EP1828101A1

EP1828101A1 - Method for producing n,n-dimethylacetamide (dmac)

Info

Publication number: EP1828101A1
Application number: EP05814359A
Authority: EP
Inventors: Horst Grafmans; Steffen Maas; Alexander Weck; Heinz RÜTTER; Michael Schulz; Karl-Heinz Ross
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2004-12-06
Filing date: 2005-12-03
Publication date: 2007-09-05
Also published as: DE102004058887A1; JP2008522996A; CN101072747A; US20080103336A1; WO2006061153A1

Abstract

The invention relates to a method for producing N,N-dimethylacetamide (DMAC) by the continuous reaction of methyl acetate (MeOAc) with dimethyl amine (DMA) in the presence of an alkaline catalyst. Said method is characterised in that the MeOAc is in the form of a methanolic solution and that between 0.0002 and 0.09 mol catalyst per mol MeOAc is used. The reaction is carried out at a temperature ranging between 90 and 140 °C and at an absolute pressure ranging between 10 and 30 bar.

Description

Process for the preparation of N, N-dimethylacetamide (DMAC)

description

The present invention relates to a process for the preparation of N, N-dimethylacetamide (DMAC) by continuous reaction of methyl acetate (MeOAc) with dimethylamine (DMA) in the presence of a basic catalyst.

DMAC finds use as a polar solvent, e.g. for polymers and for gases, as stripper, extractant, catalyst and crystallization aid. In the paint industry, DMAC, because of its high boiling temperature, is used for special binder-based coatings of polymers such as polymers. Polyamides and polyurethanes. DMAC is also used to make fibers and films and as a reaction medium. DMAC is used in the spinning of Spandex® fibers as an excipient and then at least partially recovered.

DMAC can be prepared from acetic acid and dimethylamine, e.g. according to FR-A-1, 406,279.

Carboxylic acid amides are also accessible by aminolysis of corresponding carboxylic acid esters, cf. e.g. , Organikum ', VEB German publishing house of the sciences, 1963, pages 374-375.

The article by J. P. Guthrie in J. Am. Chem. Soc. 96, pages 3608-15 (1974), relates to reaction kinetic and thermodynamic aspects, and the like. the aminolysis of carboxylic acid esters.

CA-A-1 073 467 and CA-A-1 073 468 (both General Electric Comp.) Describe the preparation of diols and N, N-dialkylamides by reacting carboxylic acid diesters with dialkylamines.

US-A-4,258,200 (Air Products) teaches the preparation of DMAC from methyl acetate and DMA in the presence of cobalt catalysts.

According to Example 1, a "20% methanol-methyl acetate azeotropic" for the reaction at 155 - 16O ⁰ F (68.4 - 71, 2 ⁰ C) is used. JP-A-02 160749 (Lion Akzo KK) relates, according to Patent Abstracts of Japan, the reaction of aliphatic Carbonsäureestern with ammonia or an amine such as Mo nomethylamin, ethylenediamine, diethylenetriamine, in the presence of an "alkali catalyst" at 50 to 180 ⁰ C, in particular 80 to 160 ⁰ C, and in the pressure range of normal pressure to 9.81 bar (10 kg »cm ² -G).

There are 0.1 to 10 mol.%, In particular 1 to 5 mol.%, Based on the carboxylic acid ester used, sodium methoxide (NaOMe) used as a catalyst.

Derwent Abstract 84-016399 / 03 (SU-A-1 004 357; Dnepr Chem. Techn. Inst.) Describes the preparation of DMAC or dimethylformamide (DMF) by reacting a 5-20% excess of corresponding methylcarboxylate in methanol with DMA at 50 - 15O ⁰ C and subsequent recycling of unreacted ester and methanol in the reaction stage.

In the example, a solution of 0.4 kg of methyl formate in 0.2 kg of methanol / h is continuously reacted with 0.2 kg of vapor DMA / h to DMF.

The two German patent applications Nos. 102004030616.8 of 24.06.04 and DE-A-10 315 214 of BASF AG relate to processes for the purification of DMAC.

The present invention has for its object to provide an improved economical, selective, energy and resource-saving process for the preparation of N, N-dimethylacetamide (DMAC). The process should provide DMAC in high yield and space-time yield and in high purity (e.g., free or quasi-free of acetic acid, high color quality).

Accordingly, a process for the preparation of N, N-dimethylacetamide (DMAC) was found by continuous reaction of methyl acetate (MeOAc) with dimethylamine (DMA) in the presence of a basic catalyst, characterized in that MeOAc as a methanolic solution and per mole of MeOAc in the range from 0.0002 to 0.09 mol of catalyst is used and the reaction is carried out at a temperature in the range of 90 to 14O ⁰ C and at an absolute pressure in the range of 10 to 30 bar.

The process according to the invention can be carried out as follows:

For DMAC synthesis, dimethylamine (DMA) is reacted continuously with a methanolic solution of methyl acetate (MeOAc), which may in particular be a secondary stream of the polyTHF preparation.

Per mole of methyl acetate are preferably in the range of 0.2 to 2.0 mol, especially 0.5 to 1, 5 mol, very particularly 0.8 to 1, 2 mol, for example 0.9 to 1, 1 mol or 1, 0 to 1, 05 mol, dimethylamine (DMA) used. The DMA used preferably has a purity of ≥ 99% by weight, in particular ≥ 99.4% by weight, and is, for example, in the range from 99.5 to 99.8% by weight.

The methanolic MeOAc solution preferably has a concentration in the range of 65 to 90 wt .-%, particularly preferably 70 to 85 wt .-%, in particular 75 to 82 wt .-%, MeOAc on.

As methanolic MeOAc solution, in a particular embodiment of the invention, an appropriate by-product stream which is used in the production of polyTHF (polytetrahydrofuran), e.g. according to the two-stage BASF process according to EP-A-3112, DE-A-197 58296 and / or DE-A-198 17 113, is used.

This methanolic MeOAc solution as a corresponding by-product stream is obtained in the workup by distillation, for example, as a methyl acetate / methanol azeotrope (boiling point: 54 ⁰ C / 1013 mbar), as in the transesterification of polyTHF diacetate (= poly- (1, 4-butanediol ) bis (acetate)) with methanol to polyTHF stoichiometric amounts of MeOAc arise.

The methanolic MeOAc solution preferably has the following contents:

MeOAc: 65 to 90 wt .-%, preferably 70 to 85 wt .-%, in particular 75 to

82% by weight,

Methanol: 10 to 30% by weight, preferably 14.8 to 25% by weight, in particular 17.6 to 22% by weight,

Dimethyl ether: 0 to 2 wt .-%, preferably 0.1 to 1, 5 wt .-%, in particular 0.2 to

1, 2 wt .-%, THF: 0 to 4 wt .-%, preferably 0.1 to 3.5 wt .-%, in particular 0.2 to

1, 5 wt .-%, and H ₂ O: 0 to 0.1 wt .-%, preferably 0 to 0.01 wt .-%, in particular 0 to

0.003 wt .-%.

In particular, the methanolic MeOAc solution consists of MeOAc, MeOH, dimethyl ether, THF and water in the amounts indicated above.

The continuous reaction is carried out at an absolute pressure in the range of 10 to 30 bar, especially 12 to 25 bar, e.g. 15 to 20 bar, carried out.

The reaction temperature is in the range of 90 to 14O ⁰ C, preferably 95-130 ⁰ C _1, in particular from 97 to 12O ⁰ C, especially 98-110 ⁰ C, for example 100 to 105 ⁰ C. Particularly suitable reactors for the reaction according to the invention are backmixing reactors such as, for example, stirred tank reactors or jet loop reactors, non-backmixing reactors such as stirred tank cascades or tubular reactors, and special designs such as reaction columns with and without internal or external VWZ volumes (VWZ = residence time), with an inside and external heat dissipation is possible.

The reaction is particularly preferably carried out in a jet loop reactor. The jet loop reactor is preferably equipped with a plug-in tube and bottom nozzle. DMA is preferably added together with the catalyst through the pumped propulsion jet and the MeOAc through the jacket jet.

To complete the conversion, the main reactor, e.g. the jet loop reactor, more preferably a post-reactor, e.g. a flow tube or a cascaded residence time tank, downstream.

The mentioned types of reactor are known to the person skilled in the art, e.g. from Ulimann's Enzyklopadie der Technischen Chemie, 4th Edition, Volume 13, p. 135 ff., and P.N. Rylander, "Hydroge- nation and Dehydrogenation" in Ullmann's Encyclopaedia of Industrial Chemistry, 5th ed. On CD-ROM.

In the process according to the invention, the basic catalyst used is preferably an alkali metal hydroxide, alkaline earth metal hydroxide, alkali metal alcoholate, alkaline earth metal alcoholate,

Alkali metal carbonate, alkaline earth metal carbonate, alkali metal bicarbonate, alkaline earth metal bicarbonate and / or an amine, in particular tertiary amine used.

The alkali metal is Li, Na, K, Rb or Cs, especially Na or

K.

The alkaline earth metal is Be, Mg, Ca, Sr or Ba, in particular Mg or Ca. When the alkoxide is preferably a d- ₄ alcoholate, in particular thanolat metal.

The particular aliphatic amine is preferably a C _3-12

Alkylamine, e.g. Triethylamine, tri-n-propylamine, tri-n-butylamine, dimethylethylamine,

Diethylmethylamine, N-methyl-piperidine, triethylenediamine (TEDA).

In the process according to the invention, no cobalt catalysts are used according to

US-A-4,258,200 is used.

Very particularly preferred catalyst in the process according to the invention is sodium methoxide (NaOMe).

The catalyst is homogeneous and / or suspended in the reaction mixture. In a continuous process per mole of methyl acetate used in the range of 0.0002 to 0.09 mol, preferably 0.002 to 0.05 mol, in particular 0.003 to 0.02 mol, of the catalyst or the catalyst mixture.

The catalyst or the catalyst mixture is advantageously used as a solution and / or suspension in a solvent or suspending agent. Preferred solvents and / or suspending agents are water and alcohols (eg C _1-4 alcohols, such as methanol, ethanol, n-propanol, n-butanol) or mixtures thereof.

In the case of an alkali metal alcoholate as catalyst, it is preferred to dissolve the alkali metal alcoholate in the alcohol corresponding to the alcoholate by protonation.

The catalyst or catalyst mixture is added to the o.g. preferred amounts are preferably used as 1 to 35 wt .-%, in particular 5 to 30 wt .-% solution or suspension.

Particularly advantageous as a catalyst NaOMe in the o.g. preferred amounts as methanolic solution, in particular as 1 to 35 wt .-% solution, especially as 25 to 30 wt .-% solution used.

The reaction of MeOAc in the process of the invention is preferably in the presence of less than 1 wt .-%, particularly less than 0.5 wt .-%, especially in the range of 0 to 0.3 wt .-%, water, respectively based on the weight of the two feedstocks MeOAc and DMA (in total).

The removal of the reaction heat of the reaction preferably takes place via an external heat exchanger. Particularly advantageously, the vapor generated in the external heat exchanger, e.g. 1, 5-bar steam, used in a synthesis plant for methylamines from methanol and ammonia.

In the process according to the invention, the liquid reactor discharge from the synthesis stage is in the range from 45 to 74.5% by weight, especially 50 to 70% by weight, DMAC, in the range from 25 to 45% by weight, especially 29 to 40 Wt .-%, methanol and a total of 0.5 to 6 wt .-%, especially 1 to 5 wt .-%, DMA, methyl acetate, catalyst (eg sodium methoxide), if necessary, catalyst solvent / -suspensionsmittel and by-products.

Through the use of methanolic MeOAc solution, which is obtained in the production of poly-THF, tetrahydrofuran (THF) and / or dimethyl ether may be such by-products. For further workup, the liquid reactor discharge can be released directly into a bubble of a distillation column.

In a particular embodiment, it is depressurized in two alternately operated distillation bubbles.

The effluent is advantageously water or an aqueous or anhydrous protic acid such as sulfuric acid, methanesulfonic acid, carboxylic acid (eg Ci _-4 carboxylic acid), particularly phosphoric acid, preferably in an amount that a complete turnover of the basic catalyst used for the corresponding acid and the corresponding Alkali metal, alkaline earth metal or ammonium salt of the protonic acid ensures added. That is to say that the basic catalyst used and present in the reactor effluent is completely neutralized by reaction with H ⁺ .

This is advantageous because the basic catalyst, e.g. Sodium methoxide, after the outgassing of residual DMA would catalyze the cleavage of DMAC.

The organic product mixture is preferably separated from existing salts by evaporation (at normal pressure or in vacuo, e.g., in a reboiler), e.g. until a precipitated salt significantly reduces the heat exchanger performance and leads to encrustations.

The bubble for the reactor discharge is then preferably changed and the residue of the old bubble evaporated as far as possible. The precipitated solid salt residue can be dissolved in water and disposed of as a solution in a sewage treatment plant.

The solids-removed and partially or totally condensed reactor effluent is worked up by distillation, e.g. in one, two, three, four or more, possibly interconnected, columns.

Preference is given to working up in three continuously operated distillation columns.

In this case, initially in a column A, preferably 0.8 to 1.2 bar, of methanol and optionally other low boilers (DMA, water, THF, methyl acetate, and the like) are removed overhead.

In the preferably downstream distillation column D for low boiler purification, a possibly aqueous methanol stream, which may contain DMA, enriched, which is for example advantageously recycled for use in a methylamine synthesis plant (in particular for DMA production). The bottom product of column A is fed to a column B. At preferably 100-500 mbar abs. Pure DMAC (≥ 99.5% by weight, in particular> 99.7% by weight, very particularly preferably> 99.8% by weight, eg in the range of ≥ 99.9 to 99.99% by weight) is used here. %), preferably via a liquid side draw, which is preferably in the reinforcing part, separated.

The head effluent of column B containing DMAC (e.g.> 98 wt% DMAC, especially 98.5 to 99.5 wt% DMAC) is preferably recycled to column A.

The bottom product of column B is separated again in a column C under normal pressure, the head discharge containing DMAC and methanol (eg about 94% by weight of DMAC and about 6% by weight of methanol) preferably also being recycled to column A. is and the bottom product of the column C (high boilers, DMAC and methanol added) for disposal, eg Combustion, passes. The third column C significantly reduces the amount of residue.

The distillative purification of DMAC can also be carried out according to one of the processes of the two German patent applications No. 102004030616.8 of 24.06.04 and DE-A-10 315 214 (both BASF AG).

According to the invention, it has been recognized that the process can advantageously also be carried out in a plant which was originally designed for the production of N, N-dimethylformamide (DMF) from carbon monoxide (CO) and DMA.

Minor modifications / additions to the system (such as post reactor, tank for DMAC and / or column interconnection) may thus be carried out in the DMF unit as e.g. in K. Weissermel, H.-J. Arpe, Industrial Organic Chemistry, Wiley-VCH, 5th Ed. 1998, page 49, or generally and principally described in JP-A2-110 92 434, advantageously both DMF and DMAC, e.g. in alternating operation, are produced. That the invention also allows the alternative or alternate production of DMAC in a DMF plant.

DMAC yields in the range of ≥ 88%, in particular ≥ 95%, very particularly ≥ 99%, e.g. 99.5 to 99.9%, (in each case based on MeOAc used), in the case of MeOAc etching sets in the range of ≥ 90%, in particular ≥ 96%, very particularly ≥ 99%, e.g. 99.5 to 100% achieved.

The DMAC space-time yields are in the range of 0.1 to 0.85 kg DMAC / (liter reactor volume • h), eg 0.2 to 0.5 kg DMAC / (liter reactor volume • h). The process according to the invention gives DMAC having a purity of> 99.5% by weight, in particular ≥99.7% by weight, very particularly ≥99.8% by weight, for example in the range of> 99.9 to 99, 99% by weight, (method and conditions for determination of purity see below), a water content ≦ 200 ppm, eg in the range from 50 to 150 ppm, (according to DIN 51777), and a Pt / Co color number ≦ 10, especially <8, eg in the range from 1 to 6, (according to DIN ISO 6271).

The acid content (calculated as acetic acid) of the DMAC is in particular ≦ 80 ppm, more particularly ≦ 70 ppm, e.g. in the range of 5 to 60 ppm, (according to DIN 53402).

All ppm data in this document are by weight (ppm by weight).

Examples

example 1

For the one-stage DMAC synthesis, 45.0 g / h of dimethylamine (DMA) with 95.5 g / h of methanolic methyl acetate (77.5% by weight), which was previously used as by-product stream in the production of poly-THF according to EP-A A-3112, DE-A-197 58 296 and / or DE-A-198 17 113 anfiel (THF content: 1, 5 wt .-%), reacted at 20 bar and 12O ⁰ C. The water content in the feed (DMA + methanolic methyl acetate) was 109 ppm.

The reaction took place in a loop reactor with an average residence time (VWZ) of 1 h and sodium methoxide (0.48 g / h) in methanolic solution (30% strength by weight) as homogeneous catalyst. The heat was removed via an external heat exchanger. The energy dissipated in the external heat exchanger can generate 1, 5-bar steam.

The liquid effluent from the synthesis step consisted of 57.7% by weight of DMAC, 34.2% by weight of methanol, 5.0% by weight of methyl acetate and a total of 3.1% by weight of DMA, tetrahydrofuran, sodium methoxide and by-products ,

Example 2

All settings from example 1 have been adopted. However, the water content of the feed stream was 550 ppm. After a short time, blockages occurred in the reactor due to precipitated sodium acetate and the experiment had to be stopped. Example 3

For the two-stage DMAC synthesis, 45.2 g / h of dimethylamine (DMA) with 92.5 g / h of methanolic methyl acetate (78.8% by weight), which was previously used as by-product stream in the production of poly-THF according to EP-A A-3112, DE-A-197 58 296 and / or DE-A-198 17 113 anfiel (THF content: 1, 0 wt .-%), reacted at 20 bar and 12O ⁰ C.

The reaction took place in a loop reactor with an average VWZ of 1 h and sodium methoxide (0.56 g / h) in methanolic solution (30% by weight) as a homogeneous catalyst. The heat was removed via an external heat exchanger. The energy dissipated in the external heat exchanger can generate 1, 5-bar steam.

The liquid discharge from the synthesis stage consisted of 53.9 wt .-% DMAC, 36.3 wt .-% methanol, 3.9 wt .-% of methyl acetate and a total of 5.9 wt .-% DMA, tetrahydrofuran, sodium methoxide and by-products ,

This discharge was conveyed in a straight pass through a tubular reactor at 12O ⁰ C, 20 bar and a mean VWZ of 1 h. The effluent consisted of 58.3 wt% DMAC, 37.3 wt% methanol, 1.1 wt% methyl acetate and a total of 3.3 wt% DMA, tetrahydrofuran, sodium methoxide and by-products.

Example 4

To a reaction effluent according to Example 3 was continuously 10 wt .-% of excess stoichiometric added to the catalyst H ₂ O to decompose the sodium methoxide. In a continuous exhaust steam bubble at 135 ° C, all volatile ingredients (1, 8 kg / h) were distilled off. The salt-like residue (245 g) collected in the bottom of the bladder within 20 operating hours and evaporated to dryness was dissolved in 1.5 kg of H ₂ O and discharged from the bladder without residue into the wastewater requiring treatment (bbA).

Example 5

A reaction effluent according to Example 3 was continuously mixed with 85% strength phosphoric acid for the stoichiometric formation of Na ₂ HPO ₄ . After catalyst decomposition and evaporation of the volatile ingredients according to Example 4, 400 g / h of the condensed mixture were fed continuously to a distillation column and at a bottom temperature of 175 ° C, a high-boiling (218 g / h) with 99.2 wt .-% DMAC and 0 , 8 wt .-% by-products deducted. In a subsequent continuous distillation, this stream was further worked up to obtain 198 g / h DMAC with 99.9% purity from a side draw.

Claims

claims

1. A process for the preparation of N, N-dimethylacetamide (DMAC) by continuous reaction of methyl acetate (MeOAc) with dimethylamine (DMA) in the presence of a basic catalyst, characterized in that MeOAc as a methanolic solution and per mol of MeOAc in the range of 0, 0002 to 0.09 mol of catalyst is used and the reaction is carried out at a temperature in the range of 90 to 14O ⁰ C and at an absolute pressure in the range of 10 to 30 bar.

2. The method according to claim 1, characterized in that one carries out the reaction at a temperature in the range of 95 to 130 ⁰ C.

3. Process according to claims 1 or 2, characterized in that one carries out the reaction at an absolute pressure in the range of 12 to 25 bar.

4. The method according to any one of the preceding claims, characterized in that MeOAc is used as a methanolic solution which is obtained in the production of polyTHF by transesterification of polyTH F-diacetate with methanol as a byproduct.

5. The method according to any one of the preceding claims, characterized in that the methanolic MeOAc solution 70 to 85 wt .-% MeOAc, 14.8 to

25 wt .-% methanol, 0.1 to 1, 5 wt .-% dimethyl ether, 0.1 to 3.5 wt .-% tetrahydrofuran (THF) and 0 to 0.01 wt .-% water.

6. The method according to any one of claims 1 to 4, characterized in that the methanolic MeOAc solution 75 to 82 wt .-% MeOAc, 17.6 to 22 wt .-% methanol, 0.2 to 1, 2 parts by weight. % Dimethyl ether, 0.2 to 1, 5 wt .-% tetrahydrofuran (THF) and 0 to 0.003 wt .-% water.

7. The method according to any one of the preceding claims, characterized in that the catalyst used is sodium methoxide.

8. The method according to the preceding claim, characterized in that the catalyst is used as a methanolic solution.

9. The method according to any one of the preceding claims, characterized in that is used per mole of methyl acetate in the range of 0.002 to 0.05 moles of catalyst.

10. The method according to any one of the preceding claims, characterized in that the reaction is carried out in a jet loop reactor.

11. The method according to the preceding claim, characterized in that the jet loop reactor has a Einsteckrohr and a nozzle lying below.

12. The method according to any one of the preceding claims, characterized in that after the reaction and before the work-up by distillation the basic catalyst present in the reactor is neutralized by reaction with a protic acid or decomposed with water.

13. Method according to the preceding claim, characterized in that the protic acid is phosphoric acid.

14. The method according to one of the two preceding claims, characterized in that after the reaction, after the neutralization with a protic acid and before the work-up by distillation, the organic product mixture is separated by evaporation of existing salts.

15. The method according to any one of the preceding claims, characterized in that the continuous work-up by distillation is carried out such that initially in a column A methanol and optionally other low boilers are separated overhead and the bottom product of the column A is fed to a column B, in the DMAC is separated with a purity of ≥ 99.7 wt .-% via a side draw.

16. The method according to the preceding claim, characterized in that in the column B, the DMAC is separated with a purity of> 99.7 wt .-% via a liquid side draw, which is located in the enrichment section of the column.

17. The method according to one of the two preceding claims, characterized in that the head discharge of the column B, containing DMAC, is recycled to the column A.

18. The method according to any one of the three preceding claims, characterized in that the bottom product of the column B is separated in a column C, wherein the head discharge, containing DMAC and methanol, to the column A is recycled.

19. The method according to any one of the four preceding claims, characterized in that the head discharge of the column A, containing methanol, is purified in a column D and used in a synthesis plant for the production of methylamines from methanol and ammonia.

20. The method according to any one of the preceding claims for the preparation of DMAC having a purity of ≥ 99.7 wt .-%, a water content ≤ 200 ppm and a Pt / Co color number ≤ 10.

21. The method according to any one of the preceding claims for the preparation of DMAC having an acid content (calculated as acetic acid) of ≤ 80 ppm.

22. The method according to any one of the preceding claims, characterized in that it is carried out in a plant in which N, N-dimethylformamide (DMF) from carbon monoxide (CO) and DMA can be prepared.