Halon Refining Method

Abstract

The present invention provides a halon purification method capable of obtaining high-purity halon by easily, safely and efficiently removing mixed bromine molecules. The halon purification method is a method for removing bromine molecules from crude halon which contains halon and bromine molecules, and comprises: a contact step for bringing the crude halon into contact with an absorbing liquid comprising an aqueous solution containing a metal iodide to obtain a liquid mixture containing the crude halon and the absorbing liquid; and a separation step for separating the halon from the liquid mixture to obtain halon and the absorbing liquid which has absorbed the bromine molecules.

Description

[Technical Field]

[0001] The present invention relates to a method for refining halon. [Background technology]

[0002] Halon is a compound used as a fire extinguisher, refrigerant, synthetic reagent, etc. Halon refers to halogenated hydrocarbons in which some or all of the hydrogen atoms of saturated or unsaturated hydrocarbons have been replaced with halogen atoms, and some or all of the halogen atoms replacing the hydrogen atoms are bromine atoms. Halon may contain bromine molecules (Br2) as impurities due to its synthesis process or thermal decomposition, but because bromine molecules are corrosive and toxic, it is preferable to remove them from halon.

[0003] Distillation is generally used as a method for removing bromine molecules from halon and purifying it. Another method for purifying halon by removing bromine molecules is a liquid phase extraction method in which halon is brought into contact with an absorption liquid to absorb the bromine molecules. Patent Document 1 proposes a technique using an aqueous solution of an organic base as the absorption liquid, and Patent Document 2 proposes a technique using an aqueous solution of a metal sulfite and a metal hydroxide as the absorption liquid. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2000-167342 [Patent Document 2] Japanese Patent Publication No. 2788477 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the distillation method requires large-scale equipment such as a distillation column, making it difficult to easily purify halon. Also, because halon and bromine molecules often have similar boiling points, it can be difficult to obtain high-purity halon. Furthermore, although the liquid phase extraction method is an excellent method in terms of processing volume and cost, there is a problem in that the absorption liquid used in the techniques of Patent Documents 1 and 2 is an alkaline solution, which may be dangerous to handle. Furthermore, when an alkaline solution is used as the absorption liquid, there is a risk that the efficiency of removing bromine molecules may be insufficient, and there is also a risk that halon may be hydrolyzed by the alkaline solution. An object of the present invention is to provide a method for purifying halon, which can easily, safely, and efficiently remove contaminating bromine molecules to obtain high-purity halon. [Means for solving the problem]

[0006] In order to solve the above problems, one aspect of the present invention is as follows [1] to [8]. [1] A halon purification method for removing bromine molecules from crude halon containing halon and bromine molecules, comprising: a contacting step of contacting the crude halon with an absorption solution comprising an aqueous solution containing a metal iodide to obtain a mixed solution containing the crude halon and the absorption solution; a separation step of separating the halon from the mixed solution to obtain the absorbing solution that has absorbed the bromine molecules and the halon; A halon refining method comprising:

[0007] [2] The method for purifying halon according to [1], wherein the metal iodide is at least one selected from alkali metal iodides and alkaline earth metal iodides. [3] The method for purifying halon according to [1], wherein the metal iodide is potassium iodide. [4] The halon purification method according to any one of [1] to [3], wherein in the contacting step, the gaseous crude halon is brought into contact with the absorption liquid, and in the separating step, the gaseous halon is extracted from the mixed liquid by gas-liquid extraction.

[0008] [5] The method for purifying halon according to any one of [1] to [4], wherein the halon has 1 or more and 3 or less carbon atoms. [6] The method for purifying halon according to any one of [1] to [4], wherein the halon has 1 or 2 carbon atoms.

[0009] [7] The method for purifying halon according to any one of [1] to [4], wherein the halon is at least one of bromomethane, tribromofluoromethane, bromodifluoromethane, dibromodifluoromethane, bromotrifluoromethane, bromoethane, dibromotrifluoroethane, dibromotetrafluoroethane, tribromotrifluoroethane, bromofluoroethylene, bromodifluoroethylene, and bromotrifluoroethylene. [8] The method for purifying halon according to any one of [1] to [7], wherein the absorption liquid further contains potassium iodate or sodium iodate. [Effects of the Invention]

[0010] According to the present invention, bromine molecules contaminated in halon can be removed simply, safely, and efficiently to obtain high-purity halon. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing an example of a refining treatment apparatus for explaining an embodiment of a halon refining method according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] An embodiment of the present invention will be described below. Note that this embodiment is merely an example of the present invention, and the present invention is not limited to this embodiment. Furthermore, various modifications and improvements can be made to this embodiment, and such modifications and improvements can also be included in the present invention.

[0013] A halon purification method according to one embodiment of the present invention is a halon purification method for removing bromine molecules from crude halon containing halon and bromine molecules, and includes a contacting step in which the crude halon is brought into contact with an absorbing solution comprising an aqueous solution containing a metal iodide to obtain a mixed solution containing the crude halon and the absorbing solution, and a separation step in which the halon is separated from the mixed solution to obtain the absorbing solution that has absorbed bromine molecules and the halon.

[0014] Halon may contain bromine molecules as impurities, but if crude halon containing halon and bromine molecules is purified by the halon purification method according to the present embodiment, the bromine molecules contaminated in the crude halon can be simply, safely, and efficiently removed, and highly pure purified halon can be obtained.

[0015] More specifically, the halon purification method according to this embodiment does not use a distillation method, and therefore does not require large-scale equipment such as a distillation column, and can easily produce highly purified halon. Furthermore, because purification is performed by a liquid-phase extraction method rather than a distillation method, highly purified halon can be obtained even from halon whose boiling point is close to that of bromine molecules. Furthermore, no alkaline solution is required as the absorption liquid, and an aqueous solution containing a metal iodide is used as the absorption liquid, which makes the method safe and easy to operate. Furthermore, because the halon does not come into contact with an alkaline solution and is therefore less susceptible to hydrolysis, bromine molecules can be efficiently removed from crude halon to produce highly purified halon.

[0016] The halon refining method according to this embodiment will be described in further detail below. [Crude halon] Although there are no particular limitations on the type of halon that can be purified by the halon purification method according to this embodiment, in consideration of the ease of separation of the halon from the mixed liquid in the separation step, halon that has low solubility in water and a low boiling point is preferred. That is, halon having a carbon number of 1 to 3 is preferred, and halon having a carbon number of 1 or 2 is more preferred.

[0017] Specifically, the halon is more preferably at least one of bromomethane (CHBr), tribromofluoromethane (CBrF), bromodifluoromethane (CHBrF), dibromodifluoromethane (CBrF), bromotrifluoromethane (CBrF), bromoethane (CHBr), dibromotrifluoroethane (CHBrF), dibromotetrafluoroethane (CBrF), tribromotrifluoroethane (CBrF), bromofluoroethylene (CHBrF), bromodifluoroethylene (CHBrF), bromotrifluoroethylene (CBrF), bromohexafluoropropane (CHBrF), bromoheptafluoropropane (CBrF), and bromotrifluoropropene (CHBrF).

[0018] The crude halon to be subjected to the halon purification method according to this embodiment may be in either a gaseous or liquid state. Halons with low boiling points, such as dibromodifluoromethane, bromotrifluoroethylene, bromohexafluoropropane, bromoheptafluoropropane, and bromotrifluoropropene, are suitable for gas-liquid separation, while halons with high boiling points, such as tribromofluoromethane and tribromotrifluoroethane, are suitable for liquid-liquid separation. The halon refining method according to this embodiment can refine crude halon containing one type of halon, or can refine crude halon containing two or more types of halon.

[0019] The concentration of bromine molecules in crude halon is not particularly limited, but in consideration of increasing the rate of removal of bromine molecules from crude halon, the number of moles of bromine molecules in crude halon is preferably 1 time or less, more preferably 0.8 times or less, and even more preferably 0.5 times or less, the number of moles of halon in crude halon. In order to make the concentration of bromine molecules in refined halon a concentration that is sufficiently low so that the corrosiveness of bromine molecules is low, the concentration of bromine molecules in refined halon is preferably 0.1 volume % or less, and to achieve this, the rate of removal of bromine molecules from crude halon is preferably 99.90% or more.

[0020] When the crude halon contains hydrogen bromide, the concentration of hydrogen bromide in the crude halon is not particularly limited. However, in consideration of increasing the rate of removal of hydrogen bromide from the crude halon, the number of moles of hydrogen bromide in the crude halon is preferably 1.5 times or less, more preferably 1 time or less, and even more preferably 0.5 times or less, the number of moles of halon in the crude halon.

[0021] [Absorption liquid] The absorbing liquid is a liquid capable of absorbing bromine molecules and is not particularly limited as long as it is an aqueous solution containing a metal iodide. However, from the viewpoints of high safety, ease of handling, and suppression of halon hydrolysis, it is preferable that the liquid is neutral rather than alkaline or acidic, and the pH may be 5 or more and 9 or less, and more preferably 6 or more and 8 or less. Therefore, the absorbing liquid needs to be an aqueous solution of a metal iodide, which is a reducing agent, but it is preferably an aqueous solution in which only a metal iodide is dissolved in water, and it is preferable that basic compounds such as metal hydroxides are not dissolved. However, as long as the liquid's neutrality is maintained, the absorbing liquid may contain other compounds such as additives.

[0022] The type of metal iodide is not particularly limited, but is preferably at least one selected from alkali metal iodides and alkaline earth metal iodides. Specific examples of alkali metal iodides include potassium iodide (KI) and sodium iodide (NaI), and specific examples of alkaline earth metal iodides include magnesium iodide (MgI), calcium iodide (CaI), and barium iodide (BaI). Among these metal iodides, potassium iodide is particularly preferred.

[0023] The amount of metal iodide contained in the absorption solution is preferably at least an amount capable of absorbing the total amount of bromine molecules to be absorbed in the absorption solution, i.e., at least one equivalent amount required for reaction with bromine molecules. In order to improve the removal rate of bromine molecules from crude halon, the amount is more preferably at least 1.5 times the equivalent amount, even more preferably at least two times, and particularly preferably at least five times.

[0024] Furthermore, the concentration of the metal iodide in the absorption solution is preferably a concentration at which the metal iodide is soluble and at which the metal bromide and iodine molecules produced by the reaction are soluble in the absorption solution. However, the concentration of the metal iodide in the absorption solution may be a concentration at which at least a portion of the metal iodide is insoluble, i.e., the absorption solution may be a slurry containing solid metal iodide. Therefore, the concentration of the metal iodide in the absorption solution is preferably 0.1 mol / L or more and 9 mol / L or less.

[0025] When the metal iodide in the absorption solution is consumed by the absorption of bromine molecules and the concentration of the metal iodide decreases, the iodine molecules generated by the above reaction become less soluble in the absorption solution, which may result in the iodine molecules precipitating from the absorption solution and causing clogging of components (e.g., piping) of the purification treatment device.

[0026] Therefore, the concentration of metal iodide in the absorption solution during the purification treatment is preferably maintained at 40% or more, more preferably 60% or more, of the initial concentration of metal iodide in the absorption solution before the purification treatment. More specifically, during the purification treatment, the concentration of metal iodide in the absorption solution is preferably maintained at 0.5 mol / L or more, more preferably 0.7 mol / L or more.

[0027] When the crude halon contains a substance other than bromine molecules that is thought to react with metal iodide (for example, when the crude halon contains hydrogen bromide (HBr), which will be described later), it is preferable to determine the amount of metal iodide contained in the absorption solution taking into consideration the amount of this substance other than bromine molecules. That is, the amount of metal iodide contained in the absorption solution is preferably at least 1 time, more preferably at least 1.5 times, even more preferably at least 2 times, and particularly preferably at least 5 times the total equivalent of the equivalent required for reaction with bromine molecules and the equivalent required for reaction with substances other than bromine molecules.

[0028] If desired, any additive may be dissolved or suspended in the absorption liquid. For example, if the crude halon contains hydrogen bromide, potassium iodate (KIO3) or sodium iodate (NaIO3) may be added as an additive to the absorption liquid to remove hydrogen bromide together with bromine molecules from the crude halon. Hydrogen bromide is removed from crude halon by the reaction shown in the following reaction formula (2). 6HBr+5KI+KIO3→ 6KBr+3I2+3H2O...(2)

[0029] When the additive is, for example, potassium iodate or sodium iodate, the amount of additive contained in the absorption solution is preferably at least an amount capable of absorbing the entire amount of hydrogen bromide to be absorbed in the absorption solution, i.e., at least one equivalent amount required for the reaction with hydrogen bromide; in order to improve the rate of removal of hydrogen bromide from crude halon, the amount is more preferably at least 1.5 times the above-mentioned equivalent amount, even more preferably at least 3 times, and particularly preferably at least 7 times. When a plurality of absorption towers are used in the absorption step, the amount of additive contained in the absorption liquid is preferably applied to the absorption liquid contained in the absorption tower located most upstream among the plurality of absorption towers connected in series.

[0030] [Contact process] The contacting step is a step of bringing the crude halon into contact with the absorbing liquid to obtain a mixed liquid containing the crude halon and the absorbing liquid, and causing the bromine molecules in the crude halon to be absorbed into the absorbing liquid. The halon purification method according to this embodiment can purify gaseous crude halon or liquid crude halon.

[0031] The method for bringing the crude halon into contact with the absorbing liquid is not particularly limited, but when the crude halon is in a liquid state, the crude halon can be brought into contact with the absorbing liquid by mixing the crude halon with the absorbing liquid, for example, in an absorption tower, and dispersing the crude halon in the liquid. When the crude halon is in a liquid state, the crude halon can be transferred by a liquid transfer pump.

[0032] Furthermore, when the crude halon is in a gaseous state, the crude halon can be contacted with the absorbing solution by a method of bubbling the crude halon into the absorbing solution, a method of spraying the absorbing solution onto the crude halon using a scrubber, etc. When the crude halon is in a gaseous state, the gaseous crude halon is contacted with the absorbing solution in the contacting step, and the gaseous purified halon is gas-liquid extracted from the mixed solution in the separation step, so the purification operation is simple and easy.

[0033] A specific example of the bubbling method is a method in which crude halon is supplied to an absorbing solution contained in an absorption tower. The crude halon can be brought into contact with the absorbing solution by blowing the crude halon into the absorbing solution through a pipe or the like inserted in the absorbing solution. By blowing the crude halon into the absorbing solution, a mixed solution containing the crude halon and the absorbing solution is obtained, and the bromine molecules in the crude halon react with the metal iodide in the absorbing solution, causing the bromine molecules to be absorbed into the absorbing solution.

[0034] For example, when potassium iodide is used as the metal iodide, bromine molecules are removed from crude halon by the reaction shown in the following reaction formula (1). Br2 + 2KI → 2KBr + I2 (1) The metal bromides and iodine molecules (I2) produced by the above reaction remain in the absorption solution, and since halon is poorly soluble in water, it is separated from the absorption solution in the separation process.

[0035] The number of absorption towers is not particularly limited and may be one or more, but in order to improve the removal rate of bromine molecules from crude halon, it is preferable to adopt a mode in which multiple absorption towers are connected in series and crude halon is continuously injected into the multiple absorption towers. When multiple absorption towers are used, the "amount of metal iodide contained in the absorption solution" explained in the above section on "Absorption Solution" preferably applies to the absorption solution contained in the most upstream absorption tower of the multiple absorption towers connected in series.

[0036] The pipes and absorption towers inserted into the absorbing solution are preferably made of materials that do not easily react with bromine molecules and halon, such as fluororesins and glass. When disposing of the absorption liquid after use in refining crude halon, it is desirable to treat the iodine molecules generated by the reaction between metal iodides and bromine molecules with sodium thiosulfate (Na2S2O3) or similar before disposal.

[0037] When gaseous crude halon is refined, the crude halon may be made gaseous by the vapor pressure of the halon, or by mixing a diluent gas such as an inert gas. When a diluent gas is mixed with the crude halon, the diluent gas may be mixed so that, for example, 10% by volume to 90% by volume of the gaseous mixture obtained by mixing the crude halon and the diluent gas is the diluent gas.

[0038] The type of inert gas used as the dilution gas is not particularly limited, but examples include nitrogen gas (N), helium (He), argon (Ar), neon (Ne), krypton (Kr), and xenon (Xe). Among these inert gases, nitrogen gas, helium, argon, neon, and krypton are preferred, and nitrogen gas and argon are more preferred. These inert gases may be used alone or in combination of two or more.

[0039] [Separation process] The separation step is a step in which halon is separated from a mixture containing crude halon and an absorbing solution to obtain an absorbing solution that has absorbed bromine molecules and purified halon. Because halon is poorly soluble in water, it is separated from the absorbing solution by gas-liquid separation or liquid-liquid separation due to the difference in specific gravity. The method for separating the halon from the mixed liquid is not particularly limited, but when the halon is in a gaseous state, the purified halon is separated from the absorbing liquid by gas-liquid separation and is discharged from the absorbing liquid, for example, through a pipe provided at the top of the absorption tower. When the halon is in a liquid state, the purified halon is separated from the absorbing liquid by liquid-liquid separation and, if the specific gravity of the halon is smaller than that of the absorbing liquid, is discharged from the absorbing tower, for example, through a pipe provided at the top of the absorption tower, and when the specific gravity of the halon is greater than that of the absorbing liquid, is discharged from the absorbing tower, for example, through a pipe provided at the bottom of the absorption tower.

[0040] [Refining Treatment Device] Next, with reference to FIG. 1, an example of the configuration of a refining treatment device capable of carrying out the halon refining method according to this embodiment and an example of a halon refining method using the refining treatment device will be described. The purification treatment apparatus of FIG. 1 includes a crude halon cylinder 1 filled with gaseous crude halon at room temperature and pressure, an inert gas cylinder 2 filled with inert gas, a first absorption tower 11 and a second absorption tower 13 for purifying the crude halon, a crude halon supply pipe 5 connecting the crude halon cylinder 1 and the first absorption tower 11, and an inert gas supply pipe 6 connecting the inert gas cylinder 2 to an intermediate portion of the crude halon supply pipe 5.

[0041] A crude halon supply unit 3 consisting of a mass flow controller or the like is provided in the upstream portion of crude halon supply pipe 5 (i.e., the portion close to crude halon cylinder 1). The crude halon in crude halon cylinder 1 is supplied to first absorption tower 11 via crude halon supply pipe 5 while the flow rate is controlled by crude halon supply unit 3.

[0042] In addition, an inert gas supply unit 4 consisting of a mass flow controller or the like is provided on the inert gas supply pipe 6. The inert gas in the inert gas cylinder 2 is supplied to an intermediate portion of the crude halon supply pipe 5 (i.e., the portion downstream of the crude halon supply unit 3) via the inert gas supply pipe 6 while the flow rate is controlled by the inert gas supply unit 4.

[0043] When gaseous crude halon is diluted with inert gas, crude halon gas is sent out to crude halon supply pipe 5 by crude halon supply unit 3, and inert gas is sent out to crude halon supply pipe 5 by inert gas supply unit 4 via inert gas supply pipe 6. As a result, crude halon gas is diluted with inert gas in the middle of crude halon supply pipe 5, and this diluted crude halon gas is supplied to first absorption tower 11 via crude halon supply pipe 5.

[0044] The first absorption tower 11 contains a first absorbing solution 12, and a bubbling pipe 16 connected to the downstream end of the crude halon supply pipe 5 is inserted into the first absorbing solution 12. Thus, the crude halon is supplied into the first absorbing solution 12 in the first absorption tower 11 and comes into contact with the first absorbing solution 12, so that the crude halon is purified in the first absorption tower 11. The first absorption tower 11 is equipped with a temperature control device (not shown) that controls the temperature of the first absorbing solution 12.

[0045] The crude halon is purified in the first absorption tower 11, and most of the bromine molecules contained therein are removed, and the crude halon undergoes gas-liquid separation from the first absorption liquid 12. The separated crude halon then reaches a portion above the liquid level of the first absorption liquid 12 in the first absorption tower 11, and is sent to the second absorption tower 13 via a connecting pipe 17 that connects the upper part of the first absorption tower 11 with the second absorption tower 13.

[0046] The second absorption tower 13 contains a second absorbing liquid 14, and the downstream end of the connecting pipe 17 is inserted into the second absorbing liquid 14. Therefore, the crude halon sent from the first absorption tower 11 is supplied to the second absorbing liquid 14 of the second absorption tower 13 and comes into contact with the second absorbing liquid 14, so that the crude halon is further purified in the second absorption tower 13. The first absorbing liquid 12 and the second absorbing liquid 14 may be the same type of absorbing liquid or different types of absorbing liquids.

[0047] Most of the bromine molecules are removed from the crude halon in the first absorption tower 11, but traces of remaining bromine molecules are removed from the crude halon in the second absorption tower 13. This results in high-purity purified halon. The purified halon is separated from the second absorption liquid 14 and reaches a portion of the second absorption tower 13 above the liquid level of the second absorption liquid 14. An exhaust pipe 18 for discharging gases inside is provided at the top of the second absorption tower 13, and the high-purity purified halon is discharged from the second absorption tower 13 to the outside via the exhaust pipe 18.

[0048] [Refining treatment conditions] The temperature conditions in the contact step are not particularly limited, but while a higher temperature increases the rate of the reaction that removes bromine molecules, if the temperature is too high there is a risk of corrosion of components (e.g., piping) of the purification treatment device, so the temperature is preferably from 5° C. to 80° C., more preferably from 10° C. to 60° C., and even more preferably from 20° C. to 60° C. The temperature conditions in the contact step, i.e., the temperature of the absorption liquid, can be controlled, for example, by a heating device or a cooling device provided in an absorption tower that accommodates the absorption liquid. The pressure conditions in the contact step are not particularly limited, but are preferably 0 MPa to 0.2 MPa, more preferably 0.1 MPa to 0.2 MPa, and even more preferably atmospheric pressure (0.1 MPa). [Example]

[0049] The present invention will be described in more detail below with reference to examples and comparative examples. Example 1 A purification process was carried out to obtain purified dibromodifluoromethane (hereinafter referred to as "purified halon") by removing bromine molecules from crude dibromodifluoromethane containing dibromodifluoromethane and bromine molecules (corresponding to the "crude halon" constitutive element of the present invention, and hereinafter referred to as "crude halon") using a purification process equipment having a configuration similar to that shown in Figure 1. The concentration of bromine molecules in the crude halon was measured using an ion chromatograph manufactured by Shimadzu Corporation, and was found to be 48.0% by volume.

[0050] This purification treatment device is equipped with two absorption towers made of Teflon (registered trademark) PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer), and each absorption tower contains 1 L of absorbing solution of the same composition. This absorbing solution is an aqueous solution of potassium iodide, a reducing agent, with a potassium iodide concentration of 1.2 mol / L and a pH of 7. Both the first upstream absorption tower and the second downstream absorption tower are equipped with temperature control devices to control the temperature of the absorbing solution, and the temperature of the absorbing solution contained in each absorption tower is maintained at 25°C (with a fluctuation of ±2.5°C) during the purification treatment.

[0051] The crude halon filled in the crude halon cylinder was sent to the crude halon supply pipe using a mass flow controller (Horiba, Ltd. mass flow controller SEC-N112MGMW) equipped in the crude halon supply unit. Nitrogen gas filled in the inert gas cylinder was sent to the crude halon supply pipe via the inert gas supply pipe using a mass flow controller (Horiba, Ltd. mass flow controller SEC-N112MGMW) equipped in the inert gas supply unit. In this way, the crude halon and nitrogen gas were mixed in the crude halon supply pipe, and the crude halon was diluted. The mixture ratio was 80% by volume crude halon and 20% by volume nitrogen gas.

[0052] The crude halon diluted with nitrogen gas was supplied to the upstream first absorption tower via a crude halon supply pipe and brought into contact with an absorbing solution in the first absorption tower, causing the bromine molecules in the crude halon to be absorbed by the absorbing solution. The crude halon discharged from the first absorption tower was then supplied to the downstream second absorption tower via a connecting pipe and brought into contact with an absorbing solution in the second absorption tower, causing the bromine molecules in the crude halon to be absorbed by the absorbing solution. As a result of the crude halon purification process in this manner, the bromine molecules were removed from the crude halon, and purified halon was obtained. Note that the potassium iodide concentrations of both the first and second absorption solutions throughout the purification process were maintained at 0.72 mol / L or higher (i.e., 60% or higher of the initial concentration).

[0053] The gas discharged from the downstream second absorption tower is a mixed gas of purified halon and nitrogen gas, and purified halon was obtained by removing nitrogen gas from this mixed gas. The method for removing nitrogen gas is not particularly limited, but in this example, the mixed gas was introduced into a cold trap cooled with dry ice, and the purified halon was liquefied in the cold trap, thereby removing nitrogen gas from the mixed gas and obtaining purified halon. The concentration of bromine molecules in the purified halon obtained by removing nitrogen gas from the mixed gas was measured using an ion chromatograph manufactured by Shimadzu Corporation, and was found to be 0.0188% by volume.

[0054] The removal rate of bromine molecules by the purification treatment was calculated according to the following formula. Removal rate (%) = [1 - [Concentration of bromine molecules in refined halon] / [Concentration of bromine molecules in crude halon]] x 100 The results are shown in Table 1. The purification treatment achieved a bromine molecule removal rate of 99.96%, meaning that bromine molecules were removed to a low concentration where corrosiveness was hardly apparent.

[0055] [Table 1]

[0056] Example 2 The crude halon was purified in the same manner as in Example 1, except that the type of absorption solution contained in the two absorption towers was a sodium iodide aqueous solution with a concentration of 1.2 mol / L. The pH of this absorption solution was 7. The results are shown in Table 1. The purification treatment achieved a bromine molecule removal rate of 99.93%, and bromine molecules were successfully removed to a low concentration where corrosiveness was hardly observed.

[0057] Example 3 The crude halon was purified in the same manner as in Example 1, except that the type of absorption solution contained in the two absorption towers was a calcium iodide aqueous solution with a concentration of 1.2 mol / L. The pH of this absorption solution was 7. The results are shown in Table 1. The purification process achieved a bromine molecule removal rate of 99.92%, and bromine molecules were successfully removed to a low concentration where corrosiveness was hardly observed.

[0058] Example 4 The crude halon was purified in the same manner as in Example 1, except that the type of absorption solution contained in the two absorption towers was a magnesium iodide aqueous solution with a concentration of 1.2 mol / L. The pH of this absorption solution was 7. The results are shown in Table 1. The purification treatment achieved a bromine molecule removal rate of 99.92%, and bromine molecules were successfully removed to a low concentration where corrosiveness was hardly observed.

[0059] Example 5 A purification treatment of crude halon was carried out in the same manner as in Example 1, except that the concentration of bromine molecules in the crude halon was 32.6% by volume. The results are shown in Table 1. The removal rate of bromine molecules by the purification treatment was 99.96%, and bromine molecules were able to be removed to a low concentration where corrosiveness was hardly observed.

[0060] Example 6 A purification treatment of crude halon was carried out in the same manner as in Example 1, except that the concentration of bromine molecules in the crude halon was 11.3% by volume. The results are shown in Table 1. The removal rate of bromine molecules by the purification treatment was 99.97%, and bromine molecules were able to be removed to a low concentration where corrosiveness was hardly observed.

[0061] Example 7 The purification treatment of crude halon was carried out in the same manner as in Example 1, except that the temperature of the absorption solution contained in the first upstream absorption tower was maintained at 45°C (with a fluctuation of ±2.5°C) during the purification treatment. The pH of this absorption solution was 7. The results are shown in Table 1. The removal rate of bromine molecules by the purification treatment was 99.99%, and bromine molecules were able to be removed to a low concentration where corrosiveness was hardly observed.

[0062] Example 8 The purification treatment of crude halon was carried out in the same manner as in Example 1, except that the temperature of the absorption solution contained in the first upstream absorption tower was maintained at 5°C (with a fluctuation of ±2.5°C) during the purification treatment. The pH of this absorption solution was 7. The results are shown in Table 1. The removal rate of bromine molecules by the purification treatment was 99.93%, and bromine molecules were able to be removed to a low concentration where corrosiveness was hardly observed.

[0063] Example 9 A crude halon purification treatment was carried out in the same manner as in Example 1, except that crude bromodifluoromethane containing bromodifluoromethane and bromine molecules was used as the crude halon. The results are shown in Table 1. The removal rate of bromine molecules by the purification treatment was 99.96%, and bromine molecules were able to be removed to a low concentration where corrosiveness was hardly observed.

[0064] Example 10 A crude halon purification treatment was carried out in the same manner as in Example 1, except that crude bromotrifluoroethylene containing bromotrifluoroethylene and bromine molecules was used as the crude halon. The results are shown in Table 1. The removal rate of bromine molecules by the purification treatment was 99.96%, and bromine molecules were able to be removed to a low concentration where corrosiveness was hardly observed.

[0065] Comparative Example 1 A crude halon purification treatment was carried out in the same manner as in Example 1, except that the type of absorption liquid contained in the two absorption towers was a sodium sulfite (Na2SO3) aqueous solution with a concentration of 1.2 mol / L. The results are shown in Table 1. The removal rate of bromine molecules by the purification treatment was 98.86%, which was lower than when a potassium iodide aqueous solution was used as the absorption liquid.

[0066] Comparative Example 2 A crude halon purification treatment was carried out in the same manner as in Example 1, except that the type of absorption liquid contained in the two absorption towers was a sodium formate (HCOONa) aqueous solution with a concentration of 1.2 mol / L. The results are shown in Table 1. The removal rate of bromine molecules by the purification treatment was 98.67%, which was lower than when a potassium iodide aqueous solution was used as the absorption liquid.

[0067] Comparative Example 3 A crude halon purification treatment was carried out in the same manner as in Example 1, except that the type of absorbing solution contained in the two absorption towers was a urea ((NH)CO) aqueous solution with a concentration of 1.2 mol / L. The results are shown in Table 1. The removal rate of bromine molecules by the purification treatment was 98.12%, which was lower than when a potassium iodide aqueous solution was used as the absorbing solution.

[0068] Comparative Example 4 A crude halon purification treatment was carried out in the same manner as in Example 1, except that the type of absorbing liquid contained in the two absorption towers was water (HO). The results are shown in Table 1. The removal rate of bromine molecules by the purification treatment was 66.30%, which was lower than when an aqueous potassium iodide solution was used as the absorbing liquid.

[0069] Example 11 Crude dibromodifluoromethane containing dibromodifluoromethane, bromine molecules, and hydrogen bromide was used as crude halon. The concentration of bromine molecules in the crude halon measured using an ion chromatograph manufactured by Shimadzu Corporation was 32.6% by volume. The concentration of hydrogen bromide in the crude halon measured by titration using a 0.05 mol / L aqueous sodium hydroxide (NaOH) solution was 15.4% by volume.

[0070] The type of absorption liquid contained in the first absorption tower was an aqueous solution of potassium iodide and potassium iodate dissolved in water. The concentration of potassium iodide in this aqueous solution was 1.2 mol / L, and the concentration of potassium iodate was 0.0934 mol / L. Except for the above two points, the crude halon was purified in the same manner as in Example 1, and bromine molecules and hydrogen bromide in the crude halon were removed. The removal rate of hydrogen bromide by the purification treatment was calculated according to the following formula. Removal rate (%) = [1 - [concentration of hydrogen bromide in refined halon] / [concentration of hydrogen bromide in crude halon]] x 100

[0071] The results are shown in Tables 1 and 2. The purification process achieved a 99.96% removal rate of bromine molecules, meaning that bromine molecules were removed to a low concentration where corrosiveness was barely apparent. Furthermore, the hydrogen bromide concentration in the purified halon, measured by titration with a 0.05 mol / L aqueous sodium hydroxide solution, was 0.00227% by volume, meaning that the purification process achieved a 99.99% removal rate of hydrogen bromide.

[0072] [Table 2] [Explanation of symbols]

[0073] 1. Crude halon cylinder 2. Inert gas cylinder 3. Crude Halon Supply Department 4. Inert gas supply section 11. First absorption tower 12. First absorption liquid 13. Second absorption tower 14. Second absorption liquid

Claims

1. A halon purification method for removing bromine molecules from crude halon containing halon and bromine molecules, comprising: a contacting step of contacting the crude halon with an absorption solution comprising an aqueous solution containing a metal iodide to obtain a mixed solution containing the crude halon and the absorption solution; a separation step of separating the halon from the mixed solution to obtain the absorbing solution that has absorbed the bromine molecules and the halon; Equipped with The method for purifying halon, wherein the metal iodide is at least one selected from the group consisting of alkali metal iodides and alkaline earth metal iodides.

2. 2. The method for purifying halon according to claim 1, wherein the metal iodide is potassium iodide.

3. 3. The halon purification method according to claim 1, wherein the gaseous crude halon is brought into contact with the absorption liquid in the contact step, and the gaseous halon is extracted from the mixed liquid in a gas-liquid manner in the separation step.

4. The method for refining halon according to any one of claims 1 to 3, wherein the number of carbon atoms in the halon is 1 or more and 3 or less.

5. The method for refining halon according to any one of claims 1 to 3, wherein the halon has one or two carbon atoms.

6. The halon purification method according to any one of claims 1 to 3, wherein the halon is at least one of bromomethane, tribromofluoromethane, bromodifluoromethane, dibromodifluoromethane, bromotrifluoromethane, bromoethane, dibromotrifluoroethane, dibromotetrafluoroethane, tribromotrifluoroethane, bromofluoroethylene, bromodifluoroethylene, and bromotrifluoroethylene.

7. 7. The method for purifying halon according to claim 1, wherein the absorption solution further contains potassium iodate or sodium iodate.

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