A process for the purification of fluorinated olefins in gas phase, a gas mixture, and preparation method and use thereof

Abstract

This invention relates to a method for purifying gaseous fluorinated olefins using at least two adsorbents with different average pore sizes.

Description

[Technical Field]

[0001] This invention relates to a method for purifying fluorinated olefins, particularly hexafluoro-1,3-butadiene. [Previous Technology]

[0002] Hexafluoro-1,3-butadiene is a colorless, gaseous, unsaturated fluorocarbon compound with alternating double bonds. It is an etchant exhibiting very high performance in plasma, ion beam, or sputtering etching during semiconductor device manufacturing. Due to its short atmospheric lifetime (< 1 day), negligible global warming potential, and inertness to the stratospheric ozone layer, hexafluoro-1,3-butadiene is an environmentally compatible gas. Hexafluoro-1,3-butadiene is marketed by Solvay under the trademark Sifren® 46.

[0003] Hexafluoro-1,3-butadiene used in the semiconductor industry must have extremely high purity. To this end, EP 1329442 A1 describes a method for purifying hexafluoro-1,3-butadiene using certain adsorbents with low average pore size, particularly molecular sieves of 5 Å, because hexafluoro-1,3-butadiene is significantly excluded from the adsorbent while impurities are adsorbed, thus avoiding harmful decomposition reactions.

[0004] WO 2020 / 164912 A1 describes a method for purifying fluorinated olefins, particularly hexafluoro-1,3-butadiene, using at least two adsorbents having an average pore size greater than 6 Å, especially a combination of silica and molecular sieve 13X.

[0005] However, depending on the initial composition of the crude hexafluoro-1,3-butadiene to be purified, especially the nature and amount of impurities present therein, existing purification methods may not be sufficiently effective. In particular, when water is present in the crude hexafluoro-1,3-butadiene to be purified, it may react with some of the adsorbents used for its purification and thus generate new impurities that may contaminate the final hexafluoro-1,3-butadiene.

[0006] Another problem is the cost of running adsorbent-based purification methods, especially since some adsorbents can be quite expensive, and the overall cost increases more than the cost required for frequent replacement or regeneration of the adsorbent.

[0007] Furthermore, most existing purification methods based on adsorbents require an activation step prior to the purification process, primarily to remove residual moisture. Activation typically involves heat treatment in a dry, inert atmosphere at temperatures typically ranging from 250°C to 400°C. This step constitutes an additional production cost because it wastes energy, time, and requires the management of the effluent. [Summary of the Invention]

[0008] Therefore, an improved method for purifying hexafluoro-1,3-butadiene remains needed. Thus, one object of this application is to provide an improved method for purifying hexafluoro-1,3-butadiene, suitable for solving at least one, and preferably several, of the above-mentioned problems. Among other objects, the present invention aims to provide a rapid, simple, economical, and / or environmentally friendly purification method that can be operated efficiently on an industrial scale, and to provide hexafluoro-1,3-butadiene with improved purity, at least suitable for electronic applications.

[0009] These and other objectives are achieved by means of the method according to the invention.

Implementation Method

[0011] Therefore, a first aspect of the present invention relates to a method for purifying hexafluoro-1,3-butadiene, the method comprising contacting a gaseous mixture containing hexafluoro-1,3-butadiene with at least one first adsorbent and at least one second adsorbent to purify the gaseous mixture, wherein the at least one first adsorbent has an average pore size greater than 10 Å and the at least one second adsorbent has an average pore size less than 4 Å. The average pore size can be measured by conventional methods known to those skilled in the art, particularly by nitrogen adsorption porosity determination.

[0012] The gaseous mixture to be purified may contain various impurities mixed with hexafluoro-1,3-butadiene, such as water, hydrofluoric acid, hydrohalogenated carbon compounds, especially hydrofluorocarbons and / or hydrochlorofluorocarbons, more particularly hydrohalogenated alkenes, especially hydrofluoroolefins and more particularly 1,1,4,4-tetrafluoro-1,3-butadiene or its isomers (hereinafter referred to as C4H2F4). These impurities may arise from the formation of byproducts, from residual solvents, from unreacted starting materials, and / or partially unreacted starting materials.

[0013] Without particular limitation, the initial purity of the crude hexafluoro-1,3-butadiene to be purified by the method according to the invention can be equal to or greater than 90% by volume, particularly equal to or greater than 95% by volume, more particularly equal to or greater than 98% by volume, and even more particularly equal to or greater than 99% by volume. In particular, the crude hexafluoro-1,3-butadiene may contain C4H2F4 from 0 ppmv to 1500 ppmv, particularly from 5 ppmv to 1000 ppmv. In particular, the crude hexafluoro-1,3-butadiene may contain water from 0 ppmv to 1500 ppmv, particularly from 8 ppmv to 1000 ppmv.

[0014] The expression "at least one" in relation to the first or second adsorbent used in the method of the present invention means that more than one adsorbent having the desired properties can be used to purify the gaseous mixture. According to one embodiment, a gaseous mixture containing hexafluoro-1,3-butadiene is contacted with only one first adsorbent and at least one second adsorbent to purify the gaseous mixture. According to another embodiment, a gaseous mixture containing hexafluoro-1,3-butadiene is contacted with at least one first adsorbent and only one second adsorbent to purify the gaseous mixture. According to yet another embodiment, a gaseous mixture containing hexafluoro-1,3-butadiene is contacted with only one first adsorbent and only one second adsorbent to purify the gaseous mixture.

[0015] At least one first adsorbent is selected from adsorbents having an average pore size greater than 10 Å. In addition to the effectiveness of such adsorbents in removing various impurities, especially water molecules, from crude hexafluoro-1,3-butadiene, their use, with the first and second adsorbents arranged in this order, can advantageously enable the purification of hexafluoro-1,3-butadiene to a level sufficient to preserve the second adsorbent from premature degradation. Because hexafluoro-1,3-butadiene itself may at least partially adsorb onto the first adsorbent, it is preferable to select a first adsorbent that is inert relative to hexafluoro-1,3-butadiene, that is, formed in a material to which hexafluoro-1,3-butadiene will not react. Within the framework of this invention, the inertness of the material of the first adsorbent can be emphasized by the absence of the formation of "new" impurities in the hexafluoro-1,3-butadiene at the outlet of the first adsorbent and / or the absence of a significant reduction in yield (typically not exceeding 5%) in the purified hexafluoro-1,3-butadiene at the end of the process run. "New" impurities refer to impurities that were not present in crude hexafluoro-1,3-butadiene before the purification process began.

[0016] According to one sub-implementation, at least one first adsorbent may be selected from adsorbents having an average pore size greater than 10 Å and less than 100 Å, more particularly greater than 10 Å and less than 50 Å, and even more particularly greater than 10 Å and less than 20 Å.

[0017] According to one embodiment, at least one first adsorbent is selected from adsorbents suitable for at least removing (i.e., adsorbing) water. This first adsorbent, together with the at least one second adsorbent, helps to obtain final hexafluoro-1,3-butadiene with very high purity. It is also particularly suitable for enhancing the lifetime of the at least one second adsorbent when the gaseous mixture is first purified with the at least one first adsorbent and subsequently with the at least one second adsorbent. In fact, among the possible impurities present in crude hexafluoro-1,3-butadiene, water is the most readily reacting with the second adsorbent. Removing water prior to purification by the at least one second adsorbent advantageously increases the efficiency of the second adsorbent because it can be specifically targeted at removing specific organic impurities, such as C4H2F4. Furthermore, by avoiding possible reactions between water and the materials constituting the second adsorbent, it avoids the formation of new impurities that would contaminate the final hexafluoro-1,3-butadiene.

[0018] Suitable adsorbents having an average pore size greater than 10 Å that can be used as the first adsorbent in the framework of this invention include silica gel, zeolite 13X, zeolite MFI, activated alumina, activated carbon, etc. Silica gel systems are preferred, especially considering their cost, their inertness to hexafluoro-1,3-butadiene, and their advantageous retention of water from the crude gas mixture containing hexafluoro-1,3-butadiene to be purified. Very suitable silica gels include the Tixosil® series from S.A. and SYLOBEAD® SG B125 supplied by Grace.

[0019] At least one second adsorbent used in the method of the present invention is selected from adsorbents having an average pore size of less than 4 Å. The pore size of the second adsorbent can help to obtain better selectivity for certain types of organic impurities that may be present in the hexafluoro-1,3-butadiene to be purified, such as hydrohalogenated carbon compounds, particularly hydrofluorocarbons (HFCs) and / or hydrochlorofluorocarbons (HCFCs), more particularly hydrohaloolefins, particularly hydrofluoroolefins (HFOs), and even more particularly 1,1,4,4-tetrafluoro-1,3-butadiene or its isomers (C4H2F4). Furthermore, it is believed that the average pore size of the second adsorbent is small enough to avoid the adsorption of hexafluoro-1,3-butadiene itself, which avoids side reactions with the second adsorbent and therefore the formation of additional impurities.

[0020] According to one sub-implementation, at least one second adsorbent may be selected from adsorbents having an average pore size greater than 1 Å and less than 4 Å, particularly greater than 2 Å and less than 4 Å and more particularly greater than 3 Å and less than 4 Å.

[0021] According to one embodiment, at least one second adsorbent is selected from adsorbents suitable for removing (i.e., adsorbing) at least one impurity selected from hydrohalogenated carbon compounds, more particularly from hydrofluorocarbons (HFCs) and / or hydrochlorofluorocarbons (HCFCs), more particularly from hydrohalogenated olefins, more particularly from hydrofluoroolefins (HFOs), and even more particularly from 1,1,4,4-tetrafluoro-1,3-butadiene and its isomers (C4H2F4).

[0022] Suitable adsorbents with an average pore size of less than 4 Å that can be used as a second adsorbent within the framework of this invention include zeolites with 8-membered ring pores. More particularly, zeolite P, sodium chabazite, synthetic chabazite (SSZ-13, SSZ-62), etc., may be mentioned. Synthetic chabazite is preferred, especially considering its selectivity for the major organic impurity 1,1,4,4-tetrafluoro-1,3-butadiene (C4H2F4) and its isomers that may be present in the hexafluoro-1,3-butadiene to be purified. Very suitable chabazite includes HCZC S (H form) from Clariant. Any reference to "chabazite" in the following specification refers to synthetic chabazite.

[0023] According to one embodiment, the gaseous mixture is first purified with at least one first adsorbent and then with at least one second adsorbent. This embodiment is particularly suitable for improving the lifetime of the second adsorbent; it makes it possible to reduce the frequency of its replacement or regeneration operations.

[0024] The final purity of hexafluoro-1,3-butadiene obtained by the method according to the present invention is equal to or greater than 99.9% by volume, more preferably equal to or greater than 99.95% by volume, more preferably equal to or greater than 99.98% by volume, and most preferably equal to or greater than 99.99% by volume.

[0025] The total amount of water that may remain in purified hexafluoro-1,3-butadiene may be less than or equal to 200 ppmv, particularly less than or equal to 160 ppmv, particularly less than or equal to 80 ppmv, particularly less than or equal to 15 ppmv, particularly less than or equal to 8 ppmv. The total amount of water that may remain in purified hexafluoro-1,3-butadiene may be equal to or greater than 0 ppmv, 0.001 ppmv, particularly equal to or greater than 0.1 ppmv, particularly equal to or greater than 1 ppmv. It can be measured by laser diode spectroscopy or gas chromatography (GC).

[0026] The total amount of hydrofluorocarbons that may remain in purified hexafluoro-1,3-butadiene may be less than or equal to 500 ppmv, particularly less than or equal to 300 ppmv, particularly less than or equal to 200 ppmv, particularly less than or equal to 150 ppmv, particularly less than or equal to 100 ppmv, particularly less than or equal to 60 ppmv. The total amount of hydrofluorocarbons that may remain in purified hexafluoro-1,3-butadiene may be equal to or greater than 0 ppmv, 0.001 ppmv, particularly equal to or greater than 0.1 ppmv, particularly equal to or greater than 1 ppmv. It can be measured by conventional methods, such as gas chromatography or mass spectrometry.

[0027] In particular, the total amount of 1,1,4,4-tetrafluoro-1,3-butadiene or its possible isomers that may remain in purified hexafluoro-1,3-butadiene may be less than or equal to 50 ppmv, particularly less than or equal to 30 ppmv, particularly less than or equal to 20 ppmv, particularly less than or equal to 10 ppmv, particularly less than or equal to 6 ppmv. The total amount of 1,1,4,4-tetrafluoro-1,3-butadiene and its isomers that may remain in purified hexafluoro-1,3-butadiene may be equal to or greater than 0 ppmv, 0.001 ppmv, particularly equal to or greater than 0.1 ppmv, particularly equal to or greater than 1 ppmv. It can be measured by any known method, such as gas chromatography or mass spectrometry.

[0028] In a more specific embodiment of the method according to the invention, at least one first adsorbent is silica gel and at least one second adsorbent is chalcogenide. Preferably, hexafluoro-1,3-butadiene is first purified by at least the silica gel and then by at least the chalcogenide. Advantageously, hexafluoro-1,3-butadiene can be purified simply and effectively by the silica gel followed by the chalcogenide without requiring any other purification means.

[0029] Preferably, the method is carried out at an initial pressure equal to or higher than 100 mbar (absolute value) and equal to or lower than 2000 mbar (absolute value).

[0030] Preferably, the method is carried out at an initial temperature equal to or higher than 5°C and equal to or lower than 40°C.

[0031] As used herein, the term “initial” is intended to refer to the temperature and pressure of a gaseous mixture prior to contact with a primary adsorbent in a sequence comprising at least the first and second adsorbents.

[0032] More preferably, the flow rate of the gaseous mixture through the adsorbent is set to be equal to or higher than 2 g / min and equal to or lower than 200 g / min.

[0033] In a preferred embodiment, at least the first and second adsorbents are present in different regions of the same adsorption cartridge. Therefore, only one adsorption cartridge is used in the purification method, and at least two adsorbents are located in different regions within one cartridge, preferably in consecutive regions, thereby allowing the gaseous mixture to come into contact with the adsorbents one after another.

[0034] In another preferred embodiment, the adsorbent used in the present invention is present in different adsorption cylinders, such that the gaseous mixture can come into contact with the adsorbent one after another and the adsorbent can be regenerated individually.

[0035] According to one embodiment, at least the first adsorbent and / or the second adsorbent, and preferably any adsorbent used in the purification method of the present invention, are not heat-treated before contact with the gaseous mixture. Compared to prior art purification methods, where the pretreatment often referred to as "activation" involves maintaining the adsorbent at elevated temperatures, typically between 150°C and 400°C, under an inert atmosphere to remove moisture before the first use of the adsorbent, the purification method of the present invention does not require such a step. It advantageously enables production savings because it avoids the waste of time and energy, as well as the management of effluents (primarily water, carbon dioxide, and the inert gas used).

[0036] The purification method can be repeated multiple times (if necessary) to achieve the desired purity of the final hexafluoro-1,3-butadiene. Therefore, a circulation loop can be set up to recover the purified hexafluoro-1,3-butadiene downstream of the purification unit and send it back upstream of the purification unit.

[0037] The purification method according to the invention may include a regeneration step of the at least one first adsorbent and / or a second adsorbent. The regeneration step may include or consist of heat treatment of the adsorbent to be regenerated, preferably at a temperature ranging from 200°C to 400°C, more preferably from 250°C to 350°C, and even more preferably from 280°C to 300°C. Pressure conditions are not particularly limited: the regeneration step can advantageously be carried out at atmospheric pressure.

[0038] The hexafluoro-1,3-butadiene purified according to the present invention can be used in pure form. However, it is generally desirable to use the hexafluoro-1,3-butadiene of the present invention as a mixture with other fluorinated etching gases to control the carbon / fluorine ratio of the gas mixture. In addition, it may be desirable to use it with a suitable inert gas (such as nitrogen, argon or xenon) or a mixture with oxygen.

[0039] Therefore, another aspect of the present invention is a method for producing a gas mixture according to the present invention, the method comprising the above-described method for purifying hexafluoro-1,3-butadiene and subsequently mixing the purified hexafluoro-1,3-butadiene with another gas selected from the group consisting of: an inert gas, oxygen and another fluorinated etching gas, and the gas mixture formed in such a method.

[0040] In particular, one object of the present invention is a gas mixture comprising hexafluoro-1,3-butadiene and at least one other gas selected from the group consisting of: an inert gas, oxygen, and another fluorinated etching gas, wherein the volume ratio of water relative to the total volume of the gas mixture is less than 200 ppmv and the volume ratio of hydrofluorocarbons is less than 500 ppmv. Specifically, in said gas mixture, the volume ratio of 1,1,4,4-tetrafluoro-1,3-butadiene or its isomers relative to the total volume of the gas mixture is preferably less than 50 ppmv.

[0041] More particularly, the gas mixture may comprise hexafluoro-1,3-butadiene and at least one other gas selected from the group consisting of: an inert gas, oxygen, and another fluorinated etching gas, wherein the volume ratio of water relative to the total volume of the gas mixture is equal to or greater than 0 ppmv and less than 100 ppmv, and the volume ratio of hydrofluorocarbons is equal to or greater than 0 ppmv and less than 200 ppmv. Specifically, in the gas mixture, the volume ratio of 1,1,4,4-tetrafluoro-1,3-butadiene or its isomers relative to the total volume of the gas mixture is preferably equal to or greater than 0 ppmv and less than 20 ppmv.

[0042] The lower limit of the aforementioned impurities may fall within the quantitative limit of the measuring instrument. For water, the quantitative limit should be below 8 ppmv, as measured by microGC. For hydrofluorocarbons, the quantitative limit should be below 4 ppm, as measured by GC.

[0043] The gas mixture of the present invention can be readily prepared by compressing or pressing a desired amount of hexafluoro-1,3-butadiene and any other desired gas into a pressure vessel.

[0044] Furthermore, the present invention relates to a method for producing semiconductor materials, solar panels, planar panels, or microelectromechanical systems (MEMS), or a method for cleaning chambers of equipment used in semiconductor manufacturing, comprising using hexafluoro-1,3-butadiene purified according to the present invention or a gas mixture according to the present invention. A preferred application is in the production of MEMS.

[0045] If the disclosure of any patent, patent application and publication incorporated herein by reference conflicts with the description of this application to the extent that it may lead to ambiguity of terminology, then this description shall take precedence.

[0046] Figure 1 shows a suitable apparatus for the method of the present invention. An initial tank C1 contains crude hexafluoro-1,3-butadiene. The amount of hexafluoro-1,3-butadiene in tank C1 can be measured by a balance. A final tank C2 is immersed in a cooling bath (a mixture of dry ice and acetone) at -78°C. A stainless steel tube A1 contains an adsorption bed. It has an inner diameter of 18 mm and a length of 406 mm. It is double-jacketed and connected to the cooling bath to cool the bed while an exothermic reaction occurs internally. The pressure and temperature of the gaseous mixture are measured before and after tube A1. All pipes are made of stainless steel.

[0047] The following describes a typical sequence of the method of the present invention using the apparatus shown in FIG1.

[0048] The adsorbents are not pretreated before use: they are loaded directly into tube A1 or stored for subsequent use.

[0049] Once the required adsorbent is loaded into tube A1, it is installed in the equipment and the equipment is checked for leaks under vacuum.

[0050] Subsequently, the final tank C2 is immersed in a cooling bath and 2500 g of crude hexafluoro-1,3-butadiene is loaded into tank C1. The pressure in tank C1 is typically in the range of 1.5 bar to 1.8 bar (absolute value).

[0051] The crude hexafluoro-1,3-butadiene is then passed through tube A1, and the purified hexafluoro-1,3-butadiene is collected by condensation in the final container C2. The flow rate is manually controlled from 5 g / min to 25 g / min by adjusting needle valves V1, V2, and V3 accordingly.

[0052] After all the crude hexafluoro-1,3-butadiene has passed through tube A1, tank C2 is isolated by closing valve V4 and then heated to room temperature.

[0053] The purified hexafluoro-1,3-butadiene sample in tank C2 was analyzed, and the analytical results were compared with those of crude hexafluoro-1,3-butadiene.

[0054] The following examples will further explain the present invention in detail, but are not intended to limit the scope of the present invention.

[0055] Example 1: Purification of hexafluoro-1,3-butadiene using a combination of silica gel and zeolite.

[0056] For this experiment, at the end of tube A1, which first comes into contact with the gaseous mixture, 1300 g of silica gel (Sylobead SG B 125 supplied by Grace Company, with an average pore size of 12.5 Å) was first loaded into tube A1 without any pretreatment. Then, at the end of tube A1 leading to the final container C2, 1300 g of chabazite (HCZC S (H form) supplied by Clariant Company, with an average pore size of 3.8 Å) was loaded into the remainder of tube A1 without any pretreatment. Thus, tube A1 contains two separate adsorption beds, the first containing silica gel and the subsequent containing chabazite. Following the typical procedure described above, an initial amount of 2500 g of hexafluoro-1,3-butadiene was purified at a flow rate of 5 g / min, a pressure of 1.2 bar (absolute value) measured by pressure gauge P2, and a temperature of 10 °C measured by thermocouple T2.

[0057] The results of the analysis of crude hexafluoro-1,3-butadiene from tank C1 and purified hexafluoro-1,3-butadiene from tank C2 are shown in Table 1.

[0058] [Table 1]: Analysis Results Impurities (ppmv) Relative to total hexafluoro-1,3-butadiene Can C1 Can C2 water < 1000 < 8 C4H2F4 < 200 < 5 Total hydrofluorocarbons (ppmv) < 1500 < 50

[0059] Some of these results are within the quantitative limits of the measuring instruments: in the case of water, the quantitative limit occurs at levels below 8 ppmv, as measured by microGC. C4H2F4 and total HFCs are quantified by GC. [Simplified Explanation of the Diagram]

[0010] [Figure 1] shows a flowchart of a device performing the method according to the present invention.

Claims

1. A method for purifying hexafluoro-1,3-butadiene, the method comprising contacting a gaseous mixture containing hexafluoro-1,3-butadiene with at least one first adsorbent and at least one second adsorbent to purify the gaseous mixture, wherein the at least one first adsorbent has an average pore size greater than 10 Å and the at least one second adsorbent has an average pore size less than 4 Å.

2. As in request item 1, where, The at least one first adsorbent has an average pore size greater than 10 Å and less than 100 Å.

3. As in request item 1, where, The at least one second adsorbent has an average pore size greater than 1 Å and less than 4 Å.

4. As in request item 1, where, The at least one first adsorbent is suitable for removing at least water molecules, and the at least one first adsorbent is silicone.

5. As in request item 1, where, The at least one second adsorbent is suitable for removing at least one impurity selected from hydrofluorocarbons and / or hydrochlorofluorocarbons, wherein the at least one second adsorbent is zeolite.

6. As in request item 1, wherein, The gaseous mixture is first purified with at least one first adsorbent and then with at least one second adsorbent.

7. As in request item 1, where, The gaseous mixture is brought into contact with at least one first adsorbent and at least one second adsorbent at an initial pressure equal to or greater than 100 mbar (absolute value) and equal to or less than 2000 mbar (absolute value).

8. As in request item 1, where, The gaseous mixture is brought into contact with at least one first adsorbent and at least one second adsorbent at an initial temperature of 5°C or higher and 40°C or lower.

9. As in request item 1, wherein, The gaseous mixture is contacted with at least one first adsorbent and at least one second adsorbent at a flow rate equal to or greater than 2 g / min and equal to or less than 200 g / min.

10. As in request item 1, wherein, The at least one first adsorbent and the at least one second adsorbent are present in different regions of the same adsorption cylinder.

11. As in request item 1, wherein, The at least one first adsorbent and the at least one second adsorbent are present in two different adsorption cylinders.

12. As in request item 1, wherein, The at least one first adsorbent and / or the at least one second adsorbent were not heat-treated before contacting the gaseous mixture.

13. A method for producing a gas mixture, the method comprising the method of any one of claims 1 to 12 and subsequently mixing purified hexafluoro-1,3-butadiene with another gas selected from the group consisting of: an inert gas, oxygen, and another fluorinated etching gas.

14. A gas mixture comprising hexafluoro-1,3-butadiene purified by any one of claims 1 to 12 and at least one other gas selected from the group consisting of: an inert gas, oxygen, and another fluorinated etching gas, wherein the volume ratio of water that may be contained therein is less than 200 ppmv and the volume ratio of hydrofluorocarbons that may be contained therein is less than 500 ppmv relative to the total volume of the gas mixture.

15. A method for producing semiconductor materials, solar panels, planar panels or microelectromechanical systems, or a method for cleaning a chamber of an apparatus for semiconductor manufacturing, comprising using hexafluoro-1,3-butadiene purified by any one of claims 1 to 12 or a gas mixture as claimed in claim 14.

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