WO2004080974A1 - A purification method of ionic liquids to obtain their high purity - Google Patents

A purification method of ionic liquids to obtain their high purity Download PDF

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WO2004080974A1
WO2004080974A1 PCT/KR2004/000499 KR2004000499W WO2004080974A1 WO 2004080974 A1 WO2004080974 A1 WO 2004080974A1 KR 2004000499 W KR2004000499 W KR 2004000499W WO 2004080974 A1 WO2004080974 A1 WO 2004080974A1
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ionic liquid
ionic
water
ionic liquids
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Doo Seong Choi
Dong Woong Choi
Eun Ju Park
Suk Ku Chang
Il Suk Byun
Wan Joo Kim
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Chemtech Research Inc
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D213/00—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members
    • C07D213/02—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members
    • C07D213/04—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members having no bond between the ring nitrogen atom and a non-ring member or having only hydrogen or carbon atoms directly attached to the ring nitrogen atom
    • C07D213/06—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members having no bond between the ring nitrogen atom and a non-ring member or having only hydrogen or carbon atoms directly attached to the ring nitrogen atom containing only hydrogen and carbon atoms in addition to the ring nitrogen atom
    • C07D213/16—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members having no bond between the ring nitrogen atom and a non-ring member or having only hydrogen or carbon atoms directly attached to the ring nitrogen atom containing only hydrogen and carbon atoms in addition to the ring nitrogen atom containing only one pyridine ring
    • C07D213/20—Quaternary compounds thereof
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07B—GENERAL METHODS OF ORGANIC CHEMISTRY; APPARATUS THEREFOR
    • C07B63/00—Purification; Separation; Stabilisation; Use of additives
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C303/00—Preparation of esters or amides of sulfuric acids; Preparation of sulfonic acids or of their esters, halides, anhydrides or amides
    • C07C303/42—Separation; Purification; Stabilisation; Use of additives
    • C07C303/44—Separation; Purification
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D231/00—Heterocyclic compounds containing 1,2-diazole or hydrogenated 1,2-diazole rings
    • C07D231/02—Heterocyclic compounds containing 1,2-diazole or hydrogenated 1,2-diazole rings not condensed with other rings
    • C07D231/10—Heterocyclic compounds containing 1,2-diazole or hydrogenated 1,2-diazole rings not condensed with other rings having two or three double bonds between ring members or between ring members and non-ring members
    • C07D231/12—Heterocyclic compounds containing 1,2-diazole or hydrogenated 1,2-diazole rings not condensed with other rings having two or three double bonds between ring members or between ring members and non-ring members with only hydrogen atoms, hydrocarbon or substituted hydrocarbon radicals, directly attached to ring carbon atoms
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D233/00—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings
    • C07D233/04—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having one double bond between ring members or between a ring member and a non-ring member
    • C07D233/06—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having one double bond between ring members or between a ring member and a non-ring member with only hydrogen atoms or radicals containing only hydrogen and carbon atoms, directly attached to ring carbon atoms
    • C07D233/08—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having one double bond between ring members or between a ring member and a non-ring member with only hydrogen atoms or radicals containing only hydrogen and carbon atoms, directly attached to ring carbon atoms with alkyl radicals, containing more than four carbon atoms, directly attached to ring carbon atoms
    • C07D233/12—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having one double bond between ring members or between a ring member and a non-ring member with only hydrogen atoms or radicals containing only hydrogen and carbon atoms, directly attached to ring carbon atoms with alkyl radicals, containing more than four carbon atoms, directly attached to ring carbon atoms with substituted hydrocarbon radicals attached to ring nitrogen atoms
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D233/00—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings
    • C07D233/54—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having two double bonds between ring members or between ring members and non-ring members
    • C07D233/56—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having two double bonds between ring members or between ring members and non-ring members with only hydrogen atoms or radicals containing only hydrogen and carbon atoms, attached to ring carbon atoms
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D249/00—Heterocyclic compounds containing five-membered rings having three nitrogen atoms as the only ring hetero atoms
    • C07D249/02—Heterocyclic compounds containing five-membered rings having three nitrogen atoms as the only ring hetero atoms not condensed with other rings
    • C07D249/08—1,2,4-Triazoles; Hydrogenated 1,2,4-triazoles
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D295/00—Heterocyclic compounds containing polymethylene-imine rings with at least five ring members, 3-azabicyclo [3.2.2] nonane, piperazine, morpholine or thiomorpholine rings, having only hydrogen atoms directly attached to the ring carbon atoms
    • C07D295/02—Heterocyclic compounds containing polymethylene-imine rings with at least five ring members, 3-azabicyclo [3.2.2] nonane, piperazine, morpholine or thiomorpholine rings, having only hydrogen atoms directly attached to the ring carbon atoms containing only hydrogen and carbon atoms in addition to the ring hetero elements
    • C07D295/037—Heterocyclic compounds containing polymethylene-imine rings with at least five ring members, 3-azabicyclo [3.2.2] nonane, piperazine, morpholine or thiomorpholine rings, having only hydrogen atoms directly attached to the ring carbon atoms containing only hydrogen and carbon atoms in addition to the ring hetero elements with quaternary ring nitrogen atoms

Definitions

  • the present invention relates to an ionic liquid purification method for preparing high purity ionic liquids which can be used as solvents for organic, inorganic and biochemical reactions or as electrolytic solutions of storage batteries, secondary batteries, or fuel batteries, by removing organic halide salts, organic salts, halide residues, acid residues or excess alkali metals from unpurified ionic liquids using liquid/liquid continuous extraction.
  • Ionic liquids are salts composed of cations and anions, and the most commonly available ionic liquids exist in the form of salts having alkylammonium, alkylphosphonium, N-alkylpyridinium, N.N'-dialkylimidazolium cations. To offer a low melting point, these cations are usually large molecules.
  • anion useful in ionic liquids examples include hexafluoro phosphate (PF ⁇ ), hexafluoro antimonite (SbF 6 ), tetrafluoro borate (BF 4 ), triflate (OTf), nonatriflate (NTfO), trifluoroacetate (TA), bis(trifluorosulfonyl)imide (NTf 2 ), and the like.
  • PF ⁇ hexafluoro phosphate
  • SbF 6 hexafluoro antimonite
  • BF 4 tetrafluoro borate
  • OTf triflate
  • NfO nonatriflate
  • TA trifluoroacetate
  • NTf 2 bis(trifluorosulfonyl)imide
  • Ionic liquids can serve as substitutes for conventional organic solvents used in chemical reactions for several reasons.
  • Low vapor pressure of the ionic liquids is one very important feature. That is, the ionic liquid has negligible vapor pressure and is capable of solving several problems of conventional organic solvents.
  • the ionic liquids are very highly polar, they are a very weakly coordinating solvent.
  • some ionic liquids are immiscible with water or organic solvents, and may have a two-phase structure. Owning to their excellent properties as solvents, the ionic liquids can take heterogeneous materials into the same phase. More recently, studies on features and uses of ionic liquids have been available.
  • Synthesis of ionic liquids is generally achieved by preparing organic halide salts using amine or phosphine and haloalkane and substituting the halides by quantitatively treating the prepared organic halide salt with metallic salts or acid.
  • a method for synthesizing 1 ,3-dialkylimidazolium ionic liquid, for example, which has been recently used, is shown in Fig. 3.
  • 1 ,3- dialkylimidazolium halide salt is first prepared using 1-alkylimidazole and haloalkane, and then halide is substituted with metallic salt or acid. The substitution is achieved by removing hydrogen-halogen using metallic salt or acid or precipitating in the form of metal-halogen.
  • 1 ,3- dialkylimidazolium sulfonate or triflate salt may be synthesized using 1- alkylimidazole and alkyl sulfonate or alkyl triflate, followed by substituting with acid. This substitution is performed by distilling and removing hydrogen- sulfonate or hydrogen-triflate using acid.
  • ionic liquids Major impurities produced during synthesis of ionic liquids are organic halide salts, organic salts, halide residues, acid residues, excess alkali metal or the like.
  • the halide ions are easily bonded with ionic liquid constituents, making it difficult to completely remove the same from the ionic liquids.
  • Typical examples of the halide include fluoride, chloride, bromide, and iodine.
  • the acid residues include hydrogen sulfonate, hydrogen carbonate, trifluoroacetate (triflate), and hydrogen halide
  • examples of the alkali metal include potassium, and sodium.
  • the amount of the organic halide salts, organic salts, halide residues, acid residues, or excess alkali metal increases.
  • a contamination problem due to impurities should be solved.
  • a halogen ion having a high covalent bonding capability reduces the activity of a catalyst.
  • the halogen ion is oxidized into halogen by reactants, and a reaction device may be eroded by the produced halogen.
  • residual halogen ions have an affect not only intrinsic physical properties but also density, flowability and electrical properties of ionic liquids. Further, when ionic liquids used as solvents of reactions, the halogen ions affect reactivity (Pure appl. chem. (2000).
  • the amount of halide residues ions in the ionic liquid must be controlled to be not greater than 1 ,000 ppm, and preferably not greater than 100 ppm. Under a more sensitive reaction condition, the amount of halide residues ions in the ionic liquid must be controlled to be not greater than 30 ppm, most preferably not greater than 5 ppm, and precipitation in the AgNO 3 reaction should be avoided.
  • Acid residues of the ionic liquid are unnecessary impurities that may participate in the reaction and act as a catalyst.
  • One way of measuring acid residues is to check the pH level of ionic water produced after washing ionic liquids with the ionic water.
  • the residual metal ions may affect physical, chemical properties of the ionic liquid, and traces of metal ions can be analyzed by elemental analysis or ion chromatography.
  • the residual impurities make it difficult to use ionic liquids in practice.
  • purification of ionic liquids is essentially necessary.
  • the ionic liquid has negligible vapor pressure and exists as a liquid at room temperature due to its low melting point. Also, the ionic liquid is very highly polar, it is dissolved in water very well. In detail, since the ionic liquid has negligible vapor pressure, it cannot be purified by a general purification method. Also, since the ionic liquid has a low melting point, it exists in a liquid phase at room temperature or low temperature, making it difficult to purify the same by recrystallization.
  • the water solubility of the ionic liquid is determined by anions contained therein.
  • Such anions as hexafluoro phosphate (PF 6 ), bis(trifluorosulfonylimide (NTf ), or hexafluoro antimonite (SbF 6 ), make the ionic liquid oil-soluble, and such anions as tetrafluoro borate (BF 4 ), triflate (OTf), or acetate (Oac), sulfonate (SO 3 CH 3 ) make the ionic liquid water- soluble (J. Phys. Chem B, vol 105, No.44, 2001).
  • the oil-soluble ionic liquid is synthesized using acid or salt and is not dissolved in water
  • washing the ionic liquids with water can applied to remove halide impurities, alkali metal impurities, or acid residues.
  • This method has a limitation in completely removing acid residues remaining in the ionic liquid to obtain high purity ionic liquids.
  • the water-soluble ionic liquid is dissolved in water (JOC 1999. 2133-2139), removing impurities by washing with water is disadvantageous in efficacy and yield.
  • the present inventors carried out earnest and constant research into highly efficient and economically effective purification method of ionic liquids. As a result, they developed a commercially large-scale, economically effective and highly efficient purification method for ionic liquids, in which impurities such as organic halide salts, organic salts, halide residues, acid residues, excess alkali metals and so on, are removed using liquid/liquid continuous extraction, thereby completing the present invention.
  • impurities such as organic halide salts, organic salts, halide residues, acid residues, excess alkali metals and so on
  • a purification method of ionic liquids comprising the steps of: preparing a mixed ionic liquid solution by dissolving unpurified ionic liquid in a solvent with ionic water alone or in combination with a cosolvent capable of forming the same phase with water and adding the prepared mixed ionic liquid solution to a continuous distillation extraction apparatus; adding an extracting organic solvent to the continuous distillation extraction apparatus; extracting ionic liquids by continuously refluxing the extracting organic solvent in the continuous distillation extraction apparatus at an appropriate temperature for an appropriate time; and removing an organic solvent by distilling ionic liquid organic solvent mixed solution recovered in a receiver of the continuous distillation extraction apparatus, and removing water by drying under reduced pressure.
  • the mixed ionic liquid solution is adjusted to have a concentration sufficient to dissolve the ionic liquid and to effectively separate impurities, that is, the solution comprising about 10% to 90% (w/w) to the solvent according to the solubility of the ionic liquid.
  • the purification efficiency may be affected by the concentration of a mixed ionic liquid solution to be extracted. That is, when the mixed ionic liquid solution is highly concentrated, residual impurities may also be extracted with the target ionic liquid, thereby lowering the extraction efficiency.
  • the concentration of the mixed ionic liquid solution that meets requirements of both impurity purification efficiency and yield must be determined in consideration of the solubility of the ionic liquid.
  • a cosolvent may be further added, and examples of the cosolvent useful in the present invention include solvents capable of forming the same phase with water, for example, methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, acetone, dioxane, or acetonitrile.
  • the extracting organic solvent is used for the purpose of maximizing the extraction efficiency during extraction and circulation processes, the extracting organic solvent should be capable of selectively extracting ionic liquids during extraction and removing impurities.
  • the organic solvent used is a solvent capable of forming two phases together with the mixed ionic liquid solution.
  • Preferred examples of the organic solvent include methylene chloride, ethyl acetate, ethyl ethanoate, tetrahydrofuran, toluene, or azeotropic mixed solvent thereof.
  • the extracting organic solvent is used in an amount of 1% to 3% (v/w) to the ionic liquid and continuously used for circulation.
  • the continuous distillation extraction apparatus can be selectively used depending on the property of the extracting organic solvent used. In other words, when an extracting organic solvent which is lighter than the ionic liquid solution is used, a distilled extraction convertible liquid/liquid continuous extractor can be used. When an extracting organic solvent which is heavier than the ionic liquid solution is used, a liquid/liquid extraction apparatus can be used. Also, any continuous distillation extractor that can be appreciated by one skilled in the art can be used compatibly with the two types of continuous distillation extractors.
  • the temperature of the mixed ionic liquid solution is adjusted to selectively extract ionic liquids only by increasing the solubility of impurities in the solvent.
  • the mixed ionic liquid solution to be purified by the extractor is kept at room temperature in the extracting step.
  • the mixed ionic liquid solution may be cooled or heated within the temperature range in which it may not be frozen or distilled.
  • the extracting organic solvent is boiled at a boiling point to then be refluxed.
  • the reflux termination time is 1 to 72 hours, preferably 2 to 24 hours, after the extracting step started.
  • the water-soluble or oil-soluble ionic liquid that can be purified by the purification method according to the present invention includes organic cations and anions, and are organic salts represented by formulas:
  • R, R', and R" are each independently a C ⁇ C ⁇ 2 primary alkyl, secondary alkyl, or tertiary alkyl group.
  • X " represents an anion capable of forming salts, e.g., MA n " , or RO " .
  • M represents elements of group VIII, IB, 2B, IIIA, or VA of Periodic Table of the Elements (CAS version), and A represents a halide, more preferably fluorine.
  • RO " is an alkylsulfonyl, haloalkylsulfonyl, phosphoryl, imide or carbonyl group.
  • ionic liquid useful in the present invention nclude imidazolium salts containing cations such as 1-ethyl-3-methyl- midazolium (EMIM), 1-methyl-3-propyl-imida ⁇ olium (PMIM), 1-butyl-3-methyl- midazolium (BMIM), 1-methyl-3-pentyl-imida ⁇ olium, PnMIM), 1-hexyl-3-methyl- imidazolium, HMIM), 1-heptyl-3-methyl-imidazolium (HpMIM), and an anion group of hexafluoroantimonate (SbF 6 ), hexafluorophosphate (PF 6 ), tetrafluoroborate (BF 4 ), bis(trifluorosulfonyl)imide (NTf 2 ), trifluoromethanesulfonate (OTf), acetate (OAc), or nitrate (N0 3 ).
  • EMIM 1-ethyl-3-methyl-
  • the entire process of the purification method according to the present invention may be repeatedly performed, preferably 1 to 3 times.
  • ionic liquids can be selectively extracted while removing impurities such as organic halide salts, organic salts, halide residues, acid residues, or excess alkali metal impurities, thereby synthesizing high purity ionic liquids in an economically effective, highly efficient manner.
  • impurities such as halide residues, alkali metal impurity, and so on, are present in an amount of not greater than 1 ,000 ppm, more preferably not greater than 100 ppm, and most preferably not greater than 5 ppm.
  • the ionic liquids have high purity of not less than 95%, more preferably not less than 99%, and most preferably not less than 99.9%. Therefore, the ionic liquid according to the present invention can be used as solvents for organic, inorganic and biochemical reactions and can be used as electrolytic solutions for storage batteries, secondary batteries and fuel batteries.
  • the purification method of the present invention a small amount of the extracting organic solvent is used and only the organic solvent is subjected to distillation and circulation, thereby extracting and purifying ionic liquids having negligible vapor pressure in an environmentally friendly, economic manner.
  • FIG. 1 is a sketch view of a liquid/liquid continuous extraction apparatus that is useful in the present invention
  • FIG. 2 is a sketch view of a distilled extraction convertible liquid/liquid continuous extractor that is useful in the present invention.
  • FIG. 3 is a schematic diagram illustrating a general synthesis method and purification method of 1 ,3-dialkylimidazolium ionic liquid.
  • the methylene chloride solution was collected from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 °C for 76 hours to remove water, thereby acquiring a desired ionic liquid, 1-butyl-3 ⁇ methylimidazolium hexafluorophosphate.
  • the obtained 1 -butyl-3- methylimidazolium hexafluorophosphate ionic liquid was repeatedly purified. Yield: 99 g (99%), residual chloride ions: 1 - 5 ppm (before repeated cycles of purification: 2 ⁇ 20 ppm), residual sodium ions ⁇ 3 ppm (before repeated cycles of purification: 1 ⁇ 5 ppm), water: 200 ppm.
  • the methylene chloride solution was collected from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 ° C for 76 hours to remove water, thereby acquiring a desired ionic liquid, 1-butyl-3-methylimidazolium hexafluoroantimonate.
  • the methylene chloride solution was recovered from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 ° C for 76 hours to remove water, thereby acquiring a desired ionic liquid, 1-butyl-3-methylimidazolium bis(trifluorosulfonyl)imide ionic liquid.
  • Example 4 Synthesis of 1-butyl-3-methylimidazolium tetrafluoroborate 70 g of 1-butyl-3-methylimidazolium chloride was added to 150 ml of acetone, and 57 g (1.1 eq.) of sodium tetrafluoroborate was added thereto and reacted for 24 hours, followed by filtering the reactant solution to remove salts. The resulting filtrate was distilled to remove acetone, giving an unpurified 1- butyl-3-methylimidazolium tetrafluoroborate ionic liquid.
  • the methylene chloride solution was collected from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 ° C for 76 hours to remove water, thereby acquiring a desired ionic liquid, 1 -butyl-3- methylimidazolium tetrafluoroborate ionic liquid.
  • the obtained 1 -butyl-3- methylimidazolium methanesulfonate ionic liquid was repeatedly purified.
  • the methylene chloride solution was collected from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 °C for 76 hours to remove water, thereby acquiring 1- ethyl-3-methylimidazolium bis(trifluorosulfonyl)imide ionic liquid.
  • the obtained 1 -ethyl-3- m ⁇ thylimida ⁇ olium bis(trifluorosulfonyl)imide ionic liquid was repeatedly purified.
  • Example 10 Synthesis of 1-ethyl-3-methylimidazolium methanesulfonate 101 g of 1-ethyl-3-methylimidazolium bromide was added to 250 ml of acetone, and 79 g (1.1 eq.) of potassium methanesulfonate was added thereto and reacted for 24 hours, followed by filtering the reactant solution to remove salts. The resulting filtrate was distilled to remove acetone, giving an unpurified 1-ethyl-3-methylimidazolium methanesulfonate ionic liquid.
  • the obtained 1-ethyl-3- methylimidazolium methanesulfonate ionic liquid was repeatedly purified. Yield: 90 g (90%), residual chloride ions: 2 - 5 ppm (before repeated cycles of purification: 2 - 50 ppm), residual potassium ions ⁇ 3 ppm (before repeated cycles of purification: 1 - 5 ppm), water: 200 ppm.
  • Example 11 Synthesis of li .M'-butyl. methyl pyrolidinium trifluoromethanesulfonate 71 g of N,N'-butyl, methyl pyrolidinium chloride was added to 250 ml of acetone, and 75 g (1.1 eq.) of potassium trifluoromethanesulfonate was added thereto and reacted for 24 hours, followed by filtering the reactant solution to remove salts. The resulting filtrate was distilled to remove acetone, giving an unpurified W,M'-butyl, methyl pyrolidinium trifluoromethanesulfonate ionic liquid.
  • methyl pyrolidinium trifluoromethanesulfonate ionic liquid was added a mixed solution of ionic water and methyl alcohol (1v/5v) to prepare a product having a concentration of about 30%, followed by transferring to a reflux device of the continuous distillation extraction apparatus. Then, methylene chloride was added to a receiver (3v/w) and refluxed at 39 - 40 ° C for about 48 hours.
  • methyl pyrolidinium methanesulfonate ionic liquid was added a mixed solution of ionic water and methyl alcohol (1v/5v) to prepare a product having a concentration of about 30%, followed by transferring to a reflux device of the continuous distillation extraction apparatus. Then, methylene chloride was added to a receiver (3v/w) and refluxed at 39 - 40 ° C for about 48 hours.
  • the methylene chloride solution was collected from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 ° C for 76 hours to remove water, thereby acquiring N,N'-butyl, methyl pyrolidinium methanesulfonate ionic liquid.
  • the obtained N,N'-butyl, methyl pyrolidinium methanesulfonate ionic liquid was repeatedly purified.
  • N-butyl pyridinium trifluoromethanesulfonate ionic liquid was repeatedly purified.
  • the methylene chloride solution was collected from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 ° C for 76 hours to remove water, thereby acquiring N-butyl pyridinium methanesulfonate ionic liquid.
  • N-butyl pyridinium methanesulfonate ionic liquid was repeatedly purified.
  • impurities such as organic halide salts, organic salts, halide residues, acid residues, or excess alkali metals can be effectively removed from ionic liquids using liquid/liquid continuous extraction.
  • impurities such as halide residues, alkali metal impurity, and so on, are present in an amount of not greater than 1 ,000 ppm, more preferably not greater than 100 ppm, and most preferably not greater than 5 ppm.
  • the ionic liquid has high purity of not less than 95%, more preferably not less than 99%, and most preferably not less than 99.9%. Therefore, the ionic liquid according to the present invention can be used as solvents for organic, inorganic and biochemical reactions and can used as electrolytic solutions for storage batteries, secondary batteries and fuel batteries.
  • the purification method according to the present invention enables mass production of high purity ionic liquids in an industrial scale effectively and economically using liquid/liquid continuous extraction.

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Abstract

Disclosed is an ionic liquid purification method for preparing high purity ionic liquids which can be used as solvents for organic, inorganic and biochemical reactions or as electrolytic solutions of storage batteries, secondary batteries, or fuel batteries, by removing organic halide salts, organic salts, halide residues, acid residues, excess alkali metals and so on, from unpurified ionic liquids using liquid/liquid continuous extraction.

Description

A PURIFICATION METHOD OF IONIC LIQUIDS TO OBTAIN THEIR HIGH
PURITY
Technical Field The present invention relates to an ionic liquid purification method for preparing high purity ionic liquids which can be used as solvents for organic, inorganic and biochemical reactions or as electrolytic solutions of storage batteries, secondary batteries, or fuel batteries, by removing organic halide salts, organic salts, halide residues, acid residues or excess alkali metals from unpurified ionic liquids using liquid/liquid continuous extraction.
Background Art
1 ,3-dialkylimidazolium cation based ionic liquids, which are liquid at room temperature, were first reported by Wilkes et al. in 1982. Although these ionic liquids having chloroaluminate anions, have been found to have various advantages, including existence in a liquid phase over a wide range of temperature, thermal stability and wide chemical window, they were proven to be reactive with specific substances and very sensitive to water. As ionic liquids which are stable in air and water, tetrafluoroborate anion based ionic liquids were developed by Wolkes and Zaworotko in 1992. Since then, numerous kinds of ionic liquids having different anions have been reported.
Ionic liquids are salts composed of cations and anions, and the most commonly available ionic liquids exist in the form of salts having alkylammonium, alkylphosphonium, N-alkylpyridinium, N.N'-dialkylimidazolium cations. To offer a low melting point, these cations are usually large molecules. Examples of the anion useful in ionic liquids include hexafluoro phosphate (PFβ), hexafluoro antimonite (SbF6), tetrafluoro borate (BF4), triflate (OTf), nonatriflate (NTfO), trifluoroacetate (TA), bis(trifluorosulfonyl)imide (NTf2), and the like. Recent research has demonstrated that ionic liquids can be used under room temperature as solvents for a wide range of chemical reactions including polymerization, hydrogenation, Friedel-Craft acylation and Diels-Alder reaction.
Ionic liquids can serve as substitutes for conventional organic solvents used in chemical reactions for several reasons. Low vapor pressure of the ionic liquids is one very important feature. That is, the ionic liquid has negligible vapor pressure and is capable of solving several problems of conventional organic solvents. Although the ionic liquids are very highly polar, they are a very weakly coordinating solvent. Also, some ionic liquids are immiscible with water or organic solvents, and may have a two-phase structure. Owning to their excellent properties as solvents, the ionic liquids can take heterogeneous materials into the same phase. More recently, studies on features and uses of ionic liquids have been available.
Synthesis of ionic liquids is generally achieved by preparing organic halide salts using amine or phosphine and haloalkane and substituting the halides by quantitatively treating the prepared organic halide salt with metallic salts or acid. A method for synthesizing 1 ,3-dialkylimidazolium ionic liquid, for example, which has been recently used, is shown in Fig. 3. In detail, 1 ,3- dialkylimidazolium halide salt is first prepared using 1-alkylimidazole and haloalkane, and then halide is substituted with metallic salt or acid. The substitution is achieved by removing hydrogen-halogen using metallic salt or acid or precipitating in the form of metal-halogen. Alternatively, 1 ,3- dialkylimidazolium sulfonate or triflate salt may be synthesized using 1- alkylimidazole and alkyl sulfonate or alkyl triflate, followed by substituting with acid. This substitution is performed by distilling and removing hydrogen- sulfonate or hydrogen-triflate using acid.
Major impurities produced during synthesis of ionic liquids are organic halide salts, organic salts, halide residues, acid residues, excess alkali metal or the like. In particular, the halide ions are easily bonded with ionic liquid constituents, making it difficult to completely remove the same from the ionic liquids. Typical examples of the halide include fluoride, chloride, bromide, and iodine. Examples of the acid residues include hydrogen sulfonate, hydrogen carbonate, trifluoroacetate (triflate), and hydrogen halide, and examples of the alkali metal include potassium, and sodium. In a case where ionic liquids are synthesized using low-priced acid or alkali metal salts, the amount of the organic halide salts, organic salts, halide residues, acid residues, or excess alkali metal, increases.
In order for ionic liquids to be used as solvents for large scale reactions, a contamination problem due to impurities should be solved. For example, when the ionic liquid is used as a solvent in a transition metal catalytic reaction, a halogen ion having a high covalent bonding capability reduces the activity of a catalyst. The halogen ion is oxidized into halogen by reactants, and a reaction device may be eroded by the produced halogen. Also, residual halogen ions have an affect not only intrinsic physical properties but also density, flowability and electrical properties of ionic liquids. Further, when ionic liquids used as solvents of reactions, the halogen ions affect reactivity (Pure appl. chem. (2000). 72(12), 2275-2287). In a reaction that is very sensitive to halide ions, the amount of halide residues ions in the ionic liquid must be controlled to be not greater than 1 ,000 ppm, and preferably not greater than 100 ppm. Under a more sensitive reaction condition, the amount of halide residues ions in the ionic liquid must be controlled to be not greater than 30 ppm, most preferably not greater than 5 ppm, and precipitation in the AgNO3 reaction should be avoided.
. Acid residues of the ionic liquid are unnecessary impurities that may participate in the reaction and act as a catalyst. One way of measuring acid residues is to check the pH level of ionic water produced after washing ionic liquids with the ionic water.
The residual metal ions may affect physical, chemical properties of the ionic liquid, and traces of metal ions can be analyzed by elemental analysis or ion chromatography. The residual impurities make it difficult to use ionic liquids in practice. Thus, in order to obtain pure ionic liquids to be used as appropriate reaction solvents or additives, purification of ionic liquids is essentially necessary.
One factor making it difficult to purify ionic liquids by a general technique is due to the physical properties of the ionic liquid. The ionic liquid has negligible vapor pressure and exists as a liquid at room temperature due to its low melting point. Also, the ionic liquid is very highly polar, it is dissolved in water very well. In detail, since the ionic liquid has negligible vapor pressure, it cannot be purified by a general purification method. Also, since the ionic liquid has a low melting point, it exists in a liquid phase at room temperature or low temperature, making it difficult to purify the same by recrystallization.
The water solubility of the ionic liquid is determined by anions contained therein. Such anions as hexafluoro phosphate (PF6), bis(trifluorosulfonylimide (NTf ), or hexafluoro antimonite (SbF6), make the ionic liquid oil-soluble, and such anions as tetrafluoro borate (BF4), triflate (OTf), or acetate (Oac), sulfonate (SO3CH3) make the ionic liquid water- soluble (J. Phys. Chem B, vol 105, No.44, 2001). Since the oil-soluble ionic liquid is synthesized using acid or salt and is not dissolved in water, washing the ionic liquids with water can applied to remove halide impurities, alkali metal impurities, or acid residues. This method, however, has a limitation in completely removing acid residues remaining in the ionic liquid to obtain high purity ionic liquids. Since the water-soluble ionic liquid is dissolved in water (JOC 1999. 2133-2139), removing impurities by washing with water is disadvantageous in efficacy and yield.
Other conventional attempts to remove halide residues, alkali metal ion, acid residues produced in the course of synthesizing ionic liquids include using silver tetrafluoroborate or reacting in propanone. However, these techniques are not effective and economic because they are costly and several problems may be presented during a scale-up process. Also, trace impurities may remain even after the purification process, disabling attainment of high purity ionic liquids (J. Electrochem.Soc, 1997. 144. 3881). In order to synthesize ionic liquids without impurities such as halide residues or alkali metal impurity, use of fluoroester compounds or alkylsulfonates, or use of carbene have been proposed. In the former case, however, there is a problem in that the acid residues used may bring undesired chemical reactions. In the latter case, a productivity problem may be presented during a scale-up process and expensive equipment is required.
In order to solve the various problems with conventional purification, the present inventors carried out earnest and constant research into highly efficient and economically effective purification method of ionic liquids. As a result, they developed a commercially large-scale, economically effective and highly efficient purification method for ionic liquids, in which impurities such as organic halide salts, organic salts, halide residues, acid residues, excess alkali metals and so on, are removed using liquid/liquid continuous extraction, thereby completing the present invention.
Disclosure of the Invention
It is an object of the present invention to provide a method of economically and efficiently purifying ionic liquids by removing impurities such as organic halide salts, organic salts, halide residues, acid residues, excess alkali metals and so on from unpurified ionic liquids.
It is another object of the present invention to provide a method of preparing ionic liquids with high purity of 95% or greater, which can be used as solvents for organic, inorganic and biochemical reactions or as electrolytic solutions of storage batteries, secondary batteries, or fuel batteries. In accordance with an aspect of the present invention, there is provided a purification method of ionic liquids, comprising the steps of: preparing a mixed ionic liquid solution by dissolving unpurified ionic liquid in a solvent with ionic water alone or in combination with a cosolvent capable of forming the same phase with water and adding the prepared mixed ionic liquid solution to a continuous distillation extraction apparatus; adding an extracting organic solvent to the continuous distillation extraction apparatus; extracting ionic liquids by continuously refluxing the extracting organic solvent in the continuous distillation extraction apparatus at an appropriate temperature for an appropriate time; and removing an organic solvent by distilling ionic liquid organic solvent mixed solution recovered in a receiver of the continuous distillation extraction apparatus, and removing water by drying under reduced pressure.
In the above-described method, the mixed ionic liquid solution is adjusted to have a concentration sufficient to dissolve the ionic liquid and to effectively separate impurities, that is, the solution comprising about 10% to 90% (w/w) to the solvent according to the solubility of the ionic liquid. In order to effectively remove impurities and purify an ionic liquid, the purification efficiency may be affected by the concentration of a mixed ionic liquid solution to be extracted. That is, when the mixed ionic liquid solution is highly concentrated, residual impurities may also be extracted with the target ionic liquid, thereby lowering the extraction efficiency. When the mixed ionic liquid solution is lightly concentrated, the removal efficiency of residual impurities increased but the amount of the residual impurities extracted per hour may be reduced. To achieve effective extraction, the concentration of the mixed ionic liquid solution that meets requirements of both impurity purification efficiency and yield must be determined in consideration of the solubility of the ionic liquid.
In order to increase the extraction efficiency, when necessary, a cosolvent may be further added, and examples of the cosolvent useful in the present invention include solvents capable of forming the same phase with water, for example, methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, acetone, dioxane, or acetonitrile.
The extracting organic solvent is used for the purpose of maximizing the extraction efficiency during extraction and circulation processes, the extracting organic solvent should be capable of selectively extracting ionic liquids during extraction and removing impurities. Also, the organic solvent used is a solvent capable of forming two phases together with the mixed ionic liquid solution. Preferred examples of the organic solvent include methylene chloride, ethyl acetate, ethyl ethanoate, tetrahydrofuran, toluene, or azeotropic mixed solvent thereof. Preferably, the extracting organic solvent is used in an amount of 1% to 3% (v/w) to the ionic liquid and continuously used for circulation.
The continuous distillation extraction apparatus can be selectively used depending on the property of the extracting organic solvent used. In other words, when an extracting organic solvent which is lighter than the ionic liquid solution is used, a distilled extraction convertible liquid/liquid continuous extractor can be used. When an extracting organic solvent which is heavier than the ionic liquid solution is used, a liquid/liquid extraction apparatus can be used. Also, any continuous distillation extractor that can be appreciated by one skilled in the art can be used compatibly with the two types of continuous distillation extractors.
According to the purification method of the present invention, in the extracting step, the temperature of the mixed ionic liquid solution is adjusted to selectively extract ionic liquids only by increasing the solubility of impurities in the solvent. Generally, the mixed ionic liquid solution to be purified by the extractor is kept at room temperature in the extracting step. However, when necessary, the mixed ionic liquid solution may be cooled or heated within the temperature range in which it may not be frozen or distilled. Also, in the extracting step, the extracting organic solvent is boiled at a boiling point to then be refluxed. The reflux termination time is 1 to 72 hours, preferably 2 to 24 hours, after the extracting step started.
After the extracting step is completed, the mixed solution of the extracted ionic liquid and the organic solvent is distilled to remove the extracting organic solvent, and dried under reduced pressure at 25 ~ 300 °C to remove residual water. The water-soluble or oil-soluble ionic liquid that can be purified by the purification method according to the present invention includes organic cations and anions, and are organic salts represented by formulas:
Figure imgf000010_0001
R
I, --S. _-Q tt* .- r*ι c+ X
^\. *" l@l x N R
Figure imgf000010_0002
(R)4N+ X and (R)4P+ X
wherein R, R', and R" are each independently a Cι~Cι2 primary alkyl, secondary alkyl, or tertiary alkyl group.
X" represents an anion capable of forming salts, e.g., MAn ", or RO".
Here, M represents elements of group VIII, IB, 2B, IIIA, or VA of Periodic Table of the Elements (CAS version), and A represents a halide, more preferably fluorine. RO" is an alkylsulfonyl, haloalkylsulfonyl, phosphoryl, imide or carbonyl group.
Specific examples of the ionic liquid useful in the present invention nclude imidazolium salts containing cations such as 1-ethyl-3-methyl- midazolium (EMIM), 1-methyl-3-propyl-imida∑olium (PMIM), 1-butyl-3-methyl- midazolium (BMIM), 1-methyl-3-pentyl-imida∑olium, PnMIM), 1-hexyl-3-methyl- imidazolium, HMIM), 1-heptyl-3-methyl-imidazolium (HpMIM), and an anion group of hexafluoroantimonate (SbF6), hexafluorophosphate (PF6), tetrafluoroborate (BF4), bis(trifluorosulfonyl)imide (NTf2), trifluoromethanesulfonate (OTf), acetate (OAc), or nitrate (N03).
To increase purifying effects, the entire process of the purification method according to the present invention may be repeatedly performed, preferably 1 to 3 times.
According to the purification method of the present invention, only ionic liquids can be selectively extracted while removing impurities such as organic halide salts, organic salts, halide residues, acid residues, or excess alkali metal impurities, thereby synthesizing high purity ionic liquids in an economically effective, highly efficient manner. In the ionic liquid prepared according to the purification method, impurities such as halide residues, alkali metal impurity, and so on, are present in an amount of not greater than 1 ,000 ppm, more preferably not greater than 100 ppm, and most preferably not greater than 5 ppm. Also, the ionic liquids have high purity of not less than 95%, more preferably not less than 99%, and most preferably not less than 99.9%. Therefore, the ionic liquid according to the present invention can be used as solvents for organic, inorganic and biochemical reactions and can be used as electrolytic solutions for storage batteries, secondary batteries and fuel batteries.
Also, according to the purification method of the present invention, a small amount of the extracting organic solvent is used and only the organic solvent is subjected to distillation and circulation, thereby extracting and purifying ionic liquids having negligible vapor pressure in an environmentally friendly, economic manner.
Brief Description of the Drawings
FIG. 1 is a sketch view of a liquid/liquid continuous extraction apparatus that is useful in the present invention; FIG. 2 is a sketch view of a distilled extraction convertible liquid/liquid continuous extractor that is useful in the present invention; and
FIG. 3 is a schematic diagram illustrating a general synthesis method and purification method of 1 ,3-dialkylimidazolium ionic liquid.
Best mode for carrying out the Invention
The present invention will now be described in more detail through embodiments.
BCAHHPLES
Example 1: Synthesis of 1-butyl-3-methylimidazolium hexafluorophosphate
57 g of 1-butyl-3-methylimidazolium chloride was added to 150 ml of acetone, and 79 g (1.1 eq.) of potassium hexafluorophosphate was added thereto and reacted for 24 hours, followed by filtering the reactant solution to remove salts. The resulting filtrate was distilled to remove acetone, giving an unpurified 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid.
To the unpurified 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid was added a mixed solution of ionic water and methyl alcohol (1v/3v) to prepare a product having a concentration of about 50%, followed by transferring to a reflux device of the continuous distillation extraction apparatus. Then, methylene chloride was added to a receiver (3v/w) and refluxed at 39 ~ 40 °C for about 12 hours. Then, the methylene chloride solution was collected from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 °C for 76 hours to remove water, thereby acquiring a desired ionic liquid, 1-butyl-3~methylimidazolium hexafluorophosphate.
Yield: 100 g (90%), halide residues ions: 2 ~ 20 ppm (before purification: 1000 ppm), residual sodium ions: 1 ~ 5 ppm (before purification: 30 ppm), water: 200 ppm.
To achieve high purity ionic liquids, the obtained 1 -butyl-3- methylimidazolium hexafluorophosphate ionic liquid was repeatedly purified. Yield: 99 g (99%), residual chloride ions: 1 - 5 ppm (before repeated cycles of purification: 2 ~ 20 ppm), residual sodium ions < 3 ppm (before repeated cycles of purification: 1 ~ 5 ppm), water: 200 ppm.
Example 2: Synthesis of 1-butyl-3-methylimidazolium hexafluoroantimonate
50 g of 1-butyl-3-methylimidazolium chloride was added to 150 ml of acetone, and 81 g (1.1 eq.) of potassium hexafluorophosphate was added thereto and reacted for 24 hours, followed by filtering the reactant solution to remove salts. The resulting filtrate was distilled to remove acetone, giving an unpurified 1-butyl-3-methylimidazolium hexafluoroantimonate ionic liquid.
To the unpurified 1-butyl-3-methylimidazolium hexafluoroantimonate ionic liquid was added a mixed solution of ionic water and methyl alcohol (1v/3v) to prepare a product having a concentration of about 50%, followed by transferring to a reflux device of the continuous distillation extraction apparatus. Then, methylene chloride was added to a receiver (3v/w) and refluxed at 39 ~ 40 °C for about 12 hours. Then, the methylene chloride solution was collected from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 °C for 76 hours to remove water, thereby acquiring a desired ionic liquid, 1-butyl-3-methylimidazolium hexafluoroantimonate.
Yield: 100 g (93%), residual chloride ions: 2 ~ 20 ppm (before purification: 500 ppm), residual sodium ions: 1 ~ 5 ppm (before purification: 7 ppm), water: 200 ppm. To achieve high purity ionic liquids, the obtained 1 -butyl-3- methylimidazolium hexafluoroantimonate ionic liquid was repeatedly purified.
Yield: 99 g (99%), residual chloride ions: 1 ~ 5 ppm (before repeated cycles of purification: 2 ~ 20 ppm), residual sodium ion < 3ppm (before repeated cycles of purification: 1 ~ 5 ppm), water: 200 ppm. Example 3: Synthesis of 1-butyl-3-methylimidazolium bisftrifluorosulfonvDimide
54 g of 1-butyl-3-methylimida∑olium chloride was added to 150 ml of acetone, and 68 g (1.1 eq.) of lithium bis(trifluorosulfonyl)imide was added thereto and reacted for 24 hours, followed by filtering the reactant solution to remove salts. The resulting filtrate was distilled to remove acetone, giving an unpurified 1-butyl-3-methylimidazolium bis(trifluorosulfonly)imide ionic liquid.
To the unpurified 1-butyl-3-methylimidazolium bis(trifluorosulfonyl)imide ionic liquid was added a mixed solution of ionic water and methyl alcohol (1v/3v) to prepare a product having a concentration of about 50%, followed by transferring to a reflux device of the continuous distillation extraction apparatus. Then, methylene chloride was added to a receiver (3v/w) and refluxed at 39 ~ 40 °C for about 12 hours. Then, the methylene chloride solution was recovered from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 °C for 76 hours to remove water, thereby acquiring a desired ionic liquid, 1-butyl-3-methylimidazolium bis(trifluorosulfonyl)imide ionic liquid.
Yield: 100 g (95%), residual chloride ions: 2 ~ 20 ppm (before purification: 100 ppm), residual sodium ions: 1 ~ 5 ppm (before purification: 30 ppm), water: 200 ppm.
To achieve high purity ionic liquids, the obtained 1 -butyl-3- methylimidazolium bis(trifluorosulfonyl)imide ionic liquid was repeatedly purified.
Yield: 99 g (99%), residual chloride ions: 1 ~ 5 ppm (before repeated cycles of purification: 2 ~ 20 ppm), residual sodium ions > 3 ppm (before repeated cycles of purification: 1 ~ 5 ppm), water: 200 ppm.
Example 4: Synthesis of 1-butyl-3-methylimidazolium tetrafluoroborate 70 g of 1-butyl-3-methylimidazolium chloride was added to 150 ml of acetone, and 57 g (1.1 eq.) of sodium tetrafluoroborate was added thereto and reacted for 24 hours, followed by filtering the reactant solution to remove salts. The resulting filtrate was distilled to remove acetone, giving an unpurified 1- butyl-3-methylimidazolium tetrafluoroborate ionic liquid.
To the unpurified 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid was added ionic water to prepare a product having a concentration of about 50%, followed by transferring to a reflux device of the continuous distillation extraction apparatus. Then, methylene chloride was added to a receiver (3v/w) and refluxed at 39 ~ 40 °C for about 24 hours. Then, the methylene chloride solution was collected from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 °C for 76 hours to remove water, thereby acquiring a desired ionic liquid, 1 -butyl-3- methylimidazolium tetrafluoroborate ionic liquid.
Yield: 100 g (93%), residual chloride ions: 2 ~ 20 ppm (before purification: 3500 ppm), residual sodium ions: 1 ~ 5 ppm (before purification: 300 ppm), water: 500 ppm.
To achieve high purity ionic liquids, the obtained 1 -butyl-3- methylimidazolium tetrafluoroborate ionic liquid was repeatedly purified.
Yield: 95 g (95%), residual chloride ions: 1 ~ 5 ppm (before repeated cycles of purification: 2 ~ 20 ppm), residual sodium ions < 3 ppm (before repeated cycles of purification: 1 ~ 5 ppm), water: 500 ppm.
Example 5: Synthesis of 1-butyl-3-methylimidazolium trifluoromethanesulfonate
65 g of 1-butyl-3-methylimidazolium trifluoromethanesulfonate was added to 150 ml of acetone, and 70 g (1.1 eq.) of potassium trifluoromethanesulfonate was added thereto and reacted for 24 hours, followed by filtering the reactant solution to remove salts. The resulting filtrate was distilled to remove acetone, giving an unpurified 1-butyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid. To the unpurified 1-butyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid was added ionic water to prepare a product having a concentration of about 50%, followed by transferring to a reflux device of the continuous distillation extraction apparatus. Then, methylene chloride was added to a receiver (3v/w) and refluxed at 39 ~ 40 °C for about 36 hours. Then, the methylene chloride solution was collected from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 °C for 76 hours to remove water, thereby acquiring 1-butyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid. Yield: 100 g (93%), residual chloride ions: 2 - 20 ppm (before purification: 3,500 ppm), residual potassium ions: 1 ~ 5 ppm (before purification: 300 ppm), water: 300 ppm.
To achieve high purity ionic liquids, the obtained 1 -butyl-3- methylimidazolium trifluoromethanesulfonate ionic liquid was repeatedly purified.
Yield: 95 g (95%), residual chloride ions: 1 ~ 5 ppm (before repeated cycles of purification: 2 ~ 20 ppm), residual potassium ions < 3 ppm (before repeated cycles of purification: 1 ~ 5 ppm), water: 300 ppm.
Example 6: Synthesis of 1-butyl-3-methylimidazolium methanesulfonate
70 g of 1-butyl-3-methylimidazolium chloride was added to 150 ml of acetone, and 71 g (1.1 eq.) of potassium methanesulfonate was added thereto and reacted for 24 hours, followed by filtering the reactant solution to remove salts. The resulting filtrate was distilled to remove acetone, giving an unpurified 1-butyl-3-methylimidazolium methanesulfonate ionic liquid.
To the unpurified 1-butyl-3-methylimidazolium methanesulfonate ionic liquid was added ionic water to prepare a product having a concentration of about 75%, followed by transferring to a reflux device of the continuous distillation extraction apparatus. Then, methylene chloride was added to a receiver (3v/w) and refluxed at 39 ~ 40 °C for about 48 hours. Then, the methylene chloride solution was collected from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 °C for 76 hours to remove water, thereby acquiring 1-butyl-3-methylimida∑olium methanesulfonate ionic liquid.
Yield: 100 g (93%), residual chloride ions: 2 - 50 ppm (before purification: 8000 ppm), residual potassium ions: 1 - 5 ppm (before purification: 300 ppm), water: 50 ppm.
To achieve high purity ionic liquids, the obtained 1 -butyl-3- methylimidazolium methanesulfonate ionic liquid was repeatedly purified.
Yield: 90 g (90%), residual chloride ions: 2 - 5 ppm (before repeated cycles of purification: 2 - 50 ppm), residual potassium ions < 3 ppm (before repeated cycles of purification: 1 - 5 ppm), water: 200 ppm.
Example 7: Synthesis of 1-ethyl-3-methylimidazolium bisrtrifluorosulfonvπimide
79 g of 1-ethyl-3-methylimidazolium bromide was added to 250 ml of acetone, and 76 g (1.1 eq.) of lithium bis(trifluorosulfonyl)imide was added thereto and reacted for 24 hours, followed by filtering the reactant solution to remove salts. The resulting filtrate was distilled to remove acetone, giving an unpurified 1-ethyl-3-methylimidazolium bis(trifluorosulfonyl)imide ionic liquid.
To the unpurified 1-ethyl-3-methylimidazolium bis(trifluorosulfonyl)imide ionic liquid was added a mixed solution of ionic water and methyl alcohol (1v/3v) to prepare a product having a concentration of about 50%, followed by transferring to a reflux device of the continuous distillation extraction apparatus. Then, methylene chloride was added to a receiver (3v/w) and refluxed at 39 - 40 °C for about 12 hours. Then, the methylene chloride solution was collected from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 °C for 76 hours to remove water, thereby acquiring 1- ethyl-3-methylimidazolium bis(trifluorosulfonyl)imide ionic liquid.
Yield: 100 g (95%), residual bromide ions: 2 - 100 ppm (before purification: 100 ppm), residual sodium ions: 1 - 5 ppm (before purification: 30 ppm), water: 200 ppm.
To achieve high purity ionic liquids, the obtained 1 -ethyl-3- mβthylimida∑olium bis(trifluorosulfonyl)imide ionic liquid was repeatedly purified.
Yield: 99 g (99%), residual chloride ion: 1 - 5 ppm (before repeated cycles of purification: 2 - 20 ppm), residual sodium ions > 3 ppm (before repeated cycles of purification: 1 - 5 ppm), water: 200 ppm.
Example 8: Synthesis of 1-ethyl-3-methylimidazolium tetrafluoroborate
114 g of 1-ethyl-3-methylimidazolium bromide was added to 250 ml of acetone, and 72 g (1.1 eq.) of sodium tetrafluoroborate was added thereto and reacted for 24 hours, followed by filtering the reactant solution to remove salts. The resulting filtrate was distilled to remove acetone, giving an unpurified 1- ethyl-3-methylimidazolium tetrafluoroborate ionic liquid.
To the unpurified 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid was added ionic water to prepare a product having a concentration of about 20%, followed by transferring to a reflux device of the continuous distillation extraction apparatus. Then, methylene chloride was added to a receiver (3v/w) and refluxed at 39 - 40 °C for about 24 hours. Then, the methylene chloride solution was collected from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 °C for 76 hours to remove water, thereby acquiring 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid.
Yield: 100 g (85%), residual chloride ions: 2 - 20 ppm (before purification: 3500 ppm), residual sodium ions: 1 - 5 ppm (before purification: 300 ppm), water: 500 ppm. To achieve high purity ionic liquids, the obtained 1 -ethyl-3- methylimidazolium tetrafluoroborate ionic liquid was repeatedly purified.
Yield: 95 g (95 %), residual chloride ions: 1 - 5 ppm (before repeated cycles of purification: 2 - 20 ppm), residual sodium ions < 3 ppm (before repeated cycles of purification: 1 - 5 ppm), water: 500 ppm.
Example 9: Synthesis of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate
85 g of 1-ethyl-3-methylimidazolium bromide was added to 250 ml of acetone, and 84 g (1.1 eq.) of potassium trifluoromethanesulfonate was added thereto and reacted for 24 hours, followed by filtering the reactant solution to remove salts. The resulting filtrate was distilled to remove acetone, giving an unpurified 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid.
To the unpurified 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid was added ionic water to prepare a product having a concentration of about 30%, followed by transferring to a reflux device of the continuous distillation extraction apparatus. Then, methylene chloride was added to a receiver (3v/w) and refluxed at 39 - 40 °C for about 36 hours. Then, the methylene chloride solution was collected from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 °C for 76 hours to remove water, thereby acquiring 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid.
Yield: 100 g (86%), residual chloride ions: 2 - 20 ppm (before purification: 2,500 ppm), residual potassium ions: 1 - 5 ppm (before purification: 300 ppm), water: 300 ppm.
To achieve high purity ionic liquids, the obtained 1 -ethyl-3- methylimidazoliurn trifluoromethanesulfonate ionic liquid was repeatedly
Yield: 95 g (95%), residual chloride ions: 1 - 5 ppm (before repeated cycles of purification: 2 - 20 ppm), residual potassium ions < 3 ppm (before repeated cycles of purification: 1 - 5 ppm), water: 300 ppm.
Example 10: Synthesis of 1-ethyl-3-methylimidazolium methanesulfonate 101 g of 1-ethyl-3-methylimidazolium bromide was added to 250 ml of acetone, and 79 g (1.1 eq.) of potassium methanesulfonate was added thereto and reacted for 24 hours, followed by filtering the reactant solution to remove salts. The resulting filtrate was distilled to remove acetone, giving an unpurified 1-ethyl-3-methylimidazolium methanesulfonate ionic liquid. To the unpurified 1-ethyl-3-methylimidazolium methanesulfonate ionic liquid was added ionic water to prepare a product having a concentration of about 75%, followed by transferring to a reflux device of the continuous distillation extraction apparatus. Then, methylene chloride was added to a receiver (3v/w) and refluxed at 39 - 40 °C for about 48 hours. Then, the methylene chloride solution was collected from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 °C for 76 hours to remove water, thereby acquiring 1-ethyl-3-methylimidazolium methanesulfonate ionic liquid. Yield: 100 g (85%), residual chloride ions: 2 - 50 ppm (before purification: 8000 ppm), residual potassium ions: 1 - 5ppm (before purification: 300 ppm), water: 50 ppm.
To achieve high purity ionic liquids, the obtained 1-ethyl-3- methylimidazolium methanesulfonate ionic liquid was repeatedly purified. Yield: 90 g (90%), residual chloride ions: 2 - 5 ppm (before repeated cycles of purification: 2 - 50 ppm), residual potassium ions < 3 ppm (before repeated cycles of purification: 1 - 5 ppm), water: 200 ppm.
Example 11 : Synthesis of li .M'-butyl. methyl pyrolidinium trifluoromethanesulfonate 71 g of N,N'-butyl, methyl pyrolidinium chloride was added to 250 ml of acetone, and 75 g (1.1 eq.) of potassium trifluoromethanesulfonate was added thereto and reacted for 24 hours, followed by filtering the reactant solution to remove salts. The resulting filtrate was distilled to remove acetone, giving an unpurified W,M'-butyl, methyl pyrolidinium trifluoromethanesulfonate ionic liquid.
To the unpurified M,M'-butyl, methyl pyrolidinium trifluoromethanesulfonate ionic liquid was added a mixed solution of ionic water and methyl alcohol (1v/5v) to prepare a product having a concentration of about 30%, followed by transferring to a reflux device of the continuous distillation extraction apparatus. Then, methylene chloride was added to a receiver (3v/w) and refluxed at 39 - 40 °C for about 48 hours. Then, the methylene chloride solution was collected from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 °C for 76 hours to remove water, thereby acquiring N,N'-buty I, methyl pyrolidinium trifluoromethanesulfonate ionic liquid.
Yield: 100 g (86%), residual chloride ions: 5 - 100 ppm (before purification: 15,000 ppm), residual potassium ions 1 - 5 ppm (before purification: 300 ppm), water: 500 ppm. To achieve high purity ionic liquids, the obtained N,N'-butyl, methyl pyrolidinium trifluoromethanesulfonate ionic liquid was repeatedly purified.
Yield: 95 g (95%), residual chloride ions: 2 - 5 ppm (before repeated cycles of purification: 5~ 100 ppm), residual potassium ions < 3 ppm (before repeated cycles of purification: 1 - 5 ppm), water: 500 ppm.
Example 12: Synthesis of N.N '-butyl, methyl pyrolidinium methanesulfonate
78 g of N,iS!'-butyl, methyl pyrolidinium chloride was added to 250 ml of acetone, and 66 g (1.1 eq.) of potassium methanesulfonate was added thereto and reacted for 24 hours, followed by filtering the reactant solution to remove salts. The resulting filtrate was distilled to remove acetone, giving an unpurified N,N'-butyl, methyl pyrolidinium methanesulfonate ionic liquid.
To the unpurified N,N'-butyl, methyl pyrolidinium methanesulfonate ionic liquid was added a mixed solution of ionic water and methyl alcohol (1v/5v) to prepare a product having a concentration of about 30%, followed by transferring to a reflux device of the continuous distillation extraction apparatus. Then, methylene chloride was added to a receiver (3v/w) and refluxed at 39 - 40 °C for about 48 hours. Then, the methylene chloride solution was collected from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 °C for 76 hours to remove water, thereby acquiring N,N'-butyl, methyl pyrolidinium methanesulfonate ionic liquid.
Yield: 100 g (90%), residual chloride ions: 5 - 200 ppm (before purification: 8000 ppm), residual sodium ions: 1 - 5ppm (before purification: 100 ppm), water: 500 ppm.
To achieve high purity ionic liquids, the obtained N,N'-butyl, methyl pyrolidinium methanesulfonate ionic liquid was repeatedly purified.
Yield: 90 g (90%), residual chloride ions: 2 - 5 ppm (before repeated cycles of purification: 5 - 200 ppm), residual potassium ions < 3 ppm (before repeated cycles of purification: 1 - 5 ppm), water: 500 ppm.
Example 13: Synthesis of N-butyl pyridinium trifluoromethanesulfonate
70 g of N-butyl pyridinium chloride was added to 200 ml of acetone, and
77 g (1.1 eq.) of potassium trifluoromethanesulfonate was added thereto and reacted for 24 hours, followed by filtering the reactant solution to remove salts.
The resulting filtrate was distilled to remove acetone, giving an unpurified N- butyl pyridinium trifluoromethanesulfonate ionic liquid.
To the unpurified N-butyl pyridinium trifluoromethanesulfonate ionic liquid was added a mixed solution of ionic water and methyl alcohol (1v/5v) to prepare a product having a concentration of about 30%, followed by transferring to a reflux device of the continuous distillation extraction apparatus. Then, methylene chloride was added to a receiver (3v/w) and refluxed at 39 - 40 °C for about 36 hours. Then, the methylene chloride solution was collected from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 °C for 76 hours to remove water, thereby acquiring U- butyl pyridinium trifluoromethanesulfonate ionic liquid.
Yield: 100 g (95%), residual chloride ions: 5 - 200 ppm (before purification: 15,000 ppm), residual potassium ions: 1 ~ 5ppm (before purification: 300 ppm), water: 500 ppm.
To achieve high purity ionic liquids, the obtained N-butyl pyridinium trifluoromethanesulfonate ionic liquid was repeatedly purified.
Yield: 95 g (95%), residual chloride ions: 2 - 5 ppm (before repeated cycles of purification: 5 - 200 ppm), residual potassium ion: < 3 ppm (before repeated cycles of purification: 1 - 5ppm), water: 500 ppm.
Example 14: Synthesis of N-butyl pyridinium methanesulfonate
73 g of N-butyl pyridinium chloride was added to 200 ml of acetone, and
64 g (1.1 eq.) of potassium methanesulfonate was added thereto and reacted for 24 hours, followed by filtering the reactant solution to remove salts. The resulting filtrate was distilled to remove acetone, giving an unpurified N-butyl pyridinium methanesulfonate ionic liquid.
To the unpurified N-butyl pyridinium methanesulfonate ionic liquid was added a mixed solution of ionic water and methyl alcohol (1v/5v) to prepare a product having a concentration of about 30%, followed by transferring to a reflux device of the continuous distillation extraction apparatus. Then, methylene chloride was added to a receiver (3v/w) and refluxed at 39 - 40 °C for about 48 hours. Then, the methylene chloride solution was collected from the receiver of the continuous distillation extraction apparatus and methylene chloride was distilled to be removed, followed by drying under reduced pressure at 60 °C for 76 hours to remove water, thereby acquiring N-butyl pyridinium methanesulfonate ionic liquid.
Yield: 100 g (95%), residual chloride ions: 5 - 200 ppm (before purification: 15,000 ppm), residual potassium ions: 1 - 5ppm (before purification: 300 ppm), water: 50 ppm.
To achieve high purity ionic liquids, the obtained N-butyl pyridinium methanesulfonate ionic liquid was repeatedly purified.
Yield: 90 g (90%), residual chloride ions: 2 - 5 ppm (before repeated cycles of purification: 5 - 200 ppm), residual potassium ions < 3 ppm (before repeated cycles of purification: 1 - 5 ppm), water: 200 ppm.
Industrial Applicability
According to the purification method of the present invention, impurities such as organic halide salts, organic salts, halide residues, acid residues, or excess alkali metals can be effectively removed from ionic liquids using liquid/liquid continuous extraction. In the ionic liquid prepared according to the purification method, impurities such as halide residues, alkali metal impurity, and so on, are present in an amount of not greater than 1 ,000 ppm, more preferably not greater than 100 ppm, and most preferably not greater than 5 ppm. Also, the ionic liquid has high purity of not less than 95%, more preferably not less than 99%, and most preferably not less than 99.9%. Therefore, the ionic liquid according to the present invention can be used as solvents for organic, inorganic and biochemical reactions and can used as electrolytic solutions for storage batteries, secondary batteries and fuel batteries.
Further, the purification method according to the present invention enables mass production of high purity ionic liquids in an industrial scale effectively and economically using liquid/liquid continuous extraction.

Claims

What is claimed:
1. A purification method of ionic liquids, comprising the steps of: preparing a mixed ionic liquid solution by dissolving unpurified ionic liquid in a solvent with ionic water alone "or in combination with a cosolvent capable of forming the same phase with water and adding the prepared mixed ionic liquid solution to a continuous distillation extraction apparatus; adding an extracting organic solvent to the continuous distillation extraction apparatus; extracting ionic liquids by continuously refluxing the extracting organic solvent in the continuous distillation extraction apparatus at an appropriate temperature for an appropriate time; and removing an organic solvent by distilling ionic liquid organic solvent mixed solution recovered in a receiver of the continuous distillation extraction apparatus, and removing water by drying under reduced pressure.
2. A purification method of ionic liquids for preparing high purity ionic liquids, comprising all the steps of the purification method of claim 1 are repeatedly performed.
3. The method of claim 1 or 2, wherein the cosolvent is methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, acetone, dioxane, acetonitrile, or mixtures thereof, and the extracting organic solvent is methylene chloride, ethyl acetate, ethyl ethanoate, tetrahydrofuran, toluene, or azeotropic mixtures thereof.
4. The method of claim 1 or 2, wherein the mixed ionic solution includes the ionic liquid in the range of about 10% to about 90% (w/w) to the solvent, and the extracting organic solvent is added at about 1 to about 3 (v/w).
5. The method of claim 1 or 2, wherein in the extracting step, the extracting organic solvent is boiled at its boiling point for reflux, and the reflux termination time is 1 to 72 hours, and preferably 2 to 24 hours, after the extracting step started.
6. The method of claim 1 or 2, wherein the ionic liquid is wafer- soluble or oil-soluble, and is one selected from the group consisting of organic salt represented by the following formulas:
Figure imgf000026_0001
N R
S) γ- ( -*' x" ^N-R- x-
I
R
(R)4N+ X~ and (R)4P+ χ~
wherein R, R', and R" are each independently a Cι~Cι2 primary al secondary alkyl, or tertiary alkyl group;
X" represents an anion capable of forming salts, MAn ", or RO", where M represents elements of group VIII, IB, 2B, IIIA, or VA of Periodic Table of the Elements, and A represents a halide, and RO" is an alkylsulfonyl, haloalkylsulfonyl, phosphoryl, imide or carbonyl group.
7. The method of claim 6, wherein the ionic liquid is imidazolium salts containing cations such as 1-efhyl-3-methyl-irnidazolium (EMIM), 1- um (PMIM), 1-butyl-3-methyl-imidazolium (BMIM), 1- um (PnMIM), 1-hexyl-3-methyl-imidazolium (HMIM), 1-
Figure imgf000027_0001
um (HpMIM), and an anion group of hexafluoroantimonate (SbFβ), hexafluorophosphate (PFβ), tetrafluoroborate
(BF4), bis(trifluorosulfonyl)imide (NTf2), trifluoromethanesulfonate (OTf), acetate (OAc), or nitrate (NO3).
8. The method of claim 1 or 2, wherein the ionic liquid comprises halide residues or alkali metal impurity in an amount of not greater than 1 ,000 ppm, more preferably not greater than 100 ppm, and most preferably not greater than 5 ppm, and has high purity of not less than 95%, more preferably not less than 99%, and most preferably not less than 99.9%.
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DE102004040016A1 (en) * 2004-08-16 2006-02-23 Friedrich-Schiller-Universität Jena Preparation of ionic liquids, useful as electrolytes, comprises reacting anion compounds with heterocyclic compounds and phosphor containing compounds, reacting the resulting product with e.g. ether and continuously isolating the product
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CN111675678A (en) * 2020-06-29 2020-09-18 国联汽车动力电池研究院有限责任公司 A kind of deep drying water removal method for ionic liquid
EP4155723A1 (en) * 2021-09-23 2023-03-29 Dräger Safety AG & Co. KGaA Electrochemical gas sensor and electrolyte for an electrochemical gas sensor
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