| 摘要 |
This invention relates to a process for the purification of a crude liquid N-vinylpyrrolidone product which comprises (I) product rectification by (a) subjecting said crude product containing at least 0.3 weight % of impurities to a temperature of between about 1.degree. and 5.degree. below the freezing point of said crude liquid to form a vinyl pyrrolidone crystalline phase and a liquid residue phase in a first crystallization step; (b) separating said liquid phase from said crystalline phase; (c) allowing said separated crystalline phase to warm gradually so as to liquify said crystals and (d) subjecting the liquified crystals of vinyl pyrrolidone to between 1 and 3 additional crystallization steps, each carried out by gradually cooling the liquified vinyl pyrrolidone to a temperature above that of the preceding crystallization step up to a of 14.4.degree.C so as to form additional vinyl pyrrolidone crystalline and liquid residue phases with separation of vinyl pyrrolidone crystals and liquid residue phases and liquification of vinyl pyrrolidone crystals between each additional recrystallization step, recovery of N-vinyl-pyrrolidone product from the final crystallization step and (II) collecting said separated liquid residues from each crystallization step and subjecting them, sequentially, individually or collectively, to fractional crystallization in order to recover additional amounts of purified vinyl pyrrolidone product. The present process is capable of achieving up to 99.999 % purity of vinyl pyrrolidone in about 98 % recovery.
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