CA2116597A1 - Method for inhibiting corrosion in aqueous systems - Google Patents

Abstract

ABSTRACT

A low phosphorus process for controlling corrosion in aqueous systems by adding to the aqueous system an effective amount of an azole, polyepoxysuccinic acid, a water soluble polymer and a topping agent to give added corrosion control.

Description

2116~97 ~ ' .
METHOD OF INHIBITING CORROSION
IN AQUEOUS SYSTEMS

FIELD OFTHE INVENTION
.: -The present invention relates to the treatment of aqueous systems 10 to reduce corrosion on the metallic surfaces in contact therewith. The inhibition of corrosion is especially desirable where heat transfer dynamics require clean surfaces.

BACK~OUND OF THE INVENTION
The problems of corrosion and attendant effects such as pitting ~ :
have troubled water systems for years. For instance, scale tends to accumulate on intemal walls of various water systems, such as boiler and cooling systems, and thereby materially lessens the operational efficiency 20 of the system. In this manner, heat transfer funcUons of the particular system are severely impeded.

.

~$ ; i ~ r~; r ~ ~

2116~97 Corrosion is a degradative electrochemical reaction of a metal with its environment. Simply stated, it is the reversion of refined metals to their natural state. For example, iron ore is iron oxide. Iron oxide is refined into steel. When the steel corrodes, it forms iron oxide which, if 5 unattended, may result in failure or destruction of the metal, causing the particular water system to be shut down until the necessary repairs can be made Typically in cooling water systems, corrosion along with pitting has 10 proven deleterious to the overall efficiency of the cooling water system.
Recently, due to the popularity of cooling treatments using ortho-phosphate to promote passivation of the metal surfaces in contact with the system water, it has become critically important to maintain relatively -:
high levels of orthophosphate in the system to achieve the desired 15 passivation without resulting in fouling or impeded heat transfer functions Environmental regulations have begun to impose increasingly more severe res~rictions on the discharge of phosphate from industrial 20 processes into loc,al rivers and streams. Phosphates originally evolved as a viable aUernative to zinc based industrial water system treatment programs which were severely restricted due to their high toxicity to fish and other aquatic life.

26 Recent environmental regulations in the Great Lakes area restricts the discharge of phosphorus (P) to a maximum of 1 ppm. Current industrial corrosion technology fails to meet these severe discharge limits. These programs rely greatly on the effective corrosion inhibiting properties of inorganic and organic phosphate combinations at levels far in excess of the 1 ppm P discharge limit.

2116~97 It is an object of this invention to provide industrial water users with an effective corrosion inhibiting treatment program which complies with environment standards for the discharge of less than 1 ppm P.

The present invention provides an effective low phosphorus method for controlling the corrosive attack of metallic surfaces in contact with aqueous systems. Examples of such systems include metal 10 processing, cooling towers and wastewater processing. Specifically, the method of the present invention comprises adding to the aqueous environment a blend of effective amounts of a polyepoxysuccinic acid (PESA), a water soluble azole compound, a water soluble polymer and various topping agents in order to enhance the corrosion inhibiting 15 properties thereof. For instance, those topping agents include ortho-phosphate, polyvalent metal salts, carboxylic or dicarboxylic acids and general metal passivators.

Th~ polyepc,xysuccinic acid material employed in the present 20 invention can be obtained by the polymerization of epoxysuccinate in the presence of calcium hydroxide or other alkaline calcium salts. The ~eneral reaction can be represented as follows:

O~Ca(OH)2/H20 ~ ~
R~ C R - ~ HO~ C ~ O)nH
~;: C=O 0=~ C' O
O ~ O
I\h ~AM M

2~ 7 A complete description of one method of preparing such a poly- ~ :
epoxysuccinic acid is included in U.S. Pat. No. 4,654,159, incorporated herein by reference.

The water soluble azole compounds employed by the present invention have the Formulae:
i) R1~,/ N~
¦ N

H
:
R1y N~

20R2/~--S/
) N C ~ N
~C--N--2~16~97 where R1, R~ are separately H, C1 to C4 alkyl, or together are part of a benzene or substituted benzene ring, and R3 = C6 to C10 alkyl. -:

Examples are 1,2,3-triazoles include benzotriazole, 4-phenol-5 1,2,3-triazole, 4-methyl-1,2,3-triazole, 4-ethyl-1,2,3 triazole, 5 methyl-1,2,3-triazole, 5-ethyl-1,2,3-triazole, 5 propyl-1,2,3 triazole, 1,2,3 tolytriazole, mercapto-benzothiazole a~d 5 butyl 1,2,3-triazole. Alkali metal or ammonium salts of these compounds may be used.
. .
The water soluble polymers of the present invention are copoly-- mers consisting of different monomeric repeat units. The first monomer is ~ .~
any unsaturated carboxylic acid or salt thereof. Examples include acrylic ~ .
acid, methacrylic acid, maleic acid, itaconic acid, vinyl acetic acid, allyl acetic acid, fumaric acid, ,B-carboxyethyl acrylate, their salts and mixtures thereof. ~ :

The second monomeric unit of the copolymer consists of mono-mers which are known to exhibit surfactant properties. Examples include hydroxylated lower alkyl (C2 C6) acrylate. The preferred moiety is 20 hydroxypropyl acrylate. This monomer and a process for polymerizing it with unsaturated carboxylic acids is disclosed in U.S. Patent 4,303,568, herein incorporated by reference.

Further examples of the second monomer include unsaturated 25 sulfonic acids such as 2-acrylamido-2-methylpropylsulfonic acid (AMPS~), 2-methacrylamido-2-methylpropylsulfonic acid, sulfo alkyl acrylate or methacrylate, allyl sulfonic acid, methallyl sulfonic acid, 3-methacrylamido-2-hydroxy propyl sulfonic acid, sulfonic acid acrylate and their salts thereof. AMPS is the preferred monomer. These acids and 30 methods of polymerization thereof are disclosed in U.S. Patent 4,618,448, herein incorporated by reference.

Additionally, the second monomer may be comprised of a sulfonate ether moiety. The preferred monomer is allyl hydroxypropyl sulfonate ether. This monomer and techniques for polymerizing it with unsaturated carboxylic acids is disclosed in U.S. Patent 4,659,482, 5 herein incorporated by reference.

The number average molecular weight of the polymers described above falls within the range of 1,000 to 1,000,000, preferably 1,500 to 500,000. The key criterion is that the polymer be water soluble.
The molar ratio of the first monomer to the second monomer, both as described above, falls within the range of 30 to 1 to 1 to 20. However, between 10 to 1 and 1 to 5 is preferred.

The orthophosphate employed in this invention may be derived from any one of a number of sources capable of generating the orthophosphate ion. Such sources include inorganic phosphoric acids, phosphonic acid salts, and organic phosphoric acid esters.

Examples of such inorganic phosphoric acids includa condensed phosphoric acids and water soluble salts thereof. The phosphoric acids include an orthophosphoric acid, a primary phosphoric acid and a secondary phosphoric acid. Inorganic condensed phosphoric acids include polyphosphoric acids such as pyrophosphoric acid, tripolyphosphoric acid and the like, metaphosphoric acids such as trimetaphosphoric acid, and tetrametaphosphoric acid.

As to the other phosphonic acid derivatives which are to be added in addition to the polymers of the present invention, there may be menSioned aminopoiyphosphonic acids such as aminotrimethylene phosphonic acid, ethylene diaminetetramethylene phosphonic acid and 5 the like, methylene diphosphonic-acid, hydroxyethylidene diphosphonic acid, 2-phosphonobutane 1,2,4, tricarboxylic acid, etc.

Exemplary organic phosphoric acid esters include phosphoric acid esters of alkyl alcohols such as methyl phosphoric acid ester, ethyl 10 phosphoric acid ester, etc., phosphoric acid esters of methyl cellosolve and ethyl cellosolve, and phosphoric acid esters of polyoxyalkylated polyhydroxy compounds obtained by adding ethylene oxide to polyhydroxy compounds such as glycerol, mannitol, sorbitol, etc. Other suitable organic phosphoric esters are the phosphoric acid esters of 15 amino alcohols such as mono, di, and tri-ethanol amines.

Inorganic phosphoric acid, phosphonic acid, and organic phosphoric acid esters may be salts, preferably salts of alkali metal, ammonia, amine and so forth.
Exemplary polyvalent metal salts which may be utilized in this invention include those capable of dissociating polyvalent metal cations in water, such as zinc, manganese, vanadium, tin and nickel. Examples of such salts include zinc chloride, zinc sulfate, nickel sulfate, nickel 25 chloride and the like.

General metal passivators consist of tungstate, molybdate, nitrite, silicate and borate.

The method of the present invention comprises adding to the aqueous environment amounts of the compounds described above effective to control the corrosion of the surfaces of the metals in contact therewith. The following concentration ranges may be employed:

PESA 1-100 ppm, preferably 10-20 ppm polymer 140 ppm, preferably 5-1 û ppm azole 1-20 ppm, preferably3~ ppm topping agent 1-500 ppm, preferably 2-200 ppm, with the proviso that the discharge limit of less than 1 ppm P is not exceeded.

The above ingredients may be added separately neat to the aqueous system to be treated or they may be first blended in an aqueous 15 solution at the discretion of the user. The treatment blend may be added either continuously or intermittently. Alternatively, a pretreatment dosage of the blended compounds may be added followed by sma!ler quantities as a maintenance dosage.

20 ExamDles The invention will now be further described with reference to specific examples which are to be regarded solely as illustrative and not as a limitation on the scope of the invention.

Recirculator Studies In order to demonstrate the effective corrosion inhibiting properties of the inventive composition, tests were conducted under recirculating 30 heat transfer conditions such as would be experienced in a cooling tower.

21165~7 In this test system heated water is circulated by a centrifugal pump through a corrosion coupon by-pass into which corrosion coupons are inserted, and past a mild stsel (AIS1-1010) heat exchanger tube contained in a plexiglass block. The inside of the exchanger tube is filled 5 with wood's metal and heated with an electric heater. The temperature of the wood's metal can be regulated. The water velocity past the corrosion coupons and heat exchanger tube can be controlled anywhere from 0 to 4.5 fVsec.
~:
The pH and temperature of the bulk water are automatically controlled. The treated water is prepared by chemical addition to deionized water. Provisions for continuous makeup and blowdown are ~ .
made by pumping fresh treated water from supply tanks to the sump, with overflow from the sump serving as blowdown.
Corrosion rates are determined by exposing pre-cleaned and weighed metal specimens for a specified period of time, after which they ~ -are removed, cleaned and reweighed. Corrosion rates are calculated by dividing the total coupon weight loss by the number of days of exposure.
The specific conditions employed are: Heat Flux = 8,000 BTUffl2/hr; Water Velocity = 3 fVsec; Water Temperature = 120F' System Retention Time = 1.4 days; low carbon steel (LCS) heat transfer probe and LCS corrosion rate probe, and LCS and admiralty (ADM) 25 coupons.

Water Chemistry: 400 ppm Ca as CaC03, 150 ppm Mg2+ as CaC03, 51 ppm SiO2; pH = 8.6.

~118~7 The treatment composition according to the invention as well as comparative treatment compositions are as shown in Table 1. The following results were obtained.
TABLE I

Corrosion Rate -.
(mpy) 1 0 Concentration Treatment(PPm) LCS ADM Comments A) ortho 1.6 1.3 0.0 moderate to B575 2.4 severe pitting TTA 3.0 corrosion AA/AHPSE 5.0 B) ortho 3.0 1.9 0.0 moderate TTA 3.0 pitting AAJAHPSE corrosion and deposition C) B575 5.0 16.0 0.1 moderateto TTA 3.0 severe general AAJAHPSE 5.0 corrosion TABLE I ~cont'd) Corrosion Rate (mpy) Concentration Treatment(PPm) LCS ADM CommQnts D) HEDP 3.3 37.00.1 severe corrosion TTA 3.0 and deposltion AA/AHPSE 5.0 E) PESA 15.0 13.00.1 severecorrosion rrA 3.0 anddeposition AA/AHPSE 5.0 F)* ortho 135.. O 0 5 0.2 superficial pltting TTA 3.0 AA/AHPSE 5.0 ~ corrosion rates are an average of two tests.
Legend:
mpy = mils per year LCS = low carbon .
ADM = admiralty brass ortho = orthophosphate generated from sodium phosphate monobasic B575 = Belcor 575: hydroxyphosphonoacetic acid TTA = tolyltriazole as representative azole AAIAHPSE = copolymer acrylic acidlallyl hydroxypropyl sulfonate ether having a 3/1 molar ratio, mw = ~ 3,000 HEDP = Dequest 2010: hydroxyethylidene diphosphonic acid PESA = polyepoxysuccinic acid . . . . ... ... .... . .... . . ..

Clearly superior results were obtained by treatment with composition F. Interestingly, neither the combination of orthophosphate, TTA and AA/AHPSE copolymer nor the combination of PESA with TTA
and AA/AHPSE yielded desirable results. In fact, these tests resulted in 5 moderate to severe corrosion of the LCS heat transfer surface.

What has been described herein above is an effective corrosion control composition and method for treating industrial water systems which complies with strict environmental discharge limits of no more than 10 1 ppm P.

While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and - modifications of this invention will be obvious to those skilled in the art.
15 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.

Claims (18)

1. A process for inhibiting corrosion on metallic surfaces in contact with an aqueous medium comprising adding to the aqueous medium an effective amount for the purpose of a corrosion inhibitor comprising an azole, polyepoxy succinic acid, a water soluble polymer and a topping agent.

2. The process of claim 1 wherein the metallic surfaces contain low carbon steel.

3. The process of claim 1 wherein the aqueous medium is a cooling tower system.

4. The process of claim 1 wherein the azole has the structure:
i) ii) iii) where R1, R2 are separately H, C1 to C4 alkyl, or together are part of a benzene or substituted benzene ring, and R3 = C6 to C10 alkyl.

5. The process of claim 4 wherein the azole is 1,2,3 tolyltriazole.

6. The process of claim 1 wherein the water soluble polymer consists of first and second monomers, the first monomer comprising an unsaturated carboxylic acid or salt thereof and the second monomer comprising a compound selected from the group consisting of an hydroxylated lower alkyl (C2-C6) acrylate, an unsaturated sulfonic acid and a sulfonate ether.

7. The process of claim 6 wherein the first monomer is selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, itaconic acid, vinyl acetic acid, allyl acetic acid, fumaric acid, .beta.-carboxyethyl acrylate and salts thereof.

8. The process of claim 6 wherein the hydroxylated lower allyl (C2-C6) acrylate is hydroxy propyl acrylate.

9. The process of claim 6 wherein the unsaturated sulfuric acid is selected from the group consisting of 2-acrylamido-2-methyl-propylsulfonic acid, 2-methacrylamido-2-methylpropylsulfonic acid, sulfo alkyl acrylate, sulfo alkyl methacrylate, allyl sulfonic acid, methallyl sulfonic acid, 3-methacrylamido-2-hydroxy propyl sulfonic acid, sulfonic acid acrylate and salts thereof.

10. The process of claim 9 wherein the unsaturated sulfonic acid is 2-acrylamido-2-methylpropylsulfonic acid.

11. The process of claim 6 wherein the sulfonate ether is allyl hydroxypropyl sulfonate ether.

12. The process of claim 6 wherein the number average molecular weight of the polymer is between 1,000 and 1,000,000.

13. The process of claim 6 wherein the molar ratio of the first monomer to the second monomer is between about 30 to 1 and 1 to 20.

14. The process of claim 1 wherein the topping agent is selected from the group consisting of orthophosphate, polyvalent metal salts, carboxylic acid, dicarboxylic acid and general metal passivators.

15. The process of claim 14 wherein the orthophosphate is selected from the group consisting of inorganic phosphonic acids, phosphonic acid salts and organic phosphonic acid esters.

16 16. The process of claim 14 wherein the polyvalent metal salts are selected from the group consisting of the salts of zinc, manganese, vanadium, tin and nickel.

17. The process of claim 14 wherein the general metal passivators are selected from the group consisting of tungstate, molybdate, nitrite, silicate and borate.

18. The process of claim 1 wherein the relative amounts of polyepoxysuccinic acid: azole: water soluble polymer: topping agemt added to the aqueous medium is 1-100 ppm: 1-20 ppm: 140 ppm: 1-500 ppm.