JP2013525322A - Purification of carboxylic esters by extractive distillation - Google Patents

Abstract

  In a process for the purification of a carboxylic acid ester, for example ethyl formate, the carboxylic acid ester to be purified is preferably present in the presence of an extractant, (a) raising the vapor of the carboxylic acid ester to be purified in a distillation column; C) distilling the extractant countercurrently in the extractive distillation zone; c) distilling off the pure carboxylic acid ester above the extractive distillation zone. The extractant is selected, for example, from diols, polyols, open chain or cyclic amides.

Description

  The present invention relates to a method for purifying a carboxylic acid ester.

  Low molecular esters, such as formate esters, are used, for example, as fragrances, insecticides, fungicides, or in organic synthesis. A variety of methods for producing low molecular weight esters are described in publications. One inexpensive manufacturing method is esterification of a carboxylic acid and an alcohol followed by distillation of the ester. In many cases, this method can be carried out very easily industrially. This is because the product in the form of an ester is a compound having a very low boiling point.

  US-A 5,302,747 describes a method for removing an ester by passing an inert gas through an esterification mixture containing an alcohol and a carboxylic acid and maintained at least at the boiling point of the alcohol.

  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 in the example of esterification of formic acid and ethanol. is there. Esterification of formic acid and ethanol yields water and ethyl formate. In the distillation of the reaction product, neither ethanol nor water can be completely separated from the ester. This is because these two substances form azeotropes with esters over a wide pressure range. Therefore, high purity ethyl formate cannot be obtained by this method.

  JP10175916 describes the production of high purity formate. Esterification of formic acid and alcohol is carried out by reactive distillation, in which case the resulting distillate is dehydrated using acetic anhydride. In the case of this method, water can certainly be removed by the use of a desiccant. Unreacted alcohol cannot be removed in an equivalent manner.

  WO 2007/099071 describes the production of esters by reactive distillation. Carboxylic acid, alcohol and entrainer are introduced into the reaction tower. The bottom stream contains the ester formed and unreacted carboxylic acid. The overhead stream contains unreacted alcohol, water and entraining agent.

  The present invention is based on the problem of defining an efficient purification method for carboxylic acid esters.

  According to the present invention, this problem is solved by a method for purifying a carboxylic acid ester in which the carboxylic acid ester is distilled in the presence of an extractant.

This method is suitable for the purification of low molecular weight carboxylic acid esters that can be evaporated without decomposition. In particular, esters of C ₁ -C ₅ -carboxylic acids and C ₁ -C ₅ -alcohols such as methyl formate, ethyl formate, propyl formate, isopropyl formate, n-butyl formate, s-butyl formate and n-pentyl formate , Methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, n-butyl acetate, s-butyl acetate and n-pentyl acetate. Preferably, the carboxylic acid ester is a formic acid ester, especially ethyl formate.

  The impurities contained in the carboxylic acid ester to be purified are usually selected from water, alcohols and free carboxylic acids. The alcohol and free carboxylic acid usually correspond to the alcohol component and carboxylic acid component of the carboxylic acid ester to be purified. However, the alcohol and free carboxylic acid can also include a different alcohol and / or a different carboxylic acid.

  The carboxylic acid ester to be purified may be, for example, a crude distillate from an esterification reaction or a transesterification reaction.

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

  The pure carboxylic acid esters obtained by the process according to the invention generally have a purity of at least 99.5% by weight, preferably at least 99.8% by weight. The purity of the carboxylic acid ester can be measured, for example, by gas chromatography, ion chromatography, titration, or pH value measurement.

  The process according to the invention is easily carried out by heating the mixture of the carboxylic acid ester to be purified and the extractant to boiling and collecting and condensing the pure carboxylic acid ester vapor. Can do.

  Preferably, however, the distillation is carried out as a fractional distillation. In this case, for the distillation, for example, as described in Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Edition, Volume 7, John Wiley & Sons, New York, 1979, p.870-881, Conventional devices are conceivable in this regard.

In a preferred embodiment,
(A) raising the vapor of the carboxylic acid ester to be purified in a distillation column;
(B) running the extractant countercurrently in the extractive distillation zone against the vapor;
(C) Measures are taken to remove pure carboxylic acid esters above the extractive distillation zone.

  “Extractive distillation zone” is understood as the part of the column in which the carboxylic acid ester to be purified and the extractant are in contact with each other under the conditions of extractive distillation. Extractive distillation utilizes the phenomenon that the fugacity of the components of the mixture to be separated is changed by the addition of an extractant. The extractant used according to the present invention selectively increases the relative fugacity of the carboxylic acid ester. For this reason, carboxylic acid esters are preferably readily boiling overhead products in the presence of extractants during distillation, while impurities such as carboxylic acids, alcohols and water are difficult to extract, ie difficult to distill. It is observed in the boiling bottom product.

  The process may be carried out batchwise, for which purpose the carboxylic acid ester to be purified is charged into a distillation kettle. The charged carboxylic acid ester to be purified is heated to boiling and steam is passed to the distillation column. In the distillation column, the extractant is introduced at the top of the column, or preferably at the side, and flows countercurrently to the vapor. The extractant is collected along with impurities in the still.

  The process may also be carried out continuously, for which purpose the carboxylic acid ester to be purified is introduced into the distillation column or the bottom of the distillation column below the extractive distillation zone and the extractant from the bottom. A containing stream is removed.

  The pure carboxylic acid ester is withdrawn above the extractive distillation zone as a side effluent or as an overhead fraction, preferably as an overhead fraction. For this purpose, the distillation column is equipped with a device for condensing and collecting the top product. A portion of the overhead condensate can be returned to the tower as reflux via a condensate distributor. The other part of the condensate is removed as product.

  The distillation may be carried out at reduced pressure, normal pressure or overpressure. A preferred pressure range is 15 mbar to 10 bar, particularly preferably 0.5 to 1.5 bar. The distillation may be carried out within a temperature range (column bottom temperature) of 20 ° C. to 250 ° C., preferably at least 50 ° C.

  The distillation column preferably comprises a structure consisting of trays, rotating structures, irregular and / or regular packing.

  In a tower tray: (i) a tray with holes or slits in the shelf; (ii) a tray with a neck or chimney covered with bubble bells, caps or hoods; (iii) a movable valve on the shelf (Iv) trays with special structures are conceivable.

  In a tower with a rotating structure, the reflux is sprayed by a rotating hopper or spread as a coating on the heated tube wall using a rotor.

  The tower used can have a random packed bed containing various packings. It can be made of any suitable material such as steel, special steel, nickel-base alloy, eg HC, copper, carbon, stone, porcelain, glass, plastic, etc. and can be ball, flat or grooved It may be of various shapes such as a ring with a surface, a ring with an internal bridge or wall opening, a wire net ring, a saddle and a helix.

  The filling having a regular shape may consist of, for example, a sheet or a woven fabric. Examples of such packings are Sulzer mesh packing BX made of metal or plastic, Sulzer layered packing Mellapak made of metal sheet, Sulzer Optiflow, Montz BSH , And structural fillings such as Kuehni's Rombopak.

  The distillation column is equipped with a device for heating the bottom of the column. This includes an evaporator attached to the bottom of the column, for example a Robert evaporator, or a circulation part with an external evaporator, for example a tube heat exchanger or a plate heat exchanger. The circulation unit is, for example, a forced circulation type or a natural circulation type.

  Suitable substance classes as extractants are preferably diols, polyols, open-chain or cyclic amides, and mixtures of the above substance classes.

  Suitable diols and polyols include, for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, dipropylene glycol, Examples include 1,5-pentanediol, 1,6-hexanediol, and glycerin.

Suitable open chain or cyclic amides include, for example, formamide, N-methylformamide, N, N-dimethylformamide, N-methylpyrrolidone, acetamide and N-methylcaprolactam.

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

  Preferably, a diol or a polyol having 3 to 5 OH groups is used as the polar extractant. Particularly preferred diols and polyols include ethylene glycol, 1,4-butanediol, and 2-methyl-1,3-propanediol, of which ethylene glycol is particularly preferred.

  Furthermore, an ionic liquid is suitable as the extractant. An ionic liquid is interpreted as a salt having a melting point of less than 100 ° C, preferably less than 80 ° C.

  Preference is given to an ionic liquid comprising at least one 5- to 6-membered heterocycle, in particular a 5-membered heterocycle, wherein the ring has at least one nitrogen atom and optionally an oxygen or sulfur atom, Particularly preferred are compounds containing at least one 5- to 6-membered heterocyclic ring, wherein the ring has 1, 2 or 3 nitrogen atoms and optionally a sulfur atom or an oxygen atom. The compounds possessed are very particularly preferred. Furthermore, aromatic heterocycles are preferred.

  Particularly preferred compounds are those having a molecular weight of less than 1000 g / mol, very particularly preferably less than 600 g / mol, in particular less than 400 g / mol.

Preferred cations are selected from compounds of the formulas (Ia) to (Iw)

ここで、
Ｒは、水素、アルキル、アルケニル、シクロアルキル、シクロアルケニル、ポリシクリル、ヘテロシクロアルキル、アリール又はヘテロアリールを表し；
一つの環炭素原子に結合している、基Ｒ¹、Ｒ²、Ｒ³、Ｒ⁴、Ｒ⁵、Ｒ⁶、Ｒ⁷、Ｒ⁸及びＲ⁹は、互いに無関係に、水素、スルホ基、ＣＯＯＨ、カルボキシレート、スルホネート、アシル、アルコキシカルボニル、シアノ、ハロゲン、ヒドロキシル、ＳＨ、ニトロ、ＮＥ¹Ｅ²、アルキル、アルコキシ、アルキルチオ、アルキルスルフィニル、アルキルスルホニル、アルケニル、シクロアルキル、シクロアルキルオキシ、シクロアルケニル、シクロアルケニルオキシ、ポリシクリル、ポリシクリルオキシ、ヘテロシクロアルキル、アリール、アリールオキシ、又はヘテロアリールを表し、その際、Ｅ¹及びＥ²は、互いに無関係に、水素、アルキル、シクロアルキル、ヘテロシクロアルキル、アリール、又はヘタリールを表し、
一つの環ヘテロ原子に結合している、基Ｒ¹、Ｒ²、Ｒ³、Ｒ⁴及びＲ⁵は、水素、ＳＯ₃Ｈ、ＮＥ¹Ｅ²、アルキル、アルコキシ、アルケニル、シクロアルキル、シクロアルケニル、ポリシクリル、ヘテロシクロアルキル、アリール、又はヘテロアリールを表し、その際、Ｅ¹及びＥ²は、互いに無関係に、水素、アルキル、シクロアルキル、ヘテロシクロアルキル、アリール、又はヘタリールを表すか、又は、
２つの隣接する基Ｒ¹〜Ｒ⁹は、これらの基が結合している環原子と一緒になって、少なくとも１の、縮合した、飽和環、不飽和環又は芳香環か、又は、１〜３０個の炭素原子を有する環系を表すこともでき、その際、該環又は該環系は、１〜５個の隣接していないヘテロ原子又はヘテロ原子含有基を有することができ、かつその際、該環又は該環系は、非置換であっても置換されていてもよく、
その際、２つのジェミナルな基Ｒ¹〜Ｒ⁹は、一緒になって、＝Ｏ、＝Ｓ又は＝ＮＲ^bを表すこともでき、その際、Ｒ^bは、水素、アルキル、シクロアルキル、アリール、又はヘテロアリールを表し、
その際、式（Ｉ．ｘ．１）の化合物において、Ｒ¹及びＲ³、又は、Ｒ³及びＲ⁵は、一緒になって、これらの基を有する環原子の間の二重結合の結合部分を表すこともでき、
式（Ｉ．ｘ．１）及び（Ｉ．ｘ．２）の化合物中のＢは、該Ｂが結合しているＣ−Ｎ−基と一緒になって、４員〜８員の、飽和環又は不飽和環又は芳香環を形成し、該環は、場合により置換されていてよく、かつ／又は、場合により他のヘテロ原子又はヘテロ原子含有基を有することができ、かつ／又は、他の縮合した、飽和、不飽和又は芳香族の、炭素環式化合物又は複素環式化合物を含むことができる。

here,
R represents hydrogen, alkyl, alkenyl, cycloalkyl, cycloalkenyl, polycyclyl, heterocycloalkyl, aryl or heteroaryl;
The groups R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁸ and R ⁹ bonded to one ring carbon atom are independently of one another hydrogen, sulfo group, COOH. Carboxylate, sulfonate, acyl, alkoxycarbonyl, cyano, halogen, hydroxyl, SH, nitro, NE ¹ E ² , alkyl, alkoxy, alkylthio, alkylsulfinyl, alkylsulfonyl, alkenyl, cycloalkyl, cycloalkyloxy, cycloalkenyl, Represents cycloalkenyloxy, polycyclyl, polycyclyloxy, heterocycloalkyl, aryl, aryloxy, or heteroaryl, wherein E ¹ and E ² independently of one another are hydrogen, alkyl, cycloalkyl, heterocycloalkyl, Represents aryl or hetaryl,
The groups R ¹ , R ² , R ³ , R ⁴ and R ⁵ bonded to one ring heteroatom are hydrogen, SO ₃ H, NE ¹ E ² , alkyl, alkoxy, alkenyl, cycloalkyl, cycloalkenyl. , Polycyclyl, heterocycloalkyl, aryl, or heteroaryl, wherein E ¹ and E ² , independently of each other, represent hydrogen, alkyl, cycloalkyl, heterocycloalkyl, aryl, or hetaryl, or
Two adjacent groups R ^{1 to} R ⁹ , together with the ring atom to which these groups are attached, are at least one fused, saturated, unsaturated or aromatic ring, or 1 to It can also represent a ring system having 30 carbon atoms, wherein the ring or the ring system can have 1 to 5 non-adjacent heteroatoms or heteroatom-containing groups, and Wherein the ring or ring system may be unsubstituted or substituted,
The two geminal groups R ^{1 to} R ⁹ can also be taken together to represent ═O, ═S or ═NR ^b , where R ^b is hydrogen, alkyl, cycloalkyl, aryl Or represents heteroaryl,
In this case, in the compound of the formula (I.x.1), R ¹ and R ³ , or R ³ and R ⁵ are combined to form a double bond between ring atoms having these groups. Can also represent parts,
B in the compounds of formulas (I.x.1) and (I.x.2), together with the C—N— group to which B is attached, is a 4- to 8-membered saturated ring Or an unsaturated or aromatic ring, which ring may be optionally substituted and / or optionally have other heteroatoms or heteroatom-containing groups and / or other Condensed, saturated, unsaturated or aromatic, carbocyclic or heterocyclic compounds may be included.

Two adjacent groups R ^{1 to} R ⁹ together with the ring atom to which these groups are attached are at least one fused, saturated, unsaturated or aromatic ring, or 1 to Represents a ring system having 30 carbon atoms, wherein the ring or ring system can have 1 to 5 non-adjacent heteroatoms or heteroatom-containing groups, wherein When the ring or the ring system may be unsubstituted or substituted, these groups are combined together as a fused structural unit, 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 - aza-1,3-propenylene, _1-C 1 ~C ₄ - alkyl-1- The-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 -Can represent dienylene.

Preferably, the group R is linear C ₁ -C ₁₈ -alkyl, 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 methyl, ethyl, 1-butyl and 1-octyl, and CH ₃ O— (CH ₂ CH ₂ O) _n -CH ₂ CH ₂ - and _{CH 3 CH 2 O- (CH 2} CH 2 O) m -CH 2 CH 2 - represents a, where, m is 0-3.

Preferably, the radicals R ^{1 to} R ⁹ are independently of one another hydrogen, C ₁ -C ₁₈ -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 N, N-dimethylamino, or N, N-diethylamino; chlorine and oligoalkylene glycol groups such as CH ₃ O— (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 0-3.

  Of the above heterocyclic cations, imidazolium ions, imidazolinium ions, pyridinium ions, pyrazolinium ions, and pyrazolium ions are preferred. Particularly preferred are imidazolium ions and 1,5-diaza-bicyclo [4.3.0] non-5-ene (DBN) and 1,8-diaza-bicyclo [5.4.0] undec- 7-ene (DBU) cation.

The anion of the ionic liquid is selected, for example, from:
formula:
BF ₄ ⁻ , PF ₆ ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ SO ₃ ) ₂ N ⁻ , CF ₃ CO ₂ ⁻ , CCl ₃ CO ₂ ⁻ , CN ⁻ , SCN ⁻ , OCN ⁻
A group of pseudohalide ions and halogen-containing compound ions;
General formula:
SO ₄ ²⁻ , HSO ₄ ⁻ , SO ₃ ²⁻ , HSO ₃ ⁻ , R ^c OSO ₃ ⁻ , R ^c SO ₃ ⁻
A group of sulfate ion, sulfite ion and sulfonate ion;
General formula:
PO ₄ ³⁻ , HPO ₄ ²⁻ , H ₂ PO ₄ ⁻ , R ^c PO ₄ ²⁻ , HR ^c PO ₄ ⁻ , R ^c R ^d PO ₄ ⁻
A group of phosphate ions;
General formula:
R ^c HPO ₃ ⁻ , R ^c R ^d PO ₂ ⁻ , R ^c R ^d PO ₃ ⁻
A group of phosphonate ions and phosphinate ions;
General formula:
PO ₃ ³⁻ , HPO ₃ ²⁻ , H ₂ PO ₃ ⁻ , R ^c PO ₃ ²⁻ , R ^c HPO ₃ ⁻ , R ^c R ^d PO ₃ ⁻
A group of phosphite ions;
General formula:
R ^c R ^d PO ₂ ⁻ , R ^c HPO ₂ ⁻ , R ^c R ^d PO ⁻ , R ^c HPO ⁻
A group of phosphonite and phosphite ions;
General formula:
R ^c COO ^-
A group of carboxylate ions.

The groups R ^c , R ^d preferably represent, independently of one another, hydrogen; C ₁ -C ₃₀ -alkyl, alkyl fully or partially substituted with halogen, or C ₆ -C ₁₄ -aryl.

Preferred anions are formate ion, acetate ion, propionate ion, butyrate ion, lactate ion, saccharate ion, carboxylate ion, bicarbonate ion, sulfate ion, sulfite ion, C ₁ -C ₄ -alkyl sulfate ion, methane sulfate. Ions, p-toluenesulfonic acid ions, trifluoroacetic acid ions, C ₁ -C ₄ -dialkyl phosphate ions and hydrogen sulfate ions.

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

  The invention is illustrated in the accompanying figures and the following examples.

  FIG. 1 schematically shows an apparatus suitable for carrying out the method according to the invention.

  A carboxylic acid ester to be purified is introduced into the distillation column 1 by feed 2 into the lower range of the distillation column 1, and an extractant is introduced into the upper range of the distillation column 1 by feed 3. A bottom product consisting essentially of an extractant and impurities is removed from the bottom 4 through a conduit 5 and partially returned to the distillation column 1 via a heating section 7 and partially , Discharged through the conduit 6. Through the conduit 8, the top product consisting of substantially pure carboxylic acid ester is removed and condensed in the cooling section 9. A part of the condensate is returned to the distillation column 1 through a conduit 10. Pure carboxylic acid ester is removed through conduit 11.

1 is a schematic view of an apparatus suitable for carrying out the method according to the invention.

Example 1 (reference example)
In a stirring vessel, about 558 g of formic acid (98 to 100% by mass) was reacted with about 276 g of ethanol (industrial use). As the catalyst, about 5.8 g of methanesulfonic acid was used. After stirring for 3 hours, the reaction mixture was distilled off via a tower (height 30 cm, filled with glass ring). About 348 g of distillate having the following composition was obtained:
About 96.5% by mass of ethyl formate,
About 2.5% by weight of water,
About 0.5% by mass of ethanol and about 0.5% by mass 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 was converted to about 104 g of 1-ethyl-3-methylimidazolium acetate. Together with a thin film evaporator. About 232 g of distillate having the following composition was obtained:
About 99.7% by mass of ethyl formate,
About 0.01% by weight of water,
About 0.23% by mass of ethanol,
Formic acid about 0.05% by weight and other compounds about 0.01% by weight.

Example 3
In a process technical simulation calculation, a mixture having a composition of about 98.0% by weight of ethyl formate, 0.5% by weight of water, 1.0% by weight of ethanol and 0.5% by weight of formic acid has 20 theoretical stages. Feeded to the tower. About 100 g / h of the mixture was introduced into the middle of the lower half of the column and about 56 g / h of ethylene glycol was introduced into the middle of the upper portion of the column. Distillation was performed at atmospheric pressure. The bottom temperature was adjusted to about 68 ° C. The fed ethylene glycol was discharged at the bottom of the column along with most of the feed mixture impurities. At the top of the column, condensed at 10 ° C. and using a reflux distributor, approximately half of the condensate was placed in the column as reflux and the other half was removed. Approximately 95 g / h of distillate having the following composition was obtained:
About 99.9% by weight of ethyl formate,
Water <0.01% by weight,
About 0.1% by mass of ethanol,
Formic acid <0.01% by mass, and other compounds <0.01% by mass.

Example 4
About 860 g of a mixture having a composition of about 98.2% by weight ethyl formate, 0.6% by weight water, and 1.2% by weight ethanol was charged to the bottom of a 60 cm long tower. The column was packed with a packing to enhance separation performance. The bottom of the column was heated to boiling using a heated double jacket. Finally, about 300 g / h of ethylene glycol was introduced into the center of the upper part of the column. Distillation was performed at atmospheric pressure. At the top of the column, condense using a water-cooled condenser (about 10 ° C.) and using a reflux distributor, approximately one-fifth of the condensate enters the column as reflux and the rest of the condensate Was taken out. Within 2 hours, about 312 g / h of distillate having the following composition was obtained:
About 99.9% by weight of ethyl formate,
About 0.01% by weight of water,
About 0.08% by mass of ethanol and other compounds <0.01% by mass.

Comparative Example 1
About 414 g of a mixture having a composition of about 96.2% by weight of ethyl formate, 0.8% by weight of ethanol, and 3.5% by weight of formic acid was charged to the bottom of a 60 cm long tower. The column was packed with a packing to enhance separation performance. The bottom of the column was heated to boiling using a heated double jacket. Distillation was performed at atmospheric pressure. At the top of the column, condense using a water-cooled condenser (about 10 ° C.), and using a reflux distributor, approximately two-thirds of the condensate is placed in the column as reflux and the remaining portion of the condensate Was taken out. Within 3 hours, approximately 341 g / h of distillate having the following composition was obtained:
About 99.0% by mass of ethyl formate,
About 0.9% by weight of ethanol and about 0.1% by weight of formic acid.

Comparative Example 2
About 860 g of a mixture having a composition of about 98.2% by weight ethyl formate, 0.6% by weight water, and 1.2% by weight ethanol was charged to the bottom of a 60 cm long tower. The column was packed with a packing to enhance separation performance. The bottom of the column was heated to boiling using a heated double jacket. Distillation was performed at atmospheric pressure. At the top of the column, condense using a water-cooled condenser (about 10 ° C.) and using a reflux distributor, approximately one-fifth of the condensate enters the column as reflux and the rest of the condensate Was taken out. A distillate having the following composition was obtained:
About 98% by mass of ethyl formate,
About 0.9% by weight of water,
About 1.0% by mass of ethanol and other compounds <0.1% by mass.

  DESCRIPTION OF SYMBOLS 1 Distillation column, 2 Feed of carboxylic acid ester to be purified, 3 Feed of extractant, 4 Column bottom, 5 Conduit, 6 Conduit, 7 Heating part, 8 Conduit, 9 Cooling part, 10 Conduit, 11 Conduit

Claims (12)

  A method for purifying a carboxylic acid ester, wherein the carboxylic acid ester to be purified is distilled in the presence of an extractant. (A) raising the vapor of the carboxylic acid ester to be purified in a distillation column;
(B) running the extractant countercurrently in the extractive distillation zone against the vapor;
The process of claim 1 wherein (c) pure carboxylic acid ester is removed above the extractive distillation zone.   3. A process according to claim 2, wherein the carboxylic acid ester to be purified is charged to the distillation kettle.   3. A process according to claim 2, wherein the carboxylic acid ester to be purified is introduced into the distillation column or the bottom of the distillation column below the extractive distillation zone and the extractant-containing stream is removed from the bottom.   5. The process as claimed in claim 2, wherein the pure carboxylic acid ester is removed as a top fraction.   6. Process according to any one of claims 1 to 5, wherein the extractant is selected from diols, polyols, open chain amides or cyclic amides.   The method of claim 6, wherein the extractant is ethylene glycol.   6. The method according to any one of claims 1 to 5, wherein the extractant is selected from ionic liquids.   The process according to any one of claims 1 to 8, 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. Process according to any one of claims 1 to 9, wherein the impurities contained in the carboxylic acid ester to be purified are selected from water, alcohols and free carboxylic acids.   11. A process according to any one of claims 1 to 10, wherein the carboxylic acid ester to be purified is ethyl formate.   12. A process according to any one of the preceding claims, wherein the pure carboxylic acid ester has a purity of at least 99.5% by weight.

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