For purification of N-vinylpyrrolidone, the following U.S. patent ,attached below, gives the method.

Saikam,

"Adding K2CO3 to the crude at room temperature, separating the organic phase and vacuum distillation once or more."

---Zhang, Aijun, Faming Zhuanli Shenqing (2012), CN 102503880 A 20120620.

Good luck