WO2000039359A1

WO2000039359A1 - Corrosion inhibitor compositions and methods to control metal corrosion in brine systems

Info

Publication number: WO2000039359A1
Application number: PCT/US1999/030562
Authority: WO
Inventors: Jasbir S. Gill; Susan P. Rey
Original assignee: Calgon Corporation
Priority date: 1998-12-29
Filing date: 1999-12-21
Publication date: 2000-07-06
Also published as: AU2205900A

Abstract

Disclosed are compositions and methods to inhibit the corrosion of metal surfaces that comprise at least one blend selected from the consisting of: I.) a) an effective amount of PBTC and b) an effective amount of HPA; II.) a) an effective amount of a POCA homopolymer and b) an effective amount of a compound selected from the group consisting of PBTC, HPA, and mixtures thereof; and III.) a) an effective amount of a POCA copolymer and b) an effective amount of HPA. Each of the blends can contain an optional azole c).

Description

CORROSION INHIBITOR COMPOSITIONS AND METHODS TO CONTROL METAL CORROSION IN BRINE SYSTEMS

This patent application claims priority based on Provisional Application Serial Nos . 60/114,087,

60/114,093, and 60/114,094 all filed on December 29, 1998.

FIELD OF THE INVENTION The present invention relates to methods of inhibiting the corrosion of metallic surfaces of water- carrying systems, and to compositions for use in such a method, particularly in which the water of the system is oxygen bearing. More particularly, the present invention relates to the use of compositions in the presence of sodium chloride and/or calcium chloride brine systems.

BACKGROUND OF THE INVENTION

Oxygen corrosion is, of course, a serious problem in any metal-containing aqueous system. The corrosion of iron and steel is of principal concern because of their extensive use in many types of industrial and municipal water systems. However, corrosion of copper and copper containing metals is also of concern and many systems use a combination of metals.

Brines are used in various industrial applications. Of particular interest are the brines used in the cooling systems or chillers, as these are widely known. These systems are supposed to be closed loop but in practice due to leaks and operational requirements, they are practically oxygen saturated. These systems are, very aggressive for corrosion, and thus corrosion control is necessary.

Brine cooling systems, such as calcium chloride, sodium chloride and lithium chloride brines, have unique corrosion problems, with sodium chloride and lithium chloride brine systems being particularly aggressive towards carbon steel. If corrosion control is not used, piping and other components must be changed frequently. In the past, generally, chromate-based products were used to inhibit corrosion in these brine systems . Chromates are soluble in these concentrated solutions and provide good corrosion protection. Subsequently, it was determined that chromium-containing products are hazardous to the environment and their use is being discontinued.

Replacement of chromates brine systems with alternatives is an ongoing process. Molybdates have been used but they are less cost-effective corrosion inhibitors. Nitrites have also been used, at very high concentrations .

A composition known as Belcor 575 is 2- hydroxyphosphono-acetic acid (HPA) , is disclosed and available from Ciba Geigy. This product is a known corrosion inhibitor as disclosed in U.S. Patent No. 5,068,059. This product, HPA, is also known as a corrosion inhibitor in brines as disclosed in U.S. Patent Nos. 4,606,890 (Example 25) and 5,292,455, the disclosures of which are incorporated herein by reference in their entirety.

There are very many compositions that are known corrosion inhibitors for steel and other metals but are not known to be very effective in brine systems. For example, 2-phosphonobutane-l, 2 , 4 tricarboxylic acid (PBTC), is disclosed in U.S. patent numbers: 3,886,207; 3,933,427; and 4,026,815.

Phosphonocarboxylic acid (POCA), is also known and is specifically phosphonate [ ( acrylic acid )_x( AMPS)_y] _n copolymer, such as Belclene 494 (AMPS is 2 acrylamido-2- methylpropyl sulfonic acid) . Also known is a similar product to POCA known as Bricorr 288, a polycarboxylic acid with a phosponate end cap that is a homopolymer (POCA homopolymer) . These are known corrosion inhibitors in general applications but not in brine systems .

Azoles are also known corrosion inhibitors, such as the mercapto benzotriazoles (MBT) , benzotriazoles (BT) , tolyltriazoles, and mixtures thereof. Specific tolyltriazoles are the hydrogenated tolyltriazoles (e.g. Cobratec 928) and sodium tolyltriazoles (NaTT) .

There is still a need for improved corrosion inhibitors for brine systems, such as sodium chloride, lithium chloride, and calcium chloride brine systems, particularly cost effective ones.

SUMMARY OF THE INVENTION

Disclosed in a first aspect of the present invention I) is a blend composition useful to inhibit the corrosion of metal surfaces that comprises; a) an effective amount of 2-phosphonobutane-l, 2, 4 tricarboxylic acid (PBTC) and b) an effective amount of hydroxyphosphono-acetic acid (HPA) .

Disclosed in a second aspect of the present invention II) is a blend composition useful to inhibit the corrosion of metal surfaces that comprises; a) an effective amount of a phosphono carboxylic acid homopolymer (POCA homopolymer) and b) an effective amount of a compound selected from the group consisting of 2- phosphonobutane-1, 2, 4 tricarboxylic acid (PBTC), hydroxyphosphono-acetic acid (HPA), and mixtures thereof. Disclosed in a third aspect of the present invention III) is a blend composition useful to inhibit the corrosion of metal surfaces that comprises; a) an effective amount of a phosponocarboxylic acid copolymer (POCA copolymer) and b) an effective amount of hydroxyphosphono-acetic acid (HPA) .

The above compositions are also useful -in the process of corrosion inhibition in various brine systems, such as sodium chloride, lithium chloride, and calcium chloride brine systems .

Another aspect of the present invention for use in non-calcium chloride brine systems comprises a corrosion inhibitor and a small amount of calcium ions (preferably about 40ppm or more as calcium chloride) , optionally in the presence of an azole. Wherein, the corrosion inhibitor is selected from the group consisting of PBTC, HPA, PAPEMP (polyamino polyether methylenephosphonate i.e. TRC-289) , POCA homopolymer, and POCA copolymer. The small amount of calcium ions added to the system helps the corrosion inhibitor function as a corrosion inhibitor. Thus, when either corrosion inhibitor is used in non-calcium chloride brine systems it is combined with an amount of calcium ions to provide enhanced corrosion inhibition in the brine system.

DETAILED DESCRIPTION OF THE INVENTION

The inventors have unexpectedly discovered various blend compositions that are very useful in the inhibition of corrosion of metal surfaces. These blend compositions are particularly useful in the metal corrosion inhibition of brine systems, such as sodium chloride and calcium chloride brine systems. The inventors have unexpectedly discovered very useful replacements of chromates in brine systems .

The inventors have also unexpectedly discovered that each of the above inhibitors, by themselves, provide improved corrosion inhibition to non-calcium chloride brine systems when a small amount of calcium ions is added to the system (about 40ppm or more) . Thus, when either PBTC, HPA, PAPEMP, POCA homopolymer, or POCA copolymer are combined with an amount of calcium ions in brine systems (e.g. sodium chloride and lithium chloride brine systems) improved corrosion inhibition is achieved. A further improvement in corrosion inhibition is seen when a third component is added, either TTNa or Cobratec 928. When treating these non-calcium chloride brines with the corrosion inhibitors of this last aspect of the present invention, the calcium ions are preferably added in the form of calcium chloride. The amount of calcium ions added or present in these systems is generally at least about 40ppm, preferably about 50 to lOOOppm, more preferably about 50 to 600ppm, with an amount of about 100 to about 300ppm calcium ions being most preferred.

Thus, the composition of the present invention that is useful to inhibit the corrosion of metal surfaces comprises; a blend selected from the group consisting of: I.) a) an effective amount of 2-phosphonobutane- 1,2,4 tricarboxylic acid (PBTC) and b) an effective amount of hydroxyphosphono-acetic acid (HPA) ; II.) a) an effective amount of a phosphonocarboxylic acid homopolymer (POCA homopolymer) and b) an effective amount of a compound selected from the group consisting of (PBTC) , (HPA) , and mixtures thereof; and

III.) a) an effective amount of a phosponocarboxylic acid copolymer (POCA copolymer) and b) an effective amount of (HPA) .

The composition according to the present invention has a synergistic effect upon the prevention of corrosion of metal surfaces when an effective amount of both a) and b) are present in the system to be treated, even at very low levels. This amount is preferably at least about lOOppm of the total corrosion inhibitors. Amounts of all corrosion inhibiting compounds can be much higher than this, depending upon desired corrosion prevention levels. However, due to costs and small incremental corrosion prevention, amounts much above lOOOppm are somewhat less preferred.

The weight ratio of a) to b) in each of the blends can vary significantly, so long as both a) and b) are present. However, this weight ratio of a) to b) preferably varies from about 1:10 to 10:1, more preferably at a weight ratio of about 40 to about 60 wt . % a) and about 40 to about 60 wt . % b) , with a ratio of a) to b) of about 50/50 being most preferred.

In the second aspect of the present invention II), the POCA homopolymer of a) is preferably a polycarboxylic acid with a phosponate end cap, more preferably a low molecular weight polymaleic acid, with Bricorr-288 being most preferred. In this aspect II) , in which component b) can be a blend of PBTC and HPA, component b) is preferably a blend of PBTC and HPA and preferably in a weight ratio of PBTC to HPA that varies from 1:10 to 10:1. In the third aspect of the present invention III), the POCA copolymer is preferably a low molecular weight phosphonate [ ( acrylic acid ) _x ( AMPS) _y ] _n copolymer, such as Belclene 494 (AMPS is 2 acrylamido-2- methylpropyl sulfonic acid) . In this phosphonate end capped POCA copolymer, x is preferably about 70 to about 90 wt . % of the monomer units, y is preferably about 10 to about 30 wt . % of the monomer units, and n is an integer between 2 and 50 (more preferably 4 to 20) . The composition according to the present invention preferably contains an azole c) , in additional to the components a) and b) . The azole of the composition according to the present invention is preferably selected from the group consisting of mercapto benzotriazoles

(MBT) , benzotriazoles (BT) , tolyltriazoles, and mixtures thereof, wherein said tolyltriazoles are preferably selected from the group consisting of hydrogenated tolyltriazoles (Cobratec 928), sodium tolyltriazoles (NaTT) , and mixtures thereof. The amount of the azole c) in said blend is preferably present in a concentration of about 1 to about 90 percent by weight.

In the composition according to the present invention the amount of component a) is preferably in a concentration of about 5 to about 90 wt . %, more preferably about 10 to about 89 wt . %, with an amount of about 40 to about 58 wt. % being most preferred. As with component a) , component b) is also preferably in a concentration of about 5 to about 90 wt . %, more preferably about 10 to about 89 wt. %, with an amount of about 40 to about 58 wt. % being most preferred. The azole c) is preferably present in the composition, and in an effective amount. This amount is preferably about 1 to about 20 wt . %, more preferably about 2 to about 10 wt . % . Thus, the weight percent of all three components of the blend with respect to each other are preferably present in a concentration of about 10 to about 89 wt. % a), about 10 to about 89 wt . % b) , and about 1 to about 20 wt. % of an azole c) . This relative concentration is more preferably about 40 to about 58 wt . % a), about 40 to about 58 wt. % b) , and about 2 to about 10 wt. % of an azole c) . Wherein a concentration of about 48 wt. % a), about 48 wt . % b) , and about 4 wt . % azole is most preferred. The composition according to the present invention, the blend of a) and b) , is preferably in a brine in a sufficient amount to inhibit the corrosion of the metal in contact with said brine. This composition is preferably added as a concentrate in a concentration in water and then diluted when added to the system and preferably contains less than 50 wt. % solids, more preferably about 42 wt. % solids.

The composition according to the present invention, the blend of a) and b) and optionally c) , is preferably present in an aqueous system in a concentration of about 100 to 1000 ppm by weight. In calcium chloride brines this amount is more preferably about 100 to about 500 ppm, with about 150 to about 300 ppm being most preferred. The concentration of the components present in said aqueous system preferably ranges, with respect to each other from about 10 to about 500 ppm a) , about 10 to about 500 ppm b) , and about 1 to about 50 ppm of an azole c) . This concentration of components is more preferably about 20 to about 300 ppm a) , about 20 to about 300 ppm b) , and about 5 to about 30 ppm of an azole; with about 50 to about 200 ppm a) , about 50 to about 200 ppm b) , and about 10 to about 20 ppm of an azole being most preferred. The composition according to the present invention is a synergistic blend of a) and b) , and optional c) . Thus the components a) , b) and optional c) of the blend are each present in an aqueous system in a concentration in an amount that results in a synergistic combination such that the corrosion inhibition of a certain concentration of each component, when added together does not equal the actual corrosion inhibition of the equivalent blend of a) and b) . The above compositions are also useful in the process of corrosion inhibition in various brine systems, such as sodium chloride, lithium chloride, and calcium chloride brine systems. Thus, the method of inhibiting the corrosion of metal surfaces according to the present invention comprises; contacting said metal surfaces with an aqueous solution of a blend selected from the group consisting of:

I.) a) an effective amount of 2-phosphonobutane- 1,2,4 tricarboxylic acid (PBTC) and b) an effective amount of hydroxyphosphono-acetic acid (HPA) ;

II.) a) an effective amount of a phosphonocarboxylic acid homopolymer (POCA homopolymer) and b) an effective amount of a compound selected from the group consisting of (PBTC), (HPA), and mixtures thereof; and

III.) a) an effective amount of a phosponocarboxylic acid copolymer (POCA copolymer) and b) an effective amount of (HPA) . The method according to the present invention for inhibiting the corrosion of metal surfaces in contact with an aqueous system preferably entails adding one or more of the above blends to said aqueous system itself. In the case of non-calcium chloride brines, one or more of the components is added to the brine system in combination with at least 50ppm calcium ions, preferably in combination with an azole.

The method according to the present invention entails the inhibition of corrosion on metal surfaces, generally a combination of different metals. These above compositions are multi-metal corrosion inhibitors and can protect systems made up of a combination of metals. These metal surfaces that are contacted with the blend of a) and b) are preferably made of iron, copper, aluminum and their alloys, such as steel, brass, copper, and combinations thereof. Mild steel and high carbon steel are the most preferred due to significant corrosion inhibition of this metal with preferred blends. The following examples are intended to illustrate the present invention but should not be considered as a limitation on the reasonable scope thereof.

Examples Experimental :

General Set-up:

Each closed system corrosion study was performed by immersing a rack of five 1.0 inch by 2.0 inch coupons of varying metallurgies in a glass reaction kettle containing 3.0 L of treated deionized water, and then blanketing the treated deionized water with saturated C0₂ scrubbed air. The air was fed through a gas sparge tube and an outlet tube was provided to enable a positive pressure of air for oxygen saturation. An Orbisphere Model 26060 Oxygen Analyzer with Sensor 2110 was used to measure the oxygen concentration. The kettles were nestled in a heating mantle connected to a variac. The variac was set to control the temperatures at 65.6° +/- 5°C . The pH was periodically measured, but not controlled.

Measurement of Coupon Corrosion Rates:

The coupons were precleaned as outlined in CPT-203- CW, "Methods of Cleaning and Polishing Specimens Before Testing" and then weighed on a five place analytical balance. Next they were placed in an ASTM D1384 corrosion test rack in the following order by metallurgy: carbon steel, stainless steel, 90/20 Cu/Ni, Admiralty brass, and copper. Teflon spacers (3/16 inch) were placed between coupons, and between end coupons and the brass legs. The center screw was covered with a Teflon insulating sleeve, before the coupons were slipped over it.

Following testing, coupons were recleaned as outlined in CPT-205-CW, "Methods For Cleaning Specimens After Testing" and then reweighed on the five place analytical balance. Corrosion rates are calculated using the weight loss method.

TABLE 1

Corrosion Studies in Calcium Chloride Brine Coupon Corrosion Rates

Conditions

65 degrees C, pH 8 0

25% CaCI2 Brine

7 days

Aeration using air which had been washed with 5%

NaOH

One carbon steel coupon, one Admiralty brass coupon, and one 9010 CuNi coupon

Carbon steel corrater tips Results : CaCl₂ Brine Corrosion Inhibition Studies

TABLE 2

TABLE 3

The test conditions were: 65°C+/-5°C pH 8.0 25% CaCl₂ Test Solution

Aeration With Air Which Has Been Washed With NaOH For C0₂ Removal

9010 CuNi , Admiralty Brass, And Carbon Steel Coupons Carbon Steel Corrater Tips The above tables illustrate a significant reduction in corrosion rates in calcium chloride brines for the preferred compositions when compared to the controls (no treatment) . Further, the blends show synergism for multi-metal corrosion inhibition when compared to the single components (lower MPY) at adequate dosage, particularly when replacing a portion of the more expensive Belcor 575.

TABLE 4

Corrosion Studies in NaCI Brine

(Coupon Corrosion Rates)

MPY

Conditions

2 85 L Brine in 3 0 L Resin Kettles pH 8 0

65 °C

Aeration TABLE 5 Corrosion Studies in 25% LiCI₂ Brine

Conditions:

2.85 L Brine in 3.0 L Resin Kettles pH 8.0

65 °C

Aeration

These tests were carried out in resin kettles . Heating mantles were used as the heat source. Variacs were used to maintain a 65°C temperature. Condensers were used to maintain the water level. The air was washed with 5% NaOH to remove C0₂ prior to aeration of the test solution, in order to maintain the pH at 8.0.

The above tables illustrate a reduction in corrosion rates in non-calcium chloride brines for the preferred compositions when compared to the controls (no treatment) . Further, the inventive compositions, with the addition of calcium ions, illustrates a significant reduction in corrosion rate (lower MPY) .

TABLE 6 Background Information on inhibitors

Claims

WHAT IS CLAIMED IS:

1. A composition useful to inhibit the corrosion of metal surfaces comprising a blend selected from the group consisting of: I.) a) an effective amount of 2-phosphonobutane-

1,2,4 tricarboxylic acid (PBTC) and b) an effective amount of hydroxyphosphono-acetic acid (HPA) ;

II.) a) an effective amount of a phosphonocarboxylic acid homopolymer (POCA homopolymer) and b) an effective amount of a compound selected from the group consisting of (PBTC) , (HPA) , and mixtures thereof; and

2. The composition according to claim 1 wherein the weight ratio of a) to b) of each of the blends varies from about 1:10 to 10:1.

3. The composition according to claim 1 wherein the blend of a) and b) further comprises an azole c) .

4. The composition according to claim 3 wherein the azole in said blend is selected from the group consisting of mercapto benzotriazoles (MBT) , benzotriazoles (BT) , tolyltriazoles, and mixtures thereof.

5. The composition according to claim 3 wherein the azole c) in said blend is present in a concentration of about 1 to about 90 percent by weight.

6. The composition according to claim 1 wherein all three components of the blend are present with respect to each other in a concentration of about 10 to about 89 wt . % a), about 10 to about 89 wt . % b) , and about 1 to _.about 20 wt . % of an azole c) .

7. The composition according to claim 1 wherein the blend of a) and b) is in a calcium chloride brine in a sufficient amount to inhibit the corrosion of the metal in contact with said brine.

8. The composition according to claim 1 wherein the blend of a) and b) is present in an aqueous system in a concentration of about 100 to about 1000 ppm by weight.

9. The composition according to claim 8 wherein the concentration of the components present in said aqueous system ranges from about 10 to about 500 ppm a) , about 10 to about 500 ppm b) , and about 1 to about 50 ppm of an azole c) .

10. The composition according to claim 1 wherein a) and b) , and optional c) of the blend are each present in an aqueous system in a concentration in an amount that results in a synergistic combination such that the corrosion inhibition of a certain concentration of each component, when added together does not equal the actual corrosion inhibition of the equivalent blend of a) and b) .

11. A method of inhibiting the corrosion of metal surfaces comprising, contacting said metal surfaces with an aqueous solution of a blend selected from the group consisting of: I.) a) an effective amount of 2-phosphonobutane- 1,2,4 tricarboxylic acid (PBTC) and b) an effective . amount of hydroxyphosphono-acetic acid (HPA) ;

12. The method according to claim 11 wherein the weight ratio of a) and b) varies from 1:10 to 10:1.

13. The method according to claim 11 wherein the metal of the metal surfaces that are contacted with the blend of a) and b) is selected from the group consisting of, iron and copper containing metals.

14. The method according to claim 13 wherein the metal of the metal surfaces that are contacted with the blend of a) and b) is selected from the group consisting of, steel, brass, and copper.

15. The method according to claim 14 wherein the metal of the metal surfaces that is contacted with the blend of a) and b) is mild steel.

16. A method for inhibiting the corrosion of metal surfaces in contact with an aqueous system, which comprises adding to said aqueous system a blend selected from the group consisting of: I.) a) an effective amount of 2-phosphonobutane- 1,2,4 tricarboxylic acid (PBTC) and b) an effective amount of hydroxyphosphono-acetic acid (HPA) ;

17. The method according to claim 16 wherein said aqueous system is a closed recirculating aqueous system.

18. The method according to claim 17 wherein said aqueous system is a closed loop recirculating aqueous brine system.

19. The method according to claim 18 wherein said aqueous system is a closed loop recirculating aqueous cooling brine system selected from the group consisting of calcium chloride brine, sodium chloride brine (containing at least 40 ppm calcium ions), and lithium chloride brine (containing at least 40 ppm calcium ions) .

20. The method according to claim 19 wherein said aqueous system is in contact with metal surfaces that are comprised of a metal selected from the group consisting of iron, copper, aluminum and their alloys, further comprising the addition of an azole wherein all three components of the blend are present in the aqueous system with respect to each other in a concentration of about 10 to about 89 wt . % of a) , about 10 to about 89 wt . % of b) , and about 1 to about 20 wt. % azole and are present in an aqueous system in a total concentration of aboμt 100 to 1000 ppm by weight.