The conventional production method for n-vinyl caprolactam products by the n-vinyl caprolactam production plant is:
In the autoclave, the caprolactam is first heated and melted into a liquid, and the solid potassium hydroxide is added to stir the reaction to form a true catalytic caprolactam potassium salt, and the water formed by the reaction is removed by vacuum distillation. After the water is removed, the air is replaced with nitrogen, and then The acetylene is introduced at a certain temperature, and the reaction is carried out while maintaining the acetylene pressure at 1.2 to 2.0 MPa. After the reaction is completed, it is transferred to a high vacuum rectification column for rectification separation to obtain an n-vinylcaprolactam product.
After the reaction was continuously fed to continuous dehydration tower is heated to melt the mixed liquid caprolactam and aqueous potassium hydroxide solution in a tower reactor, distillation under reduced pressure dewatering, the dewatered material transferred into the autoclave through the reaction of acetylene. The Zibo n-vinyl caprolactam plant introduced this method only to improve the dewatering method.
When the alkali metal is used as a catalyst, caprolactam reacts with potassium hydroxide to form potassium caprolactam and water. The presence of water affects the life of the catalyst, caprolactam potassium, and also causes caprolactam to open. The direct reaction of caprolactam with a strong basic metal can avoid the formation of trace water in the reaction. However, due to the strong activity of the metal element, it is difficult to control, and it is not suitable for industrialization at present.
The catalyst for preparing a vinylation reaction by reacting a potassium alkoxide having a large steric hindrance (such as potassium t-butoxide or potassium cyclohexoxide) with caprolactam can also prevent the formation of trace water in the reaction, and the reaction can be easily controlled. Alcohols with greater steric hindrance avoid ring opening of caprolactam, but Zibo n-vinylcaprolactam plants have warned that such catalysts are expensive.