U.S. patent application number 11/720774 was filed with the patent office on 2008-08-28 for method for the production of n,n-dimethylacetamide (dmac).
This patent application is currently assigned to Basf Aktiengesellschaft. Invention is credited to Horst Grafmans, Steffen Maas, Karl-Heinz Ross, Heinz Rutter, Michael Schulz, Alexander Weck.
Application Number | 20080207949 11/720774 |
Document ID | / |
Family ID | 35871278 |
Filed Date | 2008-08-28 |
United States Patent
Application |
20080207949 |
Kind Code |
A1 |
Grafmans; Horst ; et
al. |
August 28, 2008 |
Method For The Production Of N,N-Dimethylacetamide (Dmac)
Abstract
A process for preparing N,N-dimethylacetamide (DMAC) by
continuously reacting methyl acetate (MeOAc) with dimethylamine
(DMA) in the presence of a basic catalyst, wherein MeOAc is used in
the form of a methanolic solution which is obtained as a by-product
in the preparation of polyTHF by transesterifying polyTHF diacetate
with methanol.
Inventors: |
Grafmans; Horst; (Bad
Durkheim, DE) ; Maas; Steffen; (Bubenheim, DE)
; Weck; Alexander; (Freinsheim, DE) ; Rutter;
Heinz; (Kapellen, BE) ; Schulz; Michael;
(Worms, DE) ; Ross; Karl-Heinz; (Grunstadt,
DE) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ, LLP
P O BOX 2207
WILMINGTON
DE
19899
US
|
Assignee: |
Basf Aktiengesellschaft
Ludwigshafen
DE
|
Family ID: |
35871278 |
Appl. No.: |
11/720774 |
Filed: |
December 3, 2005 |
PCT Filed: |
December 3, 2005 |
PCT NO: |
PCT/EP05/12982 |
371 Date: |
June 4, 2007 |
Current U.S.
Class: |
564/215 |
Current CPC
Class: |
C07C 231/02 20130101;
C07C 231/02 20130101; C07C 233/05 20130101 |
Class at
Publication: |
564/215 |
International
Class: |
C07C 233/05 20060101
C07C233/05 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 6, 2004 |
DE |
102004058886.4 |
Claims
1-21. (canceled)
22. A process for preparing N,N-dimethylacetamide (DMAC) comprising
the step of continuously reacting methyl acetate (MeOAc) with
dimethylamine (DMA) in the presence of a basic catalyst, wherein
said MeOAc is in the form of a methanolic solution obtained as a
by-product in the preparation of polyTHF via transesterification of
poyTHF diacetate with methanol.
23. The process according to claim 22, wherein said reaction is
carried out at a temperature in the range from 80 to 140.degree.
C.
24. The process according to claim 22, wherein said reaction is
carried out at an absolute pressure in the range from 3 to 30
bar.
25. The process according to claim 22, wherein said methanolic
MeOAc solution comprises from 70 to 85% by weight of MeOAc, from
14.8 to 25% by weight of methanol from 0.1 to 1.5% by weight of
dimethyl ether, from 0.1 to 3.5% by weight of tetrahydrofuran
(THF), and from 0 to 0.01% by weight of water.
26. The process according to claim 22, wherein said methanolic
MeOAc solution comprises from 75 to 82% by weight of MeOAc, from
17.6 to 22% by weight of methanol, from 0.2 to 1.2% by weight of
dimethyl ether, from 0.2 to 1.5% by weight of THF, and from 0 to
0.003% by weight of water.
27. The process according to claim 22, wherein said catalyst is
sodium methoxide.
28. The process according to claim 27, wherein said catalyst is in
the form of a methanolic solution.
29. The process according to claim 22, wherein said catalyst is
present in the range of from 0.0002 to 0.09 mole per mole of
MeOAc.
30. The process according to claim 22, wherein said reaction is
carried out in a jet loop reactor.
32. The process according to claim 30, wherein said jet loop
reactor comprises an insert tube and a nozzle located at the bottom
of said jet loop reactor.
32. The process according to claim 22, comprising the additional
step of neutralizing said catalyst present in the reactor effluent
after the reaction and before distillative workup by reacting said
catalyst with a protic acid or by decomposing said catalyst with
water.
33. The process according to claim 32, wherein said protic acid is
phosphoric acid.
34. The process according to claim 32, comprising the additional
step of removing the organic product mixture after neutralization
with a protic acid and before distillative workup by evaporating
said organic product mixture from salts present after the
reaction.
35. The process according to claim 22, comprising the additional
step of continuously distillatively working-up reaction effluent in
a column A, wherein methanol and any other low boilers are
initially removed overhead in column A, followed by feeding the
bottom effluent of column A to a column B, wherein DMAC is removed
via a side draw, and wherein said DMAC has a purity of greater than
or equal to 99.7% by weight.
36. The process according to claim 35, wherein said DMAC is removed
in column B via a liquid side draw which is disposed in the
rectifying section of column B.
37. The process according to claim 35, wherein the top effluent of
column B comprises DMAC and is recycled back into column A.
38. The process according claim 35, wherein the bottom effluent of
column B is separated into a column C, wherein the top effluent of
column B is recycled into column A, and wherein said top effluent
comprises DMAC and methanol.
39. The process according to claim 35, wherein the top effluent of
column A comprises methanol and is purified in a column D.
40. The process according to claim 22, wherein the DMAC prepared
has a purity of greater than or equal to 99.7% by weight, a water
content of less than or equal to 200 ppm, and a Pt/Co color number
less than or equal to 10.
41. The process according to claim 22, wherein the DMAC prepared
has an acid content calculated as acetic acid of less than or equal
to 80 ppm.
42. The process according to claim 22, wherein said process is
carried out in a plant wherein DMF can also be prepared from carbon
monoxide and DMA.
Description
[0001] The present invention relates to a process for preparing
N,N-dimethylacetamide (DMAC) by continuously reacting methyl
acetate (MeOAc) with dimethylamine (DMA) in the presence of a basic
catalyst.
##STR00001##
[0002] DMAC finds use as a polar solvent, for example for polymers
and for gases, as paint removers, extractants, catalysts and
crystallization assistants. In the coatings industry, DMAC is used,
owing to its high boiling point, for specific coating materials
based on polymeric binders, for example polyamides and
polyurethanes. DMAC is also used for producing fibers and films and
as a reaction medium. In the spinning of Spandex.RTM. fibers, DMAC
is used as an assistant and subsequently recovered at least
partly.
[0003] DMAC may be prepared from acetic acid and dimethylamine, for
example according to FR-A-1,406,279.
[0004] Carboxamides are also obtainable by aminolysis of
corresponding carboxylic esters; cf., for example, `Organikum`, VEB
Deutscher Verlag der Wissenschaften, 1963, pages 374-375.
[0005] The article by J. P. Guthrie in J. Am. Chem. Soc. 96, pages
3608-15 (1974) relates to reaction kinetics and thermodynamics
aspects of reactions including the aminolysis of carboxylic
esters.
[0006] 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 diol esters with dialkylamines.
[0007] U.S. Pat. No. 4,258,200 (Air Products) teaches the
preparation of DMAC from methyl acetate and DMA in the presence of
cobalt catalysts.
[0008] In Example 1, a "20% methanol-methyl acetate azeotrope" is
used for the reaction at 155-160.degree. F. (68.4-71.2.degree.
C.).
[0009] JP-A-02 160749 (Lion Akzo KK) relates, according to the
Patent Abstracts of Japan, to the reaction of aliphatic carboxylic
esters with ammonia or an amine, such as monomethylamine,
ethylenediamine, diethylenetriamine, in the presence of an "alkali
catalyst" at from 50 to 180.degree. C., in particular from 80 to
160.degree. C., and in the pressure range from standard pressure to
9.81 bar (10 kgcm.sup.-2G). From 0.1 to 10 mol %, in particular
from 1 to 5 mol %, based on the carboxylic ester used, of sodium
methoxide (NaOMe) is used as the catalyst.
[0010] 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
methyl carboxylate in methanol with DMA at 50-150.degree. C. and
subsequently recycling unreacted ester and methanol into the
reaction stage. In the example, a solution of 0.4 kg of methyl
formate in 0.2 kg of methanol/h is reacted continuously with 0.2 kg
of vaporous DMA/h to give DMF.
[0011] The two German patent applications No. 102004030616.8 of 24
Jun. 2004 and DE-A-1 0 315 214 to BASF AG relate to processes for
purifying DMAC.
[0012] It is an object of the present invention to provide an
improved, economically viable, selective, energy-saving and
non-resource-intensive process for preparing N,N-dimethylacetamide
(DMAC). The process should afford DMAC in high yield and space-time
yield and in high purity (for example free or virtually free of
acetic acid, high color quality).
[0013] Accordingly, a process has been found for preparing
N,N-dimethylacetamide (DMAC) by continuously reacting methyl
acetate (MeOAc) with dimethylamine (DMA) in the presence of a basic
catalyst, which comprises using MeOAc in the form of a methanolic
solution which is obtained as a by-product in the preparation of
polyTHF by transesterifying polyTHF diacetate with methanol.
[0014] The process according to the invention can be performed as
follows:
[0015] For DMAC synthesis, dimethylamine (DMA) is reacted
continuously with a methanolic solution of methyl acetate (MeOAc),
a secondary stream of polyTHF preparation.
[0016] Preference is given to using in the range from 0.2 to 2.0
mol, particularly from 0.5 to 1.5 mol, very particularly from 0.8
to 1.2 mol, for example from 0.9 to 1.1 mol or from 1.0 to 1.05
mol, of dimethylamine (DMA) per mole of methyl acetate.
[0017] The DMA used preferably has a purity of .gtoreq.99% by
weight, in particular .gtoreq.99.4% by weight, and is, for example,
in the range from 99.5 to 99.8% by weight.
[0018] The methanolic MeOAc solution preferably has a concentration
in the range from 65 to 90% by weight, preferably from 70 to 85% by
weight, in particular from 75 to 82% by weight, of MeOAc.
[0019] In a particular embodiment of the invention, the methanolic
MeOAc solution used is a corresponding by-product stream which is
obtained in the production of polyTHF (polytetrahydrofuran), for
example by the two-stage BASF process according to EP-A-3112,
DE-A-197 58 296 and/or DE-A-198 17 113.
[0020] The methanolic MeOAc solution is obtained as a corresponding
by-product stream in the distillative workup, for example, in the
form of a methyl acetate/methanol azeotrope (boiling point:
54.degree. C./1013 mbar), since stoichiometric amounts of MeOAc are
formed in the transesterification of polyTHF diacetate
(=poly-(1,4-butanediol) bis(acetate)) with methanol to give
polyTHF.
[0021] The methanolic MeOAc solution preferably has the following
contents: [0022] MeOAc: from 65 to 90% by weight, preferably from
70 to 85% by weight, in particular from 75 to 82% by weight, [0023]
Methanol: from 10 to 30% by weight, preferably from 14.8 to 25% by
weight, in particular from 17.6 to 22% by weight, [0024] Dimethyl
ether: from 0 to 2% by weight, preferably from 0.1 to 1.5% by
weight, in particular from 0.2 to 1.2% by weight, [0025] THF: from
0 to 4% by weight, preferably from 0.1 to 3.5% by weight, in
particular from 0.2 to 1.5% by weight, and [0026] H.sub.2O: from 0
to 0.1% by weight, preferably from 0 to 0.01% by weight, in
particular from 0 to 0.003% by weight.
[0027] In particular, the methanolic MeOAc solution consists of
MeOAc, MeOH, dimethyl ether, THF and water in the above-specified
amounts.
[0028] The continuous reaction is preferably carried out at an
absolute pressure in the range from 1 to 200 bar, preferably from 3
to 100 bar, in particular from 10 to 30 bar, very particularly from
12 to 25 bar, for example from 15 to 20 bar.
[0029] The reaction temperature is preferably in the range from 20
to 200.degree. C., preferably from 60 to 140.degree. C., in
particular from 80 to 120.degree. C., very particularly from 90 to
110.degree. C., for example from 95 to 105.degree. C.
[0030] Useful reactors for the inventive reaction are in particular
backmixed reactors, for example stirred tank reactors or jet loop
reactors, nonbackmixed reactors such as stirred tank batteries or
tubular reactors, and special designs such as reaction columns with
and without internal or external delay volumes, in which internal
and external heat removal is possible.
[0031] The reaction is effected with particular preference in a jet
loop reactor. The jet loop reactor is preferably equipped with an
insert tube and nozzle at the bottom. Preference is given to adding
DMA together with the catalyst through the circulation-pumped
driving jet and the MeOAc through the outer jet.
[0032] To complete the conversion, particular preference is given
to attaching downstream of the main reactor, for example the jet
loop reactor, a postreactor, for example a flow tube or a cascaded
delay vessel.
[0033] The reactor types mentioned are known to those skilled in
the art, for example, from Ullmanns Enzyklopadie der Technischen
Chemie, 4th edition, volume 13, p. 135 ff., and P. N. Rylander,
"Hydrogenation and Dehydrogenation" in Ullmann's Encyclopedia of
Industrial Chemistry, 5th ed. on CD-ROM.
[0034] In the process according to the invention, the basic
catalyst used is preferably an alkali metal hydroxide, alkaline
earth metal hydroxide, alkali metal alkoxide, alkaline earth metal
alkoxide, alkali metal carbonate, alkaline earth metal carbonate,
alkali metal hydrogencarbonate, alkaline earth metal
hydrogencarbonate and/or an amine, in particular tertiary
amine.
[0035] The alkali metal is Li, Na, K, Rb or Cs, in particular Na or
K.
[0036] The alkaline earth metal is Be, Mg, Ca, Sr or Ba, in
particular Mg or Ca.
[0037] The alkoxide is preferably a C.sub.1-4-alkoxide, in
particular methoxide.
[0038] The amine, especially an aliphatic amine, is preferably a
C.sub.3-12-alkylamine, for example triethylamine,
tri-n-propylamine, tri-n-butylamine, dimethylethylamine,
diethylmethylamine, N-methylpiperidine, triethylenediamine
(TEDA).
[0039] In the process according to the invention, no cobalt
catalysts according to U.S. Pat. No. 4,258,200 are used.
[0040] A very particularly preferred catalyst in the process
according to the invention is sodium methoxide (NaOMe).
[0041] The catalyst is present in the reaction mixture in
homogeneous and/or suspended form.
[0042] In the continuous process, preference is given to using in
the range from 0.0002 to 0.09 mol, preferably from 0.002 to 0.05
mol, in particular from 0.003 to 0.02 mol, of the catalyst or
catalyst mixture per mole of methyl acetate used.
[0043] The catalyst or the catalyst mixture is advantageously used
in the form of a solution and/or suspension in a solvent or
suspension medium.
[0044] Preferred solvents and/or suspension media are water and
alcohols (e.g. C.sub.1-4-alcohols such as methanol, ethanol,
n-propanol, n-butanol) or mixtures thereof.
[0045] In the case of an alkali metal alkoxide as the catalyst,
preference is given to dissolving the alkali metal alkoxide in the
alcohol which corresponds to the alkoxide by protonation.
[0046] The catalyst or the catalyst mixture is used in the
abovementioned preferred amounts, preferably in the form of from 1
to 35% by weight, in particular from 5 to 30% by weight, solution
or suspension.
[0047] Particularly advantageously, the catalyst used is NaOMe in
the above-mentioned preferred amounts in the form of a methanolic
solution, in particular in the form of a from 1 to 35% by weight
solution, very particularly in the form of a from 25 to 30% by
weight solution.
[0048] The reaction of the MeOAc in the process according to the
invention is preferably carried out in the presence of less than 1%
by weight, particularly less than 0.5% by weight, very particularly
in the range from 0 to 0.3% by weight, of water, based in each case
on the weight of the two feedstocks, MeOAc and DMA (in total).
[0049] The heat of reaction is removed preferably via an external
heat exchanger. Particularly advantageously, the steam raised in
the external heat exchanger, for example 1.5 bar steam, is utilized
in a synthesis plant for methylamines from methanol and
ammonia.
[0050] In the process according to the invention, the liquid
reactor effluent from the synthesis stage consists of
in the range from 45 to 74.5% by weight, particularly from 50 to
70% by weight, of DMAC, in the range from 25 to 45% by weight,
particularly from 29 to 40% by weight, of methanol and a total of
from 0.5 to 6% by weight, particularly from 1 to 5% by weight, of
DMA, methyl acetate, catalyst (for example sodium methoxide), if
appropriate catalyst solvent/suspension medium and by-products.
[0051] As the result of the use of methanolic MeOAc solution which
is obtained in the production of polyTHF, tetrahydrofuran (THF)
and/or dimethyl ether may be such by-products.
[0052] For further workup, the liquid reactor effluent may be
decompressed directly into a boiler of a distillation column.
[0053] In a particular embodiment, decompression is effected into
two alternately operated distillation boilers.
[0054] Advantageously, water or an aqueous or anhydrous protic acid
such as sulfuric acid, methanesulfonic acid, carboxylic acid (e.g.
C.sub.1-4-carboxylic acid), in particular phosphoric acid, is added
to the effluent, preferably in an amount which ensures full
conversion of the basic catalyst used to the corresponding acid and
to the corresponding alkali metal, alkaline earth metal or ammonium
salt of the protic acid. In other words, preference is given to
fully neutralizing the basic catalyst used and present in the
reactor effluent by reacting with H.sup.+.
[0055] This is advantageous since the basic catalyst, for example
sodium methoxide, would catalyze the dissociation of DMAC after the
outgassing of residual DMA.
[0056] The organic product mixture is preferably removed from salts
present by evaporation (at standard pressure or under reduced
pressure, for example in a reboiler), for example until a salt
which precipitates out distinctly reduces the heat exchanger output
and leads to encrustations.
[0057] The boiler for the reactor effluent is then preferably
changed and the residue of the old boiler is concentrated as far as
possible by evaporation. The precipitated solid salt residue may be
dissolved in water and disposed of as a solution in a water
treatment plant.
[0058] The reactor effluent which has been evaporated off from the
solid and partially or totally condensed is worked up by
distillation, for example in one, two, three, four or more columns
which are connected to one another if appropriate.
[0059] Preference is given to effecting the workup in three
continuous distillation columns.
[0060] In one column A, methanol and any other low boilers (DMA,
water, THF, methyl acetate, inter alia) are removed overhead at
preferably from 0.8 to 1.2 bar.
[0061] In the distillation column D, preferably connected
downstream, for low boiler purification, an aqueous or anhydrous
methanol stream which may comprise DMA is enriched and is, for
example, advantageously recycled for use in a methylamine synthesis
plant (in particular for DMA preparation).
[0062] The bottom effluent of column A is fed to a column B. At
preferably 100-500 mbar abs., pure DMAC (.gtoreq.99.5% by weight,
in particular .gtoreq.99.7% by weight, very particularly
.gtoreq.99.8% by weight, for example in the range from .gtoreq.99.9
to 99.99% by weight) is removed here, preferably via a liquid side
draw which is disposed preferably in the rectifying section.
[0063] The top effluent of column B, comprising DMAC (e.g.
.gtoreq.98% by weight of DMAC, in particular from 98.5 to 99.5% by
weight of DMAC), is preferably recycled into column A.
[0064] The bottom effluent of column B is separated once more in a
column C, preferably at standard pressure, and the top effluent
comprising DMAC and methanol (e.g. approx. 94% by weight of DMAC
and approx. 6% by weight of methanol) is preferably likewise
recycled to column A and the bottom effluent of column C (high
boilers, DMAC and added methanol) passes to disposal, for example
incineration. The third column C distinctly reduces the amount of
residue.
[0065] The distillative purification of DMAC may also be effected
according to one of the processes of the two German patent
applications 102004030616.8 of Jun. 24, 2004 and DE-A-10 315 214
(both BASF AG).
[0066] It has been recognized in accordance with the invention that
the process may advantageously also be carried out in a plant which
has originally been designed for the preparation of
N,N-dimethylformamide (DMF) from carbon monoxide (CO) and DMA.
[0067] Slight modifications/plant improvements (for example
postreactor, tank for DMAC and/or relating to the column
connection) thus advantageously allows both DMF and DMAC, for
example in alternating operation, to be prepared in the DMF plant
as described, for example, in K. Weissermel, H.-J. Arpe,
Industrielle Organische Chemie, Wiley-VCH, 5th edition 1998, page
49, or in general and in principle in JP-A2-110 92 434. In other
words, the invention also enables the alternative or alternating
production of DMAC in a DMF plant.
[0068] It is possible by the process according to the invention to
achieve DMAC yields in the range of .gtoreq.88%, in particular
.gtoreq.95%, very particularly .gtoreq.99%, for example from 99.5
to 99.9% (based in each case on MeOAc used), at MeOAc conversions
in the range of .gtoreq.90%, in particular .gtoreq.96%, very
particularly .gtoreq.99%, for example from 99.5 to 100%.
[0069] The DMAC space-time yields are in the range from 0.1 to 0.85
kg of DMAC/(liter of reactor volumeh), for example from 0.2 to 0.5
kg of DMAC/(liter of reactor volumeh).
[0070] The process according to the invention affords DMAC with a
purity of .gtoreq.99.5% by weight, in particular .gtoreq.99.7% by
weight, very particularly .gtoreq.99.8% by weight, for example in
the range from .gtoreq.99.9 to 99.99% by weight (see below for
method and conditions for purity determination),
[0071] a water content .ltoreq.200 ppm, for example in the range
from 50 to 150 ppm (to DIN 51777), and
[0072] a Pt/Co color number .ltoreq.10, particularly .ltoreq.8, for
example in the range from 1 to 6 (to DIN ISO 6271).
[0073] The acid content (calculated as acetic acid) of the DMAC is
in particular .ltoreq.80 ppm, very particularly .ltoreq.70 ppm, for
example in the range from 5 to 60 ppm (to DIN 53402).
[0074] All ppm data in this document relate to the weight (ppm by
weight).
EXAMPLES
Example 1
[0075] For the one-stage DMAC synthesis, 45.0 g/h of dimethylamine
(DMA) were reacted at 20 bar and 120.degree. C. with 95.5 g/h of
methanolic methyl acetate (77.5% by weight) which had been obtained
beforehand as a by-product stream in the production of polyTHF
according to EP-A-3112, DE-A-197 58 296 and/or DE-A-198 17 113 (THF
content: 1.5% by weight). The water content in the feed
(DMA+methanolic methyl acetate) was 109 ppm.
[0076] The reaction was effected in a loop reactor with a mean
residence time (MRT) of 1 h and sodium methoxide (0.48 g/h) in
methanolic solution (30% by weight) as the homogeneous catalyst.
The heat was removed via an external heat exchanger. The energy
removed in the external heat exchanger can raise 1.5 bar steam.
[0077] The liquid effluent from the synthesis stage 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
[0078] All settings from Example 1 were adopted. However, the water
content of the feed stream was 550 ppm. After a short time, there
were blockages in the reactor as a result of precipitated sodium
acetate, and the experiment had to be stopped.
Example 3
[0079] For the two-stage DMAC synthesis, 45.2 g/h of dimethylamine
(DMA) were reacted with 92.5 g/h of methanolic methyl acetate
(78.8% by weight) which had been obtained beforehand as a
by-product stream in the production of polyTHF according to
EP-A-3112, DE-A-197 58 296 and/or DE-A-198 17 113 (THF content:
1.0% by weight), at 20 bar and 120.degree. C.
[0080] The reaction was effected in a loop reactor with a mean MRT
of 1 h and sodium methoxide (0.56 g/h) in methanolic solution (30%
by weight) as the homogeneous catalyst. The heat was removed via an
external heat exchanger. The energy removed in the external heat
exchanger can generate 1.5 bar steam.
[0081] The liquid effluent from the synthesis stage consisted of
53.9% by weight of DMAC, 36.3% by weight of methanol, 3.9% by
weight of methyl acetate and a total of 5.9% by weight of DMA,
tetrahydrofuran, sodium methoxide and by-products.
[0082] This effluent was conveyed in straight pass through a
tubular reactor at 120.degree. C., 20 bar and a mean MRT of 1 h.
The effluent consisted of 58.3% by weight of DMAC, 37.3% by weight
of methanol, 1.1% by weight of methyl acetate and a total of 3.3%
by weight of DMA, tetrahydrofuran, sodium methoxide and
by-products.
Example 4
[0083] 10% by weight of H.sub.2O, a superstoichiometric amount
relative to the catalyst, was added continuously to a reaction
effluent according to Example 3 in order to replace the sodium
methoxide. In a continuous evaporation still, all volatile
constituents (1.8 kg/h) were distilled off at 135.degree. C. The
salt residue (245 g) which had been collected within 20 operating
hours and had been concentrated to dryness in the bottom of the
still was dissolved in 1.5 kg of H.sub.2O and removed without
residue from the still into wastewater in need of treatment.
Example 5
[0084] A reaction effluent according to Example 3 was admixed
continuously with 85% phosphoric acid for the stoichiometric
formation of Na.sub.2HPO.sub.4. On completion of catalyst
decomposition and evaporation of the volatile constituents
according to Example 4, 400 g/h of the condensed mixture were fed
continuously to a distillation column, and a high boiler stream
(218 g/h) comprising 99.2% by weight of DMAC and 0.8% by weight of
by-products was drawn off at a bottom temperature of 175.degree. C.
In a subsequent continuous distillation, this stream was worked up
further, and 198 g/h of DMAC with a purity of 99.9% were obtained
from a side draw.
* * * * *