GB1579217A

GB1579217A - Her closed circuit water system composition for addition to a central heating system or ot

Info

Publication number: GB1579217A
Application number: GB2425978A
Authority: GB
Original assignee: Muetzel P S
Current assignee: Muetzel P S
Priority date: 1978-05-30
Filing date: 1978-05-30
Publication date: 1980-11-12

Description

(54) A COMPOSITION FOR ADDITION TO A CENTRAL HEATING SYSTEM OR OTHER CLOSED CIRCUIT WATER SYSTEM (71) I, PETER SIEGFRIED MUETZEL, a British Subject, of Brittannica House, 21-224 High Street, Waltham Cross, Herts, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to additives primarily for domestic central-heating systems but also having applicability to other circulating-liquid systems such as solar-heating systems or industrial heating or cooling systems or static systems such as water-thinnable paints.

A domestic central heating system basically comprises a sealed circuit of a boiler; an array of tubing usually including heat exchange coils within a tank to provide a domestic hot water system; and a number of radiators. Initially, it is filled with mains water.

Such a system deteriorates for two main reasons. Firstly, there is the effect of separated hardness salts from the water if any, and secondly, there is corrosion of the construction metal or metals, which has the effect both of attacking the metal and of producing solids and evolved gas within the system.

To deal first with the hardness salts, these appear to separate for three reasons, namely (i) the initial bringing-up to the operating temperature (ii) the progressive contacting of the liquid as it circulates with a hot spot in the boiler at a temperature higher than the normal operating temperature and (iii) chemical reaction with other substances into the water, especially alkaline-reacting substances, which are either especially added or arise with the efflux of time. These chemical hardness salts can possibly remain disseminated through the circulating water.

In such an instance they are prone eventually to effect the pump within the circuit, by accumulating on or otherwise affecting the bearings. Alternatively, the hardness salts after separation can be adherent to the metal surfaces. This adherency can be uniform or non-uniform throughout the system. In the major part of the system. it detrimentally affects heat transfer, while if it is an adherent deposit in the boiler, for example, on a hot spot, it can lead to an undesirable boiler noise when operating. Finally, it is possible for separated salts to accumulate loosely in the system. Typically they accumulate in places of slower flow, where they can eventually cause a blockage in the system.

The corrosion effects within the system are quite distinct from the separation of hardness salts, and themselves fall into two main types.

The first type is oxidic corrosion, and this is usually a short-lived problem lasting for only a few days after filling the circuit, until all the initial oxygen is used up. It may, however, be a special problem if there is any ingress of air or mains water due to wear and corrosion as described below or any installation fault, misuse or interference by an untrained person. The second form of corrosion is electrolytic or galvanic corrosion and is a continuing problem as long as the circuit operates. It arises by virtue of the electrical potential existing either between two different metals (e.g. iron or steel on the one hand and copper in the form of bronze or brass on the other) or between two different conditions of the same metal (e.g. differently stressed regions of steel having different crystal size and electrical potential).If it is of the former type, the other metal, usually copper in some or other, can either be present more or less accidentally as a consequence of the welding or soldering techinques or can be present intentionally as lengths of copper tubing. In either case, the consequence is formation of black Fe3O4 corrosion product, possibly to some extent adherent to the walls but usually in the form of a loose deposit because of its specific gravity. Thus, over a period of time the lower parts of a system tend to block with a black iron-containing sludge.

Conversely, the upper parts of the system can tend to become filled with hydrogen gas which is a further consequence of the electrolytic corrosion. Where the corrosion is to some extent adherent, it can be locally disturbed by turbulence and high rates of liquid flow, and by subsequent further reaction lead to noticeable erosion and eventual perforation at the point in question.

A special feature of the corrosion product, Fe3O4 is that it is magnetic.

Eventually it tends to clog the motor since even if only small amounts drift around the system they will be attracted by the magnetic field of the motor and accumulate at that point.

Other features characteristic of electrolytic corrosion in a system are that it is increased by the ionic concentration in the water (whether this arises from weld or soldering aids such as zinc chloride or ammonium chloride, or from other additives used) and also that it is increased by higher circuit operating temperatures, broadly speaking doubling in rate for every 30O centigrade.

There is also a third reason occasionally encountered which leads to deterioration of the system, that is to say, bacterial or fungal activity. The growth of such organic impurities is often favoured in central heating systems and in particular in the header tanks, (a) because the system remains motionless during shutdown periods and (b) because the water temperature in the header tanks is slightly higher than that of the environment. Also, certain chemical release agents used in the manufacture of plastics components such as header tanks can stimulate the growth of such organic impurities. These impurities can be bacterial or fungal, or for example blanket-like layers and slimes of the fungus fusarium aquaductum have been known to form and be drawn into the system to cause blockages.

An earlier Patent of the present Inventor is based upon the realization that instead of designing a separation protective additive formulation for the exact requirement of each individual system (as to water and to construction metals) it is possible to define a multi-purpose formulation which is entirely compatible, protects most systems both as to water and construction, and provides a flexible base formulation to which optional constituents can be added to protect against less usual problems.

This prior Patent 1 353 748 therefore envisages (I) water soluble tetraborate, to passivate any steel surface, increase the pH and thus render flux residues harmless, all of which features are basically anticorrosion features(II) a cuprosolvency inhibitor, another anti-corrosion feature intended to prevent copper ions getting into solutions in the first place (III) a heptonate or boroheptonate, to sequester the hardness salts and counteract their precipitation, especially as a result of the tetraborate addition, and (IV) a molybdate/phosphate and/or nitrite to assist in steel passivation and (in a preferred embodiment) also to inhibit precipitation of hardness salts or to remove any free oxygen in the system respectively.

The present invention may be considered as a further development of the above idea, and in one aspect comprises a composition for addition to a closed circuit water system comprising (I) sodium borophosphate, as made from orthosphosphoric acid and sodium tetraborate, whether neutral, alkaline, or acidic in nature (II) a cuprosolvency inhibitor (III) acetodiphosphonic acid and (IV) a watersoluble source of (a) molybdate ions and phosphate ions of formula PnOn+ 1 (n+2)0 where n is a positive integer and/or (b) nitrite ions.

The sodium borophosphate can alternatively be called sodium phosphoborate.

It agains appears to passivate steel members in the circuit, to render harmless any flux residues, and in general to impart anti-corrosive properties to the liquid in the circuit.

The cuprosolvency inhibitor can be one or more compounds chosen from benzotriazole, mercaptobenzothiazole or tolyltriazole. Its function, as before is to inhibit to as great extent as possible the dissolution of copper ions into the solution in the first place.

The acetodiphosphonic acid can be replaced part by sodium heptonate or sodium boroheptonate, up to a level of 50% by weight. The acetodiphosphonic acid has advantages over the other two materials which in the practice of the present invention lead to it being always present in a major proportion by weight of this type of material. The advantage appears to be not only that it sequesters the hardness salts from the water, such as calcium and magnesium salts, but also that it sequesters copper ions or the various iron ions present in the water.

The source of any nitrite ion used in the formulation according to the invention is preferably sodium nitrite. When both the nitrite and the borophosphate are present in the formulation according to the invention, their relative weight proportions can range from 10:90 to 90:10.

When the mixture of molybdate and phosphate ions are present, it is preferred for the atomic ratio of mo:P to be approximately 12 to 1.

As explained above, a long-term consequence of corrosion is the formation of perforations in the system. To minimise the detrimental effect of this, it is preferred to incorporate a leak sealant into the formulation. Thus, the formulation further preferably comprises a water-soluble salt of silicate and/or a source of metasilicate ion.

Preferably, the silicate and metasilicate are used, together.

As described above, it is also possible to encounter bacterial or fungal contamination in a circuit. Thus, the formulation according to the invention preferably further comprises a biocidal agent, usually possessing both bacterio cidal and fungicidal properties. Typically such agents are dichlorodihydroxydiphenylmethane and/or formaldehyde.

It is also preferable for the system to further comprise a water-soluble lubricant for the pump. Such a lubricant may be chosen from ethyleneglycol, polyethylene glycol, ethyl cellulose, methyl cellulose, or hydroxy ethyl cellulose, but we have found advantage in using monopropylene glycol together with or alternatively to polypropylene glycol, since these latter products are less toxic.

The formulation according to the invention can be made up as a solid, preferably particulate e.g. as a free-flowing powder, but possibly in crystal or lump form. It is also conceivable to make it up as a strong aqueous solution, e.g. having a dissolved solid content of from 15 to 35% by weight. It is most convenient, however, to define the relative amounts of material in the solid by the concentration that can jointly be attained when these are dissolved in the whole circuit.Thus, the basic formulation preferably is of proportioned that when dissolved in the circuit it can produce a solution containing 0.01 to 2.5% of the boro phosphate, 0.02 to 0.5% of the cuprosolvency inhibitor, 0.01 to 0.5 of the acetodiphosphonic acid, optionally replaced to a minor proportion with the heptonate or boro heptonate, and 0.02 to 0.8% of the molybdate/phosphate mixture and/or 0.02 to 0.50/, of the nitrite.

Moreover, sodium silicate can be present in an amount of 0.005 to 0.9% and mekasilicate in an amount of 0.002 to 0.25%. The dichlorodihydroxydiphenylmethane can be present in an amount of 0.002 to 0.1%, and the formaldehyde in the amounts of 0.02 to 0.4% based upon a 40% solution of formaldehyde. All the above percentages are by weight.

A minor optional addition is the inclusion of a wetting agent, in particular of the ethoxylated phosphate ester type.

The wetting agent serves the dual functions of (a) providing overall contact of the anticorrosive composition with the metallic surface to be treated and protected, and (b) of adding foaming properties to circulating water, which serves the specific purpose of indicating a number of typical faults occasionally found in central heating and solar heating, or cooling systems.

Foaming properties are acceptableKin a circulating system in the absence of air. The inclusion of air indicates a fault for instance pumping over via the open vent pipe into the header or expansion tank. Cascading water into the tank would build up a layer of foam. When this reaches the overflow pipe, the fault becomes noticeable by a minor flow of water from this point.

Another fault occasionally found is the presence of a micro-leak on that part of the system which is under negative pressure, in the case of pumped circulating water. Air may be drawn into the system such points, even where the porosity is too small to allow water to flow through to indicate the fault. The formation of foam from such points onward in the circulating stream enables an experienced installer or service engineer to trace and remedy the fault.

Another fault occasionally found is a leak in the coil or annulus within the domestic indirect hot water tank or cylinder. This fault renders it possible for circulating water to be intermixed with domestic hot water or industrial processing waters. This type of fault has the disadvantage of (a) causing the additive to become overdiluted, (b) causing the ingress of aerated water and additional hardness salts into the circulating system, thus leading to more rapid corrosion and the formation of hardness salt deposits in the circulating system and in (c) causing the pollution of domestic or industrial hot water with bacteria or fungi which may be present in untreated circulating water. The presence of a foaming agent in the circulating primary water would impart foaming properties to the polluted water thus providing an indication of the fault.

A further optional minor addition is of a taste spoiler with colourising properties.

For the purpose, 2,4 - dinitrophenyl hydrazine is generally suitable, the preferred addition being such that the circulating water contains at least 10 grammes per 100 litres. At great dilutions, as in the case of accidental intermixing with domestic hot water or indirect industrial processing water the polluted water would have (a) a distinctive odd taste, and (b) a yellow colour, with relatively low staining properties.

Since untreated central heating and solar heating circulating water as well as industrial cooling circuit water can contain a range of bacteria and fungi, the addition of at least this type of taste spoiler and colourising agent seem highly desirable, as without this a physician treating a patient may be unable to eradicate the source of disease following the ingestion of water polluted with such organic impurities.

A further optional addition is the inclusion of sodium meta vanadate to provide corrosion protective properties to aluminium, in systems containing only aluminium or in mixed metal installations also containing aluminium.

The invention will be further described with reference to the following specific examples.

WHAT I CLAIM IS: 1. A composition for addition to a closed circuit water system comprising (I) sodium borophosphate, as made from orthosphosphoric acid and sodium tetraborate, whether neutral, alkaline, or acidic in nature (II) a cuprosolvency inhibitor (III) acetodiphosphonic acid and (IV) a watersoluble source of (a) molybdate ions and phosphate ions of formula PnO3n+ 1 (n+210 wherein n is a positive integer and/or (b) nitrite ions.

2. A composition as claimed in claim 1 in which the cuprosolvency inhibitor is one or more of benzotriazole, mercaptobenzothiazole or tolyltriazole.

3. A composition as claimed in claim 1 or 2 in which the acetodiphosphonic acid is replaced, in an amount up to 50% of its weight by sodium heptonate or sodium boroheptonate.

4. A composition as claimed in any one preceding claim in which the source of any nitrite ion used is sodium nitrite.

5. A composition as claimed in any one preceding claim wherein both nitrite and and borophosphate are present in relation weight proportions from 10:90 to 90:10.

6. A composition as claimed in any one preceding claim in which both molybdate and phosphate ions are present in an Mo:P atomic ratio of approximately 12:1.

7. A composition as claimed in any one preceding claim further comprising a leaksealant constituted by one or more of silicate and metasilicate.

8. A composition as claimed in claim 1 in which a silicate/metasilicate mixture is used as a leak-sealant.

9. A composition as claimed in any one preceding claim further comprising a biocidal agent.

10. A composition as claimed in claim 9 in which the biocidal agent possesses both the bacteriocidal and fungicidal properties.

11. A composition as claimed in claim 10 in which the biocidal agent is dichlorodihydroxydiphenylmethane and/or formaldehyde.

12. A composition as claimed in any one preceding claim comprising a water-soluble pump lubricant.

13. A composition as claimed in claim 12 wherein the said lubricant is monopropylene, glycol, a polypropylene glycol, ethyleneglycol, a polyethylene glycol, ethylcellulose, methyl cellulose, or hydroxyethylcellulose.

14. A composition as claimed in any one preceding claim in particulate solid form as a free, flowing powder, crystals or lumps.

15. A composition as claimed in any of claims 1 to 13 in the form of a concentrated aqueous solution containing from 15 to 35% by weight of solid.

16. A composition as claimed in any one preceding claim which when dissolved in the circuit can produce a solution containing 0.01 to 2.5% of the borophosphate, 0.02 to 0.5% of the cuprosolvency inhibitor, 0.01 to 0.5% of the acetodiphosphonic acid, optionally replaced to a minor proportion with the heptonate or boroheptonate and 0.02 to 0.8% of the molybdate/phosphate mixture, and/or 0.024).5% of nitrite.

17. A composition as claimed in claim 7 or any of claims 8 to 16 as dependent thereon, containing 0.005 to 0.9% of sodium silicate, and/or 0.002 to .25 of sodium metasilicate, and/or 0.002 to .25% of sodium metasilicate.

18. A composition as claimed in claim 11 or in any of claims 12 to 17 as dependents thereon containing from 0.002 to 0.1% of dichlorodihydroxydiphenylmethane or 0.02 to 1.4% of 40% formaldehyde.

19. A composition as claimed in any one preceding claim further including a foaming and wetting agent.

20. A composition as claimed in claim 19 in which the foaming agent is of the ethoxylated phosphate ester type.

21. A composition as claimed in any one preceding claim which contains a tastespoiler with colorising properties.

22. A composition as claimed in claim 21 in which the taste spoiler is 4 - dinitrophenylhydrazine.

23. A composition as claimed in claim 1 which further includes sodium metavanadate as a protective for aluminium.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. water or indirect industrial processing water the polluted water would have (a) a distinctive odd taste, and (b) a yellow colour, with relatively low staining properties. Since untreated central heating and solar heating circulating water as well as industrial cooling circuit water can contain a range of bacteria and fungi, the addition of at least this type of taste spoiler and colourising agent seem highly desirable, as without this a physician treating a patient may be unable to eradicate the source of disease following the ingestion of water polluted with such organic impurities. A further optional addition is the inclusion of sodium meta vanadate to provide corrosion protective properties to aluminium, in systems containing only aluminium or in mixed metal installations also containing aluminium. The invention will be further described with reference to the following specific examples. WHAT I CLAIM IS:

1. A composition for addition to a closed circuit water system comprising (I) sodium borophosphate, as made from orthosphosphoric acid and sodium tetraborate, whether neutral, alkaline, or acidic in nature (II) a cuprosolvency inhibitor (III) acetodiphosphonic acid and (IV) a watersoluble source of (a) molybdate ions and phosphate ions of formula PnO3n+ 1 (n+210 wherein n is a positive integer and/or (b) nitrite ions.

24. A composition as claimed in any one

preceding claim substantially as herein described.

25. A method of treating a domestic, industrial or solar hot water system in which the composition as claimed in any one preceding claim is added.