CA1295529C - Control of corrosion in aqueous systems - Google Patents

Abstract

ABSTRACT

Corrosion of metals in contact with an aqueous solution is reduced by adding an effective amount of an oxygen scavenger selected from the group of phloroglucinol and other scavengers of the formula:

Description

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FIELD OF INVENTION

This invention relates to the addition of oxygen scavengers to aqueous solutions to reduce the corrosion of metals that are in contact with the solutions, and more particularly, to the addition of compositions comprising phloroglucinol or certain related compounds to an aqueous solution as oxygen scavengers to reduce corrosion of metal surfaces in contact with the solution.

BACKGROUND OF THE INVENTION

In processes using aqueous solutions, corrosion of metal surfaces may occur at various locations including feed lines, heaters, steam lines, process tanks and return lines. Dissolved oxygen in the water can be a principal factor influencing this corrosion, particularly where iron and steel are materials of construction. The corrosion of the iron and steel pipes, boilers, and economizers of conventional boiler systems is a well known problem; and controlling the presence of oxygen in boiler systems, particularly in the feed water section, has received considerable attention. Oxygen removal may be partially accomplished by either vacuum or thermal deaeration, or both. Complete removal of oxygen cannot be effected by these means, however, and further removal by use of a chemical scavenging agent, such as sodium sulfite, has been a customary practice.

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In recent times, the use of low pressure boilers (operating below about 150 psig) has been increasingly supplemented by use of boilers operating at moderate pressure (operating between about 150 psig and about 5 600 psig) and high pressure (operating above about 600 psig). As boiler operating temperatures and pressures have increased there has been particular interest in the performance of oxygen scavengers at these operating conditions. For example, use of sulphites at elevated temperatures and pressures may cause an increase in solids, and formation of sulfur dioxide and hydrogen sulfide, both of which can be a source of corrosion.
Scavengers such as hydrazine, hydroquinone, and certain hydroxylamines have been found to perform satisfactorily in some circumstances. In other circumstances, the efficiency with which the scavenging proceeds has not been optimal. There is thus a continuing need for alternative oxygen scavengers which can be effectively used at elevated temperatures and pressures.
Despite the toxicity of hydrazine, much recent research has concerned development of corrosion inhibitors using hydrazine and various organic products. U.S. Patent No. 3,551,349 to Kallfass suggests using hydrazines in combination with various quinone compounds including hydroxyl forms such as pyrocatechol and hydroquinone, which act as catalysts;
and U.S. Patent No. 3,843,547 to Kaufman et al.
discloses a hydrazine-hydroxyl quinone combination in further combination with various aryl amine compounds.
U.S. Patent No.'s 4,026,664 and 4,079,018 both to Noack .. . . . .

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disclose hydrazine-based corrosion inhibitors which use organometallic complexes (including those of pyrocatechol) as catalysts and quinone compounds (including hydroquinone) and their derivatives to render the compositions compatible with phosphonate scale control agents.
Other work has focused on hydroxylamines.
Japanese Patent Document SHO 57-204288 to Sato discloses using certain hydroxylamines as de-oxidants in combination with certain trivalent phenols (including pyrogallol), napthoquinones, and anthraquinones or derivatives thereof, as activating agents. Use of phloroglucine as an activator is also suggested. The invention may be practiced in boiler related systems.
Hydroquinone and some of its derivatives have also been used in corrosion inhibition. U.S. Patent No.
4,278,635 to Kerst discloses use of various dihydroxy, diamino, and amino hydroxy benzenes and their lower alkyl substituted derivatives, and particularly hydroquinone, as corrosion control agents. Use of the invention in boiler systems is disclosed. U.S. Patent No.'s 4,279,767 and 4,289,645 both to Muccitelli are directed to use of hydroquinone as an oxygen scavenger in combination with various compatible amines.
Addition to boiler feedwater is disclosed. U.S. Patent No. 4,282,111 to Ciuba also relates to a method of reducing oxygen in aqueous medium, including boiler system water, using hydroquinone. Kaufman and U.S.
Patent No. 4,363,734 to Slovinsky claim use of hydroquinone as a catalyst in combination with other oxygen scavengers, namely hydrazine and dihydroxy acetone, respective]y. Japanese Patent Publication No.
SHO 51-93741 by Sozuki et al. reports synergistic inhibition of metallic corrosion by combinations of dihydroxy-benzenes (eg. hydroquinone and methyl hydroquinone) and various carboxylic acids. Boiler water use is suggested. European Patent Publication No. 0039130 is directed to use of certain "dioxo"
aromatic compounds (ey. hydroquinone, benzoquinone, napthoyuinone, catechol), including certain organically substituted derivatives thereof, as oxygen scavengers in aqueous medium, including boiler water.
European Patent Publication No. 0054345 is directed to use of certain amir.ophenol compounds to reduce oxygen in aqueous medium such as boiler water.
~ uinones, and substituted aromatics have found application in various arts. For example, U.S. Patent No. 2,835,715 to Tiede identifies oxygen absorbing agents for certain process streams, including resorcinol, pyrogallol, phloro~lucinol, quinone, hydroquinone, chlorohydroquinone, and tertiary-butylcatechol. U.S. Patent No. 2,339,091 to McLean relates the use of various quinones, including benzoquinone and toluoquinone, as additives to halogenated organic dielectrics to inhibit the corrosion of metals in contact with the dielectric at elevated temperatures and under an electric potential.
IJ.S. Pa-tent No. 3,277,120 to Fullhart, Jr. et al.
describes use of quinones, including certain hydroxyl quinones, to stabilize phosphatizing halogenated hydrocarbon solutions. Reportedly, the addition of ... ... . ....... . .

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quinones to halogenated hydrocarbons containing phosphoric acid reduces corrosivity of the solvents, forming halohydroquinones (eg. chlorohydroquinone, dichlorohydroquinone). Formation of a precipitate comprising quinone, hydroquinone, and phosphoric acid is also described. Swedish Specification No. 308,974 discusses the use of sulfonated benzenes, hydroxy benzenes, naphthalenes, and related compounds in combination with phosphoric acid and amino acid for pickling and phosphatizing baths. U.S. Patent No.
3,965,050 to Shimogawa et al. describes addition of various quinones, including benzoquinone and naphthoquinone, within epichlorohydrin-based elastomers. The resulting polymers exhibit a lower tendency to corrode steel with which it is in contact than comparable polymers without the additive. V.S.
Patent No. 2,170,596 to Quiggle describes oxygen-absorbing solutions using catalysts such as various quinones (including pyrogallol and hydroquinone) together with reducing agents such as sulfides. U.S.
Patent No. 2,632,563 to Bell et al. discusses use of propenyl derivatives of hydroquinone as antioxidants particularly valuable in protecting fats and oils.
Synergists, including phosphoric acid and amino acids, are disclosed. U.S. Patent No. 3,273,955 to Goerrig et al. describes use of hydroxy benzenes such as pyrogallol as complexing agents and anthraquinones and their derivatives in a catalyst for boron-based reducing agents.
U.S. Patent 1,988,823 to Winning et al. describes rust remover Eormulations which include ammonium salt and an inhibitor of corrosion such as pyrogallol, hydroquinone, pyridine, or quinoline.
U.S. Patent No. 3~674,880 to Fisher describes preparation of hydroxyaromatic compounds, such as p phloroglucinol, and suggests their use as antioxidents, preservatives, and intermediates for making resins, plastics, adhesives, pharmaceuticals, and dyes. U.S.
Patent No. 3,764,629 to Gurien et al. describes preparaton of pyrocatechol derivatives and suggests their use as pharmaceutically active compounds, coccidiostats, and antioxidants. U.S. Patent Nos.
4,057,588, 4,071,555, and 4,157,450, all to Zengel et al. and U.S. Patent No. 4,296,260 to Zielke all describe processes for phloroglucinol preparation and sugqest its use as a cross-linking, vulcanizing, stabiliæing, and anti-corrosion agent; as a developing component in dye production and printing processes; as a laboratory analytical reagent; and in the preparation of coumarins, flavenols, and pharmaceuticals.

SU~RY OF THE INVENTION

Addition of phloroglucinol (C6H6O3) or related compounds to aqueous solutions, including boiler system water, inhibits the corrosion of metal in contact with the solutions by removing oxygen dissolved therein.
Thus the invention herein described specifically makes use of the oxygen scavenging capabilities of phloroglucinol and certain of its derivatives in aqueous systems, such as boiler water systems, containing dissolved air and/or oxygen. The invention is especially suited for boiler water systems consisting essentially of water containing dissolved oxygen. Indeed, the efficiency of oxygen scavenging achieved with phloroglucinol at conditions found within boiler systems is particular]y advantageous.
Accordingly, it is an object of this invention to provide a method to inhibit corrosion of metals in contact with aqueous solutions.
It is another object of this invention to remove oxygen from boiler system water.
It is another object of this invention to use a corrosion reducing agent which may be used effectively in boilers operated at elevated pressures.
These and other ob~ects and advantages of the present invention will become apparent from the following detailed description of the invention.

DETAILED DESCRIPTION

The corrosion inhibiting aqents used in this invention include water soluble phloroglucinol-related substituted benzenes of the general formula:

~Rl 3 ~ OR2 R1, R2, and R3, which may be the same or different, are each a member selected from the group consisting of hydrogen or lower alkyl having between 1 and about 8 carbon atoms. Examples of such compounds are:

1,3,5-trihydroxybenzene (phloroglucinol) l-methoxy-3,5-dihvdroxybenzene 1,3-dimethoxy-5-hydroxybenzene 1,3,5-trimethoxybenzene 1-methoxy-3,5-diethoxybenzene 1,3-dimethoxy-5-ethoxybenzene 1,3,5-triethoxybenzene 1,3,5-tripropoxybenzene Water soluble salts of these compounds may also be used. These compounds will be referred to throughout this specification as "phloroglucinol-related"
compounds. Preferably, Rl, R2, and R3 are all hydrogen. Accordingly, the preferred inhibitor of this invention is phloroglucinol itself (C6H6O3) having the general structural formula:

OH

HO ~ OE

The structural formulae above are for identification on]y. All tautomeric forms of these phloroglucinol-related compounds are within the scope of this invention. Most notably, u ~C~
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O=C~ ~ C=O
CH

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L . r~ ~ 2 ~3 representing a ketone form of phloroglucinol, will be recognized by one skilled in the art as an equivalent of the phenol form represented above.
The use of phloroglucinol-related compounds as oxygen scavengers may be practiced in various water systems, such as recirculating cooling systems.
~owever, they are particularly suited for use as oxygen scavenging additives to boiler related systems, such as, for example, boiler feedwater and boiler tank water. One suggested use is for treatment of water in a dormant boiler. In boiler water systems, corrosion may occur in feed lines, heaters, economizers, boilers, steam lines, and return lines; and the invention is intended for broad use in any boiler water system (i.e.
at pressures in the range of 0 to 1000 psig or higher).
Indeed, inasmuch as phloroglucinol-related compounds perform effectively at higher pressures and temperatures, they are seen as particularly suited for boiler water systems operating at temperatures in the 20 range of about 298F to about 637F and at pressures in the range of about 50 psig to 2000 psig. The metal surfaces exposed to these conditions are generally iron and steel.
Practice of the invention will become further apparent from the following non-limiting example.
EXAMPLE I

The oxygen scavenging activity of the chemicals was evaluated in an experimental boiler. This ?,~ ~52~

experimental boiler has been described previously in the proceedings of the Fifteenth Annual Water Conference, Engineers Society of Western Pennsylvania, pages 87-102 (1954). Essentially, it consists of a vertical steel tube fitted with three external heating loops extending from near the bottom and discharging near the center of the central tube. Boiler water circulates through each heating loop from bottom to top and steam is withdrawn from the top of the vertical tube. The heating source in each loop consists of an electrical fire-rod unit transferring heat indirectly through the walls of a heating tube.
The feedwater was saturated with oxygen by continuous aeration maintaining about 9 to 10 milligrams per liter of dissolved oxygen. This feedwater contained a total hardness of approximately 10 ppm (as CaCO3) and had a pH of about 7. Typical boiler water treatment chemicals such as sodium hydroxide (caustic soda) and disodium phosphate for alkalinity and calcium hardness control were added to the water in the boiler. The boiler water pH ranged from 11.0 to 11.5. Feedwater passed into the boiler where it was heated to a temperature of about 442F
under a pressure of about 375 psig. After steam formation, the steam was condensed through a heat exchanger. The condensate, which had a temperature of approximately 55F, was then passed through a chamber containing a standard oxygen probe. The dissolved oxygen in the condensate was measured in the chamber to determine the effectiveness of oxygen removal within the system.
Boiler water was fed through the system without addition of any oxygen scavenger until a constant dissolved oxygen reading was observed in the condensate. Once the base dissolved oxygen level in the condensate was established, phloroglucinol (as a solution containing about 0.5 weight percent phloroglucinol) was added as the sole oxygen scavenger to the boiler feedwater at a dosage of 20 parts per million (ppm). The dissolved oxygen level in the condensate was then monitored to determine a final level by which the effectiveness of the phloroglucinol could be determined. The phloroglucinol used in this run was supplied by Ishihara Sangyo Kaisha, Ltd., Tokyo, Japan.
A second run was made using hydrazine. After a base dissolved oxygen level in the condensate was established, hydrazine was added to the feedwater at a dosage of 20 ppm. The final level of oxygen in the condensate was then measured to determine the effectiveness of the hydrazine in the system.
A third run was made using sodium sulfite. After a base dissolved oxygen level in the condensate was established, sodium sulfite was added to the feedwater at a dosage of 60 ppm. The final level of oxygen in the condensate was then measured to determine the effectiveness of the sulfite in the system.
The results of these runs are summarized in Table I.

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The results shown in Table I indicate that phloroglucinol was an effective oxygen scavenger in the boiler system. It is evident that phloroglucinol-related compounds may be utilized as an oxygen scavenger in moderate and high pressure boiler systems.
The iron and steel components typically found in these systems can thus be effectively protected from oxygen-related corrosion.
The process of this invention for inhibiting corrosion of metal surfaces in contact with an aqueous solution by scavenging oxygen from the solution comprises adding in the aqueous solution an effective amount of at least one phloroglucinol-related compound.
The preferred dosage range is generally from about 0.001 ppm to about 500 ppm, with the most preferred dosage range being generally from about 0.01 ppm to about 50 ppm. Use of phloroglucinol is not confined to low, moderate or high pressure boiler systems, but may be utilized in a wide variety of other systems where aqueous solutions containing dissolved air and/or oxygen are in contact with metal surfaces. The precise dosage used in each system will be somewhat dependent on the particular system and the water characteristics therein. The preferred system water (which may contain small amounts of certain a~ditives normally used in systems such as boiler water systems for control of corrosion, scaling, sedimentation, pH, hardness and the like) consists essentially of water containing dissolved oxygen. In boiler water systems where addition is made to feedwater which will not be further aerated before it enters the boiler, a weight ratio of ... .. . .

p 1~ .3 ~ 9 phloroglucinol-related compound to oxygen dissolved in the feedwater is preferably between about 1:1 to about 20:1; most preferably about 5:1. The pH of such systems is preferably kept between 8 and 12.
The phloroglucinol-related compounds employed in the process of this invention can typically be added to the system water by conventional bypass feeders using briquettes containing the additives, by feeding the compounds as dry powder mixtures to the water, or by feeding the treatment compounds as an aqueous feed solution. Feed solutions, when used, may contain alcohol or other solvents to enhance solubility, and preferably contain 0.1 to 5 percent by weight of phloroglucinol-related scavenger; most preferably 0.5 to 1 weight percent thereof. Where, as in many boiler systems, make-up water is added to the aqueous solution, calibrated injecters can be employed to deliver predetermined amounts of the phloroglucinol-related compounds, periodically or continuously, to the aqueous solution via the make-up water line. While the scavengers may be added at locations throughout the system, the addition is preferably made at a location where there is little opportunity for additional aeration of the solution before it contacts the metal components to be protected. For example, in boiler systems, addition is preferably made to the feedwater at a location where the feedwater will not be exposed to substantial aeration before it enters the boiler.
Examples of such locations might include the feedwater line itself, or depending upon the boiler system 5~9 design, through return condensate lines or make-up water lines.
The examples describe particular embodiments of the invention. Other embodiments will be apparent to those skilled in the art from a consideration of the specification or practice of the invention disclosed herein. It is understood that modifications and variations may be practiced without departing from the spirit and scope of the novel concepts of this invention. It is further understood that the invention is not confined to the particular formulations and examples herein illustrated, but it embraces such modified forms thereof as come within the scope of the following claims.

Claims (20)

1. A method for control of oxygen corrosion of metals in contact with an aqueous solution comprising the step of adding to the aqueous solution an effective amount of an oxygen scavenger selected from the group of phloroglucinol and other scavengers of the formula:

wherein R1, R2 and R3 may be the same or different and are each a member selected from the group consisting of hydrogen, and lower alkyl having 1 to about 8 carbon atoms; or water soluble salts thereof.

2. The method of Claim 1 wherein the scavenger is added at a dosage of between about 0.001 ppm and about 500 ppm.

3. The method of Claim 1 wherein the scavenger added is phloroglucinol or a water-soluble salt thereof.

4. The method of Claim 3 wherein the scavenger is added at a dosage between about 0.01 ppm and about 50 ppm.

5. The method of Claim 3 wherein the scavenger is added at a dosage of approximately 20 ppm.

6. The method of Claim 1 particularly for use in boiler systems to protect the boiler system metals in contact with boiler water, consisting essentially of water containing dissolved oxygen, wherein the oxygen scavenger is added to the boiler water.

7. The method of Claim 6 wherein the scavenger is added at a location wherein there is no substantial further aeration of the water before it enters the boiler, and in a weight ratio to oxygen in the boiler feedwater of from about 1:1 to about 20:1.

8. The method of Claim 7 wherein the scavenger is added in a weight ratio to oxygen in the boiler feedwater at about 5:1.

9. The method of Claim 6 wherein the scavenger is phloroglucinol or a water-soluble salt thereof; and wherein the phloroglucinol is added in a weight ratio to oxygen in the boiler feedwater of from about 1:1 to about 20:1.

10. The method of Claim 6 wherein the scavenger is phloroglucinol or a water-soluble salt thereof; and wherein the phloroglucinol is added at a dosage of from about 0.01 ppm to about 50 ppm.

11. The method of Claim 6 wherein addition is made to the boiler feedwater; and the feedwater is adjusted to a pH of between about 8 and about 12.

12. The method of Claim 1 particularly adapted for use in boiler systems operating above about 150 psig and temperatures above about 298°F to protect the iron and steel boiler system components in contact with the boiler water, wherein the oxygen scavenger is added to the boiler water.

13. The method of Claim 12 wherein the scavenger is added at a dosage between about 0.01 ppm and about 50 ppm.

14. The method of Claim 12 wherein the scavenger is added at a dosage of approximately 20 ppm.

15. The method of Claim 12 wherein the scavenger is added at a location wherein there is no substantial further aeration of the water before it enters the boiler in a weight ratio to oxygen in the boiler feedwater of from about 1:1 to about 20:1.

16. The method of Claim is wherein the scavenger is added in a weight ratio to oxygen in the boiler feedwater at approximately 5:1.

17. The method of Claim 12 wherein the scavenger added is phloroglucinol or a water-soluble salt thereof.

18. The method of Claim 12 particularly adapted for use with boilers operating at pressures about 375 psig wherein the scavenger is phloroglucinol; and wherein the phloroglucinol is added at approximately 20 ppm.

19. The method of Claim 12 particularly adapted for use with boilers operating at pressures about 375 psig wherein the scavenger is phloroglucinol; and wherein the phloroglucinol is added in a weight ratio to the oxygen dissolved in the boiler feedwater at approximately 5:1.

20. The method of Claim 12 wherein addition is made to the boiler feedwater, and the feedwater is adjusted to a pH of between about 8 and about 12.