JP7851101B2 - Initial processing method - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act: Public disclosure through online presentation, date: April 9, 2021, location: Taiyo Oil Co., Ltd. (Hibiya Kokusai Building 15F, 2-2-3 Uchisaiwaicho, Chiyoda-ku, Tokyo) [Publications, etc.] Public disclosure through publication, date: July 7, 2021, mailing address: Taiyo Oil Co., Ltd. Shikoku Office (4070-2 Tane, Kikuma-cho, Imabari City, Ehime Prefecture)

This invention relates to a method for forming a water-based corrosion-preventive coating.

Steel is inexpensive and possesses excellent mechanical properties, making it widely used in various fields. However, it has the weakness of being susceptible to corrosion. To ensure the continued use of steel, a method is known that involves applying corrosion inhibitors or preservatives to the metal surface to form a protective coating, thereby preventing contamination and corrosion.

Patent Document 1 describes a method for forming a corrosion-preventive coating using a phosphate-based corrosion inhibitor in water treatment. Patent Document 2 describes a method for forming a corrosion-preventive coating using a phosphate-based corrosion inhibitor in the petroleum refining field.

Japanese Patent Publication No. 2016-037638 Japanese Patent Publication No. 2019-168162

However, when the inventors conducted corrosion tests using the conventional phosphate-based and other corrosion inhibitors mentioned above, they found that sufficient corrosion protection could not be obtained.

The inventors, through diligent research to solve the above problems, have discovered a method for forming a corrosion-preventive coating with a higher corrosion-preventive effect than conventional methods. This method involves adding (A) a component selected from the group consisting of organic phosphonic acids, phosphonocarboxylic acids, phosphinopolycarboxylic acids, carboxylic acid polymers, and inorganic phosphorus compounds, and (B) a water-soluble metal and its salt, and then bringing the mixture into contact with an iron-based metal surface.

By using the present invention, excellent corrosion prevention effects can be obtained against corrosion and fouling of iron-based metal surfaces in water treatment systems. Furthermore, by applying it to heat exchangers and heating furnaces in a shut-down petroleum refinery, sulfidation corrosion can be prevented on the iron-based metal surfaces of heat exchangers and heating furnaces even after the petroleum refinery has started operation. As a result, it is possible to prevent organic substances such as asphaltenes and sludge in the oil from being incorporated into the iron sulfide produced by sulfidation corrosion, thereby preventing the formation of composite fouling of these organic substances and iron sulfide, and preventing a decrease in heat transfer efficiency.
This allows the heat exchange efficiency of heat exchangers and heating furnaces to be maintained at a high level over the long term, which in turn reduces fuel costs and cleaning costs.

This is a block diagram of an oil refining plant. This is a schematic diagram of a corrosion testing apparatus for evaluating stain inhibitors when used with oil.

The present invention will be described in detail below, but the present invention is not limited to these descriptions.
The present invention provides a method for forming a corrosion-resistant coating, which is used to improve the surface of various iron-based metals, including iron and steel.

The mechanism of action of the corrosion-preventive coating formation method of the present invention will now be explained. By bringing an iron-based metal surface into contact with (A) a component containing one or more selected from the group consisting of phosphonocarboxylic acids, organic phosphonic acids, phosphinopolycarboxylic acids, carboxylic acid polymers, and inorganic phosphorus compounds (hereinafter referred to as (A) component), it reacts with the dissolved iron ions to form an insoluble coating, thereby suppressing the progression of surface corrosion. Furthermore, (B) a water-soluble metal and its salt (hereinafter referred to as (B) component) promotes the formation of the crystalline coating formed by (A) component, and also improves the durability of the coating. Therefore, it is believed that corrosion will be less likely to occur in water treatment systems, heat exchangers in petroleum refining plants, etc.

The corrosion-preventive coating formation method of the present invention is applicable to heat exchangers included in cooling systems and air conditioning systems in various manufacturing industries such as paper and pulp manufacturing, automobile factories, and semiconductor manufacturing plants in general water treatment systems, as well as to shut-down heat exchangers and heating furnaces in petroleum refining plants. Examples of heat exchangers covered by the present invention include shell-and-tube multi-tube heat exchangers, double-tube heat exchangers, spiral heat exchangers, plate heat exchangers, spiral tube heat exchangers, spiral plate heat exchangers, coil heat exchangers, and jacketed heat exchangers.

Next, Figure 1 shows a typical petroleum refining plant to which the corrosion-preventive coating method of the present invention is applied. In this petroleum refining plant, crude oil supplied from a crude oil storage tank (not shown) is heated to 110-140°C in a preheat exchanger 21 and then enters a desolter 22. In the desolter 22, water and inorganic components are removed, and the oil is heated to 150-180°C in a preheat exchanger 23 before being sent to a pre-flash column 24 where low-boiling point gases are separated. The oil is then further heated to 240-280°C in a preheat exchanger 25, and then heated to 350-380°C in a heating furnace 26 before being sent to an atmospheric distillation column 27. In the atmospheric distillation column 27, the fractions separated by boiling point differences are sent via a pump 28 to the shell side of the heat exchanger 25 as a heat source.

The corrosion-preventive coating method of the present invention is effective in preventing corrosion of heat exchangers 21, 23, and 25 used in this petroleum refining process, as well as in preventing corrosion inside the heating furnace 26. These are heat exchangers made of ferrous metals, including preheating exchangers, preheaters, and reboilers. In these heat exchangers made of ferrous metals, organic matter such as asphaltenes and sludge in the oil is incorporated into the iron sulfide produced by sulfidation corrosion, and a composite fouling of this organic matter and iron sulfide is easily formed. However, by applying the corrosion-preventive coating method of the present invention, heat exchangers made of ferrous metals become less susceptible to sulfidation corrosion due to the corrosion-preventive coating. As a result, iron sulfide is less likely to form, and the adhesion of the aforementioned composite fouling is also prevented.
In particular, the heat exchangers 23, 25 and the heating furnace 26 downstream of the desolder 22 reach high temperatures of 200°C or higher, making them prone to fouling, and thus the corrosion-preventive coating formation method of the present invention proves effective.

To prevent sulfidation corrosion inside the preheating exchangers 21, 23, and 25 and the heating furnace 26, components (A) and (B) can be added to points A, B, C, and D in Figure 1, and circulated within the system to form a corrosion-preventive coating.

In this invention, the organic phosphonic acid of component (A) is an organic compound having one or more phosphono groups in its molecule. Specifically, examples include 1-hydroxyethylidene-1,1-diphosphonic acid, aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, hexamethylenediaminetetramethylenephosphonic acid, and others, with 1-hydroxyethylidene-1,1-diphosphonic acid being preferred.

Phosphonocarboxylic acids are organic compounds having one or more phosphono groups and one or more carboxyl groups in their molecule. Specific examples include 2-phosphonobutane-1,2,4-tricarboxylic acid, hydroxyphosphonoacetic acid, phosphonopolymaleic acid, and phosphonosuccinic acid, with 2-phosphonobutane-1,2,4-tricarboxylic acid and phosphonopolymaleic acid being preferred. Phosphonocarboxylic acids are commercially available from Rhodia under the trade name BRICORR288 and from BWA under the trade name BELCOR585.

Phosphinopolycarboxylic acids are compounds having one or more phosphino groups and two or more carboxyl groups in their molecule. Specifically, examples include bis-poly(2-carboxyethyl)phosphinic acid obtained by reacting acrylic acid with hypophosphorous acid, bis-poly(1,2-dicarboxyethyl)phosphinic acid obtained by reacting maleic acid with hypophosphorous acid, poly(2-carboxyethyl)(1,2-dicarboxyethyl)phosphinic acid obtained by reacting maleic acid with acrylic acid and hypophosphorous acid, bis-poly[2-carboxy-(2-carboxymethyl)ethyl]phosphinic acid obtained by reacting itaconic acid with hypophosphorous acid, and reaction products of acrylic acid with 2-acrylamido-2-methylpropanesulfonic acid and hypophosphorous acid. Preferably, these are reaction products of maleic acid with acrylic acid and hypophosphorous acid, or reaction products of itaconic acid with maleic acid and hypophosphorous acid. Phosphinopolycarboxylic acids are commercially available from BWA under trade names such as BELCLENE500, BELSPERSE164, and BELCLENE400.

Carboxylic acid polymers include homopolymers of monoethylenically unsaturated carboxylic acids and their water-soluble salts, copolymers of two or more different monoethylenically unsaturated carboxylic acids and their water-soluble salts.
Examples of homopolymers of monoethylene unsaturated carboxylic acids include acrylic acid polymers, methacrylic acid polymers, maleic acid polymers, hydrolysates of maleic anhydride polymers, itaconic acid polymers, fumaric acid polymers, and the like. Examples of copolymers of two or more different monoethylene unsaturated carboxylic acids include copolymers of acrylic acid and maleic acid, copolymers of acrylic acid and itaconic acid, copolymers of maleic acid and itaconic acid, copolymers of maleic acid and fumaric acid, terpolymers of acrylic acid, itaconic acid and maleic acid, and terpolymers of acrylic acid, itaconic acid and fumaric acid. Preferably, the copolymers are homomaleic acid polymers and copolymers of maleic acid and a monoethylene unsaturated monomer copolymerizable with maleic acid, and homoitaconic acid polymers and copolymers of itaconic acid and a monoethylene unsaturated monomer copolymerizable with itaconic acid.

Here, examples of monoethylene unsaturated monomers copolymerizable with maleic acid or itaconic acid include fumaric acid; alkyl (meth)acrylates, hydroxyl alkyl (meth)acrylates; (meth)acrylamide, N-alkyl-substituted (meth)acrylamide; olefins with 2 to 8 carbon atoms such as ethylene, propylene, isopropylene, butylene, isobutylene, hexene, 2-ethylhexene, pentene, isopentene, octene, isooctene, etc.; vinyl alkyl ethers such as vinyl methyl ether and vinyl ethyl ether; and alkyl maleate esters, etc., and one or more of these are used.

The molecular weight of the maleic acid-based polymer and the itaconic acid-based polymer is preferably 300 to 20,000 as a weight-average molecular weight, but more preferably 400 to 1,000.

Inorganic phosphate compounds are inorganic compounds that have a phosphate group or phosphate skeleton in their molecule. Specifically, examples include alkali metal phosphates such as phosphoric acid, monosodium phosphate, disodium phosphate, monopotassium phosphate, and dipotassium phosphate, as well as condensed phosphates such as sodium pyrophosphate, sodium tripolyphosphate, and sodium hexametaphosphate.

In the present invention, there are no restrictions on the type of metal in component (B) of the water-soluble metal and its salt, but it is desirable that the metal and salt be soluble in water.
In this invention, "soluble in water" means that the substance is soluble in acidic, neutral, or alkaline water at 25°C at a concentration of 1 ppm or more. Preferably, it is soluble at a concentration of 100 ppm or more, and more preferably at a concentration of 500 ppm or more. At this time, the metal exists in the aqueous solution in an ionic state.

As the water-soluble metals and their salts of the present invention, alkali metals, alkaline earth metals, transition metals and their salts can be used. Specific examples include sodium and potassium as alkali metals, magnesium and calcium as alkaline earth metals, iron and copper as transition metals, and aluminum as base metals. However, alkaline earth metals and/or alkali metals are preferred. From the viewpoint of corrosion prevention effect, calcium and its salts are particularly preferred, and calcium chloride is most preferred. Furthermore, one or more of these metals and their salts may be included.
In this invention, there are no restrictions on the type of salt that can be used, but it must be soluble in water. For example, chloride salts, carbonates, and sulfates can be used, but calcium chloride is preferred because calcium salts have low solubility.

The film-forming step of the present invention involves adding components (A) and (B) and bringing them into contact with an iron-based metal surface. Preferably, the film-forming step of the present invention involves adding components (A) and (B) and bringing them into contact with the iron-based metal surface for 1 to 72 hours, more preferably 5 to 48 hours. If the contact time is less than 1 hour, the corrosion-preventive film may be formed unevenly, and the corrosion-preventive effect may be reduced.

The pH in the film-forming process of the present invention is not particularly limited, but a pH of 3.0 to 9.0 is preferred.

The amount of component (A) added to this invention as an active ingredient is 10 to 10,000 ppm, preferably 100 to 5,000 ppm. The amount of component (B) added is 100 to 2,000 ppm, preferably 500 to 1,600 ppm.

The temperature at which the aqueous solution containing components (A) and (B) of the present invention is brought into contact with an iron-based metal surface is not particularly limited as long as it is within the range of water, but is preferably less than 50°C.

There are no particular restrictions on the stirring when bringing the aqueous solution containing components (A) and (B) of the present invention into contact with an iron-based metal surface, but a turbulent flow is preferred.

In this invention, there are no restrictions on the water used; tap water, industrial water, well water, ion-exchanged water, distilled water, etc., can be used.
Furthermore, although tap water and industrial water contain metal ions such as sodium ions, calcium ions, and magnesium ions, the corrosion prevention effect is improved by adding component (B) to the aforementioned water.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples. Furthermore, various modifications are also included in this invention, provided that they do not depart from the scope of the claims and are easily conceivable by those skilled in the art.
The amount of anti-fouling agent added in the following examples and comparative examples is calculated on an active ingredient basis.

<Corrosion Test 1>
A low-carbon steel test specimen (material: JIS G3141 SPCC-SB) measuring 1 × 13 × 75 mm, polished with 400-grit sandpaper, was immersed in a solution containing predetermined amounts of components (A) and (B). The mixture was stirred for 24 hours to create a coating, which was then dried and its mass before testing was measured. Ion-exchanged water (resistivity 18 MΩ·cm) was adjusted to pH 9.4 (25°C) and used as the test solution. 100 ml of the test solution and the test specimen were placed in a sealed container, and nitrogen gas was passed through to reduce the dissolved oxygen concentration of the test solution to 10 μg/l. The container was then sealed and maintained at 70°C for 7 days. After 7 days, the test specimen was removed, any deposits were removed, and the mass after testing was measured. The corrosion rate (mdd) was calculated using the following formula. The results are shown in Table 1.
Corrosion rate (mdd) = ( _W0 - _W1 ) / (S × T)
_W0 : Mass before testing (mg), _W1 : Mass after testing (mg)
S: Surface area of the test specimen ( ^dm² )
T: Exam period (number of days)

<(A) component>
• 1-Hydroxycylidene-1,1-diphosphonic acid (HEDP, Belclene 660LA, manufactured by BWA)
• 2-Phosphonobutane-1,2,4-tricarboxylic acid (PBTC, Belclene 650, BWA)
• Polymaleic acid (molecular weight 2000, Belclene 200LA, manufactured by BWA)
• Phosphate (reagent, manufactured by Wako Pure Chemical Industries, Ltd.)
• Bis-poly(2-carboxyethyl)phosphinic acid (BELSPERSE164, manufactured by BWA)
<(B) component>
Calcium chloride ( _CaCl₂ , reagent, manufactured by Wako Pure Chemical Industries, Ltd.)
Calcium oxide (CaO, reagent, manufactured by Wako Pure Chemical Industries, Ltd.)
• Sodium bicarbonate ( _NaHCO₃ , reagent, manufactured by Wako Pure Chemical Industries, Ltd.)
- Aluminum sulfate ( _Al₂ ( _SO₄ ) _₂ , reagent, manufactured by Wako Pure Chemical Industries, Ltd.)

The results are shown in Table 1. As in Examples 1 to 16, when components (A) and (B) were added at predetermined concentrations, the corrosion rate was 7 mdd or less, whereas Comparative Example 1, which did not undergo a coating treatment, had a corrosion rate of 58 mdd. Furthermore, Comparative Examples 2 to 6, which added component (A) but not component (B), had a corrosion rate of 25 mdd or more, while Comparative Examples 7 to 10, which did not add component (A) but added component (B), had a corrosion rate almost the same as Comparative Example 1. Examples 17 to 26, in which the amount of component (B) added was varied, had a corrosion rate of 20 mdd or less, which was lower than the results for Comparative Examples 2 to 6. In addition, even though they were both calcium salts, calcium chloride in Example 1 had a superior corrosion-preventive effect compared to calcium oxide in Example 2.
From these results, it was found that the example using both components (A) and (B) provided superior corrosion protection compared to the comparative example.

<Corrosion Test 2>
A low-carbon steel test specimen (material: JIS G3141 SPCC-SB) measuring 1 × 13 × 75 mm, polished with 400-grit sandpaper, was immersed in a mixture of predetermined amounts of components (A) and (B), mixed and stirred for 24 hours, and then coated. After drying, the mass before testing was measured. The test specimen was removed and mounted on the rotating shaft 32. 250 ml of crude oil was placed inside the autoclave 31, the lid 31a was closed, and the air inside the autoclave was replaced with nitrogen. The agitator was driven to rotate the rotating shaft 32 at a stirring speed of 500 rpm, and the area around the autoclave 31 was heated to 300°C by a mantle heater (not shown) and maintained for 96 hours. After cooling to room temperature, the lid 31a was opened and the test specimen was removed. The removed test specimen was washed with hexane, dried, and then weighed. Furthermore, the test pieces that had been washed with hexane were immersed in 3.5% hydrochloric acid, and the corrosion products on the surface were calculated. The average of the values from two test pieces was used as the test result.

Adhesion amount (%) = {(Weight after hexane washing (g) - Weight after hydrochloric acid washing (g)) / Initial weight of test specimen (g)} × 100
Corrosion weight loss (%) = {(Initial weight of specimen (g) - Weight after hydrochloric acid cleaning (g)) / Initial weight of specimen (g)} × 100

The results are shown in Table 2. As in Examples 28 to 43, when components (A) and (B) were added at predetermined concentrations, the adhesion amount was 4% and the corrosion loss was 5% or less, whereas Comparative Example 1, which did not undergo a film-forming treatment, had an adhesion amount of 13% and a corrosion loss of 16%. Furthermore, Comparative Examples 12 to 16, which added component (A) but not component (B), had an adhesion amount of 8% and a corrosion loss of 11% or more, while Comparative Examples 17 to 20, which did not add component (A) but added component (B), showed results that were almost the same as Comparative Example 11 in both adhesion amount and corrosion loss. Examples 44 to 54, in which the amount of component (B) added was varied, had an adhesion amount of 7% and a corrosion loss of 10% or less, which were lower values than those of Comparative Examples 12 to 16.
From these results, it was found that, even in corrosion tests using oil, the example using both components (A) and (B) exhibited superior corrosion protection compared to the comparative example.

The present invention's method for forming a corrosion-resistant coating can be applied to the surface of ferrous metals to create a corrosion-resistant coating with a higher corrosion-resistant effect than conventional technologies. As a result, corrosion that leads to a decrease in heat transfer efficiency in heat exchangers included in water treatment systems and heat exchangers in petroleum refining plants during shutdown can be significantly reduced, contributing to stable operation.

21, 23, 25: Preheat exchanger; 22: Desolter; 24: Pre-flash column; 26: Heating furnace; 27: Distillation column; 28: Pump; 31: Autoclave; 31a: Lid; 32: Rotating shaft; 33: 6-blade turbine blade; 34, 35: Test piece

Claims (4)

A method for forming a corrosion-preventive coating on an iron-based metal surface in an aqueous system, wherein the corrosion-preventive coating formation method is for forming a corrosion-preventive coating on an iron-based metal surface of a heat exchanger and heating furnace in a petroleum refining plant that is shut down, and the method is characterized by adding (A) one or more components selected from the group consisting of organic phosphonic acid, phosphonocarboxylic acid, phosphinopolycarboxylic acid, carboxylic acid polymer and inorganic phosphorus compound, and (B) a water-soluble metal and its salt, and bringing the two into contact with the iron-based metal surface, wherein the concentration of (B) is 500 to 1600 ppm. A method for forming a corrosion-preventive coating on an iron-based metal surface according to claim 1, characterized in that (B) the water-soluble metal and its salt are alkaline earth metals and/or alkali metals and their salts. A method for forming a corrosion-preventive coating on an iron-based metal surface according to claims 1 to 2, characterized in that (B) the water-soluble metal and its salt are calcium and its salt. A method for forming a corrosion-preventive coating on an iron-based metal surface according to claims 1 to 3, characterized in that (B) the water-soluble metal and its salt are calcium chloride.