JPS6126482B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the regeneration of halogen elements from hydrogen halides and/or hydrohalic acids,
More particularly, it relates to the use of molten salts to catalytically oxidize hydrogen chloride to produce chlorine. In the production of organic chlorides for use in plastics and other products, large quantities of hydrochloric acid are often produced as a by-product or waste. This excess hydrochloric acid is conventionally utilized in abundance, if possible, or neutralized with limestone and discharged to the environment as aqueous waste. Due to the stringent restrictions placed on pollutant emissions and the rising cost of chlorine,
It has become increasingly attractive to provide a method for regenerating chlorine from the by-product hydrochloric acid. However, previous methods of regenerating chlorine from hydrochloric acid encountered engineering and economic problems that prevented their large-scale implementation. It is now known that hydrogen chloride can be oxidized using, for example, sulfur trioxide to produce a mixture of chlorine and sulfur dioxide. This process requires at least three separate processing steps to obtain a mixture from which chlorine must then be separated. Another prior method is the oxidation of hydrochloric acid with sulfur dioxide and oxygen to produce sulfuric acid and chlorine in the presence of a bed of metal oxide catalysts. The solid supported catalysts used in such systems are difficult to prepare and tend to deactivate or degrade quickly. Oxygen is also a nitrogen oxide catalyst and at least 65%
It is being used to oxidize hydrogen chloride in the presence of excess sulfuric acid with a concentration of . This method is complex and expensive as it requires many processing steps. Hydrochloric acid has also been oxidized by oxygen in molten inorganic chloride and olefin chlorine acceptors such as ethylene. Such systems must accommodate complex chemical reactions that produce a variety of different reaction products. Additionally, the inorganic chloride tends to volatilize in the reaction zone, displacing the catalyst and making separation of chlorine from the reactor effluent difficult. Additionally, working with chloride salts is corrosive to the reactor. Additionally, hydrochloric acid has been regenerated by electrolytic methods, but these are expensive and require substantial electrical energy consumption. The present invention is a simple method for regenerating halogen from hydrogen halide. This process can be carried out with relatively simple equipment, can be used economically to treat large volumes of hydrogen halides, and is especially very convenient for the regeneration of chlorine. According to a first embodiment of the invention, hydrogen halide gas produced from waste or by-product hydrohalic acid is mixed with air or oxygen, and the resulting mixture is catalytically activated in a suitable contacting device. contact with molten salt. The salts consist primarily of alkali metal pyrosulfates and sulfates, with small amounts of vanadium pentoxide serving as oxidation catalysts. The gaseous effluent stream exiting the contactor includes subject halogen, water vapor, and unreacted hydrogen halide, as well as oxygen or oxygen-depleted air. This halogen is separated from the effluent gas mixture. This unreacted oxygen and hydrogen halide can then be continuously recycled to the contactor. According to a second embodiment of the invention, hydrogen halide gas generated from waste or by-product hydrohalic acid is contacted with a catalytically active molten salt in a suitable contacting device. The salts consist primarily of alkali metal pyrosulfates and sulfates, along with a small amount of vanadium pentoxide, which serves as a source of oxygen for the reaction with the hydrogen halide. The gaseous effluent stream leaving the contact contains halogen, water vapor, and unreacted hydrogen halide, but is free of free oxygen. The halogen is separated from the effluent gas mixture and the spent brine solution is contacted with a stream of oxygen-carrying gas to regenerate the dissolved vanadium to its active, high valence state. It is an object of the present invention to provide a method for economically regenerating elemental halogens from waste or by-product hydrohalic acids, thereby avoiding environmental pollution and providing an expensive source of industrial halogens. be. An additional object of the present invention is to achieve significant energy conservation by providing a non-electrical method of halogen production. Another object of the present invention is to provide a process that minimizes the need for pretreatment, such as extensive water removal from the feed stream. Yet another object of the present invention is to provide a method for regenerating halogen from hydrohalic acid that minimizes equipment and management requirements. Yet another object of the present invention is to provide a method for oxidizing hydrogen halides in the absence of oxygen-carrying gases and in the presence of a liquid alkali metal sulfate containing an oxygen compound of vanadium. These and other objects and advantages of the invention will become apparent from the description below. Embodiments of the present invention will be described below with reference to the drawings. First Embodiment According to a first preferred embodiment of the present invention, the waste or by-product hydrochloric acid in pipeline 10 is passed through a hydrochloric acid dehydrator 12 . The hydrogen chloride gas produced in the dehydrator 12 and still containing some water vapor is directed via a pipeline 13 into a pipeline 14 containing a flow meter 16 . If the waste or by-product hydrogen chloride does not substantially contain water, of course it can be passed through the pipeline 17 without passing through the dehydrator 12.
It can be fed directly into the pipeline 14. Hydrogen chloride passes through pipeline 14 to molten salt contactor 18 where the gas contacts the molten salt mixture with a flow of oxygen moving to the contactor via pipeline 20 and flow meter 22. Metered amounts of oxygen and hydrogen chloride contact the salt, which catalyzes the oxidation of the hydrogen chloride in the following reaction. 2HC+1/2O ₂ H ₂ O+C ₂ (1) The effluent gas leaving the contactor 18 via pipeline 23 contains a large amount of water vapor and chlorine, with some residual hydrogen chloride and oxygen. Hydrogen chloride and most of the water vapor in the effluent air stream can be removed by a condenser 24 . In the condenser 24, the effluent stream is cooled until the water vapor condenses and the hydrogen chloride is dissolved to produce hydrochloric acid. If the amount of water obtained from the effluent gas is insufficient to dissolve all of the hydrogen chloride, some supplementary water should be added to the condensed steam. Such supplementary water can be obtained from the dewatering device 12 via pipeline 25. If the effectiveness of the dehydrator 12 is not sufficiently complete, the resulting effluent will actually be weak hydrochloric acid. By using dehydrator 12 as a supplementary water source to condenser 24, at least a portion of this dilute acid is recycled. The concentrated hydrochloric acid produced in the condensing device 24 is
It can be recycled by returning it via pipeline 26 to pipeline 10 upstream of dewatering device 12. The mixture leaving the condenser 24 through the pipeline 28 consists of oxygen, chlorine and a small amount of water vapor remaining. These gases are passed through a gas cleaning device 30 using sulfuric acid to absorb water vapor. As the sulfuric acid passes through this washing device 30, it is diluted by the water. This diluted acid can be continuously regenerated by passing it via pipeline 32 to a suitable sulfuric acid dehydrator 34. The sulfuric acid drying device 34 includes a heating device that evaporates water and concentrates the sulfuric acid. This reconcentrated acid is then returned to the acid cleaning device 30 via pipeline 36. The gas mixture leaving the sulfuric acid gas scrubber 30 via the pipeline 28 contains oxygen and chlorine and is suitable for many industrial applications, such as the bleaching of paper pulp, without further treatment. If liquefied chlorine is required, it can be separated from oxygen in a condenser 40 that cools this gas to liquefy the chlorine. This condensing device 4
The air stream leaving the zero consists essentially of oxygen with a residual portion of uncondensed chlorine gas. This airflow can be returned to the oxygen supply line 20 via pipeline 42 at a point upstream of flow meter 22 so that the oxygen exiting from this condenser 40 can be used for the subsequent oxidation of hydrogen chloride. The remaining chlorine in the oxygen return stream will thus also be recycled to replace the lost chlorine. Although oxygen is the preferred oxidizing gas of the present invention, other oxygen-bearing gases may also be used. Air is preferred, but if used, the gas mixture exiting condenser 40 will contain substantially less oxygen than nitrogen. This mixed gas is transferred to pipeline 4
2 to the salt gas scrubber is not advantageous. The reason is that nitrogen quickly builds up to intolerable levels. Disposal of this mixture would reduce the overall efficiency of the system. The reason is that a portion of the regenerated chlorine is lost. If the conditions in the condenser 40 are adjusted so that the gas exiting the condenser 40 contains a significant amount of chlorine, the nitrogen-bearing gas mixture itself can be made into a useful product. Such chlorine-containing mixtures are
It can be used in chlorination operations or directly in the production of chlorine products such as inorganic chlorides, hypochlorides, or certain other organic chlorides. For maximum efficiency of the overall chlorine recovery system, a proper ratio of acid to hydrogen chloride should be supplied to the salt contactor 18 and a minimum amount of water should enter the salt contactor 18 via the pipeline 14. is necessary. The stoichiometric ratio of hydrogen chloride to oxygen is
According to equation (1), there are 4 moles of hydrogen chloride for every 1 mole of oxygen gas. Under most practical operating conditions it is preferred to have an excess of oxygen. Assuming that the feed gas is substantially pure, a ratio of 3.3 to 3.7 moles of hydrogen chloride for each mole of oxygen is preferred, with a ratio of 3.5 being most preferred. In some applications, it is desirable to operate with a deficit of oxygen in the feed so that the effluent gas contains very little oxygen. Such operation would be advantageous because chlorine can be easily separated from the effluent gas since it contains less oxygen, which is more difficult to remove than hydrogen chloride. It would be disadvantageous because the efficiency of hydrogen chloride oxidation would be reduced and additional hydrogen chloride recycle capacity would be required. Also, some experimentation is necessary to determine the most suitable ratio for a given application of the invention since the presence of impurities in the feed will affect the reaction. It is important that the water content of the feed gas is low because the amount of water in the salt contactor provides equilibrium for the oxidation reaction. Referring to equation (1), excess water will drive the reaction to the left and thus prevent the formation of chlorine. Small amounts of water have virtually no effect on chlorine production, while the presence of a sufficiently large amount of water severely reduces chlorine production. To obtain the most economical operation, the cost of dewatering the feed can be weighed against the quantity and price of chlorine regenerated to determine the preferred moisture content for the feed stream. Salt compositions suitable for use with the method of the invention include an alkali metal sulfate, an alkali metal pyrosulfate and a dissolved oxidation catalyst. The oxidation catalyst is preferably _a vanadium oxygen compound such as _V2O5 . If V ₂ O ₅ is included in the salt mixture, it is preferably contained in an amount _{of 2} to 25% by weight of the salt mixture, so that the entire amount is dissolved in the melt. More preferably, the salt mixture contains 10-15% by weight _{of V2O5} . Other soluble metal compounds can be used to catalytically promote the oxidation of hydrogen chloride according to the process of this invention. These include soluble sulphates, oxides or chlorides of copper, iron, chromium or manganese and, to a lesser extent, lead, nickel, cobalt or uranium. A variety of different alkali metal sulfates and pyrosulfates are selected to formulate the majority of this mixture. Sulfates and pyrosulfates of potassium and sodium are preferred because of their abundance and advantageous properties. 5-25% by weight
A mixture containing 50-90% by weight of potassium sulfate and 50 to 90% by weight of sodium pyrosulfate is good. Preferred ranges for these sulfates are 10-20% by weight potassium sulfate and 65-70% by weight potassium pyrosulfate. Small amounts of soluble sulfates and pyrosulfates can be added to mixtures of such potassium compounds without appreciably reducing effectiveness. Moreover, the inclusion of small amounts of lithium sulfate, sodium sulfate or sulfuric acid has been found to have a desirable effect on the solidification temperature, corrosivity, SO ₃ vapor pressure, viscosity, operating temperature range, and catalyst stability of the salt mixture. It was done. The combined amount of these named substances in the salt mixture should not substantially exceed 10% by weight. Additions above this amount appear to be either undesirable or impracticable. If a suitable mixture of potassium compounds is used, the salt bath can be operated to oxidize the hydrogen chloride at a temperature range of 275°C to 475°C, with a preferred range of 325°C to 425°C. . When the gas mixture is maintained in contact with the salt bath at this temperature for at least 0.25 seconds, preferably 0.5 to 5 seconds, most of the hydrogen chloride is removed according to the reaction equation (1).
will be oxidized to chlorine. All or part of the potassium sulfate and potassium pyrosulfate in the above salt mixture can be replaced with sodium sulfate and sodium pyrosulfate. The resulting mixture will work well, but will be somewhat less thermally stable and catalytically active than the preferred mixture of potassium salts. Also, the partial pressure of SO ₃ tends to be higher than when using sodium salts at a given constant temperature. Conservatively assuming that 60% conversion of hydrogen chloride is achieved with a feed ratio of 3.5 moles of hydrogen chloride per mole of oxygen, the effluent gas exiting the salt contactor of the present invention will be: would include. That is, after removing unconverted hydrogen chloride _{and water} in the condensing device 24 and _the acid gas scrubbing device 30,
The remaining airflow has the following composition: That is, 69.0% by volume C ₂ 31.0% O ₂ If a low oxygen percentage of the final air stream is desired, it is possible to increase the ratio of hydrogen halide to oxygen entering the salt contactor, thereby reducing the additional chlorination. Hydrogen is produced, but less oxygen is produced in the effluent gas exiting the contactor. Because hydrogen chloride is readily removed from the effluent gas, the chlorine to oxygen ratio exiting the sulfuric acid scrubber can be increased without substantially increasing the size of the condenser 24. Because hydrogen chloride is readily removed from the effluent gas, the chlorine to oxygen ratio exiting the sulfuric acid scrubber can be increased without substantially increasing the size of the condenser 24. In the same apparatus, if air is used as the oxidizing gas, the estimated composition of the effluent gas leaving the salt contactor is: 13.2% by volume C ₂ 13.2 % H ₂ O 17.6 % HC 6.0 % O ₂ 50.0 % N ₂ Again, these figures are based on a modest 60% conversion of HC. After treatment in condenser 24 and acid scrubber 30 to remove water vapor and unreacted hydrogen chloride, the effluent gas will contain the following components: 19.0 % by volume C ₂ 8.6 % O ₂ 72.4 % N ₂ Examples A series of experiments were conducted to determine whether effective conversion of hydrogen chloride to chlorine could be achieved by the process of the present invention. In these experiments, a 1.4-inch inner diameter Vycor was used.
A container was used to contain the molten catalyst mixture to a depth of about 9 inches. This catalyst mixture consists of 80% by weight K ₂ S ₂ O ₇ , 10% by weight K ₂ SO ₄ and 10% by weight
It was composed of V ₂ O ₅ . The metered streams of hydrogen chloride and air were combined and then dispersed into the molten catalyst mixture by means of a pyrex frit. The effluent gas leaving this vessel was scrubbed with KI solution to remove the chlorine produced and any remaining HC present. The hydrogen chloride to oxygen ratio was kept as close to 3.5 as possible during each run so that there was a slight excess of oxygen. Each run was one hour long. At the end of each run, the total chlorine produced was determined by titrating the free iodine in the gas scrubber solution with sodium thiosulfate. The amount of unreacted hydrogen chloride was determined by titrating the gas scrubber solution with caustic soda. The results of various runs are shown in Table 1. As these results show, substantial yields were obtained even though the conditions were not optimal and the experimental setup was quite simple. These results are even more impressive when one considers that the reported HC conversions represent up to 84% of the theoretical thermodynamic conversions. The most economically important use of the salt mixture according to the invention is in the regeneration of chlorine from hydrogen chloride. For this reason, the above discussion specifically concerns chlorine. However, it should be understood that the molten salt contactor and salt mixture of the present invention can be used to oxidize hydrogen bromide and hydrogen iodide for the regeneration of bromine and iodine, respectively. Referring to FIG. 2, a general method for regenerating the halogens described above is shown. Metered amounts of oxidizing gas and waste or by-product hydrogen halide are passed through pipelines 52 and 54, respectively.
The molten salt is supplied to the molten salt contacting device 50 through. This contacting device 50 contains a salt mixture molten under the conditions described above. Upon contact with this mixture, oxygen and halide react by the following reaction. That is, 2HX+1/2O ₂ H ₂ O+X ₂ (2) X=C, Br or I Kinetics do not allow this reaction according to equation (2) to proceed to completion. For this reason, the effluent gas mixture exiting salt contactor 50 via pipeline 56 includes a mixture of water vapor, unreacted hydrogen halide gas, elemental halogen gas, and unreacted oxidizing gas. The gases of this mixture are separated by a conventional gas separation device 58.

TABLE SECOND EXAMPLE Referring to FIG. 3, a second example general method for regenerating either chlorine, bromine or iodine from their respective halides is shown. The waste or by-product hydrogen halide gas passes through the pipeline 112 to the molten salt contactor 1.
10. The contactor 110 contains a molten salt mixture containing dissolved vanadium oxygen compounds. Upon contact with this mixture, the hydrogen halide is oxidized by reaction with a vanadium compound by the following general reaction. That is: 2HX + V ₂ O ₅ →V ₂ O ₄ +X ₂ +H ₂ O (3) X=C, Br or I Kinetics do not allow this reaction according to equation (3) to proceed to completion. For this reason, the effluent gas mixture leaving salt contactor 110 via pipeline 114 contains a mixture of water vapor, unreacted hydrogen halide gas, and elemental halogen gas. It is also important to note that little or no free oxygen gas is produced in the contactor 110, so that the components of the effluent gas mixture are similar to those of the conventional gas separation device 1.
The advantage of this method is that it can be easily separated by 16. Contact with hydrogen halide reduces the vanadium in the molten salt mixture to a lower valence state. Before this salt mixture can be used again, the vanadium must be regenerated therefrom. This regeneration is carried out by passing this spent salt mixture through a pipeline 120 to a second molten salt contactor 1.
This can be accomplished by transporting it to 18. This salt mixture is now contacted with a stream of oxygen-bearing gas, such as air, introduced through pipeline 122. This vanadium reacts with oxygen in the gas and is regenerated into a high valence state.
The regenerated salt is passed through the pipeline 124 to the first
The oxygen-bearing gas is recycled or discharged to the atmosphere if economically advantageous. A very specific embodiment of the invention is seen in FIG. 4, which shows a method adapted for the regeneration of chlorine from hydrogen chloride. Pipeline 140 passes the waste or byproduct hydrochloric acid through a hydrochloric acid dehydrator 142 . The hydrogen chloride gas produced in this dehydrator 142, still containing some water vapor, is directed via pipeline 144 into pipeline 146 which includes flow meter regulator 148. If the waste or by-product hydrogen chloride is substantially free of water, it is routed through pipeline 150 to pipeline 14 without passing through dehydrator 142.
6 can be supplied directly. Hydrogen chloride in this pipeline 146 is transferred to the molten salt contactor 15
2, where the hydrogen chloride gas is contacted with a molten salt mixture containing V ₂ O ₅ which oxidizes the hydrogen chloride by a general reaction. That is, 2HC+V ₂ O ₅ →V ₂ O ₄ +C ₂ +H ₂ O (4) The effluent gas leaving contactor 152 via pipeline 154 contains a large amount of water vapor and some residual hydrogen chloride. Contains chlorine, but
Contains virtually no free oxygen. Hydrogen chloride and most of the water vapor in the effluent air stream can be removed by condenser 156. In this condenser, the effluent air stream is cooled until the water vapor condenses and the hydrogen chloride dissolves to form hydrochloric acid. If the amount of water obtained from the effluent gas is insufficient to dissolve all the hydrogen chloride, some make-up water should be added to the condensed steam. Such make-up water may be obtained from dewatering device 142 via pipeline 158. If the dehydrator 142 were weaker than fully effective, the effluent it produced would actually be weak hydrochloric acid. Condensing device 1
Dehydrator 14 as a source of supplementary water for 56
By using 2, at least a portion of the dilute acid is recycled. The concentrated hydrochloric acid produced in condenser 256 can be recycled by returning it to pipeline 140 upstream of dehydrator 142 via pipeline 160. The mixture exiting condenser 156 through pipeline 162 consists of chlorine and a small amount of water vapor remaining. These gases are scrubbed in a sulfuric acid gas scrubber 164 where the remaining water vapor is absorbed by a stream of sulfuric acid. Sulfuric acid gas cleaning equipment 16
4, it becomes diluted by water. This diluted acid can be continuously regenerated by passing it through pipeline 166 to a suitable sulfuric acid dehydrator 168 that includes a heating device to evaporate the water and concentrate the sulfuric acid. . This reconcentrated acid is then returned to the acid gas scrubber 164 via pipeline 170. The gas exiting the sulfuric acid scrubber 164 via pipeline 172 is substantially pure chlorine gas, which is suitable for various industrial applications. Hydrogen chloride is transferred to the molten salt contactor 752 by reaction (4).
When oxidized, the valence state of vanadium in this salt mixture is reduced, so
It is necessary to regenerate this vanadium to a high valence state. Such regeneration involves transferring the molten salt containing reduced vanadium to pipeline 17.
3 into a second molten salt contactor 174 in which the pipeline 178
contact with a gas carrying oxygen introduced from This vanadium is thereby oxidized to regenerate V ₂ O ₅ by the reaction of the following general equation:
That is, V ₂ O ₄ +1/2O ₂ →V ₂ O ₅ (5) The regenerated molten salts containing vanadium, now in a high valence state, exit this contactor 174 in pipeline 180 and are subjected to flow regulation. device 18
2 and returned to the salt contactor 152 for reuse. Air is the preferred oxygen-bearing regeneration gas because of its ready availability and low cost.
Air is circulated through the salt contactor 174 and then discharged directly to the atmosphere. Oxygen is another suitable gas. This is most efficiently used if the unreacted portion of the oxygen leaving this contactor 174 is returned to pipeline 178. The ratio at which hydrogen chloride and molten salt are combined in the salt contactor 152 affects the overall efficiency of the apparatus. The preferred ratio will depend on the salt composition and operating temperature, but can be readily determined by experiment. It is important that the gas in pipeline 146 has a low water content. The reason is that excess water in the salt contactor 152 will push the reaction of equation (4) to the left, thus interfering with chlorine production. Small amounts of water have little effect on chlorine production, but if large amounts of water are present, chlorine production is severely reduced. To obtain the most economical operation, the cost of dewatering the feed stock can be weighed against the quantity and price of chlorine regenerated to determine the preferred water content for the feed stock flow. . Preferred salt compositions for use in accordance with the present invention include alkali metal sulfates, alkali metal pyrosulfates, and dissolved oxygen compounds capable of reacting with hydrogen chloride to produce elemental chlorine. _{V2O5 _}
is a very active oxygen compound, which can be included in the salt mixture to the extent that it dissolves in the melt. Preferably, _V2O5 consists of 2-25% by weight of _the salt mixture, more preferably 10-15%
It consists of % by weight. Other soluble metal oxides can be used for the oxidation of hydrogen chloride according to the method of the invention. These include soluble oxides of copper, iron, chromium or manganese. Oxides of lead, nickel, cobalt or uranium are not suitable. A variety of different alkali metal sulfates and pyrosulfates can be selected to make up the volume of the mixture. Potassium and sodium sulfates and pyrosulfates are preferred due to their abundance and advantageous properties. Mixtures containing 5-25% by weight of potassium sulfate and 50-90% by weight of potassium pyrosulfate are satisfactory. Preferred ranges for these sulfates are 10-20% by weight potassium sulfate and 65-20% by weight potassium sulfate.
70% by weight potassium pyrosulfate. Small amounts of other soluble sulfates or pyrosulfates can be added to such potassium compound mixtures without significantly reducing the effectiveness of the salt mixture. Moreover, the inclusion of small amounts of lithium sulfate, sodium sulfate or sulfuric acid has been found to have a desirable effect on the solidification temperature, corrosivity, SO vapor pressure, viscosity and operating temperature of the salt mixture. The combined amount of these substances in the salt mixture should not exceed approximately 10% by weight. Additions in excess of this amount are found to be undesirable or inappropriate. When this preferred salt mixture is used,
This salt is capable of oxidizing hydrogen chloride when maintained in a temperature range of 275°C to 475°C. 325℃
Best results are obtained in the temperature range ~425°C. If gaseous hydrogen chloride is contacted with this salt mixture in this temperature range for at least 0.25 seconds, preferably 0.5 to 5.0 seconds, most of the hydrogen chloride will be converted to chlorine by the action of equation (4). It will be oxidized. The operating temperatures and residence times used in second contacting device 152 may conveniently be similar to those of first contacting device 174. However, in this contactor 174, the ratio of gas to salt is not critical as long as excess oxygen is present to drive the reaction of equation (5) as far to the right as possible. Assuming conservatively that 60% conversion of hydrogen chloride is achieved with substantially dry hydrogen chloride gas in the feed stock, the effluent gas exiting salt contactor 152 will have the following composition: 30% by volume C ₂ 30 % H ₂ O 40 % HC Example A series of experiments were conducted to determine whether favorable conversion of hydrogen chloride to chlorine could be achieved by the process of the present invention. In these experiments, a Vycor vessel placed inside a tube furnace was used to contain a molten salt mixture containing K ₂ S ₂ O ₇ , K ₂ SO ₄ and V ₂ O ₅ . A metered stream of hydrogen chloride was dispersed into the molten catalyst mixture by a Pyrex frit, and the effluent gas leaving this vessel was scrubbed with a KI solution to remove the formed chlorine and any residual HC present. . Each run was one hour long. During operation, vanadium has an apparent HC conversion of approximately
It played fine forever every time it was reduced to 50%. Regeneration was accomplished by stopping the flow of hydrogen chloride and dispersing air through the frit into the salt mixture. At the end of each run, the total chlorine produced was determined by titrating the free iodine in the gas scrubber solution with sodium thiosulfate. The amount of unreacted hydrogen chloride was determined by titrating the gas scrubber solution with caustic soda.
The results of the various runs are presented in the table. These results show that although the conditions were not optimal and the experimental setup was quite simple, substantial yields were obtained when sufficient V ₂ O ₅ was present.

Table The most economically important application for the process of the invention is in the regeneration of chlorine from hydrogen chloride. For this reason most of the foregoing discussions relate specifically to chlorine. However, it should be understood that the molten salt contactor and salt mixture of the present invention can be applied to the regeneration of free chlorine through significant conversion from hydrogen halides to the exclusion of HF. Although a preferred embodiment of this invention has been described, it will be apparent to those skilled in the art that a wide range of changes and modifications may be made without departing from the invention. For example, all or part of the potassium sulfate and potassium pyrosulfate in the above-mentioned salt mixture can be replaced with sodium sulfate and sodium pyrosulfate. Although the resulting mixtures work well, they are somewhat less thermally stable than the preferred mixtures of potash salts and are less active in the oxidation of salt hydrogen. Furthermore, when using sodium sulfate, the partial pressure of SO ₃ tends to be high at a given constant temperature. In summary, the present invention discloses a method of oxidizing hydrogen halide with a catalytically activated molten salt. The subject hydrogen halide is contacted with a molten salt comprising an oxygen compound of vanadium and an alkali metal sulfate and pyrosulfate to produce an effluent gas enriched in the halogen element. If no oxygen-bearing gas is present during this contact, the vanadium is reduced, but can be regenerated to an active, high-valence state by contacting the spent molten salt with an oxygen-bearing gas. I can do it.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a flow sheet showing a first embodiment of the method of the invention, including a special gas separation step used to separate chlorine gas; FIG. 2 is a general method of this first embodiment; a flow sheet diagram showing the
FIG. 3 is a flowchart showing a second embodiment of the present invention.
Sheet Schematics, and FIG. 4 is a flow sheet diagram illustrating a second embodiment method including a special step for the liberation of chlorine gas. 10...pipeline, 12...dehydration device, 1
3...Pipeline, 14...Pipeline, 1
6...Flowmeter, 17...Pipeline, 18...
Molten salt contact device, 20...pipeline, 22...
...Flowmeter, 23...Pipeline, 24...Condensing device, 25...Pipeline, 26...Pipeline, 28...Pipeline, 30...Gas cleaning device using sulfuric acid, 32...Pipeline, 34 …
...Appropriate sulfuric acid dehydration equipment, 36...pipeline,
38...Pipeline, 40...Condensing device, 42
... Pipeline, 50 ... Molten salt contact device, 5
2...Pipeline, 54...Pipeline, 5
6...Pipeline, 58...Gas separation device, 1
10... Molten salt contact device, 112... Pipeline, 114... Pipeline, 116... Gas separation device, 118... Second molten salt contact device, 12
0...Pipeline, 122...Pipeline,
124...Pipeline, 140...Pipeline, 142...Hydrochloric acid dehydration device, 144...
Pipeline, 146...Pipeline, 148
...flow control device, 150 ... pipeline, 1
52... Molten salt contact device, 154... Pipeline, 156... Condensing device, 158... Pipeline, 160... Pipeline, 162... Pipeline, 164... Pipeline, 166... Pipeline, 168...Sulfuric acid dehydration equipment, 170...
...pipeline, 172 ...pipeline, 17
3... Pipeline, 174... Molten salt contact device, 178... Pipeline, 180... Pipeline, 182... Flow rate adjustment device.

Claims (1)

[Claims] 1. A method for regenerating a halogen element selected from chlorine, bromine, and iodine from a corresponding hydrogen halide, comprising: a molten salt contactor containing only a liquid and a gas; contacting a hydrogen halide with a molten salt mixture comprising a pyrosulfate and a dissolved oxidizing catalyst; and further maintaining the salt mixture at an elevated temperature sufficient to oxidize a majority of the hydrogen halide. the corresponding halogenation of a halogen element selected from chlorine, bromine and iodine, characterized in that it consists of the step of producing an effluent gas stream containing mainly water vapor and said halogen element together with a small amount of unreacted hydrogen halide. How to regenerate from hydrogen. 2. Contacting an oxidizing gas with the hydrogen halide and the molten salt mixture in the molten salt contactor to promote the oxidation of the hydrogen halide and maintain the activity of the oxidizing catalyst, thereby reducing the effluent. 2. A method according to claim 1, characterized in that a relatively small amount of unreacted oxidizing gas is produced in the gas stream. 3 the halogen consists of chlorine, the hydrogen halide consists of hydrogen chloride, and the salt mixture is 5
~25 wt% _{K2SO4 and} 50-90 wt%
Contains K ₂ S ₂ O ₇ , and the temperature is between 275℃ and 475℃
3. A method according to claim 2, characterized in that: 4. Said oxidizing gas consists of oxygen, and said hydrogen chloride and said oxygen combine in relative proportions to provide no more than 4.0 moles of hydrogen chloride per mole of oxygen. The method described in Section 3. 5. The method of claim 4, wherein said hydrogen chloride and said oxygen are combined in relative proportions to provide 3.3 to 3.7 moles of hydrogen chloride per mole of oxygen. 6. The method of claim 3, wherein the hydrogen chloride and the oxidizing gas are maintained in contact with the salt mixture for at least 0.25 seconds. 7. The method of claim 3, wherein the dissolved oxidizing catalyst comprises an oxygen compound of vanadium. 8. The method of claim 7, wherein the oxidizing catalyst consists of _V2O5 and the salt mixture contains from 2 to ₂₅ % by weight of the oxidizing catalyst. 9 The salt mixture contains Li ₂ SO ₄ , Na ₂ SO ₄ ,
3. The method of claim 2, further comprising a sulfate selected from the group consisting of K ₂ SO ₄ and in an amount not substantially more than 10% by weight of said salt mixture. 10. The method of claim 9 _, wherein the salt mixture comprises about 10% by weight _Li2SO4 . 11 The salt mixture is 5 to 25% by weight of Na ₂ SO ₄
and 50 to 90% by weight of Na ₂ S ₂ O ₇ . 12. said oxidizing catalyst comprises an oxygen compound capable of reacting with said hydrogen chloride to produce an elemental halogen and water, said contacting being carried out in the substantial absence of an oxygen-bearing gas, and Claim 1, wherein said salt mixture is maintained at a high enough temperature to sustain a reaction between said oxygen compound and said hydrogen halide to produce an effluent gas substantially free of gaseous oxygen. The method described in Section 1. 13 The halogen consists of chlorine, the hydrogen halide consists of hydrogen chloride, and the salt mixture contains 5 to 25% by weight of K ₂ SO ₄ and 50 to 90% by weight of
Contains K ₂ S ₂ O ₇ , and furthermore, the temperature is between 275℃ and 475℃.
13. A method according to claim 12, characterized in that the temperature is maintained at <0>C. 14. The method of claim 13, wherein the hydrogen chloride is maintained in contact with the salt mixture for at least 0.25 seconds. 15. The method of claim 14, wherein the hydrogen chloride is maintained in contact with the salt mixture for a period of time ranging from 0.5 to 5.0 seconds. 16. The method of claim 13, wherein the dissolved oxygen compound comprises an oxide of vanadium. 17 The salt mixture is Li ₂ SO ₄ , Na ₂ SO ₄ ,
containing a sulfate selected from the group consisting of Li ₂ SO ₄ ;
13. The method of claim 12, wherein the salt mixture comprises: 18. The method of claim 17, wherein the salt mixture comprises about 10% by weight Li ₂ SO ₄ . 19 The salt mixture is 5 to 25% by weight of Na ₂ SO ₄
and 50 to 90% by _{weight of Na2S2O7} . 20 After the reaction with the hydrogen halide, a reaction product is left which is dissolved in the salt mixture, and when dissolved in the salt mixture, it reacts with oxygen in the oxygen-bearing gas with which it comes into contact, and the oxygen 13. A method according to claim 12, characterized in that the oxygen compound is selected from those compounds that regenerate the compound. 21 In a method for regenerating a halogen element selected from chlorine, bromine and iodine from the corresponding hydrogen halide, in a molten salt contactor, 5 to 25% by weight of K ₂ SO ₄ ,
50-90% by weight _{of K2S2O7} and 2-25% _by weight of
contacting a molten salt mixture containing V ₂ O ₅ with a hydrogen halide in ^the substantial absence of an oxygen-bearing gas; maintaining the salt mixture at an elevated temperature sufficient to maintain a reaction between vanadium and the hydrogen halide;
Thereby reducing at least a portion of the vanadium dissolved in the molten salt mixture to its lowest valence state (V ⁺⁴ ) and removing a small amount of unreacted halogen from the salt mixture resulting in the reduced vanadium. separating and producing an effluent gas containing mainly water vapor and said halogen element along with hydrogen hydride; and further continuing the reaction between oxygen or an oxygen-bearing gas and said dissolved and reduced vanadium. The salt mixture containing the reduced vanadium is contacted with oxygen or a gas carrying oxygen at a high enough temperature to cause the hydrogen halide to be added to the hydrogen halide. A method for regenerating a halogen element selected from chlorine, bromine and iodine from a corresponding hydrogen halide, comprising the step of regenerating the vanadium to its high valence state. 22. The method of claim 21, wherein the oxygen-bearing gas comprises air.