EP2432757A1

EP2432757A1 - Method for purifying carboxylic acids containing halogen compounds

Info

Publication number: EP2432757A1
Application number: EP10723049A
Authority: EP
Inventors: Günter FORSTER; Vijay Narayanan Swaminathan; Franz Niklaus Windlin; Thomas Leiendecker; Sebastian Peer Smidt
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2009-05-20
Filing date: 2010-05-19
Publication date: 2012-03-28
Also published as: JP2012527429A; CN102428066A; WO2010133651A1; US20120067715A1

Abstract

In a method for purifying carboxylic acids containing halogen compounds, the carboxylic acid is distilled in the presence of a heavy auxiliary base, the halide of which is liquid at the boiling point of the carboxylic acid. The auxiliary base binds the hydrogen halide contained in the carboxylic acid and/or separated from halogen compounds under a thermal effect, thus lowering the vapor pressure of the hydrogen halide such that the hydrogen halide is retained at the bottom of the distillation apparatus and does not spill over into the distillate. The fact that halide of the auxiliary base is liquid prevents the formation of solid deposits in the distillation apparatus. The carboxylic acid optionally also contains at least one light component.

Description

Process for purifying carboxylic acids containing halogen compounds

description

The present invention relates to a process for the purification of halogen compounds containing carboxylic acids.

Acylations with carboxylic acid anhydrides, such as acetic anhydride, are commonly used in the chemical industry. In this acylation, one molecule of carboxylic acid is by-produced per acyl group introduced into the target molecule. It is desirable to recover the resulting carboxylic acid for further use. However, this use of the carboxylic acid is in many cases complicated by impurities in the form of halogen compounds resulting from halogen-containing Lewis catalysts, with which the acylation and / or previous reactions are catalyzed, and optionally low-boiling components, which are derived from the solvents used.

So describes z. For example, EP-A 0087576 the esterification of tocopherol with acetic anhydride or propionic anhydride to tocopheryl acetate or tocopheryl propionate in the presence of zinc chloride and a liquid hydrocarbon as a solvent. Suitable solvents are hydrocarbons such as hexane, heptane, cyclohexane, benzene or toluene.

There is therefore a need for a process for the purification of halogen compounds containing carboxylic acids.

DE-A 211 97 44 discloses a process for purifying a carboxylic acid contaminated by halogenated materials by introducing a contaminated carboxylic acid stream into a first distillation column between its ends, removing a product stream from the upper part of the first column and placing it in a second column between their ends and removes a carboxylic acid stream from the lower part of the second column, said carboxylic acid stream is substantially free of halogenated material, an overhead fraction of the second column removed, which contains halogenated materials.

GB 850 960 describes a process for obtaining monocarboxylic acids from mixtures of monocarboxylic acids and bromine-containing compounds, in which the mixtures are distilled in the presence of a metal compound which prevents volatilization of the bromine-containing compounds. EP-A 0 135 085 discloses a process for the separation of iodine and its compounds from the carbonylation products acetic acid, acetic anhydride or ethylidene diacetate obtained in the carbonylation of dimethyl ether, methyl acetate or methanol. Treating the carbonylation products at temperatures of 20 to 250 ⁰ C with alkyl or aryl phosphines or heterocyclic aromatic nitrogen compounds and at least one of the metals copper, silver, zinc or cadmium to or compounds thereof and separating the carbonylation of the thus bound in non-volatile form of iodine distillatively.

EP-A 0 545 101 discloses a process for the purification of waste acetic acid, wherein the waste acetic acid is added in a first step with a complex-forming metal or one of its compounds and a basic compound and this mixture at a temperature between 25 and 1 18 ⁰ C. holding a period of 1 to 6 hours, distilled off in a second step, a flow and distilled off in a third step purified acetic acid from a low-volatile bubble residue overhead.

The known processes, in which inorganic bases and / or transition metal compounds are used to bind halogen compounds in the distillation residue, have the disadvantage that solid deposits can form in the distillation apparatus, which affect the trouble-free operation of the distillation apparatus.

The invention provides a process for the purification of carboxylic acids containing halogen compounds, in which the carboxylic acid is distilled in the presence of a sparingly volatile auxiliary base, the halide of which is liquid at the boiling point of the carboxylic acid.

Preferably, the distillation is carried out in the absence of transition metal compounds, and preferably in the absence of inorganic bases.

The halide of the auxiliary base is understood as meaning the reaction product of the auxiliary base with a hydrogen halide. Since the halide of the auxiliary base is liquid under the process conditions, the formation of solid deposits in the distillation apparatus is prevented and the removal of the halide in liquid form from the bottom of the distillation apparatus allows. These are decisive advantages in the distillation. In the present context, halogen is understood to mean fluorine (F), chlorine (Cl), bromine (Br) or iodine (I), preferably chlorine or bromine, in particular chlorine.

The halogen compounds to be removed according to the invention include (free) hydrogen halide and organic halogen compounds, in particular α-halocarboxylic acids. It is understood that hydrogen halides can dissociate in an equilibrium reaction to protons and halide ions. For the present purposes, therefore, halide ions are also attributed to the hydrogen halides. The inventive method is particularly applicable to carboxylic acids containing hydrogen halide, optionally in combination with organic halogen compounds.

While the depletion of the hydrogen halide moiety can be easily explained by the formation of the halide of the auxiliary base used, the observed depletion of the organic halogen compounds has not been clarified in detail. Presumably, the thermal stress decomposes the organic halogen compounds in the bottom of the distillation apparatus into hydrogen halide and halogen-free components. The hydrogen halide formed in turn can be intercepted by the auxiliary base. Organic halogen compounds in the form of α-halocarboxylic acids also have a higher acidity than (halogen-free) carboxylic acids and therefore preferably form salts with the auxiliary base. Thus, for example, chloroacetic acid or dichloroacetic acid are more acidic than acetic acid and are preferably deprotonated and thus retained in the sump as a low-volatile salt.

The process according to the invention is suitable for the purification of all carboxylic acids which are essentially distillable without decomposition.

The carboxylic acid to be purified is preferably liquid at 25 ^° C.

These include aliphatic monocarboxylic acids, in particular aliphatic monocarboxylic acids having 1 to 10 carbon atoms, such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, pivalic acid, caproic acid, ethylhexanoic acid, propylheptanoic acid, isononanoic acid and cyclopentanecarboxylic acid.

Of these, formic acid and acetic acid are most preferred.

The content of halogen compounds (calculated as halogen) in the carboxylic acid to be purified can generally be up to 5% by weight, usually up to 1% by weight, generally up to 0.1% by weight. The content of halogen compounds (calculated as halogen) in the carboxylic acid purified by the process according to the invention is generally less than 100 ppm, preferably less than 20 ppm, in particular less than 5 ppm. The total content of halogen compounds can be determined by methods known in the art of elemental analysis, z. B. by coulometric determination by combustion (eg., With a Euroglas ECS 1200 TOX analyzer (Thermo Electron GmbH, Dreieich, Germany), see, for example, BF Ehrenberger "Quantitative Organic Elemental Analysis" ISBN 3-527-28056-1 or DIN 51408 part 2, "Determination of chlorine content"). Hydrogen halide (including halide ions) can be measured by means of silver nitrate (argotometry). The proportion of organic halogen compounds can be determined as the difference between total halogen and hydrogen halide (including halide ions). If the constitution of the contaminating organic halogen compounds is known, a determination by mass spectrometry is also possible.

In one embodiment of the process according to the invention, the carboxylic acid also contains at least one low boiler. Low boilers are understood to mean compounds having a boiling point below the boiling point of the carboxylic acid to be purified. The contamination of the carboxylic acid by low boilers generally results from organic solvents in which chemical reactions, eg. As acylations with carboxylic anhydrides are carried out, as their by-product, the carboxylic acid is obtained, which is the starting material of the process according to the invention.

Suitable low-boiling components are, for example:

aliphatic hydrocarbons, such as n-pentane, pentane isomers and mixtures thereof, n-hexane, hexane isomers and mixtures thereof, n-heptane, heptane isomers and mixtures thereof, n-octane, octane isomers and mixtures thereof, isooctane, cyclohexane, methylcyclohexane, decalin;

aromatic hydrocarbons, such as benzene, toluene, o-xylene, m-xylene, p-xylene and mixtures thereof;

halogenated hydrocarbons, such as dichloromethane, trichloromethane, 1, 2-dichloroethane, 1, 2-dichloroethene, 1, 1, 1-trichloroethane;

Ethers, such as dimethyl ether, diethyl ether, tert-butyl methyl ether (MTBE), dioxane, tetrahydrofuran; Esters, such as methyl acetate, ethyl acetate;

Ketones, such as acetone, ethyl methyl ketone, cyclohexanone.

The maximum content of low-boiling carboxylic acid to be purified corresponds to the amount of low boilers which is homogeneously soluble in the carboxylic acid, generally up to 50 wt .-%, usually up to 3 wt .-% or up to 1 wt .-%. The content of low-boiling components in the carboxylic acid purified by the process according to the invention is generally less than 1% by weight, preferably less than 0.5% by weight, in particular less than 0.1% by weight.

The distillation can be carried out at reduced pressure, atmospheric pressure or overpressure. A preferred pressure range is 15 mbar to 1 bar, preferably 200 to 600 mbar. The distillation may in a temperature range (temperature at the bottom) of 20 ° to 250 ⁰ C, preferably at least 70 ⁰ C is performed.

If impurities other than halogen compounds are absent or the removal of impurities other than halogen compounds is not desired, the distillation can be carried out with sufficient boiling point difference between carboxylic acid and auxiliary base as simple distillation, i. H. essentially without mass transfer between vapors and condensate.

Preferably, however, the distillation is carried out as a fractional distillation in one or more, such as 2 or 3 distillation apparatuses. For this purpose, customary apparatus come into consideration for the distillation, as described, for example, in

Othmer, Encyclopedia of Chemical Technology, 3rd Ed., Vol. 7, John Wiley & Sons, New York, 1979, pages 870-881.

Preferably, the distillation takes place in one or more columns with internals, which consist of trays, rotating internals, disordered and / or ordered packs.

In the case of the column trays come (i) trays with holes or slots in the bottom plate; (ii) floors with necks or chimneys covered by bells, caps or hoods; (iii) trays with holes in the bottom plate covered by moving valves; (iv) floors with special constructions. In columns with rotating internals of the return is sprayed either by rotating funnel or spread by means of a rotor as a film on a heated tube wall.

Columns used in the process according to the invention may have random beds with different packing. They can be made of any suitable materials such as steel, stainless steel, nickel base alloys such as HC, copper, carbon, earthenware, porcelain, glass, plastics and in various forms such as spheres, rings with smooth or profiled surfaces, rings with inner webs or wall openings , Wire mesh rings, calipers and spirals.

Packages with regular geometry can, for. B. consist of sheets or tissues. Examples of such packings are Sulzer metal or plastic BX packages, Sulzer lamellar packs Mellapack made of sheet metal, structural packings by Sulzer (Optiflow), Montz (BSH) and Kühni (Rombopack).

The distillation column (s) is (are) provided with means for bottom heating. For this evaporators come into consideration, which are installed in the sump, such as a Robert evaporator, or a circulation with an external evaporator, eg. B. tube or plate heat exchanger. A circulation is then for example a forced circulation or a natural circulation. The distillation column (s) is (are) usually also provided with means for condensing and collecting the overhead product. About a condensate divider, a portion of the overhead condensate can be given as reflux back to the columns.

If the carboxylic acid to be purified contains low boilers, the distillation can be carried out in columns connected in series, first a low boiler fraction being withdrawn from the head in a low boiler column and then a bottom discharge from the low boiler column being passed into a pure carboxylic acid column, in which the pure carboxylic acid is separated from a high-boiling bottom residue. The low boiler fraction may consist of substantially pure low boilers and / or a low boiler carboxylic acid azeotrope.

In a simpler and therefore preferred embodiment, a mixture of the carboxylic acid to be purified and the auxiliary base is introduced into a distillation column between its head and sump. The distillation column comprises a tower section designed as a buoyancy section with a plurality of theoretical plates above the inlet, a column section designed as a stripping section below the inlet. Low boilers are withdrawn at the top of the distillation column, z. B. as pure low boilers and / or in the form of a low-boiling carboxylic acid azeotrope. The withdrawal of the pure carboxylic acid takes place in gaseous form from the lower region, the bottom or the circulation of the bottom heating of the distillation column. The auxiliary base and the halide of the auxiliary base accumulate in the swamp.

The mixture of the carboxylic acid to be purified and the auxiliary base may conveniently be reacted in a pre-reactor prior to introduction into the distillation column to complete the reaction between the hydrogen halide and the auxiliary base and / or thermal decomposition reactions of organic halogen compounds.

This embodiment is z. B. particularly suitable when the carboxylic acid is acetic acid and the low boilers heptane (including heptane isomer mixtures).

According to the invention, the distillation of the carboxylic acid takes place in the presence of a low-volatility auxiliary base. The term low volatility is intended to mean that the boiling point of the auxiliary base at the pressure at which the distillation is carried out, is higher than that of the carboxylic acid, preferably at least 35 ⁰ C higher, especially at least 50 ⁰ C higher, more preferably at least 75 ⁰ C. , higher than the boiling point of the carboxylic acid.

The auxiliary base is selected so that the halide of the auxiliary base is liquid at the boiling point of the carboxylic acid. Such liquid salts are often referred to as ionic liquids.

The auxiliary base binds the hydrogen halide present in the carboxylic acid and / or eliminated by thermal action from halogen compounds and in this way lowers its vapor pressure, so that the hydrogen halide is retained in the distillation bottoms and does not pass into the distillate.

The auxiliary base is used in stoichiometric amount or in stoichiometric excess (calculated as neutralization equivalents of the auxiliary base), based on the halogen compounds present in the carboxylic acid to be purified (calculated as halogen atoms). By neutralization equivalent we mean the imaginary fraction of the bass that can take up a proton. The auxiliary base is generally used in an amount of 1 to 30 equivalents, preferably 1 to 2 equivalents (calculated as neutralization equivalents) based on the halogen compounds present (calculated as halogen atoms). The compounds which can be used as auxiliary bases can contain phosphorus sulfur or nitrogen atoms, for example at least one nitrogen atom, preferably one to ten nitrogen atoms, particularly preferably one to five, very particularly preferably one to three and in particular one to two nitrogen atoms. Optionally, other heteroatoms, such as oxygen, sulfur or phosphorus atoms may be included.

Preference is given to those compounds which contain at least one five- to six-membered heterocycle which has at least one nitrogen atom and optionally an oxygen or sulfur atom, particularly preferably those compounds which contain at least one five- to six-membered heterocycle containing one, two or three nitrogen atoms and a sulfur or an oxygen atom, most preferably those having two nitrogen atoms.

Particularly preferred compounds are those which have a molecular weight below 1000 g / mol, very particularly preferably below 500 g / mol and in particular below 250 g / mol.

Furthermore, preference is given to those compounds which can be used as bases and are selected from the compounds of the formulas (Ia) to (Ir),

(Ia) (Ib) (Ic)

(Im) (In) (lo)

(Ip) (Iq) (Ir)

and oligomers or polymers containing these structures, wherein

R ¹ , R ² , R ³ , R ⁴ , R ⁵ and R ⁶ are each independently hydrogen, Ci-Cis-alkyl, optionally interrupted by one or more oxygen and / or sulfur atoms and / or one or more substituted or unsubstituted imino groups C 2 -C 18 -alkyl, C 6 -C 12 -aryl, C 5 -C 12 -cycloalkyl or a five- to six-membered, oxygen, nitrogen and / or sulfur-containing heterocycle or two of them together form an unsaturated, saturated or aromatic ring optionally interrupted by one or more oxygen and / or sulfur atoms and / or one or more substituted or unsubstituted imino groups, said radicals being in each case denoted by functional groups, aryl, alkyl, aryl - Loxy, alkyloxy, halogen, heteroatoms and / or heterocycles may be substituted.

Mean in it

optionally substituted by functional groups, aryl, alkyl, aryloxy, alkoxy, halogen, heteroatoms and / or heterocycles substituted Ci-Cis-alkyl, for example, methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, Hexyl, heptyl, octyl, 2-ethylhexyl, 2,4,4-trimethylpentyl, decyl, dodecyl, tetradecyl, heptadecyl, octadecyl, 1,1-dimethylpropyl, 1,1-dimethylbutyl, 1,1,3,3-tetramethylbutyl, Benzyl, 1-phenylethyl, 2-phenylethyl, α, α-dimethylbenzyl, benzhydryl, p-tolylmethyl, 1- (p-butylphenyl) -ethyl, p-chlorobenzyl, 2,4-dichlorobenzyl, p-methoxybenzyl, m-ethoxybenzyl, 2-cyanoethyl, 2-cyanopropyl, 2-methoxycarbonethyl, 2-ethoxycarbonylethyl, 2-butoxycarbonylpropyl, 1, 2-di- (methoxycarbonyl) -ethyl, 2-methoxyethyl, 2-ethoxyethyl, 2-butoxyethyl, diethoxymethyl, diethoxyethyl, 1, 3-dioxolan-2-yl, 1, 3-dioxan-2-yl, 2-methyl-1,3-dioxolan-2-yl, 4-methyl-1,3-dioxolan-2-yl, 2- isopropoxyethyl, 2-butoxypropyl, 2-octyloxyethyl, chloromethyl, 2-chloroethyl, trichloromethyl, T rifluoromethyl, 1, 1-dimethyl-2-chloroethyl, 2-methoxyisopropyl, 2-ethoxyethyl, butylthiomethyl, 2-dodecylthioethyl, 2-phenylthioethyl, 2,2,2-trifluoroethyl, 2-hydroxyethyl, 2-hydroxypropyl, 3 Hydroxypropyl, 4-hydroxybutyl, 6-hydroxyhexyl, 2-aminoethyl, 2-aminopropyl, 3-aminopropyl, 4-aminobutyl, 6-aminohexyl, 2-methylaminoethyl, 2-methylaminopropyl, 3-methylaminopropyl, 4-methylaminobutyl, 6-methylaminohexyl, 2-dimethylaminoethyl, 2-dimethylaminopropyl, 3-dimethylaminopropyl, 4-dimethylaminobutyl, 6-dimethylaminohexyl, 2-hydroxy-2,2-dimethylethyl, 2-phenoxyethyl, 2-phenoxypropyl, 3-phenoxypropyl, 4-phenoxybutyl, 6-phenoxyhexyl, 2-methoxyethyl, 2-methoxypropyl, 3-methoxypropyl, 4-methoxybutyl, 6-methoxyhexyl, 2-ethoxyethyl, 2-ethoxypropyl, 3-ethoxypropyl, 4-ethoxybutyl or 6-ethoxyhexyl and,

C 2 -C -alkyl which is optionally interrupted by one or more oxygen and / or sulfur atoms and / or one or more substituted or unsubstituted imino groups, for example 5-hydroxy-3-oxa-pentyl, 8-hydroxy-3,6-dioxo-octyl, 11-Hydroxy-3,6,9-trioxa-undecyl, 7-hydroxy-4-oxa-heptyl, 1-hydroxy-4,8-dioxa-undecyl, 15-hydroxy-4,8,12-trioxa-pentadecyl , 9-hydroxy-5-oxa-nonyl, 14-hydroxy-5,10-oxotetradecyl, 5-methoxy-3-oxa-pentyl, 8-methoxy-3,6-dioxa-octyl, 11-methoxy-3 , 6,9-trioxa undecyl, 7-methoxy-4-oxa-heptyl, 11-methoxy-4,8-dioxa-undecyl, 15-methoxy-4,8,12-trioxa-pentadecyl, 9-methoxy-5 -oxa-nonyl, 14-methoxy-5,10-oxa-tetradecyl, 5- Ethoxy-3-oxa-pentyl, 8-ethoxy-3,6-dioxa-octyl, 11-ethoxy-3,6,9-trioxa-undecyl, 7-ethoxy-4-oxa-heptyl, 1 1-ethoxy-4 , 8-dioxa-undecyl, 15-ethoxy-4,8,12-trioxa-pentadecyl, 9-ethoxy-5-oxa-nonyl or 14-ethoxy-5,10-oxa-tetradecyl.

If two radicals form a ring, then these radicals may be together 1, 3

Propylene, 1,4-butylene, 2-oxa-1,3-propylene, 1-oxa-1,3-propylene, 2-oxa-1,3-propylene, 1-oxa-1,3-propenylene, 1- Aza-1, 3-propenylene, 1-C 1 -C 4 -alkyl-1-aza-1, 3-propenylene, 1, 4-buta-1, 3-dienylene, 1-aza-1, 4-buta-1, 3-dienylene or 2-aza-1,4-buta-1,3-dienylene.

The number of oxygen and / or sulfur atoms and / or imino groups is not limited. As a rule, it is not more than 5 in the radical, preferably not more than 4, and very particularly preferably not more than 3.

Furthermore, at least one carbon atom, preferably at least two, is usually present between two heteroatoms.

Substituted and unsubstituted imino groups may be, for example, imino, methylimino, / so-propylimino, n-butylimino or fe / t-butylimino.

Furthermore mean

functional groups carboxy, carboxamide, hydroxy, di- (C 1 -C 4 -alkyl) amino, C 1 -C 4 -alkyloxycarbonyl, cyano or C 1 -C 4 -alkyloxy,

optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and / or heterocycles substituted C6-Ci2-aryl for example phenyl, ToIyI, XyIyI, α-naphthyl, ß-naphthyl, 4-diphenylyl, chlorophenyl, dichlorophenyl, tri - chlorophenyl, difluorophenyl, methylphenyl, dimethylphenyl, trimethylphenyl, ethylphenyl, diethylphenyl, / so-propylphenyl, tert-butylphenyl, dodecylphenyl, methoxyphenyl, dimethoxyphenyl, ethoxyphenyl, hexyloxyphenyl, methylnaphthyl, isopropylnaphthyl, chloronaphthyl, ethoxynaphthyl, 2,6-dimethylphenyl , 2,4,6-trimethylphenyl, 2,6-dimethoxyphenyl, 2,6-dichlorophenyl, 4-bromophenyl, 2- or 4-nitrophenyl, 2,4- or 2,6-dinitrophenyl, 4-dimethylaminophenyl, 4-acetylphenyl , Methoxyethylphenyl or ethoxymethylphenyl,

optionally substituted by functional groups, aryl, alkyl, aryloxy, alkoxy, halogen, heteroatoms and / or heterocycles substituted C5-Ci2-cycloalkyl for example cyclopentyl, cyclohexyl, cyclooctyl, cyclododecyl, methylcyclopentyl, dimethylcyclopentyl, methylcyclohexyl, dimethylcyclohexyl, diethylcyclohexyl, butylcyclohexyl, Me - thoxycyclohexyl, dimethoxycyclohexyl, diethoxycyclohexyl, butylthiocyclohexyl, chlorocyclohexyl, dichlorocyclohexyl, dichlorocyclopentyl and a saturated or unsaturated bicyclic system such as norbornyl or norbornenyl,

a five- to six-membered heterocycle having oxygen, nitrogen and / or sulfur atoms, for example furyl, thiophenyl, pyrryl, pyridyl, indolyl, benzoxazolyl, dioxolyl, dioxyl, benzimidazolyl, benzthiazolyl, dimethylpyridyl, methylquinolyl, dimethylpyrryl, methoxyfuryl, dimethoxypyridyl, Difluorpyridyl, methylthiophenyl, isopropylthiophenyl or tert-butylthiophenyl and

Ci to C4-alkyl, for example, methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl or tert-butyl.

R ¹ , R ² , R ³ , R ⁴ , R ⁵ and R ⁶ are preferably independently of one another hydrogen, methyl, ethyl, n-butyl, 2-hydroxyethyl, 2-cyanoethyl, 2- (methoxycarbonyl) -ethyl, 2

(Ethoxycarbonyl) -ethyl, 2- (n-butoxycarbonyl) -ethyl, dimethylamino, diethylamino and chloro.

Particularly preferred pyridines (Ia) are those in which one of the radicals R ¹ to R ^{5 is} methyl, ethyl or chlorine and all others are hydrogen, or R ^{3 are} dimethylamino and all others are hydrogen or are all hydrogen or R ^{2 is} carboxy or carboxamide and all others are hydrogen or R ¹ and R ² or R ² and R ^{3 are} 1, 4-butan-1, 3-dienylene and all others are hydrogen.

Particularly preferred pyridazines (Ib) are those in which one of the radicals R ¹ to R ^{4 is} methyl or ethyl and all others are hydrogen or all hydrogen.

Particularly preferred pyrimidines (Ic) are those in which R ² to R ^{4 is} hydrogen or methyl and R ^{1 is} hydrogen, methyl or ethyl, or R ² and R ^{4 are} methyl, R ³ is hydrogen and R ^{1 is} hydrogen, methyl or ethyl is.

Particularly preferred pyrazines (Id) are those in which R ¹ to R ^{4 are} all methyl or all hydrogen.

Particularly preferred imidazoles (Ie) are those in which R ¹ is independently selected from methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-octyl, 2-hydroxyethyl or 2-cyanoethyl and

R ² to R ⁴ independently of one another denote hydrogen, methyl or ethyl. Particularly preferred 1 H-pyrazoles (If) are those in which independently of one another

R ¹ is hydrogen, methyl or ethyl,

R ² , R ³ and R ⁴ are hydrogen or methyl

are selected.

Particularly preferred 3H-pyrazoles (Ig) are those in which independently of one another

R ¹ is hydrogen, methyl or ethyl,

R ² , R ³ and R ⁴ are hydrogen or methyl

are selected.

Particularly preferred 4H-pyrazoles (Ih) are those in which independently of one another

R ¹ to R ⁴ are hydrogen or methyl,

are selected.

Particularly preferred 1-pyrazolines (Ii) are those in which independently of one another

R ¹ to R ⁶ are hydrogen or methyl

are selected.

Particularly preferred 2-pyrazolines (Ij) are those in which independently of each other

R ¹ is hydrogen, methyl, ethyl or phenyl and

R ² to R ⁶ are hydrogen or methyl are selected.

Particularly preferred 3-pyrazolines (Ik) are those in which independently of each other

R ¹ or R ² is hydrogen, methyl, ethyl or phenyl and

R ³ to R ⁶ are hydrogen or methyl

are selected.

Particularly preferred imidazolines (II) are those in which independently of one another

R ¹ or R ² is hydrogen, methyl, ethyl, n-butyl or phenyl and

R ³ or R ⁴ is hydrogen, methyl or ethyl and

R ⁵ or R ⁶ is hydrogen or methyl

are selected.

Particularly preferred imidazolines (Im) are those in which independently of one another

R ¹ or R ² is hydrogen, methyl or ethyl and

R ³ to R ⁶ are hydrogen or methyl

are selected.

Particularly preferred imidazolines (In) are those in which independently of one another

R ¹ , R ² or R ³ is hydrogen, methyl or ethyl and

R ⁴ to R ⁶ are hydrogen or methyl

are selected. Particularly preferred thiazoles (lo) or oxazoles (Ip) are those in which independently of one another

R ¹ is hydrogen, methyl, ethyl or phenyl and

R ² or R ³ is hydrogen or methyl

are selected.

Particularly preferred 1,2,4-triazoles (Iq) are those in which independently of one another

R ¹ or R ² is hydrogen, methyl, ethyl or phenyl and

R ³ is hydrogen, methyl or phenyl

are selected.

Particularly preferred 1,2,3-triazoles (Ir) are those in which independently of one another

R ¹ is hydrogen, methyl or ethyl and

R ² or R ³ are selected from hydrogen or methyl or

R ² and R ^{3 are} 1, 4-buta-1, 3-dienylene and all others are hydrogen.

Among these, pyridines and imidazoles are preferred.

Very particular preference is given as bases to 3-chloropyridine, 4-dimethylaminopyridine, 2-ethyl-4-aminopyridine, 2-methylpyridine (α-picoline), 3-methylpyridine (β-picoline), 4-methylpyridine (γ-picoline), 2 -Ethylpyridine, 2-ethyl-6-methylpyridine, quinoline, isoquinoline, 1-C 1 -C 4 -alkylimidazole, 1-methylimidazole, 1, 2-dimethylimidazole, 1-n-butylimidazole, 1, 4,5-trimethylimidazole, 1, 4 Dimethylimidazole, imidazole, 2-methylimidazole, 1-butyl-2-methylimidazole, 4-methylimidazole, 1-n-pentylimidazole, 1-n-hexylimidazole, 1-n-octylimidazole, 1- (2'-aminoethyl) - imidazole, 2-ethyl-4-methylimidazole, 1-vinylimidazole, 2-ethylimidazole, 1- (2'-cyanoethyl) -imidazole and benzotriazole. Particularly preferred are 1-n-butylimidazole, 1-methylimidazole, 2-methylpyridine and 2-ethylpyridine.

Also suitable are tertiary amines of the formula (XI)

NR ^a R ^b R ^c (XI),

wherein

R ^a , R ^b and R ^c independently of one another each Ci-Cis-alkyl, optionally interrupted by one or more oxygen and / or sulfur atoms and / or one or more substituted or unsubstituted imino C2-Ci8-alkyl, C6-Ci2-aryl or C5-C12-cycloalkyl or a five- to six-membered, oxygen, nitrogen and / or sulfur-containing heterocycle or two of them together an unsaturated, saturated or aromatic and optionally by one or more oxygen and / or sulfur atoms and / or or one or more substituted or unsubstituted imino groups form interrupted ring, where the radicals mentioned may each be substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and / or heterocycles,

with the proviso that

at least two of the three radicals R ^a, R ^b and R ^c are different and the radicals R ^a, R ^b and R ^c together is at least 8, preferably at least 10, more preferably at least 12 and most preferably at least 13 carbon atoms.

R ^a , R ^b and R ^c are each independently C 1 -C 6 -alkyl, C 6 -C 12 -aryl or C 5 -C 12 -cycloalkyl and particularly preferably C 1 -C 6 -alkyl, where the radicals mentioned are each represented by functional groups, aryl, Alkyl, aryloxy, alkyloxy, halogen, heteroatoms and / or heterocycles may be substituted.

Examples of the respective groups are already listed above.

Preferred meanings for the radicals R ^a , R ^b and R ^c are methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl (n-amyl), 2- Pentyl (sec-amyl), 3-pentyl, 2,2-dimethyl-prop-1-yl (neo-pentyl), n-hexyl, n-heptyl, n-octyl, isooctyl, 2-ethylhexyl, 1, 1-dimethylpropyl, 1, 1-dimethylbutyl, benzyl, 1-phenylethyl, 2-phenylethyl, α, α-dimethylbenzyl, phenyl, ToIyI, XyIyI, α-naphthyl, ß-naphthyl, cyclopentyl or cyclohexyl.

If two of the radicals R ^a , R ^b and R ^{c form} a chain, this may be, for example, 1,4-butylene or 1,5-pentylene.

Examples of the tertiary amines of the formula (XI) are diethyl-n-butylamine, diethyl-tert-butylamine, diethyl-n-pentylamine, diethyl-hexylamine, diethyl-octylamine, diethyl (2-ethylhexyl) -amine, di n-propyl-butylamine, di-n-propyl-n-pentylamine, di-n-propyl-hexylamine, di-n-propyl-octylamine, di-n-propyl- (2-ethylhexyl) -amine, di-iso -propyl-ethylamine, di-isopropyl-n-propylamine, di-iso-propyl-butylamine, di-iso-propyl-pentylamine, di-iso-propyl-hexylamine, di-iso-propyl-octylamine, di-iso -propyl- (2-ethylhexyl) -amine, di-n-butyl-ethylamine, di-n-butyl-n-propylamine, di-n-butyl-n-pentylamine, di-n-butyl-hexylamine, di-n - butyl-octylamine, di-n-butyl- (2-ethylhexyl) -amine, Nn-butyl-pyrrolidine, N-sec-butyl-pyrrolidine, N-tert-butyl-pyrrolidine, Nn-pentyl-pyrrolidine, N, N Dimethylcyclohexylamine, N, N-diethylcyclohexylamine, N, N-di-n-butylcyclohexylamine, Nn-propyl-piperidine, N-iso-propyl-piperidine, Nn-butyl-piperidine, N-sec-butyl-piperidine, N-tert Butyl-piperidine, Nn-pentyl-piperidine, Nn-butylmorpholine, N-sec-butylmorpholine, N-tert-butylmorpholine, Nn-pentylmorpholine, N-benzyl-N-ethyl-aniline, N-benzyl-Nn-propyl-aniline, N-benzyl-N-isopropyl-aniline, N- Benzyl-Nn-butyl-aniline, N, N-dimethyl-p-toluidine, N, N-diethyl-p-toluidine, N, N-di-n-butyl-p-toluidine, diethylbenzylamine, di-n-propylbenzylamine, Di-n-butylbenzylamine, diethylphenylamine, di-n-propylphenylamine and di-n-butylphenylamine, and 1,5-diazabicyclo [4.3.0] non-5-ene (DBN).

Preferred tertiary amines (XI) are di-isopropylethylamine, diethyl-tert-butylamine, diisopropyl-butylamine, di-n-butyl-n-pentylamine, N, N-di-n-butylcyclohexylamine and tertiary Amines of pentyl isomers.

Particularly preferred tertiary amines are di-n-butyl-n-pentylamine and tertiary amines of pentyl isomers.

The melting points of the salts of the particularly preferred auxiliary bases are generally below 160 ^° C., more preferably below 100 ^° C., and very preferably below 80 ^° C.

For example, the hydrochloride of 1-methylimidazole has a melting point of about 75 ⁰ C, the hydrochloride of 2-ethylpyridine a melting point of about 55 ⁰ C. The hydrochloride of 1-butylimidazole is already liquid at room temperature. From the halide of the auxiliary base obtained as a high boiler, the free base can be recovered and returned to the process by a manner known to the person skilled in the art.

This can be done, for example, by adding the halide of the auxiliary base with a strong base, for example NaOH, KOH, Ca (OH) ₂ , lime, Na ₂ CO ₃ , NaHCO ₃ , K ₂ CO ₃ , or KHCO ₃ , optionally in a solvent , such as water, methanol, ethanol, n- or / so-propanol, n-butanol, n-pentanol or butanol or pentanol isomer mixtures or acetone releases. The auxiliary base thus released can, if it forms a separate phase separated or if it is miscible with the salt of the stronger base or the solution of the salt of the stronger base, be separated by distillation from the mixture. If necessary, one can also separate the liberated auxiliary base from the salt of the stronger base or the solution of the salt of the stronger base by extraction with an extractant. Extractants are, for example, solvents, alcohols or amines.

If necessary, the auxiliary base can be washed with water or aqueous NaCl or Na ₂ SO ₄ solution and then dried, for example by removal of optionally contained water by means of azeotropic distillation with benzene, toluene, xylene butanol or cyclohexane.

If necessary, the base can be distilled before reuse.

Another possibility of recycling is to distill the halide of the auxiliary base, the salt being thermally converted into its starting materials, i. the free base and hydrogen halide is split.

If an inorganic base is used instead of the sparingly volatile auxiliary base in the process according to the invention for the purification of halogen compounds, then, as described above, the distillation of carboxylic acids in the presence of inorganic bases leads to results which do not show all the advantages of the present invention Have method. In this procedure are used as inorganic bases alkali metal and alkaline earth metal hydroxides, such as sodium hydroxide, potassium hydroxide and calcium hydroxide, alkali metal carbonates and alkali metal bicarbonates, as well as mixtures of said alkali and alkaline earth metal salts. Preferably, aqueous solutions of these inorganic bases are used, wherein the weight ratio of the inorganic base: water is between 10:90 and 90:10, preferably between 25:75 and 75:25, particularly preferably between 40:60 and 60:40. Preference is given to alkali metal and alkaline earth metal hydroxides, in particular alkali metal hydroxides, and very particularly preferably sodium and potassium hydroxide.

Carboxylic acids containing halogen compounds include the carboxylic acids contaminated with halogen compounds described above. The contaminated carboxylic acids may contain a low-boiling component, with the low-boiling components described above being suitable in the amounts also described above. According to a preferred embodiment of this procedure, a mixture of the carboxylic acid to be purified and the inorganic base is introduced into a distillation column between its top and bottom, withdrawn low boilers at the top of the distillation column and pure carboxylic acid gaseous from the lower region, the bottom or the circulation of the sump heater Withdrawn distillation column. For distillation, the same apparatuses are considered as described above.

In a simple apparatus embodiment, the mixture of the carboxylic acid to be purified and the inorganic base is introduced into a distillation column between its head and sump. The distillation column comprises a lift section with a plurality of theoretical separation trays designed column section above the inlet, designed as a stripping section column shot below the inlet. Low boilers are withdrawn at the top of the distillation column, z. B. as pure low boilers and / or in the form of a low-boiling carboxylic acid azeotrope. The withdrawal of the pure carboxylic acid takes place in gaseous form from the lower region, the bottom or the circulation of the bottom heating of the distillation column. The inorganic base and the halide of the base accumulate in the bottom.

The mixture of the carboxylic acid to be purified and the inorganic base may conveniently be reacted in a pre-reactor prior to introduction into the distillation column to complete the reaction between the hydrogen halide and the base and / or thermal decomposition reactions of organic halogen compounds.

This embodiment is z. B. particularly suitable when the carboxylic acid is acetic acid and the low boilers heptane (including mixtures of isomers).

The process can be carried out batchwise or preferably continuously.

The inorganic base binds the hydrogen halide present in the carboxylic acid and / or eliminated by thermal action from halogen compounds salt formation and thus lowers its vapor pressure, so that the hydrogen halide is held in the distillation bottoms and not in the distillate Ü occur.

The inorganic base is used in stoichiometric amount or in stoichiometric excess (calculated as neutralization equivalents of the base), based on the halogen compounds present in the carboxylic acid to be purified (calculated as halogen atoms). Neutralization equivalent is understood to mean the imaginary fraction of the base that can take up a proton. The base is generally used in an amount of 1 to 30 equivalents, preferably 1 to 2 equivalents (calculated as neutralization equivalents) based on the halogen compounds present (calculated as halogen atoms). In the case of purification in the presence of inorganic bases, solid deposits can form in the distillation apparatus, which can impair the trouble-free operation of the distillation apparatus.

The invention is further illustrated by the following examples. In the examples, all data are in% as wt .-%.

Example 1: Separation of chloride and heptane from acetic acid by means of methylimidazole

Test 1:

In a 250 mL two-necked flask with attached column (15 cm with 8 mm Raschig rings) and distillation bridge with cooling water cooling was placed 95.00 g of acetic acid (190 ppm total chlorine, 1, 9% heptane) and gave 5.00 g of methylimidazole ( MIA) too. The contents of the flask warmed by 6 ⁰ C to 31 ⁰ C. The flask was heated in an oil bath. Distillation under normal pressure was at 129-135 ⁰ C bath temperature (BT), up to 1 19 ⁰ C bottom temperature (ST) and up to 80 ⁰ C transition temperature (ÜT) a flow (fraction 1, 1, 4 g, two-phase) on. On further heating (, 69.8 g of fraction 2, single phase) was at ⁰ to 165 C BT, up to 134 ⁰ C and ST to 95-120 ⁰ C ÜT of the main runner over. Upon further heating to 185 ⁰ C BT, to 163 ⁰ C ST and max 1 12 ⁰ C ÜT gave a wake (fraction 3, 12.8 g). 15.2 g of bottom residue were obtained.

Test 2: Test 1 was repeated, but 97.50 g of acetic acid were initially charged and 2.50 g

MIA admitted. The addition was observed some smoking and heating to 5 ⁰ C to 30 ⁰ C. Distillation under normal pressure was a flow at 131-142 ⁰ C BT, to 118.5 ⁰ C ST and 81 ⁰ C ÜT (fraction 1, 3.0g, two-phase). During further heating went up to 166 ⁰ C BT, to 145 ⁰ C ST and to 86-120 ⁰ C ÜT the main run (Fraction 2, single phase, 83.2 g). Upon further heating up to 185 ⁰ C BT, until

167 ⁰ C ST and a maximum of 60 ⁰ C ÜT gave a caster (fraction 3, 5.0 g). This gave 9.4 g of bottom residue.

Test 3:

Test 1 was repeated but with 99.00 g of acetic acid being added and 1.00 g of MIA added. The addition was observed some smoking and heating to 4 ⁰ C to 29 ⁰ C. When distilling under atmospheric pressure was a flow at 131-146 ⁰ C BT, to 1 17 ⁰ C ST and to 89 ⁰ C ÜT (Fraction 1, 2 , 9 g, two-phase). On further heating (, 90.2 g of fraction 2, single phase) was at ⁰ to 166 C BT, to 147 ⁰ C and up to 1 ST 16-120 ⁰ C ÜT of the main runner over. Upon further heating up to 185 ⁰ C BT, until

168 ⁰ C ST and a maximum of 86 ⁰ C ÜT gave a colorless caster (fraction 3, 2.0 g). 5.7 g of bottom residue were obtained.

The analysis results of tests 1 to 3 are summarized in the following table:

Example 2: Continuous separation of heptane and chloride from acetic acid

An apparatus consisting of two thin-layer evaporators with a wiper (wiper length 20 cm) was used. In a mixing bottle (1000 ml bottle), the acetic acid to be purified was introduced by means of a funnel; In addition, bottom discharge from the second thin-film evaporator was returned via a membrane metering pump. The bottle was shaken by hand to mix the contents. In the first thin film evaporator, which was flushed in countercurrent with nitrogen, fed via a diaphragm metering feed from the mixing bottle. The distillate was collected below the side condenser, the bottom was passed into a 50 oL 2-neck flask heated with a thermostat. Sump discharge was passed from the first thin film evaporator to the second thin film evaporator via a membrane metering pump. The distillate was separated via a 10 cm column with 8 mm Raschig rings and distilled off via a distillation bridge. Of the Swamp was transferred to a 500ml 2-neck flask heated with a thermostat.

Day 1: In the mixing bottle, 976.0 g of acetic acid (0.014% total chlorine) and 25.4 g of 1-methylimidazole were added.

Settings of the first thin film evaporator: 118 ° C. BT, 400 rpm, feed about 0.5 kg / h, nitrogen about 10 L / h.

Settings of second thin film evaporator: 190 ^° C. BT, 400 rpm, feed about 0.5 kg / h.

In the first thin-film evaporator distils a small amount of low boilers; the biphasic condensate is discarded. The sump is conveyed after a lead time of about 20 minutes directly into the second thin-film evaporator, in which acetic acid is obtained as a distillate, which was collected. As soon as a sump quantity of 250-350 ml was reached, the sump was conveyed into the mixing bottle (after 1 h 30 min, 2 h 10 min, 2 h 30 min, 2 h 50 min).

Distillate 1 obtained: 456.0 g Obtained distillate 2: 437.5 g Obtained distillate 3: 454.2 g

Day 2:

Acetic acid mixed with recycled sump from the second thin film evaporator was placed in the mixing bottle.

Settings of second thin film evaporator: 195 ° C BT, 400 rpm, feed about 0.5 kg / h.

In the first thin film evaporator, a small amount of low boilers distilled off (total 31.7 g); the biphasic condensate is discarded. The sump was conveyed after a lead time of about 20 minutes directly into the second thin-film evaporator, in which acetic acid is obtained as a distillate, which was collected. Once a Swamp amount of 250-350 ml_ was reached, the sump was conveyed into the mixing bottle (after 1 h 25 min, then increasingly faster in 30- 15 min cycle).

Obtained distillate 4: 409.5 g

Distillate 5: 457.3 g

Distillate 6 obtained: 400.4 g

Distillate 7 obtained: 283.0 g

After completion of the distillate removal remained 353.2 g of swamp.

The analytical results of distillates 1 to 7 are summarized in the following table:

Example 3: Continuous separation of heptane and chloride from acetic acid

The apparatus used consisted of a pre-reactor and a bubble tray column with 8 plates. The prereactor used was a 50 ml standard reactor with overflow and glass stirrer at 50 rpm. Acetic acid was fed in via a diaphragm metering pump with Teflon internals, and the base was fed via a piston metering pump with Teflon internals.

The standard bubble tray column used had a total of 8 bubble trays and was heated with electric heating jackets. The sump was a 2.5L standard reactor with two standard sanders with glass stirrer and level control, which was heated with a thermostat. Vacuum was generated by a regulated oil pump.

The feed from the prereactor was moved to the bottom 4 of the bubble tray column. The second standard ground section of the bottom reactor lid was followed by a steam outlet. The vapor was condensed in an intensive condenser. The condensate was pumped out with a diaphragm metering pump. To remove partial pressure differences, the head of the condenser was connected directly to bottom 6 (counted from the sump) via a PVC hose and a built-in needle valve. To keep the condensate level constant, excess distillate was pumped directly into the sump via a bypass with built-in diaphragm dosing pump.

The blending mixture was withdrawn via a heated bridge at the top of the column, condensed on a condenser and placed on a magnetic fluid divider set in the ratio 99: 1. The larger stream was returned to the top of the column by means of a controlled diaphragm metering pump, and the smaller stream was removed by means of a level-controlled diaphragm metering pump.

At the beginning of the experiment, 1010 g of acetic acid and 2.1 g of 1-methylimidazole (MIA) were placed in the bottom. 520 g / h acetic acid and 1.05 g / h MIA were metered into the prereactor.

A vacuum of 515 mbar was set. The bottom heating was set at 139 ⁰ C and was gradually increased to 144 ⁰ C; the heating bands were set to 100 ⁰ C / 90 ⁰ C / 60 ⁰ C / 40 ⁰ C. The temperature of the pre-reactor was 78 ⁰ C, the temperature of the condenser 94 ⁰ C. It withdrew 480 g / h of pure acetic acid.

The total chlorine content of the acetic acid used was 0.07%. In the obtained pure acetic acid, the total chlorine content was less than 10 ppm. The chloride ion content in the pure acetic acid was determined to be 4 ppm. The heptane content decreased from 1% to 0.1%.

Example 4: Continuous separation of heptane and chloride from acetic acid

The apparatus used consisted as in Example 3 of a pre-reactor and a bubble tray column with 8 trays. The prereactor is identical to Example 3. The acetic acid was premixed in a bottle with the base. The feed of the acetic acid-base mixture was carried out via a diaphragm metering pump with Teflon internals.

The standard bubble tray column used is identical to Example 3, and the bottom and the vacuum correspond to Example 3.

The feed from the prereactor was moved to the bottom 4 of the bubble tray column. The second standard ground section of the sump reactor lid was inserted Steam vent. A single bell bottom was switched in front of the intensive cooler. The steam was condensed in the intensive cooler. The condensate was conveyed out with a diaphragm metering pump. To remove partial pressure differences, the head of the condenser was connected directly to the bottom 3 (counted from the sump) via a Teflon tube and a built-in needle valve. The low boiler removal is as described in Example 3.

At the beginning of the experiment, 999.1 g of acetic acid and 0.45 g of 1-methylimidazole were initially charged in the bottom. 520 g / h of acetic acid / methylimidazole mixture (with a methylimidazole to acetic acid ratio of 0.45 g to 1 kg) were metered into the prereactor.

A vacuum of 515 mbar was set. The sump heating was set at 145 ⁰ C; the heating bands were set to 100 ⁰ C / 90 ⁰ C / 60 ⁰ C / 40 ⁰ C. The temperature of the prereactor was 78 ⁰ C, the temperature of the capacitor 94 ⁰ C. It took 480 g / h of pure acetic acid.

The total chlorine content of the acetic acid used was 0.013%, of which 50 ppm as chloride. In the pure acetic acid obtained, the total chlorine content was less than 3 ppm. The heptane content decreased from 1% to 0.1%.

Comparative Example 1: Continuous separation of heptane and chloride from acetic acid with the aid of sodium hydroxide

The standard bubble tray column used had a total of 8 bubble trays and was heated with electric heating jackets. The sump was a 2.5L standard reactor with two standard sanders with glass stirrer and level control, which was heated with a thermostat. Vacuum was generated by a regulated oil pump. The feed from the prereactor was moved to the bottom 4 of the bubble tray column. The second standard ground section of the bottom reactor lid was followed by a steam outlet. The vapor was condensed in an intensive condenser. The condensate was conveyed out with a diaphragm metering pump. To pick up partial pressure differences, the head of the chiller was over a PVC hose and built-in Needle valve directly connected to bottom 3 (counted from the sump). To keep the condensate level constant, excess distillate was pumped directly into the sump via a bypass with a built-in diaphragm dosing pump.

The blending mixture was withdrawn via a heated bridge at the top of the column, condensed on a condenser and placed on a magnetic fluid divider set in the ratio 99: 1. The larger stream was conveyed back to the top floor of the column by means of a controlled diaphragm metering pump, the smaller stream was removed by means of a state-controlled Diaphragm metering pump.

At the beginning of the experiment 999.6 g of acetic acid and 0.4 g of 50% sodium hydroxide solution were placed in the bottom. In the pre-reactor 520 g / h acetic acid-NaOH mixture were metered in the same ratio.

A vacuum of 505 mbar was set. The sump heating was set at 145 ⁰ C; the heating bands were set to 100 ⁰ C / 90 ⁰ C / 60 ⁰ C / 40 ⁰ C. The temperature of the pre-reactor was 78 ⁰ C, the temperature of the condenser 94 ⁰ C. It withdrew 480 g / h of pure acetic acid.

The total chlorine content of the acetic acid used was 0.015%. In the pure acetic acid obtained, the total chlorine content in the first five liters of discharge was 5 ppm, then at most 3 ppm. The heptane content decreased from 0.9% to 0.11 to 0.05%.

Comparative Example 2: Continuous separation of heptane and chloride from acetic acid with the aid of potassium hydroxide

The apparatus used consisted as in Example 1 of a pre-reactor and a bubble tray column with 8 trays. The prereactor is identical to Comparative Example 1. The acetic acid was premixed with the base. Acetic acid was fed in via a diaphragm metering pump with Teflon internals, and the base was fed via a piston metering pump with Teflon internals.

The standard bubble tray column used is identical to Comparative Example 1; the sump and the vacuum also correspond to Comparative Example 1.

The feed from the prereactor was moved to the bottom 4 of the bubble tray column. The second standard ground section of the sump reactor lid was inserted Steam vent. The vapor was condensed in an intensive condenser. The condensate was conveyed out with a diaphragm metering pump. To cancel out partial pressure differences, the head of the condenser was connected directly to bottom 2 (counted from the sump) via a PVC hose and a built-in needle valve. In order to keep the condensate level constant, excess distillate was pumped directly into the sump via a bypass with a built-in diaphragm metering pump.

At the beginning of the experiment, 990.5 g of acetic acid and 9.5 g of 50% potassium hydroxide solution were placed in the bottom. In the pre-reactor 520 g / h acetic acid-KOH mixture were metered in the same ratio.

A vacuum of 505 mbar was set. The sump heater was situated on 145 ⁰ C einge-; the heating bands were set to 100 ⁰ C / 90 ⁰ C / 60 ⁰ C / 40 ⁰ C. The temperature of the pre-reactor was 78 ⁰ C, the temperature of the condenser 94 ⁰ C. It withdrew 480 g / h of pure acetic acid.

The total chlorine content of the acetic acid used was 0.01%. In the obtained pure acetic acid, the total chlorine content was less than 3 ppm. The heptane content decreased from 0.9% to 0.05%.

Claims

claims

1. A process for the purification of halogen compounds containing carboxylic acids, wherein the carboxylic acid is distilled in the presence of a low volatility auxiliary base, the halide of which is liquid at the boiling point of the carboxylic acid.

2. The method of claim 1, wherein the halogen compounds are selected from chlorine compounds and bromine compounds.

3. The method of claim 2, wherein the halogen compounds are chlorine compounds.

4. The method according to any one of the preceding claims, wherein the halogen compounds comprise hydrogen halide.

5. The method according to any one of the preceding claims, wherein the auxiliary base in an amount of 1 to 30 equivalents, calculated as neutralization equivalents, based on the halogen compounds contained in the carboxylic acid to be purified, calculated as halogen atoms, is used.

6. The method according to any one of the preceding claims, wherein the carboxylic acid is selected from formic acid and acetic acid.

7. The method according to any one of the preceding claims, wherein the carboxylic acid also contains at least one low boilers.

8. The method of claim 7, wherein introducing a mixture of the carboxylic acid to be purified and the auxiliary base in a distillation column between the top and bottom, low boilers at the top of the distillation column and pure carboxylic acid gaseous from the lower region, the bottom or the circulation of the sump heater the distillation column deducted.

A process according to claim 7 or 8, wherein the carboxylic acid is acetic acid and the low boiler is heptane.

10. The method according to any one of the preceding claims, wherein the auxiliary base is selected from the formula (Ia) to (Ir),

(ig) (Ih) (II)

(Ij) (Ik) (H)

(Ip) (Iq) (Ir) where

R ¹ , R ² , R ³ , R ⁴ , R ⁵ and R ^{6 are} independently hydrogen, C 1 -C 6 -alkyl, optionally interrupted by one or more oxygen and / or sulfur atoms and / or one or more substituted or unsubstituted imino C2 - Cis-alkyl, Cβ - Ci2-aryl, C5 - Ci2-cycloalkyl or a five- to six-membered, oxygen, nitrogen and / or sulfur-containing heterocycle, where the radicals mentioned each by functional groups, aryl, alkyl, aryloxy , Alkyloxy, halogen, heteroatoms and / or heterocycles can be substituted.

1. The method according to any one of the preceding claims, characterized in that the auxiliary base is 1-n-butylimidazole, 1-methylimidazole, 2-methylpyridine or 2-ethylpyridine.