Method for purifying vinylidene fluoride

Abstract

A method for purifying vinylidene fluoride in which a first fluid, which is mainly composed of vinylidene fluoride and further contains trifluoromethane, is brought into contact with synthetic zeolite 4A to obtain a second fluid in which the mass ratio of the content of vinylidene fluoride to the total content of vinylidene fluoride and trifluoromethane is higher than the mass ratio in the first fluid.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a method for purifying vinylidene fluoride. BACKGROUND

[0002] Vinylidene fluoride is useful as a monomer of fluororesin.

[0003] For example, Patent Literature 1 describes a method for producing 2,3,3,3-tetrafluoropropene, which has: (a) a step of feeding a mixture of methyl chloride mixed with difluoromonochloromethane at a molar ratio of 3.2 to 4.7 to a reaction vessel; (b) a step of feeding a heat medium to the mixture of the aforementioned step (a) and allowing them to contact, to produce a second mixture containing 2,3,3,3-tetrafluoropropene and methyl chloride; (c) a step of drying the second mixture of the aforementioned step (b) to obtain an anhydrous second mixture; (d) a step of contacting the anhydrous second mixture of the aforementioned step (c) with a molecular sieve having a pore diameter of 4.0 A to 5.0 A to obtain a third mixture containing no methyl chloride; and (e) a step of separating 2,3,3,3-tetrafluoropropene from the third mixture of the aforementioned step (d).

[0004] Prior Art Documents

[0005] Patent Literature

[0006] Patent Literature 1: Japanese Patent No. 7014709 SUMMARY

[0007] Problems to be Solved by the Invention

[0008] However, Patent Literature 1 aims at isolating 2,3,3,3-tetrafluoropropene, and vinylidene fluoride (VdF) is positioned as an impurity. In this regard, a method for purifying VdF, which aims at isolating VdF from a composition containing VdF as a main component, is sought.

[0009] An object of one embodiment of the present application is to provide a method for purifying VdF, which can obtain VdF having a high purity from a composition containing VdF as a main component.

[0010] Solution to Problem

[0011] The present disclosure includes the following modes.

[0012] <1>

[0013] A method for purifying VdF, in which a first fluid containing VdF as a main component and further containing trifluoromethane is contacted with synthetic zeolite 4A to obtain a second fluid, the mass ratio of the content of VdF to the total content of VdF and trifluoromethane in the second fluid is higher than the mass ratio in the first fluid.​

[0014] <2>

[0015] The purification method of VdF according to <1>, wherein the ratio of the flow rate of the first fluid to the packed amount of the synthetic zeolite 4A in the reactor is 0.160 [(g / hour) / g] or less.

[0016] <3>

[0017] The purification method of VdF according to <1> or <2>, wherein the first fluid is a gas.

[0018] <4>

[0019] The purification method of VdF according to any one of <1> to <3>, wherein the content of VdF in the second fluid is 99 mass% or more with respect to the total amount of the second fluid.

[0020] Effects of the Invention

[0021] According to one embodiment of the present invention, there is provided a purification method of VdF, which is capable of obtaining high-purity VdF from a composition containing VdF as a main component. DETAILED DESCRIPTION

[0022] In the present disclosure, a numerical range indicated by "~" means a range including the numerical values written before and after "~" as the minimum value and the maximum value, respectively.

[0023] In the numerical range indicated in stages in the present disclosure, the upper limit value or the lower limit value indicated in a certain numerical range can be replaced with the upper limit value or the lower limit value of another numerical range indicated in stages. In addition, in the numerical range indicated in the present disclosure, the upper limit value or the lower limit value indicated in a certain numerical range can be replaced with the value shown in the examples.

[0024] In the present disclosure, a combination of two or more preferred modes is a more preferred mode.

[0025] In the present disclosure, in the case where a plurality of substances corresponding to each component is present, unless otherwise specified, the amount of each component refers to the total amount of the plurality of substances.

[0026] [Purification method of VdF]

[0027] In the purification method of VdF of the present disclosure, a first fluid in which the main component is VdF and which further contains trifluoromethane (R23) is brought into contact with a synthetic zeolite 4A, and a second fluid is obtained, the mass ratio of the content of VdF in the second fluid to the total content of VdF and R23 being higher than the mass ratio in the first fluid.

[0028] According to the VdF purification method of the present disclosure, components other than VdF can be efficiently removed from a composition containing VdF as a main component, and high-purity VdF can be obtained.

[0029] The boiling point of VdF is -83°C, and the boiling point of R23 is -82°C. The boiling points of VdF and R23 are close, and thus VdF and R23 are difficult to separate and purify by distillation. VdF is useful as a monomer of a fluororesin, but if a composition containing VdF and R23 as an impurity, for example, is used for a polymerization reaction, R23 that is not consumed in the polymerization reaction accumulates inside the reactor, and the polymerization reaction is hindered. As a result, a decrease in the rate of the polymerization reaction or a stop of the polymerization reaction to fail to obtain a target polymer is likely to occur, and it is desirable to produce high-purity VdF.

[0030] The present inventors found that by bringing a first fluid in which the main component is VdF and which further contains R23 into contact with synthetic zeolite 4A, R23 can be efficiently removed, and the mass ratio of the content of VdF to the total content of VdF and R23 can be increased.

[0031] On the other hand, the production method described in Patent Literature 1 aims to produce HFO-1234yf, and VdF is positioned as an impurity. In addition, since VdF is positioned as an impurity, a purification method using a composition in which VdF is a main component is not described. Furthermore, it is very inefficient to remove components other than VdF from a composition in which VdF is not a main component to obtain high-purity VdF.

[0032] Specifically, in the production method described in Patent Literature 1, about 4% of R23 and about 10% of VdF are contained in a crude gas of 355 g / hour (the total of the supply amounts of dichlorofluoromethane and methyl chloride as raw material gases), and adsorption is performed using 2.4 kg of of molecular sieves. After 79 minutes, the content of VdF is 7.22%, the content of R23 is 15.34%, and the mass ratio of the content of VdF to the total content of VdF and R23 increases. It is considered that this is because the of molecular sieves has reached the equilibrium adsorption amount. The adsorption amount of R23 until 79 minutes is about 19 g, and 0.0079 g of of molecular sieves per 1 g. The adsorption amount of R23 is very small, and it is inefficient as a purification of VdF.

[0033] <First fluid>

[0034] The main component of the first fluid used in the VdF purification method of the present disclosure is VdF, and R23 is contained.

[0035] In the present disclosure, "a main component" means that the amount of a component other than the component is relatively small. In other words, "a main component" means that the content of the component is the highest in a composition containing the component.

[0036] That is, in the first fluid in which VdF is a main component, the content of VdF is the highest.

[0037] From the viewpoint of more efficiently purifying VdF, the content of VdF in the first fluid is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 70% by mass or more, and particularly preferably 80% by mass or more, with respect to the total amount of the first fluid. The upper limit of the content of VdF is not particularly limited, and is, for example, less than 99.5% by mass.

[0038] If VdF is not a main component and a large amount of a component other than VdF is contained in the first fluid, adsorption of R23 to synthetic zeolite 4A is sometimes hindered, and desorption of R23 from synthetic zeolite 4A sometimes occurs. In contrast, in the first fluid in which VdF is a main component, adsorption of R23 to synthetic zeolite 4A proceeds rapidly, and the mass ratio of the content of VdF with respect to the total content of VdF and R23 can be increased. Even in the case where a small amount of synthetic zeolite 4A is used, by making VdF a main component, high-purity VdF can be efficiently obtained.

[0039] The content of R23 in the first fluid is more than 0% by mass. R23 is not a main component, and the content is not particularly limited.

[0040] The content of R23 in the first fluid is preferably less than 50% by mass, more preferably 40% by mass or less, further preferably 30% by mass or less, and particularly preferably 20% by mass or less, with respect to the total amount of the first fluid.

[0041] The first fluid can contain other components in addition to VdF and R23, but from the viewpoint of efficiently obtaining high-purity VdF, it is preferable that the content of other components be small. As other components, for example, a fluorinated olefin other than VdF and a hydrofluorocarbon other than R23 can be given.

[0042] The content of other components in the first fluid is preferably 20% by mass or less, and more preferably 10% by mass or less, with respect to the total amount of the first fluid.

[0043] The first fluid can be a gas or a liquid. From the viewpoint that there is no need for manufacturing equipment and the like for liquefying the composition, the first fluid is preferably a gas. On the other hand, from the viewpoint of the amount of adsorption of R23, the first fluid is preferably a liquid.

[0044] As the first fluid, for example, a reaction product containing VdF obtained by reacting various raw materials for the purpose of producing VdF can be used.

[0045] For example, using chlorodifluoroethane as a raw material, a reaction product containing VdF can be obtained by a thermal decomposition reaction. In addition, using difluoromonochloromethane and chloromethane as raw materials, a reaction product containing VdF can be obtained by a dehydrochlorination reaction.

[0046] <Synthetic zeolite 4A>

[0047] In the purification method of VdF of the present disclosure, the first fluid is brought into contact with synthetic zeolite 4A.

[0048] For example, in synthetic zeolite 3A, the pore size is small, and thus R23 cannot be adsorbed. In addition, in synthetic zeolite 5A, the pore size is large, and thus VdF is adsorbed together with R23. Therefore, in the case of using synthetic zeolite 3A or synthetic zeolite 5A, it is difficult to obtain VdF with high purity. On the other hand, VdF is not easily adsorbed to synthetic zeolite 4A, and R23 can be adsorbed to synthetic zeolite 4A, and thus in the purification method of VdF of the present disclosure, VdF with high purity can be obtained.

[0049] Synthetic zeolite 4A refers to a synthetic zeolite having an A-type crystal structure and represented by the following formula 1.

[0050] (Na a M 1 b M 2 c (Al m Si n O 2(m+n) )·xH2O …… Formula 1

[0051] In formula 1, M 1 is at least one selected from the group consisting of Li and K,

[0052] M 2 is at least one selected from the group consisting of Ca, Mg, and Ba,

[0053] a, b, c, x, m, and n are each independently an integer of 1 or more,

[0054] a, b, c, m, and n satisfy the following formula 2, formula 3, and formula 4.

[0055] a + b + 0.5c = m …… Formula 2

[0056] a(a + b + 0.5c) ≥ 0.6 …… Formula 3

[0057] n / m ≥ 1.0 …… Formula 4

[0058] a, b, c, m, and n preferably satisfy the following formula 3a and formula 4a.

[0059] a(a + b + 0.5c) ≥ 0.9... Equation 3a

[0060] 1.3 > n / m ≥ 1.0... Equation 4a

[0061] Further, the synthetic zeolite 4A is preferably a synthetic zeolite represented by the following Equation 5.

[0062] Na 12 [(AlO2) 12 SiO2) 12 · xH2O... Equation 5

[0063] As to whether or not it has an A-type crystal structure, it can be confirmed using an X-ray diffraction method.

[0064] As the synthetic zeolite 4A, for example, a zeolite labeled as 4A among A-type synthetic zeolites can be cited. As a commercial product, for example, Molecular Sieve 4A (UNION Showa K.K.) can be cited.

[0065] As to the synthetic zeolite 4A, an activation treatment can be performed before the purification of VdF. As a method of the activation treatment, for example, a method of performing a heat treatment using a dry gas at 100 to 400°C, and a method of performing a heat treatment under reduced pressure can be cited. If the activation treatment is performed, the synthetic zeolite 4A is activated, and the removal efficiency of R23 is improved.

[0066] The usage form of the synthetic zeolite 4A is not particularly limited. The first fluid can be circulated in a device filled with the synthetic zeolite 4A, or the first fluid can be filled in a container filled with the synthetic zeolite 4A, and the second fluid can be withdrawn after a prescribed time elapses.

[0067] <Second fluid>

[0068] In the purification method of VdF of the present disclosure, the second fluid is obtained by bringing the first fluid into contact with the synthetic zeolite 4A. The content of VdF in the second fluid is higher than that of the first fluid in terms of the mass ratio with respect to the total content of VdF and R23 (i.e., "VdF / (VdF + R23)").

[0069] The content of VdF in the second fluid is preferably 90% by mass or more, more preferably 95% by mass or more, further preferably 99% by mass or more, and particularly preferably 99.5% by mass or more, with respect to the total amount of the second fluid.

[0070] The content of R23 in the second fluid is preferably 1% by mass or less, more preferably 0.5% by mass or less, with respect to the total amount of the second fluid.

[0071] <Method of bringing the first fluid into contact with the synthetic zeolite 4A>

[0072] As described above, the first fluid can be a gas or a liquid. Hereinafter, a contact method in the gas phase and a contact method in the liquid phase will be described.

[0073] -Contact method in the gas phase-

[0074] As the method of contacting the first fluid with the synthetic zeolite 4A in the gas phase, a preferred method is a method of forming an adsorption layer filled with the synthetic zeolite 4A and circulating the first fluid in the adsorption layer. The method of circulating the first fluid in the adsorption layer can be either batchwise or continuous. From the viewpoint of manufacturing efficiency, the purification method of VdF of the present disclosure is preferably performed in the gas phase continuous circulation using a fixed bed reactor.

[0075] As the reactor used when circulating the first fluid in the adsorption layer, a publicly known reactor capable of forming an adsorption layer by filling the synthetic zeolite 4A can be cited. As the material of the reactor, for example, glass, iron, nickel, or an alloy having them as a main component, a fluororesin such as tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer (PFA), and the like can be cited.

[0076] The adsorption layer can be one or two or more. When the adsorption layer is two or more, they can be connected in parallel or in series.

[0077] The temperature of the first fluid at the time of contact with the synthetic zeolite 4A is not particularly limited, and from the viewpoint of obtaining VdF of higher purity, it is preferably 120°C or lower, more preferably 100°C or lower, and further preferably 80°C or lower. From the viewpoint of the adsorption efficiency of the synthetic zeolite 4A, the temperature of the first fluid is preferably -30°C or higher.

[0078] The pressure (gauge pressure) of the first fluid at the time of contact with the synthetic zeolite 4A is not particularly limited, and from the viewpoint of obtaining VdF of higher purity, it is preferably 0 to 5000 kPa, and more preferably 0 to 3000 kPa.

[0079] The contact time of the first fluid with the synthetic zeolite 4A is not particularly limited, and from the viewpoint of obtaining VdF of higher purity, it is, for example, 1 to 60 seconds.

[0080] The ratio of the flow rate [(g / hour)] of the first fluid to the packed amount [(g)] of the synthetic zeolite 4A in the reactor is preferably 0.200 [(g / hour) / g] or less, more preferably 0.160 [(g / hour) / g] or less, and further preferably 0.150 [(g / hour) / g] or less. When the above ratio is 0.200 [(g / hour) / g] or less, the contact time with the synthetic zeolite 4A becomes longer, and VdF of higher purity can be obtained.

[0081] Note that "g / hour" as a unit of the flow rate of the first fluid means the mass per hour.

[0082] Contacting method under liquid phase

[0083] As the method of contacting the first fluid, which is a liquid, with the synthetic zeolite 4A in a liquid phase, a preferred method is a method of forming an adsorption layer filled with the synthetic zeolite 4A and circulating the first fluid in the adsorption layer. Alternatively, a method of mixing the synthetic zeolite 4A with the first fluid in a reactor filled with the synthetic zeolite 4A and stirring as necessary can also be used. In the method of mixing the synthetic zeolite 4A with the first fluid in the reactor, after purification, the second fluid obtained by purification can be separated from the synthetic zeolite 4A by sedimentation or filtration. These methods can be batch or continuous.

[0084] As the reactor used when circulating the first fluid in the adsorption layer, a publicly known reactor capable of forming an adsorption layer by filling the synthetic zeolite 4A can be used. As the material of the reactor, for example, glass, iron, nickel, or an alloy having these as main components, a fluororesin such as polytetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer (PFA), or the like can be used.

[0085] As the reactor used when mixing the first fluid with the synthetic zeolite 4A, for example, an autoclave can be used.

[0086] The temperature of the first fluid at the time of contact with the synthetic zeolite 4A is not particularly limited, and from the viewpoint of obtaining VdF having a higher purity, the temperature is preferably 50°C or lower, more preferably 35°C or lower, and further preferably 10°C or lower. From the viewpoint of the adsorption efficiency of the synthetic zeolite 4A, the temperature of the first fluid is preferably -30°C or higher.

[0087] The pressure (gauge pressure) of the first fluid at the time of contact with the synthetic zeolite 4A is not particularly limited, and from the viewpoint of obtaining VdF having a higher purity, the pressure is preferably 400 to 5000 kPa, and more preferably 400 to 3000 kPa.

[0088] Examples

[0089] Hereinafter, the present disclosure will be specifically described by way of examples, but the present disclosure is not limited to these examples.

[0090] [Examples 11 to 14]

[0091] Examples 12 to 14 are examples, and Example 11 is a comparative example.

[0092] Synthetic zeolite 4A (product name "Molecular Sieve 4A", manufactured by Showa Denko K.K.) and a first fluid containing VdF and R23 were charged in a 75 mL cylinder. At this time, the temperature of the first fluid was 25°C. In Examples 11 to 14, the amount of the synthetic zeolite 4A and the contents of VdF and R23 in the first fluid (the "contents before contact" in Table 1) were adjusted as shown in Table 1. After 24 hours, the gas phase and the liquid phase were sampled, and the compositions were measured using a gas chromatograph (the "contents after contact" in Table 1). From the measurement results, the equilibrium adsorption amount of R23 adsorbed to the synthetic zeolite 4A was calculated.

[0093] [Table 1]

[0094]

[0095] As shown in Table 1, when the first fluid in which VdF is the main component and R23 is also contained was brought into contact with the synthetic zeolite 4A, the equilibrium adsorption amount of R23 was very high compared with the past, and high-purity VdF could be efficiently obtained.

[0096] [Examples 21 to 23]

[0097] Example 21 is an example, and Examples 22 and 23 are comparative examples.

[0098] In Example 21, 52.5 g of synthetic zeolite 4A (product name "Molecular Sieve 4A", manufactured by SunSeng Chemicals Co., Ltd.) was supplied with a first fluid containing VdF and R23 at 40°C at a flow rate of 25 mL / minute (4.3 g / hour). In the first fluid, the content of R23 was 1083 ppm. After a certain period of time, the composition of the outlet gas and the gas flow rate in the outlet gas were measured.

[0099] In Example 22, synthetic zeolite 3A (product name "Molecular Sieve 3A", manufactured by SunSeng Chemicals Co., Ltd.) was used instead of the synthetic zeolite 4A, and otherwise, the first fluid was circulated using the same method as in Example 21, and after a certain period of time, the composition of the outlet gas and the gas flow rate in the outlet gas were measured.

[0100] In Example 23, synthetic zeolite 5A (product name "Molecular Sieve 5A", manufactured by SunSeng Chemicals Co., Ltd.) was used instead of the synthetic zeolite 4A, and otherwise, the first fluid was circulated using the same method as in Example 21, and after a certain period of time, the composition of the outlet gas and the gas flow rate in the outlet gas were measured.

[0101] [Table 2]

[0102]

[0103] As shown in Table 2, when the first fluid in which VdF is the main component and R23 is also contained was brought into contact with the synthetic zeolite 4A in Example 21, high-purity VdF could be efficiently obtained.

[0104] On the other hand, in Example 22, the first fluid was contacted with synthetic zeolite 3A, but high-purity VdF was not obtained. It is considered that this is because the synthetic zeolite 3A has low adsorption capacity for R23.

[0105] In addition, in Example 23, the first fluid was contacted with synthetic zeolite 5A, but high-purity VdF was not obtained. It is considered that this is because the gas flow rate of the outlet gas was 0 mL / min for a certain period of time after the contact, and VdF was adsorbed together with R23 in the synthetic zeolite 5A.

[0106] [Example 31]

[0107] In Example 31, the flow rate of the first fluid was set to 50 mL / min (8.6 g / hour), and otherwise, the first fluid was circulated using the same method as in Example 21, and the composition of the outlet gas was measured after a certain period of time.

[0108] The ratio of the flow rate of the first fluid to the packed amount of the synthetic zeolite 4A in the reactor was about 0.082 [(g / hour) / g] in Example 21 and about 0.164 [(g / hour) / g] in Example 31.

[0109] [Table 3]

[0110]

[0111] As shown in Table 3, when the ratio of the flow rate of the first fluid to the packed amount of the synthetic zeolite 4A in the reactor is 0.160 [(g / hour) / g] or less, high-purity VdF can be further efficiently obtained.

[0112] Note that the disclosure of Japanese Patent Application No. 2023-030192, filed February 28, 2023, is incorporated herein by reference in its entirety. In addition, all documents, patent applications, and technical standards cited in the present specification are incorporated herein by reference to the same extent as the specific and individual citation.

Claims

1. A method for purifying vinylidene fluoride, wherein: A first fluid whose main component is vinylidene fluoride and further contains trifluoromethane is brought into contact with synthetic zeolite 4A to obtain a second fluid in which the mass ratio of the vinylidene fluoride content to the total content of the vinylidene fluoride and trifluoromethane is higher than the mass ratio in the first fluid.

2. The method for purifying vinylidene fluoride according to claim 1, wherein: The ratio of the flow rate of the first fluid to the filling amount of the synthetic zeolite 4A in the reactor is 0.160 [(g / hour) / g] or less.

3. The method for purifying vinylidene fluoride according to claim 1 or 2, wherein: The first fluid is gas.

4. The method for purifying vinylidene fluoride according to claim 1 or 2, wherein: The content of vinylidene fluoride in the second fluid is 99% by mass or more relative to the total amount of the second fluid.

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