| 摘要 |
PROBLEM TO BE SOLVED: To purify a mixture containing at least a diisocyanate monomer and a polyisocyanate composition while preventing the recovered diisocyanate monomer from being contaminated with the polyisocyanate composition by deaerating the mixture and feeding the deaerated mixture into a thin-film evaporator to separate the polyisocyanate composition from the mixture. SOLUTION: When a low-boiling component such as a diisocyanate monomer is evaporated from a mixture containing a polyisocyanate composition and a diisocyanate monomer by using a thin-film evaporator of e.g. a scrape type to obtain the polyisocyanate composition, entrainment raises the contamination of the separated low-boiling components with the polyisocyanate composition being a high-boiling component as the amount of the mixture fed into the evaporator increases. Especially, in the case of a polyisocyanate composition produced by using an agent for biuret formation such as water and accompanied by the formation of by-product gases such as carbon dioxide, the entrainment is remarkable. In order to prevent the entrainment, the mixture is deaerated before being fed into the evaporator.
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