating of the system, and may, in extreme cases, produce clogging as a final consequence of reducing the lumen-size of the conduits involved.
Scale deposits of calcium phosphate have proved to be especially troublesome because of their resistance to removal and because of the difficulties encountered in inhibiting their formation.
SUMMARY OF T~E INVENTION
The present invention offers a novel~ water-soluble, sulfated vinyl monomer which may be used to provide a family of new and improved sulfate polymers which exhibit remarkable phosphate-scale inhibitory properties. In one specific ~3i

2 -- ` " ~ ;~

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embodiment, the present invention contemplates the creation of acrylamide and acrylanilide sulfates which can be easily reacted with an alkenyl compound, such as acrylic acid, to produce water-soluble polymers exhibiting strong, scale inhibitory properties. For example, mono (~-methacrylamido-phenyl) sulfate polymers have been prepared and, when dosed at the 5 p.p.m. level, have been found to be superior to such conventional scale antagonists as the co-polymers of sulfonated styrene and maleic acid and the co-polymers of hydroxypropyl acrylate and acrylic acid.

~ 5~ ,TI~L~DL~ol~ ;nzy~
In the practice o-f the present invention, an alkylolamide or an alkylolanilide is selected as the starting material to be converked to the corresponding novel sulfate monomer by reaction with such agents as sulfuric acid, sulfur trioxlde or chlorosulfonic acid. The resultant sulfates are then polymerized with a suitable alkenyl compound, such as acrylic acid; and it has been found that the activity of the ultimate pol~mer as a scale antagonist is increased with 2Q increasing degrees of sulfation of the nitrogen-containing monomer.
In accordance with one aspect of the present invention there is provided a novel sulfate monomer having th~
following general skructural formula:

CH2~ ~ C ~_ C ~ N--R2 (I) R ~ - OSO3 wherein Rl represents either an alkyl group having one to three carbon atoms or a hydrogen atom; wherein R2 represents an alkyl group having one to three carbon atoms, a hydrogen atom or an alkylol group having one to eight carbon atoms; and wherein R3 ~27(3~
665~9-~13 represents a bond, an alkylene group having one to eight arbon atoms, or a phenyl group.
Examples of preferred sulfate monomers include mono(4-methacryla~ido-phenyl) sulfate, mono(acrylamido ethyl)sulfate, and mono(2-acrylamido-2-methyl-propyl)sulfate.
The sulfated vinyl monomers (I) of the present invention can be prepared hy sulfating an alkylolamide or an alkylolanilide having the general structural formula:
Rl O
CH2 -- C ~ N - - R (II) R --- ~ -OH
wherein R1 represents either an alkyl group having one to three carbon atoms or a hydrogen atom; wherein R2 represents an alkyl group having one to three carbon atoms, a hydrogen atom or an alkylol group haviny one to eight carbon atoms; and wherein R3 represents a bond, an alkylene group having one to eight carbon atoms, or a phenyl group, with a compound of sulfur trioxide.
Examples of preferred starting materials include p-hydroxy-methacrylanilicle and 2-hydroxy-ethylacrylamide. These compounds are advantageous from the standpoint of the amenability of their reaction products to further synthesis.
However, various aliphatic, cycloaliphatic and aromatic hydroxy compounds may find utility in the invention.
In accordance with an important feature of the present invention, the starting compound is sulfated using one of the various compounds of sulfur trioxide. The particular sulfating agent is selected on the basis of cos-t and ease of handliny and chlorosulfonic acid is generally preferred for hoth laboratory and batch scale operations where glass-lined vessels can be readily employed. When the starting hydroxy compound i5 normally solid at temperatures above 30C., it will ~ 4 ~2~
6~530-413 be first melted or suspended in a suitable solvent such as chloroform or carbon tetrachloride; and under circumstances where a particularly mild sulfation reaction i5 desired, the chlorosulfonic acid will be preliminarily complexed with ethyl ether for example. Moreover, unbalanced patterns of heat and gas evolution may be a~tenuated by initially saturating the starting compound with hydrogen chloride.
Sulfation is caused to take place at about room temperature or at a mildly elevated ~emperature of about 30-35C; and the sulfated product is advantageously dissolved in acaustic solution to facilitate separation of any solvent present and to neutralize any residual hydrochloric acid. The resultant sulfated vinyl monomer is then dried under vacuum.
Yields of the sulfated product range from 70% to over 95% of theoretical.
The sulfated vinyl monomer (I) may be reacted with itself to form a homopolymer or with one or more suitable alkenyl compounds to form a copolymer. The polymer can be formed using conventional bulk, suspension, solvent, or emulsion techniques; and it is generally desirable to conduct the polymerization under alkaline conditions about a pH of 8.0 in order to promote water-solubility of the final product.
Polymerization initiators such as diammonium peroxysulfate and sodium bisulfite are also usefully employed.
In accordance with a preferred feature of the present invention the alkenyl compound is of the following formula:

l6 R4~- _ C -- C - C-- OH (III) o wherein R5 and R6 represent either hydrogen or an alkyl ~roup having one to ~hree carbon atoms, and R4 represents either , . ~, .'~3~'~ 5 ~7~)~58 6553~ ~13 hydrogen, an alkyl group having one to three carbon atoms, or a carboxylic acid group.
Preferred alkenyl compounds for polymerization include such comparatively short~chain unsakurated carboxylic acids as acrylic acid, methacrylic acid, maleic acid and itaconic acid; and the reactant or reactants are speci~ically chosen to gi~e co-polymers and terpolymers which possess an a~erage molecular weight in the range of about 3,000 to about 250,000. These have proved to exhibit optimum activity as scale antagonists.
Ano~her aspect of the present invention includes the method of inhibiting scale formation in an industrial water system which comprises the step of adding to the water in such a system a scale-inhibiting amount a scala inhibiting agent comprising a polymer of a sulfate monomer having the general structural formula:
Rl O
CH2 ~ C ~ ~ ~ ~ N ~ R (I) R ~ OSO3 wherein Rl represents either an alkyl group having one to three carbon atoms or a hydrogen atom; wherein R2 represents an alkyl group having one to three carbon atoms, a hydrogen atom, or an alkylol group having one to eight carbon atoms; and wherein R3 represents a bond, an alkylene group having one to eight carbon atoms, or a phenyl group; and an alkenyl compound having the general structural formula:

lR6 4 C C C OH (III) wherein R5 and R6 represent either hydrogen or an alkyl group having one to three carbon atoms, and R~ represents either 5a s~
~ 6535-413 hydrogen, an alkyl group having one to three carhon atoms or a carboxyl acid group~
A preferred scale inhibi~ing amount is from about 5 to about 20 p.p.m.
While it is not deæired to be limited to any kheory, it is believed that molecules of the co-polymers and terpolymers of the present invention attach themselves, by means of adsorption on the surfaces of the incipiently developing scale crystals and, once in place, inhibit further growth of the crystal, the stronger complexing carboxylic acid moiety serving the attachment function and the more polar sulfate moiety providing the repellent mechanism.
In order to describe the invention more fully, the following working examples are given without, however, intending to limit the invention to the precise details and conditions described.
Example 1 An acrylanilide sulfate co-polymer was synthesized by first suspending 17.7 g (0.1 mol) of p-hydroxymethacrylanilide ~0 in 100 ml of methylene chloride in a suitable glass reaction vessel and then adding 12 g of chlorosulfonic acid to the suspension. Hydrogen chlorlde gas was observed evolving during the addition; and the reaction mass was mechanically stirred overnight at room temperature. The resultant product was dissolved in a solution of 60 g water and abou~ 10 g of 50%
sodium hydroxide, giving a pH

5b '51' "~

~LZ~ .8 of about 11; a~d methylene chloride was then separated by vacuum.
A yield of about 75% of sulfated monomer, observed to be a vi~cous liquid, was then determined using nuclear magnetic re~onance technique~.
A 55.5 g quantity of the sulfated monomer, estimated to be about 28~ active material, was thereafter mixed with 28.8 g of acxylic acid; and the resultant mass was heated to 65C. with mechanical agitation. Next, 3 g of diammonium peroxysulfate and 8.18 g of sodium bisulfite were added; the pH was adjusted to 7.2 10 using caustic; and the mixture was maintained at 65C. for three hourQ in continuation of agitation. The resulting co-polymer waR e~timated to contain about 13% active material with an average molecular weight of about 55,000 as determined by GPC
in aqueous solution using sulfonated polystyrene as a standard.
The effectiveness of this co-polymer as a scale inhibitor is set ~orth in Table I hereinbelow.
Exam ~ 2 A sulfate monomer was again prepared from p-hydroxymetha-crylanilide in accordance with the method of Example l; and 8.0 g 20 of this material was mixed with 12.36 g of acrylic acid, 100.7 g of water and 13.47 g of 50% sodium hydroxide. The mixture was purged with nitrogen at room temperature and heated to 62C.
Thereafter, 1.17 g of diammonium peroxysulfate was added and then 3.51 g of sodium bisulfite. The temperature of the reaction mass rose to 67C. and was thereupon cooled to 65C. where the temperature was maintained for four hours. The a~erage molecular weight of the resulting co-polymer was determined to ~e 20,000 by GPC; and its scale inhibitory efficacy is set forth in Table I

hereinbelow.
The calcium phosphate inhibitory power of various polymers has been evaluated using the following procedure, employing tes~ chemicals of reagent grade:

(1) Put 300 to 350 ml of DI water in 600 ml jacketed beakers and let stand with mila stirring until temperature is brought to 150 degrees F (70 degree~ ~) by use of a consta~t temperature water bath.
(2) Put in required ml of stock hardness solution into jacketed beakers: For 250 p.p.m. CaCO3 use 50 ml or any desired hardness -To make 2 liters of stock solutisn:
A. Dissolve 7.356 g CaC12 2H2O in 800 ml DI H2G;
B. Dissolve 6.156 g MgSO4 7H2O in 800 ml DI H20;
C. Add both solutions to 2 liter volumetricflask and dilute to colume;
D. Shake well.

(3) Add sufficient ml of treatment product into jacketed beakers while stirring Inormally 5 mls for 10 p.p~m. concentration).

(4) Add DI water to make 500 ml in jacketed beakers (add water to line on beaker with stirrer not operating).
(S) With stirring, let solutions in beakers equilibriate to 158 degrees ~.
(6) With stirring, adjust pH to 8.5 with dilute(0.1 -0.4N) NaOH.
(7) Add 5 ml of 1000 p.p.m. PO4, pH-8.5 solution to jacketed beakers and wait about 3-5 minutes while stirring.
(8) Check pH of solution in beakers and as necessary adjust pH to 8.5 + 0.1 while stirring.
(9) Let experiment run at 158 degrees F with stirring for 4 hours.
(10) After 15 minutes, check pH o~ qolutions in beaker~

~L~70;~5~3 .
and as necessary adjust pH to 8.5 + 0.1. Also, check pH of solutions every 30 to 45 minutes thereafter.
(11) After the 4 hours are up, the 801ution is immediately filtered through 0.45 micron filter paper under vacuum. The filtered solution is analyzed for o-P04 using s~andard procedure and the color is evaluated in a spectrophotometer at 700 nm.
(12) The results are reported as percent inhibition calculated by the following formula:

(residual o-P04) - (blank residual o-P04) inhibltlon - ~ X lan (initlal o-P04) - (blank residual o-P04) WHERE: ~
- inltlal-o-P04 = o-P04 concentratlon in the mixture at the beginning of the experiment.
.. residual-o-P04 ~ o~P04 concentration ln the mixture at the end of the experiment wlth stabilizer.
.. blank residual-o-P04 J o-P04 concentration in the flltrate at the end of the experiment with no stabilizer.
The foregoing procedure was utilized to compare the co polymers of Examples 1 and 2 with two commercial scale inhibitors in their ability to zttenuate the development of phosphate sc~le.
The results are as follows:

~Z70~5~3 TABLE I

PERCENT
CALCIUM PHOSPHAT~
INHIsITIO~ (POLYMER
SCALEPOLYMER COMPOSITION DOSAGE IN P.P.M.) INHIBITOR - (MOLE RATIO) Mw 5 7.51~ 15 20 commercial Sulfonated styrene/
maleic acid (75/25)18,950 8 - 87 commercial Acrylic acid/
Hydroxypropyl acryl-ate (25/75)7,350 13 75 92 Example 1 Acrylic acid/
methacrylamidophenyl sulfate (^-75% pure) (90/20) 55,000 - - 1260 82 Example 2 Acrylic acid/
methacrylamidophenyl sulfate (~ 80% pure) (80/20) 20,000 68 88 100 - 100 As will be appreciated, the co~polymer of Example 2 of the present invention is superior to the two commercial products, especially at the lowest, most economical additive level.
Example 3 An acrylamide sulfate monomer was first prepared by reacting 35 g of 2-hydroxyethylacrylamide directly with 35 g of chlorosulfonic acid at 35C. in a suitable glass vessel. The solution became viscous and finally formed a rubbery mass, and the mixture foamed extensively at the later stages in the addi-tion of the chlorosulfonic acid. The product was dissolved in sodium hydroxide solution to a pH of about 8.5.
A co polymer was synthesized by reacting 127.6 g of the acrylamide sulfate monomer with 28.8 g of acrylic acid in 129.8 g of a solution of water and 5~% sodium hydroxide. This - initial mixture was heated to 80C.; and then 2.42 g of diammo-nium peroxysulfate was introduced with 8 g of water. The reac-tion became extremely exothermic and tended to overflow the 7~

reaction vessel. Wa-ter in the amount of 17 g was next added with 7.25 g of sodium bisulfite; and this mixture was reheated to 65C. and maintained at -tha-t -temperature for three hours.
The average molecular weight of the resultant sulfate co-polymer was determined -to be 129,000 by GPC; and the per cent calcium phosphate inhibition at a dosage rate of 10 p.p.m.
of the polymer was 97% and at a dosage rate of 7.5 p.p.m. was 12%.
Examples 4, 5, 6, 7 and 8 Additional co-polymers of mono(acrylamido-ethyl) sulfate were prepared according to the me-thods described here-inabove; and the resultant products were tested for phosphate scale inhibition with the following results:

PERCENT
CALCIUM PHOSPHATE
INHIBITION (POLYMER
DOSAGE IN P.P.M.) POLYMER COMPOSITION RATIO Mw 7.5 10 . . . _ . _ .
Acrylic Acid/mono (acrylamido-ethyl) sulfate 80/2033,200 14 98 Acrylic Acid/mono (acrylamido-ethyl) sulfate 90/109,130 - 82 Acrylic Acid/mono (acrylamido-ethyl) sulfate 70/306,690 - 96 10 Acrylic Acid~mono (acrylamido-ethyl) sulfate 30/70192,000 - 97 Methacrylic Acid/mono (acrylamido-ethyl) sulfate 80/2014,300 61 87 Examples 9, 10 and 11 Various terpolymers of mono(acrylamido-ethyl) sulfate were prepared using the methods previously described. The resulting polymers were characterized by C13 NMR and GPC and residual monomers were determined by GC method. Salient properties and the calcium phosphate screening results are tabulated below:

~, ~7~ i8 PERCENT
CALCIUM PHOSPHATE
INHIBITION (POLYME~
DOSAGE IN P.P.M.) POLYMER COMPOSITION MOLE RATIO Mw 7.5 10 20 Acrylic acid/meth-acrylic acid/
Mono(acrylamido-ethyl) sulfate52.7/23.7/23.778,20099 99 Acrylic acid/meth-acrylic acid/
Mono(acylamido-ethyl)sulfate24.4/51.2/24.433,500 96 91 Acrylic acid/
acrylamidomethyl propanol/
mono(acrylamido-me-thyl propyl) sulfate 80/10/10 8,260 - 12 96 The last listed example was prepared with acrylic acid and mono(acrylamidomethyl-propyl)sulfa-te. However, the sulfate was partially hydrolyzed during polymerization to give the alcohol. Consequently, terpolymer was formed.
The speci-fic examples herein disclosed are to be considered as being primarily illustrative. Various changes beyond those described will, no doubt, occur to those skilled in the art; and such changes are to be understood as forming a part of this invention insofar as -they fall within the spirit and scope of the appended claims.

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A sulfate monomer having the general structural formula, (I) wherein R1 represents either an alkyl group having one to three carbon atoms or a hydrogen atom; wherein R2 represents an alkyl group having one to three carbon atoms, a hydrogen atom or an alkylol group having one to eight carbon atoms; and wherein R3 represents a bond, an alkylene group having one to eight carbon atoms, or a phenyl group.

2. A sulfate monomer according to claim 1 which is mono(4-methacrylamido-phenyl) sulfate.

3. A sulfate monomer according to claim 1 which is mono(acrylamidoethyl) sulfate.

4. A sulfate monomer according to claim 1 which is mono(2-acrylamido-2-methyl-propyl) sulfate.

5. A method of preparing a sulfated vinyl monomer having the general structural formula (I) wherein R1 represents either an alkyl group having one to three carbon atoms or a hydrogen atom; wherein R2 represents an alkyl group having one to three carbon atoms, a hydrogen atom or an alkylol group having one to eight carbon atoms; and wherein R3 represents a bond, an alkylene group having one to eight carbon atoms, or a phenyl group, which comprises sulfating an alkylolamide or an alkylolanilide having the general formula (II) in which R1, R2 and R3 are as defined above with a compound of sulfur trioxide and at a temperature of from ambient up to about 35°C.

6. A method according to claim 5 wherein the sulfur trioxide compound is chlorosulfonic acid.

7. A polymer obtainable by polymerizing a sulfated vinyl monomer as claimed in claim 1 with an alkenyl compound.

8. A polymer as claimed in claim 7 wherein the alkenyl compound is of the formula (III) wherein R5 and R6 represent either hydrogen or an alkyl group having one to three carbon atoms, and R4 represents either hydrogen, an alkyl group having one to three carbon atoms or a carboxyl group.

9. The method of inhibiting scale formation in an industrial water system which comprises the step of adding to the water in such a system a scale-inhibiting amount a scale inhibiting agent comprising a polymer of a sulfate monomer having the general structural formula:

(I) wherein R1 represents either an alkyl group having one to three carbon atoms or a hydrogen atom; wherein R2 represents an alkyl group having one to three carbon atoms, a hydrogen atom, or an alkylol group having one to eight carbon atoms;
and wherein R3 represents a bond, an alkylene group having one to eight carbon atoms, or a phenyl group; and an alkenyl compound having the general structural formula:

(III) wherein R5 and R6 represent either hydrogen or an alkyl group having one to three carbon atoms, and R4 represents either hydrogen, an alkyl group having one to three carbon atoms or a carboxyl acid group.

10. The method according to Claim 9, wherein said scale-inhibiting amount is from about 5 to about 20 p.p.m.