反应详情

The invention may be described with reference to the accompanying drawing. In the sole FIGURE a schematic flow diagram of one embodiment of the process of this invention is depicted. Elongated cylindrical reactor 10 is charged with a bed 11 of particulate sulfonated divinylbenzene-cross-linked polystyrene ion exchange resin. This resin is in the protonated (H+) form. While the resin is shown in a fixed bed configuration in the FIGURE, it will be appreciated that it could be in a stirred or fluidized bed configuration as well. Acetamide, acetaldehyde and water, in appropriate ratios, are continuously fed to the top of the resin bed via valved conduits 12, 14 and 15, respectively. The rate of reactant feed is regulated to provide a WHSV of from 0.01 to 2 kg of acetaldehyde/kg of resin/hour. Heat can be added to or removed from reactor 10 by means not shown as needed to control the reaction remperature, preferably between about 50° C. and about 110° C. A crude reaction product composed principally of water, unreacted acetaldehyde and acetamide, and ethylidine-bis-acetamide is continuously removed via valved conduit 16 to stripper 17. In stripper 17, a reduced pressure, generally from 600 to 200 mm of mercury absolute, is applied along with heat to maintain a bottom temperature of from about 70° to 150° C. Light materials are stripped overhead and are removed via conduit 19. These light materials include principally unreacted acetaldehyde, water and some acetamide. These light materials are condensed and may be discarded or treated to recover acetaldehyde, acetamide and water for recycle. A bottoms product, composed primarily of ethylidene-bis-acetamide and acetamide, is removed via conduit 20 to distillation column 21. Acetamide is taken overhead in column 21, condensed by means not shown, and removed via conduit 22, preferably to recycle to acetamide feed conduit 12. The bottoms product of column 21, composed of ethylidene-bis-acetamide and acetamide, is removed via conduit 24 to cracker 25. Cracker 25 is optionally equipped with agitator 26 and heating means not shown. A surface catalyst, very suitably glass powder, diatomaceous earth or a similar high surface area silicon or oxidic insoluble solid surface catalyst is charged to cracket 25 via conduit 27. The mixture of ethylidene-bis-acetamide and catalyst is heated (and optionally stirred). The cracker conditions are an absolute pressure of 30 to 100 mm of mercury and a temperature of 175° to 220° C. Under these conditions the ethylidene-bis-acetamide cracks to give vinylacetamide and acetamide. These products, as well as any residual acetamide present in the column 21 bottoms, are volatilized at the conditions of cracker 25 and are removed as an overhead via conduit 29. This overhead fraction is condensed and fed to distillation column 30. In column 30 the more volatile vinylacetamide is taken overhead, condensed, and removed as a liquid via conduit 31. Column 30 is generally operated at conditions such as a bottoms temperature of 130° to 180° C. and an absolute pressure of 30 to 100 mm of mercury. A bottoms fraction composed principally of acetamide is isolated and removed via conduit 32. Preferably, as is shown, this acetamide is recycled to feed line 12. There is real reason to remove and recover acetamide in two stages--one before and one after cracking. By so doing, the temperature in the cracker can be held at a high enough level to permit efficient cracking. Cracker 25 is equipped with bottoms take off 28 through which spent catalyst and heavy end byproducts can be withdrawn.

1. temperatureHeat can
2. additionbe added to or
3. customremoved from reactor 10
4. customthe reaction remperature, preferably between about 50° C. and about 110° C
5. customA crude reaction product
6. customis continuously removed
7. temperaturewith heat
8. temperatureto maintain a bottom temperature of from about 70° to 150° C
9. customare removed via conduit 19
10. customcondensed
11. additiontreated
12. customto recover acetaldehyde, acetamide and water for recycle
13. customis removed via conduit 20 to distillation column 21
14. customAcetamide is taken overhead in column 21, condensed by means not
15. customremoved via conduit 22
16. customis removed via conduit 24
17. customCracker 25 is optionally equipped with agitator 26
18. temperatureheating
19. additionA surface catalyst, very suitably glass powder, diatomaceous earth or a similar high surface area silicon or oxidic insoluble solid surface catalyst is charged
20. additionThe mixture of ethylidene-bis-acetamide and catalyst
21. temperatureis heated (and
22. customa temperature of 175° to 220° C