DE102005004063A1 - Method and apparatus for producing an alkali metal hypochlorite solution - Google Patents

Abstract

The invention relates to an apparatus and a method for producing an alkali metal hypochlorite solution, in particular a sodium hypochlorite solution, comprising at least one undivided electrolysis cell (12), means (20, 22, 24, 26) for supplying a brine solution having a specific volumetric flow and a certain salt concentration the electrolytic cell (12) and with a DC voltage source (18) for generating a current through the electrolytic cell (12). The current intensity is set so tightly that the concentration of chlorate obtained during the electrolysis is limited to a maximum of 1.5 g / l, preferably to 0.6 g / l (FIG. 5).

Description

The The invention relates to a process for the preparation of an alkali metal hypochlorite solution, in particular a sodium hypochlorite solution, in an undivided electrolysis cell, a brine solution with a certain volume flow and with a certain salt concentration supplied becomes. The invention further relates to a device for producing a alkali metal hypochlorite, in particular a sodium hypochlorite solution, with at least one undivided one Electrolytic cell, means for supplying a brine solution a certain volume flow and a certain salt concentration in the electrolysis cell, and with a DC voltage source for Generation of a current through the electrolytic cell.

It is a stable one desire for the production of sodium hypochlorite solutions for disinfection be used by water. While Such a "chlorination" of water in the industrial scale scale for example, in drinking water treatment at the waterworks of the cities and Municipalities carried out is, exists for mobile use, especially in disaster areas, a need for the production of sodium hypochlorite solution on site. purified Water is added to the sodium hypochlorite solution after filtering and reverse osmosis, to prevent re-nucleation.

It Mobile plants are already known to pass sodium hypochlorite solutions Produce electrolysis of seawater or brine.

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

in this connection becomes either filtered seawater or a saturated brine supplied with a metering pump of an electrolytic cell. By also dilution water flowing into the electrolysis cell becomes the concentration the brine is lowered to about 2%. In the electrolytic cell is sodium hypochlorite and hydrogen is generated, with the hydrogen separated from the sodium hypochlorite solution and with a fan to a safe concentration with air dilute and discharged to the outside becomes. The produced sodium hypochlorite solution has a concentration of about 6 g / l of active chlorine. The entire process of production of sodium hypochlorite solution is monitored by a PLC control and regulated to maximize chlorine yield if possible to ensure a low rate of waste production.

When The problem with such a system is the use of a SPS control in conjunction with corresponding sensors to look at, since this is a regular maintenance and control required. Especially in operations in disaster areas However, this can happen frequently not guaranteed become.

In another from the DE 37 04 955 A1 known plant for producing a sodium hypochlorite solution, the brine concentration in the electrolytic cell is measured by evaluating the voltage at the electrodes and the flowing current. From this, a conductivity-proportional signal is generated which is used to control a saturated saline dosing pump.

Also This system is subject to the disadvantages described above.

In another from the DE 28 06 441 A1 In the known plant for producing sodium hypochlorite solution, a diaphraqm-free electrolysis cell is used in which the ratio to the effective anode area and the effective cathode area in the electrolysis cell is at least 1.5: 1 or greater. In this way, the effective utilization of Natriumhypochlo rits and the current efficiency at steady flow conditions should 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.

Also Such a system can not guarantee optimal process control especially if on a cooling is omitted to make the process as easy as possible.

From the US 4,329,215 It is also known 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 the use of such a membrane can solve the problem of chlorate formation while the electrolysis are reduced.

Indeed is such an electrolysis cell very maintenance-intensive.

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

These The object is achieved by a process for producing an alkali metal hypochlorite solution, in particular a sodium hypochlorite solution, solved, at the one undivided electrolysis cell with a brine solution a certain volume flow and with a certain salt concentration is fed and where the current strength is set so firmly that the concentration of at the Electrolysis accumulating 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 becomes.

The The object of the invention is further characterized by an apparatus for manufacturing an alkali metal hypochlorite solution, in particular a sodium hypochlorite solution, dissolved, with at least one undivided Electrolytic cell, means for supplying a brine solution a certain volume flow and a certain salt concentration in the electrolysis cell, and with a DC voltage source for Generation of a current through the electrolytic cell, the current strength such It is fixed that the concentration of electrolysis accumulating chlorate to a maximum of 1.5 g / l, preferably to a maximum 1 g / l, more preferably limited to a maximum of 0.6 g / l.

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

Namely, according to the invention the use of an undivided electrolysis cell without a diaphragm between anode and cathode a particularly simple and low-maintenance Construction guaranteed. According to the invention was found that the production of an alkali metal hypochlorite solution with fixed parameters can be operated advantageously, by the concentration of chlorate obtained during electrolysis is limited by a fixed current. Especially has been recognized according to the invention, that the concentration of active chlorine with increasing the current across one certain value increases only disproportionately, while at the same time the generation of undesirable Chlorate by-product disproportionately high increases.

Thus, according to the invention by a suitable determination of the current on the one hand a favorable concentration of active chlorine ensured in the produced alkali metal hypochlorite solution and on the other hand the generation of undesirable Chlorate on a bearable Limited measure.

All in all The procedure can be done in this way with fixed operating parameters without the effort of a special scheme in such a favorable manner be operated that an advantageous continuous operation with a low maintenance guaranteed is

In Advantageous development of the invention here is the current between 2 and 6 amps, preferably between 2 and 4.5 amps, especially preferably set between 2.5 and 3.5 amps.

hereby will be an optimal compromise between the generated concentration ensures active chlorine and the accumulation of unwanted chlorate.

According to one Another embodiment of the invention, the brine solution with a constant salt concentration by mixing a saturated brine solution with Water produced.

On this way can be the desired one Input concentration of the electrolytic cell with brine on particularly simple way set to a favorable value become. Because the starting product is a saturated salt solution is made with water, preferably with deionized water or Drinking water is mixed, so without additional regulatory effort ensures appropriate concentration of the electrolysis cell supplied salt solution become.

alternative it is also possible to have a saline solution to use with a certain salt concentration, which with a constant flow rate conveyed into the electrolysis cell becomes.

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

On This way, sufficient chlorine yield can be guaranteed without the accumulation of unwanted 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 electrolytic cell is operated with an optimum volume flow through which an optimal yield depending on the cell size is ensured.

at the device according to the invention the DC voltage source is preferably as a constant current source educated.

On this way, the optimally set current of the Electrolysis cell particularly precise be respected.

As already mentioned, can the desired concentration the brine solution supplied to the electrolytic cell either by mixing a saturated one brine solution adjusted with water or by using a brine solution with a certain concentration become. For mixing or feeding the pre-set brine solution Dosing pumps are preferably used, through which a constant mixing ratio or a constant flow rate guaranteed is.

The Electrodes of the electrolysis cell can for example consist of a Material consisting of iron, mercury, stainless steel, titanium and / or Contains platinum. The electrodes preferably consist of uncoated titanium.

Herewith has a good yield and a high stability of the electrodes result.

It it is understood that the above and the following yet to be explained features of the invention not only in the respective specified combination, but also usable in other combinations or in isolation, 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 on the drawing. Show it:

1 the relationship between current intensity and the concentration of active chlorine or chlorate produced and the discharge temperature in an electrolysis cell according to the invention;

2 the relationship between the feed concentration of a sodium chloride solution supplied and the generated active chlorine concentration;

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

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

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

The basic structure of a device according to the invention is in 5 represented and in total with the numeral 10 designated.

The device 10 is used to prepare a Alkalimetallhypochloritlösung, in particular a Natriumhypochloritlösung, using an electrolytic cell 12 , The electrolytic cell 12 gets out of a brine tank 20 fed to a saturated salt solution prior to delivery to the electrolysis cell 12 with water from a water tank 22 is mixed. The electrolytic cell 12 is designed as a one-piece cell not divided by a membrane and has a housing made of PVDF. The electrodes 14 . 16 , which consist of uncoated titanium, are with a DC voltage source 18 connected as a constant current source to generate 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 via a line 34 with a collecting container 36 connected. The sodium hypochlorite solution produced in this process is passed through a line 38 discharged to the outside, while the hydrogen rises upward and via an exhaust pipe 40 removed and diluted to a harmless concentration. The concentration of the electrolytic cell 12 supplied saline solution is by metering pumps 24 . 26 are set, each generating a constant volume flow. The first metering pump 24 sucks from the brine tank 20 saturated saline solution with a volume flow of 42 ml / h. The second dosing pump sucks out of the water tank 22 deionized water (or drinking water) via a pipe 32 with a flow rate of 2.958 l / h. The pressure lines of the two dosing pumps 24 . 26 lead through a common line 30 into the inflow of the electrolysis cell 12 , The electrolytic cell 12 Thus, in the example shown, a volume flow of 3 l / h sodium chlorite solution is supplied, whose concentration is adjusted by the mixture of the saturated salt solution with deionized water to a value of about 5 g / l.

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

The operating parameters of the device 10 are now set so tightly that the yield of sodium hypochlorite recovery in a range favorable for sodium hypochlorite production is driven, at the same time the accumulation of unwanted chlorate is minimized.

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

1 shows the concentration of active chlorine (sodium hypochlorite, NaOCl), as well as of chlorate depending on different current levels. In addition, the discharge temperature from the electrolysis cell is applied, at a constant inlet temperature of 17 ° 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 with the following 2 - 4 ) refer to an electrolytic cell having an effective electrode area of 140 mm x 80 mm and an electrode gap of 2 mm.

How out 1 can be seen, is disproportionately formed at currents greater than 3 amps, the undesirable by-product chlorate. It is also easy to see that the flow temperature of the product also increases with increasing current.

The amperage will now be according to the invention limits the chlorate concentration in the effluent to less than 1.5 g / l is, preferably less than 1.0 g / l, particularly preferred less than 0.6 g / l or 0.5 g / l. This can be achieved with a current which is preferably set between 2.5 and 3.5 amps, optimally to 3 amps.

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

It It can be seen that from a feed concentration of more than 7 g / l, the content of active chlorine increases only slightly.

In addition, shows 3 in that, if the salt content is increased, the formation of chlorate increases disproportionately. 3 shows the concentration of active chlorine and of chlorate in the effluent and the effluent temperature of the electrolysis cell as a function of the feed concentration of NaCl (current 3A). 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 set 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, with a feed concentration of 10 g / l NaCl was used (current 3A).

It shows that in the electrolytic cell used here with a effective electrode surface of 140 mm x 80 mm with an electrode distance of 2 mm, the chlorate concentration is significantly reduced at a flow rate of 2.77 l / h and above. For the Electrolysis cell with the dimensions mentioned above is therefore used a volume flow of 3 l / h.

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

The volume 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 · 10 ^-5 m / s and 9 · 10 ^-5 m / s is selected.

This is an optimal operation in the desired range according to 4 ensured, in which the formation of chlorate is minimized.

It is understood that thus different sized electrolytic cells in the desired optimal range can be operated, provided the volume flow is determined accordingly.

Further It is understood that larger units Naturally using a plurality of electrolytic cells in any one Size built up can be.

The inventive device is characterized by its particularly simple and reliable construction and works despite the absence of a control device in an optimal range where chlorate formation is minimized is and still a high enough 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 avoid to become.

changes The active chlorine concentration was also reached at steady-state conditions after a prolonged period of operation of 30 hours and more not detected. An elaborate scheme can thus be omitted.

Claims (14)

Process for the preparation of an alkali metal hypochlorite solution, in particular a sodium hypochlorite solution, in which an undivided electrolysis cell ( 12 ) is supplied to a brine solution having 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 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. Method according to Claim 1, in which the current intensity is between 2 and 6 amps, preferably between 2 and 4.5 amps, especially preferably between 2.5 and 3.5 amps is set. The method of claim 1 or 2, wherein the brine solution with a constant salt concentration by mixing a saturated brine solution is made with water. Process according to Claim 1 or 2, in which the brine solution used is a salt solution having a specific salt concentration which is introduced into the electrolysis cell at a constant flow rate ( 12 ). Method according to one of the preceding claims, in which the salt concentration of the electrolysis cell ( 12 ) is adjusted to a value between 2 and 10 g / l, preferably between 5 and 10 g / l. Method according to one of the preceding claims, in which the electrolytic cell ( 12 ) is supplied to a brine solution having a constant volumetric flow V, the value of which is determined as a function of the effective electrode area A (in m2) according to the relationship v = w · A, where w is the flow velocity which is between 4 · 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. Device for producing an alkali metal hypochlorite solution, in particular a sodium hypochlorite solution, with at least one undivided electrolytic cell ( 12 ), Means ( 20 . 22 . 24 . 26 ) for supplying a brine solution having a certain volume flow and a certain salt concentration into the electrolysis cell ( 12 ), and with a DC voltage source ( 18 ) for generating a current through the electrolytic cell ( 12 ), characterized in that the current intensity is set such that the concentration of chlorate obtained in the electrolysis is limited to a maximum of 1.5 g / l, preferably to a maximum of 1 g / l, more preferably to 0.6 g / l , Device according to claim 7, characterized in that that the current strength between 2 and 6 amperes, preferably between 2 and 4.5 amperes, more preferably between 2.5 and 3.5 amps is set. Apparatus according to claim 8, characterized in that the DC voltage source ( 18 ) is designed as a constant current source. Apparatus according to claim 7, 8 or 9, characterized in that the means for feeding brine solution comprises a brine tank ( 20 ) with saturated brine solution and a water tank ( 22 ) with water, which in each case via a metering pump ( 24 . 26 ) with the electrolysis cell ( 12 ) are coupled. Apparatus according to claim 7, 8 or 9, characterized in that the means for feeding brine solution comprises a brine tank ( 20 ) with brine solution, which via a metering pump ( 24 ) with the electrolysis cell ( 12 ) is coupled. 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, which is set in the range between 2 and 10 g / l, preferably in the range between 5 and 10 g / l. Device according to one of claims 7 to 12, characterized in that the electrolytic cell ( 12 ) is supplied to a brine solution having a constant volumetric flow V whose value is set as a function of the effective electrode area A (in m2) according to the relationship V = w · A, where w is the flow velocity which is between 4 · 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. Device according to one of claims 7 to 13, wherein the electrolytic cell ( 12 ) Electrodes ( 14 . 16 ), which consist of a material containing iron, mercury, stainless steel, titanium and / or platinum and which preferably consist of uncoated titanium.