| 摘要 |
Polyvinyl alcohol is continuously produced by adding a vinyl ester polymer in alcoholic solution to a saponification catalyst to initiate the saponification <PICT:0848787/IV(a)/1> reaction, continuously passing the reacting mixture without substantial agitation through a reaction zone, said reacting mixture passing through in piston-like flow, and continuously removing a continuous solid mass of polyvinyl alcohol. The vinyl ester polymer is preferably polyvinyl acetate but the formate or propionate may also be used. The saponification catalysts may be sodium hydroxide, potassium hydroxide, sodium methylate or sulphuric acid. In a typical Example (No. 1), a 20,6% by weight solution of polyvinyl acetate in methanol was mixed in a mixer 1 with caustic soda solution. The mixture flowed by gravity into a reactor 2 which is a vessel 100 cms in depth, and when the mixture reached a depth of 70 cms the mixture was withdrawn at a rate to maintain this depth, the solid polyvinyl alcohol being drawn from the reaction vessel by means of 2 pairs of rollers 3 and 4. |
