TW201406998A - Undivided electrolytic cell and use thereof - Google Patents

Abstract

The present invention relates to a method for producing an ammonium peroxodisulphate or an alkali-metal peroxodisulphate, to an undivided electrolytic cell constructed from individual components and to an electrolytic apparatus constructed from a plurality of electrolytic cells of this type.

Description

Separate electrolyzer and its use

One aspect of the invention pertains to a method of making ammonium peroxodisulfate or an alkali metal peroxodisulfate.

It is known from the prior art to produce alkali metal peroxodisulfate and ammonium peroxodisulfate by anodizing an aqueous solution containing the corresponding sulfate or hydrogen sulfate and crystallization from the anolyte to extract the salt formed. . Since the decomposition voltage of this method is higher than the decomposition voltage of anodic oxygen formed by water (known as a promoter), thiocyanate in the form of sodium thiocyanate or ammonium thiocyanate is usually used to increase water at the commonly used platinum electrode. It becomes a decomposition voltage of oxygen (oxygen overpotential).

Rossberger (US Pat. No. 3,915,816 (A)) discloses a method of directly producing sodium persulfate. There is disclosed a separatorless electrolytic cell containing a platinum-coated titanium-based anode as an electrolytic cell. The current efficiency is based on the addition of a potential increase promoter.

According to DE 27 57 861, a sulfuric acid solution is used as a catholyte in a cell comprising a membrane protected cathode and a platinum anode, and an initial concentration of 5 to 9 weight is electrolyzed at a current density of at least 0.5 to 2 A/cm 2 . Percent sodium ion, 12 to 30 weight percent a sulfuric acid ion, 1 to 4 weight percent ammonium ion, 6 to 30 weight percent peroxydisulfate ion, and a potential increase accelerator (especially such as thiocyanate), an aqueous solution of a neutral anolyte, and a current efficiency of 70 Up to 80% sodium peroxodisulfate. After the peroxodisulfate crystallizes and is separated from the anolyte, the mother liquor is mixed with the cathode product, neutralized, and re-supplied to the anode.

The disadvantages of this method are:

1. Promoters must be used to minimize oxygen production.

2. In order to achieve the described high current efficiency, the anode must be spatially separated from the cathode using a suitable membrane. The diaphragm required for this is very sensitive to wear.

3. In order to obtain economically acceptable current efficiency, it is necessary to have a high current density and therefore a high anode potential.

4. Issues related to the manufacture of platinum cathodes, especially for acceptable electrical efficiency and long anode life for technical purposes. It should be noted here that continuous platinum corrosion can achieve up to 1 g/ton of product in the persulfate. This platinum corrosion both contaminates the product and results in the consumption of expensive raw materials, which in turn increases the cost of the process.

5. Therefore, only a high degree of dilution can produce a persulfate with a low solubility, namely potassium persulfate and sodium persulfate. It causes high energy output due to crystal formation.

6. When a known conversion method is used, the manufactured persulfate must be recrystallized from the ammonium persulfate solution. This usually results in a decrease in the purity of the product or even a complete impureness.

EP-B 0 428 171 discloses a method for manufacturing A filter-press-type electrolytic cell of an oxygen compound (including ammonium peroxodisulfate, sodium peroxodisulfate, and potassium peroxodisulfate). In this case, a platinum foil applied to the valve metal by heat equalization is used as the anode. It uses a solution corresponding to a sulfate as a catholyte, which solution contains a promoter and sulfuric acid. This method also has the above problems.

In the process according to DE 199 13 820, an aqueous solution containing neutral ammonium sulphate is anodized to produce peroxodisulfate. To produce a sodium or potassium salt of peroxodisulfate, a solution obtained by anodization is used using a sodium hydroxide solution or a potassium hydroxide solution containing ammonium peroxodisulfate. After crystallization and separation of the corresponding alkali metal peroxodisulfate, the mother liquor is recycled to mix the catholyte produced during the electrolysis. In this method, electrolysis is also carried out on the platinum electrode as an anode in the presence of a promoter.

Although peroxodisulfate has been extracted by anodizing at a platinum anode on a commercial scale for decades, this method still has serious drawbacks (see also above). In order to increase the oxygen overpotential and improve the current efficiency, it is always necessary to add an accelerator, also called a polarizing agent. Since the oxidation products of these promoters are necessarily formed as by-products during anodization, the toxic substances enter the anode off-gas and must be removed by air washing. High current efficiency further requires separation of the anolyte and catholyte. Anodes that are typically completely covered by platinum always require high current densities. The result is an anolyte volume, a separator and a cathodic current load, which requires additional measures to reduce the cathode current density by three-dimensionally structuring the cell and activation. In addition, a high heat load of the unstable peroxodisulfate solution will occur. In order to minimize this load, structural measures must be taken and cooling requirements are increased. Due to limited heat dissipation The electrode surface must be defined, resulting in an increased complexity of installation per cell. In order to manage high current loads, it is often necessary to use electrode support materials with high heat transfer properties that are prone to corrosion and expensive.

PAMichaud et al., Electrochemical and Solid-State Letters , 3(2) 77-79 (2000) teaches the production of peroxodisulphate by anodizing sulfuric acid using a boron doped diamond film electrode. This document teaches that this type of electrode has a higher oxygen overpotential than the platinum electrode. However, this document does not indicate any technique for producing peroxodisulphate and alkali metal peroxodisulfate using boron doped diamond film electrodes. In this case, it is particularly known that on the one hand sulfuric acid, on the other hand hydrogen sulphate (especially neutral sulphate), the behavior is very different during anodization. Although the oxygen overpotential at the boron-doped diamond film electrode is increased, in addition to the anodization of sulfuric acid, the main side reaction is the production of oxygen and ozone.

In the EP 1 148 155 B1 patent, which is hereby incorporated by reference in its entirety in the entire disclosure of the disclosure of the disclosure of the disclosure of the disclosure of the disclosure of the disclosure of the disclosure of the disclosure of This type of high current efficiency. The disadvantage of this method is that, due to the sensitivity of the above-mentioned separators, only a high degree of dilution can produce a persulfate having a low solubility (essentially potassium persulfate and sodium persulfate), ie below the solubility limit, thus causing Crystallization and salt discharge during evaporation and drying require high energy output.

It is therefore an object of the present invention to provide a process for the manufacture of ammonium peroxodisulfate and an alkali metal peroxodisulfate which overcomes the disadvantages of known processes or at least has only a low degree of disadvantage and can be used The diamond-free, non-separating cell produces persulfate, especially in electrolytes or electrolytic suspensions containing sulfate and sulfuric acid, thus in addition to the electrochemical advantages demonstrated in one part of the invention, It is also a mechanical and abrasive property which is also known for the other uses of the electrochemically oxidized sulfate in the suspension by the diamond-coated support as described above.

To achieve this object, the invention thus provides a process for the manufacture of ammonium peroxodisulphate or an alkali metal peroxodisulfate comprising at least one anode and a cathode (to be doped with trivalent or pentavalent elements and arranged An aqueous electrolyte containing a salt derived from ammonium sulfate, an alkali metal sulfate and/or a corresponding hydrogen sulfate salt in an electrolytic cell in which the diamond layer on the continuous support is used as an anode) is anodized at the anode and the cathode There is no separation electrolysis space between them, and the aqueous electrolyte does not contain an accelerator for increasing the decomposition voltage of turning water into oxygen.

The salt for anodization from ammonium sulphate, alkali metal sulphate and/or the corresponding hydrogen sulphate may be any alkali metal sulphate or the corresponding hydrogen sulphate. However, in the context of the present application, it is particularly preferred to use sodium sulphate and/or potassium sulphate and/or the corresponding hydrogen sulphate.

In the definition of the present invention, "accelerator" or "polarizer" is any means known to those skilled in the art as an additive to increase the decomposition voltage of water into oxygen or to improve current efficiency during electrolysis. An example of such a type of accelerator for use in the prior art is a thiocyanate such as sodium thiocyanate or ammonium thiocyanate. This type of accelerator is not used in the present invention. In other words, in the method of the present invention, the electrolyte has a promoter concentration of 0 g/liter. By not using a promoter in this process, for example, purification requirements for a typical electrolytic gas produced are not necessary.

The method of the present invention uses an anode comprising a diamond layer that is doped with a trivalent or pentavalent element and arranged on a continuous support. One of the advantages of this feature is that the wear resistance of the diamond coating is very high. Long-term testing has proven that the shortest life of this type of electrode is more than 12 years.

The anode used can be of any shape.

Any anode support material known to those skilled in the art can be used in this case. In a preferred embodiment, the support material of the present invention is selected from the group consisting of ruthenium, osmium, titanium, zirconium, hafnium, tantalum, molybdenum, tungsten, carbides of these elements, and/or aluminum, or a combination of these elements. The group formed.

A diamond layer doped with a trivalent or pentavalent element is applied to the support material. The doped diamond layer is thus an n-type conductor or a p-type conductor. In this case, it is preferred to use a boron-doped and/or phosphorus-doped diamond layer. The amount of doping is set to achieve the desired, usually just the right conductivity. For example, when boron is doped, the crystalline structure contains up to 10,000 ppm of boron.

The diamond layer can be applied to all or part of the surface, such as only in front of the support material or only on the back side.

Methods of applying a diamond layer are known to those skilled in the art. In particular, diamond electrodes can be fabricated by two specific chemical vapor deposition (CVD) processes. It is a microwave plasma CVD method and a hot filament CVD method. In both cases, the gas phase formed by microwave irradiation or thermal activation of the thermal filament to form a plasma is formed from methane, hydrogen, and optionally other additives (especially gaseous compounds of dopants).

The p-type semiconductor can be provided using a boron compound such as trimethylboron. N-type semiconductors use gaseous phosphorus compounds as dopants Got it. A layer of doped diamond is deposited on the crystalline crucible to obtain a particularly dense and non-porous layer - typically having a film thickness of about 1 micron. In this case, the diamond layer is preferably applied to the anode support material used in the present invention at a film thickness of from about 0.5 μm to 5 μm, preferably from about 0.8 μm to 2.0 μm, and particularly preferably about 1.0 μm.

As an alternative to depositing a diamond layer on a crystalline material, the deposition can also be carried out on a self-passivating metal such as titanium, tantalum, tungsten, or tantalum. For the preparation of particularly suitable boron-doped diamond layers on germanium single crystals, please refer to the article by P.A. Michaud above.

In the context of the present invention, it is particularly preferred to use an anode comprising a lanthanum or titanium support having a boron doped diamond layer, especially a boron doped diamond layer having up to 10,000 ppm boron in the crystalline structure.

The cathode used in the process of the present invention is preferably made of lead, carbon, tin, platinum, nickel, alloys of these elements, zirconium and/or acid resistant high grade steel, as is known in the art. The cathode can be of any shape.

In the electrolytic cell used in the present invention, the electrolytic space between the anode and the cathode is not partitioned, that is, there is no separator between the anode and the cathode. The use of a non-separated cell allows the electrolyte to have a very high solids concentration, which in turn significantly reduces the energy consumption for salt extraction (essentially crystallization and water evaporation) as the solids ratio increases, which is less than the separation of the cells. At least 25%.

In a preferred embodiment, the method of the invention is practiced in a two dimensional or three dimensional tank. In this case, the groove is preferably formed by a flat groove or a tubular groove.

Especially using tubular geometry, ie by the inner tube as the anode A tubular groove composed of a tube (preferably made of a diamond-coated crucible) and a tube other than a cathode (preferably made of acid-resistant high-grade steel) is advantageous in that it has a low material cost. It is preferred to use the annular gap as a common electrolytic space and result in uniform flow conditions, so that the flow loss is low and the utilization of the available electrolytic surface is high, which in turn represents high current efficiency. This type of groove is low in manufacturing cost compared to those known as flat grooves.

A preferred embodiment of the method of the present invention combines a plurality of electrolytic cells, preferably in a double tube bundle or in two dimensions.

The electrolyte used in the process of the present invention preferably has an acidic (preferably sulfuric acid) or neutral pH.

In a further preferred embodiment of the method of the invention, the electrolyte moves through the electrolysis cell during the process. As a result, the electrolysis temperature in the tank is avoided, which accelerates the persulfate decomposition and therefore does not wish to increase.

In a further preferred embodiment, the method includes removing the electrolyte from the electrolytic circuit. In particular, it is carried out in order to extract the produced peroxodisulfate. Accordingly, a further preferred embodiment relates to the extraction of the peroxydisulfate salt produced by crystallizing and separating crystals from the electrolyte by forming an electrolytic mother liquor, preferably from the electrolytic circuit. A further preferred embodiment comprises recycling the electrolyzed mother liquor by increasing the acid, sulfate and/or bisulfate content of the electrolysis cell, especially if the previously produced peroxodisulfate has been isolated.

In accordance with the present invention, the anodization is preferably carried out at an anode current density of from 50 to 1500 mA/cm 2 , and more preferably from about 50 to 1200 mA/cm 2 . The best current density used is 60 to 975 mA / cm ^ 2 range.

The electrolyte used in the process of the present invention preferably has a total solids content of from about 0.5 to 650 grams per liter. The (working) electrolyte preferably contains from about 100 to about 500 grams per liter of persulfate, more preferably from about 150 to about 450 grams per liter of persulfate, and most preferably from 250 to 400 grams per liter of persulfate. salt. The method of the present invention thus has a high solids concentration in the electrolyte without the need to add a potential increasing agent or accelerator, and has no exhaust gas and wastewater treatment requirements caused by it, and has high current efficiency in the production of peroxodisulfate.

Further, the electrolyte preferably contains from about 0.1 to about 3.5 moles of sulfuric acid per liter (1) of the electrolyte, more preferably from 1 to 3 moles of sulfuric acid per liter of the electrolyte, and most preferably from 2.2 to liters per liter of the electrolyte. 2.8 mol sulfuric acid.

In summary, it is particularly preferred to use an electrolyte having the following composition for the method of the present invention: 150 to 500 grams of persulfate per liter of electrolyte, and 0.1 to 3.5 moles of sulfuric acid per mole of electrolyte. The total solids content is preferably from 0.5 g/liter to 650 g/liter, more preferably from 100 to 500 g/liter, and most preferably from 250 to 400 g/liter, and the proportion of sulfate may vary herein. The ratio of the accelerator is 0 g / liter.

The invention further relates to a split-free electrolytic cell constructed from individual components, an electrolytic device constructed from a plurality of such electrolytic cells, and its use for electrolyte oxidation.

"Electrolysis" is a chemical change that occurs when an electric current passes through an electrolyte. This change is directly converted into chemical energy by electrical energy due to the reaction of the electrode and the mechanism of ion movement. The most technically significant electrochemical transformation is the electrolysis of a brine solution in which a sodium hydroxide solution and chlorine are formed. Today, inorganic peroxides are also commercially produced in electrolytic cells.

In commercial processes, it is particularly desirable that the reaction be operated with high concentrations of reagents and corresponding products. The high product concentration ensures that the final product can be simply separated, as the solvent must be removed in the event that the reaction product is in solution. This reduces the energy consumption of downstream electrolysis product preparation during electrolysis of highly concentrated electrolytes.

However, applications with very high solids ratios place high demands on the electrolyser assembly due to the abrasive effects of the electrolyte. In particular, the diaphragm which prevents the reaction product of the anode and the cathode space from being mixed in the separation electrolytic cell cannot be subjected to the electrolysis procedure for a long time at a high concentration. In the case of a high solids ratio, electrolysis can only be carried out in a non-separating tank, wherein the anode space and the cathode space do not have to be spatially separated by insertion of a suitable membrane. This type of non-separating tank is used especially when the reagents or products produced at the anode or cathode are not altered or otherwise reacted in a destructive manner by other electrode procedures.

In addition, the anode and cathode materials must also meet the mechanical requirements for high solids concentrations and must therefore be extremely wear resistant.

In order to design an electrolysis that is as economical as possible, it is necessary to construct the electrolysis cell to constitute electrolysis at the highest feasible current density. It is only possible that the anode and the cathode have good electrical conductivity and are chemically inert to the electrolyte. Graphite or platinum is usually used as the anode material. However, these materials have the disadvantage of insufficient wear resistance at high solids concentrations.

The manufacture of mechanically stable and inert electrodes is disclosed in DE 199 11 746. In this case, the electrode is coated with a layer of conductive diamond which is applied using chemical vapor deposition (CVD).

An object of the present invention is to provide a high solid concentration (up to approximately 650 g/L) and in the high current density range (up to approximately 1500 mA/cm 2 ) resulting in a continuous and optimum electrolysis cell. The electrolytic cell accommodates the electrochemical reaction to be carried out, and the individual components can be easily replaced when the tank itself is broken.

Surprisingly, this object can be achieved by an electrolytic cell comprising: (a) at least one tubular cathode, (b) at least one rod-shaped or tubular anode comprising a conductive support coated with a layer of conductive diamond, (c At least one inlet tube, (d) at least one outlet tube, and (e) at least one dispensing device.

In the electrolytic cell, the anode and the cathode are preferably arranged to be concentric with each other, and the annular gap between the inner and outer cathodes forms an electrolytic space. In this particular embodiment, the diameter of the cathode is therefore greater than the anode.

In a preferred embodiment, the electrolysis space contains no membrane or membrane. In this case, it is an electrolysis cell containing a co-electrolysis space, ie the electrolysis cell is not separated.

The spacing between the outer surface of the anode and the inner surface of the cathode is preferably between 1 and 20 mm, more preferably between 1 and 15 mm, still more preferably between 2 and 10 mm, and most preferably between 2 and 6 mm. between.

The inner diameter of the cathode is preferably between 10 and 400 mm, more preferably between 20 and 300 mm, and still more preferably between 25 and 250 mm.

In a preferred embodiment, the anode and cathode are independently of each other from 20 to 120 cm long, more preferably from 25 to 75 cm long.

The length of the electrolysis space is preferably at least 20 cm, more preferably at least 25 cm, and at most preferably 120 cm, more preferably 75 cm.

The cathode used in the present invention is preferably made of lead, carbon, tin, platinum, nickel, an alloy of these elements, zirconium and/or an iron alloy, especially high grade steel, more particularly an acid resistant high grade steel. In a preferred embodiment, the cathode is made of acid resistant high grade steel.

The base material of the rod or tube, preferably tubular anode, is preferably tantalum, niobium, titanium, zirconium, hafnium, tantalum, molybdenum, tungsten, carbides of these elements, and/or aluminum, or a combination of these elements.

The anode support material may be the same as the anode base material or may be different. In a preferred embodiment, the anode base material functions as a conductive support. Any conductive material known to those skilled in the art can be used as the conductive support. Particularly preferred support materials are tantalum, niobium, titanium, zirconium, hafnium, tantalum, molybdenum, tungsten, carbides of these elements, and/or aluminum, or combinations of these elements. It is particularly preferable to use niobium, titanium, tantalum, niobium, tungsten, or a carbide of these elements, more preferably niobium or titanium, and still more preferably niobium as a conductive support.

A layer of conductive diamond is applied to the support material. The diamond layer can be doped with at least one trivalent or at least one pentavalent main or group B element. The doped diamond layer is thus an n-type conductor or a p-type conductor. In this case, it is preferred to use a boron-doped and/or phosphorus-doped diamond layer. The amount of doping is set to achieve the desired, usually just the right conductivity. For example, when boron is doped, the crystalline structure contains up to 10,000 ppm, preferably 10 ppm to 2000 ppm of boron and/or phosphorus.

The diamond layer can be applied to all or part of the surface, preferably It is the entire outer surface of the rod or tubular anode. The conductive diamond layer is preferably non-porous.

Methods of applying a diamond layer are known to those skilled in the art. In particular, diamond electrodes can be fabricated by two specific chemical vapor deposition (CVD) processes. It is a microwave plasma CVD method and a hot filament CVD method. In both cases, the gas phase formed by microwave irradiation or thermal activation of the thermal filament to form a plasma is formed from methane, hydrogen, and optionally other additives (especially gaseous compounds of dopants).

The p-type semiconductor can be provided using a boron compound such as trimethylboron. An n-type semiconductor is obtained using a gaseous phosphorus compound as a dopant. A layer of doped diamond is deposited on the crystalline crucible to obtain a particularly dense and non-porous layer. In this case, the diamond layer is preferably applied to the conductive support used in the present invention at a film thickness of about 0.5 to 5 μm, preferably about 0.8 to 2.0 μm, and particularly preferably about 1.0 μm. In another embodiment, the diamond layer is preferably from 0.5 microns to 35 microns, preferably from 5 microns to 25 microns, and most preferably from 10 to 20 microns, applied to the conductivity used in the present invention. Support.

As an alternative to depositing a diamond layer on a crystalline material, the deposition can also be performed on a self-passivating metal such as titanium, tantalum, tungsten, or tantalum. For the preparation of a particularly suitable boron-doped diamond layer on a germanium single crystal, please refer to P.A. Michaud (Electrochemical and Solid State Letters, 3(2) 77-79 (2000)).

In the context of the present invention, it is particularly preferred to use an anode comprising a ruthenium or titanium support having a boron-doped diamond layer, especially a boron or titanium support-containing anode having a boron-doped diamond layer of up to 10,000 ppm boron.

The diamond coated electrode features very high mechanical strength and wear resistance.

Preferably, the anode and/or the cathode, more preferably the anode and the cathode, are still more preferably anodes, and the source of current is connected via a dispensing device. If the anode and cathode are connected to the source of current via the dispensing device, it must be ensured that the dispensing device is thus electrically insulated. In any case, it should be noted that there should be good electrical contact between the anode and/or cathode and the dispensing device.

The dispensing device further ensures that the electrolyte is evenly supplied into the electrolysis space by the inlet tube. Once the electrolyte has passed through the electrolysis space, the converted electrolyte (electrolyte product) is efficiently collected by at least one upstream delivery device and is directed away via the outlet tube.

The dispensing devices of the present invention are preferably each independently composed of tantalum, niobium, titanium, zirconium, hafnium, tantalum, molybdenum, tungsten, carbides of these elements, and/or aluminum, or a combination of these elements, particularly preferred. For titanium.

Preferably, the dispensing device has at least one connector for at least one outlet or inlet tube and a connector for the anode. The connector for the anode is formed on a hollow cylinder that is optionally closed, in which an anode tube or rod is mounted. In the case of a tubular anode, the hollow cylinder can seal the anode tube in the dispensing device such that no electrolyte can enter the interior of the anode. Alternatively, the connector of the anode dispensing device can include a venting opening in the anode tube. As a result, in the case where the pressure of the dispensing member is excessive, the electrolyte is prevented from flowing into the anode tube.

The optionally closed hollow cylinder of the dispensing device can be applied to the support material of the anode or even directly to the support of the diamond coated body. In the latter case, the carrier and the dispensing device are thus conductive diamond layers Separated from each other. In a particularly preferred embodiment, the dispensing device is permanently attached to the anode, particularly preferably welded. It is particularly advantageous if this is done at high currents. For example, the anode and the dispensing device can be welded by diffusion welding, electron beam welding or laser welding.

The radial holes are distributed around the hollow cylindrical periphery of the dispensing device. Preferably, the dispensing device comprises three, more preferably four, and still more preferably five radial holes. The electrolyte can be dispensed into the electrolysis space uniformly and in a flow-optimised manner via radial holes in the dispensing device and effectively deflect the electrolysis product after passing through the electrolysis space.

The electrolyte is preferably supplied to the electrolysis cell, in particular a dispensing device, via an inlet tube. The electrolysis product is preferably directed away from the electrolysis cell via an outlet tube, especially after the electrolysis product has been collected by the dispensing device.

In a preferred embodiment, the dispensing device is also formed as a sealed tubular cathode such that no electrolyte or electrolysis products can exit the cathode.

The dispensing device achieves a number of purposes, independently of each other: ̇ sealing the tubular anode such that no electrolyte can enter the interior of the anode, or regulating the pressure through the venting opening in the anode space, and/or causing the anode and/or cathode to electrically contact the current Source, and/or 配送 distribute the electrolyte evenly and in a flow-optimized manner into the electrolysis space (optimal hydraulic distribution over all exchange surfaces), and/or 有效 effectively direct the electrolysis product away from the electrolysis space, and/or ̇ Seal the tubular cathode, and / or ̇ reduce flow losses.

The assembly anode, cathode, dispensing device, and inlet and outlet tubes can be combined to form an electrolytic cell by a corresponding combination of equipment known to those skilled in the art.

Due to the modular construction of the anode, cathode, dispensing device, inlet and outlet tubes, individual components may be formed from different materials and, if damaged, may be individually exchanged or replaced. Thus, the diamond anode of the present invention can be interconnected with other components made of inexpensive materials in a simple manner to form a compact electrolytic cell.

The tubular electrolytic cell is further characterized by the use of less material and strength. Parts that wear over time (eg, due to the abrasive action of the electrolyte) can be individually replaced, and in this regard, economical material use is also ensured. In a tubular electrolytic cell, the flow passes through the electrolysis space in an optimized manner, thereby preventing flow losses and optimally using the surface for electrochemical material exchange. Due to the electrode material and the electrode assembly, a continuous and uniform electrolysis process can be performed at a high solid concentration and a high current density.

A further aspect of the invention is an electrolysis apparatus comprising at least two electrolysis cells of the invention, through which the electrolyte flows successively, and which operates electrochemically in parallel connection. Therefore, the system capacity can be flexibly designed without limitation.

The electrolysis cell of the invention or the electrolysis device of the invention is particularly suitable for electrolyte oxidation. As noted above, the separation-free cell is suitable for electrolyte oxidation if the electrolyte product, or the electrolysis products produced and converted at the anode or cathode, are not altered or otherwise reacted in a disruptive manner by other electrode procedures.

The electrolytic cell of the invention can be 50 to 1500 mA / square Between the points, preferably between 50 and 1200 mA/cm 2 , and more preferably between 60 and 975 mA/cm 2 , current density operation is therefore a commercial and economical method.

The electrolytic cell/electrolytic apparatus of the present invention may further be at 0.5 to 650 g/liter, preferably 100 to 500 g/liter, more preferably 150 to about 450 g/liter, and still more preferably 250 to 400 g/liter. It is used at very high solids concentrations.

The electrolysis cell/electrolytic apparatus of the present invention is particularly suitable for use in the anodization of sulfate to peroxydisulfate.

The electrolysis cell/electrolytic apparatus of the present invention has proven to be particularly successful in the manufacture of peroxodisulfate.

It is known from the prior art to produce alkali metal peroxodisulfate and ammonium peroxodisulfate by anodizing an aqueous solution containing the corresponding sulfate or hydrogen sulfate and crystallization from the anolyte to extract the salt formed. . Since the decomposition voltage of this method is higher than the decomposition voltage of anodic oxygen formed by water (known as a promoter or a polarizing agent), thiocyanate in the form of sodium thiocyanate or ammonium thiocyanate is usually used to increase water. The platinum electrode becomes a decomposition voltage of oxygen (oxygen overpotential).

Rossberger (US Pat. No. 3,915,816 (A)) discloses a method of directly producing sodium persulfate. There is disclosed a separatorless electrolytic cell containing a platinum-coated titanium-based anode as an electrolytic cell. The current efficiency is based on the addition of a potential increase promoter.

According to DE 27 57 861, a sulfuric acid solution is used as a catholyte in a cell comprising a membrane protected cathode and a platinum anode, and the initial concentration is electrolyzed at a current density of at least 0.5 to 2 A/cm 2 . The amount is 5 to 9 weight percent of sodium ion, 12 to 30 weight percent of sulfate ion, 1 to 4 weight percent of ammonium ion, 6 to 30 weight percent of peroxodisulfate ion, and potential increase promoter (especially such as thiocyanate The acid salt) is an aqueous solution of a neutral anolyte to produce sodium peroxodisulfate having a current efficiency of 70 to 80%. After the peroxodisulfate crystallizes and is separated from the anolyte, the mother liquor is mixed with the cathode product, neutralized, and re-supplied to the anode.

The disadvantages of this method are:

1. Promoters must be used to minimize oxygen production.

2. In order to achieve the described high current efficiency, the anode must be spatially separated from the cathode using a suitable membrane. The diaphragm required for this is very sensitive to wear.

3. In order to obtain economically acceptable current efficiency, it is necessary to have a high current density and therefore a high anode potential.

4. Issues related to the manufacture of platinum cathodes, especially for acceptable electrical efficiency and long anode life for technical purposes. It should be noted here that continuous platinum corrosion can achieve up to 1 g/ton of product in the persulfate. This platinum corrosion both contaminates the product and results in the consumption of expensive raw materials, which in turn increases the cost of the process.

5. Therefore, only a high degree of dilution can produce a persulfate with a low solubility, essentially potassium persulfate and sodium persulfate. It causes high energy output due to crystal formation.

6. When a known conversion method is used, the manufactured persulfate must be recrystallized from the ammonium persulfate solution. This usually results in a decrease in the purity of the product or even a complete impureness.

EP-B 0 428 171 discloses a filter press type electrolytic cell for producing peroxy compounds (including ammonium peroxodisulfate, sodium peroxodisulfate, and potassium peroxodisulfate). In this case, a platinum foil applied to the valve metal by heat equalization is used as the anode. It uses a solution corresponding to a sulfate as a catholyte, which solution contains a promoter and sulfuric acid. This method also has the above problems.

In the process according to DE 199 13 820, an aqueous solution containing neutral ammonium sulphate is anodized to produce peroxodisulfate. To produce a sodium or potassium salt of peroxydisulfide, a solution obtained by anodization is used using a sodium hydroxide solution or a potassium hydroxide solution containing ammonium peroxodisulfate. After crystallization and separation of the corresponding alkali metal peroxodisulfate, the mother liquor is recycled to mix the catholyte produced during the electrolysis. In this method, electrolysis is also carried out on the platinum electrode as an anode in the presence of a promoter.

Although peroxodisulfate has been extracted by anodizing at a platinum anode on a commercial scale for decades, this method still has serious drawbacks (see also above). In order to increase the oxygen overpotential and improve the current efficiency, it is always necessary to add an accelerator, also called a polarizing agent. Since the oxidation products of these promoters are necessarily formed as by-products during anodization, the toxic substances enter the anode off-gas and must be removed by air washing. High current efficiency further requires separation of the anolyte and catholyte. Anodes that are typically completely covered by platinum always require high current densities. The result is an anolyte volume, a separator and a cathodic current load, which requires additional measures to reduce the cathode current density by three-dimensionally structuring the cell and activation. In addition, a high heat load of the unstable peroxodisulfate solution will occur. In order to minimize this load Structural measures are required and cooling requirements are also increased. Due to the limited heat dissipation, the electrode surface must be defined, resulting in an increased assembly complexity per cell. In order to manage high current loads, it is often necessary to use electrode support materials with high heat transfer properties that are prone to corrosion and expensive.

PAMichaud et al., Electrochemical and Solid-State Letters , 3(2) 77-79 (2000) teaches the production of peroxodisulphate by anodizing sulfuric acid using a boron doped diamond film electrode. This document teaches that this type of electrode has a higher oxygen overpotential than the platinum electrode. However, this document does not indicate any technique for producing peroxodisulphate and alkali metal peroxodisulfate using boron doped diamond film electrodes. In this case, it is particularly known that on the one hand sulfuric acid, on the other hand hydrogen sulphate (especially neutral sulphate), the behavior is very different during anodization. Although the oxygen overpotential at the boron-doped diamond film electrode is increased, in addition to the anodization of sulfuric acid, the main side reaction is the production of oxygen and ozone.

In the EP 1 148 155 B1 patent, which is hereby incorporated by reference in its entirety in the entire disclosure of the disclosure of the disclosure of the disclosure of the disclosure of the disclosure of the disclosure of the disclosure of the disclosure of This type of high current efficiency. The disadvantage of this method is that, due to the sensitivity of the above-mentioned separators, only a high degree of dilution can produce a persulfate having a low solubility (essentially potassium persulfate and sodium persulfate), ie below the solubility limit, thus causing Crystallization and salt discharge during evaporation and drying require high energy output.

The salt for anodization from ammonium sulphate, alkali metal sulphate and/or the corresponding hydrogen sulphate may be any alkali metal sulphate or the corresponding hydrogen sulphate. However, in the context of this application, it is particularly preferred to use sodium sulfate. And / or potassium sulphate and / or the corresponding hydrogen sulphate.

In the electrolytic cell used in the present invention, the electrolytic space between the anode and the cathode is not partitioned, that is, there is no separator between the anode and the cathode. The use of a non-separated cell allows the electrolyte to have a very high solids concentration, which in turn significantly reduces the energy consumption for salt extraction (essentially crystallization and water evaporation) as the solids ratio increases, which is less than the separation of the cells. At least 25%. It is also not necessary for the present invention to use an accelerator.

In the definition of the present invention, "accelerator" is any means known to those skilled in the art as an additive to increase the decomposition voltage of water into oxygen or to improve current efficiency during electrolysis. An example of such a type of accelerator for use in the prior art is a thiocyanate such as sodium thiocyanate or ammonium thiocyanate.

The electrolyte used in the process of the present invention preferably has an acidic (preferably sulfuric acid) or neutral pH.

During this process the electrolyte is movable through the electrolysis cell in the circuit. As a result, the electrolysis temperature in the tank is avoided, which accelerates the persulfate decomposition and therefore does not wish to increase.

The electrolyte is removed from the electrolytic circuit to extract the produced peroxodisulfate. The produced peroxodisulfate can be extracted from the electrolyte by crystallizing and separating the crystal by forming an electrolytic mother liquor.

At the beginning of the electrolysis, the electrolyte used preferably has a total solids content of from about 0.5 to 650 g/l. At the beginning of the conversion, the electrolyte preferably contains from about 100 to about 500 grams per liter of persulfate, more preferably from about 150 to about 450 grams per liter of persulfate, and most preferably from 250 to 400 grams per liter. Persulfate. Use of the electrolysis cell / or electricity of the present invention The apparatus can therefore have a high solids concentration in the electrolyte without having to add a potential increasing agent or accelerator, and there is no exhaust gas and wastewater treatment requirement caused by it, and it has high current efficiency in the production of peroxodisulfate.

Further, the electrolyte preferably contains from about 0.1 to about 3.5 moles of sulfuric acid per liter (1) of the electrolyte, more preferably from 1 to 3 moles of sulfuric acid per liter of the electrolyte, and most preferably from 2.2 to liters per liter of the electrolyte. 2.8 mol sulfuric acid.

In summary, it is particularly preferred to use an electrolyte having the following composition for the method of the present invention: 150 to 500 grams of persulfate per liter of starting electrolyte, and 0.1 to 3.5 moles of sulfuric acid per liter of electrolyte. The total solid content is preferably from 0.5 g/liter to 650 g/liter, more preferably from 100 to 500 g/liter, and most preferably from 250 to 400 g/liter. The ratio of the accelerator is 0 g / liter.

1‧‧‧Inlet pipe

2a‧‧‧Distribution device

2b‧‧‧Distribution device

3‧‧‧ Electrolyte space

4‧‧‧Anode

5‧‧‧ cathode

6‧‧‧Export tube

7‧‧‧Seal

21‧‧‧Connectors for inlet or outlet pipes

22‧‧‧Connector for anode

23‧‧‧ radial holes

Figure 1 shows a comparison of current efficiencies for different cell types with or without thiocyanide (accelerator).

Figure 2a shows the current/voltage in the Pt/HIP and diamond electrodes.

Figure 2b shows the current/efficiency in Pt/HIP and diamond electrodes.

Figure 3 is a plan view of the electrolytic cell of the present invention.

Figure 4 is a cross section of the electrolytic cell of the present invention.

Figure 5 shows the individual components of the electrolysis cell of the present invention.

Figure 6 shows the delivery device.

Figure 3 shows a possible embodiment of the electrolytic cell of the present invention.

Figure 4 is a graphical representation showing the cross section of this model. The electrolyte enters the dispensing device (2a) through the inlet tube (1) and is supplied to the electrolyte space (3) in a flow-optimized manner therefrom. The electrolyte space (3) is formed by an annular gap between the outer surface of the anode (4) and the inner surface of the cathode (5). The electrolysis product is collected by the dispensing device (2b) and transferred to the outlet tube (6). A seal (7) encloses the electrolyte space between the inlet and outlet tubes and the inner surface of the cathode.

In a preferred embodiment, the dispensing device (2) can be constructed to function as a dispensing device with a sealed electrolyte space.

Figure 5 shows the individual components of the electrolysis cell of the present invention. The numbering is the same as in Figure 4. Figure 5 shows other components used to seal the cell and for the assembly, but not numbered. These components are known to those skilled in the art and can be replaced as desired.

Figure 6 is an enlarged view of the dispensing device (2). The dispensing device comprises a connector (21) for the inlet or outlet tube and a connector (22) for the anode (4). The connector for the cathode forms a hollow cylinder which is provided with an anode tube or rod (4).

The radial holes (23) are distributed around the hollow cylinder of the dispensing device. The electrolyte can be uniformly supplied into the electrolysis space via radial holes (23) in the dispensing device, and can effectively conduct the electrolysis product after passing through the electrolysis space. Preferably, the dispensing device comprises three, more preferably four, and still more preferably five radial holes.

[Examples]

Produce various peroxodisulfates according to the following institutions:

"Sodium peroxodisulfate"

Anode reaction: 2SO ₄ ^2- →S ₂ O ₈ ^2- +2e ^-

Cathodic reaction: H ⁺ +2e ^- → H ₂ ↑

Crystallization: 2Na ⁺ +S ₂ O ₈ ^2- →Na ₂ S ₂ O ₈ ↓

Total reaction: Na ₂ SO ₄ + H ₂ SO ₄ → Na ₂ S ₂ O ₈ + H ₂ ↑

"Ammonium Peroxydisulfate"

Anode reaction: 2SO ₄ ^2- →S ₂ O ₈ ^2- +2 _e ^-

Cathodic reaction: H ⁺ +2e ^- → H ₂ ↑

Crystallization: 2NH ₄ ⁺ +S ₂ O ₈ ^2- →(NH ₄ ) ₂ S ₂ O ₈ ↓

Total reaction: (NH ₄ ) ₂ SO ₄ +H ₂ SO ₄ →Na ₂ S ₂ O ₈ +H ₂ ↑

Potassium Peroxydisulfate

Anode reaction: 2SO ₄ ^2- →S ₂ O ₈ ^2- +2e ^-

Cathodic reaction: H ⁺ +2e ^- → H ₂ ↑

Crystallization: 2K ⁺ +S ₂ O ₈ ^2- →K ₂ S ₂ O ₈ ↓

Total reaction: K ₂ SO ₄ +H ₂ SO ₄ →K ₂ S ₂ O ₈ +H ₂ ↑

The following examples illustrate the manufacture of sodium peroxodisulfate in accordance with the present invention.

Two-dimensional and three-dimensional grooves composed of a boron-doped, diamond-coated tantalum anode (the diamond anode of the present invention) can be used for this purpose.

Electrolyte Starting Composition

Temperature: 25 ° C

Sulfuric acid content: 300 g / liter

Sodium sulfate content: 240 g / liter

Sodium persulfate content: 0 g / liter

Effective anode surface area in the groove pattern used:

- Tubular groove with platinum-titanium anode: 1280 square centimeters

- Tubular groove with diamond-铌 anode: 1280 cm2

- Flat groove with diamond-铌 anode: 1250 cm2

Cathode material: acid resistant high grade steel: 1.4539

Solubility limit of the system (sodium persulfate): approximately 65 to 80 g / liter

Current Density

The electrolyte is concentrated by recycling (see Figures 1 and 2).

〔result〕

From the progress of current efficiency as a function of changing the sodium persulfate content (Fig. 1), it is clear that even if no promoter is added, the diamond anode used is acceptable in this tank of about 100 g/l to about The overall operating range of 350 g/l still achieved significantly higher current efficiencies than the conventional platinum-coated titanium anodes with the addition of promoters.

Progress in current efficiency as a function of current density during the manufacture of sodium peroxodisulfate by the use of a platinum anode (comparative example) with the addition of a corresponding promoter and a boron-doped diamond anode for use in a separate separator cell It can be clearly seen (Figs. 2a and 2b) that a current density of more than 75% can be obtained at a current density of 100 to 1500 mA/cm 2 .

Conversely, however, this test shows that conventionally coated Pt foil-coated titanium anodes achieve current efficiencies of only 60 to 65% up to this operating range, despite the addition of sodium thiocyanate solution as a promoter. However, current efficiency of only 35% was achieved without the addition of a promoter, thus demonstrating the invention.

In summary, it can be confirmed that even without the addition of a potential increasing agent, the current efficiency of the diamond-coated tantalum anode is about 10% higher than that of the conventional platinum-titanium anode and the addition of the potential increasing agent, and the ratio includes a conventional platinum-titanium anode. The groove height without the addition of the potential increasing agent is about 40%.

The voltage drop of the diamond coated anode is about 0.9 volts higher than the comparative cell containing the platinum-titanium anode. Furthermore, it has been demonstrated that the current efficiency of the diamond electrode used in the present invention (without adding a promoter and increasing the total sodium peroxodisulfate content in the electrolyte) is only slowly increased by one in some test conditions, such as a current efficiency equal to or greater than 65%, An electrolyte having a sodium peroxodisulfate content of about 400 to 650 g/liter can be obtained.

Conversely, the use of conventional platinum anodes and also the use of promoters in the electrolyte yields only an equivalent peroxydisulfate concentration of about 300 grams per liter, and is obtained with a current efficiency of about 50%.

A simple test using a similar system of potassium ions from potassium sulfate produced similar good results.

It is surprising to those skilled in the art that the method of the present invention can utilize a technically fully controllable current density, spatially separates the anolyte from the catholyte and does not use a promoter, in a non-separated cell in which no promoter is added. High current efficiency and high persulfate and solids concentration are achieved with high conversion levels.

Part of the test of the present invention determines that the use of a diamond film electrode doped with a trivalent or pentavalent element in a non-separating tank and thus the production of ammonium peroxodisulfate (but mainly an alkali metal peroxodisulfate) with high current efficiency is also possible. . Surprisingly, the tank can also be used in an economically viable manner at very high solids content (ie peroxodisulfate content), while the use of accelerators can be omitted altogether and electrolysis can be carried out at high current densities, thus giving further advantages, Especially with regard to installation and purchase costs.

〔in conclusion〕

Use a non-separated cell to make the electrolyte very high The solids concentration, which in turn increases the energy consumption for salt extraction (essentially crystallization and water evaporation), is proportionally reduced by at least 25% compared to the separated tank.

Although the accelerator is not required, the purification measures required for the electrolysis gas are omitted, but the removed electrolyte can achieve a higher degree of conversion and a higher persulfate concentration.

The same manufacturing throughput can significantly reduce the operating current density of the platinum anode, whereby the ohmic losses in the system are less, thus reducing the energy required for cooling, and increasing the freedom of designing the cell and cathode.

At the same time, current efficiency and manufacturing yield can be increased in the case of an increase in current density.

Due to the excellent wear resistance of the diamond-coated anode, it can be used at very high flow rates compared to structurally similar Pt anodes.

1‧‧‧Inlet pipe

2a‧‧‧Distribution device

2b‧‧‧Distribution device

3‧‧‧ Electrolyte space

4‧‧‧Anode

5‧‧‧ cathode

6‧‧‧Export tube

7‧‧‧Seal

Claims (20)

An electrolytic cell comprising: (a) at least one tubular cathode, (b) at least one rod or tubular anode comprising a conductive support coated with a layer of conductive diamond, (c) at least one inlet tube, (d) at least one outlet tube, and (e) at least two dispensing devices. The electrolytic cell according to claim 1, wherein the annular gap between the inner anode and the outer cathode forms an electrolytic space. The electrolytic cell of claim 1 or 2, wherein the electrolytic cell comprises a common electrolytic space without a membrane. The electrolytic cell according to any one of claims 1 to 3, wherein an interval between the outer surface of the anode and the inner surface of the cathode is 1 to 20 mm. The electrolytic cell according to any one of claims 1 to 4, wherein the cathode has an inner diameter of between 10 and 400 mm. The electrolytic cell according to any one of claims 1 to 5, wherein the anode and the cathode are each independently 20 to 120 cm long. The electrolytic cell according to any one of claims 1 to 6, wherein the support system is selected from the group consisting of ruthenium, osmium, titanium, zirconium, hafnium, tantalum, molybdenum, tungsten, carbides of these elements, and/or A group of aluminum, or a combination of these elements. The electrolytic cell according to any one of claims 1 to 7, wherein the diamond layer is doped with at least one trivalent or at least one pentavalent main group or group B element, especially boron and/or phosphorus. The electrolytic cell according to any one of claims 1 to 8, wherein the cathode is made of lead, carbon, tin, platinum, nickel, an alloy of these elements, zirconium and/or an iron alloy, especially by acid resistance. Made of high grade steel. The electrolytic cell according to any one of claims 1 to 9, wherein the electrolyte of the electrolytic cell is supplied through an inlet pipe. The electrolytic cell of any one of claims 1 to 10, wherein the electrolytic product is removed via an outlet tube of the electrolytic cell. The electrolytic cell according to any one of claims 1 to 11, wherein the dispensing device dispenses electrolyte into the electrolytic space. The electrolysis cell of any one of claims 1 to 12, wherein the anode is connected to a source of current via the dispensing device. The electrolytic cell of any one of claims 1 to 13, wherein the components of the electrolytic cell are individually replaceable. The electrolytic cell of any one of claims 1 to 14, wherein the dispensing device is permanently connected to the anode. An electrolysis apparatus comprising at least two electrolyzers according to any one of claims 1 to 15, wherein the electrolyte flows through the electrolysis cell one after another, and the electrolysis cells are electrochemically connected in parallel. An electrolytic cell according to any one of claims 1 to 15 or an electrolytic device according to claim 16 for oxidizing an electrolyte. The use of claim 17 wherein the current density is between 50 and 1500 mA/cm 2 . The use of claim 17 or 18 wherein the electrolyte has a solids content of between 150 and 850 grams per liter. The use of any one of claims 17 to 19 for the manufacture of peroxodisulfate.