DE2922275A1 - HALOGENING METHOD AND ELECTROLYSIS CELL SUITABLE FOR THIS - Google Patents

Description

PATENT LAWYERS

J. RBITSTÖTTER W. KINZBBACH

PROF. DR. DR. DIPL. ING. DR. PHIL. DIPL. CHEM. W. BUNTE (1958-1976) K. P. HÖLLER DR. ING. DR. RBR. NAT. DIPL. CHBM.

TELEPHONE I (089) 37βββ3 TELBXl B2I62O8 IBAR D

BAUEHSTRASSE 22. BOOO MUNICH

Munich, May 31, 1979 M / 20 143

ORONZIO DE NORA IMPIANTI ELETTROCHIMICI SpA
Via Bistolfi 35

Milan / Italy

Halogenation processes and suitable ones Electrolytic cell

POSTAL ADDRESS 1 POST BOX 7SO, D-80OO MUNICH 43

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Active chlorine or hypochlorite is used extensively to sterilize water »i.e. not just for 'Manufacture of drinking water, but also to prevent the proliferation of bacteria, biological concretions and Algae, and also for the oxidation of organic substances in swimming pools and in industrial cooling water systems. the The amount of active chlorine for this type of treatment is about 1 to 2 mg / l. The electrolytic production of active Chlorine by electrolysis of an alkali metal chloride in place and Body, has in terms of security and control systems several advantages over using gaseous chlorine from bombs or using liquid chlorine of hypochlorite, because of transportation, storage and absolutely reliable dosing devices as well as the Need for expensive security measures.

The advantages of on-site electrolytic production of active chlorine is most evident when one considers that the active chlorine produced is entirely in the electro lyt remains dissolved and it can also be produced in any required amount if required. The amount of generated active chlorine is proportional to the electrolysis current and it is therefore sufficient to use the current in terms of the amount to regulate the water to be treated in order to obtain a chlorine content within the desired limits.

In known electrolytic processes, a dilute brine, which contains between 25 and 45 g / l sodium chloride, is circulated at least once through one or more electrolysis cells arranged in series, in order to avoid an outflowing one To obtain a solution containing 0.1 to 8 g / l active chlorine and between 24 and 40 g / l sodium chloride. The gaseous hydrogen generated at the cathode is used by the outflowing Solution ventilated, which then suitably to the main

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Stream of the water to be treated is fed to a concentration of active chlorine between about 1 and 5 mg / 1 get in the water.

Active chlorine or active halogen means the concentration of the oxidation equivalents, expressed as weight unit per electrolyte volume, multiplied by the atomic weight of the corresponding halogen (chlorine = 35.457) taking into account that 1 mole of dissolved Cl ₂ corresponds to two equivalents, 1 mole dissolved HClO corresponds to two equivalents, 1 g of ion of dissolved ClO "corresponds to two equivalents and 1 g of ion of dissolved ClO ₃ " corresponds to six equivalents according to the reaction equations:

Cl ₂ + H ₂ O > 0 + 2Cl "+ 2H ⁺

HClO > 0 + Cl "+ H ⁺

ClO "» 0 + Cl "

ClO ₃ "> 3 0+ Cl "

In practice, the active chlorine concentration, expressed in grams / liter, is practically identical to the concentration on Hypochlorite, also expressed in grams / liter. Therefore, the terms "active chlorine" and "hypochlorite" in the present description are considered to be equivalent to a first approximation.

The well-known electrolytic process as it is customary was planned and implemented, is subject to known technical limits, which have a considerable influence on the economic efficiency of the process. One of the most important conditions to have a good overall electrolytic yield Method of obtaining direct chlorination of water on the spot is to obtain one for the desired

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anodic reaction, that for chlorine discharge as high as possible current yield with respect to unwanted side reactions, especially the oxygen discharge to obtain, usually catalytic anodes were used with a small surge towards the evolution of chlorine,> dung response to this reaction against the unwanted Sauerstoffentla- to favor which takes place at anodic potentials that exceed the anodic potential of chlorine development by 400 to 450 mV.

In order to operate at economically acceptable current densities, the sodium chloride content in the electrolyte must nevertheless be 25 to 35 g / l always exceed, since lower concentrations of chloride drastically reduce the Faraday yield for the evolution of chlorine, while the amount of oxygen evolved at the anode increases. This is due to the known kinetic problems associated with the diffusion of the chloride ions to the Anode connected by the anode double layer. When working at lower concentrations of chloride in the electrolyte , the chloride ions in the anodic film are seriously depleted, which then leads to an increase in oxygen evolution. The development of oxygen leads alongside a reduction in the total current efficiency of the process also leads to a shortening of the service life of the anode, since it is rapid is worn out or quickly loses its catalytic activity whether it is made of graphite or a valve metal, which is coated with an electrocatalytic coating of precious metals or noble metal oxides.

However, the need to maintain a sufficiently high concentration of sodium chloride in the electrolyte also have some disadvantages. In the first place, a large amount of salt is lost in the drain and the salinity in the main stream of water, which is created by the addition of the

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^! liquid flowing out of the cell has been treated, increases

i!

; considerably. The ratio between the amount added to the water If active chlorine and chloride are added, expressed in g / l, j ■ is always below 0.2 and in practice rarely exceeds 0.05 to! 0.1 g / l with the known methods. Another disadvantage j j is that it is practically impossible to get the water directly! to treat by simply leading the water flow through the cell, but that one leaking from the electrolytic cell Solution containing hypochlorite and chloride must be collected in a separate container and then concentrated ι Add the solution to the electrolyte with a suitable dosing system

^; must be joined.

It is therefore the object of the present invention to provide a method ^! and a device for halogenation

of water, in which one of the ! flowing solution is obtained in which the ratio i of the active halogen content to the halide content is greater than I is 0.2, and preferably not lower than 0.3, and that it j can be carried out with high efficiency.

I Another object of the invention is to provide a method and

To create a device for the halogenation of water for sterilization purposes, in which the desired active j concentration of halogen with a low salinity is generated directly in the stream of water to be treated.

Another object of the present invention is to! a method and an apparatus for electrolytic generation of aqueous hypochlorite solutions that have a low chloride content.

Finally, it is also an object of the invention to develop new electrolytic To create cells without a diaphragm, which in particular "

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are capable of releasing anodically oxidized chemical species into the carrier electrolyte flowing through the cell, while the release of non-oxidized species into the support electrolyte is prevented.

These objects are advantageously achieved by a process for the halogenation of water, which is characterized in that is that an electrolysis current through a porous, permeable anode and a cathode, which form an electrode gap, through which water flows, an aqueous solution of an alkali metal halide, which at least 25 g / l of said halide contains, introduces through the porous permeable anode into the electrode gap and the hydrodynamic Flow through said anode is regulated so that a weight ratio in the water flowing out of the electrode gap from active halogen to halide of at least 0.2 is maintained.

This method makes it possible by electrolysis directly an aqueous solution of Al kaiimetallhypohaliten with a produce very low content of alkali metal halides and is therefore accompanied by a reduced halide consumption, while with a high degree of efficiency and a high current density can be worked. This is achieved by using two separate fluid circuits, one for the alkali metal halide solution and another for the Electrolyte, i.e. for the hypohalite solution formed.

The method of the present invention is best describable and is therefore also described with reference to the preparation of hypochlorite using Sodium chloride because of the great commercial importance of this Process, but it should be expressly pointed out that other electrolytic processes, such as the manufacture

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production of potassium hypochlorite from potassium chloride, sodium chlorate from sodium chloride, sodium hypobromite from sodium bro- ' mid, can also be carried out on the basis of the present invention »;

Preferably the brine is used as concentrated as possible det, and in the case of sodium chloride, the concentration is preferably kept in a range of 100 g / l to 300 g / l. The brine concentration can easily be kept constant if the brine is continuously supplied by an external Concentration stage can circulate and the concentrated brine - returns to the cell compartment, which through the porous anode is separated from the water flowing through the electrolytic cell.

The porous anode is preferably made of a sintered valve metal with a thickness of 0.5 to 5 mm, a porosity of 20 to 70 % and an average pore diameter of 5 to 100 microns. In a particularly preferred embodiment, the anode has a porosity of 30 to 65 % and an average pore diameter of 5 to 50 microns and is made of sintered titanium. Of course, a suitable porous valve metal anode can also be produced differently, for example by "plasma jet" deposition of a porous layer of a valve metal on a perforated structure of a valve metal, preferably an expanded sheet, which not only serves as a carrier matrix and mechanical reinforcement agent, but also acts as a Power distributor for the entire anodic surface.

The porous valve metal anode is preferably activated by Impregnation and deposition of a thin layer on the valve metal, this layer being made of a non-passivating

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available material, which is resistant to the anodic environment and with regard to the development of halogen is electrocatalytic from aqueous solutions. Suitable materials are, for example, platinum group metals, which are represented by Thermal deposition can be applied to the porous structure of the valve metal by first treating the porous valve metal with a solution containing the decomposing Salts of the metals of the platinum group are impregnated and then heated. Electroplating can also be used of precious metals such as platinum, palladium, iridium, Ruthenium, rhodium and osmium.

Metal oxides belonging to group VIII of the periodic table, catalytic oxides and other metals such as manganese, lead, tin, or mixed oxides or mixtures of oxides of the above Metals and oxides of valve metals mentioned, can also can be used to activate the porous anode. The most preferred material is a mixed oxide of titanium and ruthenium, which is produced by thermal decomposition of a solution, the titanium and ruthenium salts and possibly minor ones Contains quantities of other metal salts, such as those of cobalt, nickel and tin, in the presence of oxygen on the sintered Structure of titanium or another valve metal applied will. The electrocatalytic covers are more detailed in U.S. Patents 3,711,385 and 3,632,498.

After activation, the porous anode surface, the facing the cathode surface, optionally with a thin, porous layer of a material such as polytetrafluoroethylene or another halogenated polymer, to make the surface hydrophobic and thus delaying the transport of the aqueous phase through the porous anode. The porous layer of polytetrafluoroethylene or other suitable material can be applied to the porous anode surface, e.g., by deposition

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! a solution or an emulsion of the polymer, removal of the 'solvent and subsequent heat treatment of the upper J area. The polymer can also be sprayed on.

The method of the present invention has the great advantage over conventional methods that it can be carried out at very high current densities. At present, the current density seldom exceeds 400 to 1000 A / m ² in the known industrial processes. Above this range, an electrolyte containing a larger amount of chloride must be used in order to achieve an acceptable current efficiency for chlorine evolution, but a solution with a concentration of more than 40 g / l of chloride is economically and technically disadvantageous because of the great waste of it Chloride and because there would be excessive chloride content in the draining solution.

In the method of the present invention, it is possible to operate ^{at a current density of 4000 to 5000 A / m 2} with a chlorine discharge current efficiency higher than 85 %. If a current density of, for example, 2000 to 3500 A / m is used, it is possible to maintain a current efficiency for the evolution of chlorine which is more than 96% and which is accompanied by an extraordinary increase in the life of the anode, since the The anodes are no longer exposed to the undesired excessive evolution of oxygen, which causes a loss of the catalytic activity of the noble metal oxide coating. If one takes into account that the evolution of chlorine is thermodynamically favored over the evolution of oxygen, the fact that most of the active anodic surface is constantly wetted by the concentrated brine also favors the discharge of chlorine and effectively prevents the discharge of oxygen even at a relatively high current density.

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Meanwhile, the chloride ions, which because of the concentration gradient and also because of one, become intentional pressure gradients maintained across the porous anode, if it proves necessary, tend to move out of the concentrated solution through the porous anode into the to diffuse aqueous electrolyte in the electrode gap circulates, oxidized to chlorine as they pass through the porous anode. This will reduce the chloride losses in the electrolyte, i.e., in the hypochlorite solution produced, is considerably reduced. The weight ratio between active chlorine and chloride ions in the outflowing solution can easily be kept above 0.2 preferably held between 0.3 and 0.8.

The reduction of water takes place on the surface of the cathode, which is made of titanium, steel or another suitable material has been produced and the evolved gaseous hydrogen is extracted from the cell along with the electrolyte ventilated, while hydroxyl ions correspondingly the reaction equation

H ₂ O + e "> ~ H ₂ + OH"

are formed. The chlorine developed at the anode reacts instantaneously after the well-known chemical disproportionation with the hydroxyl ions to form hypochlorite.

Depending on the desired minimum ratio between the concentrations of active chlorine and chloride, which are contained in the water flowing out of the cell, In practice, the higher the concentration of the brine, the higher the current density very high current yield for the halogen discharge and thus low oxygen development.

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To ensure a sufficient supply of chloride ions to the anode and to prevent the development of oxygen, especially if a porous anode with low permeability is used, i.e. an anode with low porosity and / or smaller mean pore diameters, a certain Pressure drop is maintained through the porous anode to allow sufficient hydrodynamic flow of the concentrated brine through the porous anode into the electrolyte, that flows through the gap between the electrodes. It has been found that the required pressure drop is rare Exceeds 1 meter of water. In practice, a pressure of 2 to 25 cm water column is sufficient when using commercially available sintered valve metals. Under the above conditions should be an automatic control of the pressure drop between the brine compartment and the water compartment be provided in order to ensure an optimal process execution under all conditions, since possible pressure fluctuations of the electrolyte caused by temporary causes can have an adverse effect on the electrolytic water chlorination process.

In a preferred embodiment with an automatic control system, two pressure gauges are provided in the brine or in the electrolyte compartment. The algebraic difference between the pressures in the two compartments is compared with a fixed comparison signal, which can be specified to maintain a certain pressure difference and which can actuate a control valve which is installed in the part of the brine circuit that flows downwards from the brine section, sx) that the pressure difference can be kept constant across the porous anode, regardless of pressure fluctuations that can occur either in the water or in the brine circuit.

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The brine concentration in the cell compartment becomes substantial kept constant by regulating the brine recirculation rate, while the amount of water between the porous anode and the cathode flows, can be varied within wide limits, depending on the desired Hypochlorite content (i.e. active chlorine) in the effluent Solution. The speed of the electrolyte through the electric

the gap can therefore be within a range of | Vary 1 cm / second to 1 m / second.

Instead of the brine to maintain a constant brine concentration concentrated brine can also be fed back continuously into the anode compartment by means of an adjustable or automatically regulated metering pump that is able to supply the necessary hydraulic To ensure the flow of brine through the porous anode.

In addition to the current yield for the chlorine discharge at the anode, other factors can also affect the total current yield of the electr affect the lysis. In particular, that formed on the anode tends Hypochlorite to decompose with subsequent evolution of oxygen or it disproportionates to chlorate and a further cathodic reduction of the hypochlorite takes place at the cathode. During the first two chemical reactions can easily be reduced to a minimum by working at low temperatures, i.e. below 25 ° C, competition the cathodic reduction of the hypochlorite according to the reaction equation

ClO "+ H ₂ O + 2e ~ => Cl '+ 20H ~

with the evolution of hydrogen, since this standard potential decreases about 1 volt greater than the water reduction potential. Accordingly, the kinetics of this reaction is controlled by the

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Convective and diffusive transport of the hypochlorite from the anode to the cathode determined. This secondary reaction is a main reason for the entire loss of electricity yield. The loss due to this secondary reaction can be reduced if the electrolyte is passed through in a laminar flow _; allows the space between the electrodes to flow. Still it is! Mass transport of the hypochlorite from the total electrolyte j to the cathode surface proportional to the concentration of the ₍ hypochlorite in the electrolyte.

In the known methods, because of the need to maintain a relatively high chloride concentration in the electrolyte flowing through the cell, it is not possible to carry out a direct chlorination of water, ie in a low concentration of active chlorine (hypochlorite) of 1 to 2 mg / 1, and it is therefore necessary to first prepare a concentrated solution containing up to 6 to 8 g / l of active chlorine (hypochlorite), which is then diluted in or with the main stream of water. At these high concentrations of hypochlorite, the loss of yield which can be attributed to the cathodic reduction of hypochlorite is very high and the total current efficiency can drop to less than 60 % . In contrast to this, the process according to the invention allows the direct chlorination of water in concentrations of 1 to 2 mg / 1 active chlorine, the loss of yield which can be attributed to the cathodic reduction of hypochlorite being reduced. These conditions can easily be achieved by increasing the speed of the electrolyte (water) in the cell and / or by bypassing the greater part of the water flow past the inter-electrode space of the cell. However, it is also possible by the method of the present invention to obtain a draining solution having a hypochlorite content of 8 to 10 g / l by measuring the residence time of the

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Electrolytes in the cell are increased or by having multiple cells

connected in series in the usual way. ι

Another notable loss in total current efficiency is due to the anodic oxidation of the hypochlorite to chlorate according to the reaction equation

6 ClO "+ 3H ₂ O > ^2C10 3 ~ ^{+ 4C1} " + 6H ⁺ + IO ₂ + 6e ~

caused. The higher the hypochlorite concentration in the electrolyte and the higher the current density, the greater the loss due to this reaction. Consider that the hypochlorite is formed on the anode surface so it is practically impossible in conventional cells to control or reduce this loss, since the electr lytes to reduce the hypochlorite diffusion to the cathode and laminar flow imposed to prevent the cathodic reduction of the hypochlorite, the conditions of rapid Removal of the hypchlorite, which is continuously on the anodic surface is formed, only make it worse. This loss of yield is increased by the process of the present invention Invention also greatly reduced.

Indeed, it was found that the total current efficiency can be increased dramatically if a small hydrodynamic flow of brine is provided through the porous anode. This is likely due to several factors, which in a positive sense reduce the tendency of the hypochlorite to be oxidized to chlorate at the anode. One of these factors is that on the anodic double layer on the entire active surface of the anode continuously chloride ions are available to a large extent. Another possible factor could be in a component of the hydrodynamic River that tends to produce

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Subtract hypochlorite, ie remove it from the active surface of the anode. The brine flow through the porous anode also offers the advantage that the cell voltage can be reduced. On the other hand, this flow is lowered within certain limits, the weight ratio of active chlorine and chloride contained in the effluent, substantially, which could not be ignored during the experiments observation. ¹ ι

The new electrolytic cell according to the invention without a diaphragm consists of a first compartment, which contains a porous, permeable anode and a cathode, the one between the electrodes Form space, a second compartment, which is separated from the first compartment by the porous, permeable anode, one Device for introducing a solution containing anodically oxidizable chemical species into a second compartment,

a device for the circulation of an electrolyte through the electrode gap of the first compartment, a device for regulating the hydrodynamic flow of the solution contained in said second compartment the porous anode in the support electrolyte and a device for generating an electrolysis current between said Anode and cathode.

The new electrolytic cell according to the invention without a diaphragm is particularly suitable for releasing anodically oxidized chemical species (e.g. Cl ^) into a carrier electrolyte, which flows through the cell (e.g. water) while the release of non-oxidized species (e.g. Cl ") into the supporting electrolyte is prevented.

The porous anode is capable of mixing between the solution with which the second compartment of the cell is fed is, and the carrier electrolyte, which is caused by the electrode

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Interstitial cell flow, preventing a large proportion of the oxidizable chemical species passing through Diffusion or, if necessary, also pass through the porous anode by a hydrodynamic flow, anodically oxidized before they are released into the carrier electrolyte flowing through the cell.

The cell's porous anode has a thickness between 0.5 and 5 mm, a porosity between 20 and 70 % and an average pore diameter of 5 to 100 microns. Preferably the anode has a porosity between 30 and 65 % and an average pore diameter between 5 and 50 microns.

ι The porous anode is made of an anodically resistant conductive one

Material made, preferably from a sintered one

S valve metal coated with a non-passivating catalytic

table material, such as a precious metal or a precious

! metal oxide, is activated.

ι The cathode consists of a corrosion-resistant conductive Material that has a low overpotential for the cathodic reaction and thus that applied to the cell Electrolysis current supports. If hydrogen is evolved from the aqueous carrier electrolyte, the cathode is preferred wise made of valve metals, nickel, iron, silver or theirs Alloys.

The cell according to the invention can be used for a number of electrochemical Processes are used in which it is beneficial to avoid the release of non-oxidized chemical Spe ^ iei 'into the carrier electrolyte, which passes through the space between the electrodes to prevent the cell from flowing.

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In the drawings shows

Figure 1 is a schematic diagram of the invention Procedure,

FIG. 2 shows a partial cross section of the electrolysis + according to the invention cell,

Figure 3 shows a cross section of the cell of Figure 2,

FIG. 4 shows a cross section of another embodiment of the electrolysis cell according to the invention,

Figure 5 is a partial cross-section of an alternative embodiment the electrolytic cell according to the invention and

FIG. 6 shows a cross section of the cell of FIG.

With reference to FIG. 1, the device according to the invention consists of an electrolysis cell 1 which has a compartment 2 with a cathode 3 made of steel, nickel, Hastelloy, titanium or another electrically conductive material with a low Upper voltage compared to the evolution of hydrogen, and a compartment 4, which from the compartment 2 by a porous Anode 5 is separated, which consists of a sintered valve metal, which with a non-passivatable and electrocatalytic material resistant to the anodic conditions is activated. The brine circuit consists of one Saturation tank 6, in which salt and brine solution are brought into contact with one another, a circulation pump 7, preferably in the area flowing upwards to the electrolytic cell 1, a second valve 8 in the area flowing downwards from the electrolytic cell Area and a suitable direct power source.

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The electrolyte leaving compartment 2 after electrolysis contains hypochlorite and that developed at the cathode Hydrogen. A suitable gas separation container 9 allows the ventilation of the gaseous hydrogen from the outflow p the hypochlorite solution. The automatic regulation of the optimal pressure drop across the porous anode 5 can by two pressure gauges 10 and Π in the brine compartment 4 and in the water compartment 2 are accomplished. The pneumatic or electrical signals from the two pressure gauges are processed in a suitable manner by a control device tet, which in turn controls the control valve 8 via a control system actuated.

FIG. 2 shows a schematic representation of a typical embodiment the cell according to the invention, which has a first body consisting of a container 20, preferably from Titanium and which is provided with a flange 21. A porous sintered titanium anode 22, which is preferably Has been activated with Kischoxiden of ruthenium and titanium, is welded to the inner circumference of the flange 21. Inlet 23 and outlet 24 permit the brine to circulate through the compartment. A second cell body consists of a steel container 25, to the flange of which a cathode 25, preferably made of stainless steel, is welded, and a Inlet 27 and an outlet (not shown) are attached to the two ends of the container 25. The cathode 26 can consist of a plate, a net or an expanded sheet metal and it ends shortly before the two ends of the container 25 so that the electrolyte can flow between the porous anode 22 and the cathode 26. An insulating seal 28 ensures the electrical insulation of the cathode from the anode and suitable electrical feed pieces, which are not shown provide for the supply of the electric current to the anodic flange 21 and to the cathodic flange.

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FIG. 3 shows a cross section of the cell of FIG. 2 and in both drawings the same parts are provided with the same reference numerals.

Figure 4 shows another embodiment of the invention Cell, which is particularly suitable for small capacities. It consists of a porous titanium tube 41 which has been suitably activated with an electrocatalytic coating and which is welded at one end to a titanium tube 42, provided with a sealing flange 43 and at the other end is welded to another titanium tube 44. The whole is in a flanged tube 45 made of stainless steel Steel or nickel, which over two elbows 46 and 47, preferably made of an inert, non-conductive material, with an electrolyte solution line is connected and provided with suitable extensions 48 and 49 through which a hydraulic seal is made with the titanium tubes. The seal is made at one end by seal 50 and at the other End through the sealing box 40 or something equivalent. While performing the procedure is concentrated Brine circulates continuously through the inside of the titanium tube, which is connected to the positive pole of the power source, while the tube 45 is connected to the corresponding negative pole. The porous titanium tube 41 acts as an anode and the inner surface of the tube 45 acts as a cathode.

With the embodiment shown in Figure 4 with concentric tubular electrodes cells with high capacity can be realized since any desired number of elements can be joined together in one of the appearance of conventional heat exchanger tubes in a similar manner. For example, one may be similar to a heat exchanger tube Cell can be realized using activated porous titanium tubes that allow brine circulation in the casting

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and allows water to circulate within the porous tubes. The cathode can consist of a series of rods welded to one of the cell heads and concentric within are inserted into each anodic tube. Alternately, the brine can circulate through the porous titanium tubes, while the water circulates in the sheet metal pipe casing. In this case, openwork wire nets are concentric! mounted outside the porous titanium tubes and electrically connected to the casing and thus act as a cathode.

Figure 5 shows a further embodiment of the cell of the invention, which consists of a cylindrical flanged ₅ at both ends of container 51, it being possible to this container easily inserted into a conduit of water to be treated. The cylinder can be provided with two right-angled, flanged, diametrically opposed openings. The anode 52 consists of a rectangular box-shaped container, closed on all sides and made of titanium or some other valve metal, and it is inserted into one of the two openings. The box-shaped container is closed on one side by the titanium flange 53, which is adapted to the flanged opening of the cylinder. The large surfaces of the anode 52 consist at least partially of porous plates 54 made of titanium or another sintered valve metal, and the porous plates are preferably activated with mixed oxides of titanium and ruthenium.

The titanium flange 53 is provided with at least two nozzles 55 and 56 for the brine inlet and outlet and the brine is continuously inside the anodic box-shaped Tank 52 circulates to keep the brine concentration at a constant value. An isolation seal 57 provides for electrically isolating the anode from the container 51

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and the end piece 58 supplies the anode with the electric power. The cathode placed in the opposite opening

• The cell consists of two sheets 59a and 59b made of steel,

ι Nickel or stainless steel welded to the flange 60

j, which in turn is the flanged container opening

ι is adapted. A suitable end piece 61 supplies the cathode

! with electricity. The two plates that make up the cell catho-:

ι de form, are at a distance of a few millimeters from the \

j surface of the anode 52 attached and suitable on the ^!

! Spacers attached to the surface of the cathode 59a and 59b,

; such as a series of polyvinyl chloride buttons prevent the

Touching the electrodes during assembly or the process

! rens implementation.

FIG. 6 shows a cross section of the cell of FIG. 5 and in both figures the same parts are denoted by the same reference numerals. Figure 6 shows spacers 62, the consist of teflon rods with a diameter of 3.5 mm and those on the surface of the anodic box-shaped container 52 are attached.

The electrolyte or flows while the process is being carried out the dilute hypochlorite solution through the tank 51 and part of the river flows between the opposite ones Surfaces of the anode, which are essentially on the two longer sides of the box-shaped container 52 from the activated consists of porous titanium plates, and the cathode, which consists of the two sheets 59a and 59b. That on the anode The chlorine evolved reacts with the hydroxide of the alkali metal and hypochlorite is formed, while the oxygen developed at the cathode comes from the electrolysis of the water. The cell is particularly suitable for direct chlorine! tion of water, e.g. in drinking water systems or for sterilization ization of swimming pools, etc. Indeed, the in the

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Unit of time, the amount of hypochlorite or active chlorine generated can be easily controlled by monitoring the amount supplied to the cell Current varies in proportion to the total water flow through container 51.

The free cross section of the container 51 can be adjusted in a suitable manner with regard to the current supplied to the cell as a whole be dimensioned in order to achieve the required hypochlorite concentration, i.e. a concentration in the range of 0.5 to 1 mg / l. There are therefore collecting devices for the concentrated hypochlorite solution and Dosing systems no longer necessary. In addition, an automatic control can be used for regulation in a simple manner of the total current supplied to the cell proportional to the electrolyte flow can be realized in order to increase the concentration of active chlorine in the draining solution below the maximum permissible limit.

Some preferred embodiments are described in the following examples to illustrate the invention. In order to however, the invention is not intended to be limited to these specific embodiments.

Example 1_

The experiment was carried out with the device from FIG. 1 using the electrolytic cell from FIG. 2 with an apparent (projected) anodic surface of about 10 cm ² . The anode consisted of a 1.5 mm thick porous sintered titanium plate with a porosity of 65 % and an average pore diameter of 25 microns. The porous titanium substrate was degreased and then pickled in a dilute KCl solution for 1 minute and

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then completely in a solution of 5 ml of 5% HCl, 10.8 mg TiCl ₃ (calculated as metal), 9 mg RuCl ₃ (calculated as metal), 0.2 mg SnCl ₄ -SH ₂ O (calculated as Metal), 5 drops of isopropyl alcohol, and 2 to 4 drops of hydrogen peroxide submerged. The porous titanium was then ^{dried in air at 30 °} C. and then heated ^{to 350 °} C. in an air circulation oven for 10 minutes. This process was repeated several times until the porous titanium ^{showed a weight increase corresponding to 25 g / m 2} and an electrocatalytic coating was obtained. \ The Solepermeabilität the activated porous titanium anode j decreased the initial permeability to about 60%. i

A brine solution containing 300 g / l sodium chloride was j circulates continuously in the anode compartment of the time, j around fn the brine discharge a constant sodium chloride content of above 298 g / L and water was circulated through the cathode compartment. During the trial it was the temperature in the cell through the circulating water kept between 14 and 17 ° C. The hydrostatic pressure drop through the anode was kept at 0 while the current density and also the water flow was increased to the concentration of active chlorine equivalent in the draining electrolyte to keep between 100 and 500 mg / l. The cell voltages that Amounts of chloride ions in the outflowing solution and the total current yields are listed in Table I.

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TABLE I.

current
density
A / m ² Cell
tension
V CI2 equivalent
concentration
mg / 1 NaCl-Kon
centering
mg / 1 , Relationship
of active
Cl2 / NaCl Total current
yield in
% 500 4th 98 400 0.245 ι
54 y 1000 4.5 150 600 0.25 68 I.
j 2000 6th 300 1000 0.30 70 3000 7th 350 1100 0.32 65 4000 8th 350 1090 0.32 55 6000 12th 500 1000 0.46 48

The results of Table I show that the total current; Yield decreased as soon as the current density was increased above a value between about 1000 and 3000 A / m ² and this was due to an increase in the anodic polarization with an accompanying evolution of oxygen, which was caused by the electrolysis of water and the anodic oxidation of the hypochlorite to chlorate and contributed to the decrease in the total current efficiency.

The current density was now kept at 2000 A / m ² and an increasing hydrostatic pressure difference was generated through the porous anode by increasing the hydrostatic pressure on the brine in relation to the water to cross the anodic surface through the porosity of the anode to supply more chloride ions. The results are summarized in the following table II.

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M / 20 143

TABLE II

4P
cm What
column Cell
tension
V Cl £ equivalent
concentration
mg / 1 NaCl-Kon
centering
mg / 1 relationship
of active
Cl ₂ / NaCl total
power out
prey in t O 6th 300 1050 0.30 70 2.5 5.8 310 1050 0.33 74 4.0 5.1 383 1020 0.37 88.5 y 6.0 4.7 394 1200 0.33 91.2

The results of Table II clearly show that the cell voltage and thus the energy yield of the process and | The overall current efficiency can be improved extraordinarily if a minimum of hydrodynamic brine flow is generated through the porous anode by creating a certain pressure difference through the porous anode. At the same time, under these conditions, the ratio, by no means reduced between active chlorine and chloride ions in the effluent from the \ cell electrolytes, but J easily increased, by the extraordinary increase in the
Total current yield can be explained.

710 / V.

030049/0506

Claims (15)

yο7777R M / 20 143 ■ * .-. · <~ £. & t J 267.086-Germany Pate ntansp röche 1. A process for the halogenation of water, characterized in that that one passes through one of a porous permeable; Anode and a cathode electrode gap formed by which water flows through, an electrolytic current flow IHBt and that an aqueous solution of an alkali metal halide j nids that contain at least 25 g / l of said calogenide holds, through the porous permeable anode in the electrodes- j Gap can flow and that one regulates the hydrodynamic flow through the said anode so that a ßewewichtbereich from active halogen to halide In the water flowing out of the electrode gap of at least 0.2 is maintained. 2. The method according to claim t, characterized * that sodium chloride is used as the alkali metal halide and the active halogen contained in the water draining from the cell is essentially sodium hypochlorite. 3. The method according to claim 1, characterized in that the porous and permeable anode consists of a rigid element which has at least one layer of a sintered valve metal powder with a porosity between 20 and 70 % and an average pore diameter between 5 and 1100 microns * wherein the said porous valve metal layer has been activated by impregnation with an electrocatalytic material which has a low upper voltage when halogen is generated. 4. The method according to claim 3, characterized in that the valve metal is titanium and the electrocatalytic one 030049/0506 m / 20 143. <g. 2322275 267.086-6ermany Material of at least one metal selected from Group platinum, palladium ^ ruthenium, iridium, osmium and Rhodium in metallic form or as oxides exists. 5. The method according to claim t, characterized in that through the thickness of said porous permeable anode maintain a constant hydrostatic pressure differential therethrough becomes »the water column between 0 and 1 m, in a positive direction from the brine side to the electrolyte side the anode. 6. The method according to claim t »characterized in that the electrode surfaces of the electrolytic cell are arranged parallel to one another and both in parallel planes in relation to the streamlines of the flowing through the cell Lying in the water. 7. The method according to claim t, characterized in that the concentration of the brine solution in contact with the porous and permeable anode is essentially is kept constant by forced circulation of the brine through the brine compartment of the electrolysis cell and through the Concentration device »which is installed outside the electrolytic cell. 8. The method according to claim 5, characterized in that the hydrostatic pressure difference through the thickness of said porous and permeable anode is automatically kept constant by an automatic control device which is on a control valve which is arranged in the part of the brine circuit flowing downwards into the electrolysis cell, can act, the control device being operated by two pressure gauges, one of which is in the brine section of the electrolysis cell and the other in the water section of the electrolysis 030049/0506 cell is arranged. 9. A method for the electrolytic generation of an aqueous solution of sodium hypochlorite by electrolysis of a Sodium chloride solution at a temperature below 25 ° C, characterized in that water is through a Lets flow electrolytic cell, which consists of a cathode and a porous permeable anode with a low upper voltage compared to the chlorine evolution, wherein the anode surface, which is not exposed to the flow of water, is in constant contact with brine for at least 25 g / l sodium chloride containing that the hydrodynamic flow church the said porous permeable anode limited by regulating the hydrostatic pressure difference through the thickness of said anode, see above that a weight ratio of active halogen to halide contained in the solution flowing out of the cell are maintained greater than 0.2. 10. Electrolytic cell without diaphragm »characterized in that that it consists of a first compartment (2) which contains a porous, permeable anode (5} and a cathode (3) which form an electrode gap, a second compartment (4), which is separated from the first compartment (2) by the porous permeable anode (5), a device for the Circulation of an electrolyte through the second compartment (4), a device for the circulation of a second Electrolytes through the electrode gap of the first compartment (2), a device for maintaining a constant hydrostatic pressure drop between the two compartments (2, 4) through said porous anode (5) and a device for generating an electrolysis current between said cathode (3) and anode (5), consists. 030049/0508 11. Electrolytic cell according to claim 10, characterized in that the porous permeable anode (5) consists of a rigid Element with at least one layer of a sintered valve metal powder, said layer < has a porosity between 20 and 70%, a middle ren pore diameter between 5 and 100 microns and by impregnation with an electrocatalytic material has been activated. 12. Electrolysis cell according to claim 11, characterized in that the valve metal is titanium and the electrocatalytic one Material consists of at least one metal from the group consisting of platinum, palladium, ruthenium, iridium, rhodium and osmium in metallic form or as oxide is selected. 13. Electrolytic cell according to claim 12, characterized in that the electrocatalytic material and titanium dioxide Ruthenium dioxide is in solid solution form. 14. Electrolytic cell according to claim 10, characterized in that the anode is made of a sintered titanium powder Body represents. 15. Electrolytic cell according to claim 10, characterized in that the anode consists of a valve metal network, which with a layer of sintered valve metal particles is provided. 030049/0506