Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2002-11-21
2004-03-09
Powers, Flona T. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C548S555000
Reexamination Certificate
active
06703511
ABSTRACT:
The present invention relates to a process for the isolation of pure N-vinylpyrrolidone from N-vinylpyrrolidone-containing crude products.
Homopolymers and copolymers of N-vinylpyrrolidone are used widely. They are often used as monomers for the preparation of polymers for cosmetic products, for the pharmaceutical sector and for food technology. For the last-named areas, high requirements are placed on the purity of the N-vinylpyrrolidone.
On an industrial scale, N-vinylpyrrolidone is prepared by vinylation of 2-pyrrolidone with acetylene under pressure in the presence of basic catalysts, such as hydroxides and alkoxides. The product obtained after distillation usually comprises the product of value in an amount of from 98 to 99.9%, the main impurity being 2-pyrrolidone. In addition, the product also comprises a small amount of nitrogen and vinyl ether compounds, which sometimes lead to product discolorations and to the production of an odor during the polymerization.
A large number of applications require an N-vinylpyrrolidone which comprises less than 0.1% by weight of impurities. In principle, such a degree of purity can be achieved by fractional distillation. Removal of the compounds which are responsible for the product discoloration observed during the polymerization is possible only with difficulty in this way. For this reason, the distillation is often combined with an extractive work-up. DE 37 36 603, for example, describes the removal of such impurities using ion exchangers.
WO 94/18166 discloses the purification of N-vinylpyrrolidone by a multistage, fractional crystallization. In this process, a supercooled melt of the N-vinylpyrrolidone is crystallized, the mother liquor is separated off, and the crystallizate is subjected to at least one further crystallization stage. The product of value is likewise isolated from the mother liquor by multistage fractional crystallization. The process known from WO 94/18166 is based on the countercurrent principle, where in each crystallization stage the crystallizate is separated off from the crystallization residue (mother liquor), the crystallizate is passed to the next higher crystallization stage, and the crystallization residue (mother liquor) is passed to the next lower crystallization stage. The expenditure on apparatus for a crystallization process of this type is naturally high. In addition, the process is time-consuming because of the large number of crystallization stages.
EP-A 767 169 likewise describes a crystallization process for the purification of N-vinylpyrrolidone, which differs from the process known from WO 94/18166 by virtue of the fact that instead of supercooling the melt, the crystallization of the N-vinylpyrrolidone is initiated at the crystallization temperature using seed crystals. Here too, the mother liquor from the first crystallization stage is worked up by one or more successive crystallization stages. Although, as a result of the greater efficiency, fewer crystallization stages are required than in the case of the process of WO 94/18166, the expenditure on apparatus is very high for this process as well.
It is an object of the present invention to provide a process for the isolation of pure N-vinylpyrrolidone from N-vinylpyrrolidone-containing crude products, which can be operated with low expenditure on apparatus and produces N-vinylpyrrolidone of high purity. Furthermore, the process should advantageously lend itself to being incorporated into a continuous process for the preparation of N-vinylpyrrolidone.
We have found that this object is achieved by a process for the isolation of pure N-vinylpyrrolidone from N-vinylpyrrolidone-containing crude products, comprising a single-stage or multistage crystallization process, which comprises passing the mother liquor from the first crystallization stage either to a distillative and/or extractive purification, or returning it to an N-vinylpyrrolidone-containing product stream of the preparation process.
The process according to the invention for purifying N-vinylpyrrolidone may, in principle, be incorporated either into a discontinuous process, or into a continuous process for the preparation of N-vinylpyrrolidone. It is particularly advantageous to incorporate the purification process according to the invention into a continuous preparation process for N-vinylpyrrolidone.
In the process according to the invention, the pure N-vinylpyrrolidone is isolated from the crude product by crystallization of the crude product, which may be carried out in a single stage or in two or more stages. The crystallization is of course carried out such that a separation into a crystalline, N-vinylpyrrolidone-enriched phase, and a liquid, N-vinylpyrrolidone-depleted phase (mother liquor) is obtained.
According to the invention, the mother liquor, formed during the crystallization, from the first crystallization stage, i.e. the crystallization stage into which the N-vinylpyrrilidone-containing crude product is fed, is not subjected to further crystallizing work-up. Instead, the mother liquor is worked up by, according to a first process variant, introducing it to an extractive and/or distillative purification, preferably a combined extractive and distillative purification.
Distillative purification here is understood as meaning a single-stage or multistage fractional distillation in which low-boiling components, i.e. compounds with a higher vapor pressure than N-vinylpyrrolidone, and high-boiling components, i.e. compounds with a lower vapor pressure than N-vinylpyrrolidone, in particular 2-pyrrolidone itself, are separated off from the mother liquor and from the product of value. Preferably, the distillative purification is carried out as vacuum distillation. The distillation temperatures are usually in the range from 50 to 150° C. and in particular in the range from 80 to 120° C. at a pressure of from 1 to 100 torr and in particular from 5 to 20 torr. The low-boiling components produced in the process, in particular 2-pyrrolidone-containing fractions, can be returned via the crude distillation or directly to the actual preparation process. The distillative purification is preferably combined with an extractive purification.
In a second variant of the process according to the invention, the mother liquor is returned to an N-vinylpyrrolidone-containing product stream of the preparation process. Where a crude distillation of the N-vinylpyrrolidone-containing product stream is intended, the mother liquor can be returned either to the product stream before the crude distillation or to the crude distillation, or to the product stream after the crude distillation. It is preferably returned to the product stream before the crude distillation. In both cases, it is advisable to remove from the system any low-boiling fractions in a dedicated fractionating distillation. This avoids a build up in the level of these components in the crude product.
It is of course also possible to combine the distillative/extractive work-up of the mother liquor according to process variant 1 with the return of the mother liquor to the preparation process, preferably before or into the crude distillation, according to process variant 2.
In a particularly preferred embodiment of the process according to the invention, the crude product to be purified is divided into two substreams T1 and T2. The substream T1 is passed to the crystallization. The substream T2 is subjected to distillative and/or extractive work-up, as described above.
The mother liquor produced in the crystallizing work-up can then, depending on the process variant, either be returned to an N-vinylpyrrolidone-containing product stream of the preparation process, as described above, or be passed to the substream T2. Via the substream T2, the mother liquor is then passed to the distillative and/or extractive work-up. This procedure firstly has the advantage that it is possible to prepare products of varying qualities in a targeted manner according to need and the requirements for the N-vinylpyrrolidone. Secondly, this procedure permits th
Eck Bernd
Heilek Jörg
Helfert Herbert
Schmidt-Radde Martin
BASF - Aktiengesellschaft
Keil & Weinkauf
Powers Flona T.
LandOfFree
Method for obtaining pure n-vinyl pyrrolidone does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for obtaining pure n-vinyl pyrrolidone, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for obtaining pure n-vinyl pyrrolidone will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3228545