Title of Invention	“DISTILLATION OF IONIC LIQUIDS ”
Abstract	Method of distilling mixtures comprising salts having a melting point of less than 200°C at 1 bar (ionic liquids), wherein - the cation of the ionic liquid comprises a heterocyclic ring system having at least one nitrogen atom and all nitrogen atoms of the heterocyclic ring system have an organic group as substituent, - the anion of the ionic liquid is a compound having at least one carboxylate group (carboxylate for short) or at least one phosphate group (phosphate for short) and - the distance from the surface via which the heat of distillation is introduced in the distillation (vaporizer surface) to the surface at which condensation takes place (condenser surface) is less than 50 cm at at least one point, with the vaporizer surface and condenser surface themselves having at least one length dimension of greater than 50 cm.

Title of Invention

“DISTILLATION OF IONIC LIQUIDS ”

Abstract

Method of distilling mixtures comprising salts having a melting point of less than 200°C at 1 bar (ionic liquids), wherein - the cation of the ionic liquid comprises a heterocyclic ring system having at least one nitrogen atom and all nitrogen atoms of the heterocyclic ring system have an organic group as substituent, - the anion of the ionic liquid is a compound having at least one carboxylate group (carboxylate for short) or at least one phosphate group (phosphate for short) and - the distance from the surface via which the heat of distillation is introduced in the distillation (vaporizer surface) to the surface at which condensation takes place (condenser surface) is less than 50 cm at at least one point, with the vaporizer surface and condenser surface themselves having at least one length dimension of greater than 50 cm.

Full Text	FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION (See section 10, rule 13) “DISTILLATION OF IONIC LIQUIDS” BASF SE, a German Company of 67056 Ludwigshafen, Germany The following specification particularly describes the invention and the manner in which it is to be performed. Distillation of ionic liquids Description The invention relates to a method of distilling mixtures comprising salts having a melting point of less than 200°C at 1 bar (ionic liquids), wherein the cation of the ionic liquid comprises a heterocyclic ring system having at least one nitrogen atom and all nitrogen atoms of the heterocyclic ring system have an organic group as substituent, the anion of the ionic liquid is a compound having at least one carboxylate group (carboxylate for short) or at least one phosphate group (phosphate for short) and the distance from the surface via which the heat of distil lation is introduced in the distillation (vaporizer surface) to the surface at which condensation takes place (condenser surface) is less than 50 cm at at least one point, with the vaporizer surface and condenser surface themselves having at least one length dimension of greater than 50 cm. Salts having a melting point of less than 200°C, in particular a melting point of less than 100°C, are referred to as ionic liquids. Ionic liquids which are liquid at room temperature are of particular interest. It was believed for a long time that such ionic liquids could not be distilled, since it was assumed that they ultimately have no vapor pressure. In February 2006, Martyn J. Earle, Jose M.S.S. Esperancaetal published an article about the distillation of volatile ionic liquids in a bulb tube apparatus in Nature, Vol. 439,2006, pages 831 to 834. However, ionic liquids comprising halides, sulfates or carboxylates decompose and could not be distilled. WO 2005/068404 describes the distillation of ionic liquids, including those having halides and acetates as anion. A significant aspect here is that the ionic liquids can, owing to an equilibrium reaction, also be present as neutral compounds, i.e. not as salt. As a result of the distillation, these neutral compounds are removed. Continual restoration of the equilibrium state results in the entire ionic liquid distilled in the form of the neutral compounds. In the case of ionic liquids having nitrogen-comprising, heterocyclic ring systems as cation and, for example, halides or carboxylates as anion, a corresponding equilibrium state can be established if at least one nitrogen atom of the ring system is not substituted by an organic group and is thus available for an equilibrium reaction of the anion. Accordingly, only the chlorides of 1-ethylimidazole or 1-methylimidazole are distilled in the examples of WO 2005/068404. Douglas R. MacFarlane, Jennifer M. Pringleetal., Chem.Commun.,2006, pages 1905 to 1917, also disclosea distillation of ionic liquids. Here, the ability to be distilled is based on an equilibrium reaction in which the cation and anion of the ionic liquid are present as neutral acid and base. As indicated above, the neutral compounds are withdrawn from the equilibrium state and distilled. In this way, it is possible to distill imidazolium acetates in which a nitrogen atom of the heterocyclic ring system is present in protonated form (HMIM acetate in Table 4 of the article). Ionic liquids are generally not consumed but only contaminated during use. Since they are high-priced materials, there is a need for particularly effective and advantageous methods of working up and separating the anionic liquids from the mixtures obtained in use. When ionic liquids are used for dissolving cellulose, mixtures comprising ligninsor cellulose derivatives, for example, are formed. Furthermore, inexpensive processes for preparing ionic liquids are known, but these form relatively nonvolatile by-products, the reaction products obtained are discolored because of these by-products and generally appear black. Such processes are described, for example, in WO 2005/021484 (carbonate method) or in WO 91/14678 (Arduengo process). Here too, there is a need for particularly effective and advantageous methods of working up and separating the ionic liquids from the mixtures obtained in the preparation. It is therefore an object of the present invention to provide a simple and effective method of purifying or working up ionic liquids or the mixtures obtained in their preparation and/or use. We have accordingly found the method defined at the outset. Ionic liquid The ionic liquid according to the invention is a salt which is composed of at least one cation and at least one anion and has a melting point at atmospheric pressure (1 bar) of less than 200°C, in particular less than 100°C, preferably less than 75°C. It is very particularly preferably a salt which is liquid at room temperature (21°C) and atmospheric pressure (1 bar). The cation of the ionic liquid is, according to the invention, a heterocyclic ring system having at least one nitrogen atom as constituent of the ring system. All nitrogen atoms of the ring system bear an organic group as substituent. Protonation of these nitrogen atoms is therefore not possible. The substituent is preferably an organic group which comprises from 1 to 20 carbon atoms, in particular from 1 to 10 carbon atoms. It is particularly preferably a hydrocarbon group which has no further heteroatoms, e.g. a saturated or unsaturated aliphatic group, an aromatic group or a hydrocarbon group which has both aromatic and aliphatic parts. It is very particularly preferably a C1-C10-alkyl group, C1-C10-alkenyl group, e.g. an allyl group, a phenyl group or a benzyl group. In a particular embodiment, thesubstituent is a C1-C10-, in particular C1-C4-alkyl group, e.g. a methyl group, ethyl group, propyl group, i-propyl group, n-butyl group. The heterocyclic ring system is preferably an aromatic heterocyclic ring system. The cation is preferably a derivative of imidazolium, of pyrazolium or of pyridinium. The cation is particularly preferably a derivative of imidazolium. The anion of the ionic liquid is a compound having at least one carboxylate group (carboxylate for short) or at least one phosphate group (phosphate for short). As phosphates, mention may be made of PO43- or organic compounds having a phosphate group, in particular dialkylphosphates. Particularly preferred phosphates are C1-C4-dialkylphosphates, e.g. dimethylphosphate and in particular diethylphosphate. Preferred anions are carboxylates. As carboxylates, particular mention may be made of organic compounds which have from 1 to 20 carbon atoms, preferably from 1 to 10 carbon atoms, and comprise from one to three carboxylate groups, preferably one or two carboxylate groups, particularly preferably one carboxylate group. The compounds can be either aliphatic or aromatic compounds, with the term aromatic compounds referring to compounds which comprise aromatic groups. The aliphatic or aromatic compounds can, if appropriate, comprise further functional groups, e.g. hydroxy! groups, carbonyl groups or ether groups, or other heteroatoms, in particular halogens such as fluorine, chlorine or bromine, preferably fluorine, assubstituent. Very particular preference is given to aliphatic or aromatic compounds which do not comprise any further functional groups or heteroatoms apart from the oxygen atoms of the carboxylate group. As compounds having two carboxylate group, mention may be made of, for example, the anions of phthalic acid, of isophthalic acid, of C2-C6-dicarboxylic acids, e.g. oxalic acid, malonic acid, succinic acid, glutaric acid or adipic acid. As compounds having one carboxylate group, mention may be made of the anions of aromatic, aliphatic, saturated or unsaturated C1-C20-carboxylicacids, in particular alkanecarboxylic acids, alkenecarboxylic acids, alkynecarboxylic acids, alkadienecarboxylic acids, alkatrienecarboxylic acids, hydroxycarboxylic acids or ketocarboxylic acids. Suitable alkanecarboxylic acids, alkenecarboxylic acids and alkadienecarboxylic acids are also known as fatty acids. Very particularly preferred carboxylates are the anions of C1 -C10-alkanecarboxylic acids, in particular C1-C6-alkanecarboxylic acids, very particularly preferably aoetic acid (acetate) and propionic acid (propionate). Accordingly, the ionic liquid is particularly preferably an imidazolium salt of the formula where R1 and R3 are each, independently of one another, an organic radical having from 1 to 20 carbon atoms, R2, R4,and R5 are each, independently of one another, an H atom or an organic radical having from 1 to 20 carbon atoms, X is a carboxylate or phosphate and n is 1,2 or 3. Preference is given to R1 and R3 each being, independently of one another, an organic group comprising from 1 to 10 carbon atoms. The group is particularly preferably a hydrocarbon group which has no further heteroatoms, e.g. a saturated or unsaturated aliphatic group, an aromatic group or a hydrocarbon group which has both aromatic and aliphatic parts. The group is very particularly preferably a C1-C10-alkyl group, a C1-C10-alkenyl group, e.g. an allyl group, a phenyl group, a benzyl group. In particular, the group is a C1-C4-alkyl group, e.g. a methyl group, ethyl group, propyl group, i-propyl group or n-butyl group. Preference is given to R2, R4 and R5 each being, independently of one another, an H atom or an organic group comprising from 1 to 10 carbon atoms. R2, R4 and R5 are particularly preferably each an H atom or a hydrocarbon group which does not have any further heteroatoms, e.g. an aliphatic group, an aromatic group or a hydrocarbon group which has both aromatic and aliphatic parts. Very particular preference is given to an H atom or a C1-C10-alkyl group, a phenyl group or a benzyl group. Special preference is given to an H atom or a C1-C4-alkyl group, e.g. a methyl group, ethyl group, propyl group, i-propyl group or n-butyl group. In a particular embodiment, R2 is not an H atom but has to be an organic radical as mentioned above having from 1 to 20 carbon atoms, in particular a C1-C4-alkyl group. n is preferably 1. X is preferably a carboxylate, particularly preferably acetate or propionate. As ionic liquids which are particularly suitable for the method of the invention, mention may be made of those having 1,3-dialkylimidazolium and 1,2,3-triaIkylimidazolium cations (where alkyl = C1-C8) and an acetate or propionate anion, preferably an acetate anion. Very particular preference is given to the propionates and in particular acetates of 1-methy-3-ethylimidazoIium, 1,3-diethylimidazolium, 1,3-dimethylimidazolium, 1-methyl-3-butylimidazolium and 1-ethyl-2,3-dimethylimidazolium. Their mixtures The mixtures to be distilled comprise the ionic liquids in any amount. However, the content of ionic liquid in the mixture is preferably at least 5% by weight, particularly preferably at least 10% by weight, very particularly preferably at least 20% by weight, based on the total mixture; the process is also particularly suitable for mixtures having a content of at least 30 or 40% by weight of ionic liquid. The oontent of ionic liquid is generally not greater than 95% by weight, usually not greater than 90% by weight or not greater than 80% by weight. The ionic liquids can be present entirely or partly in dissociated form or in undissociated form (cation/anion pair formation). For carrying out the method of the invention, it is immaterial whether pair formation of anions and cations of the ionic liquid occurs in the liquid phaseor whether the ionic liquid is present entirely or partly in dissociated form, e.g. in the presence of water or another hydrophilic or protic solvent. Suitable mixtures for the method of the invention are, for example, mixtures comprising impurities and by-products resulting from the production processor the use of the ionic liquid. The mixtures comprise, in particular, constituents having a boiling point above 200°C (1 bar) as impurities, e.g. salts such as alkali metal acetates or natural or synthetic oligomeric or polymeric compounds such as lignin, hemicellulose or oligosaccharides. Mixtures from the production process There are various processes for preparing ionic liquids. These processes usually give mixtures which comprise not only the ionic liquid but also undesirable by-products, starting materials and other impurities. Mixtures suitable for the method of the invention are, for example, those obtained in the preparation of imidazolium salts by single-stage or multistage reaction of starting compounds selected from among: oc-dicarbonyl compounds, amino compounds, carbonyl compounds, ammonia and carbonate compounds. One production process is, for example, the carbonate method which is described in WO 2005/021484. In the carbonate method, imidazolium salts are obtained by reacting an oc-dicarbonyl compound, a carbonyl compounds (generally formaldehyde), an amino compound and ammonia in a first stage and subsequently reacting the reaction product with a carbonate (generally dimethyl carbonate) in a second stage. The mixture obtained after the first stage comprises by-products which make the total mixture appear dark to black. Mixtu res which are obtained after the first stage or after the second stage of the abovementioned production process are suitable for the method of the invention. A further process for preparing imidazolium salts is described by Arduengo et al. (WO 91/14678, Arduengo process). In this single-stage process, the imidazolium salts are prepared by reacting an ot-dicarbonyi compound, a carbonyl compound (generally formaldehyde) and an amino compound in thepresenoe of an acid. Here too, the mixture obtained is dark to black because of by-products. Mixtu res obtained by this production process are suitable for the method of the invention. Mixtu res from use Mixtu res obtained in the use of ionic liquids are likewise suitable for the method of the invention. Ionic liquids are generally not consumed but only contaminated during use. The use of ionic liquids therefore gives mixtures which comprise ionic liquids and impurities from the respective use. These mixtures can be worked up again by the method of the invention, so that the ionic liquid can be reused. Ionic liquids are frequently used as solvents for substances which are insoluble or only sparingly soluble in other solvents. Ionic liquids are suitable, for example, as solvents for cellulose and cellulose-comprising materials. After the respective use of the solution, e.g. for producing cellulose fibers from the solution, mixtures which comprise ionic liquids and, for example, still some cellulose, lignin, hemicelluloses are obtained. The method of the invention is therefore particularly useful for mixtures which are obtained by dissolution and processing of cellulose or cellulose-comprising materials. General comments on mixtures The mixtures used in the method of the invention preferably comprise only minor amounts of volatile compounds. For the present purposes, volatile compounds are compounds having a boiling point of less than 120°C, in particular less than 150°C, at atmospheric pressure (1 bar). The content of volatile compounds is preferably from 0 to 10% by weight, in particular from 0 to 5% by weight and particularly preferably from 0 to 2% by weight, based on the mixture. If volatile compounds are initially present in the mixture, they are preferably largely removed so that their content in the mixture is not more than 10% by weight, in particular not more than 5% by weight, in particular not more than 2% by weight (see above), and are particularly preferably removed completely before carrying out the method of the invention. The addition of a strong base as is described, for example, in DE 103 33 239 for producing purified imidazolium salts is not necessary according to the present invention. It is therefore preferred that no such strong base (PKB less than 0 at 1 bar, 21 °C, measured in water) or no base at all is added to the mixture. Distillation An important feature of the distillation method of the invention is that the distance from the surface via which the heat of distillation is introduced in the distillation (vaporizer surface) to the surface at which condensation takes place (condenser surface) is less than 50 cm at at least one point. The vaporizer and condenser surfaces themselves have at least one length dimension greater 50 cm, i.e. these surfaces are large compared to the distance between them. Distillation methods having a small distance between vaporizer surface and condenser surfaoeare referred to as molecular distillation. In molecular distillation, the distance between vaporizer surface and condenser surface is generally less than the mean free path length of the compounds to the distilled. For this purpose, the geometry of the apparatus and the prooess parameters (pressure and temperature) are selected appropriately. Any geometric arrangement of the condenser surface relative to the vaporizer surface in the apparatus is possible. The important thing is that these surfaces are directly opposite one another so that the molecules can travel unhindered from the vaporizer surface to the condenser surface. Possibilities are, for example, parallel arrangement of two planar surfaces or a cylindrical arrangement in which two cylinders are placed within one another and the surfaces of the two cylinders which are directly opposite one another form the vaporizer and condenser surfaces. The vaporizer surface is heated in a suitable way, generally by means of devices on the rear side; the oondenser surface is generally cooled correspondingly, likewise by means of devices on the rear side. The distanoe from the vaporizer surfaoe to the condenser surface is less than 50 cm at at least one point, in particular less than 40 cm, particularly preferably less than 30 cm. The distance from the vaporizer surface to the condenser surface is, in particular, less than the mean free path length of the ionic liquid in the gas phase at the chosen temperature and chosen pressure. The mean free path length (XM) can be determined by known methods and is given by the equation: ΛM = const x T/ (p σ2) where the symbols have the following meanings: T: Temperature P: Pressure a: Collision cross section of the ion pair (ionic liquid), corresponds to cross-sectional area of the ion pair Preferred suitable apparatuses are configured so that at least 10 percent by area, particularly preferably at least 20 percent by area, very particularly preferably at least 30 or even at least 50 percent by area, of the vaporizer surfaoe have the above minimum distance from the condenser surface. The vaporizer surface and the condenser surface can each be larger than 0.5 m2, e.g. in the case of industrial-scale apparatuses. In the method of the invention, the ionic liquid is separated off from the mixture and taken off as distillate from the condenser surface. The residue remains on the vaporizer surface. Suitable apparatuses are, for example, configured so that the residue runs off from the vaporizer surface and is collected, and the ionic liquid correspondingly runs off from the oondenser surface and is obtained as distil late. The surface temperature of the vaporizer and the pressure are preferably selected so that the distance between vaporizer surface and condenser surface is smaller than the free path length of the ionic liquid to be separated off in the gas phase. The surface temperature is preferably from 110 to 300°C, particularly preferably from 130 to 280°C and very particularly preferably from 140°C to 260°C. The pressure in the region between vaporizer surface and condenser surfaoe is preferably from 0.0001 to 10 mbar, preferably from 0.001 to 5 mbar, particularly preferably from 0.05 to 5 mbar. The distillate obtained can, for example, comprise more than 95% by weight, particularly preferably more than 97% by weight, very particularly preferably more than 99% by weight, of the ionic liquid. In particular, distillates comprising more than 99.5% by weight or more than 99.8% by weight of the ionic liquid can also be obtained by means of the method. It is therefore possible to obtain ionic liquids in high purity from any mixtures by means of the method of the invention. The method can be carried out continuously or batchwise. Examples: Ionic liquids (ILs) used Abbreviations Chemical name BMIM OAc 1-Butyl-3-methylimidazolium acetate EM IM OAc 1-Ethyl-3-methylimidazolium acetate EEIM OAc 1,3-Diethylimidazolium acetate BMIM OProp 1-Butyl-3-methylimidazolium propionate BMIM CI 1-Butyl-3-methylimidazolium chloride EMIM DEP 1-Ethyl-3-methylimidazolium diethylphosphate The IL is freed of low boilers by stirring at 120°C and 0.1 mbar for 16 hours before all distillation experiments in order to avoid foaming and spraying during the molecular distillation. The experimental set-up is shown in the accompanying sketch. The distillate runs down on the condenser surface and is collected at the bottom, while the residue correspondingly runs down on the vaporizer surface and is collected at the bottom. Example 1: Determination of the distillation temperature for EMIM OAc About 100 ml of EM IM OAc are introduced into the feed vessel for the molecular distillation, the apparatus is made inert by means of nitrogen and a vacuum of 0.05 mbar is applied. The vaporizer surface is heated to the temperature indicated and introduction of the feed is commenced at a rate of about 50 ml/h. After all the EMIM OAc has run in, the apparatus is cooled, nitrogen is admitted and the weight ratio of distillate to residue and also the purity of both parts are determined by H-NMR and the mass of decomposition products in the cold trap. The conditions are considered to be suitable when the mass ratio of distillate to residue is at least 8:2. and less than 10% of the starting material has been decomposed. In principle, the degree of distillation can be increased at a given pressure by increasing the temperature (upper limit: excessive thermal decomposition) or at a given temperature by reducing the pressure (technical limits imposed by minimum pressure which can be achieved. For EMIM OAc, the following results were obtained: Temp, of vaporizer Distillate Residue °C Mass in g Purity (H_NMR) Mass in g Purity (HNMR) 100 95% 115 >95% 130 45 >95% 55 >95% 150 96 >95% 20 >95% 170 108 >95% 10 >95% In none of the experiments was distillate found in the cold trap to the vacuum pump. Example 2: Distillation of EEI M OAc Crude EEIM OAc is prepared by reaction of formaldehyde, glyoxal and ethyiamine in water comprising acetic acid and freed of low boilers by evaporation first at 10 mbar/80°C and then as described above at 0.1 mbar/120°C. The crude product is dark brown. 200 g of this crude product are fed into the molecular distillation at 0.05 mbar and a wall temperature 170°C (vaporizer surface) over a period of 2 hours. 190 g of clear colorless distillate, which according to H-NMR is pure (>95%) EEI M OAc, and 10 g of a black, tar-like residue are obtained. No volatile constituents are collected in the cold trap. Example 3: Distillation of EMIM OAc 200 g of EM IM OAc which has previously been used five times for the dissolution of cellulose (pulp from Tembec Inc. type 10A) and recovery of the cellulose by dilution with 10 times its amount of water (see WO 03/029329) are used as starting material. After each precipitation, the EM IM OAc was recovered from the aqueous supernatant solution by distilling off the water at 120°C/1 mbar and was reused without further purification. It was freed of low boilers as described above before the molecular distillation. The EMIM OAc fed to the distillation comprises about 6% by weight of secondary component (e.g. lignin) from the cellulose and is yellowish brown (Gardener color number = 16). 200 g of this EMIM OAc are introduced into the molecular distillation at 0.05 mbar and a wall temperature of 170°C over a period of 4 hours. 170 g of clear colorless EM IM OAc which according to H-NMR has a purity of >95% are obtained as distillate. 30 g of a black, tar-like material which is not characterized further are obtained as residue. Example 4: Distillation of various I Ls About 100 g in each case of the IL indicated in the table are introduced into the molecular distillation at 0.05 mbar and the wall temperature indicated over a period of 2 hour. The mass ratio of distillate to residue was determined. IL Wall temp. Distillate Residue °C %by weight %by weight BMIMOAc 170 90 10 Both >95% BMIMOAc (H-NMR) EElMOAc 170 90 10 Both >95% EElMOAc (H-NMR) BMIMOProp 170 90 10 Both >95% BMIM OProp (H-NMR) EMIMDEP 170 0 100 Both >95% EMIMDEP (H-NMR) EMIMDEP 240 12 88 Both>95%EMIM DEP (H-NMR) EMIMDEP 250 54 46 Both >95% EMIMDEP (H-NMR) BMIM CI* 170 0 100 >95% BMIM CI (H-NMR) BMIM CI* 250 13 85 Distillate > 50% of butylimi-dazole and ethyl imidazole Claims 1. A method of distilling mixtures comprising salts having a melting point of less than 200°C at 1 bar (ionic liquids), wherein the cation of the ionic liquid comprises a heterocyclic ring system having at least one nitrogen atom and all nitrogen atoms of the heterocyclic ring system have an organic group as substituent, - the anion of the ionic liquid is a compound having at least one carboxylate group (carboxylate for short) or at least one phosphate group (phosphate for short) and the distance from the surface via which the heat of distillation is introduced in the distillation (vaporizer surface) to the surface at which condensation takes place (condenser surface) is less than 50 cm at at least one point, with the vaporizer surface and condenser surface themselves having at least one length dimension of greater than 50 cm. 2. The method according to claim 1, wherein the cation is an imidazolium cation. 3. The method according to claim 1 or 2, wherein the substituents on the nitrogen atoms in the heterocyclic ring system are C1-C10-alkyl groups. 4. The method according to any of claims 1 to 3, wherein the ionic liquid is an imidazolium salt of the formula I where R1 and R3 are each, independently of one another, an organic radical having from 1 to 20 carbon atoms, R2, R4, and R5 are each, independently of one another, an H atom or an organic radical having from 1 to 20 carbon atoms, X is a carboxylate and n is 1,2 or 3. 5. The method according to claim 4, wherein R2 is an organic radical having from 1 to 20 carbon atoms. 6. The method according to any of claims 1 to 5, wherein the mixtures comprise from 10 to 95% by weight of the ionic liquid. 7. The method according to any of claims 1 to 6, wherein the mixtures are mixtures which are obtained in the preparation of ionic liquids by single-stage or multistage reaction of starting compounds selected from among: α-dicarbonyl compounds, amino compounds, carbonyl compounds, ammonia and carbonate compounds. 8. The method according to any of claims 1 to 6, wherein the mixtures are mixtures which are obtained in the use of ionic liquids. 9. The method according to any of claims 1 to 8, wherein the mixtures comprise further constituents having a boiling point above 200°C (1 bar) as impurities, e.g. salts such as alkali metal acetates or natural or synthetic oligomeric or polymeric compounds such as lignin, hemicellulose or oligosaccharides. 10. The method according to any of claims 1 to 9, wherein the mixtures comprise constituents having a boiling point lower than the boiling point of the ionic liquid (more volatile compounds) in amounts of from 0 to 10% by weight. 11. The method according to any of claims 1 to 10, wherein more volatile compounds are separated off beforehand so that their proportion in the mixture is not more than 10% by weight, in particular not more than 5% by weight. 12. The method according to any of claims 1 to 11, wherein at least 10 percent by area of the vaporizer surface is at a distance of less than 50 cm from the condenser surface. 13. The method according to any of claims 1 to 12, wherein the vaporizer surface and the condenser surface are each larger than 0.5 m2. 14. The method according to any of claims 1 to 13, wherein the distillation is carried out at a surface temperature of the vaporizer of from 110°C to 300°C and a pressure of from 0.0001 to 10 mbar. 15. The method according to any of claims 1 to 14, wherein the distillate obtained comprises more than 97% by weight of the ionic liquid. Distillation of ionic liquids Abstract Method of distilling mixtures comprising salts having a melting point of less than 200°C at 1 bar (ionic liquids), wherein the cation of the ionic liquid comprises a heterocyclic ring system having at least one nitrogen atom and all nitrogen atoms of the heterocyclic ring system have an organic group as substituent, the anion of the ionic liquid is a compound having at least one carboxylate group (carboxylate for short) or at least one phosphate group (phosphate for short) and the distance from the surface via which the heat of distillation is introduced in the distillation (vaporizer surface) to the surface at which condensation takes place (condenser surface) is less than 50 cm at at least one point, with the vaporizer surface and condenser surface themselves having at least one length dimension of greater than 50 cm.

Full Text

FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION (See section 10, rule 13)
“DISTILLATION OF IONIC LIQUIDS”
BASF SE, a German Company of 67056 Ludwigshafen,
Germany
The following specification particularly describes the invention and the manner in which it is to be performed.

Distillation of ionic liquids
Description
The invention relates to a method of distilling mixtures comprising salts having a melting point of less than 200°C at 1 bar (ionic liquids), wherein
the cation of the ionic liquid comprises a heterocyclic ring system having at least one nitrogen atom and all nitrogen atoms of the heterocyclic ring system have an organic group as substituent,
the anion of the ionic liquid is a compound having at least one carboxylate group (carboxylate for short) or at least one phosphate group (phosphate for short) and
the distance from the surface via which the heat of distil lation is introduced in the distillation (vaporizer surface) to the surface at which condensation takes place (condenser surface) is less than 50 cm at at least one point, with the vaporizer surface and condenser surface themselves having at least one length dimension of greater than 50 cm.
Salts having a melting point of less than 200°C, in particular a melting point of less than 100°C, are referred to as ionic liquids. Ionic liquids which are liquid at room temperature are of particular interest. It was believed for a long time that such ionic liquids could not be distilled, since it was assumed that they ultimately have no vapor pressure.
In February 2006, Martyn J. Earle, Jose M.S.S. Esperancaetal published an article about the distillation of volatile ionic liquids in a bulb tube apparatus in Nature, Vol. 439,2006, pages 831 to 834. However, ionic liquids comprising halides, sulfates or carboxylates decompose and could not be distilled.
WO 2005/068404 describes the distillation of ionic liquids, including those having halides and acetates as anion. A significant aspect here is that the ionic liquids can, owing to an equilibrium reaction, also be present as neutral compounds, i.e. not as salt. As a result of the distillation, these neutral compounds are removed. Continual restoration of the equilibrium state results in the entire ionic liquid distilled in the form of the neutral compounds. In the case of ionic liquids having nitrogen-comprising, heterocyclic ring systems as cation and, for example, halides or carboxylates as anion, a corresponding equilibrium state can be established if at least one nitrogen atom of the ring system is not substituted by an organic group and is thus available for an equilibrium reaction of the anion. Accordingly, only the chlorides of 1-ethylimidazole or 1-methylimidazole are distilled in the examples of WO 2005/068404.
Douglas R. MacFarlane, Jennifer M. Pringleetal., Chem.Commun.,2006, pages 1905 to

1917, also disclosea distillation of ionic liquids. Here, the ability to be distilled is based on an equilibrium reaction in which the cation and anion of the ionic liquid are present as neutral acid and base. As indicated above, the neutral compounds are withdrawn from the equilibrium state and distilled. In this way, it is possible to distill imidazolium acetates in which a nitrogen atom of the heterocyclic ring system is present in protonated form (HMIM acetate in Table 4 of the article).
Ionic liquids are generally not consumed but only contaminated during use. Since they are high-priced materials, there is a need for particularly effective and advantageous methods of working up and separating the anionic liquids from the mixtures obtained in use. When ionic liquids are used for dissolving cellulose, mixtures comprising ligninsor cellulose derivatives, for example, are formed. Furthermore, inexpensive processes for preparing ionic liquids are known, but these form relatively nonvolatile by-products, the reaction products obtained are discolored because of these by-products and generally appear black. Such processes are described, for example, in WO 2005/021484 (carbonate method) or in WO 91/14678 (Arduengo process). Here too, there is a need for particularly effective and advantageous methods of working up and separating the ionic liquids from the mixtures obtained in the preparation.
It is therefore an object of the present invention to provide a simple and effective method of purifying or working up ionic liquids or the mixtures obtained in their preparation and/or use.
We have accordingly found the method defined at the outset.
Ionic liquid
The ionic liquid according to the invention is a salt which is composed of at least one cation and at least one anion and has a melting point at atmospheric pressure (1 bar) of less than 200°C, in particular less than 100°C, preferably less than 75°C. It is very particularly preferably a salt which is liquid at room temperature (21°C) and atmospheric pressure (1 bar).
The cation of the ionic liquid is, according to the invention, a heterocyclic ring system having at least one nitrogen atom as constituent of the ring system. All nitrogen atoms of the ring system bear an organic group as substituent. Protonation of these nitrogen atoms is therefore not possible. The substituent is preferably an organic group which comprises from 1 to 20 carbon atoms, in particular from 1 to 10 carbon atoms. It is particularly preferably a hydrocarbon group which has no further heteroatoms, e.g. a saturated or unsaturated aliphatic group, an aromatic group or a hydrocarbon group which has both aromatic and aliphatic parts. It is very particularly preferably a C1-C10-alkyl group, C1-C10-alkenyl group, e.g. an allyl group, a phenyl group or a benzyl group.

In a particular embodiment, thesubstituent is a C1-C10-, in particular C1-C4-alkyl group, e.g. a methyl group, ethyl group, propyl group, i-propyl group, n-butyl group.
The heterocyclic ring system is preferably an aromatic heterocyclic ring system.
The cation is preferably a derivative of imidazolium, of pyrazolium or of pyridinium.
The cation is particularly preferably a derivative of imidazolium.
The anion of the ionic liquid is a compound having at least one carboxylate group (carboxylate for short) or at least one phosphate group (phosphate for short).
As phosphates, mention may be made of PO43- or organic compounds having a phosphate group, in particular dialkylphosphates. Particularly preferred phosphates are C1-C4-dialkylphosphates, e.g. dimethylphosphate and in particular diethylphosphate.
Preferred anions are carboxylates.
As carboxylates, particular mention may be made of organic compounds which have from 1 to 20 carbon atoms, preferably from 1 to 10 carbon atoms, and comprise from one to three carboxylate groups, preferably one or two carboxylate groups, particularly preferably one carboxylate group.
The compounds can be either aliphatic or aromatic compounds, with the term aromatic compounds referring to compounds which comprise aromatic groups. The aliphatic or aromatic compounds can, if appropriate, comprise further functional groups, e.g. hydroxy! groups, carbonyl groups or ether groups, or other heteroatoms, in particular halogens such as fluorine, chlorine or bromine, preferably fluorine, assubstituent.
Very particular preference is given to aliphatic or aromatic compounds which do not comprise any further functional groups or heteroatoms apart from the oxygen atoms of the carboxylate group.
As compounds having two carboxylate group, mention may be made of, for example, the anions of phthalic acid, of isophthalic acid, of C2-C6-dicarboxylic acids, e.g. oxalic acid, malonic acid, succinic acid, glutaric acid or adipic acid.
As compounds having one carboxylate group, mention may be made of the anions of aromatic, aliphatic, saturated or unsaturated C1-C20-carboxylicacids, in particular alkanecarboxylic acids, alkenecarboxylic acids, alkynecarboxylic acids, alkadienecarboxylic acids, alkatrienecarboxylic acids, hydroxycarboxylic acids or ketocarboxylic acids. Suitable alkanecarboxylic acids, alkenecarboxylic acids and

alkadienecarboxylic acids are also known as fatty acids.
Very particularly preferred carboxylates are the anions of C1 -C10-alkanecarboxylic acids, in particular C1-C6-alkanecarboxylic acids, very particularly preferably aoetic acid (acetate) and propionic acid (propionate).
Accordingly, the ionic liquid is particularly preferably an imidazolium salt of the formula

where
R1 and R3 are each, independently of one another, an organic radical having from 1 to 20 carbon atoms,
R2, R4,and R5 are each, independently of one another, an H atom or an organic radical having from 1 to 20 carbon atoms,
X is a carboxylate or phosphate and
n is 1,2 or 3.
Preference is given to R1 and R3 each being, independently of one another, an organic group comprising from 1 to 10 carbon atoms. The group is particularly preferably a hydrocarbon group which has no further heteroatoms, e.g. a saturated or unsaturated aliphatic group, an aromatic group or a hydrocarbon group which has both aromatic and aliphatic parts. The group is very particularly preferably a C1-C10-alkyl group, a C1-C10-alkenyl group, e.g. an allyl group, a phenyl group, a benzyl group. In particular, the group is a C1-C4-alkyl group, e.g. a methyl group, ethyl group, propyl group, i-propyl group or n-butyl group.
Preference is given to R2, R4 and R5 each being, independently of one another, an H atom or an organic group comprising from 1 to 10 carbon atoms. R2, R4 and R5 are particularly preferably each an H atom or a hydrocarbon group which does not have any further heteroatoms, e.g. an aliphatic group, an aromatic group or a hydrocarbon group which has both aromatic and aliphatic parts. Very particular preference is given to an H atom or a C1-C10-alkyl group, a phenyl group or a benzyl group. Special preference is given to an H atom or a C1-C4-alkyl group, e.g. a methyl group, ethyl group, propyl

group, i-propyl group or n-butyl group.
In a particular embodiment, R2 is not an H atom but has to be an organic radical as mentioned above having from 1 to 20 carbon atoms, in particular a C1-C4-alkyl group.
n is preferably 1.
X is preferably a carboxylate, particularly preferably acetate or propionate.
As ionic liquids which are particularly suitable for the method of the invention, mention may be made of those having
1,3-dialkylimidazolium and 1,2,3-triaIkylimidazolium cations (where alkyl = C1-C8) and an acetate or propionate anion, preferably an acetate anion.
Very particular preference is given to the propionates and in particular acetates of 1-methy-3-ethylimidazoIium, 1,3-diethylimidazolium, 1,3-dimethylimidazolium, 1-methyl-3-butylimidazolium and 1-ethyl-2,3-dimethylimidazolium.
Their mixtures
The mixtures to be distilled comprise the ionic liquids in any amount. However, the content of ionic liquid in the mixture is preferably at least 5% by weight, particularly preferably at least 10% by weight, very particularly preferably at least 20% by weight, based on the total mixture; the process is also particularly suitable for mixtures having a content of at least 30 or 40% by weight of ionic liquid.
The oontent of ionic liquid is generally not greater than 95% by weight, usually not greater than 90% by weight or not greater than 80% by weight.
The ionic liquids can be present entirely or partly in dissociated form or in undissociated form (cation/anion pair formation). For carrying out the method of the invention, it is immaterial whether pair formation of anions and cations of the ionic liquid occurs in the liquid phaseor whether the ionic liquid is present entirely or partly in dissociated form, e.g. in the presence of water or another hydrophilic or protic solvent.
Suitable mixtures for the method of the invention are, for example, mixtures comprising impurities and by-products resulting from the production processor the use of the ionic liquid.
The mixtures comprise, in particular, constituents having a boiling point above 200°C (1 bar) as impurities, e.g. salts such as alkali metal acetates or natural or synthetic oligomeric or polymeric compounds such as lignin, hemicellulose or oligosaccharides.

Mixtures from the production process
There are various processes for preparing ionic liquids. These processes usually give mixtures which comprise not only the ionic liquid but also undesirable by-products, starting materials and other impurities.
Mixtures suitable for the method of the invention are, for example, those obtained in the preparation of imidazolium salts by single-stage or multistage reaction of starting compounds selected from among: oc-dicarbonyl compounds, amino compounds, carbonyl compounds, ammonia and carbonate compounds.
One production process is, for example, the carbonate method which is described in WO 2005/021484.
In the carbonate method, imidazolium salts are obtained by reacting an oc-dicarbonyl compound, a carbonyl compounds (generally formaldehyde), an amino compound and ammonia in a first stage and subsequently reacting the reaction product with a carbonate (generally dimethyl carbonate) in a second stage. The mixture obtained after the first stage comprises by-products which make the total mixture appear dark to black.
Mixtu res which are obtained after the first stage or after the second stage of the abovementioned production process are suitable for the method of the invention.
A further process for preparing imidazolium salts is described by Arduengo et al. (WO 91/14678, Arduengo process). In this single-stage process, the imidazolium salts are prepared by reacting an ot-dicarbonyi compound, a carbonyl compound (generally formaldehyde) and an amino compound in thepresenoe of an acid. Here too, the mixture obtained is dark to black because of by-products.
Mixtu res obtained by this production process are suitable for the method of the invention.
Mixtu res from use
Mixtu res obtained in the use of ionic liquids are likewise suitable for the method of the invention.
Ionic liquids are generally not consumed but only contaminated during use.
The use of ionic liquids therefore gives mixtures which comprise ionic liquids and impurities from the respective use. These mixtures can be worked up again by the method of the invention, so that the ionic liquid can be reused.

Ionic liquids are frequently used as solvents for substances which are insoluble or only sparingly soluble in other solvents. Ionic liquids are suitable, for example, as solvents for cellulose and cellulose-comprising materials. After the respective use of the solution, e.g. for producing cellulose fibers from the solution, mixtures which comprise ionic liquids and, for example, still some cellulose, lignin, hemicelluloses are obtained. The method of the invention is therefore particularly useful for mixtures which are obtained by dissolution and processing of cellulose or cellulose-comprising materials.
General comments on mixtures
The mixtures used in the method of the invention preferably comprise only minor amounts of volatile compounds.
For the present purposes, volatile compounds are compounds having a boiling point of less than 120°C, in particular less than 150°C, at atmospheric pressure (1 bar).
The content of volatile compounds is preferably from 0 to 10% by weight, in particular from 0 to 5% by weight and particularly preferably from 0 to 2% by weight, based on the mixture.
If volatile compounds are initially present in the mixture, they are preferably largely removed so that their content in the mixture is not more than 10% by weight, in particular not more than 5% by weight, in particular not more than 2% by weight (see above), and are particularly preferably removed completely before carrying out the method of the invention.
The addition of a strong base as is described, for example, in DE 103 33 239 for producing purified imidazolium salts is not necessary according to the present invention. It is therefore preferred that no such strong base (PKB less than 0 at 1 bar, 21 °C, measured in water) or no base at all is added to the mixture.
Distillation
An important feature of the distillation method of the invention is that the distance from the surface via which the heat of distillation is introduced in the distillation (vaporizer surface) to the surface at which condensation takes place (condenser surface) is less than 50 cm at at least one point.
The vaporizer and condenser surfaces themselves have at least one length dimension

greater 50 cm, i.e. these surfaces are large compared to the distance between them.
Distillation methods having a small distance between vaporizer surface and condenser surfaoeare referred to as molecular distillation. In molecular distillation, the distance between vaporizer surface and condenser surface is generally less than the mean free path length of the compounds to the distilled. For this purpose, the geometry of the apparatus and the prooess parameters (pressure and temperature) are selected appropriately.
Any geometric arrangement of the condenser surface relative to the vaporizer surface in the apparatus is possible. The important thing is that these surfaces are directly opposite one another so that the molecules can travel unhindered from the vaporizer surface to the condenser surface.
Possibilities are, for example, parallel arrangement of two planar surfaces or a cylindrical arrangement in which two cylinders are placed within one another and the surfaces of the two cylinders which are directly opposite one another form the vaporizer and condenser surfaces.
The vaporizer surface is heated in a suitable way, generally by means of devices on the rear side; the oondenser surface is generally cooled correspondingly, likewise by means of devices on the rear side.
The distanoe from the vaporizer surfaoe to the condenser surface is less than 50 cm at at least one point, in particular less than 40 cm, particularly preferably less than 30 cm.
The distance from the vaporizer surface to the condenser surface is, in particular, less than the mean free path length of the ionic liquid in the gas phase at the chosen temperature and chosen pressure. The mean free path length (XM) can be determined by known methods and is given by the equation:
ΛM = const x T/ (p σ2)
where the symbols have the following meanings:
T: Temperature P: Pressure
a: Collision cross section of the ion pair (ionic liquid), corresponds to cross-sectional area of the ion pair
Preferred suitable apparatuses are configured so that at least 10 percent by area, particularly preferably at least 20 percent by area, very particularly preferably at least 30 or even at least 50 percent by area, of the vaporizer surfaoe have the above minimum

distance from the condenser surface.
The vaporizer surface and the condenser surface can each be larger than 0.5 m2, e.g. in the case of industrial-scale apparatuses.
In the method of the invention, the ionic liquid is separated off from the mixture and taken off as distillate from the condenser surface. The residue remains on the vaporizer surface. Suitable apparatuses are, for example, configured so that the residue runs off from the vaporizer surface and is collected, and the ionic liquid correspondingly runs off from the oondenser surface and is obtained as distil late.
The surface temperature of the vaporizer and the pressure are preferably selected so that the distance between vaporizer surface and condenser surface is smaller than the free path length of the ionic liquid to be separated off in the gas phase.
The surface temperature is preferably from 110 to 300°C, particularly preferably from 130 to 280°C and very particularly preferably from 140°C to 260°C.
The pressure in the region between vaporizer surface and condenser surfaoe is preferably from 0.0001 to 10 mbar, preferably from 0.001 to 5 mbar, particularly preferably from 0.05 to 5 mbar.
The distillate obtained can, for example, comprise more than 95% by weight, particularly preferably more than 97% by weight, very particularly preferably more than 99% by weight, of the ionic liquid. In particular, distillates comprising more than 99.5% by weight or more than 99.8% by weight of the ionic liquid can also be obtained by means of the method.
It is therefore possible to obtain ionic liquids in high purity from any mixtures by means of the method of the invention.
The method can be carried out continuously or batchwise.

Examples:
Ionic liquids (ILs) used
Abbreviations Chemical name
BMIM OAc 1-Butyl-3-methylimidazolium acetate
EM IM OAc 1-Ethyl-3-methylimidazolium acetate
EEIM OAc 1,3-Diethylimidazolium acetate
BMIM OProp 1-Butyl-3-methylimidazolium propionate
BMIM CI 1-Butyl-3-methylimidazolium chloride
EMIM DEP 1-Ethyl-3-methylimidazolium diethylphosphate
The IL is freed of low boilers by stirring at 120°C and 0.1 mbar for 16 hours before all distillation experiments in order to avoid foaming and spraying during the molecular distillation.
The experimental set-up is shown in the accompanying sketch. The distillate runs down on the condenser surface and is collected at the bottom, while the residue correspondingly runs down on the vaporizer surface and is collected at the bottom.
Example 1:
Determination of the distillation temperature for EMIM OAc
About 100 ml of EM IM OAc are introduced into the feed vessel for the molecular distillation, the apparatus is made inert by means of nitrogen and a vacuum of 0.05 mbar is applied. The vaporizer surface is heated to the temperature indicated and introduction of the feed is commenced at a rate of about 50 ml/h.
After all the EMIM OAc has run in, the apparatus is cooled, nitrogen is admitted and the weight ratio of distillate to residue and also the purity of both parts are determined by H-NMR and the mass of decomposition products in the cold trap.
The conditions are considered to be suitable when the mass ratio of distillate to residue is at least 8:2. and less than 10% of the starting material has been decomposed. In principle, the degree of distillation can be increased at a given pressure by increasing the temperature (upper limit: excessive thermal decomposition) or at a given temperature by reducing the pressure (technical limits imposed by minimum pressure which can be achieved.
For EMIM OAc, the following results were obtained:

Temp, of vaporizer Distillate Residue
°C Mass in g Purity (H_NMR) Mass in g Purity (HNMR)
100 95% 115 >95%
130 45 >95% 55 >95%
150 96 >95% 20 >95%
170 108 >95% 10 >95%
In none of the experiments was distillate found in the cold trap to the vacuum pump.
Example 2:
Distillation of EEI M OAc
Crude EEIM OAc is prepared by reaction of formaldehyde, glyoxal and ethyiamine in water comprising acetic acid and freed of low boilers by evaporation first at 10 mbar/80°C and then as described above at 0.1 mbar/120°C. The crude product is dark brown.
200 g of this crude product are fed into the molecular distillation at 0.05 mbar and a wall temperature 170°C (vaporizer surface) over a period of 2 hours.
190 g of clear colorless distillate, which according to H-NMR is pure (>95%) EEI M OAc, and 10 g of a black, tar-like residue are obtained. No volatile constituents are collected in the cold trap.
Example 3:
Distillation of EMIM OAc
200 g of EM IM OAc which has previously been used five times for the dissolution of cellulose (pulp from Tembec Inc. type 10A) and recovery of the cellulose by dilution with 10 times its amount of water (see WO 03/029329) are used as starting material. After each precipitation, the EM IM OAc was recovered from the aqueous supernatant solution by distilling off the water at 120°C/1 mbar and was reused without further purification. It was freed of low boilers as described above before the molecular distillation. The EMIM OAc fed to the distillation comprises about 6% by weight of secondary component (e.g. lignin) from the cellulose and is yellowish brown (Gardener color number = 16).
200 g of this EMIM OAc are introduced into the molecular distillation at 0.05 mbar and a wall temperature of 170°C over a period of 4 hours.

170 g of clear colorless EM IM OAc which according to H-NMR has a purity of >95% are
obtained as distillate.
30 g of a black, tar-like material which is not characterized further are obtained as
residue.
Example 4:
Distillation of various I Ls
About 100 g in each case of the IL indicated in the table are introduced into the molecular distillation at 0.05 mbar and the wall temperature indicated over a period of 2 hour. The mass ratio of distillate to residue was determined.

IL Wall temp. Distillate Residue
°C %by weight %by weight
BMIMOAc 170 90 10 Both >95% BMIMOAc (H-NMR)
EElMOAc 170 90 10 Both >95% EElMOAc (H-NMR)
BMIMOProp 170 90 10 Both >95% BMIM OProp (H-NMR)
EMIMDEP 170 0 100 Both >95% EMIMDEP (H-NMR)
EMIMDEP 240 12 88 Both>95%EMIM DEP (H-NMR)
EMIMDEP 250 54 46 Both >95% EMIMDEP (H-NMR)
BMIM CI* 170 0 100 >95% BMIM CI (H-NMR)
BMIM CI* 250 13 85 Distillate > 50% of butylimi-dazole and ethyl imidazole

Claims
1. A method of distilling mixtures comprising salts having a melting point of less
than 200°C at 1 bar (ionic liquids), wherein
the cation of the ionic liquid comprises a heterocyclic ring system having at least one nitrogen atom and all nitrogen atoms of the heterocyclic ring system have an organic group as substituent,
- the anion of the ionic liquid is a compound having at least one carboxylate group (carboxylate for short) or at least one phosphate group (phosphate for short) and
the distance from the surface via which the heat of distillation is introduced in the distillation (vaporizer surface) to the surface at which condensation takes place (condenser surface) is less than 50 cm at at least one point, with the vaporizer surface and condenser surface themselves having at least one length dimension of greater than 50 cm.
2. The method according to claim 1, wherein the cation is an imidazolium cation.
3. The method according to claim 1 or 2, wherein the substituents on the nitrogen
atoms in the heterocyclic ring system are C1-C10-alkyl groups.
4. The method according to any of claims 1 to 3, wherein the ionic liquid is an
imidazolium salt of the formula I

where
R1 and R3 are each, independently of one another, an organic radical having from 1 to 20 carbon atoms,
R2, R4, and R5 are each, independently of one another, an H atom or an organic radical having from 1 to 20 carbon atoms,

X is a carboxylate and n is 1,2 or 3.
5. The method according to claim 4, wherein R2 is an organic radical having from 1 to 20 carbon atoms.
6. The method according to any of claims 1 to 5, wherein the mixtures comprise from 10 to 95% by weight of the ionic liquid.
7. The method according to any of claims 1 to 6, wherein the mixtures are mixtures which are obtained in the preparation of ionic liquids by single-stage or multistage reaction of starting compounds selected from among: α-dicarbonyl compounds, amino compounds, carbonyl compounds, ammonia and carbonate compounds.
8. The method according to any of claims 1 to 6, wherein the mixtures are mixtures which are obtained in the use of ionic liquids.
9. The method according to any of claims 1 to 8, wherein the mixtures comprise further constituents having a boiling point above 200°C (1 bar) as impurities, e.g. salts such as alkali metal acetates or natural or synthetic oligomeric or polymeric compounds such as lignin, hemicellulose or oligosaccharides.
10. The method according to any of claims 1 to 9, wherein the mixtures comprise constituents having a boiling point lower than the boiling point of the ionic liquid (more volatile compounds) in amounts of from 0 to 10% by weight.
11. The method according to any of claims 1 to 10, wherein more volatile compounds are separated off beforehand so that their proportion in the mixture is not more than 10% by weight, in particular not more than 5% by weight.
12. The method according to any of claims 1 to 11, wherein at least 10 percent by area of the vaporizer surface is at a distance of less than 50 cm from the condenser surface.
13. The method according to any of claims 1 to 12, wherein the vaporizer surface and the condenser surface are each larger than 0.5 m2.
14. The method according to any of claims 1 to 13, wherein the distillation is carried out at a surface temperature of the vaporizer of from 110°C to 300°C and a pressure of from 0.0001 to 10 mbar.

15. The method according to any of claims 1 to 14, wherein the distillate obtained comprises more than 97% by weight of the ionic liquid.

Distillation of ionic liquids
Abstract
Method of distilling mixtures comprising salts having a melting point of less than 200°C at 1 bar (ionic liquids), wherein
the cation of the ionic liquid comprises a heterocyclic ring system having at least one nitrogen atom and all nitrogen atoms of the heterocyclic ring system have an organic group as substituent,
the anion of the ionic liquid is a compound having at least one carboxylate group (carboxylate for short) or at least one phosphate group (phosphate for short) and
the distance from the surface via which the heat of distillation is introduced in the distillation (vaporizer surface) to the surface at which condensation takes place (condenser surface) is less than 50 cm at at least one point, with the vaporizer surface and condenser surface themselves having at least one length dimension of greater than 50 cm.

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Patent Number

268927

Indian Patent Application Number

224/MUMNP/2010

PG Journal Number

40/2015

Publication Date

02-Oct-2015

Grant Date

23-Sep-2015

Date of Filing

04-Feb-2010

Name of Patentee

BASF SE

Applicant Address

67056 Ludwigshafen Germany

Inventors:

#	Inventor's Name	Inventor's Address
1	MASSONNE Klemens	Höhenweng 8 67098 Bad Dürkheim Germany
2	SIEMER Michael	D3 2 68159 Mannheim Germany
3	MORMANN Werner	Brucknerweg 6 57076 Siegen Germany
4	LENG Wei	Stöltingstrasse 11 49448 Lemförde Germany

PCT International Classification Number

C07B 63/00,C07C 51/44,C07C 53/10

PCT International Application Number

PCT/EP2008/060743

PCT International Filing date

2008-08-15

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10 2007 041 416.3	2007-08-31	Germany