LT6060B - Corosion inhibitor for deicing fluids - Google Patents

Abstract

The present invention is related to a stable and non-toxic anti-corrosive additive, specifically a corrosion inhibitor, comprising tris(hydroxymethyl)aminomethane salts with organic and inorganic acids. The anti-corrosive additive can be used for protecting aluminum and steel surfaces against corrosion in water solutions of glycols and glycerol such as aircraft deicing and anti-icing fluids or heat transfer and cooling liquids. This anti-corrosive additive also performs acidity stabilizing, bacteriostatic and antioxidative functions.

Description

Technical field

The surface of the aircraft fuselage and its controls must be kept clean of any contamination during use. During the cold season, snow, ice, frost or other forms of frozen water on planes are particularly dangerous. Not only can it impair the control of the aircraft, it can also be the cause of an accident. When preparing an airplane for a winter flight, the snow-ice coating that forms during parking is removed from its surfaces using aircraft deicing fluid (ADF). They are described in SAE Aircraft Material Specification (AMS) 1424 and International Standard ISO 11075: 2007. These fluids are also called Type I fluids. These fluids are usually mixtures of antifreeze agents (freezing buffers) and water, with various additives. Before being sprayed on airplane surfaces, they are usually diluted with water - depending on the ambient temperature (usually 50% .Ready To Use - RTU) and spray-heated to 60-80 ° C under high pressure. Type I fluids provide only limited de-icing protection (typically up to 10 minutes). Often, there is a time lag between the de-icing procedure and the take-off of the airplane, which requires longer protection of the airplane surfaces from the formation of snow or ice when snowing or in the event of a snowfall. For this purpose, aircraft anti-icing fluid AAF is used. They are described in SAE AMS 1428 and ISO 11078: 2007, also known as Type II, Type III, and Type IV fluids. In addition to freezing agents (freezing buffers), water and other additives similar to Type I fluids, they contain pseudoplastic thickeners. It is these thickeners that allow the fuselage surfaces of the aircraft to form a gel-like coating that prevents ice and snow from attaching to those surfaces. At rest, this pseudoplastic coating is stable for 20 minutes to 2 hours, depending on concentration and ambient conditions, but as the aircraft moves and accelerates, the viscosity of the coating decreases significantly and drains away from the surfaces of the aircraft. In other words, the viscosity of these pseudoplastic fluids decreases and their fluidity increases with increasing force.

These de-icing and anti-icing fluids, in addition to their direct function of protecting aircraft surfaces from icing, must also be safe for all materials used in the construction of aircraft: aluminum, steel and titanium alloys, painted surfaces, plastics and others. Also, these fluids and their use should cause minimal impact on the environment, such as: low toxicity to aquatic organisms, etc.

State of the art

The bulk of the de-icing fluid consists of a mixture of antifreeze agents (freezing buffers) and water. Prior art anti-freeze and anti-icing agents for the production of anti-icing fluids as described in GB I 026150A are ethylene glycol, propylene glycol and glycerol and / or mixtures thereof. In most cases, the deicing fluids contain from 40 to 88% of such glycols and / or glycerol.

In addition to anti-freezing agents (freezing buffers) and water, there are various additives in de-icing fluids. Such accessories are:

a. fluid surface tension regulators and / or reducing agents that promote the wetting of airplane surfaces, reduce the surface tension of melt water and / or form a hydrophobic monolayer on airplane surfaces, thereby partially preventing re-icing of those surfaces. Such substances are, for example, polyalcohol amines, preferably diethanolamine or triethanolamine, as described in GB1202697A or EP194899B1. Also used are nonionic surfactants, such as dioctylphenol and ethylene glycol ethers in GB1272464A, or C13C15 alcohols alkoxylated from 11 to 20 alkoxide molecules, N-methyl-N-oleylglycine as disclosed in US5759436A, organic phosphates: phosphoric and / or phosphinic acids organic ester salts as disclosed in US020050087720A1 and all other surfactants described in US5817252.

b. acidifying and / or stabilizing the solution at pH 7-10, preferably pH 8-9. The glycols in the de-icing fluids, in particular glycerol, are oxidized by oxygen in the air, and the resulting oxidation products increase the acidity of the solution, which not only further decreases solution stability, but also increases the risk of corrosion on treated metal surfaces. Such acidification of liquids must be compensated by buffers containing acidifying agents. These are mainly phosphates - sodium, potassium and ammonium, borates, salts of carboxylic acids; the basic components are the alkalis of sodium and potassium or their carbonates, butyl, nonylamines, mono-, di-, triethanolamines; acidic components - phosphorus, boron, organic mono- and acid (4-8 C atoms), benzoates as described in US6921495B2 and others.

It is also noted in US 5708068A that some amines, including triethanolamine, reduce the thermal stability of such solutions.

c. antioxidants - inhibits the oxidation of airborne organic substances - especially glycols and / or glycerol - with oxygen in the air. These may be sodium, potassium, or ammonium sorbates, or benzoates as disclosed in US7105105B2.

e. antimicrobial, bacteriostatic - stops the growth of bacteria, yeasts, fungi and molds in these fluids. These are usually sodium azide, quaternary ammonium salts such as n-alkyldimethylbenzylammonium, n-alkyltrimethylammonium (where alkyl is C12-C18), sodium, potassium or ammonium benzoates and others as described in CA2503859A1.

f. corrosion inhibitors - protect the metals used in aircraft manufacturing: aluminum, magnesium alloys, carbon steel and titanium from corrosion. A wide variety of prior art corrosion inhibitors are used for deicing fluids, such as those described in US7875203B2: alkali metal phosphates, salts of phosphoric esters such as ethyl, dimethyl, isopropyl phosphate, as well as thiourea, sodium nitrate, butin-1,4 -diol, imidazoles such as 1H-imidazole, methylimidazole, benzimidazole, triazoles such as benzotriazole, tolyltriazole. Triazoles are desirable, as they not only provide good protection against corrosion on metal surfaces, but are also flame retardants - inhibiting ignition. Also known as anticorrosive additives are other materials known in the art: boric, silicon, fatty, amber, sebacine, alkali metal salts of polyaspartic acid, Sandocotin 8132 (Sandoz AG) - usually 0.1 to 1% (w / w). .

In addition to these components, paint is commonly added to de-icing fluids and, if required, anti-foaming agents or other additives.

With the advent of the use of de-icing and de-icing fluids, ecological problems have arisen. When used, these liquids usually go completely untreated into sewage networks and sometimes into natural water bodies. This leads to the following ecological problems:

a. some of the antifreeze agents, such as ethylene glycol, are toxic to mammals, including humans. This problem is solved by the phasing out of the use of ethylene glycol in the production of de-icing and de-icing fluids.

b. most of the substances that reduce freezing point get into water bodies and are rapidly degraded - biologically oxidized. At this time, water-dissolved oxygen is used for this oxidation and, consequently, aquatic animals die due to its deficiency (see: Aquatic Toxicity and Biochemical Oxygen Demand, Airport Cooperative Research Program, Web-Only Document 3). , (2008) There are several ways to prevent this, one of which is the improved use of de-icing fluids, which is disclosed in US4032090A, which is spray-heated to 90 ° C, which allows the de-icing fluid to be used with more dilute water. to regulate the rate of biodegradation (BOD Biological Oxygen Consumption) of such liquids such that de-icing fluids produced from a mixture of rapidly biodegradable materials, propylene glycol, or glycerin, and slowly biodegradable triethylene glycol, are adapted to provide the appropriate biodegradation rate, the airport has biological v oilers or not - see patent VV02001029146A1. Efforts are also being made to switch to antifreeze agents derived from natural-renewable sources, such as 1,3-propanediol produced from carbohydrates by fermentation - cf. US7972530B2 and other similar materials as described in US20110024673A1 and US20120104305A1. Another way is to look for completely different antifreeze agents other than glycols. One such example is given in US20030034478A1. It describes a de-icing fluid that has a freezing point in the form of triethanolamine and formate salt. Another patent, US8187489B1, proposes an anti-aircraft deodorizer of ionic liquids, choline salts.

c. toxicity of some commonly used surfactant degradation products. Such are the degradation products of acylphenol ethoxylates alkylphenols as disclosed in WO02011103295A1. They are replaced with less harmful alkanol ethoxylates.

d. toxic and hardly biodegradable components - the most commonly used corrosion inhibitors are benzotriazole and tolyltriazole. They degrade slowly - accumulate in living organisms and poison them (see D.A. Pillard et al., Wat. Res., 35 (2001), 557-560). At present, these corrosion inhibitors are almost no longer in use, but only partially replaced by alkali metal polyaspartates, or polyglutamates, as described in WO02002099004A1.

Nor is triethanolamine, which is completely organic and often used in de-icing and de-icing fluids. It degrades rather slowly and its impurities and degradation products, di- and monoethanolamine, are sufficiently toxic to aquatic organisms (see G. Libralato et al., Journal of Hazardous Materials, 176 (2010) 535-539). In addition to ecological problems there are other disadvantages of these fluids. For example, alkaline and alkaline earth metal salts in de-icing and anti-molding applications can cause impact corrosion on hot titanium aircraft engine components as mentioned in patent CA2387923A1. The same salts are also largely responsible for the failure of the carbon fiber composite brakes of aircraft - catalytic oxidation.

In this way, increasingly stringent ecological, anti-icing efficiency and safety requirements are forcing the search for new materials and compositions suitable for de-icing fluids.

The essence of the invention

It is an object of the present invention to provide an anti-corrosion additive system suitable for de-icing and anti-icing fluids from alkylene glycols and / or glycerol. Such an anticorrosive additive system must provide sufficient protection against corrosion of the alloys used in the manufacture of aircraft and, at the same time, be non-toxic and thermally stable.

Description of Embodiment of the Invention

The anti-corrosion system of the present invention contains three salts of (hydroxymethyl) aminomethane (also known as TRIS, THAM, or 2-amino-2-hydroxymethylpropane-1,3-diol, hereinafter TRIS) with organic and inorganic acids. According to its chemical structure, TRIS is an amino-alcohol and is thus essentially close to those commonly used in anticorrosive systems, such as triethanolamine. However, TRIS has so far not been used in de-icing, de-icing, or other anticorrosive compositions, except in one case, for protecting steel in the presence of Cl'ions in complexes with Zn ² + ions (see S. Rajendran et al., Chemistry: An Indian Journal, 4, (2009).

Surprisingly, TRIS in combination with other known anticorrosive components, borates and phosphates, is better suited to corrosion protection of aluminum plate than triethanolamine (TEA), imidazole (IMDZ), 2-amino-2-methyl-1- propanol (AMP) or diethanol glycolide (diethanolamine and glycine amide - DE.GLA) and even better than some commercial de-icing fluids.

The test solutions of amino alcohols and other components are prepared as follows:

1. Mix 42 g propylene glycol / glycerol (6: 4 w / w) in 50 g deionized water;

2. To the resulting solution 1. add 1 g of sodium tetraborate decahydrate (Na ₂ B ₄ 0 _7. 10 H 2 O - borax) in a 10% solution prepared as follows: 50 g of propylene glycol and glycerol (6: 4 by weight) and 40 g of deionized Add 10 g of sodium tetraborate decahydrate in portions and stir until dissolved.

3. To a solution obtained by the second is added 0.15 g of trisodium phosphate - dodecahydrate (Na3P0 _fourth 12

H ₂ O);

4. To the solution obtained 3. add 0.2 or 0.1 g of the amino alcohol to be tested;

5. To solution 4 add deionized water to 100 g.

Mixtures containing:

A mixture of propylene glycol and glycerol (6: 4 by weight) - 42.5% by weight;

2. Sodium tetraborate - decahydrate (Na ₂ B ₄ 0 ₇ · 10 H ₂ O) - 0.1%;

3. Disodium phosphate dodecahydrate (Na ₃ PO ₄ .12 H ₂ O) - 0.15%;

4. Test for amino alcohol 0.2 or 0.1% (as in Table 1);

5. Deionized water - up to 100%

Such mixtures are based on glycol glyceryl concentration and freezing point and are semi-diluted commercial deicing type I fluids - RTU. For comparison, Kilfrost DF Pl plus was diluted with deionized water 50% (w / w) and solution 0 containing all components except amino alcohols.

In table no. 1 shows the amount of amino alcohols in the solutions tested and their effect on fully immersed aluminum alloy 2024 "alclad 60x40x0.5 mm plates over 1 week (7 days -168 hours) at a constant temperature of 40 ° C (similar to ASTM F 483). used for testing the icing liquids), expressed as a weight change (WGT change) units - mg / ^cm2 / 24 hrs.

Table 1.

Appendix % WGT Change, mg / ^cm2 / 24 hrs Kilfrost DF Plus 50% -0,00016 O II O 0.00040 TRIS 0.1 -0.00001 TEA 0.2 -0,00058 AMP 0.2 0.00173 IMDZ 0.1 0.00058 DE.GLA 0.1 0.00018

This change in weight due to corrosion is also shown in Figs. 1.

TRIS is a well known in the art, typically having an acid stabilizing role as a component of pH buffers. This material is used particularly intensively in biotechnology and biochemistry or even medicine, mainly due to its low toxicity and other ecological safety, as well as its stability and ease of use. Therefore, it is reasonable to use TRIS not only as a component of the anti-corrosion system, but also as an acid stabilizer. TRIS has a pKa of 8.07, which means it can be a base component in buffers of pH 7 to 9, which is almost ideally suited to the requirements of de-icing fluids. The pH-stabilizing buffers usually mix two components, basic and acidic. The acidic component of the present invention has been selected so that its solutions are minimally toxic, thermally stable and have other positive properties such as bacteriostatic and / or antioxidant. It is also desirable that they be known in the art as non-corrosive or, more preferably, have anti-corrosion properties.

In this case, these are:

a. benzoic acid, known in the art as a bacteriostatic and antioxidant agent, is sometimes used as a food preservative, and is also known as a component of anti-corrosive compositions;

b. 2-hydroxybenzoic (salicylic) acid - known in the art as a bactericidal and antiseptic agent, which is why it is used intensively in medicine;

c. 4-Hydroxybenzoic acid (4HyBA) - Known as a popular antioxidant due to its low toxicity. It is also known as a component of some anticorrosive compositions;

d. boric acid - in the form of boric acid or sodium tetraborate decahydrate (borax). Boric acid is known in the art for its bactericidal, insecticidal, fungicidal and preservative properties. Also, it is an anti-pyretic, a flame retardant. Sodium tetraborate is also known as a water softener.

Solutions containing TRIS and the acids listed above are mixed as follows:

1. In deionised water, 50 g dissolve in 0.32 g TRIS.

2. Mix solution J, 1. in portions, by adding:

- benzoic acid 0,18 g, or

- 0.2 g of 4-hydroxybenzoic or 2-hydroxybenzoic (salicylic) acid.

3. To solution 2. add 42.5 g propylene glycol / glycerin mixture (6: 4 by weight), deionized water to 100 g and mix thoroughly. The solutions thus prepared have a pH of 8.1 ± 0.05.

A solution containing 0,05 g of sodium tetraborate decahydrate in addition to TRIS and 4-hydroxybenzoic acid is prepared as follows:

2. To the resulting solution 2. add 0.5 g of sodium tetraborate - decahydrate (borax) 10% solution prepared as follows: Add 50 g of propylene glycol / glycerin (6: 4 by weight) and 40 g of deionized water in portions 10 g of sodium tetraborate - decahydrate and stir until dissolved.

4. to the resulting solution 3. add 42.25 g of a mixture of propylene glycol and glycerol (6: 4 by weight), deionized water to 100 g and mix thoroughly.

For comparison, Kilfrost DF Plus was diluted with deionized water 50% (w / w) and a solution 0 containing only propylene glycol, glycerol (6: 4 w / w), total 42.5% and deionized water up to 100%. .

In table no. Figure 2 shows the amount of additives in the studied samples and their effect on fully immersed aluminum alloy 2024 alclad 60x40x0.5 mm plates over a period of 1 week (7 days - 168 hours) at a constant temperature of 40 ° C (as described previously). weight change (WGT change) units - mg / ^cm2 / 24 hrs. This is also illustrated in Figs. 2.

Table 2.

Appendix % WGT Change mg / ^cm2 / 24 hrs Kilfrost DF Plus 50% -0,00016 O II O 0.00025 Benzoine 0.18 0.00012 Salicilo 0.2 -0,00024 4HYBA 0.2 0.00016 4HYBA Borax 0.2 0.05 0.00001

Similar studies have also been carried out on anodized aluminum plates and titanium plates. After the experiments, no signs of corrosion were observed on these plates.

The corrosion effect of these solutions on carbon steel was also investigated.

In table no. Figure 3 shows the amount of additives in the samples tested and their effect on fully immersed carbon steel 50x28x1.5 mm plates over a period of 1 week (7 days -168 hours) at a constant temperature of 40 ° C expressed in mg / WGT Change. cm ^2/24 hrs. This is also illustrated in Figs. 3.

Table 3.

Appendix % WGT Change mg / ^cm2 / 24 hrs Kilfrost DF Plus 50% -0.011212 "0 0 -0.00405 Benzoine 0.18 -0,00021 Salicilo 0.2 -0,00079 4HYBA 0.2 -0.00126 4HYBA 0.2 0.00005 Borax 0.05

The thermal stability of all the solutions tested was determined as follows: Samples of the solutions in sealed glass bottles were stored at a constant temperature of 90 ° C for 30 days. The solution used for comparison was a mixture of 42.5 g propylene glycol / glycerol (6: 4 by weight), 0.2 g triethanolamine and deionized water up to 100 g. The study showed that the mixture containing triethanolamine begins to turn yellow and then browns in about a week, whereas the solutions containing the salts of TRIS remain essentially unchanged for a longer period of time.

According to the results of these studies, TRIS mixtures - salts with the acids listed above, preferably with benzoic acid or 4-hydroxybenzoic acid - provide good anti-corrosion protection for aluminum alloys and especially for carbon steel. Particularly good protection - some synergistic effect is achieved when the solution additionally contains small amounts of borates, possibly due to the specific interaction between the borates and the polyhydric alcohols, in this case TRIS, glycerol and / or propylene glycol. These solutions contain non-toxic components and are thermally stable and are therefore well suited as anti-corrosion additives for de-icing, de-icing and other cooling and heat-dissipating agents based on glycols and / or glycerol and water.

Claims (10)

Definition of the Invention 1. An anticorrosive additive characterized in that it contains three (hydroxymethyl) aminomethane salts with organic and inorganic acids. An anti-corrosion additive according to claim 1, characterized in that it contains three (hydroxymethyl) aminomethane salts with organic aromatic acids such as benzoine or 2-hydroxybenzoic (salicylic) or 4-hydroxybenzoic acid and / or inorganic acids such as of boron or phosphorus. 3. An anticorrosive additive according to one of claims 1 to 2, characterized in that its content of 0.1-1% in the mixtures which still contains propylene glycol and / or glycerol or a mixture thereof (2085%) and water (up to 100%) prevents aluminum alloys and carbon steel against corrosion. Anti-corrosive additive according to one of Claims 1 to 3, characterized in that it is present in an amount of from 0.1 to 1% in mixtures which still contain propylene glycol and / or glycerol or a mixture thereof (2085%), alkali metals and / or glycerol borates ( 0.01-0.05%) and / or alkali metal phosphates (0.01-0.05%) and water (up to 100%), protects aluminum alloys and carbon steel from corrosion. 5. An anticorrosive additive according to any one of claims 1 to 4, characterized in that it can be used for the production of de-icing and de-icing of aircraft fuselage surfaces, and of cooling and heat transfer fluids from glycols and / or glycerol or mixtures thereof. Anti-corrosion additive according to one of Claims 1 to 5, characterized in that it contains organic compounds - tris (hydroxymethyl) aminomethane benzoate, 2-hydroxybenzoate (salicylate), or 4-hydroxybenzoate, which are solutions of low toxicity. Anti-corrosion additive according to one of Claims 1 to 6, characterized in that it contains thermally stable solutions of tris (hydroxymethyl) aminomethane benzoate, 2-hydroxybenzoate (salicylate) or 4-hydroxybenzoate. Anti-corrosion additive according to one of Claims 1 to 7, characterized in that it is also a buffer stabilizing pH 7-9, preferably pH 8-8,5. Anti-corrosion additive according to one of Claims 1 to 8, characterized in that it also contains a solution containing propylene glycol and / or glycerol and water and a stabilizing antioxidant. Anti-corrosion additive according to one of Claims 1 to 9, characterized in that it also contains a solution containing propylene glycol and / or glycerol and water and a stabilizing agent for bacterial growth.