CORROSION INHIBITORS FOR COOLING WATER APPLICATIONS

Abstract

A new corrosion inhibitor composition containing a carboxylic acid and its water soluble salts with zinc can be used for corrosion inhibition on the carbon steel pipe and heat exchangers in industrial cooling water. This new composition of matter contains less carboxylic acid and Zn2+ than previous formulations and still have >90% corrosion inhibition. It is disclosed that the synergistic effect of combining the carboxylic acid with very small amounts of Zn results in a product with good corrosion inhibition properties that is more environmentally friendly than the current common phosphonate corrosion inhibitors; particularly for use in cooling water applications.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to corrosion inhibitors. The present invention particularly relates to corrosion inhibitors for use in cooling water applications.

2. Background of the Art

Corrosion may be a serious problem in industrial cooling water applications. It causes many undesirable consequences, including heat transfer reduction, increasing cleanings, equipment repairs and replacements, and even unscheduled shutdowns. There are numerous approaches to prevent corrosion in cooling water applications. One of the most effective approaches is to use chemicals to treat cooling water to inhibit the occurrence of corrosion.

The common corrosion inhibitors include orthophosphate, polyphosphates, phosphonates, molybdates, silicates, nitrites, etc. Among these corrosion inhibitors, phosphorus based corrosion inhibitors are widely used for carbon steel corrosion control in cooling water applications because they have good cost effectiveness and performance. However, cooling water is eventually discharged into surface water, and there are more and more concerns on the impact of phosphorus on the environment due to algal bloom. Furthermore, the presence of phosphorus may react with the calcium ions in cooling water to form calcium phosphate scale, which causes the fouling and blocking of pipelines and heat transfer reductions. Therefore, non-phosphorus (non-P) inhibitors are needed for corrosion control in cooling water applications.

This invention discloses the art of novel, high performance non-phosphorus chemical corrosion inhibition treatment program which can be used in cooling water applications for preventing the carbon steel corrosion. This treatment program is more environmentally friendly than the current common phosphorus corrosion inhibitors.

SUMMARY OF THE INVENTION

In one aspect, the invention is a method for preventing or mitigating corrosion in cooling water comprising treating the cooling water with an additive comprising a soluble zinc salt and a soluble carboxylic acid salt.

In another aspect, the invention is a method for preventing or mitigating corrosion in cooling water comprising treating the cooling water with an additive comprising a soluble zinc salt and a compound selected from the group consisting of gluconic acid, saccharic acid, a water soluble gluconate salt, saccharic acid salt, and combinations thereof.

In still another aspect, the invention is a method for preventing or mitigating corrosion in cooling water comprising treating the cooling water with an additive comprising a soluble zinc carboxylate.

Another aspect of the invention is a method for preventing or mitigating corrosion in cooling water comprising treating the cooling water with an additive comprising a compound selected from the group consisting of zinc gluconate, the salt of zinc and saccharic acid, and combinations thereof.

Other compounds may also be included in the additives of this application. For example, in addition to the zinc salts already discussed above, scale inhibitors, yellow metal corrosion inhibitors, such as tolyltriazole and benzotriazole, dispersants, deodorants, biocides, and dyes may also be included in the additives.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of this application, the term cooling water is defined as water used for heat exchangers in commercial processes such as chemical plants and refineries. Generally cooling water streams will have a pH of from about 7.0 to 9.2. Often they are buffered and sometimes have been treated to remove excessive dissolved solids.

The composition of this invention may contain sufficient amounts of each of the components to provide, when added to cooling water: 30-300 parts per million (ppm) by weight carboxylic acid or its soluble salts; and up to 10 ppm by weight of soluble zinc salts. In one embodiment the additive may include: 30-180 ppm by weight carboxylic acid and its soluble salts and up to 4 ppm by weight of soluble zinc salts.

In one aspect, the invention is a method for preventing or mitigating corrosion in cooling water comprising treating the cooling water with an additive comprising a soluble zinc salt and a soluble carboxylic acid salt. In some embodiments, the soluble carboxylic acid salt is a compound selected from the group consisting of a soluble gluconic acid salt, a soluble saccharic acid salt, and combinations thereof.

The soluble zinc salts may be any known to those of ordinary skill in the art to be both soluble and free from counter ions that may be problematic in cooling water. For example, zinc chloride and zinc bromide and even zinc hydroxide may be used while zinc phosphate would be undesirable. Other salts that may be used with the method of the application include, but are not limited to zinc carbonate, zinc borate, zinc nitrate, and combinations thereof. Hydrates may also be used, particularly where the hydrate may be soluble while the unhydrated salt is not.

The additive of the application may be a zinc carboxylate salt or it may be the product of admixing a first salt and a second salt with the first salt being a soluble zinc salt and the second salt being a soluble carboxylic acid salt. In one embodiment, the zinc salt is selected from the group consisting of a soluble gluconic acid salt, a soluble saccharic acid salt, and combinations thereof.

The additives in the application may include other compounds. For example, in addition to the zinc salts already discussed above, yellow metal corrosion inhibitor such as tolyltriazole or benzotriazole, scale dispersants, deodorants, biocides, dyes, may also be included in the additives.

The Carboxylic Acid(s)

The carboxylic acid component of the additive may be selected from the group consisting of gluconic acid and saccharic acid, and other carboxylic acids and their derived polycarboxylic acids, as well as their water soluble salts. In one embodiment, gluconic acid and its sodium salt, saccharic acid and its potassium and calcium salts are used to prepare the additives of the method of the disclosure.

Zinc

The additives useful with the method of the disclosure may, in one embodiment, be prepared using zinc chloride. In other embodiments, the water soluble zinc salts may be selected from the group consisting of zinc sulfate and zinc oxide.

The additive may be prepared using any methods known to those of ordinary skill in the art of preparing zinc salts and admixtures comprising zinc salts. Hydrates may be used, especially where a salt would otherwise be insoluble or difficult to handle.

While not wishing to be bound by any theory, it is nevertheless believed that the carboxylic acids useful with the method of the application are those that do not coordinate too strongly with the zinc. For example gluconic acid, a mono-carboxylic acid and saccharic acid, a dicarboxylic acid may both be used with the method of the application and are very efficient for preventing corrosion. In contrast however, butane tetracarboxylic acid and malic acid, a four functional and two functional acid respectively, show corrosion inhibition performance, but higher dosage are needed to obtain same inhibition efficiency than those of gluconic acid and saccharic acid.

EXAMPLES

The following examples are provided to illustrate the present invention. The examples are not intended to limit the scope of the claims and they should not be so interpreted. Amounts are in weight parts or weight percentages unless otherwise indicated.

Examples 1-30

The composition of a cooling water sample shown in Table 1 is treated according to the conditions set forth in Table 2. Carbon steel 1010 (CS 1010) coupons are used and corrosion is determined by using the technique of linear polarization resistance. Chemical concentrations used are expressed in parts per million (ppm). The unit of corrosion rate is in mils per year (mpy). The inhibition efficiency in Table 2 was calculated by equation (1)

$\begin{array}{cc}\mathrm{Inhibition}\mathrm{Efficiency}=\left(\frac{\mathrm{Corrosion}{\mathrm{Rate}}_{\mathrm{Blank}}-\mathrm{Corrosion}{\mathrm{rate}}_{\mathrm{Dosage}}}{\mathrm{Corrosion}{\mathrm{Rate}}_{\mathrm{Blank}}}\right)\times 100\%& \left(1\right)\end{array}$

where Corrosion Rate_Blank is the corrosion rate without any additions of chemical treatments, Corrosion rate_Dosage is the corrosion rate with specific dosages of chemicals.

Comments Regarding the Examples

The combination of zinc with gluconate and saccharate salts were very efficient, needing only 60 or fewer parts per million to reduce 90% of the corrosion rate of carbon steel coupon observed in the blanks. The gluconic acid is a monocarboxylic acid. The saccharic acid is a dicarboxylic acid but it has a hydroxyl group on every carbon between the acid groups which hinders free rotation about the axis of the two acidic groups. More tests with other compounds, such as either di- or higher functional acids, or the compounds included other groups such as amino groups, showed inhibition performance with higher or even much dosages to reach 90% corrosion inhibition.

TABLE 1
Na+ (ppm)   273
Ca2+ (ppm)  200
Mg2+ (ppm)  50
Fe2+ (ppm)  0.5
HCO3− (ppm) 100
Cl− (ppm)   500
SO42− (ppm) 496

TABLE 2
				Butane-					Poly-
	Citric	Tartaric	Sodium	tetra-	Saccharic	Malic	Glycolic	Erythorbic	aspartic		Corr.
	Acid	Acid	Gluconate	carboxylic	Acid	Acid	acid	acid	acid	Zn2+	Rate	Inhibition
Example	(ppm)	(ppm)	(ppm)	acid(ppm)	(ppm)	(ppm)	(ppm)	(ppm)	(ppm)	(ppm)	(mpy)	Efficiency
1	0	0	0	0	0	0	0	0	0	0	27	N/A
2	0	0	0	0	0	0	0	0	0	2	30	N/A
3	60										19.2	28.9
4	60									2	15.9	41.1
5	180									2	1.49	94.5
6	120									2	9.19	66.0
7	30		30							2	7.47	72.3
8		60									23.9	11.5
9		60	60								14	48.1
10		60								2	8.8	67.4
11		120								2	2.78	89.7
12		30	60							2	1.03	96.2
13		30	30							2	3.87	85.7
14		180	60								10.8	60.0
15		180								2	0.94	96.5
16			60						60		23.4	13.3
17			30							2	3.04	88.7
18			180								7.09	73.7
19			60							2	1.5	94.4
20				60							15.9	41.1
21				60						2	15	44.4
22					60						4.88	81.9
23					60					2	0.73	97.3
24					180						1.73	93.6
25						60				2	10.4	61.5
26						180				2	6.82	74.7
27							60			2	16.4	39.3
28								60		2	10.4	61.5
29								180		2	3.78	86.0
30									60	2	8.64	68.0

Claims

1. A method for preventing or mitigating corrosion in cooling water systems comprising treating the cooling water with an additive comprising a soluble zinc salt and a soluble carboxylic acid salt.

2. The method of claim 1 wherein the soluble zinc salt is selected from the group consisting of: zinc chloride, zinc bromide, zinc hydroxide, zinc carbonate, zinc borate, zinc nitrate, and combinations thereof.

3. The method of claim 2 wherein the soluble zinc salt is selected from the group consisting of: zinc chloride, zinc bromide, zinc hydroxide and combinations thereof.

4. The method of claim 1 wherein the soluble carboxylic acid salt is selected from the group consisting of a soluble gluconic acid salt, a soluble saccharic acid salt, and combinations thereof.

5. The method of claim 1 wherein the additive, when added to cooling water is present at a concentrations sufficient to provide from about 30 to about 300 ppm by weight carboxylic acid or its soluble salts.

6. The method of claim 5 wherein the additive, when added to cooling water is present at a concentrations sufficient to provide from about 30 to about 180 ppm by weight carboxylic acid or its soluble salts.

7. The method of claim 1 wherein the additive, when added to cooling water is present at a concentration sufficient to provide up to 10 ppm by weight of soluble zinc salts.

8. The method of claim 1 wherein the additive, when added to cooling water is present at a concentration sufficient to provide up to 4 ppm by weight of soluble zinc salts.

9. The method of claim 1 wherein the additive additionally comprises a composition selected from the group comprising: scale inhibitors, yellow metal corrosion inhibitors, dispersants, deodorants, biocides, dyes, and combinations thereof.

10. A method for preventing or mitigating corrosion in cooling water comprising treating the cooling water with an additive comprising a soluble zinc salt and a compound selected from the group consisting of gluconic acid, saccharic acid, a water soluble gluconate salt, a water soluble saccharic acid salt, and combinations thereof.

11. The method of claim 9 wherein the water soluble saccharic acid salt is selected from the group consisting of its potassium salts, its calcium salts, and combinations thereof.

12. The method of claim 9 wherein the water soluble gluconate salt is its sodium salt.

13. The method of claim 9 wherein the additive, when added to cooling water is present at a concentrations sufficient to provide from about 30 to about 300 ppm by weight of gluconic acid, saccharic acid, a water soluble gluconate salt, a water soluble saccharic acid salt, and combinations thereof.

14. The method of claim 12 wherein the additive, when added to cooling water is present at a concentrations sufficient to provide from about 30 to about 180 ppm by weight of gluconic acid, saccharic acid, a water soluble gluconate salt, a water soluble saccharic acid salt, and combinations thereof.

15. The method of claim 9 wherein the additive additionally comprises a composition selected from the group comprising: scale inhibitors, yellow metal corrosion inhibitors, dispersants, deodorants, biocides, dyes, and combinations thereof.

16. A method for preventing or mitigating corrosion in a cooling water system comprising treating the cooling water with an additive comprising a soluble zinc carboxylate.

17. The method of claim 14 wherein the soluble zinc carboxylate is present at a concentration of from 30 to about 300 ppm by weight.

18. The method of claim 14 wherein the additive additionally comprises a composition selected from the group comprising: scale inhibitors, yellow metal corrosion inhibitors, dispersants, deodorants, biocides, dyes, and combinations thereof.

19. A method for preventing or mitigating corrosion in cooling water comprising treating the cooling water with an additive comprising a compound selected from the group consisting of zinc gluconate, the zinc salt of saccharic acid, and combinations thereof.

20. The method of claim 16 wherein the additive additionally comprises a composition selected from the group comprising: scale inhibitors, yellow metal corrosion inhibitors, dispersants, deodorants, biocides, dyes, and combinations thereof.