Production Method of N-Vinyl-2-Pyrrolidone

Abstract

High-purity NVP can be produced by comprising at least two crystallization processes and supplying the mother liquor from the first crystallization process to the second crystallization process. Further, high-purity NVP can be obtained continuously and stably without plugging caused by depositing of crystals on the heat transfer surface of a crystallizer by controlling the water content in a feed NVP solution at the inlet of the crystallizer so as to be not lower than 0.7% by weight and not higher than 10% by weight.

1 . A method for producing N-vinyl-2-pyrrolidone comprising:
 preparing at least two crystallization processes;   supplying a feed N-vinyl-2-pyrrolidone to a first crystallization process;   supplying a mother liquor from the first crystallization process to a second crystallization process; and   supplying crystals from the crystallization processes to a crystal purification process where a sweating phenomenon is applied.   
   
   
       2 . A method according to  claim 1 , wherein the mother liquor from the second crystallization process is sent back to the second crystallization process. 
   
   
       3 . A method for producing N-vinyl-2-pyrrolidone by crystallization comprising:
 controlling a water content in a feed N-vinyl-2-pyrrolidone solution at an inlet of a crystallizer so as to be not lower than 0.7% by weight and not higher than 10% by weight based on the total weight of the N-vinyl-2-pyrrolidone solution; and   supplying the feed N-vinyl-2-pyrrolidone solution to a crystallization process.   
   
   
       4 . A method according to  claim 3 , wherein a pH value of the feed N-vinyl-2-pyrrolidone solution before supplying to the crystallization process is within the range of from 6.0 to 13.0. 
   
   
       5 . A method according to  claim 3 , wherein a temperature of the feed N-vinyl-2-pyrrolidone solution before supplying to the crystallization process is within the range of from 7.0° C. to 30.0° C. 
   
   
       6 . A method according to  claim 3 , wherein the feed N-vinyl-2-pyrrolidone contains at least one selected from the group consisting of distilled N-vinyl-2-pyrrolidone and N-vinyl-2-pyrrolidone recovered from a purification process. 
   
   
       7 . A method according to  claim 3 , wherein the water content is within the range of not lower than 0.8% by weight and not higher than 7% by weight, based on the total weight of the N-vinyl-2-pyrrolidone solution.