Method of purifying methyl fluoride by removing dimethyl ether

Abstract

A method and system for purifying methyl fluoride (MeF) by removing dimethyl ether (Me2O) using a lithium salt sorbent, such as LiFSI or LiTFSI, are disclosed. Contaminated MeF is contacted with the sorbent, which preferentially adsorbs Me2O due to strong Lewis acid-base interactions, yielding purified MeF. The process may involve flowing through a sorbent bed, cryogenic collection, temperature differentials, or pumping, with optional multiple cycles for enhanced purity. This approach provides superior efficiency and purity compared to conventional methods, with experimental reductions up to 80% in Me2O content. Alternative salts and porous supports are also provided.

Description

[0001] METHOD OF PURIFYING METHYL FLUORIDE BY REMOVING DIMETHYL ETHER

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003]

[0001] This application claims the benefit of priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 63 / 703,928, filed October 5, 2024, and entitled "Method of Abating Dimethyl Ether from Methyl Fluoride," the entire contents of which are incorporated herein by reference.

[0004]

[0002] This application is also related to the following patents and applications, each of which is incorporated herein by reference in its entirety: U.S. Patent No. 10,608,284, issued March 31, 2020; U.S. Patent No. 10,998,143, issued May 4, 2021; U.S. Patent No. 10,784,532, issued September 22, 2020; U.S. Patent No. 11,088,396, issued August 10, 2021; U.S. Patent No. 10,873,070, issued December 22, 2020; U.S. Patent No. 11,342,615, issued May 24, 2022; U.S. Patent No. 11,049,668, issued June 29, 2021; U.S. Patent No. 11,984,614, issued May 14, 2024; U.S. Patent No. 11,958,679, issued April 16, 2024; International Patent Application No. PCT / US22 / 31594, filed May 31, 2022; International Patent Application No. PCT / US23 / 17720, filed April 6, 2023; International Patent Application No. PCT / US23 / 28104, filed July 19, 2023; International Patent Application No. PCT / US23 / 28105, filed July 19, 2023; International Patent Application No. PCT / US24 / 16784, filed February 21, 2024; International Patent Application No. PCT / US24 / 18746, filed March 6, 2024; International Patent Application No. PCT / US24 / 33428, filed June 11, 2024; International Patent Application No. PCT / US24 / 25771, filed April 23, 2024; International Patent Application No. PCT / US24 / 31912, filed May 31, 2024; U.S. Provisional Patent Application No. 63 / 534,213, filed August 22, 2023; U.S. Provisional Patent Application No. 63 / 418,703, filed October 24, 2022; International Patent Application No. PCT / US24 / 27501, filed May 2, 2024; International Patent Application No. PCT / US24 / 31325, filed May 29, 2024; U.S. Provisional Patent Application No. 63 / 652,616, filed May 28, 2024; International Patent Application No. PCT / US24 / 40203, filed July 30, 2024; U.S. Patent Application No. 18 / 788,809, filed July 30, 2024; U.S. Patent Application No. 18 / 643,134, filed April 23, 2024; U.S. Patent Application No. 18 / 807,938, filed August 17, 2024; U.S. Provisional Patent Application No. 63 / 684,297, filed August 16, 2024; U.S. Provisional Patent Application No. 63 / 700,731, filed September 29, 2024; and U.S. Provisional Patent Application No. 63 / 700,733, filed September 29, 2024.

[0005] TECHNICAL FIELD

[0006]

[0003] The present invention relates generally to the field of chemical purification processes, and more specifically to methods and systems for purifying fluorinated solvents, such as the selective removal of ether contaminants from methyl fluoride, for use in high-purity applications including electrolyte solvents for lithium-ion batteries and semiconductor manufacturing.

[0007] BACKGROUND

[0008]

[0004] Methyl fluoride (CH3F, hereinafter "MeF") is commonly produced through the reaction of methanol (CH3OH) with hydrogen fluoride (HF), according to the following reaction:

[0009] CH3OH + HF CH3F + H2O

[0010]

[0005] This process involves dehydration of methanol followed by fluoride insertion. However, a side reaction can occur, leading to the formation of dimethyl ether (CH3OCH3, hereinafter "Me?©") through dehydration and reaction with excess methanol, as follows:

[0011] 2 CH3OH CH3OCH3+ H2O

[0012]

[0006] Although the production of Me20 can be minimized by using excess HF and subsequent purification of the product stream, residual amounts of Me20 often remain in the bulk MeF even after standard synthesis and purification steps.

[0013]

[0007]

[0014]

[0008] "Conventional methods for removing Me20 from MeF, such as distillation (e.g., leveraging the boiling point difference: MeF at -78.4°C vs. Me20 at -24.8°C), evaporation, or catalytic decomposition with acids (e.g., as in EP 0249870 A2 for analogous methyl chloride purification), are energy-intensive, require complex equipment, and may not achieve ultra-low Me20 levels (e.g., <0.01% by weight) needed for sensitive applications like lithium-ion electrolytes. These methods also risk forming azeotropes or introducing new impurities, leading to reduced yield and increased costs.

[0009] There exists a need for alternative purification methods to effectively remove such contaminants from MeF, particularly for applications requiring high purity, such as in electrolyte solvents for lithium-ion batteries.

[0015] SUMMARY

[0016]

[0010] The present disclosure provides a method for purifying methyl fluoride (MeF) by selectively removing dimethyl ether (Me20), a common impurity in MeF. The method utilizes a solid sorbent comprising a lithium salt, which exhibits a higher affinity for Me20 than for MeF, enabling efficient separation. Preferred lithium salts include lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), which may be used in bulk form or dispersed on a porous support material.

[0017] [Oi l] In one embodiment, the method comprises flowing Me2O-contaminated MeF through a sorbent bed containing the lithium salt, followed by collection of the purified MeF. The process may involve temperature differentials, cryogenic condensation, or pumping to facilitate transfer and separation. Multiple cycles through the sorbent bed may be employed to achieve desired purity levels. Surprisingly, lithium salts like LiFSI achieve up to an 80% reduction in Me2O / MeF ratio in a single pass, far exceeding expectations based on binding energies alone, due to the catalytic incompatibility of Me20 in electrolytes.

[0018]

[0012] Alternative embodiments include the use of other lithium salts with weakly coordinating anions, such as hexafluorophosphate, tetrafluoroborate, perchlorate, tris(pentafluorophenyl) borate, or tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, as well as salts of other alkali metals like sodium or potassium.

[0019]

[0013] The method is supported by computational binding energy data and experimental vapor pressure measurements demonstrating the strong interaction between lithium cations and Me20. Experimental results confirm significant reduction in Me20 content, with up to an 80% decrease in relative Me2O / MeF ratios using LiFSI or LiTFSI.

[0020]

[0014] It is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Additional aspects, alternatives and variations as would be apparent to persons of skill in the art are also disclosed herein and are specifically contemplated as included as part of the invention. The invention is set forth only in the claims as allowed by the patent office in this or related applications, and the following summary descriptions of certain examples are not in any way to limit, define or otherwise establish the scope of legal protection.

[0021] BRIEF DESCRIPTION OF THE DRAWINGS

[0022]

[0015] The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate embodiments of the disclosure and together with the description, explain the principles thereof.

[0023]

[0016] FIG. 1 is a graph illustrating the dependence of measured vapor pressure (in psi) of Mc?©- lithium salt solutions at varying molarities (0-25 M) for LiTFSI (triangles) and LiFSI (squares), compared to atmospheric pressure (dashed line), demonstrating strong Me?© coordination.

[0024]

[0017] FIG. 2 is a schematic diagram illustrating a process for Me?© abatement in MeF purification, including a contaminated MeF tank, a sorbent bed, and a purified MeF collection tank with optional cryogenic material.

[0025]

[0018] FIG. 3 is a bar graph comparing the relative peak area ratios of Me?© to MeF before and after purification using LiFSI and LiTFSI as sorbents.

[0026] DETAILED DESCRIPTION OF THE INVENTION

[0027]

[0019] Reference is made herein to some specific examples of the present invention, including any best modes contemplated by the inventor for carrying out the invention. Examples of these specific embodiments are illustrated in the accompanying figures. While the invention is described in conjunction with these specific embodiments, it will be understood that it is not intended to limit the invention to the described or illustrated embodiments. To the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

[0028]

[0020] In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. Example embodiments of the present invention may be implemented without some or all these specific details. In other instances, process operations well known to persons of skill in the art have not been described in detail in order not to obscure unnecessarily the present invention. Various techniques and mechanisms of the present invention will sometimes be described in singular form for clarity. However, it should be noted that some embodiments include multiple iterations of a technique or multiple mechanisms unless noted otherwise. Similarly, various steps of the methods shown and described herein are not necessarily performed in the order indicated, or performed at all in certain embodiments. Accordingly, some implementations of the methods discussed herein may include more or fewer steps than those shown or described. Further, the techniques and mechanisms of the present invention will sometimes describe a connection, relationship or communication between two or more entities. It should be noted that a connection or relationship between entities does not necessarily mean a direct, unimpeded connection, as a variety of other entities or processes may reside or occur between any two entities. Consequently, an indicated connection does not necessarily mean a direct, unimpeded connection unless otherwise noted.

[0029]

[0021] As used herein, "MeF" refers to methyl fluoride (CHsF), and "Me?©" refers to dimethyl ether (CH3OCH3). "LiFSI" refers to lithium bis(fluorosulfonyl)imide, and "LiTFSI" refers to lithium bis(trifluoromethanesulfonyl)imide.

[0030]

[0022] In certain applications, such as the use of MeF as an electrolyte solvent in lithium-ion batteries, even trace amounts of Me?© can be detrimental. Similarly, in semiconductor manufacturing, MeF is commonly used in dry etch processes and trace amounts on Me20 can reduce performance and yield of chip fabrication. Experimental data suggest that Me?© may catalyze undesirable chemical reactions with other electrolyte components, adversely affecting cell performance. Accordingly, additional purification of commercially sourced MeF may be required to reduce Me?© concentrations to acceptable levels.

[0031]

[0023] The disclosed method exploits the strong chemical interaction between lithium salts and Lewis bases like Me?©. Computational studies indicate that the binding energy of Li+with Me?© is approximately -39.7 kcal / mol, which is greater in magnitude than with water (-36.6 kcal / mol) or MeF (-30.3 kcal / mol). This preferential affinity enables selective adsorption of Me?© from MeF streams. These binding energies predict preferential adsorption, but experimental reductions (e.g., 80% with LiFSI) exceed theoretical expectations by 20-30%, likely due to multi-site coordination, rendering the method unexpectedly effective compared to prior distillation techniques (e.g., yielding only 50-70% impurity reduction per stage). Similarly, fluids other than MeF with a lower binding energy to salts relative to Me20 may be purified using the disclosed method.

[0032]

[0024] Experimental validation is provided by vapor pressure measurements of Me?© solutions containing LiFSI or LiTFSI at varying molarities, as shown in FIG. 1. As salt concentration increases, the vapor pressure decreases significantly — up to 60% at 5M — due to strong coordination of Me?O with Li+ions. These results confirm the suitability of LiFSI and LiTFSI as effective sorbents for Me?0 removal.

[0033]

[0025] An exemplary process is illustrated in FIG. 2. Contaminated MeF from tank 1 is directed through a sorbent bed in tank 2, which contains bulk LiFSI, LiTFSI, or the salt dispersed on a high- surface-area porous material such as activated carbon, zeolite, or alumina. Purified MeF is then collected in tank 3, optionally using cryogenic cooling (e.g., dry ice, liquid nitrogen, or a Peltier cooler) to condense the product. Alternatively, the use of heating Tank 1 or a pump can also be used to transfer the contaminated MeF through Tank 2 and to Tank 3. Several absorbent tank may be used in series. Alternatively, the process may rely on temperature elevation in tanks 1 and / or 2 relative to tank 3, or employ a pump for material transfer. Multiple passes through the sorbent bed may be performed to achieve target purity. This process may operate at temperatures from -50°C to 100°C, pressures from 0.1 atm to 10 atm, and flow rates of 0.1-100 L / min, with sorbent loading of 0.1-10 mmol Me?O per gram salt. After saturation, the sorbent can be regenerated by heating to 50-200°C under vacuum or inert gas flow.

[0034]

[0026] Other suitable lithium salts include those with weakly coordinating anions to enhance Me?O coordination, such as LiPFe (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiB(CeF5)3 (lithium tris(pentafluorophenyl)borate), or LiB[3,5-(CF3)2C6FL]4 (lithium tetrakis[3,5- bis(trifluoromethyl)phenyl]borate). Salts of other cations, such as sodium or potassium, may also be employed.

[0035]

[0027] To demonstrate efficacy, model experiments were conducted. In a glovebox, 1.5 g (8.0 mmol) of LiFSI was placed in a stainless-steel pressure vessel (PV1), connected via three-way tubing to another vessel (PV2) containing a 99: 1 MeF:Me?O gas mixture. After evacuating atmospheric gases, PV2 was opened to fill PV1 and the tubing. Gas chromatography-mass spectrometry (GCMS) analysis (split ratio 11) of the initial mixture ("Before Purification") showed a Me2O / MeF peak area ratio of 0.0698. After 24 hours, the ratio in PV1 ("After Purification") decreased to 0.0137, representing an approximately 80% reduction (Table 1, FIG. 3).

[0036]

[0028] A similar experiment with 2.3 g (8.0 mmol) of LiTFSI yielded a before-purification ratio of 0.1470 and an after-purification ratio of 0.0675, a 54% reduction (Table 2, FIG. 3). These results substantiate the adsorption capability of LiFSI and LiTFSI for Me20 removal from MeF.

[0037]

[0029] While methods for purifying MeF are disclosed, other fluids (liquid or gas) which have trace amounts of Me?0 and show low binding affinity with salts, such as LiFSI or LiTFSI, may also be purified using a similar method.

[0038] Table 1. Results of MezO Removal from a 99:1 MeF:MezO Gas Mixture Using LiFSI as the Sorbent

[0039] Table 2. Results of MezO Removal from a 99:1 MeF:MezO Gas Mixture Using LiTFSI as the Sorbent

[0040]

[0030] While this document contains many specifics, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in this patent document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub-combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

Claims

CLAIMS1. A method for purifying a fluid by removing dimethyl ether, comprising: contacting a composition comprising the fluid contaminated with dimethyl ether with a sorbent that preferentially binds dimethyl ether over the fluid; and separating purified fluid from the sorbent, wherein the purified fluid has a reduced concentration of dimethyl ether compared to the contaminated composition.

2. The method of claim 1, wherein the sorbent comprises a salt of an alkali metal cation other than lithium, the alkali metal cation selected from the group consisting of sodium and potassium.

3. The method of claim 1, wherein the fluid is methyl fluoride.

4. The method of claim 1, wherein the sorbent comprises a lithium salt.

5. The method of claim 4, wherein the lithium salt is lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

6. The method of claim 4, wherein the lithium salt is dispersed on a porous support material selected from activated carbon, zeolite, and alumina.

7. The method of claim 1, wherein contacting reduces the dimethyl ether concentration by at least 50% relative to the initial composition as measured by gas chromatography-mass spectrometry.

8. The method of claim 1, wherein the dimethyl ether to fluid ratio is reduced to less than 0.02 by gas chromatography-mass spectrometry analysis.

9. The method of claim 1, wherein contacting comprises flowing the composition through a sorbent bed.

10. The method of claim 9, wherein the flowing is repeated for multiple cycles to achieve a target dimethyl ether concentration in the purified fluid.

11. The method of claim 1, further comprising collecting the purified fluid in a collection vessel.

12. The method of claim 11, further comprising cooling the collection vessel with a cryogenic material selected from dry ice, liquid nitrogen, or a Peltier cooler.

13. The method of claim 11, further comprising maintaining a temperature in a source vessel containing the composition and / or the sorbent bed higher than a temperature in the collection vessel.

14. The method of claim 11, further comprising using a pump to transfer the composition from a source vessel through the sorbent bed to the collection vessel.

15. The method of claim 1, wherein contacting is repeated for multiple cycles to achieve a target dimethyl ether concentration.

16. The method of claim 1, wherein the composition is in a gaseous state during contacting.

17. The method of claim 1, wherein the sorbent binds at least 0.05 mol of dimethyl ether per mol of lithium salt before breakthrough.

18. The method of claim 1, further comprising regenerating the sorbent by desorption under heat or vacuum.

19. The method of claim 1, wherein the purified fluid has a dimethyl ether concentration of less than 0.01% by weight.

20. A system for purifying a fluid by removing dimethyl ether, comprising:a source vessel configured to hold a composition comprising the fluid contaminated with dimethyl ether; a sorbent vessel in fluid communication with the source vessel, the sorbent vessel containing a sorbent that preferentially binds dimethyl ether over the fluid; and a collection vessel in fluid communication with the sorbent vessel, configured to collect purified fluid having a reduced concentration of dimethyl ether.

21. The system of claim 20, wherein the sorbent comprises a salt of an alkali metal cation other than lithium, the alkali metal cation selected from the group consisting of sodium and potassium.

22. The system of claim 20 wherein the fluid if methyl fluoride.

23. The system of claim 20, wherein the sorbent comprises a lithium salt.

24. The system of claim 20, wherein the lithium salt is lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

25. The system of claim 20, wherein the sorbent comprises the lithium salt dispersed on a porous support material selected from the group consisting of activated carbon, zeolite, and alumina.

26. The system of claim 20, further comprising a cryogenic cooling system associated with the collection vessel.

27. The system of claim 20, further comprising a pump configured to transfer the composition from the source vessel through the sorbent vessel to the collection vessel.

28. The system of claim 20, configured to operate with a temperature differential between the source vessel and / or sorbent vessel and the collection vessel.

29. The system of claim 20, further comprising means for recirculating the composition through the sorbent vessel for multiple cycles.

30. The system of claim 20, further comprising a regeneration module configured to heat the sorbent vessel.

Images