Corrosion inhibiting compositions

Details Corrosion inhibiting compositions Corrosion inhibiting compositions

2002-09-04

2003-11-11

Pezzuto, Helen L. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S258000, C526S259000, C526S264000, C526S265000, C526S266000, C526S271000, C526S288000, C526S307300, C526S317100, C526S328500, C526S331000, C526S336000, C526S342000, C526S345000, C526S347000, C526S348000

Reexamination Certificate

active

06646082

ABSTRACT:

The present invention relates to compositions which inhibit corrosion of metals in contact with aqueous and non-aqueous systems. More particularly, the invention is directed to introducing oligomeric and polymeric compositions as fluid additives in aqueous systems that are effective corrosion inhibitors over a wide range of pH and render metals passive to repeated attack by oxidants and oxidizing biocides. In addition, the invention relates to anti-corrosive coating compositions applied to metallic components.
Metallic components used in industrial processes and heating ventilation and air conditioning (HVAC) operations that are in contact with fluid media such as, for example, cooling water experience three major problems: metal corrosion, deposition of solids and the growth of microorganisms. The three problems are interrelated in that the ability to control one problem often influences the ability to effectively control the remaining problems. The most common method to address the problems is to add a combination of chemical agents and corrosion inhibitors to the fluid media in contact with the metallic components. Polymeric dispersants and phosphonates are commonly used to inhibit the deposit of solids referred to as scale. Biocidal compositions, in particular oxidizing biocides such as chlorine or bromine, are often used to control the deposition and growth of microorganisms. The most challenging problem in the development of new anti-corrosive compositions is providing effective chemical agents which inhibit corrosion and which do not produce an adverse environmental impact themselves or upon treatment with oxidizing biocides.
Corrosion may be defined as the gradual weight loss of a metallic component through some chemical process or series of chemical reactions. Metals in contact with aqueous systems such as sea water, fresh water and brackish water and exposed to oxidants contained therein such as chlorine, acid, bleach, caustic and dissolved oxygen are prone to corrosion. Metal alloys incorporating one or more corrosion resistant metals (e.g. Ti, Cr, Ni) are one means of improving corrosion resistance. However, such alloys are costly, difficult to process and manufacture, and experience problems with corrosion at joints, welds, and under repeated exposure to corrosive agents. Inorganic compositions such as chromates, phosphates and zinc compositions and organic compositions such as tolyltriazole (TTA) and benzotriazole (BZT) are corrosion inhibitors applied to metals or added to fluids in contact with metal components which inhibit or slow down the rate of metal corrosion. Azoles, for example, are film forming compositions that adsorb to metallic surfaces and provide a barrier to contact with an aqueous system. The effectiveness of a particular composition is usually a trade off of its anti-corrosion properties as compared to its inherent limitations such as cost, long term performance and environmental impact. Since metal corrosion occurs under a variety of environmental conditions, specific inhibitor compositions have been developed to provide corrosion resistance for specific situations.
A common corrosion inhibitor for metals are film forming azoles such as tolyltriazole (TTA) and benzotriazole (BZT). TTA has been usefully employed as a corrosion inhibitor for metallic components manufactured from copper and copper alloys. When such metals protected with TTA films are exposed to oxidizing biocides such as chlorine, however, the corrosion protection breaks down. After breakdown, it is difficult to form new protective films in TTA treated aqueous systems that are periodically or continuously chlorinated. Very high dosages of TTA are frequently applied in an attempt to improve performance, often with limited success. Other problems associated with combining triazoles and oxidizing biocides in aqueous systems include by-products that are less effective corrosion inhibitors, by products which are volatile and that have objectionable odors and halogen containing by products that are toxic to the environment if released from the aqueous system. Moreover, it is believed that the decomposition product of TTA may be more toxic than TTA, which itself is toxic to fish populations. Under the conditions found in cooling water treatment equipment, the decomposition product of TTA is believed to be an N-chlorinated compound, which is relatively volatile and susceptible to removal by stripping in the cooling tower, further reducing the levels of corrosion inhibitor and oxidizing biocide in the system.
When copper containing metals corrode, excessive concentrations of copper are released and subsequently discharged in to rivers that often serve as reservoirs of cooling water. The toxic effects of copper on fish populations and other organisms in aqueous ecosystems is well established. In addition, excessive concentrations of copper ions can redeposit on mild steel components, setting up a galvanic oxidation-reduction couple leading to severe metal pitting.
U.S. Pat. No. 5,391,636 discloses polyamine condensates of styrene/maleic anhydride copolymers as corrosion inhibiting compositions. The corrosion inhibiting effects of the copolymers are primarily due to their ability to form films on metal surfaces. However, such compositions are only effective at inhibiting corrosion of metal surfaces exposed to highly acidic aqueous environments (i.e. pH values <1). Accordingly, it would be desirable to provide new corrosion inhibiting compositions that form effective barriers between metallic surfaces and aqueous systems over a wide range of pH, that are resistant to oxidizing biocides and that have minimal environmental impact.
The inventors recognized a need to provide polymeric compositions having substantive film forming ability that are effective corrosion inhibitors over a wide pH range in aqueous and non-aqueous systems and that can withstand repeated and prolonged chemical attack by oxidizing biocides such as chlorine. The inventors discovered a new class of polymeric corrosion inhibiting compositions incorporating pendant heterocyclic groups which are surprisingly effective copper corrosion inhibitors and remain substantive on metallic surfaces over a wide pH range in aqueous and non-aqueous systems, are resistant to oxidizing biocides, and are substantially impervious to repeated or prolonged exposure to corrosive agents.
The present invention provides a polymer comprising one or more repeating units selected from a functionalized imide component of Formula Ia, a functionalized amide component of Formula Ib and combinations of Formulas Ia and Ib:
wherein n is 0 or 1; R and R
1
are independently selected from hydrogen, methyl, and C
2
-C
4
alkyl; R
2
is selected from C
1
-C
8
branched and straight chain alkyl groups, C
2
-C
8
branched and straight chain alkenyl groups, C
3
-C
8
cyclic alkyl groups, C
6
-C
10
unsaturated acyclic, cyclic and aromatic groups, C
2
-C
4
alkylene oxide groups and poly(C
2
-C
4
alkylene)m oxides, wherein m=2-20; a pendant heterocycle which comprises unsaturated or aromatic heterocycles having one or more hetero atoms selected from N, O, S and combinations thereof, the pendant heterocycle chemically bonded to R
2
via a hetero atom which is part of the pendant heterocycle or a carbon atom of the pendant heterocycle; R
3
is selected from hydrogen, methyl, ethyl, C
3
-C
18
branched and straight chain, alkyl and alkenyl groups; and R
4
is selected from H, CH
3
, C
2
H
5
, C
6
H
5
and C
3
-C
18
branched or straight chain alkyl and alkenyl groups.
Accordingly, the present invention provides a corrosion inhibiting polymer comprising:
i) at least one repeating unit selected from a functionalized imide component of Formula Ia, a functionalized amide component of Formula Ib and combinations of Ia and Ib;
ii) at least one ethylenically unsaturated monomer component selected from maleic anhydride, itaconic anhydride, cyclohex-4-enyl tetrahydrophthalic anhydride, and monomers of Formula II:
CH(R5)═C(R6)(R7)  Formula II
 wh

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