EP2560945A2

EP2560945A2 - Purification of carboxylic esters by extractive distillation

Info

Publication number: EP2560945A2
Application number: EP11718314A
Authority: EP
Inventors: Helmut Kronemayer; Ellen Dahlhoff; Andreas Lanver
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2010-04-19
Filing date: 2011-04-18
Publication date: 2013-02-27
Also published as: JP2013525322A; WO2011131609A3; KR20130051453A; CN102858733A; WO2011131609A2

Abstract

In a process for purifying carboxylic esters such as ethyl formate, a carboxylic ester to be purified is distilled in the presence of an extractant, preferably by (a) allowing vapour of the carboxylic ester to be purified to ascend in a distillation column; (b) conveying the extractant in countercurrent to the vapour in an extractive distillation zone; (c) taking off pure carboxylic ester above the extractive distillation zone. The extractant is selected, for example, from among diols, polyols, open-chain or cyclic amides.

Description

Purification of carboxylic acid esters by extractive distillation The invention relates to a process for the purification of carboxylic acid esters.

Low molecular weight esters such as formic acid esters find z. B. as fragrances, insecticides, fungicides or in organic synthesis application. Processes for the preparation of low molecular weight esters are widely described in the literature. A cost-effective production possibility is the esterification of carboxylic acid and alcohol with subsequent distillation of the ester. This process is in many cases technically very easy to carry out because the product in the form of the ester is the lowest-boiling compound. In US-A 5,302,747 a process is described in which an inert gas is passed through an esterification mixture containing an alcohol and a carboxylic acid and maintained at least at the boiling temperature of the alcohol to drive off the ester. The production of high-purity esters, in particular formic acid esters, with a purity of more than 99.5% by weight, in particular more than 99.8% by weight, is difficult, as will be explained below with reference to the esterification of formic acid with ethanol. In the esterification of formic acid with ethanol, water and ethyl form form. In the distillation of the reaction product, neither ethanol nor water can be completely separated from the ester, since both substances form azeotropes with the ester over wide pressure ranges. As a result, highly pure ethyl formate can not be obtained in this way.

JP 10175916 describes the preparation of highly pure formic acid esters. The esterification of formic acid and alcohol is carried out by reactive distillation, wherein the resulting distillate is dehydrated by means of acetic anhydride. In this method, although water can be removed by the use of drying agents. Unreacted alcohol can not be removed in a comparable manner.

WO 2007/099071 describes the preparation of esters by a reactive distillation. In a reaction column, a carboxylic acid, an alcohol and an entraining agent are introduced. The bottom stream comprises the ester formed and unreacted carboxylic acid. The top stream comprises unreacted alcohol, water and entrainers. The invention has for its object to provide an efficient method for the purification of carboxylic acid esters. According to the invention the object is achieved by a process for the purification of carboxylic acid esters, in which distilling a carboxylic acid ester in the presence of an extractant.

The process is suitable for purifying low molecular weight carboxylic acid esters which can be evaporated without decomposition. There are mainly the esters of C1-C5-

Carboxylic acids with C 1 -C 8 -alcohols, such as methyl formate, ethyl formate, propyl formate, isopropyl formate, n-butyl formate, sec-butyl formate and n-pentyl formate, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, n-butyl acetate, sec-butyl acetate and n-pentyl acetate. The carboxylic acid ester is preferably a formic acid ester, in particular ethyl formate.

The impurities contained in the carboxylic acid ester to be purified are usually selected from water, alcohol and free carboxylic acid. The alcohol and the free carboxylic acid usually correspond to the alcohol and carboxylic acid constituents of the carboxylic acid ester to be purified. However, the alcohol and the free carboxylic acid may also comprise a foreign alcohol and / or a foreign carboxylic acid.

In the carboxylic acid ester to be purified, it may, for. B. to a crude distillate of an esterification reaction or transesterification reaction.

The purity of the carboxylic ester to be purified is generally 50 to 99.5% by weight, usually 95 to 99% by weight.

The pure carboxylic acid ester obtained by the process according to the invention generally has a purity of at least 99.5 wt .-%, preferably at least 99.8 wt .-%, on. The purity of the carboxylic acid ester may, for. B. by gas chromatography, ion chromatography, titrimetric methods or pH measurements can be determined. The process according to the invention can be carried out in a simple manner by heating a mixture of the carboxylic acid ester to be purified and the extractant to boiling and collecting and condensing the vapors of the pure carboxylic acid ester. Preferably, however, the distillation is carried out as a fractional distillation. Conventional equipment suitable for this purpose are, for example, those described in Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Ed., Vol. 7, John Wiley & Sons, New York, 1979, pages 870-881.

In a preferred embodiment, one proceeds in such a way that one

(a) causing vapors of the carboxylic ester to be purified to rise in a distillation column;

(b) passing the extractant to the vapor in an extractive distillation zone;

(c) stripping pure carboxylic acid ester above the extractive distillation zone.

By "extractive distillation zone" is meant a column section in which the carboxylic acid ester to be purified and the extractant come into contact with each other under conditions of extractive distillation. The extractive distillation makes use of the phenomenon that the fugacity of the constituents of the mixture to be separated changes as a result of the addition of the extractant. Extractants used in accordance with the invention selectively increase the relative fugacity of the carboxylic acid ester. For this reason, the carboxylic acid ester in the distillation in the presence of the extractant is preferably in the low-boiling overhead product, while the impurities such as carboxylic acid, alcohol and water, in the extract, the heavier-boiling bottom product of the distillation, find again. The process can be carried out batchwise, for which purpose the carboxylic acid ester to be purified is introduced in a distillation bubble. The submitted to be purified carboxylic acid ester is heated to boiling and the vapors passed through the distillation column. Into the distillation column, the extractant is introduced at the top or preferably laterally and leads to the vapor. The extractant collects with the impurities in the distillation bubble.

Alternatively, the process can be carried out continuously, for which purpose the carboxylic ester to be purified is introduced below the extractive distillation zone into the distillation column or into the bottom of the distillation column and an extractant-containing stream is withdrawn from the bottom.

The pure carboxylic acid ester is withdrawn above the extractive distillation zone as a side draw or as a top fraction, preferably as a top fraction. For this purpose, the distillation column is provided with means for condensing and collecting the head sample. provided. About a condensate divider, a portion of the overhead condensate can be given as reflux back to the column. The other part of the condensate is withdrawn as a product. The distillation can be carried out at reduced pressure, atmospheric pressure or overpressure. A preferred pressure range is 15 mbar to 10 bar, more preferably 0.5 to 1.5 bar. The distillation can be carried out in a temperature range (bottom temperature) of 20 ° to 250 ° C, preferably at least 50 ° C. The distillation column preferably contains internals which consist of trays, rotating internals, disordered and / or ordered packings.

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.

The columns used can have random beds with different packing. They can be made of any suitable material such as steel, stainless steel, nickel base alloys such as HC, copper, carbon, stoneware, porcelain, glass, plastics, and in various forms such as spheres, rings with smooth or profiled surfaces, rings with internal webs or wall penetrations, wire mesh rings, calipers and spirals.

Packages with regular geometry can, for. B. from sheets or tissues exist. Examples of such packages are Sulzer metal or plastic BX packages, Sulzer multi-plate Mellapack sheet metal packings, structural packings from Sulzer (Optiflow), Montz (BSH) and Kühni (Rombopack).

The distillation column is 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. Suitable classes of substances which are suitable as extractants are preferably diols, polyols, open-chain or cyclic amides and mixtures of the mentioned classes of substances. Examples of suitable diols and polyols are ethylene glycol, diethylene glycol,

Triethylene glycol, polyethylene glycol, 1, 3-propanediol, 2-methyl-1, 3-propanediol, 1, 4-butanediol, dipropylene glycol, 1, 5-pentanediol, 1, 6-hexanediol and glycerol called.

Examples of suitable open-chain or cyclic amides are formamide, N-methylformamide, N, N-dimethylformamide, N-methylpyrrolidone, acetamide and N-methylcaprolactam.

Preferably, the extractant has a boiling point (under atmospheric pressure) which is at least 30 ° C higher, in particular at least 100 ° C higher than the boiling point (under normal pressure) of the carboxylic acid ester to be purified.

The polar extractants used are preferably diols or polyols having 3 to 5 OH groups. As particularly preferred diols and polyols are called ethylene glycol, 1, 4-butanediol, 2-methyl-1, 3-propanediol, of which ethylene glycol is particularly preferred.

Suitable extractants are ionic liquids. By ionic liquids are meant salts having a melting point below 100 ° C., preferably below 80 ° C. Preference is given to those ionic liquids whose cation constituent contains at least one five- to six-membered heterocycle, in particular a five-membered heterocycle, which has at least one nitrogen atom and optionally an oxygen or sulfur atom. Particular preference is given to those compounds which have at least one five- to five-membered ring contain six-membered heterocycle having one, two or three nitrogen atoms and optionally a sulfur or an oxygen atom, most preferably those having two nitrogen atoms. Further preferred are aromatic heterocycles.

Particularly preferred compounds are those which have a molar mass of less than 1000 g / mol, very particularly preferably less than 600 g / mol and in particular less than 400 g / mol.

Preferred cations are selected from the compounds of the formulas (La) to (lw), 

(Ι.ο ') (I.P) (l-q) (l-q')

(i-q ") (l.r) (l.r ') (l.r")

(l.s) (l.t) (I.u) (l.v)

(lw) (lx1) (lx2)

(i y) (l.z)

wherein

R is hydrogen, alkyl, alkenyl, cycloalkyl, cycloalkenyl, polycyclyl, heterocycloalkyl, aryl or heteroaryl; Radicals R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁸ and R ⁹ attached to a ring carbon atom independently of one another represent hydrogen, a sulfo group, COOH, carboxylate, sulfonate, acyl , Alkoxycarbonyl, cyano, halogen, hydroxyl, SH, nitro, NE ¹ E ² , alkyl, alkoxy, alkylthio, alkylsulfinyl, alkylsulfonyl, alkenyl, cycloalkyl, cycloalkyloxy, cyclo- alkenyl, cycloalkenyloxy, polycyclyl, polycycloxy, heterocycloalkyl, aryl, aryloxy or heteroaryl, where E ¹ and E ² independently of one another are hydrogen, alkyl, cycloalkyl, heterocycloalkyl, aryl or hetaryl, radicals R ¹ , R ² , R ³ , R ⁴ , and R ⁵ , which are bonded to a ring hetero atom, are hydrogen, SO ₃ H, NE ¹ E ² , alkyl, alkoxy, alkenyl, cycloalkyl, cycloalkenyl, polycyclyl, heterocycloalkyl, aryl or heteroaryl, where E ¹ and E ^{2 are} independently hydrogen, alkyl, cycloalkyl, heterocycloalkyl, aryl or hetaryl, or two adjacent radicals R ¹ to R ⁹ together with the ring atoms to which they are attached, for at least one fused, saturated, unsaturated or aromatic ring or a ring system having 1 to 30 carbon atoms, wherein the ring or the ring system may have 1 to 5 non-adjacent heteroatoms or heteroatom-containing groups and wherein the ring or the ring system unsu may be substituted or substituted, where two geminal radicals R ¹ to R ^{9 may} also together stand for = 0, = S or = NR ^b , wherein R ^{b is} hydrogen, alkyl, cycloalkyl, aryl or heteroaryl, where in the compounds of Formula (lx1) R ¹ and R ³ or R ³ and R ^{5 can} also stand together for the binding portion of a double bond between the ring atoms which carry these radicals,

B in the compounds of the formulas (Ix1) and (Ix2) together with the CN group to which it is attached forms a 4- to 8-membered, saturated or unsaturated or aromatic cycle which is optionally substituted and / or which may optionally have further heteroatoms or heteroatom-containing groups and / or may comprise further fused saturated, unsaturated or aromatic carbocycles or heterocycles.

Two adjacent radicals R ¹ to R ^9, together with the ring atoms to which they are attached, form at least one fused, saturated, unsaturated or aromatic ring or a ring system having from 1 to 30 carbon atoms, the ring or the ring system not being adjacent to 1 to 5 Heteroatoms or heteroatom-containing groups may have and wherein the ring or the ring system may be unsubstituted or substituted, these radicals may together as fused building blocks preferably 1, 3-propylene, 1, 4-butylene, 1, 5-pentylene, 2- Oxa-1,3-propylene, 1-oxa-1, 3-propylene, 1-oxa-1,3-propenylene, 3-oxa-1, 5-pentylene, 1 -zaza-1, 3-propenylene, I - C1-C4 Alkyl 1 -aza-1, 3-propenylene, 1,4-buta-1,3-dienylene, 1-az-1, 4-buta-1,3-dienylene or 2-aza-1,4-butanea 1, 3-dienylene mean.

The radical R is preferably linear C 1 - to C 18 -alkyl, such as, for example, methyl, ethyl, 1-propyl, 1-butyl, 1-pentyl, 1-hexyl, 1-heptyl, 1-octyl, 1-decyl, 1 - dodecyl, 1 - tetradecyl, 1 -hexadecyl, 1 -octadecyl, very particularly preferably represents methyl, ethyl, 1 - ₃ 0- butyl and 1-octyl, and CH (CH2CH20) n-CH ₂ CH 2 and CH 3 CH ₂ 0- ( CH ₂ CH ₂ 0) _m - CH ₂ CH ₂ - with m is 0 to 3. Preferably, the radicals R ¹ to R ^{9 are} independently hydrogen; C1-C18 alkyl, such as methyl, ethyl, 1-butyl, 1-pentyl, 1-hexyl, 1-heptyl, 1-octyl; phenyl; 2-hydroxyethyl; 2-cyanoethyl; 2- (alkoxycarbonyl) ethyl such as 2- (methoxycarbonyl) ethyl, 2- (ethoxycarbonyl) ethyl or 2- (n-butoxycarbonyl) ethyl; N, N- (C 1 -C 4 -dialkyl) amino, such as Ν, Ν-dimethylamino or Ν, Ν-diethylamino; Chlorine and radicals of oligoalkylene glycol, such as CH ₃ 0- (CH ₂ CH ₂ O) n-CH ₂ CH ₂ or CH ₃ CH ₂ O- (CH ₂ CH ₂ O) n-CH ₂ CH ₂ - where n is 0 to 3.

Among the above-mentioned heterocyclic cations, imidazolium ions, imidazolinium ions, pyridinium ions, pyrazolinium ions and pyrazolium ions are preferable. Particularly preferred are the imidazolium ions and cations of 1, 5-diazabicyclo [4.3.0] non-5-ene (DBN) and 1, 8-diazabicyclo [5.4.0] undec-7-ene (DBU).

The anion of the ionic liquid is selected, for example, from the group of pseudohalides and halogen-containing compounds of the formulas: BF ₄ -, PF ₆ ^" , CF ₃ SO ₃ -, (CF ₃ S0 ₃ ) ₂ N-, CF ₃ CO ₂ -, CCI ₃ CO ₂ -, CN-, SCN -, OCN-; the group of sulphates, sulphites and sulphonates of the general formulas:

S0 ₄ ² -, HSO4-, SO3 ² -, HSO3-, R ^c OS0 ₃ -, R ^c S0 ₃ -; the group of phosphates of the general formulas:

PO4 ³ -, HPO4 ² -, H2PO4 -, R ^c P0 ₄ ^{2 "} , HR ^c P0 ₄ ^" , R ^c R ^d P0 ₄ -; the group of phosphonates and phosphinates of the general formula

R ^c HP0 ₃ -, R ^c R ^d P0 ₂ -, R ^c R ^d P0 ₃ -; the group of phosphites of the general formulas:

PO3 ³ -, HPO 3 ² -, H2PO3-, R ^c P0 ₃ ^{2 ",} R ^c HP0 _^3", R ^c R ^d ₃ P0 -; the group of phosphonites and phosphinites of the general formulas:

R ^c R ^d ₂ P0 ^", R ^c HP0 ₂ -, R ^c R ^d PO-, R ^c ^HPO"; the group of carboxylic acids of the general formula:

R ^c COO-.

The radicals R ^c , R ^d are preferably each independently hydrogen; C 1 -C 30 -alkyl, alkyl which is completely or partially substituted by halogen, or C 6 -C 14 -aryl. Preferred anions are formate, acetate, propionate, butyrate, lactate, saccharinate, carbonate, bicarbonate, sulfate, sulfite, C 1 -C 4 -alkyl sulfates, methanesulfonate, tosylate, trifluoroacetate, C 1 -C 4 -dialkyl phosphates and hydrogen sulfate.

Particularly suitable ionic liquids are 1-ethyl-3-methylimidazolium acetate and 1-n-butyl-3-methylimidazolium acetate.

The invention is further illustrated by the accompanying drawings and the following examples.

Fig. 1 shows schematically a suitable for carrying out the method according to the invention plant.

Into a distillation column 1, the carboxylic acid ester to be purified is introduced into the lower region of the distillation column 1 via the feed 2 and the extractant is introduced into the upper region of the distillation column 1 via the feed 3. From the bottom 4 bottom product, which consists essentially of extractant and impurities, withdrawn via the line 5 and partially returned via the heater 7 in the distillation column 1 and partially discharged via the line 6. Via the line 8 overhead product, which consists essentially of the pure carboxylic acid ester, withdrawn and condensed in the cooler 9. A portion of the condensate is recycled via line 10 into the distillation column 1. Via line 1 1 pure carboxylic acid ester is withdrawn. Example 1 (Reference Example)

There were about 558 g of formic acid (98-100 wt .-% strength) with about 276 g of ethanol (technically) reacted in a stirred tank. The catalyst used was about 5.8 g of methanesulfonic acid. After stirring for 3 hours, the reaction mixture was passed through a co lonne (30 cm high, filled glass rings) distilled off. About 348 g of distillate with the following composition were obtained: about 96.5% by weight of ethyl formate,

about 2.5% by weight of water,

about 0.5 wt .-% ethanol and

about 0.5% by weight of other compounds (including formic acid). Example 2

About 664 g of a mixture containing about 99.2% by weight of ethyl formate, 0.02% by weight of water, 0.8% by weight of ethanol and 0.4% by weight of formic acid together with about 104 g of 1 were introduced Ethyl 3-methylimidazolium acetate to a thin film evaporator. About 232 g of distillate of the composition were obtained: about 99.7% by weight of ethyl formate,

about 0.01% by weight of water,

about 0.23 wt% ethanol,

about 0.05% by weight of formic acid and

about 0.01% by weight of other compounds.

Example 3

In a procedural simulation calculation was a mixture with the composition of about 98.0 wt .-% ethyl formate, 0.5 wt .-% water, 1, 0 wt .-% ethanol, 0.5 wt .-% formic acid Column fed with 20 theoretical stages. About 100 g / h of the mixture was introduced to the middle of the lower half of the column and about 56 g / h of ethylene glycol was introduced to the middle of the top of the column. The distillation was carried out at atmospheric pressure. A sump temperature of about 68.degree. C. was set. At the bottom of the column, the supplied ethylene glycol was discharged with most of the impurities of the feed mixture. At the top of the column was condensed at 10 ° C and with the help of a reflux divider about half of the condensate was given as reflux to the column, the other half was withdrawn. About 95 g / h of distillate of the composition were obtained: about 99.9% by weight of ethyl formate,

<0.01% by weight of water,

about 0.1% by weight of ethanol, <0.01% by weight of formic acid and

<0.01% by weight of other compounds.

Example 4

About 860 g of a mixture having the composition of about 98.2% by weight of ethyl formate, 0.6% by weight of water, 1.2% by weight of ethanol were placed in the bottom of a 60 cm-long column which was used for increasing the separation performance was filled with packing. The sump was heated to boiling by means of a heated double jacket. Finally, about 300 g / h of ethylene glycol were introduced into the middle of the top of the column. The distillation was carried out at atmospheric pressure. At the top of the column was condensed by means of a water-cooled condenser (about 10 ° C) and using a reflux divider about one fifth of the condensate as reflux to the column, the remaining portion of the condensate was withdrawn. About 312 g / h distillate of the composition were obtained within 2 hours: about 99.9% by weight of ethyl formate,

about 0.01% by weight of water,

about 0.08 wt .-% ethanol and

<0.01% by weight of other compounds.

Comparative Example 1

About 414 g of a mixture having the composition of about 96.2% by weight of ethyl formate, 0.8% by weight of ethanol, 3.5% by weight of formic acid were placed in the bottom of a 60 cm-long column which was used to increase the separation performance was filled with packing. The sump was heated to boiling by means of a heated double jacket. The distillation was carried out at atmospheric pressure. At the top of the column was condensed by means of a water-cooled condenser (about 10 ° C) and with the help of a reflux divider about two-thirds of the condensate as reflux to the column, the remaining portion of the condensate was withdrawn. About 341 g / h distillate of the composition was obtained within 3 hours: about 99.0% by weight of ethyl formate,

about 0.9 weight percent ethanol and

about 0.1% by weight of formic acid.

Comparative Example 2 About 860 g of a mixture having the composition of about 98.2% by weight of ethyl formate, 0.6% by weight of water, 1.2% by weight of ethanol were placed in the bottom of a 60 cm-long column which was used for increasing the separation performance was filled with packing. The sump was heated to boiling by means of a heated double jacket. The distillation was carried out at atmospheric pressure. At the top of the column was condensed by means of a water-cooled condenser (about 10 ° C) and using a reflux divider about one fifth of the condensate as reflux to the column, the remaining portion of the condensate was withdrawn. Distillate of the composition was obtained: about 98% by weight of ethyl formate,

about 0.9% by weight of water,

about 1, 0 wt .-% ethanol and

<0.1% by weight of other compounds.

Claims

claims

Process for the purification of carboxylic acid esters, in which a distilled carboxylic acid ester to be purified in the presence of an extractant.

The method of claim 1, wherein

(a) causing vapors of the carboxylic acid ester to be purified to rise in a distillation column;

(b) passing the extractant to the vapor in an extractive distillation zone;

Process according to Claim 2, in which the carboxylic acid ester to be purified is initially charged in a distillation bubble.

Process according to Claim 2, in which the carboxylic acid ester to be purified is introduced below the extractive distillation zone into the distillation column or into the bottom of the distillation column and withdraws an extractant-containing stream from the bottom.

Method according to one of claims 2 to 4, wherein the pure carboxylic acid ester is removed as a top fraction.

A process according to any one of the preceding claims wherein the extractant is selected from diols, polyols, open chain or cyclic amides.

A process according to claim 6, wherein the extractant is ethylene glycol.

8. The method according to any one of claims 1 to 5, wherein the extractant is selected from ionic liquids.

9. The method according to any one of the preceding claims, wherein the boiling point of the extractant is at least 30 ° C higher than the boiling point of the carboxylic acid ester to be purified.

10. The method according to any one of the preceding claims, wherein the impurities contained in the carboxylic acid ester to be purified are selected from water, alcohol and free carboxylic acid.

1 1. A process according to any one of the preceding claims wherein the carboxylic acid ester to be purified is ethyl formate.

12. The method according to any one of the preceding claims, wherein the pure carboxylic acid ester has a purity of at least 99.5 wt .-%.