Raschig Process

(Ⅱ) oxide from ammonia combustion is reacted with ammonium hydrogen carbonate solution and air:

The resulting ammonium nitrite solution is reacted with sulfur dioxide at 0 to 5 °C and pH 2 to 4.5 forming ammonium disulfonate:

The yield based on nitrite is ca. 90%. Finally, the disulfonate is hydrolyzed at 100°C in a relatively slow reaction:

The hydroxylamine content in this solution, which also contains ammonium sulfate, is ca. 70g/L. In an integrated caprolactam manufacturing plant using the Raschig process for hydroxylamine production, ca. 1.8 kg of ammonium sulfate is produced per kg of caprolactam.

Nitrogen(Ⅱ) Oxide Reduction Process

Nitrogen(Ⅱ) oxide in 80 to 90% yield is produced by the catalytic combustion of ammonia in oxygen in the presence of water vapor on a platinum-rhodium catalyst:

In the BASF process this is reduced with hydrogen to hydroxylamine on a platinum catalyst on carbon substrates suspended in dilute sulfuric acid. In the Inventa process palladium is used.

The expected formation of ammonia in a side reaction is largely suppressed by process control measures, e.g. high hydrogen pressure, low hydrogen ion concentration and low temperature, and through a selective poisoning of the catalyst. The yield based on nitrogen(Ⅱ) oxide is ca. 90%.

The quantity of ammonium sulfate byproduct is this process is ca. 0.8 kg per kg of caprolactam produced. The hydroxylamine content in the solution amounts to ca. 115 g/L.

Reduction Process (DSMMPO-Stamicarbon)

solution is reduced to hydroxylamine with hydrogen under pressure on a suspended precious metal catalyst (substrate: activated charcoal) in the presence of phosphoric acid (HPO: Hydroxylamine Phosphate Oxime):

After separating off the catalyst, the solution is directly reacted with a solution of cyclohexanone in toluene forming cyclohexanone oxime:

After the separation of residual organic substances, the aqueous phase is reacted with nitrogen oxides and atmospheric oxygen and reused as "recycled solution".

Ammonium ions formed in the side reactions during the hydrogenation are oxidized with nitrogen oxides to nitrogen in this step. The yield based on the ammonia utilized is ca. 58%. There are no ammonium salt byproducts.