# US 5,710,284 A · Purification of N-vinylpyrrolidone by crystallization

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- Number: US 5,710,284 A
- Document ID: US5710284A
- Status: Granted
- Kind: A
- Application number: 08/708,820
- Filed: 1996-09-09
- Granted: 1998-01-20
- Earliest claimed: 1995-10-02
- Assignees: BASF SE
- Inventors: Martin Schmidt-Radde; Herbert Helfert; Bernd Eck; Bernhard Maltry
- Web page: https://patentgrep.com/patent/US5710284A

## CPC

- C07D 207/267: with only hydrogen atoms or radicals containing only hydrogen and carbon atoms directly attached to the ring nitrogen atom
- C07D: HETEROCYCLIC COMPOUNDS (macromolecular compounds C08)

## Abstract

In a process for purifying N-vinylpyrrolidone by crystallization in a crystallizer, those surfaces of the crystallizer from which crystals grow during the crystallization are covered with an N-vinylpyrrolidone seed layer before the crystallization.

## Claims

### Claim 1

A process for purifying N-vinylpyrrolidone by crystallization in a crystallizer, wherein those surfaces of the crystallizer from which crystals grow during the crystallization are covered with an N-vinylpyrrolidone seed layer before the crystallization.

### Claim 2 (depends on 1)

The process as claimed in claim 1, wherein the seed layer is produced by freezing a molten film of N-vinylpyrrolidone.

### Claim 3 (depends on 1)

The process as claimed in claim 1, wherein the seed layer is produced by applying a two-phase layer of N-vinylpyrrolidone melt or solution with suspended N-vinylpyrrolidone crystals.

### Claim 4 (depends on 1)

The process of claim 1, wherein the crystallization is carried out in three crystallization stages, of which two are purification stages and one is a stripping stage.

### Claim 5 (depends on 4)

The process as claimed in claim 4, wherein the crystals leaving the particular crystallization stage are used to produce the seed layer.

### Claim 6 (depends on 4)

The process as claimed in claim 4, wherein the crystallization residue emerging from the first crystallization stage is partly returned to this crystallization stage.

### Claim 7 (depends on 6)

The process of claim 6, wherein the ratio of emerging to returned crystallization residue is from 0 to 1.0.

### Claim 8 (depends on 6)

The process of claim 6, wherein the ratio of emerging to returned crystallization residue is from 0.1 to 0.95.