Method for purifying N-(2-hydroxyethyl)-2-pyrrolidone
A method for purifying N-(2-hydroxyethyl)-2-pyrrolidone (HEP) is disclosed. The method comprises crystallizing crude HEP to produce HEP crystals and a mother liquor, and separating the HEP crystals from the mother liquor. In one method of the invention, crystallization is induced by adding an HEP seed crystal to the crude HEP. In a preferred method, the crystallization is performed in the presence of 1–4 wt. % of added water. HEP can be successfully crystallized to a purity greater than 99.9%.
1. A method which comprises: (a) crystallizing liquid, crude N-(2-hydroxyethyl)-2-pyrrolidone (HEP) by adding an HEP seed crystal to produce HEP crystals and a mother liquor; and (b) separating the HEP crystals from the mother liquor.
2. The method of claim 1 wherein the crystallization is performed at room temperature.
3. The method of claim 1 performed in the presence of 1 to 4 wt. % of water based on the amount of crude HEP.
4. The method of claim 3 performed in the presence of 2 to 3 wt. % of water based on the amount of crude HEP.
5. The method of claim 3 wherein the crude HEP/water mixture is chilled to less than −5° C. to induce crystallization.
6. The method of claim 5 wherein the crude HEP/water mixture is chilled to less than −10° C. to induce crystallization.
7. The method of claim 5 wherein the HEP crystals have a purity greater than 99%.
8. The method of claim 5 wherein the HEP crystals have a purity greater than 99.9%.
9. A method which comprises: (a) crystallizing liquid, crude N-(2-hydroxyethyl)-2-pyrrolidone (HEP) in the presence of 1 to 4 wt. % of water based on the amount of crude HEP at a temperature less than −5° C. to produce HEP crystals and a mother liquor; and (b) separating the HEP crystals from the mother liquor, wherein the HEP crystals have a purity greater than 99%.
10. The method of claim 9 wherein the crystallization is performed in the presence of 2 to 3 wt. % of water.
11. The method of claim 9 wherein the crystallization is performed at a temperature less than −10° C.
12. The method of claim 9 wherein the HEP crystals have a purity greater than 99.9%.
13. A method which comprises: (a) crystallizing liquid, crude N-(2-hydroxyethyl)-2-pyrrolidone (HEP) in the presence of 1 to 4 wt. % of water based on the amount of crude HEP to produce HEP crystals and a mother liquor; and (b) separating the HEP crystals from the mother liquor.
14. The method of claim 13 wherein the crude HEP is crystallized in the presence of 2 to 3 wt. % of water based on the amount of crude HEP.
15. The method of claim 13 wherein the crude HEP/water mixture is chilled to less than −5° C. to induce crystallization.
16. The method of claim 15 wherein the crude HEP/water mixture is chilled to less than −10° C. to induce crystallization.
17. The method of claim 13 wherein the HEP crystals have a purity greater than 99%.
18. The method of claim 13 wherein the HEP crystals have a purity greater than 99.9%.
19. The method of claim 13 wherein crystallization is repeated until HEP of a desired purity is obtained.