This invention relates to compositions useful as additives for aqueous systems in order to inhibit the corrosion of metal surfaces which are in contact with these systems, to methods of inhibiting corrosion which comprise adding these novel compositions to aqueous systems and to aqueous systems which contain certain novel combinations of known corrosion inhibitors.

There have been a very large number of proposals to inhibit the corrosion of metal surfaces which are in contact with water which comprise adding various chemicals and formulated

products to the aqueous system. A wide variety of products are used in this application. One class of compounds which are widely employed as corrosion inhibitor in aqueous systems are

organic phosphonetes and polyphosphonates. However, there remains a need for new products which are more effective or more cost effective in reducing corrosion.

USP 4689200 discloses the use of 2-hydroxy phosphono acetic acid or a water soluble salt thereof as an additive for aqueous systems in order to inhibit the corrosion of metal in contact

with that aqueous system. This disclosure also suggests that the 2-hydroxy phosphono acetic acid may be used in conjunction with other known corrosion inhibitors. Among the many

known corrosion inhibitors which are mentioned in this disclosure are phosphonic acids and

their salts. USP 4689200 also proposes that the 2-hydroxy phosphono acetic acid may be

used in conjunction with other additives and in particular scale inhibiting additives. Among many known scale inhibitors which are mentioned are the phosphino polycarboxylic acids

which are described in British Patent 1458235. EPA 277412 describe a process for the

reduction of corrosion of iron bused metals in contact with aqueous systems which comprises adding combination of hydroxy phosphono acetic acid and water soluble l-acrylamilo-2-methyl propane sulphuric acid copolymer with acrylic or metharylic acid to that aqueous system.

EPA 516346 discloses a process for the production of phosphono (co)telomers which are useful as scale inhibitors and corrosion inhibitors in aqueous systems. The telomeric portion of these compounds may be derived from a wide variety of olefinic compounds including 2-acrylamido-2-methyl propane sulphonic acid (AMPS) or from mixtures of such olefins including in particular mixtures of AMPS and acrylic acid. The use of these phosphonic (co)telomers in conjunction with other compounds known to be useful in the treatment of aqueous systems is also proposed. Amongst a very large number of such compounds which are mentioned as being known is 2-hydroxy phosphono acetic acid.

We have now discovered a particular phosphono cotelomer which interacts synergistically with known organophosphorus corrosion inhibitors which contain at least one phosphonic acid group as part of their molecular structure to provide improved corrosion inhibiting properties. Further since the phosphono cotelomer also exhibits scale inhibiting and dispersing activity the

novel combination of these two materials is useful in the treatment of aqueous systems in order to inhibit scale formation and the deposition of paniculate materials whilst at the same time inhibiting corrosion of metal surfaces.

The phosphono cotelomer which has been discovered to be useful in the compositions of this invention is that derived from a combination of acrylic acid and 2-acrylamido 2-methyl propane sulphonic acid (AMPS). The production of such a cotelomer is described in EPA

516346. However, there is no disclosure in the prior art of a composition comprising this cotelomer and an organophosphorus corrosion inhibitor.

Accordingly from one aspect this invention provides a composition useful as an additive to

aqueous systems in order to inhibit the corrosion of metal surfaces in contact with that aqueous system which comprises:

(i) an organophosphorus corrosion inhibitor having the formula I

or a water soluble salt thereof, in which R ₃ may represent a group having the formula CO _j H, a group having the formula P(=O)(OH) ₂ , a grup having the formula CH ₂ CH ₂ P(=O)(OH) ₂ or a group having the formula NR _j R _g may be the same or different resperesent a hydrogen atom; a methyl group; and x is an integer having a value of 1 or 2;

R-, and R ₄ may which may be the same or different, represent a hydrogen atom, a hydroxyl group, an alkyl group comprising from 1 to 8 carbon atoms, a group having

the formula CO-H, -(CH-)^ where n is zero or an integer having a value of from 1 to 4, or an amine group having the formula -NH,.

Preferably R _j represents a group having the formula CO-H or a group having the formula P(=O)(OH) ₂ ; R _j represents a hydrogen atom or a methyl group; and R ₄ represents a hydroxyl group.

(ii) a phosphono cotelomer having the formula:

II

and A represents a copolymeric residue containing at least one repeat unit having the formula πi

III

wherein R, represents a hydrogen atom or a methyl group

and at least one repeat unit having the formula IV

IV

or a water soluble salt thereof.

The phosphono telomer may be any compound of Formula II which is sufficiently water soluble to be effective. It may comprise repeat units of Formula III and repeat units of Formula IV in a wide range of proportions. The ratio of the number of units of formula HI to the number of units of formula IV may vary from 99: 1 to 1 :99 but is more usually in the range 25:1 to 1 :25. The most preferred polymers useful according to this invention are those wherein this ratio is in the range 20: 1 to 2: 1 ie, those which contain a greater proportion of the repeat unit having the formula III.

The cotelomers of formula II will typically have a molecular weight Mw of from 500 to 10,000 and more preferably of from 2,000 to 4,000. These cotelomers may be produced by a variety of processes which are known to the art. Generally these processes comprise the reaction of a monomer of formula III typically acrylic acid or methacrylic acid with the monomer of formula IV which is 2-acrylamido-2-methyl propane sulphonic acid (hereinafter for convenience AMPS) in the presence of a hypophosphite telogen. Such processes have been described in USP 4046707, EPA 150706, EPA 360746 and EPA 516346. The

phosphonate telomers are preferably produced by the aqueous process which is described in

EPA 516346. Such process typically comprise (a) the reaction of hypophosphorous acid or a hypophosphite with a carbonyl compound which is typically acetone, (b) reacting the product from (a) with the (meth)acrylic acid and the AMPS in the presence of a free radical initiator and converting the product of step (b) to the desired phosphonate (co)telomer by reaction eg, with hypochlorite. The process may vary according to the teachings of EPA 516346.

In particular a variety of carbonyl compounds may be employed in step (a) representative examples being formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, methylethyl ketone, diethyl ketone, dipropyl ketone, dibutyl ketone, cyclopentanone and cyclohexanone. The products obtained from these processes are aqueous solutions which may be used as such in the compositions or they may be purified prior to use. The phosphonate cotelomers are produced in their acid form and they may be wholly or partially neutralised prior to use. Where the compositions of this inventions are added to alkaline media neutralisation may take place in situ and neutralisation at this production stage may thereby be irrelevant.

The second component of the compositions useful in this invention is a organophosphonate corrosion inhibitor. Having the general formula I a number of such compounds are known and used in the art. A preferred group of phosphonates of formula I, which are useful according to this invention are those wherein at least one of the groups R, and R ₄ represents a hydrogen atom. Particularly preferred phosphonates within this group include those wherein the other of the groups R, and R ₄ also represents a hydrogen atom or a hydroxyl group -OH an amine group - NH _j or a carboxylic acid group - CO-H.

A second preferred group of compounds are those of the formula I wherein R- represents a group of the formula (CH-)n CH-H or (CH-)PO(OH-) wherein n is zero or an integer having a value of from 1 to 4.

The most preferred phosphonates for use in the present invention are generally those which

are in use or have been proposed to be useful as corrosion inhibitors in aqueous media.

Specific examples of these phosphonates include 2-hydroxyphosphono acetic acid, hydroxyethylidene diphosphonic acid (HEDP), hydroxy propylidene diphosphonic acid,

hydroxy isobutylidene diphosphonic acid, 2-phosphono butane- 1,2,4 tricarboxylic acid, amino

tris(methylene phosphonic acid), diethylene triamino penta (methylene phosphonic acid),

phosphonoacetic acid, 2-phosphonopropionic acid, 2-phosphonoheptanoic acid, 2-hydroxy-2 -methyl phosphonoacetic acid, 2-hydroxy-2-butyl phosphonoacetic acid, 3 -phosphono-3 -hydroxy butyric acid, 2-phosphonoethane-l,2-dicarboxylic acid, methane diphosphonic acid, 1,2-ethanediphosphonic acid, 1,3 -propane- diphosphonic acid,

hydroxymethyl diphosphonic acid, 2-amino-phosphonoacetic acid, 2-amino-2-methyl

phosphonoacetic acid, nitrilo-tris- methylene phosphonic acid, methylamino-bis-methylene phosphonic acid, phosphonomethyl glycine, any of these phosphates may be useful according to this invention.

Preferred phosphonates are 2-hydroxyphosphono acetic acid. The hydroxyethylidene

diphophosonic acid and 2-phosphonobutane 1,2,4 tricarboxylic acid, 2-hydroxyphosphono

acetic acid has been described in USP 3032500 and EPA 0050792. It can be prepared by known methods eg, by reacting orthophosphorous acid, a salt or a solution thereof, or phosphorus trichloride with glyoxylic acid or a salt or a solution thereof. Hydorxyethyliclene

disphosphonic acid and 2- phophono butant 1,2,4 tricarboxylic acid are also articles of commerce which are widely used as corrosion inhibitors in aqueous media.

The phosphonate corrosion inhibitors may be used as the free acid or as a wholly or partially neutralised salt thereof. Examples of suitable salts include the lithium, sodium, potassium, calcium, strontium, magnesium, ammonium, methylamine, ethylamine, n-propylamine, triethylamine, n-butylamine, n-hexylamine, octylamine, ethanolamine, diethanolamine, triethanolamine and morpholine salts.

The mixtures of phosphonate corrosion inhibitors and the phosphono cotelomers exhibit synergy over the entire range of proportions. Thus the ratio of the weight of one to the other may vary from 99: 1 to 1 :99. However, in general we prefer they are employed in proportions in which the weight ratio of phosphonate to phosphono cotelomer lies in the range 4: 1 to 1 :4. The proportions used in a particular application will be chosen so as to balance the benefits of performance against cost. When the phosphonate is 2-hydroxyphosphonoacetic acid the proportion of 2-hydroxyphosphonoacetic acid will generally be increased to provide a greater degree of corrosion inhibition. However, where a cost effective corrosion inhibitor is required it may be preferred to utilise a higher proportion of the phosphono cotelomer as this is the less costly component of the mixture.

The amount of the mixture which is added to an aqueous medium will generally be the same as is currently known in the art. Typically the mixture will be added so as to result in a

concentration of from 0.1 to 50,000 ppm of the mixture of additives in the aqueous system. More usually this concentration will be in the range 0.5 to 100 ppm and most preferably will be in the range 1.0 to 50 ppm.

The phosphonate and the phosphono cotelomers are generally compatible and may be mixed together prior to their addition to an aqueous system. The addition of such mixtures to aqueous systems which are in contact with a metal surface in order to inhibit the corrosion of that surface constitutes a further aspect of the invention. The phosphonate and the phosphono cotelomer may be added separately to aqueous systems and processes involving this separate addition constitute a further aspect of the invention.

The phosphonate and phosphonate cotlomers may be used in combination to inhibit corrosion in soft waters (typically containing less than 30ppm Calcium icons) and hard waters (typically containing say lOOpp, or more of calcium ions.

The mixture of compounds of this invention may be used alone, or in conjunction with other compounds known to be useful in the treatment of aqueous systems.

In the treatment of systems which are completely aqueous, such as cooling water systems, air-conditioning systems, steam-generating systems, sea-water evaporator systems, hydrostatic

cookers, and closed circuit heating or refrigerant systems, further corrosion inhibitors may be

used such as, for example, water soluble zinc salts; phosphates; polyphosphates; nitrates, for

example, sodium nitrate; nitrites, eg, sodium nitrite; molybdates, eg, sodium molybdate, tungstates eg, sodium tungstate; silicates, eg, sodium silicate; benzotriazole, bis-benzotriazole or copper deactivating benzotriazole or tolutriazole derivatives eg, their Mannich base derivatives; mercaptobenzotriazole; N-acyl sarcosines especially sodium N-lauryl sarcosinate; N-acylimino diacetic acids; alanolamines especially the ethanolamines; fatty amines; and organic acids, for example, polymaleic acid and benzoic acid, p tert butyl benxoic acid, disodim sebecute, triethanolamine laurate, so-nonanoic acid.

Moreover, in such completely aqueous systems, the inhibitor used according to the invention may be used in conjunction with further dispersing and/or threshold agents, eg,polymaleic acid

polymerised acrylic acid (or its salts), eg, copolymers of acrylic acid and hydroxyalkylated acrylic acid, and substituted derivatives of polymaleic and polyacrylic acids and their copolymers phosphino- polycarboxylic acids (as described in British Patent 1458235), the cotelomeric compounds described in European Patent Application 150706, hydrolysed polyacrylonitrile, polymerised methacrylic acid and its salts, polyacrylamide and copolymers thereof with acrylic and methacrylic acids, lignin sulphonic acid and its salts, tannin, napthalene sulphonic acid/formaldehyde condensation products, starch and its derivatives, cellulose, acrylic acid/lower alkyl hydroxyacrylate copolymers, eg, those described in US Patent Specification No: 4029577, styrene/maleic anhydride copolymers and sulphonated styrene homopolymers, eg, those described in US Patent Specification No: 4374733 and combinations thereof.

Other agents which may be incorporated into water treatment compositions or this convention include precipitating agents such as alkali metal orthophosphates, carbonates: oxygen scavengers such as alkali metal sulphites and hydrazines; sequestering agents such as nitrilotriacetic acid and its salts; antifoaming agents such as silicones, eg, polydimethylsiloxanes, distearylsebacamide, distearyl adipamide and related products derived from ethylene oxide and/or propylene oxide condensations, fatty alcohols such as capryl alcohols and their ethylene oxide condensates and biocides, eg, amines, quaternary ammonium compounds, chloro-phenols, sulphur-containing compounds such as sulphones, methylene bis thiocyanates and carbamates, isothiazolones, brominated propionamides, triazines, phosphonium compounds, chlorine and chlorine-release agents, bromine and bromine release agents and organometallic compounds such as tributyl tin oxide.

If the system to be treated by the method of the invention is not completely aqueous, eg, an aqueous machining fluid formulation, it may be eg, a water dilutable cutting or grinding fluid.

The aqueous machining fluid formulations of the invention may be eg, metal working formulations. By "metal working", we mean reaming, broaching, drawing, spinning, cutting, grinding, boring, milling, turning, sawing, non-cutting shaping or rolling. Examples of water-dilutable cutting or grinding fluids into which the corrosion inhibiting combinations of this invention may be incorporated include

a) aqueous concentrates of one or more corrosion inhibitors, and optionally one or more anti-wear additives, used at dilutions of 1 : 50 to 1 : 100, which are usually employed as grinding fluids; b) polyglycols containing biocides, corrosion inhibitors and anti-wear additives which are used at dilutions of 1 :20 to 1 :40 for cutting operations and 1 :60 to 1 :80 for grinding; c) semi-synthetic cutting fluids similar to (b) but containing in addition 10 to 25% oil with sufficient emulsifier to render the water diluted product translucent; d) an emulsifiable mineral oil concentrate containing, for example, emulsifiers, corrosion inhibitors, extreme pressure/antiwear additives, biocides, anti-foaming agents, coupling agents etc; they are generally diluted from 1 : 10 to 1 :50 with water to a white opaque emulsion; e) a product similar to (d) containing less oil and more emulsifier which, on dilution to the range 1 : 50 to 1 : 100, gives a translucent emulsion for cutting or grinding operations.

For those partly-aqueous systems in which the aqueous system component is an aqueous machining fluid formulation, the synergistic mixtures according to the invention may be used as such, or in admixture with other additives, eg, known further corrosion inhibitors and/or

extreme-pressure additives.

Examples of other corrosion inhibitors which may be used in these aqueous systems, in addition to the inhibitor composition used according to the invention, include the following groups:

a) Organic acids, their esters or ammonium, amine, alkanol-amine and metal salts, for example, benzoic acid, p-tert-butyl benzoic acid, disodium sebacate, triethanolamine laurate, iso-nonanoic acid, triethanolamine salt of (p-toluene sulphonamido caproic acid), triethanolamine salt of benzene sulphonamido caproic acid, triethanolamine salts of 5-ketocarboxylic acid derivatives as described in European Patent No: 41927, sodium N-lauroyl sarcosinate or nonyl phenoxy acetic acid; b) Nitrogen containing materials such as the following types: fatty acid alkanolamides; imidazolines, for example, l-hydroxy-ethyl-2-oleyl-imidazolines; oxazolines; triazoles for example, benzotriazoles, or their Mannich base derivatives; triethanolamines; fatty amines; inorganic salts, for example, sodium nitrate; and the carboxy-triazine

compounds described in European Patent Applications No: 46139; c) Sulphur containing compounds such as the following types: sodium, calcium or barium petroleum sulphonates, or heterocyclics, for example, sodium mercaptobenzothiazole. Nitrogen containing materials, particularly triethanolamine, are preferred.

Examples of extreme pressure additives which may be present in the systems treated according to the present invention include sulphur and/or phosphorus and/or halogen containing materials, for instance, sulphurised sperm oil, sulphurised fats, tritolyl phosphate, chlorinated paraffins or ethoxylated phosphate esters.

The partly-aqueous system treated by the method of the present invention may also be aqueous surface-coating compositions, eg emulsion paints and aqueous coatings for metallic substrates.

The aqueous surface-coating composition may be, eg, a paint such as styrene-acrylic copolymer emulsion paint, a resin, latex, or other aqueous based polymer surface-coating systems, to coat a metal substrate. The inhibitor composition used according to the invention may be employed to prevent flash rusting of the metal substrate during application of the surface coating and to prevent subsequent corrosion during use of the coated metal.

In aqueous surface-coating compositions treated by the method of the invention the inhibitor composition may be used singly, or in admixture with other additives, eg, known corrosion inhibitors, biocides, emulsifiers and/or pigments.

Examples of biocides which may be used in these aqueous systems include the following:

Phenols, and alkyl and halogenated phenols, for example, pentachlorophenol, o-phenylphenol,

o-phenyoxyphenol and chlorinated o-phenoxyphenol, and salicylanilides, dia ines, triazines and organometallic compounds such as organomercury compounds and organotin compounds.

Examples of pigments which may be used in these aqueous systems include titanium dioxide, zinc chromate, iron oxide and organic pigments such as the phthalocyanines.

The invention is illustrated by the following example

Example One

A corrosion test was carried out assessing the ability of various blends of 2-hydroxy¬ phosphonoacetic acid, hydroxyethylidene diphosphonic acid and 2-phosphonobutane 1,2,4-tricarboxylic acid (A) with a phosphonated (co)telomer having a molecular weight of 2000 to 3000 derived from acrylic acid and AMPS (B) in the following water-

Calcium ions. 150 ppm as CaCO ₃ Magnesium ions: 75 ppm as CaCO ₃ Total Alkalinity 350 ppm as CaCO ₃

Chloride ions: 200 ppm as Cl ^" ion

Sulphate ions: 200 ppm as SO ₄ ion

pH: 8

The test is carried out by using two cleaned and pre-weighed mild steel coupons which are secured to a stainless steel shaft by means of a threaded PTFE holder. The coupons are then rotated at 150 rpm for 42 hours at 40°C in the above aerated water with the additive present at a total concentration of 20 ppm (actives). The aeration rate used is 1 litre per minute per test.

After 42 hours the coupons are removed, cleaned and weighed and the corrosion rate was

calculated using equation below.

Weight loss of 2 coupons (mg) = Corrosion rate (mdd)

Surface area of 2 coupons (dm ² )x Time (days)

Corrosion rate (mdd)x 0.183 (factor for mild steel from the density of mild steel) = mpy mdd = milligrams weight loss/dm ² /day mpy = Mis per year

Mis = 1/1000 th inch

The lower the corrosion rate (mdd) or mpy the better the protection to corrosion of mild steel by the additive.

The results are shown in figures 1, 2 and 3.