Preparation of N-methyl-2-pyrrolidone (NMP)

Details Preparation of N-methyl-2-pyrrolidone (NMP) Preparation of N-methyl-2-pyrrolidone (NMP)

2001-02-01

2002-02-19

Higel, Floyd D. (Department: 1626)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

Reexamination Certificate

active

06348601

ABSTRACT:

The present invention relates to a process for preparing N-methyl-2-pyrrolidone (=1-methyl-2-pyrrolidinone, NMP)
Owing to its ready volatility, thermal stability, high polarity and aprotic properties, NMP is suitable as a solvent for polymers and as a solvent for numerous organic syntheses, e.g. alkylations or preparation of carboxylic acids and their derivatives.
NMP is industrially important for, in particular, the separation of acetylene from cracker gas or of butadiene from C
4
fractions, for the extraction of aromatics or for the absorption of acidic constituents in gas scrubbers.
The industrial preparation of NMP is predominantly carried out by reaction of gamma-butyrolactone (&ggr;-BL) with monomethylamine (MMA) in a tube reactor, e.g. a shaft reactor, at from 200 to 350° C. and superatmospheric pressure, e.g. about 10 MPa (Ullmann's Encyclopedia of Industrial Chemistry, 5
th
ed, Vol. A22, pages 458 to 459 (1993)).
For example, JP-A-10 158 238 (Derwent Abstr. 98-393443/34) describes the reaction of &ggr;-BL with excess MMA at from 250 to 300° C. in the presence of water to form NMP.
JP-A-1 190 667 (Derwent Abstr. 89-260914/36) describes the preparation of NMP by reaction of &ggr;-BL with excess MMA, with the MMA remaining unreacted after the reaction and also the dimethylamine (DMA) and trimethylamine (TMA) obtained as by-products together with added water are returned to the reaction of &ggr;-BL with excess MMA.
JP-A-7 218 751 (Derwent Abstr. 35795T-E) reports the synthesis of NMP by heating &ggr;-BL or open-chain derivatives thereof with DMA and/or TMA at above 200° C. In an example, the reaction of &ggr;-BL with aqueous DMA at 270° C./3 h gives NMP in a yield of 80%.
JP-A-1 186 864 (Derwent Abstr. 89-259000/36) discloses the preparation of N-alkylated lactams by reaction of the corresponding lactones with secondary amines in the presence of water via the corresponding N,N-dialkyl-omega-hydroxycarboxamides as intermediates. According to Example 1 of this patent application, the reaction of &ggr;-BL with aqueous DMA gives an NMP yield of 60% and additionally forms methylamides of &ggr;-hydroxybutyric acid. In the single further example according to the application, too, an NMP yield of 60% is reported for the corresponding reaction of &ggr;-BL with DMA.
JP-A-l 186 863 (Derwent Abstr. 89-258999/36) describes the preparation of N-alkylated lactams by reaction of corresponding lactones with tertiary amines or with tertiary or quaternary ammonium compounds in the presence of water with elimination of a corresponding alcohol. According to Example 1 of this patent application, the reaction of &ggr;-BL with aqueous TMA gives an NMP yield of 8% and forms large amounts of by-products such as methylamides of &ggr;-hydroxybutyric acid, 2-pyrrolidone and &ggr;-hydroxybutyric acid.
The methylamines monomethylamine (MMA), dimethylamine (DMA) and trimethylamine (TMA) are prepared industrially in a continuous process by (exothermic) reaction of ammonia with methanol in the presence of a catalyst at elevated temperature (e.g.; Kirk-Othmer, Encyclopedia of Chemical Technology, 4
th
ed., Vol. 2, pages 373 to 375 (1992) and Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., Vol. A16, pages 535 to 541 (1990)).
Catalyst used are acid catalysts, in particular solid acid catalysts such as silicon oxides (silica, SiO
2
), aluminum oxides (alumina, Al
2
O
3
), silica-alumina (Sio
2
.Al
2
O
3
), titanium oxides (titania, TiO
2
), tungsten oxides, phosphates (AlPO
4
), zeolites and clays (method 1) or metal catalysts such as cobalt-, nickel- or copper-containing catalysts (e.g. copper chromite) (method 2). The catalyst is usually installed as a fixed bed.
The reaction temperatures in method 1 are generally from 300 to 500° C., in particular from 390 to 430° C., and the reaction temperatures in method 2 are generally from 130 to 250° C.
In method 1, the pressure is generally from 790 to 3550 kPa, in particular from 1500 to 3000 kPa; method 2 is usually carried out in the presence of hydrogen.
In these reactions of ammonia with methanol, a mixture of the methylamines MMA, DMA and TMA together with water is always obtained. The total selectivity to the methylamines is about 94%, secondary reactions are dissociations to form CO, CO
2
, CH
4
, H
2
and N
2
(cf., for example, K. Weissermel et al., Industrielle Organische Chemie, 3
rd
edition, pages 53 to 54 (1990)).
The crude reaction product comprising essentially ammonia, water, possibly unreacted methanol and the methylamines is fractionated by means of a continuous multistage, technically complicated distillation (combination of various pressure distillations and extractive distillations). A typical process diagram for the synthesis of methylamines and their isolation is shown in FIG. 2 in Kirk-Othmer, Encyclopedia of Chemical Technology, 4
th
ed., Vol. 2, pages 375 (1992), which is hereby incorporated by reference.
For example, in a distillation sequence which is technically complicated overall, ammonia and part of the TMA is firstly separated from the reaction mixture and the remaining TMA is subsequently separated off in an extraction column using water. Ammonia is returned to the reaction. In a subsequent dewatering column, MMA and DMA are separated off by the top and separated from one another in a separate column. Methanol is taken off at a side outlet of the dewatering column and separated from water in a separate column and returned to the synthesis. DMA and TMA can likewise be returned in principle to the reaction of NH
3
with methanol, with mixtures of MMA, DMA and TMA again being formed from DMA and TEA under the reaction conditions (thermodynamic equilibrium; cf, for example, Ullmann's Encyclopedia of Industrial Chemistry, 5
th
ed., Vol. A16, page 537 (1990)).
Further configurations of the methylamine production process may be found in J. Ramioulle et al., Hydrocarbon Processing, July 1981, pages 113 to 117 (cf., for example, FIG. 6 on page 117 of this document), which is hereby likewise incorporated by reference.
A disadvantage of the processes of the prior art for preparing NM? from ammonia, methanol and &ggr;-BL is that the MMA required for the reaction with &ggr;-BL firstly has to be isolated from the crude reaction product from the synthesis of methylamines by means of a technically very complicated distillation cascade (plurality of distillation columns connected in series) (as described above).
It is an object of the present invention to overcome the disadvantages of the prior art by finding an efficient, selective, economical and technically less complicated process for preparing NMP in high yields (based on &ggr;-BL) and high space-time yields from ammonia, methanol and &ggr;-BL.
We have found that this object is achieved by a process for preparing N-methyl-2-pyrrolidone (NMP), which comprises preparing a mixture comprising monomethylamine, dimethylamine and trimethylamine and ammonia in a first process step by reacting ammonia with methanol at elevated temperature in the presence of a catalyst, separating off the ammonia, reacting the mixture comprising the methylamines with gamma-butyrolactone (&ggr;-BL), in a molar ratio of monomethylamine to &ggr;-BL of at least 1 in a second process step at elevated temperature and superatmospheric pressure, separating NMP and unreacted methylamines from the reaction product and returning unreacted methylamines to the first process step for reaction with methanol and ammonia.
According to the present invention, the technically very complicated fractionation of the crude reaction product from the reaction of methanol with ammonia to give the individual methylamines MMA, DMA and TMA or the corresponding binary mixtures (e.g. MMA+DMA) can be dispensed with.
The process of the present invention can be carried out as is follows:
Ammonia is reacted with methanol in the presence of an acid catalyst, particularly preferably a solid acid catalyst (e.g. AlO
x
), o r a metal catalyst, with the catalyst particularly preferably being installed in the reac

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