Methods for preparing dry-strengthening compounds, especially glyoxylated polyacrylamide.

Abstract

The invention relates to a method for producing a dry strengthening agent, particularly glyoxalated polyacrylamide, in which ethanedial (glyoxal) is added to an aqueous solution of polyacrylamide while being agitated with a circulation pump. In said method, the reaction is started by adding a base, particularly a strong base at a basic pH value, particularly a pH value of higher than 8, and is left to react while being agitated and / or circulated, and once a predetermined reaction time has passed, the reaction is stopped by adding an acid while being agitated and / or circulated. The method is carried out as a discontinuous method in which a quantitative reaction of the ethanedial with a surplus amount of polyacrylamide in an aqueous basic medium is open-loop and / or closed-loop controlled on the basis of at least one and preferably at least two of the following factors: a) turbidimetric analysis, b) pH value adjustment depending on the temperature, c) pH value adjustment depending on the reaction time, d) drop in pH value or e) current consumption of the circulation pump.

Description

METHOD FOR THE PRODUCTION OF A DRY FIRMING AGENT FROM GLYOXYLATED POLYACRYLAMIDE The present invention relates to a process for producing a dry solidifier, in particular glyoxylated polyacrylamide, in which an aqueous solution of polyacrylamide is mixed with ethandial (Giyoxal) while stirring by means of a circulation pump, the reaction is started by adding a base, in particular a strong base, at a basic pH value, in particular a pH value greater than 8, and is allowed to react while stirring and / or circulating, whereupon, after a predetermined reaction time, the reaction is stopped by adding an acid while stirring and / or circulating. Methods for producing dry strengtheners for the paper industry are known, with most of these methods operating continuously. In such methods, a substantially aqueous reaction mixture of a vinylamide polymer and a reactive cellulose agent is typically allowed to react at a basic pH for a predetermined time. A number of factors, such as the temperature of the incoming water, the pH of the reaction mixture, the consumption of the reactive cellulose material, the concentration of the vinylamide polymer before and during adduct formation, and the like, are measured to stop the reaction in a timely manner once the desired adduct has been formed. To ensure timely reaction termination, in addition to a variety of other measurements, viscosity measurements have already been performed to determine the degree of reaction.Most known processes result in products that are not manufactured in situ but are transported to the end user by tanker truck and diluted there to the concentration required for the reaction, which is approximately 3 to 4%. A disadvantage of these known processes is that enormous quantities of liquid must be transported, and furthermore, despite the addition of stabilizers, the products degrade during transport, thus reducing their overall shelf life. US Patent 7,875,676 describes a process for the preparation of a reactive cellulose-polyvinylamide adduct in which an aqueous reaction mixture of vinylamide polymer and reactive cellulose agent is continuously reacted, and the viscosity is measured during the reaction. If the viscosity does not exceed 30 cP at a temperature of 25°C, the reaction is stopped. Such processes, in which- When the viscosity of the adduct is measured, it is problematic that if the point at which the reaction is stopped is missed, i.e., if the viscosity increases too much, a water-insoluble gel is formed, which cannot be used as a dry solidifier. Furthermore, such glyoxylated adducts contain significant amounts of organic materials or solvents, such as organic oils, which are not only expensive but also highly volatile, thus limiting the use of such adducts. WO 2009 / 059725 describes glyoxylated N-vinylamines, in which a mixture of acrylamide and diethylmethylammonium chloride is glyoxylated. The reaction is monitored solely by measuring turbidity, making it impossible to determine the exact end point or when a quantitative reaction has occurred. Furthermore, commercially available glyoxylated polyvinylamide adducts suffer from a very short shelf life of only a few weeks. This shelf life depends on the pH, concentration, and storage temperature, which is problematic in practical applications, as freshly delivered or readily available adduct must always be ensured. In order to operate at least somewhat economically with such a procedure, products are delivered which have too high a concentration of the vinylamide polymer for use and therefore must be diluted before actual use in order to make a meaningful implementation possible. Finally, in most known processes, when the desired viscosity is reached, a large amount of unreacted glyoxal remains in the product, resulting in the disadvantage that such a product cannot be used as a dry hardener. The use of glyoxylated polyacrylamide as a dry strengthener for paper and cardboard is employed, as is the use of reactive, water-soluble vinylamide copolymers of cellulose, which are modified with glyoxal or reactive cellulose agents to be thermosetting. However, due to the use of glyoxal as a crosslinking agent, these products present a problem regarding the stability and storage of such substances. Pensions, which due to reduced stability have storage periods of between approximately 3 and 6 weeks. The invention aims to provide a method for producing a dry hardener that enables the quantitative conversion of glyoxal in the reaction mixture, thus providing a universally applicable dry hardener, particularly one that can be used immediately after production and offers extended storage stability. The invention further aims to provide a method for producing a dry hardener that can be carried out with such precision that the quantitative conversion of glyoxal in the reaction mixture can be determined without doubt. To solve this problem, the process according to the invention is essentially characterized in that the process is carried out as a discontinuous process in which a quantitative reaction of the ethanedial with an excess amount of polyacrylamide in an aqueous, basic environment is carried out by at least one, preferably at least two of the factors selected from: a) Turbidity measurement, b) pH adjustment depending on temperature, c) pH adjustment depending on the reaction time, d) drop in pH value or e) Power consumption of the circulation pump The process is controlled and / or regulated. Because the process is carried out as a batch process, the quantitative reaction of the ethandial with an excess of polyacrylamide in an aqueous, alkaline environment can be controlled or regulated in any given batch, depending on a number of factors. By simultaneously measuring at least two of these factors during the reaction, it is possible to produce a reproducible or precisely reproducible product in every batch. The individual factors, of which two are used simultaneously as control variables, are a) the turbidity measurement It has been found that the change in turbidity is an indicator of the degree of conversion of the reaction, with the reaction mixture exhibiting an initial turbidity typically in the range of 5 to 15 NTU. If the turbidity has increased by a certain amount during the reaction, this indicates that the desired degree of conversion has been reached and further conversion can be prevented by adding acid. If the reaction is not stopped by adding acid, the turbidity continues to increase. Preferably, the turbidity measurement is performed as a differential measurement, thus excluding the initial turbidity value from the measurement and ensuring a consistently unambiguous result. b) pH adjustment via temperature In general, it should be noted that the reaction of polyacrylamide with ethanedial always occurs when the solution has a basic pH value. The reaction time varies depending on the pH value, which would otherwise require relatively complex control of the system. Surprisingly, however, it has been found that the reaction time remains essentially constant or can be preset, and that reaction times between 12 and 18 minutes represent the optimum between excessively long reaction times, which would significantly reduce the system's capacity, and excessively short reaction times, which would lead to increased fouling on the tank walls and in the system's piping. Therefore, in addition to pH, temperature is also a crucial factor in controlling the reaction rate. However, since it is practically impossible to keep the temperature of a reaction mixture constant, the invention adjusts the pH value via temperature. This means that a temperature correction factor is entered, and the pH value is automatically decreased or increased by a specific value for each degree of temperature difference. For example, 20 °C can be chosen as the setpoint. c) pH value adjustment via reaction time It is also possible to correct the pH value via the reaction time. Essentially, this involves setting a pH value by which the target pH value is adjusted if there is a time deviation before the quantitative conversion is achieved. Furthermore, a minimum pH value is defined by which the target pH value is adjusted in the event of several consecutive time deviations. The pH value may be reduced, just as a maximum pH value is defined, to which the target pH value may be increased in the event of several consecutive time deviations. According to the invention, pH correction only occurs after a predetermined number of exceedances or falls below the target value, thus preventing the need for immediate correction with every deviation. If the desired reaction time is exceeded or fallen short of by a certain value in a batch (where a dead zone, i.e., a range that is not included in the measurement, can also be defined), the deviating reaction time is stored. If the same deviation occurs in the next batch, a correction is automatically made. d) Drop in pH value During the reaction of glyoxylated polyacrylamide with ethanedial, a drop in pH is measured. The reaction can therefore be controlled or regulated such that, when this pH drop is observed, the reaction is stopped, as it then also indicates that the reaction has proceeded quantitatively. e) Power consumption or circulation pump Finally, it is possible to control or regulate the reaction via the power consumption of the circulation pump, which is integrated into a system in which the reaction according to the invention is carried out. Here, the circulation pump exhibits a steadily increasing power consumption during the reaction, which at the end of the quantitative conversion abruptly settles to a constant, non-increasing value, thus indicating the end of the reaction. This power consumption of the circulation pump, which is displayed and optionally recorded, can therefore also be used to control the process. According to the invention, at least two of these parameters are measured or determined to provide a reliable indication of the reaction's end, i.e., the quantitative conversion of ethandial or glyoxal with polyacrylamide. Surprisingly, such a process now makes it possible to produce an adduct of polyacrylamide and glyoxal that exhibits significantly increased storage stability compared to conventional adducts, while simultaneously reducing the adduct's water content. This can be attributed to the absence of residual amounts of unreacted glyoxal. According to the invention, particularly reliable process control and, above all, quantitative conversion of the ethandial are achieved when, as demonstrated in a further study, The invention corresponds to the use of polyacrylamide and ethanedial in a ratio of 3:1 to 10:1, in particular 5:1 to 6:1. In particular, when the pH drop is used as one of the control variables for determining the end of the reaction, the process, as is a further development of the invention, is carried out such that the reaction of polyacrylamide and ethanedial is stopped by lowering the pH of the reaction mixture to a value between 2 and 6, particularly between 3.5 and 4.5, by adding acid. As soon as a pH drop of approximately 0.3 is observed, the reaction is stopped by adding acid, and the pH of the system is lowered to values ​​between 2 and 6, particularly between 3.5 and 4.5. Any acid can be selected from sulfuric acid, sulfurous acid, hydrochloric acid, hydrofluoric acid, acetic acid, citric acid, phosphoric acid, adipic acid, and oxalic acid.When the process according to the invention is carried out using turbidity measurement and / or pH drop as control variables, the process is conducted such that acidification is carried out after the onset of a pH drop of at least 0.1 to approximately 1, in particular 0.3, and / or after an increase in the turbidity of the reaction mixture of 4 to 10 NTU, in particular 6 NTU. In particular, when both factors, namely the pH drop and the increase in turbidity, are taken into account, it is possible to determine the end of the reaction precisely and to stop the reaction immediately after reaching the quantitative conversion of polyacrylamide with ethanedial by adding acid. According to a further development of the invention, when pH adjustment is carried out via temperature, the procedure is as follows: starting from a reaction mixture temperature of 25 °C, the pH value is lowered and raised as the temperature of the reaction mixture increases, according to the formula pH Start = Base pH + [(Temp Start - 20 °C) . F], where the Base pH represents a preselected value, the pH Start is determined by the reaction and represents the starting value for the next pending reaction, the Temp Start is the temperature at the beginning of the reaction, and F is a multiplier between 0.03 and 0.08. This approach avoids the need for immediate process control every time there is a slight temperature deviation, as the reaction temperature cannot be kept absolutely constant over time. Rather, with such a process, it is possible to adjust the target pH value of the reaction mixture with very small deviations by selecting a temperature correction factor, as described above. In a preferred embodiment of this process, the pH value is raised or lowered using a temperature correction factor chosen between 0.03 and 0.08, particularly 0.05. For example, starting from a predetermined temperature of, say, 20 °C, the pH value is automatically decreased or increased by an adjustable, predefined value that cannot be further changed, per degree of temperature difference, with such a correction factor being chosen between 0.03 and 0.08, particularly 0.05.Finally, according to the invention, various temperature correction factors can be preselected depending on the respective reaction temperatures. For example, a COLD temperature correction factor, which is freely adjustable, since at COLD reaction temperatures of, for example, 10 °C require a higher pH increase to keep the reaction time constant; a WARM temperature correction factor, which is also freely adjustable, for example, to keep the pH as low as possible at high reaction temperatures, such as 30 °C; and finally, the NORMAL temperature correction factor, which is the factor selected for the normally preselected reaction temperature. This presetting is usually made depending on the season or the climate zone in which the system is installed, since the temperature in a factory hall is typically strongly influenced by the prevailing outside temperature.To ensure maximum utilization of the reaction plant, the inventive process is further developed such that the reaction of polyacrylamide with ethanedial is carried out for a predetermined constant time between 2 and 30 minutes, preferably 6 to 20 minutes, and particularly 12 to 18 minutes. This predetermined constant time, between a maximum of 32 minutes and a minimum of 6 minutes, and preferably between 12 and 18 minutes, allows for complete conversion of polyacrylamide and glyoxal at typically prevailing temperatures. The time variations depend on whether the reaction is carried out at higher or lower ambient temperatures, which also affect the temperature in the production hall, and / or at higher or lower water temperatures. If, in particular, reaction control is achieved by adjusting the pH value as a function of the reaction time, the method according to the invention is further developed such that, with a fixed constant reaction time, a pH adjustment of 0.1 to 1.0, in particular 0.2 to 0.4, is made after at least one detection of a deviation of between 1 and 10 minutes, in particular 2 to 4 minutes, from the fixed reaction time. This procedure avoids the situation where a pH adjustment is made for every slight deviation of the reaction time from the fixed reaction time until the reaction is complete. Instead, the actual deviation from the fixed time is measured, and only then is the pH adjusted, thereby successfully shifting the reaction time back towards the fixed reaction time. A particularly elegant method for controlling the process of producing a dry-strengthening agent by reacting polyacrylamide with glyoxal is achieved by, as a further development of the invention, lowering the pH of the reaction mixture with acid once a constant current draw of the circulation pump is reached in the range of 0.1 A to 1 A, particularly 0.2 A to 0.6 A, relative to an initial value. With such a process control, the moment when the current draw of the circulation pump reaches a constant value is clearly identifiable, whereupon acid is added immediately to stop the reaction. This type of control thus makes it possible to carry out the reaction quantitatively.Particularly reliable results in controlling the process for producing a dry strengthener obtained by reacting polyacrylamide with glyoxal are achieved according to the invention by conducting the process in such a way that the control and / or regulation of the process is carried out by monitoring a combination of the factors a) and b); a), b) and c); a) and d); a), b), c) and d); a), d) and e); b) and d); b) and e); b), c) and d) or b), d) and e). The invention is explained in more detail below with reference to an exemplary embodiment and the schematic process flow shown in the figure. In this figure, Fig. 1 shows the construction of a device for carrying out the method for producing a dry hardener according to the invention, and Fig. 2 shows a plot which shows the current consumption of the circulation pump, the pH value and the change in turbidity during the reaction. Figure 1 schematically shows a process flow for the production of a dry solidifier consisting of glyoxylated polyacrylamide, in which an aqueous solution of polyacrylamide is reacted with ethanedia (Glyoxal) in a batch reactor. Glyoxal is fed from a storage tank 1 into a reactor 3 via a metering pump 2 and a plurality of valves. Simultaneously, polyacrylamide is fed into the reactor 3 from at least one tank container 4, preferably two separately switchable tank containers 4, via a metering pump 5 and also via a plurality of control valves (not described in detail). In addition to the feeding of glyoxal and polyacrylamide, starter water from a fresh water tank 6 is introduced into the reactor 3, particularly before or simultaneously with the reactant, via a line 7 and open valves 8 and 9.The water, glyoxal, and polyacrylamide are fed in either in this order or simultaneously, with the metering pumps 2 and 5 being switched on at the same time and programmed to dose the desired molar ratio of glyoxal and polyacrylamide. Simultaneously with the switching on of metering pumps 2 and 5, a stirrer 10 provided in reactor 3 is switched on, as is the schematically depicted circulation pump 11, which also contributes at least partially to mixing the reactants. After the desired amount of glyoxal and polyacrylamide solution has been added to the water, the feed pumps 2 and 5 are switched off, the valves 8 and 9 are closed, and the feed of reactants is stopped. Simultaneously with the stopping of the reactant addition, the addition of caustic soda, e.g.,Sodium hydroxide solution is added from a lye tank 13 until the desired pH value of the reaction, e.g., pH 9, is reached. To precisely adjust the lye concentration and, in particular, the pH value, valves 14 and 15 are opened in addition to switching on the lye supply pump 12. These valves control the supply of water, either fresh water from the fresh water tank 6 or, in some cases, rinse water from the rinse water tank 16, to the concentrated lye solution. This allows a sufficiently diluted lye solution to be dosed into reactor 3 to precisely adjust the desired pH value. With the start of the lye dosing, and especially upon reaching the basic pH value, e.g., 9, the reaction of the reactants in reactor 3 begins. The following factors are continuously recorded: the temperature of the reaction mixture, the turbidity of the reaction mixture, the pH value, and the current consumption of the circulation pump. Pump 1 1. Upon reaching at least one of the following parameters, namely reaching a predetermined turbidity value, reaching a constant current draw of the circulation pump, or reaching a predetermined pH drop, the reaction is stopped by switching on the acid pump 17 and thus by adding acid, for example, sulfuric acid from an acid storage tank 18, into the reactor 3. To adjust the appropriate concentration of the acid to be added, fresh water from the fresh water tank 6 is fed into the acid supply line 19 to the reactor 3 by opening valve 20. At the time of acid dosing, valves 8 and 9 for supplying fresh water to the reactor to adjust the initial concentration of the reactants, as well as valves 14 and 15, which are intended to adjust the concentration of the base, are closed.The corresponding valves, which allow the individual storage tanks to be isolated from their metering pumps or lines, are also closed. For the sake of simplicity, the control valves shown in Fig. 1, whose function is self-explanatory, will not be described in detail. The acid pump 17 is switched off again when a pH value of approximately 3 to 4 is reached, and the circulation pump 11 remains switched on. Additionally, valve 21 and, if applicable, valve 22 are opened to discharge the product into a storage tank 23 and to discharge any waste directly at 24. From storage tank 23, the product is then fed directly to the paper machine. After all reactants and the required amount of fresh water, as well as the required amount of alkali to start the reaction, have been added to reactor 3 at the beginning of the process, and the pH value has been adjusted to the desired value for the reaction, the reaction of the reactants in reactor 3 begins. The stirring device 10 is activated, as is the circulation pump 11. For monitoring the reaction, at least one bypass circuit is activated by opening the corresponding valves in order to measure at least one of the following values: pH value of the reaction mixture, current consumption of the circulation pump, and a turbidity measurement. For turbidity measurement, the valve 26, which is interposed in the bypass line 25, is opened so that the circulation pump 11 circulates the reaction mixture continuously, at least via this circuit. A turbidity meter 27 is also connected in this circuit, which continuously measures the turbidity of the reaction mixture. The valves 28 and 29 are designed so that after the end of a cycle... The turbidity meter can then be rinsed with fresh water to ensure that any deposits are completely removed before the next measurement. Simultaneously or separately from the turbidity measurement, a second bypass line 32 can be activated by opening valves 30 and 31, in which at least two pH probes 33 and 34 are connected. Regarding the pH measurement cycle, it should be noted that this can be activated simultaneously with the turbidity measurement cycle or separately from it. Finally, a separate cleaning circuit is provided for cleaning the pH probes, which includes an air supply 35 to the individual probes, as well as a flushing circuit 36 ​​for the individual pH probes, and a drain 37. This flushing circuit 36 ​​is operated as follows: After completion of the process, valves 30 and 31 are closed, so that the pH probes are isolated from the rest of the system.During cleaning of pH probes 33 and 34, a valve 38 connected to the drain 37 is opened, and liquid is drained from the shut-off section of the circulation line used for pH measurement. Each pH probe has an associated flushing valve that directly applies flushing water from the circuit 36 ​​to the respective pH probe 33 or 34. The flushing water is sprayed under pressure onto probes 33 and 34 to remove the deposits resulting from the reaction on the pH probes. For efficient cleaning, a cycle is performed in which one probe is first sprayed with flushing water, then a valve connected to the air supply 35 belonging to that pH probe is opened to expel flushing water from the line, and subsequently, the second pH probe is treated in the same way as the first.Such a cycle is repeated several times, after which all valves are closed and the air is expelled from the line with the help of flushing water, and at least one of the valves 30 or 31 is reopened to equalize the pressure in the line. After such a rinsing sequence, it is ensured that each pH probe is free of deposits, which are already formed during the reaction of glyoxal with polyacrylamide, and that in the next reaction of the reactants a pH probe without any deposits can be provided, thus enabling an exact pH measurement. After the reaction product has been discharged from reactor 3 and before the start of a new cycle, as explained above, to avoid measurement errors that may occur during the reaction of water, glyoxal, and polyacrylamide in the plant's pipelines and also in the The probes are cleaned of any deposits that have formed as far as possible to maintain the system's measurement accuracy. Deposits in the tanks and pipes do not pose a problem in this type of reaction; however, deposits on pH probes slow down their measurement speed, thereby reducing measurement accuracy and, in particular, the system's response time. With a delayed response, it is no longer possible to stop the reaction early and precisely, potentially leading to excessively long response times, resulting in production losses and product degradation. This is why the cleaning cycle for the pH probes described above is performed. Figure 2 shows a plot of several parameters measured during the reaction of glyoxal and polyacrylamide in aqueous solution. The abscissa represents time in minutes. In Figure 2, curve A represents the change in turbidity during the reaction, curve B represents the pH value measured during the reaction, and curve C represents the current consumption of the circulation pump during the reaction. It is clearly evident that curve A shows a relatively constant turbidity value of approximately 3.5 NTU until about 40 minutes. From 40 minutes to about 59 minutes, this turbidity value rises sharply to about 10.9 NTU and then drops vertically. At 59 minutes, the reaction was stopped by the addition of acid, as can be seen on the plotted curve B.Curve B shows that base was added to glyoxal and polyacrylamide between 37 and 40 minutes, as clearly indicated by the rise in pH. Between 40 and 59 minutes, the pH slowly decreased from the initial value of approximately 9.6 to approximately 9.3 and then dropped sharply, indicating the start of the acid addition to the reaction mixture. This indicates that the reaction time in the example shown in Fig. 2 is approximately 19 minutes. Similarly, graph C shows that the current draw of the circulation pump initially remains essentially constant at an initial value of approximately 9.8 A, that it begins to increase slowly, essentially linearly, about 5 minutes after the end of the addition of the lye, and that upon reaching a current draw of approximately 10.3 A, the current draw of the circulation pump again reaches a constant value. A circulation pump, such as the Grundfos F&B Hygia II KYY 65 / 65 / 7 5 / 2, can be used. This value is reached when the acid addition has begun, i.e., when the reaction has been stopped by the addition of acid and further reaction of Giyoxal and polyacrylamide has been prevented by the acid addition. From this point on, the current consumption of the circulation pump is constant again. The total discharge is between 0.1 A and 1 A, specifically between 0.2 A and 0.6 A. As can be seen from these three curves A, B and C, all three curves are to be used to control or regulate the reaction, especially if limit values ​​are defined beforehand, such as by how many NTU the turbidity may increase until the reaction is complete, by how many A the current consumption of the circulation pump may increase until the reaction is complete, and by how many units the pH value may drop during the reaction of Giyoxal and polyacrylamide in order to be able to trace back to a complete reaction. The method according to the invention is further explained with practical examples. General procedural management A pre-calculated quantity of water is placed in a mixing tank. Simultaneously or after all the water has been added, ethandial and polyacrylamide are added to the tank and mixed using a stirring device and the circulation pump. The reaction is initiated by adding the base at a pH value above 8, after which the reaction and its completion are monitored by at least one of the following measurements: a. Turbidity measurement, b. pH adjustment depending on temperature, c. pH adjustment depending on the reaction time, d. drop in pH value , e. Power consumption of the circulation pump, and f. Deviation of the turbidity from the trend line. Example 1 Turbidity measurement and pH correction depending on the reaction time In the reaction described above, the turbidity increases by 6 NTU during the reaction. Measurement of the reaction time shows that it is 18 minutes, 3 minutes longer than the previous measurement. Since the given target value of 15 minutes deviates, a pH correction is subsequently performed for the initial pH value, which was 8.5, by 0.2 pH units in order to correct the reaction time for the next batch towards the target reaction time. Example 2 Turbidity measurement and measurement of the current consumption of the circulation pump During the reaction, which was scheduled to last 15 minutes, the turbidity increased by 6 NTU and simultaneously the current draw of the circulation pump increased from 0.2 A to 0.6 A, whereupon the reaction was immediately stopped with acid, since the changes for both values, which had been determined before the start of the reaction, were achieved within the specified time, so that the desired degree of conversion was reached. Example 3 Control via the pH drop and turbidity increase During the reaction of Giyoxal and polyacrylamide, the pH drops by 0.3 units. After an increase in turbidity of 5 NTU is observed, the reaction is stopped with acid. Similarly, control via the pH drop and the current draw of the circulating pump is possible. In this case, after a pH drop of 0.3 units is observed, the pump's current draw is checked and found to have increased from 0.2 A to 0.6 A. In this case, the reaction is immediately stopped by adding acid, as the predefined changes for both values ​​are reached within the specified time. Example 4 Control via the pH drop over a defined conversion time The reaction time of Giyoxal and polyacrylamide is preset to 15 minutes. The pH drop is measured and found to have decreased by 0.3 after only 13 minutes, indicating that the reaction is complete. The reaction is stopped by adding acid. This process is repeated a second time with the same result, whereupon a pH correction is made by lowering it by 0.2 units for the next reaction. This increases the reaction time due to the lower basicity of the reaction. Example 5 pH correction at a set temperature The initial reaction temperature is 25°C. The pH value for the start of the reaction is adjusted to the actual conditions according to the following formula: pH value (baseline at 20°C) + (temperature of initial reaction - 20°C x 0.05) = pH value. In this case, the baseline pH value at 20°C is 9, so using this formula results in a pH value of 9.25, which decreases by 0.3 units during the course of the reaction. At a pH of 8.95, the reaction can be stopped by adding acid, as it is considered complete.

Claims

Page 1 of 2 pages of Claims 1. A method for the preparation of dry-strengthagents, particularly of glyoxylated polyacrylamide, in which an aqueous solution of polyacrylamide is supplemented with ethene dialol (glioxal) under stirring by recirculation pump, the reaction is initiated by the addition of a base, particularly a strong base, at a basic pH, specifically a pH greater than 8, and allowed to react under stirring and / or recirculation. When the reaction is stopped by the addition of an acid under stirring and / or recirculation after completion, the specified reaction time is between 2 and 30 minutes. Characterized by the method being performed as a discontinuous process in which the quantitative reaction of ethene dialol with an excess amount of polyacrylamide in an aqueous basic medium is controlled and / or directed by at least two of the following factors: a) measurement of turbidity; b) adjustment of pH as a function of temperature; c) adjustment of pH as a function of reaction time; d) reduction of pH or e) Using electrical current for the circulating pump.The characteristic method under Presumption 1 involves the use of polyacrylamide and ethane dialol in ratios of 3:1 to 10:1, particularly 5:1 to 6:

13. The characteristic method under Presumption 1 or 2 involves the reaction of polyacrylamide and ethane dialol being stopped by acidification, by lowering the pH of the reaction mixture to a value between 2 and 6, particularly between 3.5 and 4.

54. The characteristic method under Presumption 3 involves acidification resulting in a subsequent reduction of the pH of the reaction mixture by at least 0.1 to approximately 1, particularly 0.3, and / or after an increase in the reactance of the reaction mixture by 4 to 10 NTU, particularly 6 NTU5. The characteristic method under Presumption 1, 2, or 3, based on a reaction mixture temperature of 25 °C, involves a pH reduction with increasing temperature of the reaction mixture and further increase with decreasing temperature according to the formula: initial pH + base pH + [(initial temperature - 20 °C).[F] where the base pH constitutes the preceding value, the initial pH is the result of the reaction and constitutes the initial value for the next reaction, the initial temperature represents the stop-start temperature of the reaction, and F is a multiplier between 0.03 and 0.

08.

6. The characteristic method according to claim 5 is that the increase or decrease in pH is performed by a multiplier F corresponding to a temperature correction factor between 0.03 and 0.08, specifically 0.05 (page 2 of number 2, page 7).

7. The characteristic method according to claim 5 or 6 is that the reaction of polyacrylamide with ethene dialol is performed over a predetermined fixed time interval between 6 and 20 minutes, specifically 12 and 18 minutes.

8. The characteristic method according to claim 5, 6 or 7 is that at the fixed reaction time, a pH adjustment of 0.1 to 1.0, specifically 0.2 to 0.4, is then performed after at least one detection of a deviation between 1 and 10 minutes, specifically 2 to 4 minutes from the reaction time. 9.The characteristic method under Reputation 1, 2, or 3 is that the reduction of the pH of the reaction mixture is achieved by the assistance of the acid when a constant current of the circulating pump is applied relative to the initial value in the range of 0.1 amperes to 1 ampere, specifically 0.2 amperes to 0.6 amperes is achieved.

10. The characteristic method under Reputation 1 through 9 is that the control and / or direction of such method is achieved by observing a combination of factors a) and b); a), b) and c); a) and d); a), b), c) and d); a), d) and e); b) and d); b) and e); b), c) and d); or b), d) and e);.