Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C209/00—Preparation of compounds containing amino groups bound to a carbon skeleton
  • C07C209/82—Purification; Separation; Stabilisation; Use of additives
  • C07C209/84—Purification
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
  • C07F9/00—Compounds containing elements of Groups 5 or 15 of the Periodic Table
  • C07F9/02—Phosphorus compounds
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C209/00—Preparation of compounds containing amino groups bound to a carbon skeleton
  • C07C209/82—Purification; Separation; Stabilisation; Use of additives
  • C07C209/86—Separation
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C211/00—Compounds containing amino groups bound to a carbon skeleton
  • C07C211/62—Quaternary ammonium compounds
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C211/00—Compounds containing amino groups bound to a carbon skeleton
  • C07C211/62—Quaternary ammonium compounds
  • C07C211/63—Quaternary ammonium compounds having quaternised nitrogen atoms bound to acyclic carbon atoms
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
  • C07F9/00—Compounds containing elements of Groups 5 or 15 of the Periodic Table
  • C07F9/02—Phosphorus compounds
  • C07F9/025—Purification; Separation; Stabilisation; Desodorisation of organo-phosphorus compounds
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
  • C07F9/00—Compounds containing elements of Groups 5 or 15 of the Periodic Table
  • C07F9/02—Phosphorus compounds
  • C07F9/28—Phosphorus compounds with one or more P—C bonds
  • C07F9/54—Quaternary phosphonium compounds
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
  • C07F9/00—Compounds containing elements of Groups 5 or 15 of the Periodic Table
  • C07F9/02—Phosphorus compounds
  • C07F9/28—Phosphorus compounds with one or more P—C bonds
  • C07F9/54—Quaternary phosphonium compounds
  • C07F9/5407—Acyclic saturated phosphonium compounds
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
  • C07F9/00—Compounds containing elements of Groups 5 or 15 of the Periodic Table
  • C07F9/02—Phosphorus compounds
  • C07F9/547—Heterocyclic compounds, e.g. containing phosphorus as a ring hetero atom
  • C07F9/6564—Heterocyclic compounds, e.g. containing phosphorus as a ring hetero atom having phosphorus atoms, with or without nitrogen, oxygen, sulfur, selenium or tellurium atoms, as ring hetero atoms
  • C07F9/6568—Heterocyclic compounds, e.g. containing phosphorus as a ring hetero atom having phosphorus atoms, with or without nitrogen, oxygen, sulfur, selenium or tellurium atoms, as ring hetero atoms having phosphorus atoms as the only ring hetero atoms
  • C07F9/65688—Heterocyclic compounds, e.g. containing phosphorus as a ring hetero atom having phosphorus atoms, with or without nitrogen, oxygen, sulfur, selenium or tellurium atoms, as ring hetero atoms having phosphorus atoms as the only ring hetero atoms the ring phosphorus atom being part of a phosphonium compound

Definitions

• the present invention relates to methods for purifying quaternary onium salts. More specifically, the present invention relates to methods for purifying [0 quaternary onium salts containing ionic impurities, e.g. halides, as well as acidic impurities.
• ionic impurities e.g. halides
• Quaternary onium salts are highly soluble and readily dissociate in many L 5 non-aqueous as well as aqueous solvents. This property enables many solvents, which conventionally are not considered as having the ability to support electrical conductivity, to be used as an effective electrolyte medium.
• Quaternary onium cations, and in particular tetraalkylammonium cations, are relatively electrochemically stable. That is, these cations are relatively stable -0 against electrochemical reduction processes.
• the resulting electrolyte can be used in a wide variety of electrochemical applications such as carbon-based electrode supercapacitors. See e.g. U.S. 5,086,374, which is incorporated herein by 15 reference.
• the electrochemical stability of a substance is represented by its so called electrochemical window, possessing Volts (V) as a unit and determined by cyclic voltammetry (CV). The higher the value in Volts (or "the wider" the electrochemical window), the more stable the corresponding material is against oxidation or reduction processes.
• the general trend of cation stability is:
• the wideness of the electrochemical window is generally very sensitive to impurities, especially residual halides. Since halides are generally oxidized much easier than, for example, perfluorinated anions, halide contaminants in an electrolyte can frequently lead to significantly lower electrochemical stability. Further "free acid” has been identified as a critical parameter, e.g. low ppm-levels of tetrafluoroboronic acid in onium tetrafiuoroborate electrolytes. By applying a certain voltage to an acid containing electrolyte, the free acid equilibrates with gaseous compounds causing problems, e.g., reduced lifetimes, in the devices that use such products.
• quaternary onium salts are commercially prepared by reacting alkylamines with alkylfluorides, alkylchlorides, alkylbromides, or alkyliodides to form alkylammonium halides. These alkylammonium halides are then converted into quaternary onium salts essentially free of fluoride, chloride, bromide, or iodide via methods known in the art, such as the one described in WO
• ionic impurities such as halide and free acid can be removed from non-aqueous quaternary onium salt solutions by contacting the salt solutions with an ion exchange material that a) has been charged with anions, preferably anions that are more electrochemically stable than the halide impurities and/or b) works as a scavenger.
• Preferred embodiments of the present methods are generally less costly and more versatile compared to many conventional crystallization methods for separating halides from quaternary onium salts and their anhydrous solutions.
• certain preferred embodiments of the present invention comprise (i) providing a non-aqueous solution of one or more quaternary onium salts having at least one ionic impurity, e.g. halide and/or free acid at a first concentration; (ii) providing an ion exchange material charged with anions, preferably electrochemically stable anions and/or in the free fo ⁇ n; and (iii) contacting the salt solution with the ion exchange material to produce a nonaqueous quaternary onium salt solution having a second ionic impurity concentration, wherein the second ionic impurity concentration is lower than the first ionic impurity concentration.
• ionic impurity e.g. halide and/or free acid at a first concentration
• Figure 1 depicts a cyclic voltammogram for a non-aqueous quaternary onium salt solution reference containing chloride as an impurity.
• Figure 2 depicts a cyclic voltammogram for the salt solution reference after one treatment with anion exchange materials according to the present invention.
• Figure 3 depicts a cyclic voltammogram for the salt solution reference after two treatments with anion exchange materials according to the present invention.
• Figure 4 depicts a cyclic voltammogram for the salt solution reference after three treatments with anion exchange materials according to the present invention.
• Figure 5 depicts an ion chromatogram illustrating the separation of inorganic anions and the order of elution (Joachim Weiss, Ionenchromatographie, 2. reprint 1991, ISBN 3-527-28236-x).
• one preferred step of the present invention is providing a non-aqueous quaternary onium salt solution having a first concentration of ionic impurities, like halides and/or free acid.
• quaternary onium salt it is meant a salt having a cation that can be represented as (R a R b R c R d )A + , wherein A is P or N and R a ; R b , R c , and R d are, independently of each other, a Ci-Ci 2 alkyl, a member of a C 2 -C 20 unsaturated heterocyclic, or a single, double, or non-localized pi bond, provided that a combination of bonds result in a tetravalent N or P.
• salt includes both the crystalline structure of the compound as well as the compound when it is dissolved in a solvent.
• salt solution means solution having at least one salt that is at least partially dissolved in a solvent.
• liquid onium salt means a salt that can be at least partly dissociated without the use of a solvent.
• some quaternary onium salts described herein have such low melting points that they are liquid at room temperature and also partly dissociated and therefore conductive without any other material (such as a solvent) being present.
• Such liquid salts are also referred to in the art as "Ionic Liquids”.
• onium salt as used herein, is not limited to a compositions of a singular onium salt, but can include a plurality of different onium salts.
• halide it is meant an ion of fluoride, chloride, bromide, iodide, or some combination thereof.
• free acid it is meant a proton, usually present as dissociated proton with a counter ion or in the form of a non- dissociated acid molecule.
• quaternary onium salts according to the present invention are selected based upon their electrical conductivity, solubility, and electrochemical stability.
• Quaternary onium salts that may be practiced with the present invention preferably have the formula [A + R 4 ] [Z " ], wherein A is trivalent atom such as nitrogen or phosphorous; R is independently a substituted or un-substituted Ci -
• Ci 2 alkyl a substituted or un-substituted fluoroalkyl, or a member of a 5- or 6- member saturated, unsaturated, or aromatic cyclic or heterocyclic, or a member of a polycyclic structure.
• Particularly preferred are quaternary onium salts according to Formula I, II, III, or IV:
• A is nitrogen or phosphorous; n and m are independently 0 or 1 ;
• Ri — R 4 , Rio, Ri 5 , R 24 , and R 25 are independently a substituted or unsubstituted Ci - Ci 2 alkyl, substituted or unsubstituted fluoroalkyl, member of a five or six member saturated, unsaturated, or aromatic cyclic or heterocyclic structure, or member of a polycyclic structure (e.g., spiro-, condensated-, or bridged-structure, or some combination thereof);
• R 5 - Rg, Rn - Ri 4 , Ri 6 -R 23 are independently H, F, Cl, substituted or unsubstituted Ci - Ci 2 alkyl, substituted or unsubstituted fluoroalkyl, member of a five or six member saturated, unsaturated, or aromatic cyclic or heterocyclic structure, or member of a polycyclic structure (e.g., spiro-, condensated-, or bridged-structure, or some combination thereof);
• Di - Og are independently carbon, nitrogen, sulfur, or oxygen provided that: at least three of Di - D5 are carbon; at least two of D 6 - D 9 are carbon;
• n is 0 for its corresponding R group; the bond between any two adjacent D members is single, double, or aromatic; the bond between A and either of its two adjacent D members is single, double, or aromatic provided that A is tetravalently bonded;
• D 1O - D 13 are independently carbon, nitrogen, sulfur, or oxygen provided that: at least two of Di 0 - Di 3 are carbon; when a D ring member is carbon, n and m are 1 for their corresponding R groups; when a D ring member is nitrogen, n is 1 and ni is 0 for their corresponding R groups; when a D ring member is oxygen or sulfur, n and m are 0 for their corresponding R groups; Z is a negatively charged, electrochemically stable anion, such as for example, BF4 " , [BF x (C y F 2y+1-z H z )4- x ]n " in which the ligands (C y F 2y+ i -z H z ) may be identical or different, l ⁇ x ⁇ 3, l ⁇ y ⁇ 8 and 0 ⁇ z ⁇ 2y+l, PF 6 " , [PF x (C y F 2 y+i- z H z
• Compounds of the structure in Formula I are quaternary onium salts that, when dissolved in a solvent, preferably form a cation having a central nitrogen or phosphorous atom joined by four organic groups and a negatively charged, electrochemically stable anion.
• the organic groups attached to the central atom are independently Ci — Ci 2 alkyls, or Ci — Ci 2 fiuoroalkyls.
• alkyl groups that constitute the quaternary alkyl ammonium cation are: a methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group, n-hexyl group, isohexyl group, n-decyl group, n-dodecyl group, n-octadecyl group, cyclopentyl group, cyclohexyl group, and the like; and, those in which one, or two or more, hydrogen atoms comprising this unsubstituted alkyl group are substituted with a substituent such as fluorine, e.g trifluromethyl or 2,2,2 trifluoroethyl groups; an aryl group, for example,
• Examples of two alkyl groups forming a cyclic group are tetramethylene, pentamethylen, hexamethylene and di(2-ethoxy)ether group.
• Preferably cations are tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetra butylammonium, tetra-n-propylammonium, tetra-n- butylammonium, tetra-n-pentylammonium, tetra-n-hexyl ammonium, ethyl trimethylammonium, 2,2,2 trifluoroethyl trimethylammonium, 2,2,2 trifluoroethyl triethylammonium, ethyl tri(trifluromethyl) ammonium, methyl tri(trifluromethyl) ammonium, benzyltrimethylammonium, benzyltriethylam
• propyl includes n- propyl, i-propyl, butyl includes n-butyl, i-butyl, s-butyl, t-butyl.
• Particularly preferred cations include methyltriethylammonium, spiro- 1,1' -bipyrrolidinium, spiro- 1 , 1 ' -bipiperidinium, spiro- 1,1' -pyrrolidinium piperidinium, spiro- 1,1'- pyrrolidinium morpholinium, benzyltrimethylammonium, benzyltriethylammonium, trimethyl(2-methoxyethyl)ammonium, trimethyl[2-(2- methoxyethoxy)ethyl]ammonium etc.
• the negatively charged anion Z is selected from the group consisting of BF 4 " , PF 6 " , CF 3 S(V and N(SO 2 CFs) 2 " .
• Compounds of the structure in Formula II are quaternary onium salts that, when dissolved in a solvent, form a negatively charged anion and an optionally substituted 6-member unsaturated heterocyclic cation, preferably having one nitrogen and five carbon ring members, such as pyridinium, 2-methylpyridinium, 3-methylpyridinium, 4-methylpyridinium, 2,6-dimethylpyridinium, quinolinium, isoquinolinium, acridinium or phenanthridinium;, or two nitrogen and four carbon ring members, such as pyridazinium, pyrimidium, pyrazinium or phenazinium; one nitrogen and one oxygen ring member, such as morpholinium, 2-methyl morpholinium or 3-methyl morpholinium.
• one nitrogen and five carbon ring members such as pyridinium, 2-methylpyridinium, 3-methylpyridinium, 4-methylpyridinium, 2,6-dimethylpyridinium, quinolinium, is
• the functional groups attached to the ring atoms are independently fluorine, hydrogen or Ci - Ci 2 alkyls, preferably independently methyl, ethyl, propyl or butyl.
• the cation is pyridinium and the anion is tetrafluoroborate .
• Compounds of the structure in Formula III are quaternary onium salts that, when dissolved in a solvent, preferably form a negatively charged anion and an optionally substituted 5 -member unsaturated heterocyclic cation, preferably having either one or two nitrogen ring members, such as pyrrolium, imidazolium, pyrazolium, indolium, isoindolium, quinazolinium or indozolium; three nitrogen ring members, such as triazolium, one nitrogen and one sulfur ring member, such as thiazolium, or one nitrogen and one oxygen ring member, such as oxazolium.
• nitrogen ring members such as pyrrolium, imidazolium, pyrazolium, indolium, isoindolium, quinazolinium or indozolium
• three nitrogen ring members such as triazolium, one nitrogen and one sulfur ring member, such as thiazolium, or one nitrogen and one oxygen ring member, such as o
• the functional groups attached to the ring atoms are independently independently fluorine, hydrogen or Ci — Ci 2 alkyls, preferably independently methyl, ethyl, propyl or butyl.
• the cation is diethylimidazolium, ethylmethylimidazolium, or butylmethylimidazolium and the anion is tetrafluoroborate, CF 3 SO 3 " or N(SO 2 CF 3 ) 2 '
• Compounds of the structure in Formula IV are quaternary onium salts that, when dissolved in a solvent, preferably form a negatively charged anion and an optionally substituted 5-member saturated heterocyclic cation, preferably having either one or two nitrogen ring members, such as pyrrolidinium, pyrazolidinium, imidazolidinium, indolinium, isoindolinium, , three nitrogen ring members, such as triazolium, one nitrogen and one sulfur ring member, such as thiazolium, or one nitrogen and one oxygen ring member, such as oxazolium.
• nitrogen ring members such as pyrrolidinium, pyrazolidinium, imidazolidinium, indolinium, isoindolinium
• three nitrogen ring members such as triazolium, one nitrogen and one sulfur ring member, such as thiazolium, or one nitrogen and one oxygen ring member, such as oxazolium.
• the functional groups attached to the ring atoms are independently fluorine, hydrogen or Ci - Ci 2 alkyls, preferably independently methyl, ethyl, propyl, butyl or cyclic alkyls preferably independently pyrrolidinium, piperidinium or morpholinium thereby forming a spiro compound.
• the cation is diethylpyrrolidinium, ethylmethylpyrrolidinium, propylmethylpyrrolidinium, butylmethylpyrrolidinium, spiro-IJ'-bipyrrolidinium, spiro- l,r-bipiperidinium, spiro- 1 -pyrrolidinium 1 '- piperidinium or spiro- 1 -pyrrolidinium 1 '-morpholinium and the anion is tetrafluoroborate.
• the salt solutions form an electrically conductive electrolyte.
• the concentration of the onium salts in the nonaqueous solution is at least about 0.5 mol/L, more preferably at least about 1.0 mol/L.
• Certain preferred salt solutions of the present invention comprise one of the above-described quaternary onium salts dissolved in at least one non-aqueous solvent. Certain other preferred salt solutions comprise a combination of at least two quaternary onium salts dissolved in at least one non-aqueous solvent.
• Particularly preferred combinations of salts include the combinations of imidazolium tetrafluoroborate and pyrazolium tetrafluoroborate; methyltriethylammonium tetrafluoroborate and ethylmethylimidazolium tetrafluoroborate; methyltriethylammonium tetrafluoroborate and ethylmethylimidazolium tetrafluoroborate; ethylmethylimidazolium tetrafluoroborate and ethylmethylpyrazolium tetrafluoroborate; and methyltriethylammonium tetrafluoroborate, ethylmethylimidazolium tetrafluoroborate and ethylmethylpyrazolium tetrafluoroborate.
• the organic solvent in the non-aqueous solution is preferably at least one solvent selected from the group consisting of: an organic, cyclic carbonate, such as ethylene carbonate, propylene carbonate, butylene carbonate, and the like; an organic, linear carbonate such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and the like; gamma-butylrolactone; sulfolane or some derivative thereof; nitrile, such as acetonitrile, propionitrile and the like; dinitrile, such as glutaronitrile, and the like; and combinations of these.
• the concentration of halide in low purity quaternary onium salts could be above 20 weight percent.
• low purity solutions having a halide content of not greater than about 5000 parts per million (ppm) are preferred, at least in part, because they allow for the present invention to occur in a compact system of columns. In certain embodiments, it is even more preferred that the low purity solutions have a halide content of from about 20 to about 2000 ppm.
• Quaternary onium salt solutions having a halide concentration of not greater than about 20 parts per million are generally considered pure, as that term is used herein, and are generally acceptable for products providing long life spans in accordance with preferred embodiments of the present invention.
• the concentration of free acids in low purity quaternary onium salt liquids could be above 10 weight percent. Practically, the corresponding low purity liquids which have a free acid content of not greater than 5000 parts per million are preferred, at least in part, because they allow for the present invention to occur in a compact system of columns. Even more preferred are low purity solutions having a free acid content of from about 20 to about 2000 parts per million. Quaternary onium salt solutions having a free acid concentration of not greater than about 30 parts per million are generally considered pure, as that term is used herein, and are generally targeted to achieve long lifetime and non-corrosiveness in accordance with the present invention. Another preferred step of the present invention is providing an ion exchange material charged with electrochemically stable anions.
• ion exchange materials are those which can exchange an ion (i.e. an atom or molecule that has lost or gained an electron and thus acquired an electrical charge) that is attached to the exchange material for a similarly charged ion from a solution.
• Ion exchange materials generally have greater selectivity for ions with increasing valence or charge. Among ions with the same charge, higher affinities are generally seen for ions with a higher atomic number. These affinity relationships are reversed in concentrated solutions, allowing for regeneration of the exchange material.
• Ion exchange materials suitable for the present invention include, but are not limited to, materials that have immobile exchange sites and materials that have mobile exchange sites.
• suitable materials having immobile ion exchange sites include, but are not limited to, resins such as those forming a solid 3-dimensional polymer network that is essentially insoluble in the reaction media.
• suitable materials having mobile ion exchange sites include, but are not limited to liquid polycation salts that are essentially insoluble in the reaction media, such as polyammonium ionic liquid sulfonamides (PILS) and the like. Resins are generally preferred due to the ease at which the desired product can be separated from the exchange material.
• Resins are typically synthetically produced solid organic particles in the form of beads that have a distinct number of immobile ion sites which set the maximum quantity of exchanges per unit of resin.
• Preferred resins according to the present invention are weakly basic anion and Type-1 strong base anion resins based upon a styrene-divinylbenzene (DVB) copolymer and having either a gel or macroporous physical structure.
• Gel resins are generally homogeneous crosslinked polymers having exchange sites evenly distributed throughout the bead. Macroporous resins have sponge-like structure of relatively larger pores than gel resins and therefore permit access to interior exchange sites.
• macroporous resins have better physical stability as compared to gels, gel resins typically have better operating efficiencies and cost less. Thus, a determination of the most appropriate resin will depend upon the particular application involved and one skilled in the art could readily make such a determination without undue experimentation in view of the teachings contained herein.
• Ion exchange resins are preferably generally spherical in shape and, preferably, of substantially similar or uniform dimensions to accommodate the swelling and contraction of the resin bead during exhaustion and regeneration.
• Average bead diameter is preferably from about 2000 to about 250 ⁇ m, and more preferably from about 900 to about 250 ⁇ m.
• Styrene-DVB resins according to the present invention can be manufactured by processes known in the art. These resins are also commercial available as, for example, Dow Chemical's DOWEX 21K Cl, DOWEX 21K XLT,
• the resin is preferably charged before use with anions.
• This charging process imparts negatively charged ions to the resin which are then available for exchange with similarly charged ions in the salt solution to be purified. Therefore, the solution utilized in this process preferably supplies anions to the resin that are more electrochemically stable than the halide ion impurities which are sought to be removed from the salt solution.
• the resin is charged with acid solution, wherein the acid anions attach to the resin.
• the resin is in case of a weakly basic resin type not charged before use or in the case of chloride containing strong base resin types conditioned with e.g. caustic soda, water and an appropriate solvent.
• the resin utilized in this process preferably removes free acid from the solution via an adsorption.
• the ion exchange resins may be provided in any configuration adaptable for use with the present invention.
• these resins are provided in one or, more preferably, multiple ion exchange columns that can be arranged in parallel or, more preferably, in series.
• Other embodiments of the present invention include resins that are provided in fixed or fluid ion exchange beds.
• the present invention also comprises in preferred embodiments, the step of contacting the salt solution with the ion exchange material to produce a quaternary onium salts solution having a second concentration of halide which is less than the first concentration of halide.
• the ion exchange material has a greater selectivity for more electrochemically stable ions, such as tetrafluoroborate, than the halide ions which are to be removed.
• electrochemically stable ions such as tetrafluoroborate
• the exchange material tends to favor ions having a higher atomic number or a larger size. Referring to Figure 5, ion chromatography of anions in an aqueous solution shows that weakly adsorbed anions are eluated earlier than strongly adsorbed anions.
• the graph illustrates that fluoride is first eluated, followed by chloride, nitrate, monohydrogenphosphate, sulfate, tetrafluoroborate, and iodide. Therefore, chloride will not be adsorbed in the presence of an excess of tetrafluoroborate and, thus, chloride can generally not be eliminated from an aqueous solution containing tetrafluoroborate. Likewise, fluoride can generally not be adsorbed in the presence of an excess of tetrafluoroborate due to the in-situ formation of hydrolyzing tetrafluoroborate anions.
• anion exchange materials have a greater affinity for halide ions if the exchange is carried out in a non-aqueous solution. This unexpected property allows reversal of the exchange direction so that the exchange materials remove halide anions from the salt solutions, even when the halide anions are present in very low concentrations.
• the halide concentration of the purified salt solution is less than about 10 percent of the concentration of the crude salt solution (i.e. the first concentration).
• the second concentration of halide in the salt solution is less than about 100 parts per million by weight, more preferably less than about 5 parts per million by weight, and even more preferably less than about 1 parts per million by weight.
• steps (a) through (c) of the present invention may be repeated one or more times to iteratively reduce the halide concentration in the salt solution. Preferably, these steps are repeated once, and more preferably, these steps are repeated two or more times.
• the halide exchange efficiency for salt solutions comprising a nonaqueous solvent in accordance with the present invention is generally higher if the salt solution has a residual water content of not greater than about 1000 parts per million by weight. Therefore, in certain preferred embodiments, the salt solution in the exchange process has a residual water content of not greater than about 5 weight percent, more preferably not greater than about 1000 ppm.
• residual water refers to the water content in the polymer network of the ion exchange resin.
• at least a portion of the residual water may be optionally removed by a drying process before or during the step of reducing halide ion concentration.
• drying processes known in the art are amenable to the present invention, including molecular sieves drying or azeotropic distillation.
• the purified salt solution can be further diluted or concentrated by ordinary methods or used as it is e.g. to fill electrochemical cells or to work as reaction media in chemical synthesis reactions or the purified salt can be isolated by removing the solvent from the solution.
• the reduction of ionic impurities can be run as a batch process, usually as a multistep, or as a continuous process, usually with column equipment known by people skilled in the art. Further the reduction steps can be carried out separately or in series, e.g. lead-lag or merry-go-round set-up.
• the procedure requires at least one type of resin being appropriately conditioned.
• Ion Exchange In a glovebox with a dry and oxygen free argon atmosphere, 300g of a 1 molar solution of tetraethylammonium tetrafluoroborate (TEA-BF 4 ) in acetonitrile containing impurities (as described in WO 2004/039761) and a water content of 292 parts per million is stirred for 1 hour with 5.6 g of the charged anion exchange resin prepared as described above. The TEA-BF 4 solution is then removed from the solid anion exchange resin and a sample of the solution is taken and dried to the desired water content below 20 ppm. The final moisture content of the solution is determined by a Karl-Fisher titration method and the halide content is determined by ion chromatography.
• TEA-BF 4 tetraethylammonium tetrafluoroborate
• the sample is subjected to cyclic voltammetry (CV) to determine its "voltage window".
• CV cyclic voltammetry
• the sample is placed in a cell having a working electrode, a counter electrode, and a test electrode, which is immediately adjacent but not touching the working electrode.
• the electrodes in the cell are connected to an apparatus applying cyclic voltage, called a potentiostat, which is configured to adjust the current between the working and counter electrodes to maintain a "desired voltage" between the working electrode and the reference electrode.
• the voltage between the reference electrode and the working electrode can be varied as a function of time in a programmed manner.
• the voltage window is determined by progressively increasing the desired voltage (in both the positive and negative directions) until there is a precipitous increase in the current required to drive the working and counter electrodes to maintain the desired voltage.
• the sharp rise in current at the end voltages generally indicates the breakdown voltage of the electrolyte solution, meaning that the salt or the solvent is undergoing an irreversible, destructive reduction reaction at the negative end voltage or an oxidation reaction at the positive end voltage.
• This ion exchange procedure is iteratively repeated a second and a third time with the solution. Samples are taken each time, dried and characterized in the same way.
• the reference material was prepared from the same raw material in an identical way except that it is not treated with any anion exchange resin before drying.
• the resin concurrently reduces the concentration of F, Cl, and Br.
• the methods of the present invention are not limited to reducing only these ions, but in fact can reduce all halide ions as well as sulfate. Examples 4-6:
• lOOg of charged styrene macroporous anion exchange resin (sold under the trade designation Amberjet 4600 Cl) is provided.
• This resin is brought into intimate contact with 300 ml caustic soda (concentration: 5%) by adding the resin to the solution and mixing for one hour. The liquid was then separated from the resin.
• a new 300 ml batch of caustic soda (concentration: 5%) is provided, added, and mixed as before to the resin from the first separation step.
• the liquid from the second mixing step is then separated from the resin.
• the resin is washed with 250 ml of water four times.
• the resin was washed with 300 ml of an organic solvent, e.g. acetonitrile and dried for several days under vacuum and temperature up to 40° C.
• lOOg of charged styrene gel anion exchange resin (sold under the trade designation Duolite A7) is provided. This resin is washed with 250 ml of water four times. The resin was washed with 300 ml of an organic solvent, e.g. acetonitrile and dried for several days under vacuum and temperature up to 40° C.
• an organic solvent e.g. acetonitrile
• a 1 molar solution of tetraethylammonium tetrafluoroborate (TEA-BF 4 ) in acetonitrile containing impurities (as described in WO 2004/039761, which is incorporated herein by reference) and a water content of 292 parts per million is stirred for 1 hour with 5.6 g of the weakly basic anion exchange resin prepared as described above.
• the TEA-BF 4 solution is then removed from the resin and a sample of the solution is taken and dried to the desired water content below 20 ppm.
• the final moisture content of the solution is determined by a Karl-Fisher titration method and the free acid content is determined by titration. As shown in the table below, the resin concurrently reduces the concentration of free acid.
• Example 3 The process for Example 3 is repeated (three treatments), except that the TEA-BF 4 solution for the anion exchange process contains different concentrations of water during the exchange process.
• the examples demonstrate that the ion exchange reactivity at a water content of 20 parts per million is lower than the ion exchange reactivity at a water content of 500 ppm.
• Example 3 The process for Example 3 is repeated, except that different anion exchange resins are utilized.
• the examples demonstrate that the ion exchange process is not limited to a specific ion exchange resin.

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