CZ20003565A3 - Automatic check method and control of content of surface-active substances in aqueous cleansing agent - Google Patents

Abstract

The method consists in being programmatically controlled (a) take a sample from the aqueous working solution in advance (b) where appropriate, the sample is freed from solids; c) the sample is optionally diluted in a predetermined or as specified result of preliminary determination with water, d) the surfactant content is determined selective adsorption, electrochemically, chromatographically, cleaved to volatile compounds by displacement of volatile compounds by stripping and detecting them, or by adding a reagent thereto changes the interaction of the sample with electromagnetic radiation proportionally to the surfactant content and by measuring this change (e) the result of the determination is stored on one of the media and / or used as a basis for further calculations and / or the results of the determination and / or further calculations shall be \ t from which it is possible to initiate according to predetermined criteria interventions concerning the treatment of the bath.

Description

Technical field

The invention relates to a process for controlling and controlling aqueous process solutions containing anionic and / or cationic surfactants. Examples of such process solutions are alkaline scouring baths for large-scale textile washing, cleaning surfaces for hard surfaces, as well as surfactants containing iron phosphate solutions. In particular, the method is designed to solve technical processes in the metalworking industry, such as in the manufacture of automobiles. The method makes it possible to check the functional capability of the process solution, characterized by the "surfactant content" parameter, and, if necessary or automatically, to supplement or initiate other process interventions relating to the treatment of the bath, or on the basis of an external requirement. In particular, the method is designed so that the results of the determination of the surfactants can be transferred to a location remote from the site of the process solution. In addition, it is possible to interfere with the automatic measurement process from any location of the solution at a remote location or initiate additional dosing or other interventions concerning the treatment of the bath. For example, a "remote location of the process solution" can be found in one of the higher-level process control systems, the plant control center where the process solution is present, or even somewhere outside the plant.

BACKGROUND OF THE INVENTION

Cleaning metal parts before further processing is a standard task in the metalworking industry. For example, metal parts can be contaminated with pigment residues, dust, metal abrasion, corrosion-protecting oils, cooling lubricants, or molding aids. Such impurities must be removed with a suitable cleaning solution prior to further processing, such as in particular corrosion protection-related treatments (eg phosphating, chrome plating, anodizing, complex fluoride treatment, etc.) or painting. Spraying, dipping or combined processes are suitable. If surfactants containing aqueous process solutions which additionally contain phosphoric acid are used for the purification, in addition to the purification, so-called non-phosphating layers are also carried out simultaneously. At the same time, the cleaned metal parts are coated with an amorphous phosphate and / or oxide protection layer. Such methods as the combined cleaning and corrosion protection procedures are described in FIG.

Kov φ φ · ♦ · · Φ · Ι φ φφ metalworking industry considerably widespread. When used on iron-containing technical materials, they are abbreviated as 'iron phosphating'.

Non-phosphating industrial cleaning agents used in the metalworking industry are generally alkaline (pH values in the range of about 7 and above, for example 9 to 12). Their basic components are alkali (hydroxides, carbonates, silicates, phosphates, alkali metal borates), as well as non-ionic and / or anionic surfactants. Often, the detergent compositions also contain complexing agents (gluconates, polyphosphates, aminocarboxylic acid salts such as ethylenediaminetetraacetate or nitriloacetate, phosphonic acid salts such as hydroxyethane diphosphonic acid salts, phosphonobutantricarbonate salts, corrosion-protecting agents such as C 6 -C 12 -carboxylic acids, alkanolamines and suds inhibitors, such as, for example, C 6 -C 16 -alkoxy end-capped alkoxylates in the alkyl moiety If the cleaning baths contain no anionic surfactants, cationic surfactants may be used. The cleaning compositions may contain both non-ionic and ionic surfactants.

As nonionic surfactants, the detergent compositions generally comprise ethoxylates, propoxylates and / or ethoxylates / propoxylates of alcohols or C 6 -C 16 alkyl amines, which may also contain closed end groups. Alkyl sulfates and alkyl sulfonates are widely used as anionic surfactants. Alkylbenzene sulphonates may still be encountered, which are disadvantageous from an environmental point of view. Suitable cationic surfactants are, in particular, cationic alkylammonium compounds having an alkyl radical having 8 or more C atoms:

It is known in the art that nonionic surfactants can be determined manually in an aqueous process solution, such as in a cleaning bath, by means of a color indicator. Typically, a reagent is added to the sample taken from the process solution to form a colored complex with the nonionic surfactants. The color complex is preferably extracted into an organic solvent which is not miscible with water in any ratio and subsequently its light absorption at a certain wavelength is determined photometrically. Tetrabromophenolphthalein ethyl ester can be used as the coloring agent, for example. Before extraction into an organic solvent, preferably into • 4 ·····

4 · 4 · »» A chlorinated hydrocarbon is added to the process solution with some buffer solution for pH = 7.

It is further known that nonionic surfactants can be determined in the presence of ionic surfactants. The ionogenic surfactants are separated from the sample by means of ion exchangers. Non-ionic non-ionic surfactants not bound to the ion exchanger are determined by the refractive index column of the exiting solution.

For example, anionic and cationic surfactants can be detected in aqueous solutions by titration with Hyamine® 1622 (= N-benzyl-N, N-dimethyl-N-4 (1.1.3.3.-tetramethylbutyl) -phenoxy-ethoxyethylammonium chloride) and potentiometric determination of the end of the titration point. To this end, a known amount of sodium dodecyl sulfate is added to the sample, titrated with Hyamine, and the end point of the titration is determined using an ion-selective electrode.

As an alternative to this process, anionic surfactants can also be determined by titration with 1,3-didecyl-2-methylimidazolium chloride. An ion-selective membrane electrode is used as a detector. The electrode potential depends on the concentration of the measured ions in the solution.

According to the result of this determination of the surfactants associated with the expense of human labor, the equipment operating personnel replenishes the process solution with one or more replenishment component (s). Thus, this method requires the operating personnel to remain at the site of the apparatus at least at certain times of the determination of the surfactants. This method is therefore very demanding in terms of staff numbers, especially in multi-shift operation. Documentation of results for control and quality assurance is also an additional effort.

In contrast, the present invention aims to automate and document the control of process solutions by determining bath surfactants in such a way that at least the surfactant determination results are stored on a data carrier and / or printed. Preferably, the measuring device used should be self-monitoring and calibrated, and in case of malfunction it should send an alarm message to a remote location. Furthermore, it should preferably be possible to check the functional capability of the measuring device and the measurement results directly from a remote location. In addition, it should be possible to interfere with the measurement process and treatment interventions from a remote location. Trying for remote

4 4 · control should be achieved by reducing personnel expenditure on control and management of process solutions.

SUMMARY OF THE INVENTION

This task is solved by a method of automatic control and control of the surfactant content of a given aqueous process solution, with

a) take a sample of a predetermined discovery from the aqueous process solution,

b) the sample is freed from solids if desired,

(c) if desired, the sample is diluted with water in a predetermined or as a result of preliminary determination of the observed ratio;

(d) the surfactant content shall be determined by selective adsorption, electrochemical, chromatographic, cleavage into volatile compounds, stripping of volatile compounds by stripping and detecting them, or by adding an agent which alters the interaction of the sample with electromagnetic radiation in proportion to the surfactant content and

(e) the result of the determination is stored on a data carrier and / or used as a basis for further calculations and / or the result of the determination and / or further calculations is transferred to a remote location.

Particularly suitable as an aqueous process liquid is a solution of a cleaning agent for hard surfaces, in particular for metal surfaces or an iron phosphating solution. Such process solutions are well known in the art and are widely used in the metalworking industry.

In sub-step a), the sample volume taken can be firmly programmed in the control portion for the alkalinity measurement method of the measuring device used. It is preferred that the sample volume can be changed from a remote location. Further, the control program may be designed such that the volume of the sample to be used is bound to the result of the previous measurement. The sample volume can be selected, for example, the greater the lower the surfactant content of the process solution. The accuracy of the surfactant determination can be optimized in this way.

When referring to a "remote location" in the sense of the method of the present invention, this is understood to mean a location that is not in immediate or at least optical contact * * * · · · · ··· ♦ «· · ♦ ·· With working solution. For example, a “remote location” can be a central process control system that controls and controls a cleaning bath as part of a coherent way of treating metal surfaces. A "remote location" may also be the central control room from which the process as a whole is controlled and controlled and, for example, is located in a room other than the process solution. However, some off-site location is also considered as a “remote location”. This makes it possible for the operating solution to be checked and controlled by specialists who are away from the plant containing the operating solution. This solution becomes considerably more rare when specially trained personnel stay in place of the process solution.

Suitable data links by which the results of the surfactant determination as well as the control commands can be transmitted are available in the prior art.

Between sampling and actual measurement, it may be desirable to discard the sample by optional sub-step b) of solids. This procedure is not necessary for a process solution that is low on solids. However, at a high solids content, the valves of the measuring device may become clogged, and sensors, such as electrodes, may become clogged with dirt. Therefore, removal of solids from the sample can be recommended. This can occur automatically by filtration or by using a cyclone or centrifuge.

In sub-step c), the sample can optionally be diluted in a predetermined or as a result of a previously determined ratio with water. In sub-step d), the surfactant content is then determined by different methods, which will be explained in more detail below.

The result of the determination can then be stored in one of the data carriers in sub-step e). In addition or alternatively to this solution, the result can be used as a basis for further calculations. The result of the determination or the result of further processing can be transmitted to a remote location and stored there again on one of the data carriers and / or retrieved. The term 'result of the determination' means that the result is either passed on to a superior process control system or displayed in a human-readable form or printed. At the same time, instead of displaying, respectively. The result should be that the results of the individual determinations are stored for at least a predetermined period of time on one of the data carriers so that they can subsequently be used, for example, for quality assurance purposes. Determination of surfactant results tf tf tf tftfftf tff tff

However, substances as such may not be directly used as such to output data or to store them on data carriers. Rather, they can be used directly as a basis for further calculations, whereby the results of these additional calculations are displayed or stored. Instead of the actual surfactant concentration values at a given moment, for example, trends in surfactant concentration and / or their relative changes can be displayed, or the actual surfactant content values can be converted to "% of the nominal value".

In the simplest case, the method of the invention operates by repeating sub-steps a) to e) after a predetermined time interval. The predetermined time interval is governed by the requirements of the process solution operator and may include any arbitrary time interval from about 5 minutes to several days. For quality assurance, it is preferred that the time intervals entered are between 5 minutes and 2 hours, for example. Thus, for example, measurements can be made every 15 minutes.

However, it is also possible to carry out the process according to the invention in that steps a) to e) are repeated after as many shorter time intervals as the results of two successive determinations differ. Thus, the control system for the method of the invention can itself decide whether the time intervals between the individual determinations should be shortened or extended. Of course, it is necessary to give the control system a command at which differences between the results of two consecutive determinations should be selected which time intervals should be selected.

The process according to the invention can further be carried out by carrying out the sub-steps a) to e) at any desired time interval on the basis of an external requirement. Thus, for example, immediate monitoring of the surfactant content of the process solution can be carried out when quality problems are detected in successive process steps. Thus, the surfactant content can be measured by 'time-based' (at fixed time intervals) or 'event-based' (upon detected changes or due to external requirements).

Preferably, the invention according to the invention is carried out in such a way that the measuring device used is self-monitoring and, if necessary, additionally calibrated. For this purpose, it may be remembered that after a predetermined period of time or after a predetermined number of determinations, or on the basis of an external requirement, by means of control measurements of one or more standard solutions, the performance of the measuring device used is checked. In this control, a standard solution with a known surfactant content is measured with this control. This control corresponds most closely to reality when a standard process solution is used as the standard solution, the composition of which is as close as possible to the solution to be controlled.

It is also contemplated in the method of the present invention that, by means of control measurements of one or more standard solutions, the performance of the measuring device used is checked when two successive measurements differ by a predetermined value. By this procedure it is possible to distinguish whether the detected deviations in the surfactant content correspond to reality and whether they require intervention in the treatment of the bath or whether they are the result of an error in the measuring system.

Depending on the result of the inspection of the measuring equipment used, the determinations of the surfactant content made between the current and the previous inspection measurements can be labeled with a so-called status identifier, which indicates the reliability of these determinations. If, for example, successive control measurements aimed at checking the measuring device have shown that the device is operating faultlessly, the determination of the surfactant content can be provided with a status identifier "in order". If the results of the control measurements differ by a predetermined minimum difference, in the meantime, the determination of the surfactant content can be provided with a "doubtful" status identifier, for example.

It may also be remembered that depending on the result of the inspection of the measuring equipment used, the automatic determination of the surfactant content is continued and / or one or more of the following actions are performed: analysis of deviations detected, correction of the measuring device; , sending a status identifier or alarm signal to a superior process control system or monitoring device, i.e. to a remote location. Thus, the measuring device can, if desired, decide according to predetermined criteria whether it is sufficiently functional to continue to determine the surfactant content or whether deviations that require manual intervention are detected.

The process can be designed in such a way that the surfactants whose content is to be determined in the process solution are non-ionic surfactants. To determine these, some reagent may be added in sub-step d), which will change - V · V • and A and · · A «V A A A * A a A A A A A

AAAA AND AAA AAAA AA A * The interaction of the sample with electromagnetic radiation in proportion to the content of non-ionic surfactants, whereupon the changes in this interaction are measured.

Thus, for example, such an agent may be a complex of two substances A and B, wherein nonionic surfactants displace substance B from the complex with substance A, thereby changing the color or fluorescence properties of substance B. For example, substance B may be a fluorescent substance or a colorant which may complex for example with dextrans or starch as examples of substance A. As a component of the complex, substance B must have certain colors or fluorescence related to the property. When extruded from the complex, these properties change. By measuring the absorption of light or fluorescent radiation, it is then possible to detect what proportion of Compound B is not complexed with Compound A. In doing so, Compound A is selected such that by adding nonionic surfactants Compound B is extruded from the complex and instead forms complex with nonionic surfactants. In this case, the amount of complex A of the extruded substance B is proportional to the added amount of nonionic surfactants. From the change in light absorption or fluorescence caused by the amount of substance B released, the amount of niotensides added can be inferred.

As the reagent, for example, a tetrafenylborate ion cationic dye salt can be used. Nonionic surfactants can extrude the dye from this salt after it has been converted to a cationic barium complex by the addition of barium ions. This method of converting non-ionic surfactants to cationically charged complexes and thereby making them accessible to reactions that respond to cations is referred to in the literature as "activation" of nonionic surfactants. This method is described, for example, in Vyras K., Dvorak V., Zeeman 1: (1989) Analyst 114, p. 1435 and others. The amount of cationic dye released from the agent is proportional to the amount of nonionic surfactants present. If the absorption spectrum of the dye changes during this release, the amount of dye released can be determined by photometric measurement of a suitable absorbent belt.

This assay method can be simplified by using a suitable salt of a cationic dye which is soluble only in some organic, water-immiscible solvent, while the released dye as such is water-soluble and leads to the coloring of the aqueous phase. Of course, the reverse procedure is also suitable: a water-soluble salt of an organic dye is used, the released dye being soluble only in the organic phase. By releasing the dye in exchange for non-ionic surfactants and extracting the released dye.

The dye can always be determined photometrically in this phase in each phase until the second phase.

This assay method is also suitable for the determination of cationic surfactants. These substances are already positively charged to the person, so that the above described "activation" of barium cations is eliminated.

The agent may furthermore be a compound which itself forms a complex with anionic surfactants which exhibits color or fluorescence properties other than the free agent. Thus, for example, the optical region agent may be colorless while its complex with nonionic surfactants absorbs in the optical region of the electromagnetic oscillation, so it shows a certain color. Alternatively, the maximum light absorption, i.e. the color, of the unbound reagent differs from that of the complex with the nonionic surfactants. However, the agent may also exhibit certain fluorescent properties that change when complexed with nonionic surfactants. Thus, for example, the free agent can fluoresce while complexing with nonionic surfactants "quenches" the fluorescence. In all cases, the concentration of the complex formed by the agent and the nonionic surfactants and thus the concentration of the nonionic surfactants themselves can be determined by measuring the light absorption at the wavelength to be predetermined or by measuring the fluorescent radiation.

In sub-step d), an agent is preferably added which forms a complex with the non-ionic surfactants which can be extracted into an organic solvent which is not miscible with water in any ratio. The complex is then extracted from the non-ionic surfactants and the added reagent into an organic solvent that is not miscible with water in any ratio. This can occur by intensive mixing of the two phases, for example by shaking or preferably by mechanical stirring. After this extraction step, the contact of both phases is terminated so that the phases are separated into aqueous and organic phases. If desired, the completeness of the phase separation can be checked by suitable methods, such as by determining the electrical conductivity or by measuring turbidity caused by light absorption or scattering.

This is followed by the actual measurement of the surfactant content. To this end, the organic phase, which contains a complex of non-ionic surfactants and an added agent, is exposed to electromagnetic radiation which may interact with the organic phase

10 .....

Dissolved complex. As electromagnetic radiation, for example, visible or ultraviolet radiation can be used, whose absorption by the complex from non-ionic surfactants and from the added agent is measured. However, it is also conceivable, for example, to use an agent whose complex with non-ionic surfactants provides a characteristic signal in nuclear or electron spin resonance measurements. The signal strength, expressed as attenuation of electromagnetic oscillations in a given frequency band (absorption), can be correlated with the concentration of the complex. Emission effects can be used instead of absorption effects to determine concentrations. For example, a reagent whose complex with non-ionic surfactants in an organic solvent absorbs electromagnetic radiation of a certain wavelength and instead emits electromagnetic radiation of greater wavelength, the intensity of which is measured, may be selected. By way of example, measurement of fluorescence radiation by irradiating a sample with visible or ultraviolet light may in principle measure the interaction of the organic phase with electromagnetic radiation immediately after the phase separation in the same vessel in which the phase separation was performed. However, according to the measurement method used to determine the interaction of the organic phase with the electromagnetic radiation, it is preferable to drain the organic phase or part thereof and transfer it to a proper measuring device via suitable piping. In this way, cells which are most suitable for the measurement can then be advantageously used. In this sense, the preferred embodiment consists in separating the organic phase from the aqueous phase after sub-step f) (not mentioned so far !!!) and transferring it to the measuring device. In this separation of the organic phase, it is particularly recommended that the organic solvent, which is not miscible with water in any ratio, is some halogen-containing solvent with a specific gravity higher than water. After phase separation, the organic phase is then located at the bottom of the vessel and can be pumped down.

Suitable halogen-containing solvents are, for example, dichloromethane or higher-boiling halogenated hydrocarbons, in particular fluorine and chlorine-containing hydrocarbons, such as trifluorotrichloroethane. After use, these solvents must be disposed of in accordance with local legislation. Since this operation can be costly, it is possible to regenerate the solvent used, for example by mixing with activated carbon and / or distillation, and to use it again in carrying out this measurement method.

11 9999 9 9 9 9 9 9

In one preferred embodiment of the invention, a composition is added as an agent, which in the organic phase enters the color reaction with the nonionic surfactant. As an interaction of the organic phase with electromagnetic radiation, it is then possible to measure the absorption of light at a predetermined wavelength. A conventional photometer is suitable for this. For example, tetrabromophenolphthalein ethyl ester may be used as a coloring agent. In this case, a buffer solution for a pH of about 7 must be added to the process solution sample. For example, the buffer system may be an aqueous solution of acid and medium phosphates. Preferably, the amount of buffer is substantially greater than the amount of surfactant sample containing the process solution.

When using tetrabromophenolphthalein ethyl ester as a coloring agent, the light absorption measurement in sub-step g) is preferably performed at a wavelength of 610 nm,

In a preferred embodiment, the determination of the content of nonionic surfactants using 3,3,5,5-tetrabromophenolphthalein ethyl ester can be carried out as follows:

Prepare a solution of the indicator containing 100 mg of 3,3,5,5-tetrabromophenolphthalein ethyl ester in 100 ml of ethanol. In addition, a buffer solution is prepared by mixing 200 ml of a commercially available buffer solution for pH = 7 (acidic potassium phosphate / medium sodium phosphate) and 500 ml of a trimol potassium chloride solution with 1000 ml of water.

For the determination, 18 ml of said buffer solution is placed in a suitable container.

Add 2 ml of indicator. Add 50 μΐ of the sample solution. The combined solutions are stirred for about 3 minutes and then 20 ml of dichloromethane are added to the mixture. Then stir the contents of the container vigorously for approximately 1 minute. It then waits for the phases to separate, which may require 20 minutes for example. The organic phase is then separated and measured on a photometer at 610 nm. For example, a cuvette with a thickness of 10 mm is suitable as a cuvette for analysis. The surfactant content is determined by a calibration curve.

If the surfactant content is so small that the determination becomes uncertain, the volume for measuring the sample used can be increased. If the surfactant content is so high that light absorption is greater than 0.9, it is recommended to dilute the sample before measurement.

12 .....

· · * * * * * * * * * * * * * »» »»

Irrespective of the selected method, a correlation between the signal strength and the concentration of non-ionic surfactants must be established and stored prior to calibration using known-concentration surfactant solutions. When measuring light absorption, calibration may also be performed using suitable colored glasses. As an alternative to the previous calibration, the addition of a known surfactant / reagent complex of known concentration or a multiple increase in its concentration and re-measurement of the interaction with electromagnetic radiation can be inferred from the surfactant content of the sample.

As an alternative to determining the interaction of a non-ionic surfactant binding agent or a non-ionic surfactant from the extruded electromagnetic radiation complex, the content of nonionic surfactants can be determined chromatographically. Using this method, preferably any oils and fats are removed from the sample. This can be done, for example, with an absorbent. Thereafter, a sample, which may optionally contain ionic surfactants, is applied to a column of anionic and / or cationic ion exchangers, which is preferably arranged in the manner of a column for high pressure liquid chromatography. The concentration of the non-ionic surfactants in the solution which has been deionized and leaves the ion exchange column is preferably determined by refractive index. The quantitative evaluation is preferably carried out by the external standard method. The measurement is made by comparing the pure solvent from the reference cell and the solvent to the substance to be analyzed from the detector cell. Suitable solvents are water or a water / methanol mixture.

Before starting a series of measurements, the HPLC-type ion exchange system must be calibrated and the detector reference cell flushed with solvent for 20 minutes. Different concentrations of non-ionic surfactant solutions to be measured are used for calibration. Calibration solutions and sample solutions must be degassed for example in an ultrasonic bath for 5 minutes before being sprayed into an HPLC-like system. Defined degassing is important because of the sensitivity of refractive index detection to differing solvent qualities.

.......

· 4 4 • »* * * * * * * * * *

About ··

If a sample of the solution is mixed with methanol before it is applied to an HPLC-like ion exchange column, insoluble salts may precipitate. These must be filtered with a suitable microfilter prior to loading the sample into a system similar to HPLC.

This method is known for off-line determination of non-sulfated fractions in organic sulphates or sulphonates (DIN EN 8799).

The following method is also suitable for the determination of nonionic surfactants: The nonionic surfactants are resolved with hydrogen halide, preferably hydrogen iodide, to form volatile alkyl halides, preferably alkyl iodides. By introducing a gas stream into the sample, volatile alkyl alcohol genes are expelled and are detected with a suitable detector. The Electron Capture Detector is suitable for this detection. This procedure is known as a method for characterizing fatty acid ethoxylates (DGF Einheitsmethode H-III17 (1994)).

The surfactants may also be anionic surfactants. Their content in the sample solution is determined electrochemically during sub-step d). For this purpose, anionic surfactants are titrated with suitable reagents, the titration being monitored by varying the electrical potential of a suitable measuring electrode.

For example, the pH of the sample is adjusted to between 3 and 4, preferably to about 3.5, titrated with a titrating agent in the presence of ion-sensitive membrane electrodes and measuring the change in electrode potential. This method can be increased by adding to the sample one of the C 1 -C 3 alcohols, preferably methanol. 1,3-Didecyl-2-methylimidazolium chloride is particularly suitable as the titrant. Some ion-sensitive membrane electrodes, preferably PVC membranes, serve as the measuring electrode. Such an electrode is known as the "High Sense Electrode". A silver electrode is preferably used as the reference electrode. The potential is generated preferably by a specific interaction between the ion-carrier contained in the PVC-electrode and the ions to be determined in the solution to be measured. This interaction leads, in the form of an equilibrium reaction, to the transport of the measured ions from the solution to be measured into the membrane and thus to create a certain difference in electrical potential at the "solution / membrane" phase interface. This potential difference can be measured potentiometrically against a reference electrode. The amount of ion transport from the measured solution to the membrane is concentration-dependent. Theoretically, the relationship between the concentration of ions to be measured and the electrical potential can be described.

15 ··· · ··· · * ·· «· ··

Nemstovou equation. However, due to possible interferences, it is preferable to determine the relationship between the electrode potential and the concentration of ions to be measured by calibration with reference solutions.

In addition to anionic surfactants, cationic surfactants can also be determined in the process solution to be controlled. For this purpose, a method which is also suitable for the determination of anionic surfactants can be used. This method is also electrochemically determined. A predetermined amount of sodium dodecyl sulfate is added to the sample, titrated with Hyamine (N-benzyl-N, N-dimethyl-N-4 (1.1.3.3.tetramethylbutyl) -phenoxyethoxyethylammonium chloride) and the end point of the titration determined by ionogenic surfactant. electrode sensitive substances.

In addition to the aforementioned methods, methods for the determination of surfactants are those in which the surfactants are absorbed on suitable surfaces and the effects from which it is possible to deduce the surfactant occupancy of the surfaces are measured. Since the surface occupancy of the surfactants below the saturation state can be considered to be proportional to the surface area of the surfactants, after appropriate calibration, the surfactant content of the solution sample can be inferred from changes in the surface properties of the surfactants.

Thus, for example, the surfactants can be absorbed on the surface of the oscillating quartz crystal and measured changes in the oscillation frequency of the crystal. Another method consists in absorbing the surfactants on an optionally suitably treated light guide surface. This leads to a change in the refractive index as light passes from the light guide to the surrounding medium, which is reflected in the light guide's ability to conduct light. According to the refractive index, the light in the light guide diminishes differently or does not reach the end of the light guide at all at the end of the light guide. By comparing the light intensity at the end of the light guide with the light intensity supplied at the beginning, it is possible to determine the degree of surfactant occupancy of the light guide surface and thus the surfactant content in the surrounding medium. The complete reflection collapses at a certain surfactant content threshold, which can also be used to characterize the working solution surfactant content.

The process of the invention can be applied to any process solutions. In particular, it is designed for process solutions in the metalworking industry, such as in the manufacturing industry.

15 ···· · ··· ···· · · ··. The aqueous process solution may be, for example, a cleaning agent solution. Such detergent solutions are used, for example, to clean automobile bodies before phosphating. In the control and control of such detergent solutions, it can be remembered that when the surfactant content falls below a predetermined minimum or external requirement, some device is activated which dispenses one or more replenishers into the detergent solution. As a replenishment component, for example, a replenishment solution is included which contains all the active ingredients of the cleaning solution in the correct proportions. The make-up solution may contain, in addition to the controlled surfactants, other active ingredients of the cleaning solution, such as, for example, other surfactants, builders, alkalis, complexing compounds and corrosion inhibitors. Alternatively, the make-up solution may contain only surfactants, while the other active ingredients of the cleaning solution are dosed later, if necessary, by means of separate regulations, by means of stroke control or enforcement control.

In this case, it is possible to vary the size of the added dose as such or to change the time intervals between the individual additions in the case of predetermined added doses. This can be done, for example, by means of metering pumps or by weight control. In the method according to the invention, it is thus envisaged, on the one hand, that a certain amount of replenishment component is additionally metered into the process solution at certain deviations from the nominal value (in particular when the performance of the measuring device has been verified by control measurements). On the other hand, however, this additional dosage can also be carried out on the basis of an external requirement, for example from a remote location, independently of the actual surfactant content.

In another embodiment of the invention, the process solution is replenished depending on the throughput of a predetermined amount of replenishment component per unit of power. Thus, for example, it is possible to determine, for a body cleaning solution, how much of the replenishment component is added to each cleaned body. According to the present invention, the control of the surfactant content or the interruption of the basic dosage serves to enable the success of the predetermined addition to be controlled and documented, as well as to obtain a more constant method of operation of the cleaning bath. In this way, quality fluctuations can be reduced.

• · · · · · ·

4 »* 4 4 4 4 4 4 · 44 4 ·» · lg ··········· · ··

Preferably, the measurement system used in the present invention is designed to automatically control the loading and / or consumption states of the reagents used (color and fluorescent reagents, titration solutions, standard and test solutions, solvents, buffers, or auxiliary solutions) and, if it falls below the specified minimum fill level, it sends a warning message. In this way, it is possible to prevent the measuring device from becoming inoperable due to the lack of the necessary chemicals. Monitoring of filling conditions may be by known methods. For example, chemical containers can stand on scales that register the weight of chemicals at any time. Or a float may be used. Alternatively, the minimum fill level can be controlled by a conductive electrode immersed in a chemical container. The warning message to be sent from the measuring device is preferably transmitted to a remote location so that corresponding interventions can be initiated from there. In general, the method according to the invention provides that the results of the determination and / or control measurements and / or calibrations and / or status identifiers are transmitted to the remote location continuously or at predetermined time intervals and / or on demand. In this way, the control personnel, who do not need to be in the place of the process solution, are kept informed of the actual surfactant content. Depending on the results of the measurements and control measurements, the necessary corrective interventions can be carried out automatically via the process control system or by manual intervention.

The method according to the invention naturally assumes that the corresponding device is already available. The device comprises a control unit, preferably a computer control, which controls the course of the measurement as a function of time and / or events occurring. In addition, the equipment shall have the necessary reagent containers, piping, valves, dosing and measuring equipment, etc., to control and measure the sample streams. The materials should be adapted to the purpose of use, for example stainless steel and / or plastics. The control electronics of the measuring device should have an appropriate I / O interface to communicate with any remote location.

The method according to the invention makes it possible, on the one hand, to control the surfactant content of the process solutions on site and, without manual intervention, to initiate predetermined corrective actions. This increases process safety and achieves consistently reliable cleaning results. Deviations from the nominal values can be detected soon enough and these deviations can be automatically or manually corrected before the process result deteriorates. On the other hand, the measured data is preferably transferred to a remote location, so that the operator and supervisor conducting the operation are kept informed of the status of the process solution even when the φφΦΦΦΦΦΦΦΦΦΦΦΦφφφφ ·φφφφφφφφφ

17 ···· φ ······· · ··· not in its immediate vicinity. In this way, the need for personnel to control and control the cleaning bath can be substantially reduced. By documenting the data obtained by the method of the present invention, modern quality assurance requirements are met. Consumption of chemicals can be documented and optimized

Claims (31)

PATENT CLAIMS A method of automatically controlling and controlling the surfactant content of an aqueous cleaning solution, wherein the method is controlled by a program a) takes a sample of a predetermined volume from the aqueous process solution, b) the sample is freed from solids if desired, (c) if desired, the sample is diluted with water in a predetermined or as a result of preliminary determination of the observed ratio; (d) the surfactant content shall be determined by selective adsorption, electrochemical, chromatographic, cleavage into volatile compounds, ejection of such volatile compounds by stripping and / or detecting or adding an agent which alters the interaction of the sample with electromagnetic radiation in proportion to the surfactant content and interaction, (e) the result of the determination is stored on a data carrier / or used as a basis for further calculations and / or the result of the determination and / or further calculations is transferred to a remote location not in optical contact with the detergent solution and of anionic or cationic substances below a predetermined minimum value, some devices are activated which dispense one or more replenishers into the solution. Method according to claim 1, characterized in that the sub-steps a) to e) are repeated after a predetermined time interval. Method according to claim 1, characterized in that the sub-steps a) to e) are repeated after as many shorter time intervals as the results of two successive determinations differ significantly from one another. Method according to claim 1, characterized in that the sub-cocs a) to e) are carried out on the basis of an external requirement. Method according to one or more of Claims 1 to 4, characterized in that after a predetermined period of time or after a predetermined number of determinations, or • · · · ♦ · · 19 on the basis of an external requirement by checking measurements of one or more standard solutions, it checks the functional capability of the measuring equipment used. Method according to one or more of Claims 1 to 4, characterized in that, by means of control measurements of one or more of the standard solution (s), the performance of the measuring device used is checked when two successive measurements differ by a predetermined value. Method according to one or both of Claims 5 and 6, characterized in that, according to the result of the inspection of the measuring device used, between the current and the previous inspection measurements, the surfactant determinations are marked with a so-called status identifier. substances. Method according to one or both of Claims 5 and 6, characterized in that, depending on the result of the inspection of the measuring device used, the automatic determination of the surfactant content is continued and / or one or more of the following actions are performed: analysis of detected deviations; the device, terminating the determination of the surfactant content, sending a status identifier or alarm signal to a superior process control system or monitoring device. Method according to one or more of Claims 1 to 8, characterized in that the surfactants are non-ionic surfactants. 10. The method of claim 9, wherein in step d), an agent is added which alters the interaction of the sample with electromagnetic radiation in proportion to the surfactant content, and the change in the interaction is measured. 11. The method of claim 10, wherein the agent is a complex of two compounds A and B, wherein the nonionic surfactants displace compound B from the complex with substance A, thereby altering the color or fluorescence properties of compound B. • »····· · · 2 (Τ · 12. The method of claim 10, wherein the agent is a compound that forms a complex with anionic surfactants that exhibits different color or fluorescence properties than the free compounds. • · ·· 13. A process according to claim 12, wherein in step d), an agent is added which, with the nonionic surfactants, forms an extractable complex with any water-immiscible organic solvent in any ratio. the sample is extracted with an organic solvent, the phases are separated into aqueous and organic phases and the interaction of the organic phase with electromagnetic radiation is measured. 14. The process according to claim 13, wherein after phase separation, the organic phase is separated from the aqueous phase. Process according to one or both of Claims 13 and 14, characterized in that a halogen-containing solvent with a density greater than water is used as any water-immiscible organic solvent. Method according to one or more of Claims 13 to 15, characterized in that a compound is added as a reagent which, in the organic phase, enters the color reaction with the non-ionic surfactant and that the absorption of light is measured as the interaction of the organic phase with electromagnetic radiation. at a predetermined wavelength. 17. The process of claim 16 wherein the reagent is ethyl tetrabromophenolphthalein and the aqueous cleaning solution is mixed with a buffer solution for a pH = 7. 18. The method of claim 17, wherein the measurement of light absorption in sub-step g) is performed at a wavelength of 610 mm. 19. The method of claim 9, wherein the content of nonionic surfactants is determined by chromatography. Method according to claim 19, characterized in that, if desired, oils and fats are removed from the sample by means of an absorbent, optionally present ionic surfactant. ·· φφφφ The anionic and / or cationic ion exchanger column is removed and the change in refractive index of the solution which has been cleared of ionic surfactants leaving the ion exchanger column is measured. 21. The method of claim 9, wherein the nonionic surfactants are cleaved with hydrogen halide to form volatile alkyl halides, the volatile alkyl halides being stripped and then detected. Method according to one or more of Claims 1 to 8, characterized in that the surfactants are anionic surfactants whose content is determined electrochemically in sub-step d). The method according to claim 22, characterized in that the pH of the sample is adjusted to a value between 3 and 4, preferably to about 3.5, titrating the sample with a titrating agent in the presence of ion-sensitive membrane electrodes. and the change in electrode potential is measured. 24. The method of claim 23, wherein one of the C 1 -C 3 alcohols is added to the sample. The process according to one or both of claims 23 and 24, characterized in that 1,3-didecyl-2-methylimidazolium chloride is used as the titrating agent. Method according to one or more of Claims 1 to 8, characterized in that the surfactants are cationic surfactants whose content is determined electrochemically in sub-step d). 27. The method of claim 22 or claim 26, wherein a known amount of sodium dodecyl sulfate is added to the sample, and the sample is titrated with Hyamine (N-benzyl-N, N-dimethyl-N-4 (1,1,3.3). (tetramethyl-butyl) (phenoxyethoxyethylammonium chloride) and the end-point of the titration are determined using an ion-selective electrode. • t · t 4 »4 22 ··. * · ........... Method according to one or more of Claims 1 to 8, characterized in that the surfactants are adsorbed on the surface of the oscillating quartz and the crystal oscillation frequency changes are measured. Method according to one or more of Claims 1 to 8, characterized in that the surfactants selectively adsorb water to the light surface and detect the change in the refraction of light on the light guide surface. Method according to one or more of Claims 1 to 29, characterized in that the filling states and / or the consumption of the reagents used are automatically checked and a warning message is issued when the filling level falls below a specified minimum filling level. Method according to one or more of Claims 1 to 30, characterized in that the results of the determination and / or control measurements and / or calibrations and / or status identifiers are transmitted continuously or at predetermined time intervals and / or or a site requirement different from the site.