Method for producing highly polymerizable n-vinyl carboxylic acid amide monomer
A method for producing a highly polymerizable N-vinyl carboxylic acid amide monomer includes (A) melting a crude N-vinyl carboxylic acid amide monomer comprising 50 to 88 mass % of an N-vinyl carboxylic acid amide monomer by heating, followed by cooling for precipitation, and subjecting precipitated N-vinyl carboxylic acid amide monomer crystals to solid-liquid separation (step (A)), and (B) further dissolving the N-vinyl carboxylic acid amide monomer crystals separated in the step (A) in a mixed solvent of ethyl acetate and an aliphatic hydrocarbon having 6 to 7 carbon atoms, then performing crystallization, performing solid-liquid separation, and recovering an N-vinyl carboxylic acid amide monomer purified product (step (B)), wherein a mass ratio of ethyl acetate/N-vinyl carboxylic acid amide monomer crystal in step (B) is 0.01 to 0.5, and a mass ratio of aliphatic hydrocarbon having 6 to 7 carbon atoms/N-vinyl carboxylic acid amide monomer crystal in step (B) is 0.5 to 3.0.
1. A method for producing a highly polymerizable N-vinyl carboxylic acid amide monomer, comprising
(A) a step of melting a crude N-vinyl carboxylic acid amide monomer comprising 50 to 88 mass % of an N-vinyl carboxylic acid amide monomer by heating, followed by cooling for precipitation (cooling crystallization), and subjecting precipitated N-vinyl carboxylic acid amide monomer crystals to solid-liquid separation (step (A)), and
(B) a step of further dissolving the N-vinyl carboxylic acid amide monomer crystals separated in the step (A) in a mixed solvent of ethyl acetate and an aliphatic hydrocarbon having 6 to 7 carbon atoms, then performing crystallization (solvent crystallization), performing solid-liquid separation, and recovering an N-vinyl carboxylic acid amide monomer purified product (step (B)), wherein
a mass ratio of ethyl acetate/N-vinyl carboxylic acid amide monomer crystal in the step (B) is 0.01 or more and 0.5 or less, and
a mass ratio of aliphatic hydrocarbon having 6 to 7 carbon atoms/N-vinyl carboxylic acid amide monomer crystal in the step (B) is 0.5 or more and 3.0 or less.
2. The method for producing a highly polymerizable N-vinyl carboxylic acid amide monomer according to claim 1 , wherein the mass of the ethyl acetate is 0.003 to 1.0 based on the mass of the aliphatic hydrocarbon having 6 to 7 carbon atoms.
3. The method for producing a highly polymerizable N-vinyl carboxylic acid amide monomer according to claim 1 , wherein the crystallization in the step (A) is carried out by melting the crude N-vinyl carboxylic acid amide monomer at 30° C. to 80° C., followed by cooling to −20° C. to 20° C.
4. The method for producing a highly polymerizable N-vinyl carboxylic acid amide monomer according to claim 1 , wherein the crystallization in the step (B) is carried out by dissolving the N-vinyl carboxylic acid amide monomer crystals in the mixed solvent of ethyl acetate and an aliphatic hydrocarbon having 6 to 7 carbon atoms at 30° C. to 80° C., followed by cooling to −20° C. to 20° C.
5. The method for producing a highly polymerizable N-vinyl carboxylic acid amide monomer according to claim 1 , wherein the aliphatic hydrocarbon having 6 to 7 carbon atoms used in the step (B) is at least one selected from normal hexane, cyclohexane, normal heptane, cycloheptane, and methylcyclohexane.
6. The method for producing a highly polymerizable N-vinyl carboxylic acid amide monomer according to claim 1 , wherein a method for the solid-liquid separation in the step (A) and the step (B) is separation by filtration.
7. The method for producing a highly polymerizable N-vinyl carboxylic acid amide monomer according to claim 1 , wherein the N-vinyl carboxylic acid amide monomer is an N-vinylacetamide monomer.