METHOD AND DEVICE FOR PRODUCING CHLORINE DIOXIDE

Abstract

In order to provide a method with which the costs incurred in conventional methods for producing chlorine dioxide according to the chlorite-acid method can be significantly lowered, a method is proposed according to the invention, in which an acid, a chlorite and optionally water are introduced into a reactor, wherein in the method the reaction temperature in the reactor is determined and the quantity of acid, chlorite and/or water which is/are introduced into the reactor is chosen such that the acid introduced into the reactor is introduced into the reactor with a molar excess relative to the chlorite introduced into the reactor, wherein the level of the molar excess is varied with the level of the reaction temperature determined. In addition, the present invention relates to a device which is suitable for implementing the method according to the invention.

Claims

1. Method for producing an aqueous solution of chlorine dioxide in which an acid, a chlorite and optionally water are introduced into a reactor, characterized in that in the method the reaction temperature in the reactor is determined and the quantity of acid, chlorite and/or water which is/are introduced into the reactor is chosen such that the acid introduced into the reactor is introduced into the reactor with a molar excess relative to the chlorite introduced into the reactor, wherein the level of the molar excess is varied with the level of the reaction temperature determined.

2. Method according to claim 1, characterized in that the acid introduced into the reactor is introduced into the reactor at a reaction temperature determined in the range of from 10 to 40 C. with a molar excess in the range of from 2.0 to 3.5 relative to the chlorite introduced into the reactor.

3. Method according to claim 1, characterized in that the level of the molar excess increases with the level of the reaction temperature.

4. Method according to claim 1, characterized in that the level of the molar excess at a reaction temperature in the range of from 10 to <25 C. lies in the range of from 2.0 to 2.5, at a reaction temperature in the range of from 25 to <30 C. lies in the range of from 2.5 to 3.0 and at a reaction temperature in the range of from 30 to <40 C. lies in the range of from 3.0 to 3.5.

5. Method according to claim 1, characterized in that the reaction temperature is determined using the temperature in the reactor, on the reactor outer wall, on a line for introducing acid, chlorite and/or water into the reactor, in a container from which acid, chlorite and/or water to be introduced into the reactor are kept or on the container wall thereof or in the air in the environment in which the method is implemented.

6. Method according to claim 1, characterized in that the molar excess is varied depending on the duration of the reaction time as well as depending on the level of the reaction temperature.

7. Method according to claim 6, characterized in that the acid is introduced into the reactor with a molar excess in the range of from 2.0 to 3.5 relative to the chlorite with a reaction time in the range of from 1 to 100 minutes, wherein the value of the molar excess becomes greater with the duration of the reaction time from a reaction time of 20 minutes.

8. Method according to claim 1, characterized in that the level of the molar excess with a reaction time in the range of from 1 to <4 minutes lies in the range of from 2.0 to 2.5, with a reaction time in the range of from 4 to 30 minutes lies in the range of from 2.5 to 3.0 and with a reaction time in the range of from >30 to 40 minutes lies in the range of from 3.0 to 3.5.

9. Method according to claim 1, characterized in that the acid is selected from the group consisting of sulfuric acid and hydrochloric acid.

10. Method according to claim 1, characterized in that the chlorite is an aqueous solution of selected from the group consisting of potassium chlorite and sodium chlorite.

11. Device (1) for producing an aqueous solution of chlorine dioxide, wherein the device has a reactor (11), a first line (5) for introducing an acid into the reactor (11), a second line (6) for introducing a chlorite into the reactor (11) and optionally a third line (7) for introducing water into the reactor (11), characterized in that the device has an apparatus (13) for determining the reaction temperature in the reactor (11) and a control unit (12) for controlling the flow of acid, chlorite and/or water via the first, second and/or third line (5, 6, 7) into the reactor (11), wherein the control unit (12) is set up such that the acid introduced into the reactor (11) is introduced into the reactor (11) with a molar excess relative to the chlorite introduced into the reactor (11), wherein the molar excess varies with the level of the reaction temperature.

12. Device according to claim 11, characterized in that the device (1) implements a method according to claim 1.

13. Device according to claim 11, characterized in that the reactor (11) is a flow reactor.

14. Device according to claim 11, characterized in that the device has at least one of the following apparatuses: a metering pump for the acid, a metering pump for the chlorite, a metering pump for the water, a valve (8, 9, 10) on the first, second and/or optional third line (5, 6, 7), a flow control on the first, second and/or optional third line, a container (2, 3, 4) for the acid, for the chlorite and/or optionally for water.

Description

[0058] To demonstrate the advantages connected with the present invention, reference is made to the attached figures. There are shown in:

[0059] FIG. 1: the stoichiometric chlorine dioxide yield at a reaction temperature of 15 C. with different reaction times and when a molar acid excess in the range of from R=1 to 3 is used,

[0060] FIG. 2: the stoichiometric chlorine dioxide yield at a reaction temperature of 25 C. with different reaction times and when a molar acid excess in the range of from R=1 to 3 is used,

[0061] FIG. 3: the stoichiometric chlorine dioxide yield at a reaction temperature of 35 C. with different reaction times and when a molar acid excess in the range of from R=1 to 3 is used, and

[0062] FIG. 4: a schematic representation of a particular embodiment of the device according to the invention for producing an aqueous solution of chlorine dioxide.

EXAMPLES

[0063] In order to investigate the influence of the quantities of chlorite and acid used as well as the influence of the reaction temperature and the reaction time on the yield of chlorine dioxide, laboratory tests were carried out. For this, a gas-tight glass syringe with a volume of 25 ml was used, which acts as the reactor in the laboratory approach. A PTFE stopper was used to seal the syringe, with the result that the syringe with its contents can be incubated in a water bath. The gas-tight glass syringe is to be regarded as a batch reactor, in which a 5-ml chlorine dioxide sample can be taken at a particular time point (reaction time).

[0064] In the laboratory test hydrochloric acid with a concentration of 9 wt.-% was used as acid. The chlorite was provided in the form of an aqueous sodium chlorite solution with a concentration of 7.5 wt.-%. These concentrations are chosen such that when mixed together in identical volumes the hydrochloric acid is present in a three-fold molar excess relative to the chlorite. In order to achieve a smaller molar excess or even an equimolar ratio (R=1), the hydrochloric acid solution used must be diluted correspondingly.

[0065] The quantitative determination of the chlorine dioxide produced is effected iodometrically.

[0066] The curves represented in FIG. 1 show that at a reaction temperature of 15 C. the yield of chlorine dioxide increases with a higher molar acid ratio relative to the chlorite used. With an increasing acid ratio, the reaction rate also increases, which is to be recognized in the shift of the peak from a molar excess of R=1.5. Over wide ranges of the reaction time the required chlorine dioxide yields of at least 85% (stoichiometric) are not achieved with molar excesses in the range of from R=1 to 2. This is only guaranteed from a molar excess of R=2.5.

[0067] It is to be recognized from the curves represented in FIG. 2, which show the results at a reaction temperature of 25 C., that with reaction times between 10 and 30 minutes in principle a molar acid ratio of R=2 would be sufficient in order to obtain a yield of 85% and more. With a molar excess of R=2.5, this is also still possible with a reaction time of up to 40 minutes.

[0068] It can be read from the curves of FIG. 3, which reflect the ratios at a reaction temperature of 35 C., that yields of at least 85% can be reliably achieved with a reaction time of up to 40 minutes only with a molar excess R=3.

[0069] It can be seen from the present results that at temperatures of 15 C. and 25 C. and with a reaction time of from 10 to 30 minutes a molar acid ratio of R=2 can be used in order to achieve a yield of at least 85%, as is required by the DVGW worksheets. However, should the reaction time be longer than 30 minutes, at reaction temperatures of 15 C. and 25 C. at least an acid ratio of R=2.5 must be used in order to stabilize the required yield of 85% and not to reduce it through the chlorine dioxide decomposition starting in an intensified manner at these temperatures. At a reaction temperature of 35 C. and with a reaction time of from 10 to 20 minutes, a molar acid ratio of R=2 can be sufficient in order to achieve the required yield. However, if the reaction times become greater than 20 minutes, an acid ratio of R=3 is necessary in order to compensate for the chlorine dioxide decomposition.

[0070] FIG. 4 shows a schematic representation of a specific embodiment of a chlorine dioxide system 1 according to the invention for producing chlorine dioxide. In this chlorine dioxide system 1 a container 2 for the acid, a container 3 for the chlorite and a container 4 for water are provided. In an alternative embodiment of the present invention the device has no container 4 for water.

[0071] The containers 2, 3 and 4 for acid, chlorite and water are connected to the reactor 11 via pipelines 5, 6 and 7, in order to be able to introduce the respective fluid into the reactor vessel. In the embodiment without water container 4 no line 7 for the water is provided either.

[0072] In the embodiment represented here valves 8, 9 and 10, via which the flow of fluid through the lines 5, 6 and 7 can be altered, are provided on the lines 5, 6 and 7. The control of the valves 8, 9 and 10, and thus the control of the flow volumes, is effected via the control unit 12, which is connected to the respective valve 8, 9 or 10 via signal lines 15, 16 and 17. In an alternative embodiment of the present invention, instead of the valves represented, other metering apparatuses are used, such as e.g. metering pumps.

[0073] A thermometer 13, which measures the temperature on the outer wall of the reactor vessel in the embodiment represented here and transmits the measured temperature to the control unit 12 via the signal line 14, is provided on the reactor 11.

[0074] In the control unit 12, the molar excess (R) of acid necessary for the necessary minimum yield of 85% chlorine dioxide is determined using the reaction temperature measured by the thermometer 13, and the metering of acid and/or chlorite and/or water (if a water container 4 is present) is controlled accordingly via the valves 8, 9 and/or 10. The reaction time, which depends on the capacity at which the chlorine dioxide system 1 is run at the given time point, is also taken into account here.

[0075] The chlorine dioxide solution produced by the chlorine dioxide system 1 in the reactor 11 is conducted via the outlet 18 to where the chlorine dioxide solution is to be used.

LIST OF REFERENCE NUMBERS

[0076] 1 device for producing chlorine dioxide (chlorine dioxide system) [0077] 2 container for acid [0078] 3 container for chlorite [0079] 4 container for water [0080] 5 line for acid [0081] 6 line for chlorite [0082] 7 line for water [0083] 8 valve for acid [0084] 9 valve for chlorite [0085] 10 valve for water [0086] 11 reactor [0087] 12 control unit [0088] 13 thermometer [0089] 14 signal line for temperature [0090] 15 signal line for acid flow [0091] 16 signal line for chlorite flow [0092] 17 signal line for water flow [0093] 18 outlet for chlorine dioxide solution