EP1841899A1

EP1841899A1 - Method and device for producing an alkali metal hypochlorite solution

Info

Publication number: EP1841899A1
Application number: EP06700215A
Authority: EP
Inventors: Andreas Siemer; Andreas Schwarz; Norbert Maier
Original assignee: Kaercher Futuretech GmbH
Current assignee: Kaercher Futuretech GmbH
Priority date: 2005-01-21
Filing date: 2006-01-05
Publication date: 2007-10-10
Also published as: US20080017519A1; WO2006077016A1; DE102005004063A1

Abstract

The invention relates to a device and a method for producing an alkali hypochlorite solution, especially a sodium hypochlorite solution. The inventive device comprises at least one electrolytic cell (12), means (20, 22, 24, 26) for feeding a brine solution having a defined volume flow rate and a defined salt concentration to the electrolytic cell (12), and a DC voltage source (18) for generating a current flowing through the electrolytic cell (12). The intensity of current is fixedly set in such a manner that the concentration of the chlorate produced during electrolysis is limited to a maximum of 1.5 g/l, preferably 0.6 g/l.

Description

Method and apparatus for producing an alkali metal hypochlorite solution

The invention relates to a process for the preparation of an alkali metal hypochlorite solution, in particular a sodium hypochlorite solution, in which an undivided electrolysis cell is supplied with a brine solution having a specific volumetric flow and with a specific salt concentration. The invention further relates to a device for producing an alkali metal hypochlorite solution, in particular a sodium hypochlorite

Solution, comprising at least one undivided electrolysis cell, means for supplying a brine solution having a certain volume flow and a certain salt concentration in the electrolysis cell, and with a DC voltage source for generating a current through the electrolysis cell.

There is a continuing need to produce sodium hypochlorite solutions used to disinfect water. While such a "chlorination" of water on a large scale, for example in the treatment of drinking water in the waterworks of cities and communities is carried out for mobile use, especially in disaster areas, a need for the production of sodium hypochlorite solution on the ground. Purified water is added to the sodium hypochlorite solution after filtration and reverse osmosis to prevent re-nucleation.

There are already known mobile plants to produce sodium hypochlorite solutions by electrolysis of seawater or brine.

Such systems are offered by the company Wallace & Tiernan GmbH, Günzburg, under the name OSEC-S® and OSEC-B®.

Here either filtered seawater or a saturated brine with a metering pump is fed to an electrolysis cell. By dilution water, which also flows into the electrolysis cell, the concentration of the brine is adjusted to approx. 2% lowered. In the electrolytic cell sodium hypochlorite solution and hydrogen is generated, the hydrogen separated from the Natriumhypochloritlösung and with a fan on a safe concentration diluted with air and discharged into the open air. The sodium hypochlorite solution produced has a concentration of about 6 g / l of active chlorine. The entire process of producing sodium hypochlorite solution is monitored and controlled by a PLC to ensure optimum chlorine yield with the least possible waste production.

A problem with such a system is the use of a PLC control in conjunction with corresponding sensors, since this requires regular maintenance and control. However, this is often not the case when it comes to operations in disaster areas.

In a further known from DE 37 04 955 Al plant for producing a sodium hypochlorite solution, the brine concentration in the electrolysis cell is measured by evaluating the voltage across the electrodes and the flowing current. From this, a conductivity-proportional signal is generated which is used to control a saturated saline dosing pump.

This system is also subject to the disadvantages described above.

In another known from DE 28 06 441 Al plant for the production of sodium hypochlorite a diaphragm-free electrolysis cell is used, in which the ratio to the effective anode area and the effective cathode area in the electrolytic cell is at least 1, 5: 1 or greater. In this way, the effective use of the sodium hypochlo- Rits and the current efficiency at stationary flow conditions can be improved. According to a variant of this embodiment, the electrolytic cell is additionally cooled in order to reduce the amount of sodium chlorate formed.

Even such a system can not ensure optimal process control, especially if it is dispensed with a cooling to make the process as simple as possible.

It is further known from US 4,329,215 to use an electrolysis cell for sodium hypochlorite production in which the anode compartment and the cathode compartment of the electrolytic cell are separated by an ion exchange membrane which is impermeable to anions, gases and liquids.

By using such a membrane, the problem of chlorate formation during electrolysis can be reduced.

However, such an electrolysis cell is very maintenance-intensive.

Against this background, the invention has for its object to provide a method and apparatus for producing a Alkalimetallhypochloritlösung, whereby the simplest possible, trouble-free and low-maintenance construction is guaranteed and yet sufficient concentration of alkali metal hypochlorite solution can be produced.

This object is achieved by a process for the preparation of an alkali metal hypochlorite solution, in particular a sodium hypochlorite solution, in which an undivided electrolysis a brine solution is supplied with a certain volume flow and with a certain salt concentration, and wherein the current strength is set such that the concentration of chlorate obtained during the electrolysis to a maximum of 1, 5 g / l, preferably to a maximum of 1 g / l, is particularly preferably limited to a maximum of 0, 6 g / l.

The object of the invention is further achieved by a device for producing a Alkalimetallhypochloritlösung, in particular a Natriumhypochloritlösung, with at least one undivided electrolysis cell, means for supplying a brine solution with a certain volume flow and a certain salt concentration in the electrolytic cell, and with a DC voltage source for generating a Current through the electrolytic cell, wherein the current is set so tightly that the concentration of accumulating during electrolysis chlorate to a maximum of 1, 5 g / l, preferably limited to a maximum of 1 g / l, more preferably to a maximum of 0, 6 g / l is.

The object of the invention is completely solved in this way.

According to the invention, a particularly simple and low-maintenance construction is ensured by the use of an undivided electrolysis cell without a diaphragm between anode and cathode. According to the invention, it has been found that the production of an alkali metal hypochlorite solution with fixed parameters can be advantageously carried out by limiting the concentration of chlorate obtained during electrolysis by a fixed current. In particular, it has been recognized according to the invention that the concentration of active Chlorine increases only disproportionately with increasing the current strength beyond a certain value, while at the same time the production of undesirable chlorate as a byproduct increases disproportionately.

According to the invention is thus ensured by a suitable determination of the current on the one hand, a favorable concentration of active chlorine in the alkali metal hypochlorite solution produced and on the other hand limited the production of undesirable chlorate to a tolerable level.

Overall, the method can be operated in this way with fixed operating parameters without the expense of a special scheme in such a favorable manner that an advantageous continuous operation is guaranteed with low maintenance.

In an advantageous embodiment of the invention in this case the current is set between 2 and 6 amps, preferably between 2 and 4, 5 amps, more preferably between 2, 5 and 3, 5 amps.

This ensures an optimal compromise between the generated concentration of active chlorine and the accumulation of undesired chlorate.

According to a further embodiment of the invention, the brine solution is prepared with a constant salt concentration by mixing a saturated brine solution with water. In this way, the desired input concentration of the electrolytic cell with salt solution can be set to a favorable value in a particularly simple manner. Since the starting product used is a saturated salt solution which is mixed with water, preferably with deionized water or drinking water, a suitable concentration of the salt solution supplied to the electrolysis cell can be ensured without additional control effort.

Alternatively, it is also conceivable to use a salt solution with a specific salt concentration, which is conveyed with a constant flow rate into the electrolysis cell.

In an advantageous development of the invention, the salt concentration of the brine solution supplied to the electrolysis cell is adjusted to a value between 2 and 10 g / l, preferably between 5 and 10 g / l.

In this way, a sufficient chlorine yield can be ensured without the accumulation of undesirable chlorate increases excessively.

In a further embodiment of the invention, the electrolysis cell is supplied with the brine solution having a constant volumetric flow V whose value is determined as a function of the effective electrode area A (in m ² ) according to the relationship V = w • A, where w is the flow velocity between 4 x 10 ^-5 m / s and 12 x 10 ^-5 m / s, preferably between 6 x 10 ^-5 m / s and 9 x 10 ^-5 m / s. In this way, the electrolysis cell is operated with an optimum volume flow, which ensures optimum yield depending on the cell size.

In the device according to the invention, the DC voltage source is preferably designed as a constant current source.

In this way, the optimally defined current strength of the electrolytic cell can be maintained particularly precise.

As already mentioned, the desired concentration of the brine solution supplied to the electrolytic cell can be adjusted either by mixing a saturated brine solution with water or by using a brine solution having a certain concentration. To mix or supply the preset brine solution metering pumps are preferably used by the constant mixing ratio or a constant flow rate is guaranteed.

The electrodes of the electrolytic cell may for example consist of a material containing iron, mercury, stainless steel, titanium and / or platinum. The electrodes preferably consist of uncoated titanium.

This has resulted in a good yield and high stability of the electrodes.

It is understood that the features of the invention mentioned above and those yet to be explained not only in the particular combination given, but also in others Combinations or alone can be used without departing from the scope of the invention.

Further features and advantages of the invention will become apparent from the following description of a preferred embodiment with reference to the drawings. Show it:

Figure 1 shows the relationship between current and the concentration of active chlorine or chlorate and the discharge temperature in an electrolysis cell according to the invention.

Fig. FIG. 2 shows the relationship between the feed concentration of a sodium chloride solution fed in and the active chlorine concentration produced; FIG.

Fig. Figure 3 shows the relationship between the feed concentration of sodium hypochlorite and the concentration of active chlorine and chlorate produced and the discharge temperature;

Fig. 4 shows the relationship between the volume flow used and the concentration of generated active chlorine and chlorate and

Fig. 5 is a simplified schematic diagram of a device according to the invention.

The basic structure of a device according to the invention is shown in FIG. 5 and generally designated by the numeral 10. The apparatus 10 is used to produce a Alkalimetallhypochloritlösung, in particular a Natriumhypochloritlösung, using an electrolytic cell 12. The electrolysis cell 12 is fed from a brine tank 20, a saturated salt solution, which is mixed before being supplied to the electrolytic cell 12 with water from a water tank 22. The electrolysis cell 12 is designed as a one-piece, not divided by a membrane cell and has a housing made of PVDF. The electrodes 14, 16, which are made of uncoated titanium, are connected to a DC voltage source 18, which is designed as a constant current source to produce a constant current of 3 amps at a voltage of about 3.5 to 4.5 volts. In the electrolytic cell, sodium hypochlorite is formed from the aqueous sodium chloride solution upon release of hydrogen. The output of the electrolysis cell is connected via a line 34 to a collecting container 36. The sodium hypochlorite solution produced in this case is discharged to the outside via a line 38, while the hydrogen rises upwards and is discharged via an exhaust gas line 40 and diluted to a harmless concentration. The concentration of the electrolytic cell 12 salt solution supplied is adjusted by metering pumps 24, 26, each generating a constant volume flow. The first metering pump 24 sucks in the brine tank 20 saturated salt solution at a flow rate of 42 ml / h. The second dosing pump sucks from the water tank 22 deionized water (or drinking water) via a line 32 with a flow rate of 2.958 l / h. The pressure lines of the two metering pumps 24, 26 open via a common line 30 in the inflow of the electrolytic cell 12. The electrolytic cell 12 is thus supplied in the example shown, a volume flow of 3 l / h sodium chlorite solution, the concentration of the mixture of the saturated salt solution with deionized water is adjusted to a value of about 5 g / l.

In Fig. 5 is further indicated that the levels of the brine tank 20, the water tank 22 and the collecting container 36 are preferably monitored with a level monitoring, which may include about level sensors 42, 44, 46 and float switch (not shown).

The operating parameters of the device 10 are now set such that the yield of Natriumhypochloritgewinnung is driven in a favorable range for the production of sodium hypochlorite, wherein at the same time the accumulation of undesirable chlorate is minimized.

This will be explained in more detail below with reference to FIGS. 1-4.

Fig. 1 shows the concentration of active chlorine (sodium hypochlorite, NaOCl) and of chlorate depending on different current strengths. In addition, the discharge temperature from the E- lektrolysezelle is applied, at a constant flow temperature of 17 ⁰ C. The flow rate in the example shown is 3.5 l / h at a sodium chloride concentration of 10 g / l. All measurement results (also in the following FIGS. 2 to 4) relate to an electrolytic cell with an effective electrode area of 140 mm x 80 mm and an electrode gap of 2 mm.

As can be seen from Fig. 1, at currents of more than 3 amperes the disproportionate by-product chlorate is formed disproportionately. temperature of the product also increases with increasing current.

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The current intensity is now limited according to the invention in such a way that the chlorate concentration in the effluent is less than 1.5 g / l, preferably less than 1.0 g / l, more preferably less than 0.6 g / l or 0.5 g / l. l is. This can be achieved with a current that is preferably set between 2, 5 and 3.5 ampere, optimally to 3 amps.

In Fig. 2, the influence of the inlet concentration of NaCl on the active chlorine content is shown in the sequence, wherein a current of 3 amps was used.

It can be seen that the content of active chlorine increases only insignificantly from an inlet concentration of more than 7 g / l.

In addition, Fig. 3 shows that with an increase in the salt content, the chlorate formation increases disproportionately. Fig. FIG. 3 shows the concentration of active chlorine and of chlorate in the effluent and how the discharge temperature of the electrolysis cell as a function of the inflow concentration of NaCl (current 3 A). It is therefore a compromise between the chlorine yield on the one hand and the chlorate formation that should be avoided on the other.

Preferably, therefore, the feed concentration is set to a value between 2 and 10 g / l, preferably to 5 g / l. 4 shows the influence of the volume flow of salt solution supplied on the concentration of active chlorine and chlorate in the effluent, wherein a feed concentration of 10 g / l NaCl was used (current 3 A).

It can be seen that in the electrolytic cell used here with an effective electrode area of 140 mm × 80 mm with an electrode gap of 2 mm, the chlorate concentration is significantly reduced at a flow rate of 2.77 l / h and above. For the electrolytic cell with the dimensions mentioned above, therefore, a volume flow of 3 l / h is used.

The optimum volume flow with which the electrolytic cell is to operate, of course, depends on the geometric dimensions of the cell. The dimensions of the cell used are 140 x 80 mm electrode area at a distance of 2 mm. The volume flow and the cell size are functionally linked to one another, since with larger cells the throughput (and the yield) increases proportionally as a function of the ion migration rate.

The volumetric flow V is preferably determined as a function of the effective electrode area A (in m ² ) according to the relationship V = w • A, where w is the flow velocity which is between 4 × 10 ^-5 m / s and 12 × 10 ^-5 m / s, preferably between 6 x 10 ^-5 m / s and 9 x 10 ^-5 m / s.

This is an optimal operation in the desired range shown in FIG. 4 ensures that the formation of chlorate is minimized. It is understood that thus different sized electrolysis cells can be operated in the desired optimum range, provided that the volume flow is set accordingly.

Further, it should be understood that larger units may of course be constructed using a plurality of electrolytic cells of any size.

The device according to the invention is characterized by its particularly simple and reliable construction and works despite the absence of a control device in an optimal range in which the formation of chlorate is minimized and yet a sufficiently high sodium hypochlorite concentration is achieved.

Since the influencing variable of the temperature is difficult to influence in practical use and the temperature influence was relatively low in the investigations shown, the temperature was taken into account merely by limiting the current intensity (discharge temperature increases with increased current intensity). Cooling measures can thus be avoided.

Changes in the active chlorine concentration were not observed in steady state conditions even after a prolonged period of operation of 30 hours and more. A complex regulation can thus be omitted.

Claims

claims

A process for the preparation of an alkali metal hypochlorite solution, in particular a sodium hypochlorite solution, in which an undissolved electrolysis cell (12) is supplied with a brine solution having a given volume flow and salt concentration, and wherein the current is adjusted such that the concentration of electrolysis accumulating chlorate is limited to a maximum of 1, 5 g / l, preferably to a maximum of 1 g / l, more preferably to a maximum of 0, 6 g / l.

2. The method of claim 1, wherein the current is set between 2 and 6 amps, preferably between 2 and 4, 5 amps, more preferably between 2, 5 and 3, 5 amps.

3. The method of claim 1 or 2, wherein the brine solution is prepared with a constant salt concentration by mixing a saturated brine solution with water.

4. The method of claim 1 or 2, wherein as the brine solution, a salt solution is used with a certain salt concentration, which is promoted with a constant Förderström in the electrolysis cell (12).

5. The method according to any one of the preceding claims, wherein the salt concentration of the electrolytic cell (12) supplied brine solution is adjusted to a value between 2 and 10 g / l, preferably between 5 and 10 g / l.

6. The method according to any one of the preceding claims, wherein the electrolysis cell (12) is supplied with a brine solution having a constant volume flow V, the value of which is determined in dependence on the effective electrode area A (in m ² ) according to the relationship V = w • A. where w is the flow rate is between 4 • IGT ⁵ m / s and 12 • 10 ^-5 m / s, preferably is between 6 • 10 ^"s m / s and 9 • ^{10" 5} m / s is selected.

7. An apparatus for producing an alkali metal hypochlorite solution, in particular a sodium hypochlorite solution, with at least one undivided electrolysis cell (12), means (20, 22, 24, 26) for supplying a brine solution having a certain volume flow and a certain salt concentration into the electrolytic cell (12), and with a DC voltage source (18) for generating a current through the electrolysis cell (12), characterized in that the current intensity is set such that the concentration of chlorate obtained during the electrolysis to a maximum of 1, 5 g / l, preferably to a maximum 1 g / l, more preferably limited to 0, 6 g / l.

8. The device according to claim 7, characterized in that the current intensity is set between 2 and 6 amps, preferably between 2 and 4, 5 amperes, more preferably between 2, 5 and 3, 5 amps.

9. Apparatus according to claim 8, characterized in that the DC voltage source (18) is designed as a constant current source.

10. The apparatus of claim I ₁ 8 or 9, characterized in that the means for supplying brine solution include a brine tank (20) with saturated brine solution and a water tank (22) with water, each having a metering pump (24, 26) the electrolysis cell (12) are coupled.

11. The device according to claim 7, 8 or 9, characterized in that the means for supplying brine solution having a brine tank (20) with brine solution, which is coupled via a metering pump (24) with the electrolysis cell (12).

12. The device according to one of claims 7 to 11, characterized in that the electrolysis cell (12) is fed to a brine solution having a constant salt concentration in the range between 2 and 10 g / l, preferably in the range between 5 and 10 g / l is set.

13. The device according to one of claims 7 to 12, characterized in that the electrolytic cell (12) is supplied with a brine solution having a constant volume flow V whose value as a function of the effective electrode area A (in m ² ) according to the relationship V = w • A is set, where w is the flow velocity that is between 4 x 10 ^-5 m / s and 12 x 10 ^-5 m / s, preferably between 6 x 10 ^-5 m / s and 9 x 10 ^-5 m / s , is selected.

14. Device according to one of claims 7 to 13, wherein the electrolysis cell (12) electrodes (14, 16), which consist of a material containing iron, mercury, precious steel, titanium and / or platinum and which preferably consist of uncoated titanium.