The present invention relates to the use of a secondary amine as a corrosion inhibiting and antimicrobial agent espe¬ cially in an aqueous alkaline industrial fluid, such as an aqueous metal working fluid. The effects of the secondary amine are especially favourable at a pH value above 8. Water-based alkaline industrial fluids, such as metal work¬ ing fluids, hydraulic fluids, coolants and cleaning fluids, undergo after some time of use or storage undesirable changes which can be related to the fact that the components included in the fluids are degraded by bacteria, fungi and other micro- organisms. The microbial degradation considerably reduces the life and the performance of the fluids. For example the micro¬ bial degradation of the fluids may destroy the corrosion inhibiting and lubricating properties. From an economic point of view, it is therefore of great importance that microbial degradation of fluids of this type be minimised.

Well-known antimicrobial agents used in metal working fluids are formaldehyde or compounds giving off formaldehyde. Since formaldehyde readily evaporates from the fluid in open systems, the formaldehyde content will be successively reduced and the surrounding air contaminated with formaldehyde at the same time.

Other antimicrobial agents are quaternary ammonium com¬ pounds, but their use, e.g. in metal working fluids, has in¬ volved many practical problems, for instance because of reac- tion with organic acids and anionic surfactants that may be present in the formulation.

The use, as antimicrobial agents, of reaction products of boric acid and a number of organic compounds, such as alkanol-

amines and carboxylic acids is also known in cutting fluids. However, such reaction products have been found to have a relatively low antimicrobial effect, primarily on fungi, and must therefore be used in relatively large amounts. From articles by E.O. Bennett, e.g. his article in J.A. Soc. Lubr. Eng., 3_5 (1979), 137-144, U.S. Patent No.4,749,503, and European Patent Application 412 089, it is known that secondary and tertiary alkanolamine compounds substituted by hydrocarbon groups having 1-18 carbon atoms have an antimicrobial effect in cutting fluids and coolants.

The use of a number of alkoxylated amines and alkanolamines in order to obtain a tool life extension is known from European Patent Applications Nos. 196,810 and 192,358. For metal working fluids containing N-methylethanolamine a lowered susceptibility to the growth of mold and bacteria is reported. From the

European Patent 180,561 it is also known that certain tertiary alkanolamines have corrosion inhibiting effects in metal working fluids.

Alkanolamines, such as monoethanolamine, diethanolamine, diisopropanolamine and triethanolamine, have frequently been used as corrosion inhibiting agents in aqueous alkaline in¬ dustrial fluids. From US patents 3 280 029 and 4 976 919 and European Publication No 180,561, it is well-known to use secondary and tertiary alkyl alkanolamines as corrosion in- hibiting agents.

According to the present invention it has now been found that secondary amines having the formula

R(Y) _S NHX (I) in which R is an hydrocarbon group having 2-12 carbon atoms, Y is the group -CH(0H)CH ₂ -, -CH ₂ CH(OH)CH ₂ ~, or -0(CH ₂ ) ₃ -, X is an alkyl group having 2-3 carbon atoms and substituted with hydroxyl groups in the 2-position or in the 2- and 3-positions, and s is 0 or 1 with the condition that when s is 0, then X is

an alkyl group substituted in the 2- and 3-positions, or a salt thereof, have good corrosion inhibiting effects as well as excellent antimicrobial effects and can be used in the prepara¬ tion of aqueous alkaline industrial fluids, such as metal working fluids, hydraulic fluids, coolants, heat transfer media and cleaning fluids. These industrial fluids contain organic compounds for achieving specific technical effects. As the industrial fluids are often stored and/or used for a long time they are frequently subject to attacks by microorganisms whereby the amount of the organic compounds are reduced as well as the desired effects e.g. anticorrosion effects obtained by their presence. It is a well-known fact that especially aqueous metal working fluids are strongly exposed to bacteria and fungi. However, the secondary amines of formula I have proved to be very effective as anticorrosion and antimicrobial agents under the conditions present in aqueous synthetic and semi- synthetic metal working fluids. The fact that the secondary amines have antimicrobial efficacy also directly supports the maintenance of corrosion inhibiting properties of the same amines. The aqueous alkaline fluid of the invention may be in the form of an emulsion, microemulsion, colloidal solution or a true solution.

Preferred embodiments of the secondary amines of formula I are those encompassed by the formulae RCH(OH)CH ₂ NHC ₂ H ₄ OH (II)

RO(CH ₂ ) ₃ NHC ₂ H ₄ OH (III)

ROCH ₂ CH(OH)CH ₂ NHC ₂ H ₄ OH (IV), and

RNHCH ₂ CH(OH)CH ₂ 0H (V) in which R has the meaning stated above, or a salt thereof. Especially compounds having the R-groups not directly linked to the nitrogen atom, i.e. the compounds with formulae II, III and IV, or a salt thereof, have a good iron corrosion inhibit¬ ing effect.

The secondary amine compound of the formula I exhibit ex¬ cellent antimicrobial effects in synthetic formulations while in semisynthetic formulations those compounds having formula III usually are preferred. The amounts to be used of the secondary amines may vary within wide limits due to the speci¬ fic application area but it is normally from 0.001 - 10% by weight, preferably from 0.01 - 2% by weight.

The secondary amines of the formula I may easily be prepared by conventional methods. For example secondary amine compounds of formula II and IV may be prepared by reacting an olefin epoxide, preferably a linear alpha-olefin or the corresponding chloroglyceryl ether with an excess of monoethanolamine at a temperature of 80-120°C and 60-80°C respectively. Secondary amines of formula III may be prepared by reacting an alcohol with acrylonitrile in the presence of alkali such as NaOH or KOH, or the corresponding alcolates. The obtained nitrile compound is hydrogenated into a primary amine in the presence of a conventional hydrogenation catalyst and then ethoxylated to a secondary amine of formula III. If desired the secondary amine containing reaction mixture is purified by fractional distillation. By reacting 2,3-epoxy-l-propanol with an excess of a primary amine, secondary amines of formula V are obtained in high yields with respect to the epoxy compound. If desired, the secondary amine may be used in form of a salt soluble in water and/or oil. Especially preferred are salts with pharma¬ ceutically acceptable anions. Specific examples of salts are phosphates, sulphates, phosphonates, sulphonates and carboxy- lates. The acyclic hydrocarbon group R in the secondary amine of formula (I) may be straight or branched, saturated or unsaturated. Preferably it is a straight hydrocarbon group with 4-10 carbon atoms. Most preferably R is a C ₆ _ ₈ -alkyl group. Examples of suitable groups are butyl, hexyl, octyl and decyl.

The metal working fluid according to the invention has preferably a pH value of at least 8, most preferably between 8 and 10, and contains a secondary amine having the formula I or a salt thereof in an amount of 0.001 to 10% by weight, prefer- ably 0.01 to 2% by weight.

In addition to the secondary amine the metal working fluid may contain lubricants and other corrosion inhibitors.

The corrosion inhibitors are normally present in an amount of 0.1-10%, preferably 0.2-3%, by weight of the metal working fluid. Examples of suitable corrosion inhibitors are besides the secondary amines of formula I, other amine compounds, such as mono-, di- or triethanolamine, alkali metal hydroxides, triazole or thiadiazole compounds, monocarboxylic acids having 6-11 carbon atoms and dicarboxylic acids, preferably having 6- 12 carbon atoms, such as azelaic acid or sebacic acid, alkyl- or aryl-sulphonamidocarboxylic acids; inorganic acids, such as boric acid, and conventional reaction products between boric acid and/or carboxylic acids with organic compounds, such as alkanolamines. Examples of corrosion inhibitors are also the amine compounds described in European Publication No. 180,561. In order to increase the friction-reducing capacity, the metal working fluids may also contain lubricants. They are usually selected from the group consisting of esters or amides of mono- or dicarboxylic acids having at least 10 carbon atoms in the acyl groups; monocarboxylic acids having 12 or more carbon atoms; dicarboxylic acid having more than 12 carbon atoms; organic phosphate esters containing one or two hydro¬ carbon groups having 6-18 carbon atoms; nonionic alkylene oxide adducts having a molecular weight above 400, such as polypropy- lene glycol or randomly distributed polypropylene ethylene glycols or block polymers of ethylene and propylene oxide and mixtures thereof; and oils. The amount of the lubricant is 0.05-10%, preferably 0.1-2%, by weight of the metal working

fluid. Preferably the monocarboxylic acid lubricants are coconut fatty acids, oleic acid, groundnut acids and rapeseed acids and esters and amides of these acids with polyols, such as glycerol, trimethylolpropane, pentaerythritol and polyalky- lene glycols, and alkanolamines respectively. The hydrocarbon groups of the organic phosphate esters can be octyl, nonyl, decyl,dodecyl,tetradecyl and hexadecyl as well as their corre¬ sponding unsaturated alkenyl groups. Anionic lubricants also have a corrosion-preventing capacity against iron. The metal working compounds containing an oil as a lubricant have often the form of an emulsion or a colloidal solution. With the term "oil" is here understood a class of substances of synthetic, mineral, vegetable or animal origin. Usually, they are from petroleum or are petroleum-derived but synthetic hydrocarbons such as poly-alpha-olefins (PAO's) or alkylates, such as alkyl benzenes, are also used. These compositions also include emulsifying agents which are usually nonionic and/or anionic surfactants. Examples of anionic surfactants are alkylaryl sulphonates, such as dodecylbenzene sulphonates, alkylsulphates; such as sulphates of alcohols or alkoxylated alcohols; sulphated esters, such as sulphated castor oil; and phosphates of alcohols or ethoxylated alcohols. Examples of nonionic surfactants are alkoxylated alkyl phenols, alcohols, carboxylic acids, alkanolamines, alkylamines and alkylamides. The alkoxylation agent is normally an alkylene oxide containing 2-4 carbon atoms. Preferably at least 50% of the alkyleneoxy groups are ethyleneoxy groups and they may be either arranged " in blocks or distributed at random. In a preferred embodiment the polyoxyalkylene is end-capped with propyleneoxy and/or butyleneoxy units in order to obtain a low-foaming surfactant. The anionic and nonionic surfactants are normally so chosen that they contain 8-20 carbon atoms in a hydrocarbon residue.

By the amount of ethyleneoxy units in the surfactant the HLB- balance can be further regulated.

In addition to corrosion inhibitors and lubricants, the metal working fluid may advantageously also contain pH-adjust- ing agents, metal complex stabilizers, defoamers, perfumes, viscosity-adjusting and solubility-improving agents in known manner. Suitable solubility-improving agents are glycols, such as hexylene glycol; alcohols, such as tridecanol and oleyl- alcohol; and glycol ethers, such as butyldioxitol and butyl- trioxitol.

Aqueous heat tranfer media are for instance used in cooling towers, municipal hot water distribution systems and building heating systems, while coolants are used in metal working and quenching processes. Heat tranfer media and coolants of the invention usually contains, in addition to the secondary amine of formula I or a salt thereof, corrosion inhibitors, metal complexing agents, antiscaling agents, dispersing agents and/or pH-regulating agents. The hydraulic fluids may also contain lubricants and viscosity regulating agents. The cleaning fluids contain beside the secondary amine with the formula I or a salt thereof, a surfactant with micelle forming power. The surfactant is anionic, cationic, amphoteric or nonionic. Normally an anionic surfactant or a combination of a nonionic surfactant and an anionic surfactant is preferred. The cleaning fluids also comprise conventional additives, such as inorganic builders, defoamers, foam boosters, metal complex¬ ing agents, solubilizers and corrosion inhibitors.

The present invention is further illustrated by the follow¬ ing Examples. Example 1

A semi-synthetic metal working fluid concentrate having an concentration of 5% by weight was prepared from the following components.

components % by weight

Refined paraffinic oil 40.8-48.3

Sodium petroleum sulphonate (Mwt 440) 14.0

Oleic acid 10.0 Chlorinated paraffin (65% chlorine) 8.0

50% aqueous potassium hydroxide 3.2

Water 2.0

Neopentyl glycol dioleate 5.0

Hexylene glycol 4.0-10.0 Tridecanol, branched 0.5-2.0

Amine in accordance with tables 1-4 5.0

In order to obtain homogeneous compositions hexylene glycol and tridecanol may be incorporated in larger amounts than the minimum amount in the table above. The increased amounts added are balanced by corresponding reductions in the amount of the refined paraffinic oil.

Anticorrosion performance was established using a modified version of The Institute of Petroleum IP 287/82 test method. In the modified procedure deionised water was used instead of a synthetic water of 200 ppm of calcium carbonate in the prepara¬ tion of the test emulsion. Cast iron chips were placed on Whatman number 6 filter paper and wetted with the above formu¬ lation diluted with water for 2 hours at ambient temperature. The percentage area stained was recorded.

The following tables show the anticorrosion performance where emulsions were tested at pH 9.0 and 9.5. pH of the formulations was varied using acetic acid/KOH.

¹ ^ Diisopropanolamine

¹⁾ Diisopropanolamine

- ¹ -- Diisopropanolamine

From the results it is evident that all the secondary amines of the invention have good corrosion inhibiting effects. Especially the secondary amines having formulae II, III and IV exhibit excellent anticorrosion properties.

Example 2

Semi-synthetic and synthetic metalworking fluids were prepared from the following base formulations with the amines disclosed in tables 5-12.

Semi-synthetic concentrate Synthetic concentrate formulation formulation

%

The amines were added in amounts of 4, 10 and 20% to provide 1000, 2500 and 5000 ppm amine when diluted with water to a fluid concentration of 2.5%. In order to obtain homogeneous compositions tridecanol may be added in larger amounts than the minimum amounts in the table above. The increased amounts added are balanced by corresponding reductions in the amount of the mineral oil. The diluted fluids were subsequently tested with respect to their bactericidal and fungicidal effects by adding standardised bacterial and fungal inocula which were originally isolated from contaminated metalworking fluids. The inocula used in the tests were prepared as described below.

Standardised Inoculum Preparation

(i) Bacteria

100 ml mineral salts media containing 2% trisodium citrate as sole carbon source (pH 9.0) in Erhlen yer flasks were inoculated with 1 ml of a culture of Pseudomonas aeruginosa at an optical cell density of 2.0 measured at 650 nm (Perkin-Elmer UV-Vis Spectrophotometer, model Lambda 2) . These inocula were incubated at 30°C in an orbital incubator rotating at 200 rp . During exponential growth (18 hour culture) , further media were sub-inoculated in the same way, and the remaining culture harvested for testing of the diluted formulations. This sub- culturing procedure was continued until the end of the test period. The cultures were harvested by centrifugation at 4000 rpm for 20 minutes (MSE Mistral 2000) . The resulting bacterial pellet was resuspended in sterile Hanks saline buffer solution and recentrifuged. Three such washes were performed. Prior to the final wash, the optical density was adjusted to 2.0 (650 nm) and the volume of suspension noted. After the third wash the bacterial cells were resuspended in Hanks saline buffer to one tenth of the original volume to provide a con¬ centrated inoculum containing approximately 1 x 10 ¹⁰ cells ml ^{" 1} . This suspension was used as inoculum in the tests.

(ii) Fungi

100 ml mineral salts media containing 2% glucose as sole carbon source were introduced into Erhlenmyer flasks and inoculated with 1 ml of a homogenised culture of Cephalosporium sp. The inocula were incubated at 30°C in an orbital incubator rotating at 200 rpm. After 24 hours the fungus was homogenised and subcultured as already described into glucose supplemented mineral salts media. The remaining culture was centrifuged at

4000 rpm for 20 minutes. After decanting the spent growth medium, the fungal pellet was resuspended in Hanks saline buffer and recentrifuged. After 3 washes, the final fungal pellet was resuspended in one tenth of the original volume of buffer used to provide a concentrated inoculum. This material was used as inoculum in the testing of the diluted formula¬ tions.

Test method 2.5 ml of the formulations were diluted with 97.5 ml of sterile mineral salts media introduced in 250 ml Erhlenmyer flasks. These dilutions were adjusted to pH 9.5 by adding HC1 or KOH. 200 microlitres of the standardised inocula were then added, either daily for the full experimental period providing a multiple inoculation, or singly, at the start of the test with an inoculum consisting of a cell density equivalent to the cumulative multiple inoculum. In this way, the investigation compared (i) the efficacy of the said amines following repeated additions where fresh supplementary biomass was introduced over a period to simulate a continuous contamination situation (i.e multiple inoculum test) and (ii) the efficacy of the said amines where a single presentation of biomass is performed and the long term effects on growth or survival can be monitored independently from the addition of fresh biomass (i.e single inoculation test) . Total biomass levels in both tests were comparable.

Both fluid types were inoculated separately with the bacterial and fungal biomass to avoid possible inhibitory interactions. The semi-synthetic fluids were tested over an experimental period of 28 days, whereas satisfactory differen¬ tiation of amine performance could be achieved after 14 days in the synthetic fluids. All fluids were incubated throughout the test at 30°C in an orbital incubator rotating at 200 rpm.

The survival of inocula, both in the multiple and single tests were monitored daily. Fungi were monitored using conventional plate counting following growth on malt extract agar (plus chloramphenicol) after serial dilution. Bacteria were enumerated directly using the rapid automated bacterial impedance technique (RABIT) .

The following results were obtained.

Table 5. R-CH(OH)CH ₂ NHC ₂ H ₄ OH. Efficacy against Cephalosporium.

Table 7. R-OCH ₂ CH(OH)CH ₂ -NHC ₂ H ₄ OH. Efficacy against Cephalo¬ sporium.

Table 8. R-NH-CH ₂ CH(OH)CH ₂ OH. Efficacy against Cephalosporium.

Table 9. R-CH(OH)CH ₂ -NHCH ₂ CH ₂ OH. Efficacy against Pseudomonas aeruginosa.

Table 10. R-0(CH ₂ ) ₃ -NHCH ₂ CH ₂ OH. Efficacy against Pseudomonas aeruginosa.

Table 11. R-OCH ₂ CH(OH)CH ₂ -NHCH ₂ CH ₂ OH. Efficacy against Pseudo- monas aeruginosa.

Table 12. R-NHCH ₂ CH(OH) CH ₂ OH. Efficacy against Pseudomonas aeruginosa.

It is evident that the secondary amines of the invention have excellent antimicrobial effects. Especially good results are shown by the alkanolamines of formula III in the semi- synthetic formulations, while all alkanolamines of the formulae II, III, IV and V exhibit excellent results in the synthetic formualtions.