Cleaning solution and method for its production

Abstract

The invention relates to an aqueous cleaning solution for removing rouging deposits, containing at least one complexing agent for complexing iron(II) ions and / or iron(III) ions, wherein the cleaning solution further comprises: - at least one oxidizing agent, wherein the at least one oxidizing agent is a salt of peroxodisulfuric acid; - at least one catalyst, wherein the at least one catalyst is a salt of hydrofluoric acid. Furthermore, uses of the cleaning solution according to the invention and methods for preparing such a cleaning solution are specified within the scope of the invention.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to an aqueous cleaning solution for removing rouging deposits that can form on media-contacting surfaces of corrosion-resistant, stainless steels. The aqueous cleaning solution contains at least one complexing agent to complex iron(II) ions and / or iron(III) ions. Furthermore, the invention provides uses of the cleaning solution according to the invention and methods for producing such a cleaning solution. STATE OF THE ART

[0002] Corrosion-resistant stainless steels, for example, alloyed with a high chromium content of at least 11.5%, can still corrode after a certain period of service after contact with certain media, especially hot pure water and / or pure steam. The resulting corrosion products are referred to as "rouging."

[0003] Particularly in production plants, for example in the pharmaceutical industry, the bioprocess industry and the semiconductor industry, as well as in medical technology plants or products that have to be sterilized on a regular basis using hot steam and / or with the help of special chemicals, depending on the application, after a certain period of operation, for example after several months or years, corrosion products in the form of rouging deposits can form on media-wetted surfaces of otherwise corrosion-resistant, stainless steels, which must be removed regularly.

[0004] In particular, ultrapure water of WFI (Water for Injection) quality, which is used in the aforementioned pharmaceutical, bioprocessing, semiconductor, and / or medical technology plants, is very aggressive towards the stainless steel surfaces of pipelines and vessels. The associated corrosion effects or rouging deposits, which appear on the media-wetted surfaces of such plants or plant components, are further intensified when degassed, heated ultrapure water or the pure steam generated with it are transported in such plants.

[0005] Depending on their nature and color, such rouging coatings can be divided into the following rouge classes 1, 2, or 3 according to the guideline for Bioprocessing Equipment (BPE) prepared by the American Society of Mechanical Engineers (ASME) (see ASME BPE Guideline, Appendix D): Rouge Class 1: The particulate rouging deposits consist of various iron oxides, primarily hematite (Fe2O3) with small amounts of Fe(II) oxides or hydroxides, and are easier to remove by wiping than other deposits. Such rouging deposits according to Rouge Class 1 are predominantly orange, orange-red, or brown in color. Rouge Class 2: Rouging deposits of Rouge Class 2 consist mainly of iron(III) oxide, hematite (Fe2O3), as well as chromium and / or nickel oxides and carbon, usually occur in both particulate and surface-bound form, and are only partially wipeable. The color spectrum of such rouging deposits ranges from orange-red to blue and purple to gray. The use of suitable cleaning chemicals is required to remove rouging deposits according to Rouge Class 2. Rouge Class 3: Rouging coatings according to Rouge Class 3 consist mainly of iron(II,III) oxide, magnetite orFe 3 0 4 , and occur as surface-bound layers that can no longer be wiped off. Particularly when used in pure steam systems up to 180°C, very solid, closed red to blue-black oxide layers can form. Such particularly stable rouging deposits according to rouge class 3, which contain iron(II,III) oxide, can usually only be removed using conventional etching processes, which damage or roughen the underlying steel surface in the process. This is particularly disadvantageous with electropolished surfaces, since rouging deposits can re-form particularly quickly on surfaces roughened by etching processes.

[0006] Without being bound by any theory, rouging appears to transform the media-wetted, corrosion-resistant steel surface layer from a chromium oxide-rich passive layer into an iron oxide-rich rouging layer, a process referred to as "rouge inversion." The resulting rouging deposits are thus a widespread corrosion effect, whereby the previously intact, chromium oxide-rich passive layer of a corrosion-resistant steel surface initially collapses locally due to environmental conditions, such as contact with hot, clean water, resulting in increased iron oxide formation as a corrosion effect on the steel surface.

[0007] In addition, rouging particles can detach from their original location due to flow processes and be transported to other locations within a production plant and deposited there again.

[0008] Various cleaning agents for removing rouging deposits are already known from the state of the art.

[0009] For example, EP 3 269 844 A1 discloses an aqueous cleaning solution consisting of several components for removing so-called blacking deposits from corresponding media-contacting surfaces of stainless steels. The term "blacking deposits" refers to stubbornly adhering magnetite layers that are dark in color and thus correspond to rouging deposits of rouging class 3. The proposed cleaning solution consists, among other ingredients, of an organic acid in the form of a saturated dicarboxylic acid or hydroxycarboxylic acid, preferably oxalic acid, an oxidizing agent, preferably hydrogen peroxide, and an inorganic fluoride, in particular ammonium bifluoride.

[0010] A disadvantage of the cleaning solution disclosed in EP 3 269 844 A1, however, is that the calcium and magnesium salts formed during the cleaning process, particularly when oxalic acid is used, are difficult to dissolve. Therefore, when cleaning steam systems with this cleaning solution, an additional upstream descaling step of the production facility to be cleaned with nitric acid is required, which is, however, complex. A further disadvantage of the cleaning solution disclosed in EP 3 269 844 A1 is that the use of dicarboxylic acid or hydroxycarboxylic acid, in particular oxalic acid, in combination with an inorganic fluoride, in particular ammonium bifluoride, which decomposes at the prevailing low pH values ​​of less than 2 (pH < 2), produces a pickling solution that undesirably etches stainless steel surfaces treated with it.This accelerates the formation of rouging deposits on steel surfaces roughened by etching. Furthermore, this cleaning solution is only suitable for single use and cannot be reused once the corrosion layer has been removed. Disposing of the contaminated pickling solution, however, is expensive and problematic for environmental reasons.

[0011] WO 2008 / 119533 A1 relates to a method for removing corrosion layers that can be used as a derouging solution. The corrosion remover contains both a biological complexing agent and a buffer system with an organic acid, which are mixed together so that the pH of the corrosion remover is between approximately 3 and 6.

[0012] One of the disadvantages is that this corrosion remover forms an anti-corrosive protective film on the treated metal surface after the corrosion layer has been removed, which is why the process known from WO 2008 / 119533 A1 is not suitable for cleaning tasks, particularly in the pharmaceutical, bioprocess or semiconductor industries.

[0013] The document DE 10 2015 114 481 A1 relates to an aqueous-neutral derouging solution containing sodium sulfite or potassium sulfite as a reducing agent and a multi-efficient acid that produces a dissolving effect and a complexing effect on metal(II) ions. The derouging solution may contain sodium thioglycolate and / or ascorbic acid as an additional reducing agent.

[0014] The use of harmful, toxic, and sensitizing (H317) sodium thioglycolate as a component of such a derouging solution is not only detrimental from an environmental perspective, but also no longer meets current safety requirements for the use of generic cleaning solutions for removing rouging deposits. If ascorbic acid is added to the derouging solution as an additional reducing agent, the reductive properties of the ascorbic acid are overshadowed by the reductive reaction conditions of the other components. In any case, the derouging solution disclosed in DE 10 2015 114 481 A1 is unsuitable for removing stubborn rouging deposits according to Rouge Class 3.

[0015] Furthermore, the publication US 2010 / 0078040 A1 discloses a method for using an aqueous cleaning solution to remove rouging deposits on stainless steels, where methylglycine or ethanoldiglycine, for example, can be used as complexing agents. However, the preparation and handling of this cleaning solution is complicated: The complexing agent is added later, after an inorganic reducing agent, preferably containing dithionite or disulfite, has been mixed into the aqueous solution. To increase the cleaning effect, the aqueous cleaning solution should be sprayed onto the corrosion layer to be removed in an oxygen-free protective gas atmosphere, preferably under a nitrogen blanket. In addition to the complicated handling, another disadvantage is that this cleaning solution has a reductive effect and is unsuitable for removing firmly adhering rouging deposits according to Rouge Class 3.

[0016] In summary, the conventional cleaning solutions known to date from the prior art for removing rouging deposits have at least the following disadvantages: In some cases, reducing agents are used to produce such conventional cleaning solutions, which are unstable, making their storage complex and expensive. Particularly under acidic conditions, the cleaning solutions known from the prior art can have a corrosive effect or develop an undesirable pickling effect. The steel surfaces to be cleaned are chemically attacked due to the undesirable etching processes that occur, and new rouging deposits form even more quickly on the steel surfaces in contact with the media after cleaning. Furthermore, the cleaning solutions and cleaning processes known from the prior art have disadvantages with regard to occupational safety for the persons handling them. OBJECT OF THE INVENTION

[0017] It is therefore an object of the invention to overcome the aforementioned disadvantages of the prior art and to provide an aqueous cleaning solution for derouging, i.e., for removing rouging class 3 rouging deposits on corrosion-resistant, stainless steels, which reliably and selectively dissolves rouging deposits without etching the underlying steel surfaces or roughening them through acid attack. Furthermore, an aqueous cleaning solution for derouging is to be provided that is easier to produce, store, and use than conventional cleaning solutions. Furthermore, it is an object of the invention to provide uses of the cleaning solution according to the invention and methods for producing such a cleaning solution. PRESENTATION OF THE INVENTION

[0018] To achieve the above-mentioned object of the invention, an aqueous cleaning solution for removing rouging deposits is provided, containing at least one complexing agent to complex iron(II) ions and / or iron(III) ions, wherein the cleaning solution further contains the following: at least one oxidizing agent, wherein the at least one oxidizing agent is a salt of peroxodisulfuric acid; at least one catalyst, wherein the at least one catalyst is a salt of hydrofluoric acid.

[0019] In addition to the aforementioned ingredients, the aqueous cleaning solution contains at least a portion of water. Depending on the application, the cleaning solution according to the invention can be provided as a ready-to-use one-component system with a comparatively larger proportion of water, with the aforementioned components already present in a diluted aqueous cleaning solution. A ready-to-use cleaning solution offers the advantage of simple and safe handling and is immediately ready for use for cleaning rouged surfaces without any further dosing or mixing steps.

[0020] Alternatively, the cleaning solution according to the invention can also be provided in the form of a concentrate with a comparatively lower proportion of water, which is diluted accordingly before use by the measured addition of water. In this case, the cleaning solution according to the invention, when formulated as a concentrate solution, forms a first component of a multi-component system, which must be suitably diluted with water as the second component in order to obtain a ready-to-use cleaning solution for removing rouging deposits. Providing a cleaning solution according to the invention as a concentrate solution offers the advantage that, for cleaning large production facilities in particular, a comparatively smaller volume of concentrated cleaning agent needs to be provided on site than is the case with a ready-to-use diluted cleaning solution with a higher water content.

[0021] Depending on the composition of such a concentrate solution and the respective storage conditions, in particular the respective storage temperature, the concentrate solution may have a comparatively high viscosity, be present as a suspension with a pasty consistency, or be provided as a saturated solution with a solid solid, for example, in the form of crystalline precipitates. As soon as such a concentrate solution is diluted with the appropriate amount of additional water, any inhomogeneities such as a solid solid or precipitate dissolve again upon stirring of the diluted cleaning solution, resulting in a ready-to-use cleaning solution with a homogeneous composition.

[0022] Due to simplified storage and logistics, the use of the cleaning solution according to the invention as a cleaning agent concentrate, which is only diluted on site by adding water to make it ready for use, can offer cost advantages and enable particularly economical and efficient system cleaning.

[0023] In its basic formulation, the aqueous cleaning solution according to the invention can consist of: a proportion of water; at least one oxidizing agent, wherein the at least one oxidizing agent is a salt of peroxodisulfuric acid; at least one complexing agent suitable for complexing iron(II) ions and / or iron(III) ions; at least one catalyst, wherein the at least one catalyst is a salt of hydrofluoric acid.

[0024] In preferred further embodiments of the invention, which are set out in the dependent claims and in the following description, the aqueous cleaning solution may further contain further components or ingredients.

[0025] According to the invention, at least one oxidizing agent is a salt of peroxodisulfuric acid. Peroxodisulfuric acid H 2 S 2 O 8 has a strong oxidizing effect. Its salts, the peroxodisulfates, are usually extremely soluble in water and are used as strong oxidizing agents.

[0026] For example, potassium peroxodisulfate (potassium persulfate, K 2 S 2 O 8 ), sodium peroxodisulfate (sodium persulfate, Na 2 S 2 O 8 ) and ammonium peroxodisulfate (ammonium persulfate, (NH 4 ) 2 S 2 O 8 ) may be mentioned as salts of peroxodisulfuric acid, which can be used as oxidizing agents in the cleaning solution within the scope of the invention.

[0027] The alkali metal salt sodium persulfate, cited as an example, advantageously exhibits a very high solubility of approximately 550 g / l (at 20°C) in water. Furthermore, sodium persulfate offers the advantage of high temperature stability and good storage stability, since the melting point of sodium persulfate is approximately 180°C, and thermal decomposition of this salt compound only occurs above this temperature. Along with its high temperature stability, the use of sodium persulfate as an oxidizing agent enables a controlled release of the oxidizing agent in the aqueous cleaning solution.

[0028] In comparison, the ammonium salt ammonium persulfate, mentioned as an example, begins to decompose thermally at temperatures of around 120°C and is therefore less stable for storage. However, ammonium persulfate also offers the advantage of very high solubility of around 620 g / l (at 20°C) in water.

[0029] Due to their high solubility in water, both sodium persulfate and ammonium persulfate are suitable for use as oxidizing agents, in particular for producing a cleaning solution according to the invention as a concentrate solution with a low water content.

[0030] In comparison, potassium persulfate has a lower solubility of approximately 50 g / l (at 20°C) in water. The use of potassium persulfate as an oxidizing agent is therefore particularly suitable for the preparation of a cleaning solution according to the invention in a ready-to-use, diluted formulation with a higher water content.

[0031] According to the invention, the cleaning solution contains at least one complexing agent which is suitable for complexing iron(II) ions and / or iron(III) ions.

[0032] Depending on the individual cleaning task, different complexing agents can be used to complex the iron(II) ions and / or iron(III) ions.

[0033] Ascorbic acid or amino acids, for example, can serve as complexing agents. These complexing agents are advantageously naturally occurring substances that are readily biodegradable.

[0034] Alternatively, salts of methylglycinediacetic acid (abbreviated to MGDA; C 7 H 8 NNa 3 O 6 ), in particular the trisodium salt of methylglycinediacetic acid, which forms stable chelate complexes with cations with a charge number of at least +2, can be used as complexing agents.

[0035] Likewise, salts of iminodisuccinates (abbreviated to IDS) can be used as complexing agents. For example, tetrasodium iminodisuccinate (also known as iminodisuccinate tetrasodium salt; C 8 H 7 NNa 4 O 8 ), a sodium salt of iminodisuccinic acid, is a possible complexing agent suitable for complexing iron(II) and / or iron(III) ions.

[0036] These complexing agents are also characterized by good biodegradability and good environmental compatibility.

[0037] The cleaning solution according to the invention contains at least one catalyst, wherein the at least one catalyst is a salt of hydrofluoric acid.

[0038] The salts of hydrofluoric acid or hydrofluoric acid (HF) are called fluorides, are usually particularly soluble in water, and exhibit good storage stability. Depending on availability, different fluorides can be used as catalysts in the invention.

[0039] For example, ammonium fluoride (NH 4 F) or ammonium bifluoride (ammonium hydrogen difluoride; NH 4 HF 2 ) can be used as acidic ammonium salts of hydrofluoric acid as catalysts in the cleaning solution. Alternatively, potassium fluoride (KF) or potassium hydrogen difluoride (KHF 2 ) can be used as potassium salts of hydrofluoric acid as catalysts in the cleaning solution. Likewise, sodium fluoride (NaF) or sodium hydrogen difluoride (NaHF 2 ) can be used as sodium salts of hydrofluoric acid as catalysts in the cleaning solution. The aforementioned fluorides, each of which is considered, differ slightly in their catalytic effect.

[0040] Due to the temperature stability and good storage capacity, it can be advantageous if the at least one oxidizing agent in the cleaning solution according to the invention is a metal salt of peroxodisulfuric acid, preferably potassium persulfate (K 2 S 2 O 8 ) or sodium persulfate (Na 2 S 2 O 8 ).

[0041] In order to be able to clean particularly stubborn or firmly adhering rouging deposits of rouge class 3, it can be advantageous if the cleaning solution according to the invention contains at least one further oxidizing agent, preferably hydrogen peroxide (H 2 O 2 ).

[0042] Possible further oxidizing agents which can be contained in or added to an aqueous cleaning solution according to the invention in order to increase its cleaning effect are, for example, cerium(IV) salt compounds or ozone (O 3 ).

[0043] It may be particularly advantageous if the cleaning solution according to the invention contains hydrogen peroxide or, if appropriate, hydrogen peroxide is added to the cleaning solution according to the invention.

[0044] Hydrogen peroxide is readily available, a largely stable liquid compound of hydrogen and oxygen, and acts as a very strong oxidizing agent against most substances. As such, it reacts violently with substances such as copper, brass, and potassium iodide, thus acting as a powerful bleaching and disinfectant. In aqueous solutions with a low, diluted concentration of less than 8 wt.% hydrogen peroxide, only general safety rules for handling are required.

[0045] Advantageously, the cleaning effect of the cleaning solution according to the invention for removing firmly adhering corrosion layers can be further increased by adding at least one further oxidizing agent, preferably hydrogen peroxide as a further oxidizing agent.

[0046] In a preferred embodiment of the invention, the at least one catalyst in the aqueous cleaning solution can be a metal salt of hydrofluoric acid, preferably potassium hydrogen difluoride (KHF 2 ) or sodium hydrogen difluoride (NaHF 2 ).

[0047] Metal salts of hydrofluoric acid are stable in storage and usually easily soluble.

[0048] Potassium hydrogen difluoride is a stable potassium salt of hydrofluoric acid with a melting point of approximately 240°C and a high solubility of approximately 180 g / l (at 20°C) in water. Potassium hydrogen difluoride also has the advantage of not decomposing, even at high process temperatures of, for example, 80°C in the cleaning solution, which can be achieved during the removal of rouging deposits, and of not lowering the pH value of the cleaning solution. Sodium hydrogen difluoride, as the hygroscopic sodium salt of hydrofluoric acid, has a slightly lower melting point of approximately 160°C and a lower solubility of approximately 33 g / l (at 20°C) in water.

[0049] Both alkali metal salts of hydrofluoric acid offer the advantage that the pH value of the cleaning solution remains constant even at higher catalyst concentrations, so that the cleaning solution according to the invention can also be used in the weakly acidic to pH-neutral range at pH values, for example, from pH = 5.0 to pH = 7.0.

[0050] In order to provide a cleaning solution according to the invention which acts as gently as possible, the at least one complexing agent can contain or be at least one amino acid, preferably glycine HOOC-CH 2 -NH 2 .

[0051] The use of one or more amino acids as complexing agents in a cleaning solution according to the invention offers the advantage that amino acids can be used in a correspondingly high concentration, if necessary, depending on the layer thickness of the corrosion residues or rouging deposits to be removed, without noticeably changing the pH value of the cleaning solution.

[0052] Amino acids such as glutamine or glycine act as comparatively weak complexing agents for iron(III) ions (Fe 3+< ) and can be advantageously used in cleaning solutions according to the invention for removing weak rouging deposits, preferably of rouge class 2.

[0053] The use of such a cleaning solution according to the invention with at least one amino acid as a complexing agent offers the advantage of extremely gentle removal of rouging deposits while simultaneously causing minimal side effects for the stainless steel surfaces being cleaned. Undesirable, aggressive etching of the base material to be cleaned can be virtually eliminated with proper application of the cleaning solution according to the invention in this mild formulation.

[0054] Glutamine has a higher complex formation constant than glycine. Glutamine's solubility in water (at 20°C) is approximately 35 g / l. As the smallest and simplest amino acid, glycine is preferred as a complexing agent for the cleaning solution according to the invention because thermal decomposition of glycine only begins at temperatures of approximately 230°C, allowing for particularly stable storage. Furthermore, glycine advantageously exhibits a high solubility of approximately 250 g / l (at 20°C) in water.

[0055] In this embodiment of the invention, in which at least one amino acid is used as a complexing agent for the preparation of the aqueous cleaning solution, a cleaning solution for the particularly gentle removal of rouging deposits, in particular of rouge class 2, can be provided, which has a pH value of 4.0 to 8.0, preferably a pH value of 5.0 to 7.0.

[0056] The slightly acidic to essentially neutral pH range of this cleaning solution offers clear advantages in terms of occupational safety when handling such a cleaning solution.

[0057] It may be particularly useful if, according to this embodiment of the invention, a ready-to-use cleaning solution is provided as a one-component system, which cleaning solution has the following composition: from 80 to 90% by weight of water, from 1 to 4% by weight, preferably from 2 to 3% by weight, of at least one salt of peroxodisulphuric acid, preferably potassium persulphate or sodium persulphate, from 1 to 4% by weight, preferably from 2 to 3% by weight, of at least one salt of hydrofluoric acid, preferably potassium hydrogen difluoride or sodium hydrogen difluoride, from 8 to 12% by weight, preferably from 9 to 11% by weight, of at least one amino acid, preferably glycine.

[0058] This ready-to-use cleaning solution is used for the gentle removal of rouging deposits and is particularly practical and safe to use. As already explained in detail above, this cleaning solution exhibits very high temperature stability and a long shelf life, as the listed ingredients are each stable. As a single-component system, this cleaning solution according to the invention can be provided on-site, for example, in a pharmaceutical, bioprocess, semiconductor, or medical technology facility, for use as needed to remove rouging deposits from plant components.

[0059] As an alternative to the aforementioned one-component system, it may be advantageous for logistical and economic reasons, particularly for applications where large quantities of cleaning solution are required to remove rouging deposits, to use the cleaning solution according to the invention as a two-component system, wherein the concentrated cleaning solution, i.e. the cleaning solution concentrate, has the following composition before dilution with water: from 10 to 20% by weight of water, from 8 to 18% by weight, preferably from 10 to 16% by weight, of at least one salt of peroxodisulphuric acid, preferably potassium persulphate or sodium persulphate, from 8 to 18% by weight, preferably from 10 to 16% by weight, of at least one salt of hydrofluoric acid, preferably potassium hydrogen difluoride or sodium hydrogen difluoride, from 54 to 64% by weight, preferably from 56 to 62% by weight, of at least one amino acid, preferably glycine.

[0060] The transport of such a concentrated cleaning solution, i.e. only the cleaning solution concentrate as the first component of a two-component system, is simpler and more cost-effective than using a ready-to-use cleaning solution as a one-component system. The cleaning solution concentrate is delivered to a pharmaceutical, bioprocessing, semiconductor, or medical technology facility and made available there, advantageously requiring only a reduced storage volume on site. If necessary, the cleaning solution concentrate can be diluted with water on site to obtain a ready-to-use cleaning solution for removing rouging deposits. When the cleaning solution concentrate is diluted with water, any precipitates in the concentrate dissolve, resulting in a homogeneous, ready-to-use cleaning solution. The cleaning solution concentrate can conveniently be stirred while water is being added.A further advantage is the increased storage stability of the concentrated cleaning solution due to the lower water content.

[0061] According to a further embodiment of the invention, in a particularly effective cleaning solution which is also suitable for removing rouging deposits of rouge class 3, the at least one complexing agent can be ascorbic acid (with the molecular formula C 6 H 8 O 6 ; IUPAC nomenclature: (5R)-5-[(1S)-1,2-dihydroxyethyl]-3,4-dihydroxy-5-hydrofuran-2-one ) or contain ascorbic acid.

[0062] The cleaning solution according to the invention, in which ascorbic acid (vitamin C) acts as a complexing agent, can be used in particular for the effective ablation of steam rouge layers of rouge class 3, which adhere firmly to media-wetted surfaces of stainless steel. Ascorbic acid is an excellent complexing agent for iron(II) ions (Fe2+<) and has the ability to reduce iron(III) ions (Fe3+<) to iron(II) ions (Fe2+<) in a so-called inner-sphere reaction. The ascorbic acid can then advantageously be oxidized again, for example by hydrogen peroxide (H2O2) and can then be reused essentially without loss or with only comparatively little consumption (make-up). The use of ascorbic acid as a complexing agent in a cleaning solution according to the invention is therefore not only particularly effective for cleaning particularly firmly adhering corrosion layers orof rouging coverings according to Rouge Class 3, but can also be recycled several times in a particularly sustainable manner, which is particularly economical and environmentally friendly.

[0063] In this embodiment of the invention, a cleaning solution with ascorbic acid as a complexing agent can be provided, which has a pH value of 1.0 to 5.0, preferably a pH value of 1.5 to 4.5.

[0064] This cleaning solution proves to be very effective for removing heavy rouging deposits of rouge class 3, such as steam rouge.

[0065] It may be particularly useful if, according to this embodiment of the invention, a ready-to-use cleaning solution as a one-component system has the following composition: from 82 to 97.5% by weight of water, from 0.5 to 4% by weight, preferably from 1 to 3% by weight, of at least one salt of peroxodisulfuric acid, preferably potassium persulfate or sodium persulfate, from 0 to 4% by weight, preferably from 0.5 to 3% by weight, of a further oxidizing agent, preferably hydrogen peroxide, from 0.5 to 4% by weight, preferably from 1 to 3% by weight, of at least one salt of hydrofluoric acid, preferably potassium hydrogen difluoride or sodium hydrogen difluoride, from 1.5 to 6% by weight, preferably from 2 to 5% by weight, of ascorbic acid.

[0066] This ready-to-use cleaning solution proves highly effective for removing heavy rouging deposits of Rouge Class 3, such as steam rouge. To further increase the cleaning effect, the cleaning solution may optionally contain up to 4% by weight of an additional oxidizing agent. Hydrogen peroxide can preferably be included in the cleaning solution as an additional oxidizing agent in a comparatively small proportion of up to 4% by weight, preferably 0.5 to 3% by weight. For safety reasons, a portion of the additional oxidizing agent, preferably hydrogen peroxide, can also be added later to the ready-to-use aqueous cleaning solution.

[0067] Particularly for applications where large quantities of cleaning solution are required to remove rouging deposits, it may be advantageous in this embodiment of the invention to use the cleaning solution according to the invention as a two-component system, wherein the concentrated cleaning solution has the following composition before dilution with water: from 10 to 20% by weight of water, from 16 to 26% by weight, preferably from 18 to 24% by weight, of at least one salt of peroxodisulphuric acid, preferably potassium persulphate or sodium persulphate, from 16 to 26% by weight, preferably from 18 to 24% by weight, of at least one salt of hydrofluoric acid, preferably potassium hydrogen difluoride or sodium hydrogen difluoride, from 38 to 48% by weight, preferably from 40 to 46% by weight, of ascorbic acid.

[0068] Reference is made to the advantages and beneficial effects mentioned above.

[0069] For safety reasons, it may be advantageous in a further development of the invention for the concentrated cleaning solution to be free of hydrogen peroxide. This variant of the invention advantageously improves the storage life of the concentrated cleaning solution, particularly when stored at higher temperatures in storage facilities with poor temperature control.

[0070] The object of the invention mentioned at the outset is also achieved by using a cleaning solution according to the invention according to claim 5 or 6, in which the at least one complexing agent contains or is at least one amino acid, preferably glycine HOOC-CH 2 -NH 2 , for removing rouging deposits containing iron(III) oxide at a cleaning temperature of 20 to 60°C, preferably at a cleaning temperature of at most 50°C.

[0071] As already explained at the beginning, rouging coatings containing iron(III) oxide mainly in the form of hematite Fe 2 O 3 are referred to as rouge class 2.

[0072] The moderate application temperatures mentioned offer advantages in terms of occupational safety when handling the cleaning solution according to the invention.

[0073] The use of a concentrated cleaning solution according to claim 7, which is adjusted by adding water to a proportion of 80 to 90 wt.% water in the diluted cleaning solution, can be particularly cost-effective and efficient in order to remove rouging deposits containing iron(III) oxide with this diluted, ready-to-use cleaning solution at a cleaning temperature of 20° to 60°C, preferably at a cleaning temperature of at most 50°C.

[0074] As already explained, the use of a concentrate simplifies logistics by reducing the number of transports, but also increases the storage stability of the concentrated cleaning solution due to the lower water content.

[0075] The object of the invention mentioned at the outset is also achieved by using a cleaning solution according to the invention according to claim 8 or 9, in which the at least one complexing agent contains or is ascorbic acid, for removing rouging deposits containing iron(II,III) oxide at a cleaning temperature of 20° to 80°C, preferably at a cleaning temperature of 30° to 70°C.

[0076] As already explained at the beginning, such rouging coatings that mainly contain iron(II,III) oxide in the form of magnetite or Fe 3 O 4 are referred to as rouge class 3. The iron(II,III) oxide-rich rouging coatings form particularly firmly bonded layers that can no longer be wiped off.

[0077] The moderate application temperatures compared to the use of conventional cleaning solutions offer advantages in terms of handling and occupational safety when using the cleaning solution according to the invention.

[0078] The use of a concentrated cleaning solution according to claim 10, which is adjusted by adding water to a proportion of 82 to 97.5 wt.% water in the diluted cleaning solution, in order to use this diluted, ready-to-use cleaning solution to remove rouging deposits containing iron(II,III) oxide at a cleaning temperature of 20° to 80°C, preferably at a cleaning temperature of 30° to 70°C, can be particularly cost-effective and efficient. If necessary, up to 4 wt.% hydrogen peroxide can then be added as a further oxidizing agent to the cleaning solution already diluted by adding water, in order to further increase the cleaning effect of the diluted, ready-to-use cleaning solution. It should be noted, however, that the cleaning solution as a concentrate without further oxidizing agent is usually longer lasting than after the addition of, for example, hydrogen peroxide H 2 O 2 .

[0079] In order to produce a ready-to-use cleaning solution according to claim 5 or 6 from a concentrated cleaning solution according to claim 7, a method according to the invention for producing a cleaning solution is provided, which comprises the following steps: Providing a concentrated cleaning solution according to claim 7; diluting the concentrated cleaning solution with water until a proportion of 80 to 90 wt.% water is established in the diluted cleaning solution.

[0080] We would like to point out again the advantages of using a cleaning agent concentrate already mentioned above - in particular the simplified logistics and increased storage stability of the concentrate.

[0081] In an alternative process variant according to the invention, a ready-to-use cleaning solution according to claim 8 or 9 can be prepared from a concentrated cleaning solution according to claim 10, wherein the process according to the invention comprises the following steps: Providing a concentrated cleaning solution according to claim 10; diluting the concentrated cleaning solution with water until a proportion of 82 to 97.5 wt.% water in the diluted cleaning solution is established; optionally admixing up to 4 wt.% hydrogen peroxide into the diluted cleaning solution. WAYS OF IMPLEMENTING THE INVENTION

[0082] In the following, some embodiments are given for removing rouging deposits using cleaning solutions according to the invention. Example A: pH-neutral steam derouging of thin rouging deposits

[0083] In this example, a vein clamp, i.e. a medical device coated with a homogeneous rouging coating with black discoloration according to rouge class 3, was cleaned with a cleaning solution according to the invention.

[0084] To prepare the cleaning solution, 2 g of potassium hydrogen difluoride KHF 2 , 2 g of potassium persulfate K 2 S 2 O 8 and 9 g of glycine were dissolved in 87 g of water at room temperature of around 25°C. The ready-to-use cleaning solution had a pH of 5.3. The cleaning solution was heated to 50°C and then the blackened vein clamp was placed in this heated cleaning solution. After 15 minutes of cleaning, the vein clamp was removed from the cleaning solution and the dark rouging deposits were completely removed from the vein clamp. The pH of the used cleaning solution after removal of the vein clamp was determined to be between 4.8 and 4.9. The cleaning solution used contained 87 wt.% water, 2 wt.% potassium hydrogen difluoride KHF 2 , 2 wt.% potassium persulfate K 2 S 2 O 8 and 9 wt.% glycine. Example B: Steam derouging of heavy rouging deposits

[0085] In this example, a material sample from the vessel wall of a steam line operating at approximately 140°C, which had been in use in a pharmaceutical production plant for more than 20 years, was cleaned with a cleaning solution according to the invention. The material sample to be cleaned exhibited crystalline, surface-bound magnetite deposits on the steam-exposed inner side, thus rouging deposits according to Rouge Class 3, consisting primarily of iron(II,III) oxide, magnetite, or Fe 3 O 4 .

[0086] To prepare the cleaning solution, 2 g of potassium hydrogen difluoride KHF 2 , 2 g of potassium persulfate K 2 S 2 O 8 , and 5 g of ascorbic acid were completely dissolved in 85 g of water at room temperature of approximately 25°C. The solution was then mixed with 6 g of a 35% hydrogen peroxide (H 2 O 2 ) solution. The ready-to-use cleaning solution had a pH of 4.3.

[0087] The ready-to-use cleaning solution was heated to 80°C, and then the sample material from the steam line contaminated with magnetite deposits was immersed in this heated cleaning solution. After 60 minutes of cleaning, the sample material was removed from the cleaning solution, and the rouging deposits were completely removed. The steam-exposed interior of the steam line was cleaned to a bright metallic finish. The used cleaning solution had a pH value of 2.7 after removal of the workpiece.

[0088] The cleaning solution used contained 89 wt% water, 2 wt% potassium persulfate K 2 S 2 O 8 , 2 wt% potassium hydrogen difluoride KHF 2 , 2 wt% hydrogen peroxide H 2 O 2 and 5 wt% ascorbic acid. Example C: Steam derouging of heavy rouging deposits

[0089] In this example, a material sample from a plate heat exchanger was cleaned. Non-wipeable, firmly adhering rouging deposits of Rouge Class 3 were present on both the steam side, i.e., the side of the plate heat exchanger exposed to superheated steam, and the water side of the material sample to be cleaned, opposite the steam side and exposed to water. The firmly adhering rouging deposits on the steam side ("steam rouge") and on the water side of the plate heat exchanger each had a powdery surface structure.

[0090] For the cleaning solution used in Example C, approximately half the concentration of the cleaning solution previously used in Example B was used.

[0091] To prepare the cleaning solution, 40 g of potassium hydrogen difluoride KHF 2 , 40 g of potassium persulfate K 2 S 2 O 8 , and 100 g of ascorbic acid were completely dissolved in 3700 g of water at room temperature of approximately 25°C. The solution was then mixed with 120 g of a 35% hydrogen peroxide (H 2 O 2 ) solution. The ready-to-use cleaning solution had a pH of 4.0.

[0092] The ready-to-use cleaning solution was heated to 70°C, and then the material sample of the plate heat exchanger contaminated with magnetite deposits was immersed in this heated cleaning solution. After 60 minutes of cleaning, the material sample was removed from the cleaning solution, and the rouging deposits were completely removed except for a few localized areas. The used cleaning solution was orange in color and had a pH value of 2.5 after removal of the workpiece.

[0093] The cleaning solution used contained 94.5 wt% water, 1 wt% potassium persulfate K 2 S 2 O 8 , 1 wt% potassium hydrogen difluoride KHF 2 , 1 wt% hydrogen peroxide H 2 O 2 and 2.5 wt% ascorbic acid.

[0094] The used cleaning solution was then heated again to 60°C, and the pre-cleaned material sample of the plate heat exchanger was immersed in the heated cleaning solution for another 120 minutes. After removing the material sample from the cleaning solution again, it was found that even the previously present locally adhering rouging deposits had been satisfactorily cleaned after the second cleaning.

[0095] In the used cleaning solution, another material sample was also cleaned: a pipe section of a (black) steam line with external rouging deposits and internal "steam rouge" deposits, each of Rouge Class 3. This additional material sample was also cleaned at a used cleaning solution temperature of 60°C for a cleaning time of 120 minutes. After cleaning this material sample, the firmly adhering rouging deposits on both sides of the steam line were completely removed. A visual inspection using a microscope showed bright metallic surfaces on both sides of the steam line.

Claims

1. Aqueous cleaning solution for removing rouging deposits, containing at least one complexing agent to complex iron(II) ions and / or iron(III) ions, characterized in that the cleaning solution further contains: - at least one oxidizing agent, wherein the at least one oxidizing agent is a salt of peroxodisulfuric acid; - at least one catalyst, wherein the at least one catalyst is a salt of hydrofluoric acid.

2. Cleaning solution according to claim 1, characterized in that the at least one oxidizing agent is a metal salt of peroxodisulphuric acid, preferably potassium persulphate or sodium persulphate.

3. Cleaning solution according to claim 1 or 2, characterized in that the cleaning solution contains at least one further oxidizing agent, preferably hydrogen peroxide.

4. Cleaning solution according to one of claims 1 to 3, characterized in thatthe at least one catalyst is a metal salt of hydrofluoric acid, preferably potassium hydrogen difluoride or sodium hydrogen difluoride.

5. Cleaning solution according to one of claims 1 to 4, characterized in that the at least one complexing agent contains or is at least one amino acid, preferably glycine, wherein the cleaning solution preferably has a pH of 4.0 to 8.0, particularly preferably a pH of 5.0 to 7.

0.

6. Cleaning solution according to claim 5, having the composition: - from 80 to 90 wt.% water, - from 1 to 4 wt.%, preferably from 2 to 3 wt.%, of at least one salt of peroxodisulphuric acid, preferably potassium persulphate or sodium persulphate, - from 1 to 4 wt.%, preferably from 2 to 3 wt.%, of at least one salt of hydrofluoric acid, preferably potassium hydrogen difluoride or sodium hydrogen difluoride, - from 8 to 12 wt.%, preferably from 9 to 11 wt.%, of at least one amino acid, preferably glycine.

7. Concentrated cleaning solution according to claim 5, having the composition: - from 10 to 20 wt.% water, - from 8 to 18 wt.%, preferably from 10 to 16 wt.%, of at least one salt of peroxodisulfuric acid, preferably sodium persulfate, - from 8 to 18 wt.%, preferably from 10 to 16 wt.%, of at least one salt of hydrofluoric acid, preferably potassium hydrogen difluoride, - from 54 to 64 wt.%, preferably from 56 to 62 wt.%, of at least one amino acid, preferably glycine.

8. Cleaning solution according to one of claims 1 to 4, characterized in that which contains or is at least one complexing agent ascorbic acid, wherein the cleaning solution preferably has a pH of 1.0 to 5.0, particularly preferably a pH of 1.5 to 4.

5.

9. Cleaning solution according to claim 8, having the composition: - from 82 to 97.5 wt.% water, - from 0.5 to 4 wt.%, preferably from 1 to 3 wt.%, of at least one salt of peroxodisulfuric acid, preferably potassium persulfate or sodium persulfate, - from 0 to 4 wt.%, preferably from 0.5 to 3 wt.%, of at least one further oxidizing agent, preferably hydrogen peroxide, - from 0.5 to 4 wt.%, preferably from 1 to 3 wt.%, of at least one salt of hydrofluoric acid, preferably potassium hydrogen difluoride or sodium hydrogen difluoride, - from 1.5 to 6 wt.%, preferably from 2 to 5 wt.%, of ascorbic acid.

10. Concentrated cleaning solution according to claim 8, having the composition: - from 10 to 20 wt.% water, - from 16 to 26 wt.%, preferably from 18 to 24 wt.%, of at least one salt of peroxodisulfuric acid, preferably sodium persulfate, - from 16 to 26 wt.%, preferably from 18 to 24 wt.%, of at least one salt of hydrofluoric acid, preferably potassium hydrogen difluoride, - from 38 to 48 wt.%, preferably from 40 to 46 wt.%, of ascorbic acid, wherein the concentrated cleaning solution is preferably free from a further oxidizing agent, particularly preferably free from hydrogen peroxide.

11. Use of a cleaning solution according to claim 5 or 6 for removing rouging deposits containing iron(III) oxide at a cleaning temperature of 20° to 80°C, preferably at a cleaning temperature of at most 50°C.

12. Use of a cleaning solution according to claim 8 or 9 for removing rouging deposits containing iron(II,III) oxide at a cleaning temperature of 20° to 80°C, preferably at a cleaning temperature of 30° to 70°C.

13. Use of a concentrated cleaning solution according to claim 10 after dilution with water to a proportion of 82 to 97.5 wt.% water in the diluted cleaning solution, wherein optionally up to 4 wt.% of at least one further oxidizing agent, preferably hydrogen peroxide, is added to the water-diluted cleaning solution, for removing rouging deposits containing iron(II,III) oxide at a cleaning temperature of 20° to 80°C, preferably at a cleaning temperature of 30° to 70°C.

14. A method for producing a cleaning solution according to claim 5 or 6, comprising the following steps: - providing a concentrated cleaning solution according to claim 7; - diluting the concentrated cleaning solution with water until a proportion of 80 to 90 wt.% water in the diluted cleaning solution is established.

15. A process for producing a cleaning solution according to claim 8 or 9, comprising the following steps: - Providing a concentrated cleaning solution according to claim 10; - Diluting the concentrated cleaning solution with water until a proportion of 82 to 97.5 wt.% water is established in the diluted cleaning solution; - Optionally, admixing up to 4 wt.% of at least one further oxidizing agent, preferably hydrogen peroxide, into the diluted cleaning solution.

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