METHOD FOR THE PURIFICATION OF 1,2-DIFLUORETHYLENE (HFO-1132)

Description

Technical Field

[0001] The present disclosure relates to a method for purifying 1,2-difluoroethylene (HFO-1132).Background Art

[0002] 1,2-Difluoroethylene (HFO-1132) is referred to as a candidate of an alternative refrigerant component for mixed refrigerants of HFC, such as R410A (which is a mixed refrigerant of two components, i.e., HFC-32 and HFC-125) used as a refrigerant for air conditioners. HFO-1132 has two isomers, i.e., trans-1,2-difluoroethylene (HFO-1132(E)) and cis-1,2-difluoroethylene (HFO-1132(Z)).

[0003] A typically known purification method for reducing water and other impurities from a composition comprising HFO-1132 and water comprises bringing the composition into contact with a zeolite (molecular sieves), calcium chloride, silica gel, activated carbon, concentrated sulfuric acid, or the like to achieve dehydration. For example, WO 2015 / 125877 discloses bringing a fluid comprising HFO-1132 into contact with a synthetic zeolite to achieve dehydration.

[0004] GB-A-2 439 209 discloses a method of drying a fluid comprising a fluoropropene, comprising contacting the fluid with a desiccant comprising a molecular sieve having openings which have a size across their largest dimension of 0.3-0.5 nm (3-5 Å).Summary of InventionTechnical Problem

[0005] An object of the present disclosure is to provide a method for purifying HFO-1132 to a high purity while suppressing the isomerization and loss of HFO-1132.Solution to Problem

[0006] The present invention thus provides a method for purifying HFO-1132 comprising (1) contacting a composition comprising HFO-1132(E) and / or HFO-1132(Z) and water with a zeolite with an SiO 2 / Al 2 O 3 ratio of ≥ 5.0 to reduce the water content of the composition.

[0007] Preferred embodiments of the invention are as defined in the appended dependent claims and / or in the following detailed description.Advantageous Effects of Invention

[0008] According to the present disclosure, HFO-1132 can be purified to a high purity while suppressing the isomerization and loss of HFO-1132.Description of Embodiments

[0009] The present inventors conducted extensive research, and found that HFO-1132 can be purified to a high purity while suppressing the isomerization and loss of HFO-1132 by bringing a composition comprising HFO-1132 and water into contact with a specific zeolite when purifying HFO-1132 by reducing the water from the composition.

[0010] The present invention has been completed as a result of further research based on these findings.

[0011] Herein, unless otherwise specified, 1,2-difluoroethylene (HFO-1132) refers to trans-1,2-difluoroethylene (HFO-1132(E)) and / or cis-1,2-difluoroethylene (HFO-1132(Z)). More specifically, HFO-1132 refers to HFO-1132(E) alone, HFO-1132(Z) alone, or a mixture of HFO-1132(E) and HFO-1132(Z) (in any mixing ratio, unless otherwise specified). Further, a range indicated by "A to B" means A or more and B or less, unless otherwise specified.

[0012] The present invention is based on the finding that HFO-1132 can be purified to a high purity while suppressing the isomerization and loss of HFO-1132 by bringing a composition comprising HFO-1132 and water into contact with a zeolite with an SiO 2 / Al 2 O 3 ratio of ≥ 5.0 to reduce the water content from the composition. In particular, the degree of isomerization of HFO-1132 (isomerization percentage) in the purification process is kept low (including the case where isomerization does not occur). The isomerization percentage is preferably < 0.1 vol.%.

[0013] The present method for purifying HFO-1132 can be specified as follows.

[0014] A method for purifying 1,2-difluoroethylene, which is HFO-1132, comprising contacting a composition comprising trans-1,2-difluoroethylene, which is HFO-1132(E), and / or cis-1,2-difluoroethylene, which is HFO-1132(Z), and water with a zeolite with an SiO 2 / Al 2 O 3 ratio of ≥ 5. to reduce the water content from the composition.

[0015] The general description for the above composition comprising HFO-1132 and water (purification target) is as set out below. The total content of HFO-1132(E) and HFO-1132(Z) in the composition may be set widely from a range of, for example, 10 to 99.99 vol.%.

[0016] Examples of the composition comprising HFO-1132 and water include a composition comprising water that can be incorporated during the production of HFO-1132. Specific examples of the composition include a product of dehydrofluorination reaction of 1,1,2-trifluoroethane, and a product of isomerization reaction of HFO-1132(E) and / or HFO-1132(Z) in the presence of a metal catalyst.

[0017] The composition can also comprise impurities other than water. Examples of impurities include at least one member selected from intermediates, isomers, and by-products that can be incorporated during the production of HFO-1132 (e.g., hydrogen fluoride, fluoroethylene, difluoroethylene, trifluoroethylene, 1,1,1-trifluoroethane, propylene, acetylene, difluoromethane, trifluoromethane, and fluoromethane).

[0018] The present method is, in particular, characterized in that a composition comprising HFO-1132(E) and / or HFO-1132(Z), and water is used as the purification target, and a specific zeolite is used to keep the degree of isomerization of HFO-1132 (isomerization percentage) during the purification process low, preferably as low as < 0.1 vol.% (including the case where isomerization does not occur).

[0019] Thus, after the purification step, a purified product that contains a reduced content of water and in which the isomerization of HFO-1132 is suppressed (variation in the ratio of E / Z vol.% is suppressed) can be recovered in the recovery step. Further, the use of a zeolite with an SiO 2 / Al 2 O 3 ratio of ≥ 5.0 in the purification step suppresses the adsorption of HFO-1132 to the zeolite; accordingly, the isomerization and loss of HFO-1132 can be suppressed, and HFO-1132 can be purified to a high purity.

[0020] Next, zeolites, which function as an adsorbent for adsorbing and removing water according to the present invention, are described. In the present invention, zeolites can adsorb and remove not only water, but also one or more impurities in addition to water; however, below, the adsorption and removal of water is particularly described.

[0021] Zeolites are a type of clay mineral, and are hydrous aluminosilicates containing alkali or alkaline earth metals with a rigid anionic framework with regular channels (tubular pores) and cavities.

[0022] Zeolites are typically represented by         (M I< , M II< 1 / 2 ) m (Al m Si n O 2(m+n) )• x H 2 O (n ≥ m) (M I< : e.g. Li +< , Na +< or K +< , and M II< : e.g. Ca 2+< , Mg 2+< or Ba 2+< ), and cations compensate the negative charge of the framework of the aluminosilicates.

[0023] The type of cations in zeolites is not limited, and the cations may be typically H +< , Li +< , Na +< , K +< , Ca 2+< , Mg 2+< and Ba 2+< .

[0024] The basic structural unit of zeolites is a tetrahedral structure of SiO 4 or AlO 4 (together, TO 4 tetrahedron); these units infinitely continue in the three-dimensional direction to form crystals. Zeolite crystals are porous, and usually have a pore diameter of 0.2-1.0 nm. Zeolites have molecular sieve properties, with which molecules that are larger than the pore size cannot enter into the pores. In addition to the molecular sieve effect of the pores based on their backbone structure, zeolites have properties such as solid acidity, ion exchange capacity, catalytic activity, and adsorption capacity.

[0025] The description for the zeolite used in the present invention is as set out above, with the further requirement that in the present method a zeolite with an SiO 2 / Al 2 O 3 ratio of ≥ 5.0 is used. In the present method, the upper limit of the SiO 2 / Al 2 O 3 ratio in the zeolite is not limited, and may be about 2000. That is, the SiO 2 / Al 2 O 3 ratio is preferably 5.0-2,000, and more preferably 5-100.

[0026] In the present method, a composition comprising HFO-1132 and water is brought into contact with a zeolite with an SiO 2 / Al 2 O 3 ratio of ≥ 5.0 to reduce the water content from the composition, whereby HFO-1132 can be purified to a high purity while suppressing the isomerization and loss of HFO-1132. In particular, the degree of isomerization of HFO-1132 (isomerization percentage) in the purification process is kept low, preferably as low as < 0.1 vol.% (more preferably < 0.01 vol.%) (including 0 vol.% thereof, i.e., below the detection limit by gas chromatography).

[0027] Since the SiO 2 / Al 2 O 3 ratio is ≥ 5.0, the efficiency in terms of adsorption and removal of water can be improved while keeping the isomerization percentage of HFO-1132 and the possibility of HFO-1132 itself being adsorbed to the zeolite low, which enables HFO-1132 to be efficiently purified while keeping the loss in the purification step due to, for example, isomerization low.

[0028] Zeolites with an SiO 2 / Al 2 O 3 ratio of ≥ 5.0 are commercially available. Examples include ZSM-5 (produced by Tosoh Corporation) and ferrierite (produced by Tosoh Corporation). These zeolites may be used alone, or in a combination of two or more as long as they satisfy the requirement of the SiO 2 / Al 2 O 3 ratio.

[0029] In the present method, the method, conditions, etc., for bringing the composition as the purification target comprising HFO-1132 and water into contact with a zeolite with an SiO 2 / Al 2 O 3 ratio of ≥ 5.0 are as described in the following.

[0030] In the present invention, bringing a composition comprising HFO-1132 and water as a purification target into contact with a zeolite means allowing the composition to pass through a device (e.g., a column) filled with the zeolite, or introducing the composition into a container filled with the zeolite.

[0031] In the present invention, the zeolite is used as an adsorbent (a material for adsorbing and removing impurities). When the composition as the purification target is brought into contact with (allowed to pass through) the zeolite, water contained in the composition is adsorbed and removed by the zeolite.

[0032] In the present invention, to effectively adsorb and remove water, the composition as the purification target and the zeolite are preferably brought into contact in a mass ratio of (100:1)-(1:10), more preferably (50:1)-(1:5), and even more preferably (10:1)-(1:3). In the present disclosure, the amount of zeolite for use is, for example, such that 10 g of zeolite filling material (e.g., a stainless steel column) is used for 10-100 g of the composition as the purification target.

[0033] In the present invention, the zeolite may be subjected to activation treatment before use. The conditions of the activation treatment are not limited. Examples include a drying treatment comprising, for example, heating in vacuum (13,33-0,13 Pa (10 -1< to 10 -3< mmHg)) overnight at a temperature of 200-350°C. In the present invention, however, zeolites that are not subjected to activation treatment can also be suitably used.

[0034] In the present invention, the mode of use of zeolites is not limited. The composition as the purification target may be allowed to pass through a device (e.g., a column) filled with the zeolite. Alternatively, the composition as the purification target may be introduced into a container filled with the zeolite, and a purified product may be recovered after a predetermined amount of time has elapsed.

[0035] In the present invention, the temperature at which the composition as the purification target is brought into contact with the zeolite is not limited; and is set in consideration of, for example, the boiling point of HFO-1132 contained in the composition as the purification target. Contacting at a lower temperature is usually preferred since side reactions (e.g., isomerization reactions) are suppressed at the time of contact. The temperature is preferably 0-100°C. From this range, for example, a temperature of 0-50°C or 50-100°C may be selected.

[0036] In the present invention, the time of contacting the composition as the purification target with the zeolite is not limited, and may be freely set as long as the amount of impurities (including water) contained in the recovered product after purification can be reduced to a target degree or less. More specifically, the time may be set according to, for example, the passing-through speed, the filling time, and the temperature.

[0037] In the present invention, the zeolite for use may be in the form of powders, granules, or pellets. The zeolite may also be used as a molded body. Industrially, the zeolite is preferably used as a molded body. The shape of the molded body is not limited, and is preferably, for example, cylindrical with a diameter of 0.5-5 mm and a length of 1-15 mm, or spherical with a diameter of 0.5-10 mm.

[0038] In the present disclosure, the method for producing a molded body of zeolite is not limited. For example, a conventionally known method that uses kaolin clay as a binder may be used.Purified Product with Reduced Water Content

[0039] As described above, the present method is capable of purifying HFO-1132 to a high purity while suppressing the isomerization and loss of HFO-1132 by bringing a composition comprising HFO-1132 and water into contact with a specific zeolite to reduce the water content from the composition. The purified product containing a reduced content of water obtained through the purification method above can be specified as follows.

[0040] A purified product containing trans-1,2-difluoroethylene (HFO-1132(E)) and / or cis-1,2-difluoroethylene (HFO-1132(Z)), and water, wherein the water content is ≤ 100 ppm (w / w) .Examples

[0041] The present invention is described in detail below with reference to Examples and Comparative Examples.

[0042] In the Examples and Comparative Examples, the purity of HFO-1132 and the impurity concentration were measured with the following measuring device under the following measuring conditions. The water content was measured with the following moisture meter.Measuring device: gas chromatography (with an FID detector) Measurement conditions: GS-GasPro column

[0043] Calculation of purity: calculated using the GC peak area ratio Measurement of water content: measured with a Karl Fischer moisture meter.Example 1

[0044] Five grams of molecular sieves ZSM-5 (SiO 2 / Al 2 O 3 ratio: 40.0) were weighed and added to a cylinder, followed by vacuum-drying at 250°C for 2 hours.

[0045] After drying, the resulting product was allowed to cool to room temperature, and 10 g of gas containing trans-1,2-difluoroethylene (HFO-1132(E)) (water content: 200 ppm) was added to the cylinder, followed by heating at 50°C for 3 hours.

[0046] After heating, the resulting product was allowed to cool, and the gas in the cylinder was recovered by vacuum-degassing and subjected to composition analysis by gas chromatography.Example 2

[0047] The same procedure was performed as in Example 1, except that the heating temperature (50°C) was changed to 100°C.Comparative Example 1

[0048] The same procedure was performed as in Example 1, except that molecular sieves 5A (average pore size: > 4 Å, SiO 2 / Al 2 O 3 ratio: 2.0) were used.Comparative Example 2

[0049] The same procedure was performed as in Example 1, except that molecular sieves 5A were used, and the heating temperature (50°C) was changed to 100°C. Table 1Starting materialComp. Ex. 1Comp. Ex. 2Ex. 1Ex.26Molecular sieves 5AZSM-5Heating temperature (°C)-5010050100Water content (ppm)20213151921HFO-1132(E) (%)95.1492.8491.6495.1695.08HFO-1132(Z)(%)trace0.351.49tracetraceHFO-1123 (%)0.030.030.030.020.02HFC-32 (%)0.01tracetracetracetraceHFO-1141 (%)0.070.060.060.060.06HFC-143a (%)4.696.726.784.714.80Propylene (%)0.06tracetrace0.050.04

[0050] The results shown in Table 1 clearly indicate that the methods for purifying HFO-1132 of Examples 1 and 2, which use a zeolite with an SiO 2 / Al 2 O 3 ratio of ≥ 5.0, are capable of purifying HFO-1132 to a high purity while suppressing the isomerization and loss of HFO-1132.

Claims

1. A method for purifying HFO-1132 comprising (1) contacting a composition comprising HFO-1132(E) and / or HFO-1132(Z) and water with a zeolite with an SiO2 / Al2O3 ratio of ≥ 5.0 to reduce the water content of the composition.

2. The method of claim 1, wherein the isomerization percentage of the HFO-1132 in the step is < 0.1 vol.%.

3. The method of claim 1 or 2, wherein step (1) is performed at a temperature of 0-100°C.

4. The method of any of claims 1-3, wherein the zeolite is ZSM-5.

5. The method of any of claims 1-4, wherein the composition further comprises at least one of fluoroethylene, difluoroethylene, trifluoroethylene, 1,1,1-trifluoroethane, and propylene.

6. The method of any of claims 1-5, wherein the composition is a product of a dehydrofluorination reaction of 1,1,2-trifluoroethane.

7. The method of any of claims 1-5, wherein the composition is a product of an isomerization reaction of HFO-1132(E) and / or HFO-1132(Z) in the presence of a metal catalyst.