DE10257391A1 - Continuous or discontinuous machine dishwashing of soiled tableware comprises applying acidic aqueous cleaning solution to soiled tableware and performing alkaline treatment before and/or after acidic treatment - Google Patents

Abstract

Continuous or discontinuous machine dishwashing comprises applying an acidic aqueous cleaning solution to the soiled tableware; and removing the acidic aqueous cleaning solution and the soil in at least one following step. At least one alkaline treatment takes place before and/or after the acidic treatment. The alkaline and acidic aqueous cleaning solutions at least partially neutralize one another. Independent claims are also included for: (1) an institutional dishwashing machine comprising several tanks arranged adjacent one another in known manner on the cascade principle and from which rinse or wash liquor is sprayed onto the tableware and then drains back into the tanks, wherein the tanks intended for acidic cleaning steps are made of and/or lined with acid-resistant material; and (2) a single-tank washing machine, e.g. a domestic dishwasher, made of and/or lined with acid-resistant material, particularly in the places where it comes into contact with acidic cleaning solutions.

Description

The present invention relates rely on a mechanical process for cleaning dishes or other surfaces contaminated with food residues. there it is particularly about the continuous or discontinuous Process of automatic dishwashing, which is both simple and also multi-tank machines exercised can be improved.

Usually Dishwashing methods are carried out in such a way that the dishes soiled with leftovers, for example Trays, cutlery and lipstick residues include glasses in a pre-wash zone or in a pre-wash cycle, i.e. before the actual one Washing process, sprayed with water or outshines become. This water is cold or preheated fresh water, cooling water phrase condensation, but mostly overflow water from a wash liquor, which is usually sprayed onto the dishes at low pressure and through relatively large wash arm openings becomes. Following this prewash zone or prewash cycle the dishes get into the actual washing zone or the washing cycle, where the dishes are sprayed with a washing liquor.

The wash liquor usually exists from water with a temperature of about 50 ° C to 65 ° C, to which a cleaner is added is. For fats, starches, Dyes and protein with sufficient security to remove the water z. B. powdery or liquid Detergent added, with the result that about 0.1 to 0.3% by weight of active washing substances in the cleaning solution available. The resulting wash liquor is usually different arranged nozzles sprayed on the objects to be cleaned. On this removes the dirt on the dishes, at least swollen or softened and partially released. In a subsequent rinse zone or in a rinse cycle the swollen or softened food or dirt residues are removed with water. At the same time, the wash liquor is rinsed off. In the subsequent rinsing step with rinse water this usually exists from fresh water and a rinse aid, which usually ensures that just a wafer-thin film of water remains on the dishes that run in downstream drying zones and / or evaporate.

The machine requirements are different depending on the application in the commercial and household sector. The cleaning machines contain in the commercial area depending on the type and area of application several tanks arranged one behind the other, from which rinsing or Wash liquor is sprayed against the laundry passing through the machine. The tanks are usually cascaded together, whereby the flushing or wash liquor, the tanks one after the other from the wash goods outlet end to Laundry inlet end goes through. At the outlet end fresh water is usually supplied to the machines. The needed amount of detergent is also in at least one as a metering tank designated wash tank dosed. Usually detergent is dosed automatically depending on of conductivity or the pH of the wash liquor or, if appropriate, also by means of a time or clock controlled dosing pump. It may also be possible that separate dosing of several components takes place. For example it happens that a lye-based solution based on an aqueous Alkali hydroxide solution is presented. This basic solution can then be used as needed or added several additives become. The dosage of these additives usually takes place proportional to the addition of the base lye or time-controlled. If desired, The dosage of the additives can also depend on the cycle of the laundry transporting the machine Chain. Furthermore, dosing of additives or the increase in the additive concentration due to the detection of the Proportion of additive in the base lye via sensory detection of a Tracers, which is contained in the additive, possible.

Like in the EP 282 214 was a frequently occurring problem in the past that even with the use of relatively large amounts of cleaning agents in regular conventional cleaning, periodic basic cleaning steps could not be completely dispensed with. The purpose of basic cleaning is to remove deposits that have built up over the course of time but are not immediately optically recognizable from water-insoluble starch in particular. During this basic cleaning, the objects, preferably the dishes, are occasionally treated with washing liquor which contains a multiple of the usual concentration of active substances. This represents a heavy pollution of the wastewater EP 282 214 apart. By improving the efficiency of cleaning, attempts have been made to reduce the amount of work, the water and chemical consumption and thus also the burden on the environment, while at the same time ensuring that cleaning is carried out sufficiently well. The EP 282 214 tries to solve the problem by spraying a highly concentrated cleaning formulation onto the soiled objects, followed by an exposure phase, and then removing the cleaning solution and dirt in one or more subsequent stages.

As stated, the EP 282 214 as an essential aim of the invention to reduce the pollution of the waste water. Nevertheless, a closer look at the entire process makes it clear that an essential aspect was not taken into account in the pollution of wastewater. When treating wastewater, it is usually imperative that the wastewater corresponds to before or during treatment corresponding treatment plants has a certain pH value. Depending on the type of preparation, this pH value is usually close to the neutral point of water. Depending on the legislation, there are even country-specific wastewater regulations that prescribe a specific pH value for the wastewater. This means nothing more than that in the case of strongly acidic or strongly alkaline wastewater, chemicals have to be added again for neutralization before further treatment. In other words, the chemistry involved in the cleaning process according to the EP 282 214 can be saved, on the one hand, no longer pollutes the wastewater, on the other hand, however, chemicals have to be used afterwards to neutralize the wastewater flowing off before the water treatment. The bears this problem EP 282 214 in no way bill. On the contrary, in the entire revelation of the EP 282 214 only alkaline cleaning agents are mentioned and recommended. For example, column 3 from line 15 explicitly deals with the cleaning agents to be used. From column 3, line 24 in particular, it is disclosed that, for example, alternating spraying with high alkalinity and subsequent lower alkalinity could have advantages. It is then explained that a further advantage of the system is that chemicals which are usually not compatible with one another, for example oxidizing substances such as hypochlorite with water treatment substances such as NTA, could be used alongside one another in the process. Below in column 3 from line 42 it is stated that various substances are known which can improve penetration and promote the dissolving and detaching of the dirt. Furthermore, the EP 282 214 A1 from that a basic formulation will typically contain a source of alkalinity and a source of a sequestering agent. Based on such formulations, it is possible to prepare for special problems, such as tea residues or other residues that can appear on dishes. When reading these passages of text EP 282 214 and even when reading the example following in column 4 from row 3, it is inevitable for the person skilled in the art that it is customary to carry out such processes with alkaline formulated agents. All the more so since this also corresponds to current practice. In practice, however, the problem arises that, due to the high amounts of alkalinity, which, depending on the process, can be attributed to high amounts of alkaline cleaning solutions and / or to high concentrations of alkaline detergent substances, the resulting wastewater has a high pH , So it is also and precisely when the teaching of the present is followed EP 282 214 required, often even prescribed by wastewater regulations, to neutralize the alkalinity used for the cleaning process before or during the treatment of the wastewater with acids to a certain pH value.

Accordingly, the object of the present invention was to provide a method which, on the one hand, with respect to the cleaning in the EP 282 214 posed problem without having to do basic cleaning. In addition and in delimitation to EP 282 214 the object of the present invention was to keep the effort for neutralization before or during treatment in wastewater treatment plants as low as possible. If possible, care should be taken to ensure that the application requirements with regard to mechanical and other requirements are met.

• a) das Aufbringen einer sauren wässrigen Reinigungslösung auf das zumindest teilweise verschmutzte Geschirr, und
• b) die Entfernung der genannten sauren wässrigen Reinigungslösung und des Schmutzes in einem oder mehreren Folgeschritten,

wobei die mindestens eine alkalische Behandlung vor und/oder nach der sauren Behandlung stattfinden kann und sich die alkalische und mindestens eine saure wässrige Reinigungslösung wenigstens teilweise neutralisieren.The present invention relates to a process for the continuous or discontinuous mechanical cleaning of dishes, in which the dishes are treated at least in one process step with an acidic solution and in another process step with an alkaline cleaning solution

• a) the application of an acidic aqueous cleaning solution to the at least partially soiled dishes, and
• b) the removal of said acidic aqueous cleaning solution and the dirt in one or more subsequent steps,

wherein the at least one alkaline treatment can take place before and / or after the acidic treatment and the alkaline and at least one acidic aqueous cleaning solution are at least partially neutralized.

In the method according to the invention, that said acidic cleaning solution selected one or more acids contains the mineral and / or organic acids, with particular preference at least one acid that is selected is from sulfuric acid, Nitric acid, Phosphoric acid, formic acid, Acetic acid, propionic acid, Glycolic acid, Citric acid, maleic acid, Lactic acid, gluconic acid, alkanesulfonic acid, amidosulfonic acid, succinic acid, glutaric acid, adipic acid, phosphonic acids, polyacrylic acids or Mixtures of the same and very particularly preferably of formic acid, glycolic acid, gluconic acid, amidosulfonic acid or the alkanesulfonic acids, especially methanesulfonic acid or mixtures thereof is.

The aqueous acid to be sprayed on according to the invention preferably contains cleaning solution as further components a corrosion inhibitor and / or a conventional one Complexing agents, particularly preferably selected from the phosphonic acids, in particular Dioctylphosphonsäure.

In the context of the method according to the invention, it is also preferred that the acidic cleaning solution mentioned contains between 0.01 and 10% by weight, based on one or more washing-active substances the cleaning solution, it being particularly preferred if said acid cleaning solution contains less than 0.9% by weight, very particularly preferably less than 0.8% by weight and in particular less than 0.5% by weight or more washing-active substances, based on the cleaning solution.

The exact conditions depend even according to the more specific circumstances in practice and the application requirements for the Method. Exists, for example, due to the specified plant-specific circumstances in practice, there is a risk of corrosion if the acid concentration is too high in the acidic cleaning solution, then it is recommended to use weakly acidic cleaning solutions an active acid content of less than 0.9% by weight, very particularly preferably less than 0.8 wt .-% and in particular less than 0.5 wt .-% to use. Depending on the machine requirements, weakly acidic cleaning solutions can also have the advantage that the consumption in the caustic baths, in the possibly acidic solution is carried away, is not too high.

Apart from the application technology requirements, when considering the overall process, this method of operation is also delimited EP 282214 due to the partial neutralization, less polluted waste water is reached. This ensures that less effort is required before further treatment of the wastewater.

When carrying out the method according to the invention it is further preferred that said acidic aqueous cleaning solution via a certain contact time (during who doesn't spray any further will) act on the dishes and dirt, whereby the contact time is preferably 2 to 100 seconds, particularly preferably 5 to 100 seconds and most preferably 8 to 25 seconds is, it is also preferred if the dishes during the the contact time mentioned is not deliberately sprayed.

In a further preferred embodiment the acid cleaning solution mentioned is a fine, gentle mist-like spray sprayed on the dishes.

Another preferred embodiment of the method according to the invention is that the acidic cleaning solution mentioned as Foam is applied to the dishes.

It is at this point noted that other conceivable forms of application are also in question come or the success of the method does not depend on the type of application depends alone. For example one said cleaning solution also by dripping or by thin film cleaning on the market (TFC) apply known Ecolab processes to the dishes.

It is preferred that depending on Type of application for this suitable nozzles or other aids are used. Preferably at execution of the method according to the invention the said acidic cleaning solution before the last rinse cycle or the last rinse zone applied.

There is also a preferred one embodiment of the method according to the invention in that before treatment with the acidic cleaning solution mentioned, a Alkaline treatment of the dishes takes place, their pH value especially preferably greater than 10, although it may also be preferred that after treatment an alkali treatment with the acid cleaning solution mentioned the dishes are made, but it is particularly preferred is when the dishes a total of at least three cleaning steps is subjected and before and after treatment with the aforementioned acidic cleaning solution an alkaline treatment of the dishes is carried out.

It should also be stated that for the Case that in the inventive method at least two alkaline steps occur, it is particularly preferred is that the previous alkaline step in the process order is a has a lower pH than that in the process order latter alkaline step. This is beneficial to the drain at one between the two alkaline steps mentioned acidic step if possible to keep low.

It is preferred in the above alkaline treatment in the process of the invention the dishes with one or more aqueous cleaning solutions Bring contact, preferably between 0.1 and 4 wt .-% of an alkali carrier of a hydroxide selected from sodium, potassium hydroxide or mixtures thereof.

As another preferred alkali carrier, in addition to or instead of hydroxides selected from sodium and potassium hydroxide Examples include alkali silicates, ethanolamines, such as triethanolamine, Diethanolamine and monoethanolamine and alkali carbonates of alkali carrier, preferably of a hydroxide selected made from sodium, potassium hydroxide. Of course, other alkali carriers can also be used as it is primarily a matter of raising the pH.

Another subject of the present Invention is directed to a commercial dishwasher, which contains several tanks which are cascaded together in a known manner and from which rinsing or washing liquor is sprayed against the dishes, then again to drain into the tanks, the tanks that are used when the inventive method for one or more acidic cleaning steps are provided, from more acid resistant ones Material exist and / or with acid-resistant Material are lined.

The present invention also relates to a one-tank washing machine, for example a domestic dishwasher which can be used in a method according to the invention and, in particular at the points which come into contact with acidic cleaning solutions, consists of acid-resistant material and / or is lined with acid-resistant material.

Examples

• a) 1 Minute reinigen mit einer 0,3 Gew.%igen wässrigen Lösung eines üblichen gleichbleibenden alkalischen Reinigungsmittels (ca. 17 Gew.% Alkalihydroxid, 14 Gew.% Tripolyphosphat und 1,5 Gew.% Alkalihypochlorit sowie ca. 1 Gew.% Alkali-Silikat und Rest Wasser).
• b) Flächendeckendes Einsprühen der Teller mit von Versuch zu Versuch andersartigen Ansprühlösungen, deren Zusammensetzung in Tabelle 1 näher beschrieben ist.
• c) 30 Sekunden einwirken lassen der aufgetragenen Ansprühlösung.
• d) 2 Minuten reinigen mit einer Lösung gemäß a).

For each experiment, 10 new, dry dinner plates are soiled with starch contamination at room temperature using a standardized test method. For this purpose, a composition containing about 6% aqueous maize starch is cooled to 75 ° C. after boiling and about 4 ml of this is applied to each plate with a brush. The plates treated in this way are left to stand for at least 3 hours and then allowed to dry for 16 hours at approx. 100 ° C. After the plates had cooled, comparative tests were carried out in a Krefft ^{© one-} tank dishwasher according to the following scheme.

• a) Clean for 1 minute with a 0.3% by weight aqueous solution of a common, constant alkaline cleaning agent (approx. 17% by weight alkali hydroxide, 14% by weight tripolyphosphate and 1.5% by weight alkali hypochlorite and approx. 1% by weight Alkali silicate and the rest water).
• b) Area-wide spraying of the plates with different spray solutions from test to test, the composition of which is described in more detail in Table 1.
• c) Allow the spray solution applied to act for 30 seconds.
• d) Clean for 2 minutes with a solution according to a).

The cleaning and spraying solutions were made available on the basis of softened water. The cleaning temperature in the Krefft ^® single-tank dishwasher was 60 ° C.

There were initially 6 attempts after the one described Scheme carried out maintaining the composition of the cleaning solutions a) and d) was and only the spraying solution from Try to try changed has been.

The cleaning results were ever after cleaning success with numbers of 1 (no cleaning success recognizable) to 10 (complete Removal of impurities).

The results of the 6 trials are can be seen from Table 1.

Table 1: Cleaning results in tests according to the described scheme, whereby only the spray solution was changed from test to test

As can be seen from Table 1, by far the best cleaning results in experiments 3 to 5 scored. Here came a spraying solution Methanesulfonic acid solution for Commitment. The cleaning principle existed for this very advantageous So in that case first alkaline, then acidic and then alkaline cleaned again.

Further research showed that similar Results also with other acids were to be achieved. The organic ones should be emphasized in particular acids formic acid, Glycolic acid, gluconic, amidosulfonic or other alkanesulfonic acids, in particular with an alkane chain of 1 to 4 carbon atoms.

As can be seen from this simple test arrangement, this pH change in use enables excellent cleaning results to be achieved even at acid concentrations below 0.5% by weight of active acid content. It is also clear that at lower acid concentrations the undesired partial neutralization within the cleaning process, for example due to the dishes Tender residual amounts of cleaning solution, which is treated in the next step with a cleaning solution of opposite pH value, to a lesser extent.

Claims (20)

Process for continuous or discontinuous machine cleaning of dishes in which the dishes at least in one process step with an acidic and in another Process step treated with an alkaline cleaning solution will be comprehensive a) applying an acidic aqueous cleaning solution on the at least partially soiled dishes, and b) the Removal of said acidic aqueous cleaning solution and the dirt in one or more subsequent steps, in which the at least one alkaline treatment before and / or after the acidic treatment can take place and the alkaline and at least an acidic watery cleaning solution at least partially neutralize. embodiment according to claim 1, characterized in that said acidic aqueous cleaning solution or more acids selected contains from the mineral and / or organic acids. embodiment according to claim 2, characterized in that at least one acid is present, the selected is from sulfuric acid, Nitric acid, Phosphoric acid, formic acid, Acetic acid, Propionic acid, glycolic acid, citric acid, maleic acid, lactic acid, gluconic acid, alkanesulfonic acid, amidosulfonic acid, succinic acid, glutaric acid, adipic acid, oxalic acid, benzoic acid, phosphonic acids, polyacrylic acids or Mixtures of the same. embodiment according to claim 3, characterized in that at least one acid is present, from formic acid, Glycolic acid, gluconic, amidosulfonic or the alkanesulfonic acids, especially methanesulfonic acid or mixtures thereof is. embodiment according to one or more of claims 1 to 4, characterized in that that said acidic aqueous cleaning solution between 0.01 and 10% by weight of one or more detergent substances, based on the cleaning solution, contains. embodiment according to claim 5, characterized in that said acid aqueous cleaning solution less than 0.9% by weight, preferably less than 0.8% by weight and particularly preferably less than 0.5% by weight of one or more wash-active Contains substances related to the cleaning solution. embodiment according to one or more of claims 1 to 6, characterized in that that one called the acidic aqueous Cleaning solution over a certain contact time (during who doesn't spray any further will act on the dishes and dirt, whereby the contact time of the acidic aqueous cleaning solution mentioned the dishes preferably 2 to 100 seconds, particularly preferably 5 to 100 seconds and most preferably 8 to 25 seconds is. embodiment according to claim 7, characterized in that the dishes during the the contact time mentioned is not deliberately sprayed. embodiment according to one or more of claims 1 to 8, characterized in that that said acidic aqueous cleaning solution as a fine, gentle mist-like spray sprayed on the dishes becomes. embodiment according to one or more of claims 1 to 8, characterized in that that said acidic aqueous cleaning solution is applied to the dishes as foam. embodiment according to one of the claims 9 or 10, characterized in that the application via suitable for this Nozzles are done. embodiment according to one or more of claims 1 to 11, characterized in that that said acidic aqueous cleaning solution before the last rinse cycle or the last rinse zone is applied. embodiment according to one or more of claims 1 to 12, characterized in that that before treatment with said acidic aqueous cleaning solution the dishes are alkaline. embodiment according to claim 13, characterized in that for said alkaline treatment the dishes are watery cleaning solution is used, whose pH is greater than 10. embodiment according to one or more of claims 1 to 14, characterized in that that after treatment with said acidic aqueous cleaning solution the dishes are alkaline. embodiment according to one or more of claims 13 to 15, characterized in that that the dishes a total of at least three cleaning steps is subjected to, before and after treatment with said acidic aqueous cleaning solution an alkaline treatment of the dishes is carried out. embodiment according to one or more of claims 13 to 16, characterized in that that with the alkaline treatment mentioned, the dishes with a or more aqueous cleaning solutions is brought into contact, preferably between 0.1 and 4 wt .-% of an alkali carrier of a hydroxide selected from sodium, potassium hydroxide or mixtures thereof. embodiment according to one or more of claims 1 to 17, characterized in that that the pH of the wastewater discharged from the process is below 12, preferably less than 11. Commercial dishwasher that has multiple tanks contains which are cascaded together in a known manner and from which rinsing or washing liquor sprayed against the dishes will to subsequently to run back into the tanks, characterized in that the Tanks that according to one or more of the claims 1 to 18 for one or more acidic cleaning steps are provided acid-resistant Material exist and / or with acid-resistant Material are lined. Single-tank washing machine, e.g. household dishwasher, the for a method according to a or more of the claims 1 to 16 is suitable, and on the basis of a method according to claims 1 to 18 with acidic cleaning solutions in touch coming out of acid resistant Material exists and / or with acid-resistant Material is lined.