Hydroxylamine ammonium salts rearrangement

Current production of s-caprolactam is mainly based on the reaction of cyclohexanone with hydroxylamine and subsequent rearrangement of the intermediate oxime. Undesirable ammonium sulfate is co-produced well in excess of s-caprolactam, i.e., 0.9-2.9 kg in the oximation step and 1.5-1.8 kg in subsequent Beckmann rearrangement, for 1 kg of product. The salt, of little commercial value, is sold for use in fertilizers or can be incinerated for the recovery of sulfur (Figure 23). 

The conventional process (Figure 2.32a) involves the reaction of cyclohexanone tvith hydroxylamine sulfate (or another salt), producing cyclohexanone oxime that is subjected to the Beckmann rearrangement in the presence of stoichiometric amounts of sulfuric acid or oleum. The overall process generates about 4.5 kg of ammonium sulfate per kg of caprolactam, divided roughly equally over the two steps. The Sumitomo process (Figure 2.32b) instead produces virtually no waste and allows caprolactam to be obtained in >98% yield (based on cyclohexanone 93% based on FI2O2). 

Reaction of cyclohexanone with hydroxylamine-which is produced as a sulfate salt by the air oxidation of ammonia to nitric acid, followed by catalytic hydrogenation in the presence of sulfuric acid and ammonia yields an intermediate, cyclohexanone oxime, which undergoes Beckmann rearrangement to caprolactam in the presence of stoichiometric amounts of sulfuric acid. Large quantities of salt are produced in both reactions, making it a very wasteful process Approximately 4.5 kg of ammonium sulfate salt is generated per kilogram of caprolactam that is produced. 

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