Halogenated alkane refining process

Abstract

Provided is a halogenated alkane refining method that can easily, safely, and efficiently remove mixed bromine molecules to obtain a high-purity halogenated alkane. The halogenated alkane refining method is a method for removing bromine molecules from a crude halogenated alkane containing a halogenated alkane and bromine molecules, and includes: a contact step of bringing the crude halogenated alkane into contact with an absorbent solution prepared from an aqueous solution containing a metal iodide to obtain a mixed solution containing the crude halogenated alkane and the absorbent solution; and a separation step of separating the halogenated alkane from the mixed solution to obtain the absorbent solution having absorbed the bromine molecules and the halogenated alkane.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for refining halogenated alkane. BACKGROUND

[0002] Halogenated alkane is a compound that is utilized as a fire extinguishing agent, a cooling medium, a synthetic reagent, and the like. Halogenated alkane refers to a halogenated hydrocarbon in which a part or all of hydrogen atoms of a saturated hydrocarbon or an unsaturated hydrocarbon are replaced with halogen atoms, and a part or all of the halogen atoms replacing the hydrogen atoms are bromine atoms.

[0003] In halogenated alkane, bromine molecules (Br2) as impurities are sometimes mixed due to a synthetic process, thermal decomposition, or the like thereof, but since bromine molecules have corrosiveness and toxicity, it is preferable to remove them from halogenated alkane.

[0004] As a method for refining halogenated alkane by removing bromine molecules therefrom, a distillation method is generally used.

[0005] Further, as another method for refining halogenated alkane by removing bromine molecules therefrom, there is a liquid extraction method in which halogenated alkane is brought into contact with an absorption liquid to absorb bromine molecules in the absorption liquid. In Patent Literature 1, a technique of using an aqueous organic base solution as the absorption liquid is proposed, and in Patent Literature 2, a technique of using an aqueous solution of a metal sulfite and a metal hydroxide as the absorption liquid is proposed.

[0006] Prior Art Documents

[0007] Patent Literature

[0008] Patent Literature 1: Japanese Patent Publication No. 2000-167342

[0009] Patent Literature 2: Japanese Patent Publication No. 2788477 SUMMARY

[0010] Problems to be Solved by the Invention

[0011] However, the distillation method requires a large-scale device such as a distillation column, and thus has a problem that it is difficult to simply refine halogenated alkane. Further, since the boiling points of halogenated alkane and bromine molecules are sometimes close, it is sometimes difficult to obtain halogenated alkane with high purity.

[0012] Further, the liquid extraction method is an excellent method in terms of the treatment amount and cost, but since the absorption liquid used in the techniques of Patent Literatures 1 and 2 is an alkali solution, it has a problem that the operation can be accompanied by danger. Further, if an alkali solution is used as the absorption liquid, the removal efficiency of bromine molecules can become insufficient, and halogenated alkane can be hydrolyzed due to the alkali solution.

[0013] An object of the present application is to provide a halogenated alkane refining method that can easily, safely, and efficiently remove a bromine molecule mixed in to obtain a high-purity halogenated alkane.

[0014] Method for solving the problem

[0015] To solve the above problem, one aspect of the present application is described in the following [1] to [8].

[0016] [1] A halogenated alkane refining method that removes a bromine molecule from a crude halogenated alkane containing the halogenated alkane and the bromine molecule, the method comprising the steps of:

[0017] a contact step of bringing the crude halogenated alkane into contact with an absorbing solution prepared from an aqueous solution containing a metal iodide to obtain a mixed solution containing the crude halogenated alkane and the absorbing solution; and

[0018] a separation step of separating the halogenated alkane from the mixed solution to obtain the absorbing solution in which the bromine molecule is absorbed and the halogenated alkane.

[0019] [2] The halogenated alkane refining method according to [1], wherein the metal iodide is at least one selected from the group consisting of alkali metal iodides and alkaline earth metal iodides.

[0020] [3] The halogenated alkane refining method according to [1], wherein the metal iodide is potassium iodide.

[0021] [4] The halogenated alkane refining method according to any one of [1] to [3], wherein in the contact step, the crude halogenated alkane in a gaseous state is brought into contact with the absorbing solution, and in the separation step, the halogenated alkane in a gaseous state is gas-liquid extracted from the mixed solution.

[0022] [5] The halogenated alkane refining method according to any one of [1] to [4], wherein the halogenated alkane has a carbon atom number of 1 or more and 3 or less.

[0023] [6] The halogenated alkane refining method according to any one of [1] to [4], wherein the halogenated alkane has a carbon atom number of 1 or 2.

[0024] [7] The halogenated alkane refining method according to any one of [1] to [4], wherein the halogenated alkane is at least one selected from the group consisting of bromomethane, tribromofluoromethane, bromodifluoromethane, dibromodifluoromethane, bromotrifluoromethane, bromoethane, dibromotrifluoroethane, dibromotetrafluoroethane, tribromotrifluoroethane, monofluoromonobromoethylene, bromodifluoroethylene, and bromotrifluoroethylene.

[0025] [8] The halogenated alkane refining method according to any one of [1] to [7], wherein the absorbing solution further contains potassium iodate or sodium iodate.

[0026] Effects of the Invention

[0027] According to the present application, bromine molecules mixed into a halogenated alkane can be removed simply, safely, and efficiently to obtain a high-purity halogenated alkane. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 FIG. 1 is a schematic view showing an example of a refining apparatus for illustrating one embodiment of a halogenated alkane refining method according to the present application. DETAILED DESCRIPTION

[0029] One embodiment of the present application will be described below. Note that this embodiment shows one example of the present application, and the present application is not limited to this embodiment. In addition, various modifications can be made to this embodiment, and such modified examples can also be included in the present application.

[0030] The halogenated alkane refining method according to one embodiment of the present application is a halogenated alkane refining method for removing bromine molecules from a crude halogenated alkane containing a halogenated alkane and bromine molecules, and includes a contact step of bringing the crude halogenated alkane into contact with an absorbent solution prepared from an aqueous solution containing a metal iodide to obtain a mixture liquid containing the crude halogenated alkane and the absorbent solution, and a separation step of separating the halogenated alkane from the mixture liquid to obtain the absorbent solution in which the bromine molecules are absorbed and the halogenated alkane.

[0031] Bromine molecules are sometimes mixed as impurities in a halogenated alkane, but if a crude halogenated alkane containing a halogenated alkane and bromine molecules is refined by the halogenated alkane refining method according to this embodiment, bromine molecules mixed in the crude halogenated alkane can be removed simply, safely, and efficiently to obtain a high-purity refined halogenated alkane.

[0032] If described in detail, the halogenated alkane refining method according to this embodiment can obtain a high-purity refined halogenated alkane simply because it does not use a distillation method, and thus does not require a large-scale apparatus such as a distillation column. In addition, because the refining is not a distillation method but a liquid-phase extraction method, a high-purity refined halogenated alkane can be obtained even for a halogenated alkane whose boiling point is close to that of bromine molecules. Further, because an aqueous solution containing a metal iodide is used as the absorbent solution instead of an alkali solution, the method is highly safe and easy to operate. Further, because the halogenated alkane is not brought into contact with the alkali solution, the halogenated alkane is not easily hydrolyzed, and thus bromine molecules can be removed efficiently from the crude halogenated alkane to obtain a high-purity refined halogenated alkane.

[0033] The halogenated alkane refining method according to this embodiment will be described in further detail below.

[0034] [Crude Halogenated Alkane]

[0035] The type of halogenated alkane that can be refined by the halogenated alkane refining method according to the present embodiment is not particularly limited, but if the ease of separation in the separation step is taken into consideration, it is preferable that the halogenated alkane be one that has low solubility in water and a low boiling point. That is, it is preferable that the halogenated alkane be one having a carbon atom number of 1 or more and 3 or less, and more preferable that the halogenated alkane be one having a carbon atom number of 1 or 2.

[0036] Specifically, the halogenated alkane is further preferably at least one of bromomethane (CH3Br), tribromo fluoromethane (CBr3F), bromodifluoromethane (CHBrF2), dibromodifluoromethane (CBr2F2), bromotrifluoromethane (CBrF3), bromoethane (C2H5Br), dibromotrifluoroethane (C2HBr2F3), dibromotetrafluoroethane (C2Br2F4), tribromotrifluoroethane (C2Br3F3), fluorobromovinyl (C2H2BrF), bromodifluoroethylene (C2HBrF2), bromotrifluoroethylene (C2BrF3), bromohexafluoropropane (C3HBrF6), bromoheptafluoropropane (C3BrF7), and bromotrifluoropropene (C3H2BrF3).

[0037] The crude halogenated alkane that is supplied to the halogenated alkane refining method according to the present embodiment can be in a gaseous state or in a liquid state. Halogenated alkanes such as dibromodifluoromethane, bromotrifluoroethylene, bromohexafluoropropane, bromoheptafluoropropane, and bromotrifluoropropene, which have low boiling points, are suitable for gas-liquid separation, and halogenated alkanes such as tribromo fluoromethane and tribromotrifluoroethane, which have high boiling points, are suitable for liquid-liquid separation.

[0038] In addition, the halogenated alkane refining method according to the present embodiment can refine a crude halogenated alkane containing one type of halogenated alkane, and can also refine a crude halogenated alkane containing two or more types of halogenated alkanes.

[0039] The concentration of bromine molecules in the crude halogenated alkane is not particularly limited, but if the removal rate of bromine molecules from the crude halogenated alkane is taken into consideration, the number of moles of bromine molecules in the crude halogenated alkane is preferably 1 times or less, more preferably 0.8 times or less, and further preferably 0.5 times or less, the number of moles of the halogenated alkane in the crude halogenated alkane. In order to make the concentration of bromine molecules in the refined halogenated alkane a concentration that is sufficiently low in terms of corrosion caused by bromine molecules, the concentration of bromine molecules in the refined halogenated alkane is preferably 0.1% or less by volume, and therefore the removal rate of bromine molecules from the crude halogenated alkane is preferably 99.90% or more.

[0040] The concentration of hydrogen bromide in the crude halogenated alkane in the case where the crude halogenated alkane contains hydrogen bromide is not particularly limited, but if the removal rate of hydrogen bromide from the crude halogenated alkane is taken into consideration, the number of moles of hydrogen bromide in the crude halogenated alkane is preferably 1.5 times or less, more preferably 1 times or less, and further preferably 0.5 times or less, the number of moles of the halogenated alkane in the crude halogenated alkane.

[0041] Absorption liquid

[0042] The absorption liquid is a liquid that can absorb bromine molecules, and is not particularly limited as long as it is an aqueous solution containing a metal iodide, but from the viewpoints of safety, ease of handling, and suppression of hydrolysis of halogenated alkanes, it is preferable that the liquid be neutral, not alkaline or acidic, and the pH can be 5 or greater and 9 or less, and more preferably 6 or greater and 8 or less. Thus, the absorption liquid needs to be an aqueous solution of a metal iodide as a reducing agent, but it is preferable that the aqueous solution be one in which only the metal iodide is dissolved, and it is preferable that an alkaline compound such as a metal hydroxide not be dissolved. However, if the liquid property of the absorption liquid is maintained to be neutral, the absorption liquid can contain other compounds such as additives.

[0043] The kind of the metal iodide is not particularly limited, but it is preferable that it be at least one selected from the group consisting of alkali metal iodides and alkaline earth metal iodides. As specific examples of the alkali metal iodides, potassium iodide (KI), sodium iodide (NaI) can be given, and as specific examples of the alkaline earth metal iodides, magnesium iodide (MgI2), calcium iodide (CaI2), barium iodide (BaI2) can be given. Of these metal iodides, potassium iodide is particularly preferable.

[0044] As for the amount of the metal iodide contained in the absorption liquid, it is preferable that it be an amount that is capable of absorbing the total amount of the bromine molecules that should be absorbed in the absorption liquid, that is, an amount that is 1 times or more of the equivalent amount required for the reaction with the bromine molecules. In order to increase the removal rate of the bromine molecules from the crude halogenated alkane, it is more preferable that it be 1.5 times or more of the above-mentioned equivalent amount, it is further preferable that it be 2 times or more, and it is particularly preferable that it be 5 times or more.

[0045] Further, the concentration of the metal iodide in the absorption liquid is preferably a concentration at which the metal iodide can be dissolved, and a concentration at which the metal bromide and iodine molecules generated by the reaction can be dissolved in the absorption liquid. However, the concentration of the metal iodide in the absorption liquid can be a concentration at which at least a part of the metal iodide cannot be dissolved, that is, the absorption liquid can be a slurry in which solid metal iodide is mixed. Thus, the concentration of the metal iodide in the absorption liquid is preferably 0.1 mol / L or more and 9 mol / L or less.

[0046] If the metal iodide in the absorption liquid is consumed by absorbing the bromine molecules, the concentration of the metal iodide decreases, and the iodine molecules generated by the above-mentioned reaction do not easily dissolve in the absorption liquid. As a result, the iodine molecules precipitate from the absorption liquid, and the members of the refining treatment device (for example, the piping) can be clogged.

[0047] Therefore, the concentration of the metal iodide in the absorption solution during the refining treatment is preferably maintained at 40% or more of the concentration of the metal iodide in the original absorption solution before the refining treatment, and more preferably 60% or more. More specifically, the concentration of the metal iodide in the absorption solution is preferably maintained at 0.5 mol / L or more, and more preferably 0.7 mol / L or more during the refining treatment.

[0048] In the case where a substance other than a bromine molecule is considered to react with the metal iodide is contained in the crude halogenated alkane (for example, in the case where hydrogen bromide (HBr) described later is contained in the crude halogenated alkane), the amount of the metal iodide contained in the absorption solution is preferably determined also considering the amount of the substance other than the bromine molecule. That is, the amount of the metal iodide contained in the absorption solution is preferably 1 times or more of the total equivalent amount of the equivalent amount required for the reaction with the bromine molecule and the equivalent amount required for the reaction with the substance other than the bromine molecule, more preferably 1.5 times or more, further preferably 2 times or more, and particularly preferably 5 times or more.

[0049] In the absorption solution, an arbitrary additive can be dissolved or suspended as needed and mixed. For example, in the case where the crude halogenated alkane contains hydrogen bromide, if potassium iodate (KIO3) or sodium iodate (NaIO3) is mixed as an additive in the absorption solution, hydrogen bromide can be removed from the crude halogenated alkane together with the bromine molecule.

[0050] Hydrogen bromide is removed from the crude halogenated alkane by the reaction shown in the following reaction formula (2).

[0051] 6HBr + 5KI + KIO3→ 6KBr + 3I2 + 3H2O (2)

[0052] If the additive is, for example, potassium iodate, sodium iodate, the amount of the additive contained in the absorption solution is preferably the amount capable of absorbing the total amount of hydrogen bromide that should be absorbed in the absorption solution, that is, 1 times or more of the equivalent amount required for the reaction with hydrogen bromide, and more preferably 1.5 times or more of the above equivalent amount, further preferably 3 times or more, and particularly preferably 7 times or more in order to improve the removal rate of hydrogen bromide from the crude halogenated alkane.

[0053] In the case where a plurality of absorption columns are used in the absorption step, the amount of the additive contained in the absorption solution is preferably applied to the absorption solution accommodated in the absorption column on the most upstream side among the plurality of absorption columns connected in series.

[0054] [Contacting Step]

[0055] The contacting step is a step of bringing the absorption liquid into contact with the crude halogenated alkane to obtain a mixed liquid containing the crude halogenated alkane and the absorption liquid, and to cause bromine molecules in the crude halogenated alkane to be absorbed in the absorption liquid. The halogenated alkane refining method according to the present embodiment can refine a gaseous crude halogenated alkane, or can refine a liquid crude halogenated alkane.

[0056] The method of bringing the absorption liquid into contact with the crude halogenated alkane is not particularly limited, but in the case where the crude halogenated alkane is in a liquid state, the crude halogenated alkane can be brought into contact with the absorption liquid by a method of mixing the crude halogenated alkane with the absorption liquid, for example, in an absorption tower so as to be dispersed in the liquid. In the case where the crude halogenated alkane is in a liquid state, the crude halogenated alkane can be transferred by a liquid feed pump.

[0057] Further, in the case where the crude halogenated alkane is in a gaseous state, the crude halogenated alkane can be brought into contact with the absorption liquid by a method of bubbling the crude halogenated alkane into the absorption liquid, a method of spraying the absorption liquid into the crude halogenated alkane by a scrubber, or the like. In the case where the crude halogenated alkane is in a gaseous state, the absorption liquid is brought into contact with the gaseous crude halogenated alkane in the contacting step, and the gaseous refined halogenated alkane is gas-liquid extracted from the mixed liquid in the separation step, and thus the refining operation is simple and easy.

[0058] As a specific example of the above-mentioned bubbling method, there can be mentioned a method of supplying the crude halogenated alkane to the absorption liquid housed in the absorption tower. If the crude halogenated alkane is blown into the absorption liquid via a pipe or the like inserted into the absorption liquid, the absorption liquid can be brought into contact with the crude halogenated alkane. By blowing the crude halogenated alkane into the absorption liquid, a mixed liquid containing the crude halogenated alkane and the absorption liquid is obtained, and bromine molecules in the crude halogenated alkane react with the metal iodide in the absorption liquid, and the bromine molecules are absorbed in the absorption liquid.

[0059] For example, in the case where potassium iodide is used as the metal iodide, the bromine molecules are removed from the crude halogenated alkane by the reaction shown in the following reaction formula (1).

[0060] Br2+ 2KI → 2KBr + I2 (1)

[0061] The metal bromide and iodine molecules (I2) generated by the above-mentioned reaction remain in the absorption liquid, and the halogenated alkane is hardly soluble in water, and thus is separated from the absorption liquid in the separation step.

[0062] The number of absorption towers is not particularly limited and can be one or more, but in order to improve the removal rate of bromine molecules from the crude halogenated alkane, it is preferable to adopt a scheme in which a plurality of absorption towers are connected in series and the crude halogenated alkane is continuously blown into the plurality of absorption towers. In the case where a plurality of absorption towers are used, the "amount of metal iodide contained in the absorption liquid" described in the above "absorption liquid" item is preferably applied to the absorption liquid housed in the absorption tower on the most upstream side among the plurality of absorption towers connected in series.

[0063] The pipes into which the absorption liquid is inserted and the absorption towers are preferably formed of a material that is not easily reacted with bromine molecules and halogenated alkanes. As such a material, for example, fluororesin, glass, and the like can be given.

[0064] In the case where the absorption liquid after being used for the purification of the crude halogenated alkane is discarded, it is desirable to treat the iodine molecules generated by the reaction of the metal iodide with the bromine molecules with sodium thiosulfate (Na2S2O3) or the like and then discard them.

[0065] In the case where the gaseous crude halogenated alkane is purified, the crude halogenated alkane can be made gaseous by the vapor pressure possessed by the halogenated alkane, or can be made gaseous by mixing a dilution gas such as an inactive gas. In the case where a dilution gas is mixed in the crude halogenated alkane, it is preferable to mix the dilution gas in a manner such that 10% by volume or more and 90% by volume or less of the gaseous mixture obtained by mixing the crude halogenated alkane with the dilution gas becomes the dilution gas.

[0066] The type of the inactive gas used as the dilution gas is not particularly limited and, for example, nitrogen (N2), helium (He), argon (Ar), neon (Ne), krypton (Kr), and xenon (Xe) can be given. Among these inactive gases, nitrogen, helium, argon, neon, and krypton are preferable, and nitrogen and argon are more preferable. These inactive gases can be used singly in one kind or two or more kinds can be used in combination.

[0067] [Separation Step]

[0068] The separation step is a step of separating the halogenated alkane from the mixed liquid containing the crude halogenated alkane and the absorption liquid, and obtaining the absorption liquid in which bromine molecules are absorbed and the purified halogenated alkane. The halogenated alkane is difficult to dissolve in water, and thus is separated from the absorption liquid by gas-liquid separation or liquid-liquid separation according to the difference in specific gravity.

[0069] The method for separating the halogenated alkane from the mixed solution is not particularly limited, but in the case where the halogenated alkane is in a gaseous state, the halogenated alkane is separated from the absorption solution by gas-liquid separation, and is discharged from the absorption tower, for example, through a pipe provided at the upper portion of the absorption tower. In the case where the halogenated alkane is in a liquid state, the halogenated alkane is separated from the absorption solution by liquid-liquid separation, and is discharged from the absorption tower, for example, through a pipe provided at the upper portion of the absorption tower in the case where the specific gravity of the halogenated alkane is smaller than that of the absorption solution, or through a pipe provided at the lower portion of the absorption tower in the case where the specific gravity of the halogenated alkane is larger than that of the absorption solution.

[0070] 〔Refining treatment device〕

[0071] Next, a configuration example of a refining treatment device capable of implementing the halogenated alkane refining method according to the present embodiment, and an example of the halogenated alkane refining method using the refining treatment device will be described with reference to Figure 1 A configuration example of a refining treatment device capable of implementing the halogenated alkane refining method according to the present embodiment, and an example of the halogenated alkane refining method using the refining treatment device will be described with reference to

[0072] Figure 1 The refining treatment device of the present embodiment is provided with a crude halogenated alkane bottle 1 filled with crude halogenated alkane which is a gas at normal temperature and normal pressure, a non-active gas bottle 2 filled with non-active gas, a first absorption tower 11 and a second absorption tower 13 which perform refining of the crude halogenated alkane, a crude halogenated alkane supply pipe 5 which connects the crude halogenated alkane bottle 1 and the first absorption tower 11, and a non-active gas supply pipe 6 which connects the non-active gas bottle 2 and the intermediate portion of the crude halogenated alkane supply pipe 5.

[0073] A crude halogenated alkane supply portion 3 composed of a mass flow controller or the like is provided at the upstream side portion of the crude halogenated alkane supply pipe 5 (i.e., the portion close to the crude halogenated alkane bottle 1). The crude halogenated alkane of the crude halogenated alkane bottle 1 is controlled in flow rate by the crude halogenated alkane supply portion 3, and is supplied to the first absorption tower 11 via the crude halogenated alkane supply pipe 5.

[0074] Further, a non-active gas supply portion 4 composed of a mass flow controller or the like is provided in the non-active gas supply pipe 6. The non-active gas of the non-active gas bottle 2 is controlled in flow rate by the non-active gas supply portion 4, and is supplied to the intermediate portion of the crude halogenated alkane supply pipe 5 (i.e., the portion on the downstream side compared to the crude halogenated alkane supply portion 3) via the non-active gas supply pipe 6.

[0075] In the case where the crude halogenated alkane gas is diluted with the non-active gas, the crude halogenated alkane gas is sent out from the crude halogenated alkane supply part 3 to the crude halogenated alkane supply pipe 5, and the non-active gas is sent out from the non-active gas supply part 4 to the crude halogenated alkane supply pipe 5 via the non-active gas supply pipe 6. Thus, the crude halogenated alkane gas is diluted with the non-active gas in the middle part of the crude halogenated alkane supply pipe 5, and the diluted crude halogenated alkane gas is supplied to the first absorption tower 11 via the crude halogenated alkane supply pipe 5.

[0076] The first absorption liquid 12 is housed in the first absorption tower 11, and the downstream end of the bubble tube 16 connected to the crude halogenated alkane supply pipe 5 is inserted into the first absorption liquid 12. Thus, the crude halogenated alkane contacts the first absorption liquid 12 by being supplied to the first absorption liquid 12 in the first absorption tower 11, and the refining treatment of the crude halogenated alkane is performed in the first absorption tower 11. Further, a not-shown temperature control device for controlling the temperature of the first absorption liquid 12 is provided in the first absorption tower 11.

[0077] The refining treatment is performed in the first absorption tower 11, and the crude halogenated alkane from which most of the bromine molecules are removed is separated from the first absorption liquid 12. Further, the separated crude halogenated alkane reaches a part above the liquid surface of the first absorption liquid 12 in the first absorption tower 11, and is sent to the second absorption tower 13 via the connection pipe 17 connecting the upper part of the first absorption tower 11 to the second absorption tower 13.

[0078] The second absorption liquid 14 is housed in the second absorption tower 13, and the downstream end of the connection pipe 17 is inserted into the second absorption liquid 14. Thus, the crude halogenated alkane sent from the first absorption tower 11 contacts the second absorption liquid 14 by being supplied to the second absorption liquid 14 in the second absorption tower 13, and further refining treatment of the crude halogenated alkane is performed in the second absorption tower 13. Further, the first absorption liquid 12 and the second absorption liquid 14 can be the same kind of absorption liquid, or can be different kinds of absorption liquid.

[0079] Most of the bromine molecules are removed from the crude halogenated alkane in the first absorption tower 11, but the remaining trace amount of bromine molecules is removed from the crude halogenated alkane in the second absorption tower 13. Thus, a high-purity refined halogenated alkane can be obtained. The refined halogenated alkane is separated from the second absorption liquid 14, and reaches a part above the liquid surface of the second absorption liquid 14 in the second absorption tower 13. In the upper part of the second absorption tower 13, a gas discharge pipe 18 for discharging the gas inside is provided, and the high-purity refined halogenated alkane is discharged to the outside from the second absorption tower 13 via the gas discharge pipe 18.

[0080] 〔Refining treatment conditions〕

[0081] The temperature conditions in the contact process are not particularly limited, but higher temperatures result in a faster reaction rate to remove bromine molecules. On the other hand, if the temperature is too high, components of the refining apparatus (such as piping) may corrode. Therefore, it is preferable to have a temperature of 5°C or higher and 80°C or lower, more preferably 10°C or higher and 60°C or lower, and even more preferably 20°C or higher and 60°C or lower. The temperature conditions of the contact process, i.e., the temperature of the absorbent, can be controlled, for example, by a heating or cooling device provided in the absorption tower that contains the absorbent.

[0082] The pressure conditions in the contact process are not particularly limited, but are preferably 0 MPa or more and 0.2 MPa or less, more preferably 0.1 MPa or more and 0.2 MPa or less, and even more preferably atmospheric pressure (0.1 MPa).

[0083] Example

[0084] The following examples and comparative examples illustrate the present invention in more detail.

[0085] [Example 1]

[0086] Use with Figure 1 The purification apparatus shown is configured similarly to the one used in the purification process, performing purification treatment to remove bromine molecules from crude dibromodifluoromethane (equivalent to "crude haloalkanes" as a constituent element of this invention, hereinafter referred to as "crude haloalkanes") containing dibromodifluoromethane and bromine molecules to obtain purified dibromodifluoromethane (hereinafter referred to as "purified haloalkanes"). The concentration of bromine molecules in the crude haloalkanes was determined using an ion chromatograph manufactured by Shimadzu Corporation, and the result was 48.0% by volume.

[0087] The refining apparatus comprises two absorption towers formed from Tefron PFA (tetrafluoroethylene / perfluoroalkoxyethylene copolymer), each containing 1 L of absorbent with the same composition. This absorbent is an aqueous solution of potassium iodide as a reducing agent, with a concentration of 1.2 mol / L and a pH of 7. Furthermore, both the upstream first absorption tower and the downstream second absorption tower are equipped with temperature control devices to control the temperature of the absorbent. The temperature of the absorbent contained in each absorption tower is maintained at 25°C (with a fluctuation range of ±2.5°C) during the refining process.

[0088] The crude halogenated alkane filled in the crude halogenated alkane bottle was sent to the crude halogenated alkane supply pipe using a mass flow controller (manufactured by HORIBA STEC, INC., mass flow controller SEC-N112MGMW) provided in the crude halogenated alkane supply section. In addition, the nitrogen filled in the non-reactive gas bottle was sent to the crude halogenated alkane supply pipe via the non-reactive gas supply pipe using a mass flow controller (manufactured by HORIBA STEC, INC., mass flow controller SEC-N112MGMW) provided in the non-reactive gas supply section. The crude halogenated alkane was diluted by mixing the crude halogenated alkane with the nitrogen in the crude halogenated alkane supply pipe by this operation. The mixing ratio was 80 vol% of the crude halogenated alkane and 20 vol% of the nitrogen.

[0089] The crude halogenated alkane diluted with the nitrogen was supplied to the first absorption tower on the upstream side via the crude halogenated alkane supply pipe, and was brought into contact with the absorption liquid in the first absorption tower, and the bromine molecules in the crude halogenated alkane were absorbed in the absorption liquid. Subsequently, the crude halogenated alkane that had come out of the first absorption tower was supplied to the second absorption tower on the downstream side via the connecting pipe, and was brought into contact with the absorption liquid in the second absorption tower, and the bromine molecules in the crude halogenated alkane were absorbed in the absorption liquid. The purification treatment of the crude halogenated alkane was performed by this operation, and as a result, the bromine molecules were removed from the crude halogenated alkane, and a purified halogenated alkane was obtained. In addition, the potassium iodide concentrations of the first and second absorption liquids during the purification treatment were maintained at 0.72 mol / L or more (i.e., 60% or more of the initial concentration).

[0090] The gas that had come out of the second absorption tower on the downstream side was a mixture gas of the purified halogenated alkane and the nitrogen, and therefore, the purified halogenated alkane was obtained by removing the nitrogen from the mixture gas. The method of removing the nitrogen was not particularly limited, but in the present embodiment, the mixture gas was introduced into a cold trap that had been cooled with dry ice, and the purified halogenated alkane was liquefied in the cold trap, and thereby the nitrogen was removed from the mixture gas to obtain the purified halogenated alkane. The concentration of the bromine molecules in the purified halogenated alkane obtained by removing the nitrogen from the mixture gas was measured by an ion chromatograph manufactured by SHIMADZU CORPORATION, and the result was 0.0188 vol%.

[0091] The removal rate of the bromine molecules by the purification treatment was calculated according to the following formula.

[0092] Removal rate (%) = [1 - [concentration of bromine molecules in purified halogenated alkane] / [concentration of bromine molecules in crude halogenated alkane]] x 100

[0093] The results are shown in Table 1. The removal rate of the bromine molecules by the purification treatment was 99.96%, and the bromine molecules could be removed to a low concentration at which corrosion was not substantially exhibited.

[0094]

[0095] [Example 2]

[0096] The kind of the absorption solution housed in the two absorption towers was changed to a 1.2 mol / L aqueous sodium iodide solution, and otherwise the same operation as in Example 1 was performed to carry out the purification treatment of the crude halogenated alkane. The pH of the 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 the bromine molecules could be removed to a low concentration at which corrosion was not substantially exhibited.

[0097] [Example 3]

[0098] The kind of the absorption solution housed in the two absorption towers was changed to a 1.2 mol / L aqueous calcium iodide solution, and otherwise the same operation as in Example 1 was performed to carry out the purification treatment of the crude halogenated alkane. The pH of the absorption solution was 7. The results are shown in Table 1. The removal rate of bromine molecules by the purification treatment was 99.92%, and the bromine molecules could be removed to a low concentration at which corrosion was not substantially exhibited.

[0099] [Example 4]

[0100] The kind of the absorption solution housed in the two absorption towers was changed to a 1.2 mol / L aqueous magnesium iodide solution, and otherwise the same operation as in Example 1 was performed to carry out the purification treatment of the crude halogenated alkane. The pH of the absorption solution was 7. The results are shown in Table 1. The removal rate of bromine molecules by the purification treatment was 99.92%, and the bromine molecules could be removed to a low concentration at which corrosion was not substantially exhibited.

[0101] [Example 5]

[0102] The concentration of bromine molecules in the crude halogenated alkane was changed to 32.6 vol%, and otherwise the same operation as in Example 1 was performed to carry out the purification treatment of the crude halogenated alkane. The results are shown in Table 1. The removal rate of bromine molecules by the purification treatment was 99.96%, and the bromine molecules could be removed to a low concentration at which corrosion was not substantially exhibited.

[0103] [Example 6]

[0104] The concentration of bromine molecules in the crude halogenated alkane was changed to 11.3 vol%, and otherwise the same operation as in Example 1 was performed to carry out the purification treatment of the crude halogenated alkane. The results are shown in Table 1. The removal rate of bromine molecules by the purification treatment was 99.97%, and the bromine molecules could be removed to a low concentration at which corrosion was not substantially exhibited.

[0105] [Example 7]

[0106] The purification treatment of the crude halogenated alkane was performed in the same manner as in Example 1, except that the temperature in the purification treatment of the absorption solution housed in the first absorption tower on the upstream side was maintained at 45°C (fluctuation range: ±2.5°C). The pH of the 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 the bromine molecules could be removed to a low concentration at which corrosion was not substantially exhibited.

[0107] [Example 8]

[0108] The purification treatment of the crude halogenated alkane was performed in the same manner as in Example 1, except that the temperature in the purification treatment of the absorption solution housed in the first absorption tower on the upstream side was maintained at 5°C (fluctuation range: ±2.5°C). The pH of the 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 the bromine molecules could be removed to a low concentration at which corrosion was not substantially exhibited.

[0109] [Example 9]

[0110] The purification treatment of the crude halogenated alkane was performed in the same manner as in Example 1, except that crude bromodifluoromethane containing bromodifluoromethane and bromine molecules was used as the crude halogenated alkane. The results are shown in Table 1. The removal rate of bromine molecules by the purification treatment was 99.96%, and the bromine molecules could be removed to a low concentration at which corrosion was not substantially exhibited.

[0111] [Example 10]

[0112] The purification treatment of the crude halogenated alkane was performed in the same manner as in Example 1, except that crude bromotrifluoroethylene containing bromotrifluoroethylene and bromine molecules was used as the crude halogenated alkane. The results are shown in Table 1. The removal rate of bromine molecules by the purification treatment was 99.96%, and the bromine molecules could be removed to a low concentration at which corrosion was not substantially exhibited.

[0113] [Comparative Example 1]

[0114] The purification treatment of the crude halogenated alkane was performed in the same manner as in Example 1, except that the kind of the absorption solution housed in the two absorption towers was changed to a sodium sulfite (Na2SO3) aqueous solution having 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%, and the removal rate of bromine molecules was lower as compared with the case where the potassium iodide aqueous solution was used as the absorption solution.

[0115] [Comparative Example 2]

[0116] The kind of the absorbent solution housed in the two absorption towers was changed to a 1.2 mol / L aqueous sodium formate (HCOONa) solution, and otherwise the same operation as in Example 1 was performed to carry out the purification treatment of the crude halogenated alkane. The results are shown in Table 1. The removal rate of bromine molecules by the purification treatment was 98.67%, which was lower than the case where an aqueous potassium iodide solution was used as the absorbent solution.

[0117] [Comparative Example 3]

[0118] The kind of the absorbent solution housed in the two absorption towers was changed to a 1.2 mol / L aqueous urea ((NH2)2CO) solution, and otherwise the same operation as in Example 1 was performed to carry out the purification treatment of the crude halogenated alkane. The results are shown in Table 1. The removal rate of bromine molecules by the purification treatment was 98.12%, which was lower than the case where an aqueous potassium iodide solution was used as the absorbent solution.

[0119] [Comparative Example 4]

[0120] The kind of the absorbent solution housed in the two absorption towers was changed to water (H2O), and otherwise the same operation as in Example 1 was performed to carry out the purification treatment of the crude halogenated alkane. The results are shown in Table 1. The removal rate of bromine molecules by the purification treatment was 66.30%, which was lower than the case where an aqueous potassium iodide solution was used as the absorbent solution.

[0121] [Example 11]

[0122] A crude dibromodifluoromethane containing dibromodifluoromethane, bromine molecules, and hydrogen bromide was used as the crude halogenated alkane. The concentration of bromine molecules in the crude halogenated alkane was 32.6 vol% as measured by an ion chromatograph manufactured by Shimadzu Corporation. In addition, the concentration of hydrogen bromide in the crude halogenated alkane was 15.4 vol% as measured by titration using an aqueous sodium hydroxide (NaOH) solution having a concentration of 0.05 mol / L.

[0123] In addition, the kind of the absorbent solution housed in the first absorption tower was changed to an aqueous solution obtained by dissolving potassium iodide and potassium iodate in water. The concentration of potassium iodide in the aqueous solution was 1.2 mol / L, and the concentration of potassium iodate was 0.0934 mol / L.

[0124] The purification treatment of the crude halogenated alkane was performed in the same manner as in Example 1 except for the above two points, and the removal of bromine molecules and hydrogen bromide in the crude halogenated alkane was performed.

[0125] The removal rate of hydrogen bromide by the purification treatment was calculated in accordance with the following formula.

[0126] Removal rate (%) = 〔1- [concentration of hydrogen bromide in refined halogenated alkane] / [concentration of hydrogen bromide in crude halogenated alkane]〕 x 100

[0127] The results are shown in Tables 1, 2. The removal rate of bromine molecules by the refining treatment was 99.96%, and bromine molecules could be removed to a low concentration at which corrosion was not substantially exhibited. Further, the concentration of hydrogen bromide in the refined halogenated alkane, as determined by titration using a 0.05 mol / L aqueous sodium hydroxide solution, was 0.00227 vol%, and the removal rate of hydrogen bromide by the refining treatment was 99.99%.

[0128]

[0129] Explanation of symbols

[0130] 1 ••• crude halogenated alkane bottle

[0131] 2 ••• inactive gas bottle

[0132] 3 ••• crude halogenated alkane supply section

[0133] 4 ••• inactive gas supply section

[0134] 11 ••• first absorption column

[0135] 12 ••• first absorption liquid

[0136] 13 ••• second absorption column

[0137] 14 ••• second absorption liquid

Claims

1. A halogenated alkane refining method of removing bromine molecules from a crude halogenated alkane containing the halogenated alkane and the bromine molecules, the method comprising: a contact step of bringing the crude halogenated alkane into contact with an absorbing solution prepared from an aqueous solution containing a metal iodide, to obtain a mixed solution containing the crude halogenated alkane and the absorbing solution; and a separation step of separating the halogenated alkane from the mixed solution, to obtain the absorbing solution having absorbed the bromine molecules and the halogenated alkane.

2. The halogenated alkane refining method according to claim 1, wherein the metal iodide is at least one selected from the group consisting of alkali metal iodides and alkaline earth metal iodides.

3. The halogenated alkane refining method according to claim 1, wherein the metal iodide is potassium iodide.

4. The halogenated alkane refining method according to any one of claims 1 to 3, wherein in the contact step, the crude halogenated alkane in a gaseous state is brought into contact with the absorbing solution, and in the separation step, the halogenated alkane in a gaseous state is gas-liquid extracted from the mixed solution.

5. The halogenated alkane refining method according to any one of claims 1 to 3, wherein the halogenated alkane has a carbon atom number of 1 or more and 3 or less.

6. The halogenated alkane refining method according to any one of claims 1 to 3, wherein the halogenated alkane has a carbon atom number of 1 or 2.

7. The halogenated alkane refining method according to any one of claims 1 to 3, wherein the halogenated alkane is at least one selected from the group consisting of bromomethane, tribromofluoromethane, bromodifluoromethane, dibromodifluoromethane, bromotrifluoromethane, bromoethane, dibromotrifluoroethane, dibromotetrafluoroethane, tribromotrifluoroethane, monofluoromonobromoethylene, bromodifluoroethylene, and bromotrifluoroethylene.

8. The halogenated alkane refining method according to any one of claims 1 to 3, wherein the absorbing solution further contains potassium iodate or sodium iodate. ​ ​

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