GB2372743A - Non-toxic bioresistant lactic acid amides and preparation thereof - Google Patents

Abstract

The invention relates to lactic acid amides of alkanolamines. These amides may be used as alternative to more toxic boric acid based compounds. The properties of bio-resistance, corrosion resistance and lubricity of the compounds are further enhanced by admixing this with diamines and carboxylic acids.

Description

NON-TOXIC BIO-RESISITANT COMPOUND AND PROCESS FOR PRODUCING SUCH COMPOUND Field of the Invention This invention relates to a non-toxic bio-resistant compound suitable for use in water-based fluids, such as metalworking fluids and hydraulic fluids, to a process for producing such a compound and to water-based fluids containing such a compound.

Background to the Invention In the quest to produce water-mix metalworking fluids with higher levels of biostability, boric acid started to be used in the early 1970s. When combined with an alkanolamine, boric acid forms an amide that works as a co-emulsifier imparting high degrees of bio-stability to the formulations in which it is used. These properties were a dramatic improvement over the limited sulphonate/biocide fortified products they replaced. US-A-3 429 909 and US-A-3 764 593 both disclose compounds of this type, produced by the reaction of boric acid with a secondary aminoalcohol and a carboxylic acid.

The trend with water-mix metalworking fluids since this time has been towards materials which are less harmful to users and to the environment. The movement of the metal working industry into less harmful materials, spurred on by regulation and legislation, has effectively displaced such materials as phenols, nitrites, phenoxyethanols, triazines, heavy metals, secondary amines, short chain chlorinated paraffins and formaldehyde for the preparation of water soluble fluids. It has also been found that boric acid is harmful, for example having an adverse affect on fertility. Its use is coming under increasing scrutiny and is already restricted or prohibited in some countries, where R60 labelling (skull and crossbones) is obligatory.

Some of the advantages enjoyed by the use of boron-based products stem from their bio resistance in emulsion systems, their corrosion inhibiting properties when used with ferrous metals and their pH stabilising properties. When coupled with boron's relatively economical pricing, boron-based products have hitherto provided a practical solution to the needs of the metal working industry.

However, there is now a need for a bio-resistant emulsifying compound which does not involve the use of boric acid, but which performs as well as conventional com pounds.

Lactic acid (2-hydroxy propionic acid) has long been known for its preservative properties in the food industry and for its anti-microbial properties in the cosmetics and household cleaner industries. Lactic acid is therefore recognised for its safety and its environmental friendliness. However, its application to the metal working industry has never seriously been contemplated because of its lack of corrosion-preventing properties as regards ferrous materials.

Summary of the Invention According to the invention, there is provided a non-toxic bio-resistant compound, which comprises the reaction product of lactic acid with an alkanolamine.

Preferably, the alkanolamine is ethanolamin.

Further benefits can be achieved if the compound also comprises a diamine.

Specific examples of suitable diamines include, amongst others; cyclohexylaminopro- pylamine, diethylaminoethylamine, methylaminopropylamine and ethylaminoethylamine.

Yet further benefits can be achieved if the compound comprises a carboxylic acid. Specific examples of suitable carboxylic acids include, amongst others; monocarboxylic acid, dicarboxylic acid, tri-carboxylic acid and poly-oxy-carboxlic acid. Alterna tively, the compound may comprise an amide containing carboxylic acid.

The invention also provides a process for producing a bio-resistant emulsifying compound, which comprises heating the alkanolamine to an elevated temperature and adding lactic acid such that an exothermic reaction is initiated.

Preferably, the combined material is then heated to a temperature within the range of approximately 70-150oc. The temperature may be held at approximately 90 C for approximately 1 hour.

The alkanolamine is preferably monoethanolamine and it has been found that heating to 70-150oC before addition of the lactic acid is sufficient to initiate the reaction. Preferably, the lactic acid is added to the monoethanolamine in a ratio by weight of 40: 60. The end point is reached when one mol of water has been produced in the reaction.

Alternatively, the alkanolamine may be triethanolamine.

Advantageously, a diamine and/or a carboxylic acid may be included in the reac tion.

The invention also encompasses a water-based fluid comprising a composition according to any of the preceding paragraphs.

The compound of the invention is referred to herein as a"lactamide".

A water-based fluid may be made up of a number of different components, in various w/w concentrations, in addition to a lactamide compound according to the invention.

Detailed Description of the Preferred Embodiments Broadly, a range of bio-resistant corrosion inhibitors, both emulsifying and nonemulsifying, are produced in accordance with the invention, based on 2-hydroxy propi- onic (lactic) acid and which have the same desired properties of corrosion protection and pH buffering as are currently obtained with boron-based products. The compounds resulting from the reaction according to the invention are to be referred to as lactamides.

In general, a condensation reaction is carried out by reacting excess aminoalcohol with 2-hydroxy propionic acid under specified reaction conditions. However, it is appreciated that the introduction of further materials into the reaction produces lactamides with improved characteristics, such as improved anti-corrosion properties.

Thus, the inclusion of a diamine in the reaction has been shown to improve both the anti-corrosion properties and the bio-resistance properties of the resultant lactamide.

Also, a condensation reaction is carried out by reacting excess amino-alcohol with 2-hydroxy propionic acid linked with carboxylic and dicarboxylic acids under specified reaction conditions leads to the production of lactamides with enhanced properties.

Variations in the reaction conditions and the types of carboxylic acid used produce, amongst other things; improved corrosion protection, improved bio-resistance, improved lubricating properties and enhanced wetability.

More specific research into the characteristics of the lactamides produced as a result of introducing carboxylic acid into the reaction has revealed a pattern. It has been

found that the introduction of carboxylic acids with between 6 and 12 carbon atoms in its molecule leads to the production of lactamides with improved anti-corrosion proper ties, enhanced wetability and improved lubrication properties. Specific examples of suit able C - C 12 carboxylic acids include, although not exclusively ; sebacic acid, azelaic acid, dodecanedoic acid, isononanoic acid, caproic acid, caprylic acid and neodecanoic acid.

The introduction of carboxylic acids consisting of between 12 and 24 carbon atoms leads to the production of lactamides with a range of corrosion, bacterial-and fungal-resistant properties. Specific examples of suitable C12 - C24 carboxylic acids in clude, amongst others; tall oil, oleic acid, coconut fatty acid, lauric acid, soya fatty acid, rapeseed fatty acid, castor oil fatty acid and undecylinic acid. Detailed testing has shown that in particular, undecylinic acid improves fungal resistance, and rincinoleic acid improves bacterial resistance.

It is also appreciated that the introduction of both a diamine and a carboxylic acid will lead to the production of a lactamide with yet further enhancements to its emulsifying and lubricating properties.

The target levels of the diamine and/or carboxylic acid containing compound required to achieve the desired results in a finished metalworking or other fluid are between 100-500 p. p. m.

It is of further note that the introduction of a diamine and/or carboxylic acid can also be made to the compound at room temperature subsequent to the condensation reaction has finished.

In order to assess the suitability of lactic acid based products relative to established boron based products, samples of both types were subjected to a Standard Wet State Challenge Test. Samples of 5% emulsion solutions were first stored at 40 C for four weeks prior to testing. The test itself subjects each sample to 10 successive inoculations (challenges) to replicate contamination either on a plant or in storage. The effect of each such contamination is to deactivate a portion of the bio-resistant material present in the sample. This impacts on the life and effectiveness of the sample. Heavy contamination will lead to the bio-resistant material becoming completely spent, leaving no residual protection.

The boron-based and lactic acid-based samples were challenged with : Bacteria (Shewanella putrefaciens, Pseudomonoas fluorescens, Pseudomonoas aeruginosa, Pseudomonoas oleovorans, Alcalagenes faecalis, Citrobacter freundii); Fungi (Fusarium solanii, Acremonium strictum, Aspergillus terreus); and Yeast (Rhodotorula rubra).

In each successive challenge, there was a 100% kill rate of all inoculant for both the boron-based and the lactic acid-based samples. This confirms the effectiveness of the lactic acid-based product in comparison with the long-established boron-based product.

Standard Test Methods are available to investigate the effectiveness of corrosion-resistant materials. Method P125 is designed to assess the ability of watermix cutting fluid emulsions/solutions to prevent the rusting of components during machining, typically of cast iron. Briefly, the method involves first preparing a grey cast iron plate by regrinding, if necessary, to a smooth surface; wiping with toluene, washing with acetone and drying. Next, the treated surface is rubbed with No. 0 emery cloth, cleaned with acetone and dried. The surface may need to be reground if marks are still apparent after rubbing with the emery cloth.

Steel milling are sieved to remove dust, washed in acetone and air-dried. Four portions are located centrally of the prepared plate without touching each other or the edges of the plate. The fluid to be tested is applied by pipette to each portion (approximately 2ml per 2g portion) and the plates with their samples placed in a test chamber at a maintained temperature for e. g. 24 hours. The milling are discarded, the plate washed with acetone then toluene and finally rubbed with a filter paper soaked in toluene. The surface of the plate is then inspected for pits, staining and corrosion.

Test method IP287 is designed to assess the ability of watermix cutting fluid emulsions/solutions to prevent rusting of machines and components during machine operations. Briefly, the method involves first preparing an emulsion of the test sample to a required dilution, ranging between 1.0 to 10.0% V/V, in synthetic or actual hard water. Cast iron chips (e. g. 2.0 0. 1g) are placed on a filter paper in a petri dish and 2ml of the selected dilution placed by pipette onto the chips to wet them thoroughly.

The dish is covered and kept at preferably 20 3 C for 2 hours, after which the chips are removed, the filter paper rinsed in tap water and left to dry. This is done for each dilution in the selected range. The filter papers are then inspected for staining.

Tests conducted using formulations equivalent to those containing boron have obtained results that show formulations ranging from high oil content to synthetic solutions provide equal and comparative corrosion performance.

An example of typical lactamide compound, which contains further organic acids to improve corrosion performance, has the following general composition: 42.33% Triethanolamin 90% aqueous 20.33% Monoethanolamine 100% 22.34% Dicarboxylic acid 15.00% Lactic acid 80% aqueous.

The manufacturing process involves heating the amines to a temperature in the range of approximately 70-150oC before adding the lactic acid and other materials, mentioned above, and holding the temperature for approximately 1 hour.

A typical formulation for a semi-synthetic metal-cutting fluid containing a compound in accordance with the invention would be: 10% lactamide 8% Rapeseed Diethanolamide 3% Triethanolamine 90% 16% Distilled Tall Oil 25% Naphthenic base oil 23.6% Water 8% Glycol Coupling Agent 3% Butyl DI-Glycol Ether 3% Biocide/Fungicide 0.4% Antifoam Agent A synthetic cutting solution using this lactomide could then be made according to the following formulation : 30.0% Lactomide 1.0% Biocide 10.0% Ethylene Glycol 58. 9% Water 0. 1 % Benzatriazol Although the examples of lactamide containing fluids given are for cutting solutions, it is appreciated that the properties of lactamide are such that it can be beneficially added to other fluids, such as hydraulic fluids and water treatments.

Claims (21)

1. CLAIMS 1. A non-toxic bio-resistant compound, which comprises the reaction product of lactic acid with an alkanolamine.
2. 2. A compound according to claim 1, wherein the alkanolamine is ethanolamine.
3. 3. A compound according to any claim 1 or 2, which also comprises a diamine.
4. 4. A compound according to any claim 3, wherein the diamine is one of the following : a) a) cyclohexylaminopropylamine ; b) b) diethylaminoethylamine ; c) c) methylaminopropylamine ; d) d) ethylaminoethylamine.
5. 5. A compound according to any of the preceding claims, also comprising a carboxylic acid.
6. 6. A compound according to claim 5, wherein the carboxylic acid is one of the following: a) a) monocarboxylic acid; b) b) dicarboxylic acid ; c) c) tri-carboxylic acid ; d) d) poly-oxy-carboxlic acid
7. 7. A compound according to any claims 1 to 4, which also comprises an amide containing carboxylic acid.
8. 8. A water-mix fluid, comprising a compound as defined in any of the preceding claims.
9. 9. A water-mix fluid, comprising a compound according to claim 1 together with further components, in a specific formulation such; Triethanolamin 12.5% w/w Lactamide 10.0% w/w Diethylene Glycol 10.0% w/w BTZ 0.2% w/w Water 67.3% w/w
10. 10. A water-mix fluid, comprising a compound according to claim 1 together with further components, in a specific formulation such ; Triethanolamine 12. 5% w/w Lactamide 10.0% w/w Cyclohexyl Amino Propylamin 3.0% w/w Diethylene Glycol 10.0% w/w BTZ 0. 2% w/w Water 64.3% w/w
11. 11. A water-mix fluid, comprising a compound according to claim 1 together with further components, in a specific formulation such; Triethanolamine
12. 12. 5% w/w Lactamide 10.0% w/w Cyclohexyl Amino Propylamin 3.0% w/w Teklube Dicarboxylic Acid 5. 0% w/w BTZ 0. 2% w/w Water 69.3% w/w 12. A water-mix fluid, comprising a compound according to claim 1 together with further components, in a specific formulation such; Triethanolamine 12. 5% w/w Lactamide 10.0% w/w Teklube Dicarboxylic Acid 5. 0% w/w BTZ 0. 2% w/w Water 72.3% w/w
13. 13. A process for producing a non-toxic bio-resistant compound, which comprises heating a alkanolamine to an elevated temperature and adding lactic acid such that an exothermic reaction is initiated.
14. 14. A process according to claim 13, wherein the combined material is heated to a temperature within the range of 70-150oc.
15. 15. A process according to claim 13 or 14, wherein the combined material is heated to a temperature of 90Oc.
16. 16. A process according to claim 13, 14 or 15, wherein the alkanolamine is monoethanolamine.
17. 17. A process according to claim 16, wherein the lactic acid is added to the monoethanolamine in a ratio by weight of 40: 60.
18. 18. A process according to claim 13,14 or 15, wherein the alkanolamine is triethanolamine.
19. 19. A process according to any of claims 13 to 18, wherein a diamine is introduced into the reaction.
20. 20. A process according to any of claims 13 to 19, wherein a carboxylic acid is introduced into the reaction.
21. 21. A non-toxic bio-resistant compound, substantially as described.