LU101645B1 - Amino Acids as Green Neutralizing Agent for Acidic Corrosion Inhibitors - Google Patents

Abstract

With the present invention, sustainable systems for corrosion inhibition in the processing of metals (in particular iron, aluminum and magnesium) are made available. These systems being in full accordance with the principles of green chemistry comprise an amino acid as neutralizing component for an acidic corrosion inhibitor, whereby the amino acid is used in deprotonated form. The resulting metalworking fluids may be water- or oil-based or semi synthetic formulations. The neutralization of acidic corrosion inhibitors with the claimed system comprising an amino acid consistently achieves convincing results and, together with acidic corrosion inhibitors from corresponding sources, completely renewable systems for corrosion inhibition are provided.

Description

METALL-CHEMIE TECHNOLOGIES GMBH Hamburg, 17 February 2020 HUT01645 Our reference: U 2014 / WI Metall-Chemie Technologies GmbH Kaiser-Wilhelm-Str. 93, 20355 Hamburg Amino Acids as Green Neutralizing Agent for Acidic Corrosion Inhibitors

BACKGROUND OF THE INVENTION The use and manufacture of metalworking fluids (MWFs) represent a major cost-factor | in the industrial processing of metals. MWFs play a significant role in processes like drilling, forming, grinding, or cutting of metals. Besides their lubricating capabilities, in these applications MWFs are used as coolants. This is achieved by conducting and dissipating accruing heat and reducing friction between a work piece and the tool and, therefore, influence the heat generation. MWFs are not only used for iron and steel but also for processing light metals, such as aluminum, magnesium, and their alloys, and are crucial in order to avoid thermal damage of the material of the work piece and to reduce wear on the tool. | MWFs can be divided in three groups: Oil-based, water-based, and emulsions. Water- | based formulations may be composed in form of fairly complicated solutions containing up to 300 different additives. One important group of such additives are | acidic corrosion inhibitors including but not limited to sulfonates, organic boron compounds, fatty acids, carboxylates, and phosphonates. For their use in neutral or alkaline media they are usually composed of an acid and a base to neutralize the acid.

Typically, amino alcohols are used for such a neutralization. Besides 2-Amino- | 30 2-methylpropanol (AMP) and 1-Aminopropan-2-ol (MIPA), Triethanolamine (TEA) is one of the predominantly used bases for this purpose. However, despite its comprehensive usage TEA has some major downsides. In the past it has been linked to allergic contact dermatitis, seawater ecotoxicity, and carcinogenic activity. Wl:anm

-2- Additionally it is listed on the “EU Control List of Dual-Use Items”, which entails further regulation and higher expenses.

Thus, there is a general need for the replacement of commonly used amino alcohols like TEA with more environmentally friendly and less toxic bases for the neutralization | of acidic corrosion inhibitors to be used as components of MWFs. While some attempts to utilize simple amino acids as “green” acidic corrosion inhibitors may have been made, salts of amino acids as neutralizing agents for acidic corrosion inhibitors have not been used so far. Proteinogenic as well as other amino acids are — unlike TEA | 10 and other commercially used organic amines and amino alcohols — nontoxic and non- hazardous. Additionally, they are easily available from renewable sources.

DETAILED DESCRIPTION OF THE INVENTION With the present invention it has been found that readily available amino acids (including proteinogenic amino carboxylic acids, such as arginine and glycine, analogues and derivatives thereof, such as aminocaproic acid, as well as amines with other acid functionalities like a sulfonic acid group, a phosphonic acid group, or a phosphoric acid group, such as taurine), which are nontoxic, nonvolatile, and available in big tonnages from bio-renewables, can be used as highly efficient green neutralizing agents for corrosion inhibition in alkaline media - replacing environmentally problematic TEA and similar organic amines that are each, for several reasons, environmentally problematic.

With the present invention it was surprisingly found that the use of amino acids (such as methionine, glycine, glutamic acid, serine, arginine, histidine, alanine, lysine, aminocaproic acid, or taurine; each used in their deprotonated form - e.g. in form of | solutions of their sodium, potassium, or lithium salts) in the neutralization of acidic | corrosion inhibitors leads to very effective anticorrosive systems that are, in view the aforementioned problems of commonly used bases, highly advantageous. In

-3- comparison to mixtures of the same acidic corrosion inhibitors with the standard neutralizing agent triethanolamine (TEA), the amino acids of the present invention provide at least similar — in several cases increased — efficacies. The amino acids can be formulated with a broad range of acidic corrosion inhibitors including aliphatic, cycloaliphatic, and aromatic carboxylic acids, sulfonates, phosphonic and phosphoric acids, boric acid, tall oil derived acids, and others. Typical examples of acidic corrosion inhibitors to be used with the present invention are azelaic, sebacic, undecanoic, and dodecanoic acid, triazintriyltriiminotrihexanoic acid (TC®) arylsulfonamido carboxylic acid (ASCplus®), 11-phosphonoundecanoic acid (PUDA), phosphonobutanetricarboxylic acid (PBTC), aminotris(methylenephosphonic acid)- N-oxide (ATMP-N-Oxide), or hexamethylenediaminetetra (methylenephosphonic acid) (HDTMP) but also phosphonic acid derivatives of terpenes and fatty acids, such as phosphonic acids derived from geraniol, citronellol or pinene.

The preferred amino acids of the present invention are proteinogenic amino acids, B- alanine, y-aminobutyric acid, aminocaproic acid and taurine; most preferred are glycine, alanine, lysine, methionine, taurine, and aminocaproic acid (ACA).

In view of the aforementioned advantages of amino acids, which are non-toxic and available from renewable sources, and in view of their surprising efficacy in mixtures with acidic corrosion inhibitors, the present invention provides highly advantageous anticorrosive additives for MWFs that can be used in the industrial processing of numerous metals. It was well noted that neutralized amino acids and acidic corrosion inhibitors can easily be formulated into stable solutions in water, which can be stored at room temperature for months. In addition, it is remarkable that highly concentrated compositions can be formulated, as for example 98 g of TC®, 80 g of amino caproic acid, and 24,4 g of NaOH in 100 ml of water or 84,6 g of TC®, 39,1 g of glycine, and 22,1g of NaOH in 100 ml of water

Comparisons of the commonly used neutralizing agent, TEA, with the neutralizing agents in accordance of the present invention, amino acids, which are used in deprotonated form (in form of their salts or in equimolar mixtures with, e.g., NaOH), showed that the latter may further increase the efficacy of the employed acidic corrosion inhibitors. As known from the art, simple inorganic bases, such as NaOH, that are used to neutralize acidic corrosion inhibitors do not result in efficient anti- corrosion systems, and while we do not want to be bound to this theory, it is expected that the amino acids interfere with the metal surfaces on their own and, thus, stabilize the layer formed by the primary acidic corrosion inhibitor. In particular, glycine, taurine, and ACA lead to highly efficient anticorrosive systems. While the amino acids are already effective at low concentrations (such as one molar equivalent, relative to the amount of the acidic corrosion inhibitor and the number of acid functions in the acidic corrosion inhibitor) and while the amino acids may be used also in higher concentrations, the preferred molar ratios of the amino acid (with one equivalent of base, such as NaOH or KOH) and the anticorrosive acid is 1/1 — 3/1 per acid group of the anticorrosive acid; preferably, the ratio is 1.5/1 per acid group of the anticorrosive acid. E.g., in the case of TC containing three carboxylic acids, the preferred ratio is 4.5 equivalents of the amino acid and NaOH — thus, the absolute molar ratio of the components (amino acid/NaOH/TC) is 4.5/4.5/1.

As demonstrated in the Chip-Filter-Test, the amino acids of the present invention provide highly effective anti-corrosion systems for steel. In addition, in the Co- Leaching-Test it was demonstrated that some amino acids in accordance with the present invention prevent Co-leaching and can be used successfully when handling Co-containing steel-alloys; while taurine resulted in a system with a Co-Leaching- Index similar to that observed with a mixture neutralized by TEA, ACA shows better results than the current gold-standard for low Co-leaching applications MIPA. Corrosion inhibition is not only important when handling iron or steel, it is also important when processing light metal alloys of, e.g., aluminum or magnesium. While

-5- commonly used carboxylic acid additives like TC are not capable of preventing corrosion or staining on light metal alloys, mixtures of octylphosphonic acid (OPA) and TEA provide some corrosion inhibition on aluminum.

In the corresponding tests (with a copper containing hardened Al-alloy used in aerospace applications, AL 5083, | 5 an aluminum-alloy mostly used for welding and marine applications, AL 2024, and a | standard wrought magnesium-alloy containing 3% aluminum and 1% zinc used for example in automotive industry, MG AZ31), it was surprisingly found that the amino acids of the present invention (such as glycine or ACA, each with an equimolar amount of NaOH) can act as full and extremely valuable substitutions of the environmentally problematic TEA.

In case of AL 5083 and MG AZ31, the amino acids of the present invention showed some effect even with TC and the mixtures of the present invention outperformed those of the prior art.

Additionally, in view of the results achieved with aluminum and magnesium, it can plausibly be expected that the amino acids of the present invention can also be used to neutralize acidic corrosion inhibitors, when formulating efficacious anticorrosive systems for the processing of other metals and alloys, such as titanium and zirconium.

With the present invention it has been demonstrated that in combinations with acidic corrosion inhibitors, amino acids, which are highly beneficial due to their general biocompatibility, cost effectiveness, and nontoxicity, allow to replace harmful and problematic TEA - in applications on steel, aluminum, and magnesium. . The amino acids of the present invention are compatible with a range of acidic corrosion inhibitors, such as phosphonic and/or carboxylic acids commercially used for steel and aluminum.

These new systems achieve corrosion scores as good as or even better than the corresponding TEA based additives of the prior art.

Additionally, with the present invention anticorrosive systems entirely based on renewable resources become available — e.g., by using the amino acids of the present invention as neutralizing agents for natural product-derived acidic corrosion inhibitors, such as geranylphosphonic acid, pinene derived phosphonic acid (PDPA), or

-6- 11-phosphonoundecanoic acid (PUDA). These fully renewable mixtures are highly efficient anticorrosives and can be utilized in the processing of steel, aluminum, and even magnesium. The corrosion inhibitors of the present invention fit the ongoing need of green chemistry to develop technologies and materials that are intrinsically nontoxic to living organisms and the environment and that minimize harmful waste.

EXPERIMENTAL SECTION Syntheses 11-Phosphonoundecanoic acid (PUDA) may be synthesized from undecylenic acid via palladium-catalyzed hydrophosphorylation with H3PO2. Geranylphosphonic acid can be synthesized via palladium catalyzed dehydrative allylic substitution with H3PO2 and geraniol and subsequent oxidation with iodine and DMSO. PDPA may be obtained via radical addition of ammonium hypophosphite with triethylborane to B-pinene and subsequent oxidation with iodine and DMSO (scheme 1).

-7- HPO, Pd,(dba); Xantphos, DMF, 0 OH 120° NNN 20°C, 16h oh OH Ö 99% >> RSS Undecylenic acid UND-PA

1.H2PO3, Pdz(dba)s, Xantphos, DMF, 80°C, 16h

2.1, DMSO,

THF OH 60°C 12 h HA AA AAAA ‘ "Op A A HO 60% I

O Geraniol Geranylphosphonic acid

1. NH4,PH202, BEts MeOH, rt, 3h

2.1, DMSO, THF, HO 60°C, 4 h Op _—_— 67% 0 B Pinene PDPA Scheme 1. Possible syntheses of the natural product-derived phosphonic acids. Chip-Filter-Test The evaluation of the rust preventive properties of water-miscible coolants was conducted with 2 mL 3 w.-% solutions (calculated to the acid) and 2.0 g sieved grey cast 25 chips for 2 h according to DIN 51360-02-A.

-8- Table 1: Results of the Chip-Filter-Test of TC (3 w.-%) neutralized with TEA or amino acids of the present invention (in form of their sodium salt). me [oe [a 0 [Geese |v ome [we [us [0 Aa [ee [no om [es wo [wee | es | oy |e

HK [Re A *Used as disodium salt.

-9. | Table 2. Conditions and corrosion scores of Chip-Filter-Tests of various acidic corrosion inhibitors (acid, each in a concentration of 3 w.-%) in combination with TEA or an amino acid for neutralization. ; CTT Commas | Tw KK

[2] sens a [om 3 | 0]

BE I RUE 47 | Omer 5 [0 0 | | 0 S| Dodeamedieasid | 3 | 000 0] (SR se [ooo | oo] mA as [oo | 0 |v LE | Geo | 5 [00 | oo | AN | 5 [0 | 8 | or | 0] * Used as Sodium salt. ** 4.5 eq of amino acid and 4 eq of NaOH. ***after 16 h at 60°C.

Staining Assay. The evaluation of corrosion inhibition for light metal alloys was conducted with 2.5 mL of an aqueous solution containing up to 4 weight % of the acidic corrosion inhibitor and 1*3 cm plates of aluminum or magnesium alloys for 24 hat 40°C. The plates were placed in a small glass vessel with half of their surface being covered by the test medium. Subsequently, the staining was rated on a scale from 0 (No Staining) to 4 (strong staining). The optical assessment of staining was performed in accordance to Watanabe et al. (S. Watanabe, J. Oleo Sci. 2008, 57, 1- 10).

-10 - Table 3. Conditions and scoring of TC, PUDA, PDPA and OPA in combination with | TEA, Glycine and ACA on Al 2024. Performed in hardwater (10° dH) at 40°C for 24h.

Aluminum 2024 Staining Scores / Concentration [TTT Entry Acid Eq. of Base 2% 3% 4%

PTE LT IE LES pm ws te en [oo] ms | 5 over ET Ce | ws (ren 1 | 0 | 0 pre | 0 | me [oo pe | 0 Jomo | 0 | 0 || pre | 50 een 0 | © | som | 0 | me [oo EE oom | a0 japon] 0 | 0 | ©

-11- Table 4. Conditions and scoring of TC, PUDA, PDPA and OPA in combination with TEA, Glycine and ACA on Al 5083. Performed in hardwater (10° dH) at 40°C for 24h. Aluminum 5083 Staining Scores / Concentration of

I Entry | Acid Eq. of Base 2% 3% 4% Cee CEs em so

ERKENNEN [Fon | 5 Aa 00 | 0 Comm so | mo | oo CP |e oven oo sr | so aceon] 0 | 0 Com [sw [wm [vo | 0 0 om a | 0 | 0 0

-12- Table 5. Conditions and scoring of TC, PUDA, PDPA and OPA in combination with TEA, Glycine and ACA on Mg AZ31. Performed in hardwater (10° dH) at 40°C for 24h. Magnesium AZ31 Staining Scores / Concentration of ee Entry Acid Eq. of Base 2% 3% 4% la TT [POR [as [acumen] a TT

BALANCE om pe | 81 TE Don [epee | 8 TE Co-Leaching Another parameter to consider for the industrial usage of metal working fluid is their Co-Leaching characteristics. AMP and MIPA are marketed as low leaching additives. Several amino acids were examined. For realistic results the solution was pH-adjusted to match the pH value of the mixture in the Chip-Filter-Assay.

225 mg Co-Powder( < 150 um, 99.9% trace metal basis) was suspended in 15 ml of a 1 w.-% aqueous solution of the amine (in case of the amino acids and taurine, the pH value was adjusted with sodium hydroxide) and heated under reflux for 24 hours. The suspension was cooled to room temperature, filtered and the Co-concentration of the

13. LU101645 filtrated was measured directly via F-AAS.

The pH adjustment was based on the pH values of the chip-filter-assay.

Table 6. Detected Co-concentrations and pH values for each tested amine.

The concentration was measured from the filtrate via F-AAS [wwe [on TS Cee ee Ol mew wwe] *Used as sodium salt.

Claims (10)

14. LU101645

1. Use of an amino acid as neutralizing component for an acidic corrosion inhibitor in the formulation of a metalworking fluid, wherein the amino acid is used in deprotonated form as its salt with a base; preferably in form of its alkali metal- or earth alkali metal salts (such as the sodium, potassium, or lithium salt) or in form of a mixture with NaOH, KOH, or LiOH. |

7. The use of claim 1, wherein the amino acid is a proteinogenic amino carboxylic acid, an analogue or derivative thereof, or an amine with another acid functionality (such as a sulfonic acid group, a phosphonic acid group, or a phosphoric acid group).

3. The use of claim 1 or 2, wherein a. the amino acid is glycine, methionine, aminocaproic acid (ACA), or taurine, b. the acidic corrosion inhibitor is triazintriyltriiminotrihexanoic, arylsulfonamido carboxylic acid, sebacic acid, undecanoic -, dodecanoic acid , azelaic acid, tall oil derived acids, sulfonates and/or phosphonic — and phosphoric acids, and/or c. the metal is iron, aluminum, magnesium, titanium, zirconium or a corresponding alloy (such as Al 5083, Al 2024, or Mg AZ31).

4. The use of claims 1-3, wherein the amino acid is present in an amount of one molar equivalent or more (relative to the number of acid functions of the acidic corrosion inhibitor), preferably in an amount of 1-3, most preferably in an amount of

1.5 molar equivalents.

15. LU101645

5. Metalworking fluid comprising an acidic corrosion inhibitor and an amino acid, wherein the amino acid is used in deprotonated form as its salt with a base; preferably in form of its alkali metal- or earth alkali metal salts (such as the sodium, potassium, or lithium salt) or in form of an equimolar mixture with NaOH, KOH, or LiOH.

6. The metalworking fluid of claim 5, wherein the amino acid is glycine, methionine, aminocaproic acid (ACA), or taurine, or a salt thereof, preferably the sodium, potassium, or lithium salt.

7. The metalworking fluid of claim 5 or 6, wherein the amino acid is present in an amount of one molar equivalent or more (relative to the number of acid functions of the acidic corrosion inhibitor), preferably in an amount of 1-3, most preferably in an amount of 1.5 molar equivalents.

8. The metalworking fluid of claims 5-7, wherein the acidic corrosion inhibitor is a phosphonic acid derivative of a terpene or a fatty acid. |

9. The metalworking fluid of claims 5-8 being water-based, oil-based, or in form of an emulsion.

10. Use of the metalworking fluid of claims 5-9 in the processing of iron, aluminum, magnesium, titanium, zirconium or a corresponding alloy (such as Al 5083, Al 2024, or Mg AZ31).