WO2007121785A1

WO2007121785A1 - Composition for stabilizing chlorine-containing alkaline solutions

Info

Publication number: WO2007121785A1
Application number: PCT/EP2006/061793
Authority: WO
Inventors: Siegfried Bragulla; Christina Kohlstedde; Lars Houborg
Original assignee: Ecolab Inc.
Priority date: 2006-04-24
Filing date: 2006-04-24
Publication date: 2007-11-01

Abstract

The invention relates to a composition for stabilizing chlorine containing alkaline solutions comprising (i) a phosphono compound of the general formula (I) in which each of R1, R2 and R3 represents H, -(CH2)x-COOH wherein x is 1 to 4, or -COOH and R1, R2 and R3 can be the same or different, with the proviso that at least one carboxyl group is present in the compound according to general formula (I), and (ii) a silicate. The invention further relates to a method for stabilizing chlorine containing alkaline is solutions and to stabilized chlorine containing alkaline solutions.

Description

Composition for stabilizing chlorine-containing alkaline solutions

[0001] The present invention relates to a composition for stabilizing chlorine- containing or chlorine releasing alkaline solutions, to a method for stabilizing these solutions and to the stabilized solutions.

[0002] Chlorine-containing and chlorine-releasing compounds are widely used in cleaning, sanitizing, disinfection, and water treatment. In the following the expression "chlorine-containing" is also used for compositions containing chlorine releasing compounds. Chlorine-containing compositions normally comprise a source of alkalinity, a solution of a hypochlorite salt in water, and further additives, for example surfactants. Hypochlorites are cheap, effective biocides and are used widely in hospitals, agriculture, dairying, food processing, public health and hygiene. Often sodium hypochlorite which is a chlorine-releasing compound is used. It decomposes with increasing temperature and under the influence of light and certain metal ions containing salts. The bacterial effect of sodium hypochlorite is caused by the non-ionized hypochlorous acid (HOCI) which is believed to be responsible for the bactericidal activity of chlorine, hypochlorites, and other chlorine-releasing agents. Hypochlorous acid is produced by a dissociation reaction of chlorine with water to hypochlourous acid and hydrochloric acid. Hypochlorous acid ionises to give H⁺ and OCI^" ions. The concentration of HOCI and hence the bactericidal efficiency depends on the pH of the solution. The more acidic the solution is the more hypochlorous acid is present in the solution.

[0003] Also other chlorine-containing compounds are known, for example other inorganic hypochlorite salts like calcium hypochlorite, or organic chlorine releasing compounds like chloramine T, dichloramine T, and trichloroisocyanuric acid. All these compounds release chlorine in the presence of water.

[0004] An important field for this kind of cleaning agents are plants of the food industry in which the cleaning is carried out as a cleaning in place (CIP) or a cleaning out of place (COP). The cleaning-in-place procedure is often used to clean difficult-to-reach inner surfaces of an article, a machine or a plant. It is carried out by circulating the cleaning solution through the machine whereby the surface to be cleaned gets into contact with the cleaning solution. If it is possible to 5 disassemble the corresponding parts of the machine or if the surfaces to be cleaned are easily accessible the cleaning solution is directly applied to the surface. This procedure is called cleaning out of place (COP).

[0005] US 4,228,048 describes a liquid alkaline concentrate which is used as a foam cleaner for food plants. The cleaner comprises sodium hydroxide, io sodium silicate, and small amounts of sodium hypochlorite between 0.05 - 5 wt.%.

[0006] US 2002/0151455 A1 describes a bleach cleaner composition showing excellent bleach cleaning power to fungi on resin parts and furthermore having an excellent storage stability of the hypochlorite at high temperatures. The composition comprises an alkali metal salt of a hypochlorous acid, a quaternary ammo- i s nium salt, surfactant, and at least one compound selected from cumene sulfonic acid, xylene sulfonic acid, tuloene sulfonic acid, and alkali metal salts thereof. Furthermore the compositions contains an alkali metal hydroxide and water and optionally an amphoteric surfactant.

[0007] Normally the chlorine-containing products are sold as concentrate

20 solutions. For use these concentrate solutions are normally diluted with water to prepare a use solution which is then applied in the cleaning, disinfecting or sanitizing process.

[0008] The liquid concentrates are produced as clear solutions. It was observed that these products showed strong black precipitations already after 25 short storage times. These decomposed or partly decomposed product concentrates do not fulfil the usual quality standards and can not be used in cleaning processes by the customers. [0009] Hence it is the object of the present invention to provide a composition for stabilizing chlorine-containing alkaline solutions so that the occurrence of black precipitations after storage of the cleaning composition concentrates is avoided.

[0010] This technical problem is solved by a composition for stabilizing chlorine-containing alkaline solutions comprising

(i) a phosphono compound of the general formula (I)

in which each of R¹, R² and R³ represents H, -(CH₂)_x-COOH wherein x represents 1 to 4, or -COOH and R¹, R² and R³ can be the same or different, with the proviso that at least one carboxyl group is present in the compound according to general formula (I), and

(ii) a silicate.

[0011] During the investigation of the problem of the strong black precipitation in the composition concentrates it was first assumed that these black precipi- tations are caused by impurities in the raw materials especially by heavy metals present in the sodium hydroxide and by other impurities present in the hypochlorite solution. [0012] However, even if the raw material is produced in non-corroded equipment and if strongly defined qualities are used for the raw materials nevertheless the black precipitation occurs.

[0013] Several laboratory tests were done to find out how to avoid the strong black precipitation in these solutions. Several complexing agents for heavy metals were tested. However, they could not prevent the black precipitation. In these tests for instance complexing agents like EDTA, NTA, phosphonate, phosphate, polyacrylate, and also other complexing agents were tested without success.

[0014] During intensive studies it was finally discovered that only a very specific combination of a complexing agent with a silicate is able to prevent the occurrence of the strong black precipitation. It was observed that by using a phos- phono compound according to the general formula (I) and a silicate it was possible to avoid the strong black precipitation in the concentrates. Even when the concen- trates were stored for more than six months no black precipitation was observed.

[0015] It was furthermore discovered that the use of only one of these compounds, could not prevent the strong black precipitation in the chlorine containing concentrate solution.

[0016] Therefore it seems that there is a synergistic effect between the phosphono compound and the silicate compound which leads to the prevention of the strong black precipitation in the chlorine-containing alkaline concentrates.

[0017] The expression "chlorine-containing alkaline solution" is defined throughout the specification and the claims as an alkaline solution containing chlorine or chlorine-releasing compounds like for instance sodium hypochlorite, chloramine T, dichloramine T, trichloroisocyanuric acid. Also other chlorine- releasing compounds can be used. [0018] These compounds have the characteristic that they release chlorine at certain temperatures or certain pH values. This chlorine reacts with water to hypochlorous acid which is believed to be responsible for the bactericidal effect of chlorine.

[0019] In a preferred embodiment the silicate which is used in the composition according to the invention is an alkali metal silicate, preferably a sodium silicate or a potassium silicate, and most preferred a sodium water-glass and/or a potassium water-glass.

[0020] The phosphono compound is preferably a compound in which each of the groups R¹ and R² represents hydrogen and R³ represents a carboxy methyl group or a carboxy group. It is essential that in the phosphono compound according to general formula (I) at least one carboxyl group is present.

[0021] In a further preferred embodiment the phosphono compound according to general formula (I) is a compound in which R¹ is hydrogen and each of R² and R³ represents a carboxy methyl group or a carboxy group. It is furthermore preferred that the groups R¹, R², and R³ each represent a carboxy methyl group or a carboxy group. The most preferred phosphono compound is 2-phosphono butane 1 ,2,4-tricarboxylic acid.

[0022] In the examples it is shown that a combination of the phosphono compound and silicate even in small amounts stabilizes a chlorine-containing alkaline solution so that the occurrence of black precipitations is totally avoided.

[0023] A further subject of the present invention is a method for stabilizing a chlorine-containing alkaline solution comprising the steps of providing a composition according to the invention and adding the composition to the chlorine- containing alkaline solution. By using this method the chlorine-containing alkaline solution is stabilized preventing the dark precipitation in the solution. [0024] A further subject of the invention is a stabilized aqueous chlorine- containing solution. This solution comprises relating to the whole composition

10 - 40 wt-% NaOH and/or KOH 20 - 70 wt-% NaOCI and/or KOCI

0.1 - 15 wt-% Phosphono compound according to the invention and 0.05 - 10 wt-% silicate according to the invention.

[0025] In a preferred embodiment the stabilized aqueous chlorine-containing solution has the following composition

15 - 35 wt-% NaOH and/or KOH,

35 - 60 wt-% NaOCI and/or KOCI,

0.5 - 10 wt-% Phosphono compound according to the invention and

1 - 5 wt-% silicate according to the invention.

[0026] The stabilized aqueous chlorine-containing solution can furthermore contain additives like for example, corrosion inhibitors, fragrances, dyes, antiseptic agents, UV absorbers, reducing agents, buffers, viscosity modifying agents, or mixtures thereof.

[0027] The stabilized chlorine containing alkaline solution of the present invention may also comprise other components typically used in alkaline cleaning compositions like sequestrants, surfactants, disinfectants, bleaching agents, oxidants, builders, solubilizers, solvents or mixtures thereof. Some of those compounds may also have several functions. For example oxidizing agents like hypochlorite which generate active chlorine also exhibit disinfecting properties besides their cleaning booster properties.

[0028] The present composition is preferably free of any alkali metal perborate. In a particularly preferred embodiment the present composition contains sodium hypochlorite, potassium hypochlorite or mixtures thereof and no other bleaching or oxidizing agent.

[0029] The stability of the chlorine containing alkaline solution can be i m- proved by further adding one or more sequestrants. This applies in particular if calcium or magnesium salts are used as corrosion inhibitors, since the cations of Mg or Ca form water insoluble hydroxides in alkaline solutions. Appropriate sequestering agents can be exemplified by ethylene diamine tetraacetic acid, nitrilo triacetic acid, phosphates in particular polyphosphates such as pentasodium triphosphate, polyhydroxycarboxylic acids, citrates, in particular alkali citrates, dimercaprol, triethanol amine, crown compounds. Under the alkaline conditions in the aqueous solution the above mentioned acids usually will be present in the form of their salts, preferably in the form of their sodium or potassium salts. However, when producing the composition according to the invention the acids as well as the corresponding salts may be used.

[0030] The one or more sequestering agents should be contained in the composition in a total amount of from 2 to 35 wt.%, preferably of from 5 to 25 wt.% and more preferred of from 9 to 20 wt.% based on the total composition in order to obtain a sufficient sequestering performance.

[0031] An improved cleaning performance of the stabilized solution accord- ing to the present invention may be achieved if one or more surfactants are additionally added to the composition. However, in case surfactants are used it has to be guaranteed that they are functioning under the highly alkaline conditions of the solutions obtained from the composition. Although all kinds of surfactants, i.e. anionic, cationic, non-ionic and amphoteric, may be applied especially appropriate surfactants for use in the present invention represent anionic and/or non-ionic surfactants.

[0032] Suitable anionic surfactants are exemplified by alkyl arene sulfonates, in particular alkyl benzene sulfonates and alkyl naphthalene sulfonates, alkylsulfonates, preferably comprising 12 to 18 carbon atoms in the alkyl moiety, α- olefin sulfonates preferably containing 12 to 17 carbon atoms in the olefin moiety, or alkyl sulfates preferably having 11 to 17 carbon atoms in the alkyl moiety, or mixtures thereof. Usually, said compounds are used in the form of their alkali salts, in particular in the form of their sodium salts. An especially advantageous anionic surfactant represents sodium lauryl sulfate. Anionic surfactants may improve the cleaning performance but also the stability of the composition.

[0033] Although non-ionic surfactants like alkoxylated, in particular ethoxy- lated and/or propoxylated, fatty alcohols or fatty amines, which also may be alkyl- terminated, for example butyl-terminated, are suitable in the composition according to the present invention as well it is preferred to use aminoxides which correspond to the formula R⁴R⁵R⁶NO, wherein R⁴ to R⁶ independently represents an aliphatic or cyclic hydrocarbon residue having 1 to 20 carbon atoms and wherein at least one and preferably only one of R⁴ to R⁶ has a hydrocarbon residue with at least 11 carbon atoms. It is also possible to use a mixture of several aminoxides. Preferred aminoxides represent coconut alkyl dimethylamine oxide or lauryl di- methylamine oxide.

[0034] Further non-ionic surfactants which may be used in the present composition represent alkyl polyglucosides. The alkyl group of alkyl polyglucosides generally is derived from native fats or oils or petrochemically produced alcohols. The sugar moiety typically is derived from reducing sugars having 5 or 6 carbon atoms.

[0035] Cationic surfactants for use in the composition according to the present composition can be exemplified by quaternary ammonium salts. They preferably represent saturated or unsaturated compounds which are derived from esterifying trialkanol amine, in particular triethanol amine, with fatty acids and subsequent quaternization with appropriate alkylation agents. Suitable fatty acids have 12 to 18 carbon atoms, such as lauric acid, myristic acid, palmitic acid, oleic acid or stearic acid. It is particularly preferred to use mixtures of fatty acids as obtained in technical processes like the acid mixtures derived from coconut oil, palm kernel oil, rapeseed oil or tallow oil.

[0036] In a particularly preferred embodiment the one or more surfactants are contained in the stabilized solution in a total amount of from 1 to 30 wt.%, preferably of from 2 to 20 wt.% and more preferred of from 4 to 15 wt.% based on the total composition.

[0037] Taking the above description into account depending on the kind of soil and the form and location of the metal surface to be cleaned it may be either possible to use a foaming cleaner or a non-foaming cleaner wherein the non- foaming may be achieved by completely omitting any kind of surfactant or by using low-foaming surfactants.

[0038] In order to obtain a homogenous solution it may be helpful to further add one or more solubilizers. In particular they facilitate the dispersion of organic components such as the one or more surfactants in the aqueous solution. Suitable solubilizers are exemplified by sodium, potassium, ammonium and alkanol ammonium salts of sulfonates of xylene, toluene, ethylbenzoate, isopropylbenzene, naphthalene or alkyl naphthalene, phosphate esters of alkoxylated alkyl phenols, phosphate esters of alkoxylated alcohols and sodium, potassium and ammonium salts of alkyl sarcosinates, as well as mixtures thereof.

[0039] In a preferred embodiment the one or more solubilizers are contained in the stabilized solution in a total amount of from 1 to 35 wt.%, preferably of from 5 to 25 wt.% and more preferred of from 9 to 20 wt.%.

[0040] The stabilized solution according to the present invention may additionally contain one or more other compounds commonly used in cleaning compo- sitions like ones selected from the group comprising disinfectants, builder substances, solvents and bleaching agents. Those compounds preferably are contained in the stabilized solution according to the invention in a total amount of from 0 to 20 wt.%, preferably of from 2 to 15 wt.%, more preferred below 10 wt.%.

[0041] Typically, the compounds exemplified above in connection with the oxidants also function as bleaching agents. However, this does not exclude to use compounds as bleaching agents which are not mentioned above.

[0042] Suitable builders are exemplified by sodium carbonate, sodium sesquicarbonate, sodium sulfate, sodium hydrogencarbonate, phosphates like pentasodium triphosphate, nitrilo triacetic acid or its salt, respectively, citric acid or its salt, respectively, mixtures thereof.

[0043] Appropriate disinfectants beside the ones mentioned above in connection with oxidants for use in the stabilized solution according to the present invention represent aldehydes such as formaldehyde, glyoxal or glutaraldehyde, phenol derivatives and alcohols or mixtures thereof.

[0044] Chlorine-containing compounds in the sense of the invention are compounds which release chlorine. Examples for these compounds are hypochlorite salts, chloramine T, dichoramine T, trichloroisocyanuric acid, chlorine itself. The bactericidal effect of chlorine is believed to come from [be due to] the activity of hypochlorous acid which is produced by the reaction of chlorine in water dependent on the pH of the solution. Hypochlorous acid is believed to react with an inactivate enzymes that are essential for bacterial metabolism particularly triose phosphate dehydrogenase.

[0045] The stabilized aqueous chlorine-containing solution according to the invention does not show any dark or black precipitation even after storage times of several months and up to half a year. This guarantees that the customer receives a high-quality product which is stabilized for a long time not showing any decomposition or destabilization. [0046] The following examples show specific embodiments of the invention without limiting the invention to these specific embodiments.

EXAMPLES

[0047] Table 1 shows several compositions 1 to 4 according to the invention which are compared with comparative examples 5 to 10. To evaluate the effect of the stabilization the compositions were stored for ten weeks at room temperature and after that a visual evaluation of the degree of dark precipitation was made. In this evaluation the following grades were given:

0 = no dark precipitation, 1 = minimum of dark precipitation, however, acceptable, 2 = some precipitation not acceptable, 3 = many precipitations, not acceptable.

[0048] From table 1 can be seen that if the phosphono compound is used together with sodium water-glass or potassium water-glass no dark precipitations (examples 3, 4) or only a minimum of dark precipitation (examples 1 , 2) were observed.

[0049] From the comparative examples can be seen that the use of the phosphono compound alone did not show this effect. The grade for the precipia- tion is 3 which means that the amount of dark precipitation is high and not acceptable for the product.

[0050] Dark precipitation is also observed when only sodium or potassium water-glass is used (see comparative examples 9 and 10) without the phosphono compound. In these comparative examples grade 3 was given and cases many dark precipitations were found after ten weeks storage time. As previously mentioned also the use of complexing agents like EDTA, NTA, or gluconate could not prevent the dark precipitation in the chlorine-containing solutions (see comparative examples 6, 7, 8).

[0051] From table 1 can be seen that only the specific combination of the phosphono compound and silicate is able to prevent the dark precipitation in the chlorine-containing solutions.

[0052] Further experiments were made to evaluate the stability of the stabi- lized aqueous chlorine-containing solutions according to the invention even after longer storage times. Table 2 shows the results of examples 11 , 12, and 13. These examples are compositions which were stabilized with potassium water- glass and the phosphono compound 2-phosphono-1 ,2,4-tricarboxylic acid.

[0053] The experiments show that even after three months in all three example solutions no dark precipitations occurred. After six months there were still no dark precipitations but only some traces of light precipitations in the solutions which are acceptable as most of the product is not stored longer then 5 month before use.

[0054] The experiments impressively show that the composition according to the invention comprising the phosphono compound according to general for- mula (I) and a silicate can successfully stabilize aqueous chlorine-containing alkaline solutions. This stabilization results in solutions which do not show any dark precipitations even after six months storage time. Compared to the state of the art where such dark precipitations were already observed after some days this is a great improvement over the state of the art keeping the product quality and meeting the high demands on the product.

Claims

1. Composition for stabilizing chlorine containing alkaline solutions comprising

(i) a phosphono compound of the general formula (I)

in which each of R¹, R² and R³ represents H, -(CH2)χ-COOH wherein x is 1 to 4, or -COOH and R¹, R² and R³ can be the same or different, with the proviso that at least one carboxyl group is present in the compound according to gen- eral formula (I), and

(ii) a silicate

2. Composition according to claim 1 , wherein the silicate is an alkali metal silicate.

3. Composition according to claim 2, wherein the alkali metal silicate is a sodium silicate or a potassium silicate.

4. Composition according to claim 3, wherein the alkali metal silicate is a sodium water-glass and/or a potassium water-glass.

5. Composition according to claim 1 , wherein each of R¹ and R² represents H and R³ represents a carboxymethyl group or a carboxy group.

6. Composition according to claim 1 , wherein R¹ represents H and each of R², R³ represents a carboxymethyl group or a carboxy group.

7. Composition according to claim 1 , wherein R¹ and R² and R³ each represents a carboxymethyl group or a carboxy group.

8. Composition according to claim 1 , wherein the phosphono compound is 2- phosphonobutane 1 ,2,4-tricarboxylic acid.

9. Method for stabilizing chlorine containing alkaline solutions comprising the steps of providing a composition according to claims 1 to 8 and adding the composition to the chlorine containing alkaline solution.

10. Method according to claim 9, wherein the stabilization prevents dark precipitations in chlorine containing alkaline solutions.

11.Stabilized aqueous chlorine containing solution comprising relating to the whole composition: 10 - 40 wt-% NaOH and/or KOH 20 - 70 wt-% NaOCI and/or KOCI

0.1 - 15 wt-% Phosphono compound according to claims 1 to 8 0.05 - 10 wt-% silicate according to claims 1 to 8.

12. Stabilized aqueous chlorine containing solution according to claim 11 comprising relating to the whole composition: 15 - 35 wt-% NaOH and/or KOH 35 - 60 wt-% NaOCI and/or KOCI 0.5 - 10 wt-% Phosphono compound 1 - 5 wt-% silicate

13. Stabilized aqueous chlorine containing solution according to claim 11 or 12 further comprising as additives sequestrants, surfactants, corrosion inhibitors, disinfectants, bleaching agents, oxidants, builders, solubilizers, solvents, fragrances, dyes, antistatic agents, UV absorbers, reducing agents, buffers, vis- cosity modifying agents or mixtures thereof.