DEVICE AND METHOD FOR THE PRODUCTION OF CHLORINE DIOXIDE

Description

[0001] The present invention relates to a device and a method for producing chlorine dioxide.

[0002] Chlorine dioxide is a chemical compound of chlorine and oxygen with the molecular formula ClO₂. At room temperature, chlorine dioxide is an amber-colored, explosive, and toxic gas with a pungent, chlorine-like odor.

[0003] The applications of chlorine dioxide are based on its action as an oxidizing agent. It is the most important bleaching agent in elemental chlorine-free bleaching of pulp, especially paper, where it has almost completely replaced elemental chlorine. Chlorine dioxide is also increasingly used for disinfection in food production, for example, in the filling of PET bottles. Furthermore, it is used in drinking water treatment for disinfection instead of chlorine. It is as effective against bacteria as, or even more effective than, chlorine, and unlike chlorine, it is also effective against viruses and many protozoa (single-celled organisms).

[0004] Many methods can be used to produce chlorine dioxide. The most common method uses hydrochloric acid and sodium chlorite as starting materials, as the production of chlorine dioxide from these two components is permitted under drinking water regulations. The reaction proceeds according to the equation: 5 NaClO₂ + 4 HCl → 4 ClO₂ + 5 NaCl + 2 H₂O

[0005] Other substances can also be reacted with sodium chlorite or with other chlorites. Instead of hydrochloric acid, other acids such as sulfuric acid or acid-forming agents such as peroxodisulfates (e.g., sodium, potassium, or ammonium peroxodisulfate), hypochlorous acid, and others are suitable. Chlorites with other cations, such as alkali chlorites and alkaline earth chlorites, can be used instead of sodium chlorite.

[0006] Chlorine dioxide gas can also be produced from chlorates and perchlorates. This reaction occurs, for example, in the reaction of sodium perchlorate (obtained by the electrolysis of sodium chloride) with hydrochloric acid according to the equation: 2 NaClO₃ + 4 HCl → 2 ClO₂ + Cl₂ + 2 NaCl + 2 H₂O

[0007] Many proposals already exist for devices used to produce chlorine dioxide. The difficulties lie in achieving the most complete conversion possible within a reasonable timeframe while avoiding explosive concentrations of chlorine dioxide gas. These are usually concentrations up to a maximum of 20,000 ppm. Solutions in water are not explosive, provided they cannot produce a chlorine dioxide-air mixture with more than 10% chlorine dioxide by volume. Examples of known devices and processes can be found, among others, in DE 967 375 A, DE 31 28 817 A1, DE 32 18 475 A1, DE 32 39 029 A1, WO 2009 / 084854 A2, EP 2 662 328 A1, DE 10 2010 001 699 A1, US 6,051,135 A and EP 2 662 328 A1. Furthermore, it is known to produce chlorine dioxide from solid, dry compositions. Examples of this can be found in WO 2012 / 019587 A1, EP 933 991 B1, US 4,547,381 A and US 2,482,891 A.

[0008] Since corrosive starting materials, products, and byproducts are involved in chlorine dioxide production, the selection of materials for the equipment is limited, and the pumps and dosing devices that can be used must also be specially designed. For example, a water jet pump is often preferred for processes that use negative pressure, and glass capillaries are frequently used for dosing. Otherwise, hoses and pumps whose product-contacting parts are made of partially and / or perfluorinated plastics are used.

[0009] Existing methods and equipment are perceived as cumbersome in practice when there is a continuous need for large quantities of chlorine dioxide. This is because it takes a very long time to quantitatively separate the toxic and potentially explosive chlorine dioxide gas from the reaction solution, thus enabling safe disposal of the solution. Separation is usually achieved by aeration with air, for example, via an inlet pipe or a frit. The time required for quantitative purification of the chlorine dioxide limits the achievable capacities of known systems. Due to the corrosiveness of the reactants and the chlorine dioxide product, circulating the reaction solution requires very expensive pumps with wetted parts made of fluorinated materials, which require extensive maintenance to ensure operational reliability.The task therefore remains to find simpler and thus more cost-effective and fault-resistant systems and to accelerate the separation of the reaction product chlorine dioxide in order to increase plant safety.

[0010] Surprisingly, it has now been discovered that a device known as a mixed-air water lifter for pumping water can be used as a very simple and cost-effective pump for circulating gas and liquid while simultaneously desorbing gas, without the need for mechanically moving parts. The reactor tube, through which gas bubbles, allows for much faster degassing of the reaction solution compared to previously known systems due to its enormous surface area. This, in turn, significantly increases the plant capacity. Such a system is also known as a mammoth pump and is also used as an airlift reactor and a bubble pump. In a mammoth pump, a relatively large gas flow is pumped into a relatively narrow tube in which a liquid is connected to a reservoir of liquid outside, for example, a second leg of a U-tube.The lower density of the gas-liquid mixture in the pipe causes it to rise compared to the liquid in the corresponding reservoir. The mammoth pump principle is used in practice for pumping liquids containing solids, for example, for pumping wastewater containing microorganisms or activated sludge, or for circulating aquarium water. Bubble pumps, instead of using gas introduced by a pump, utilize the steam generated by heating the liquid; coffee machines are an example of this. Airlift reactors serve as bioreactors in which the reaction fluid containing microorganisms must be brought into contact with a large quantity of gas, usually oxygen. The gas flow ensures both the supply of the gas and a very intensive yet gentle mixing process.The present invention combines the principles of the mammoth pump and the airlift reactor by pumping the reaction liquid, as in the mammoth pump, while utilizing the thorough mixing, analogous to the airlift reactor. According to the invention, the focus is not on gentle or solids-tolerant pumping, but rather on mixing, degassing, and pumping without a mechanical pump coming into contact with the medium. The large gas-liquid interface created by the mammoth pump allows the chlorine dioxide to be extracted / stripped from the reaction solution in a very short time.

[0011] The present invention thus solves the aforementioned problems by means of a device for the production of chlorine dioxide comprising a two-legged reactor having a small cross-sectional area of ​​the legs relative to the leg height, wherein the legs are connected at the top and bottom, a gas inlet at the lower end of one leg, a gas outlet in the upper region of the second leg, a connection of the legs, a reactant inlet at the upper end of the first or second leg, a liquid outlet at the lower end of the reactor, an absorption device with a water supply, a gas inlet and a gas outlet, and a pump for circulating a gas from the pump via the gas inlet through the first leg to the gas outlet and further to the gas inlet of the absorption device, through the latter to the gas outlet and to the pump, wherein the leg diameter, leg height, liquid level and gas flow are adjustable.that a stable liquid flow in the reactor can be set. The problem is further solved by a process for the production of chlorine dioxide, in which reactants for conversion to chlorine dioxide are introduced at the top into one leg of a two-leg reactor, which has a small cross-sectional area of ​​the legs relative to the leg height, the legs being connected at the top and bottom, gas is pumped into the first leg at the bottom and discharged at the top of the second leg, the amount of gas being measured such that the liquid is circulated by the gas flow in the reactor and the gas with the formed chlorine dioxide is directed from the reactor into an absorption device, where the contained chlorine dioxide is dissolved in water and the gas separated from the chlorine dioxide flows back from the absorption device to the pump.

[0012] The strong gas flow achieves very efficient discharge of the generated chlorine dioxide, while still allowing the use of a small pump in terms of power and materials, since essentially neither chlorine dioxide nor reactants and byproducts enter the pump. Designing the device requires coordinating the leg diameter, leg height, liquid level, and gas flow. Theoretical details and formulas for calculation can be found in W. Maltry, "On the Dimensioning of Mammoth Pumps," Deutsche Agrartechnik 18, 1968, pp. 233–235. The device according to the invention is operated in such a way as to achieve a stable liquid flow rate. However, the operation recommended in the publication, between the point of optimal efficiency and maximum liquid flow, is not necessary.

[0013] In principle, all known reactants for the formation of chlorine dioxide are suitable as starting materials. The selection is primarily based on price and availability; dosability and byproducts also play a role. Furthermore, the choice of starting materials depends on the intended use of the chlorine dioxide. For example, particularly pure chlorine dioxide is required for the disinfection of drinking water. Consequently, the starting materials should not produce any gaseous byproducts. For this and other applications with corresponding purity requirements, solutions of chlorite and acid are therefore preferred as starting materials. Hydrochloric acid and alkali chlorite, especially sodium chlorite, are well-suited examples.

[0014] The concentration of the reactants is adjusted to the reactor. Excessively high concentrations of chlorine dioxide, generally more than 10 vol% chlorine dioxide in the gas phase, which can occur at normal ambient temperature from a concentration of 10 g chlorine dioxide per liter of water, must be avoided. This limits the concentration and / or feed rate of the reactants. On the other hand, reactants with lower concentrations require more time to react, and the yield of chlorine dioxide per unit time is lower, so the concentrations should not be too low either. In practice, concentrations of 0.1 to 1.5 mol / L chlorite can be effectively managed with reactor leg cross-sectional areas in the range of 1 to 30 cm². For example, a sodium chlorite reactant concentration of up to 3.5 wt% can be handled at a 1:1 ratio with the acid (1.75 wt% in the reaction solution) without monitoring the gas flow.For higher concentrations, the dosage must be adjusted to the discharge rate.

[0015] The reactant is preferably dosed using metering pumps. For continuous operation, a safety circuit is preferably provided which stops the dose of reactants if the pump for circulating the gas fails or other defined conditions occur, e.g., failure of a reactant dose or of the water supply to the absorption device. Other dosing methods are also possible, e.g., via gravity and capillaries, preferably with shut-off valves.

[0016] As already mentioned, the concentration of the reactants is limited so that, under the set conditions of gas flow, water supply, etc., no explosive concentrations of chlorine dioxide are formed. On the other hand, the highest possible concentration is sought in order to produce as much chlorine dioxide as possible per unit of time. Generally, an excess of acid is used, but equimolar amounts of reactants or a slight excess of chlorite are also possible. Preferably, 0.05 to 5 mol / l of chlorite is used, particularly preferably 0.1 to 3 mol / l, and most preferably 0.2 to 1.5 mol / l. The molar ratio of chlorite to acid is preferably 1:1 to 1:5, particularly preferably 1:2 to 1:4, and most preferably 1:2.5 to 1:3.5. The values ​​in this paragraph refer to monovalent reactants.When reactants of divalent or higher valency are used, the quantities must be adjusted according to the valency, unless not all valencies react.

[0017] For the production of small quantities of chlorine dioxide, batch operation is possible, in which the reactants are fed into the reactor sequentially or pre-mixed all at once. In this case, the liquid is also only drained all at once after the reaction and outgassing of the chlorine dioxide are complete. Generally, a continuous feed of reactants is preferred, with the discharge of the liquid being either continuous or batchwise. For continuous operation, it is preferred to connect several two-armed reactors in series, for example, two, three, four, five, six, seven, or even more, particularly preferably three, four, or five.

[0018] The gas used is preferably air, but any other oxidation-stable gas is also possible, such as carbon dioxide or nitrogen. Air is particularly simple and inexpensive, however. If necessary, purified air can be used.

[0019] Furthermore, it is advantageous if the device has a pressure equalization mechanism. An activated carbon filter is preferably used for this purpose, which simultaneously protects the system from the introduction of contaminants and retains small residual amounts of chlorine dioxide.

[0020] The reactor according to the invention has two legs whose cross-sectional area is small compared to their height. For example, cross-sectional area to height ratios in the range of 0.001 to 0.2 units of length are suitable, preferably 0.01 to 0.1 units of length, and particularly preferably 0.02 to 0.05. This corresponds, for example, to cross-sectional areas of 0.5 to 20 cm² (diameters of 0.8 to 5 cm) at heights of 10 to 500 cm. Reactor leg cross-sectional areas of 1 to 10 cm² at heights of 50 to 120 cm are particularly preferred, especially cross-sectional areas of 2 to 5 cm² and heights of 70 to 100 cm.

[0021] The legs can be tubes with a round, oval, or angular cross-section, e.g., square or rectangular, preferably round. Suitable materials include glass or oxidation-resistant and heat-resistant plastics such as PVC and Teflon.

[0022] The static liquid level of the reactants in the arms is conveniently adjusted to approximately ½ to ¾ of the arm height. In batch operation, this is achieved by adding appropriate quantities of reactants. In continuous operation, the feed rates of the reactants are adjusted to match the output rate of the reaction solution.

[0023] A scrubber tower is typically used as the absorption device. For example, a tube—preferably filled with packing material such as glass beads or Raschig rings—is suitable. The tube can have a round, oval, or angular cross-section, e.g., square or rectangular, but preferably round. Glass or oxidation-resistant and heat-resistant plastics such as PVC and Teflon are particularly suitable materials. In the absorption device, the gas containing chlorine dioxide is introduced from the reactor at the bottom, while water is supplied from the top. The water can flow in through one opening, be supplied through several openings, or be sprayed in. The amount of water and the size of the absorption device are adjusted to the amount of chlorine dioxide and the gas velocity so that essentially all of the chlorine dioxide dissolves in the water.Since chlorine dioxide has a very high solubility in water and the dissolution process is rapid, a large absorption device and small volume of water are not required. For the reactor dimensions mentioned above, a water flow rate in the range of 30 to 1000 l / h, preferably 30 to 300 l / h, was well suited to the absorption device.

[0024] The absorption device has an outlet at its lower end, preferably a siphon, through which the produced chlorine dioxide solution is discharged. A quantity of chlorine dioxide solution corresponding to the amount of water supplied is obtained, typically with a concentration in the range of 100 mg / l to 3000 mg / l, preferably from 400 mg / l to 1000 mg / l. The solution can, for example, be directed into a storage tank and stored there, or it can be used directly, e.g., added to a drinking water system. Substances for stabilizing the chlorine dioxide can also be introduced into the storage tank, provided the application of the chlorine dioxide solution permits. However, a particularly pure chlorine dioxide solution is often the most effective stabilization method.

[0025] The gas drawn off at the gas outlet of the absorption device contains no chlorine dioxide or only negligible amounts, such as less than 1 ppm, and in particular less than 0.05 ppm. It therefore has no corrosive or oxidizing properties, allowing the use of simple pumps. For example, an air circulator pump with an EPDM diaphragm coated with a thin layer of PTFE is suitable. A usable flow rate is, for example, 100 to 6000 l / h, preferably 400 to 1000 l / h or 1000 to 3000 l / h, depending on the required gas flow.

[0026] The gas flow generated by the pump is dimensioned to circulate the liquid within the reactor. Factors influencing this include the diameter of the reactor leg, the height difference between the gas inlet and the top of the first leg, and the difference between the gas inlet and the liquid's static level in the reactor. Figure 1The diagram, reproduced in Wikipedia, shows legs with a diameter of 40 cm and more, illustrating the interaction. Further details can be found, for example, in the aforementioned article by W. Maltry. This demonstrates that the reactor and method according to the invention differ significantly from known devices and methods that use air to drive off the chlorine dioxide. All previous proposals used a much smaller gas flow relative to the reactor cross-sectional area, as this flow was not intended for pumping the liquid. Similarly, only the mammoth pump principle enables correspondingly high gas flows, since previously, overflow and, even more so, spillage had to be avoided at all costs. For the aforementioned reactor dimensions, gas flows of 200 to 800 l / h, preferably 400 to 600 l / h, were well suited according to the invention.For differing diameters, leg heights, and liquid levels, appropriate adjustments must be made. These can be determined by a person skilled in the art either experimentally or computationally.

[0027] As mentioned previously, a cascade with several two-armed reactors, sharing a common reactant feed, pump, and absorption device, is preferably used for the production of larger quantities of chlorine dioxide. The pump is connected to the gas inlet of the first reactor, while the reactant feed and absorption device are connected to the last reactor. The gas from the gas outlet of the first reactor is fed into the gas inlet of the second reactor, and so on. The reactants are fed to the last reactor, the liquid from the last reactor is fed into the penultimate reactor, and so on, with the fully reacted and degassed liquid being discharged from the first reactor.

[0028] Preferably, the reactants and water are supplied via electrically driven metering valves, allowing a control system to monitor the gas flow, reactant, and water supply to be in a suitable ratio. In the event of a pump failure, a water supply failure, or a failure of one of the reactant feeds, an emergency shutdown is expediently implemented. This prevents the formation of dangerous chlorine dioxide concentrations and the release of large quantities of unreacted reactants.

[0029] The invention will be explained with reference to the following figures and examples, without, however, being limited to the specifically described embodiments. Unless otherwise stated or necessarily evident from the context, percentages refer to weight, or, if in doubt, to the total weight of the mixture.

[0030] The invention also relates to all combinations of preferred embodiments, provided these are not mutually exclusive. The terms "approximately" or "about" in conjunction with a numerical value mean that values ​​at least 10% higher or lower, or 5% higher or lower, and in any case values ​​1% higher or lower, are included.

[0031] The figures show Fig. 1 a nomogram for the operation of mammoth pumps Fig. 2 a first embodiment of the device according to the invention and Fig. 3 a second embodiment.

[0032] In Figure 2A two-armed reactor 1 is shown, which has a first arm 2 and a second arm 3. The reactor 1 also has a gas inlet 4 at the lower end of the first leg 2, a gas outlet 5 in the upper region of the second leg 3, a connection V between the legs, a reactant inlet 6 at the upper end of the first leg 2, a liquid outlet 7 at the lower end of the first leg 2, an absorption device 8 with a water supply 9, a gas inlet 10, a gas outlet 11 and a product outlet 13, and a pump 12 for circulating a gas from the pump 12 via the gas inlet 4 through the first leg 2 to the gas outlet 5 in the upper region of the second leg 3, further to the gas inlet 10 of the absorption device 8, through this to the gas outlet 11 and to the pump 12. The absorption device 8 is a scrubber tower with a siphon 13 as a product outlet for discharging the chlorine dioxide solution.The product solution is stored in a reservoir 14. For pressure equalization, the reservoir 14 is connected to the lower end of the absorption device 8. An activated carbon filter 15 is also provided for pressure equalization within the device.

[0033] The embodiment in Figure 2This reactor is particularly suitable for batch operation. During operation, hydrochloric acid and sodium chlorite solution, for example, in approximately equimolar quantities or preferably with an acid excess of approximately 1:3, are introduced as reactants into the first arm 2 of the reactor 1 via the reactant inlet 6. The liquid level of the reactants is advantageously set to approximately ½ to ¾ of the arm height. The pump 12 is then started and introduces, for example, air as a gas into the gas inlet 4. The airflow is regulated so that it pumps the liquid upwards in the first arm until it flows through the connection V into the second arm 3. At this point, the air and liquid separate. The air, containing the chlorine dioxide driven off the liquid, flows through the gas outlet 5 and the gas inlet 10, here a hose, into the siphon 13 of the absorption device 8. From there, the air flows upwards through the washing tower 8 in countercurrent with the water introduced through the water supply 9.The water dissolves the chlorine dioxide from the air and flows through the siphon 13 into the storage tank 14. The air, separated from the chlorine dioxide, is fed from the gas outlet 11 into the pump 12 and from there back into the gas inlet 4. After the reaction of the reactants is complete and the chlorine dioxide has been driven out of the liquid in the reactor, the water supply 9 and the pump 12 are switched off, and the liquid, which essentially only contains sodium chloride and, if applicable, excess acid, is drained through the outlet 7, e.g., directly into the sewer.

[0034] In Figure 3 A device particularly suitable for continuous operation is shown, wherein analogous parts have the same reference numerals as in Figure 2The device comprises three two-legged reactors 1, 1' and 1". Each of these has a gas inlet 4, 4' and 4", a gas outlet 5, 5' and 5", as well as first legs 2, 2', 2", second legs 3, 3' and 3", reactant inlets 6, 6', 6" and liquid outlets 7, 7', 7". The device has only one pump 12 and a scrubber 8 as an absorption device, as well as an activated carbon filter 15 and a storage tank 14. Pump 12 and absorption device 8 operate in the same way as for Figure 2 described. However, the device in Figure 3A continuous supply of reactants is provided via reactant inlet 6" and a continuous liquid discharge via outlet 7. The liquid volumes of the supplied reactants and the discharged liquid are set equal, and the inlet rate is regulated so that a static liquid level of approximately ½ to ¾ of the leg height is maintained in reactors 1, 1', and 1'. Air is pumped into inlet 4 of reactor 1, exits its second leg 3 at gas outlet 5 enriched with chlorine dioxide, and is introduced from there into gas inlet 4' of the second reactor 1'. There, the air absorbs further chlorine dioxide from the more concentrated liquid in leg 2' and passes via gas outlet 5' into gas inlet 4" of the third reactor 1". In this reactor, further chlorine dioxide is absorbed and then dissolved in the water introduced via feed 9 in the scrubber tower 8. The reactants take the reverse route.They flow into the reactant inlet 6" of the last reactor 1", and via the liquid outlets 7" and 7' into the reactant inlets 6' and 6 of reactors 1' and 1.

[0035] In this embodiment, the reactants and water are supplied via electrically driven metering valves, so that a control system (not shown) can monitor whether the gas flow, reactant, and water supply are in a suitable ratio. An emergency shutdown is performed if pump 12, water supply 9, or one of the reactant inlets fails. Example 1

[0036] In a device accordingly Figure 2200 ml of 3.5% aqueous sodium chlorite solution and 200 ml of 4.5% hydrochloric acid were added. The pump was switched on and pumped air through the reactor at a rate of 420 l / h for 10 minutes. During this time, 0.7 ml / min of water was fed into scrubbing tower 8. This yielded 7 l of chlorine dioxide solution with a concentration of 0.48 mg / l, corresponding to a yield of approximately 84%.

[0037] This example demonstrates significantly improved mixing of the reaction solution and desorption of chlorine dioxide. After just 10 minutes, the reaction solution was colorless, meaning that essentially all the chlorine dioxide had been released. This process takes 30 minutes in conventional reactors with an airflow that does not circulate the liquid. Consequently, the device and method according to the invention achieve increased performance. The used liquid contains much less chlorine dioxide than in previous devices, thus simplifying disposal. As with previous proposals, the product solution contains pure chlorine dioxide, without reactants or byproducts. The device is considerably more economical than previous systems, as special, corrosion-resistant pumps would be required to circulate liquids containing chlorine dioxide. The large pump allows for very rapid circulation and, in this example, achieved a circulation rate of approximately...At 144 l / h, the 400 ml of liquid in the reactor was circulated approximately 6 times per minute. A chlorine dioxide-resistant pump for direct media contact with this capacity costs approximately €2500 and requires regular maintenance. The mammoth pump is driven solely by the gas flow, meaning the pump itself, which moves the gas flow, has no contact with the media. Reference symbol list

[0038] 1, 1', 1"Reactor 2, 2', 2"First leg 3, 3', 3"Second leg 4, 4', 4"Gas inlet 5, 5', 5"Gas outlet 6, 6', 6"Reactant inlet 7, 7', 7"Liquid outlet V, V', V"Connection between first and second leg 8Absorption device 9Water supply 10Gas inlet 11Gas outlet 12Pump 13Siphon 14Storage tank 15Activated carbon filter

Claims

1. Device for the production of chlorine dioxide comprising a twin-arm reactor (1, 1', 1") which has a cross-sectional area of the arms (2, 2', 2", 3, 3', 3") that is small in comparison to the height of the arms, wherein the arms are connected at top and bottom, a gas inlet (4, 4', 4") at the lower end of a first arm (2, 2', 2"), a gas outlet (5, 5', 5") in the upper region of the second arm (3, 3', 3"), a connection (V, V', V") between the arms (2, 2', 2", 3, 3', 3"), a reactant inlet (6, 6', 6") at the upper end of the first or second arm (2, 2', 2", 3, 3', 3"), a liquid outlet (7, 7', 7") at the lower end of the reactor (1, 1', 1"), an absorption device (8) with a water supply (9), a gas entry (10), a gas exit (11), and a product outlet (13), and a pump (12) for circulating a gas from the pump (12) via the gas inlet (4') through the first arm (2) to the gas outlet (5) and on to the gas entry (10) of the absorption device (8), through this to the gas exit (11) and to the pump (12), wherein the arm diameter, arm height, liquid level, and gas flow can be coordinated so that a stable liquid transport in the reactor (1, 1', 1") is adjustable.

2. Device according to claim 1, characterized in that electrically driven metering valves are provided for dosing the reactants, preferably with a safety circuit which stops the dosage of the reactants if the pump (12) for circulating the gas or a reactant metering device or the water supply (9) to the absorption device (8) fails.

3. Device according to claim 1 or 2, characterized in that several twin-arm reactors (1, 1', 1") are connected in series, preferably two, three, or four, wherein the pump (12) is connected to the first reactor (1) and the absorption device (8) is connected to the last reactor (1").

4. Device according to claim 1, 2, or 3, characterized in that the device has a pressure equalization mechanism (15), preferably a filter, in particular an activated carbon filter.

5. Device according to one of claims 1 to 4, characterized in that the arms (2, 2', 2", 3, 3', 3") have ratios of cross-sectional area to height in the range from 0.001 to 0.2 length units, preferably from 0.01 to 0.1 length units, and particularly preferred from 0.02 to 0.05.

6. Device according to one of claims 1 to 5, characterized in that the arms (2, 2', 2", 3, 3', 3") have cross-sectional areas from 0.5 to 20 cm2, preferably from 1 to 10 cm2, in particular from 2 to 5 cm2, at heights from 10 to 500 cm, preferably from 50 to 120 cm, in particular from 70 to 100 cm.

7. Device according to one of claims 1 to 6, characterized in that the arms (2, 2', 2", 3, 3', 3") are tubes with a round, oval or angular, preferably round, cross-section and / or are made of glass or oxidation-stable and heat-resistant plastic, in particular of PVC or Teflon.

8. Device according to one of claims 1 to 7, characterized in that the absorption device (8) is a washing tower, preferably a tube filled with packing material such as glass balls or Raschig rings.

9. Device according to one of claims 1 to 8, characterized in that the water supply (9) is formed by one or more openings or by a nozzle.

10. Device according to one of claims 1 to 9, characterized in that the absorption device (8) has a siphon as a product outlet (13).

11. Method for the production of chlorine dioxide, characterized in that - reactants for conversion to chlorine dioxide are introduced at the top into one arm of a twin-armed reactor, which has a cross-sectional area of the arms that is small compared to the arm height, the arms being connected at the top and bottom, - gas is pumped into a first arm at the bottom and is discharged in the upper region of the second arm, - wherein the amount of gas is dimensioned such that the liquid is circulated by the gas flow in the reactor, and - the gas with the chlorine dioxide formed is passed from the reactor into an absorption device, where the chlorine dioxide contained therein is dissolved in water, and - the gas separated from the chlorine dioxide flows back from the absorption device into the pump.

12. Method according to claim 11, characterized in that solutions of chlorite and acid, preferably hydrochloric acid and aqueous alkali chlorite, in particular sodium chlorite, are used as reactants.

13. Method according to claim 11 or 12, characterized in that air, carbon dioxide, or nitrogen, preferably air, is used as the gas.

14. Method according to one of claims 11 to 13, characterized in that the amount of water and the size of the absorption device are adjusted to the amount of chlorine dioxide and gas velocity so that essentially all of the chlorine dioxide dissolves in the water, in particular so that the gas flowing back to the pump contains less than 1 ppm chlorine dioxide.

15. Method according to one of claims 11 to 14, characterized in that the reactants are fed into the reactor one after the other or premixed at once.

16. Method according to one of claims 11 to 14, characterized in that the reactants are continuously fed into the reactor, preferably into a final reactor of a cascade with several twin-arm reactors, which have a common reactant feed, pump, and absorption device, wherein the pump is connected to the gas inlet of the first reactor, while the reactant feed and absorption device are connected to the last reactor, and the gas from the gas outlet of the first reactor is fed into the gas inlet of the second reactor, etc., the liquid is fed from the last reactor into the penultimate reactor, etc., and the completely reacted and degassed liquid is discharged from the first reactor.

17. Method according to one of claims 11 to 16, characterized in that the reactants and the water are supplied via electrically driven metering valves and a control system monitors that the gas flow, reactant supply, and water supply are in a suitable ratio, wherein an emergency shutdown occurs in the event of a failure of the pump or the water supply or one of the reactant feed streams.