BECHAMP REDUCTION

MANUFACTURE OF ANILINE FROM NITROBENZENE BY BECHAMP REDUCTION

1 Raw materials 

Basis: 1 metric ton aniline

Nitrobenzene: 1390 kg

Iron borings: 1600 kg

Hydrochloric acid: 125 kg

2 Manufacture 

Crude nitrobenzene is charge into a reducer (reactor) fitted with an efficient reflux condenser. The reducer is a steam jacketed cast iron enclosed cylindrical vessel containing an agitator. Cast iron borings (turnings) or powder (free from oil and non - ferrous metals), water and catalyst are added gradually, in small quantities, to the nitrobenzene. Generally 10 to 20% of the total iron is added at the beginning and the mixture is heated by steam to reflux temperature (200°C). The remaining iron is added over a period of time at a rate determined by the proper pressure temperature balance. The addition rate is fast enough to maintain lively reflux by the heat generated from the exothermic reaction, yet slow enough to prevent excessive hydrogen, pressure build up.

The water required for the reaction is generally in the form of aniline water recovered from the separator or column and is added to the reducer in bulk at the start or in small quantities along with the iron additions. Dilute (30%) HCl acid is added along with the water as catalyst. The acid reacts with the iron borings. Forming catalytically active iron salts. Subsequent runs may utilize aniline hydrochloric acid mother liquor as the source of the catalyst and some of the reaction water; the weight ratio of reactants is approximately 115 parts of iron borings, 0.27 parts of 100% hydrochloric acid and 60 parts of water per 100 parts of nitrobenzene. After the last addition, the reaction is heated with steam to maintain lively reflux.

At the end of the reduction (about 10 hrs. for 2250kg charge), the aniline is separated from the reducer charge by one or more of several methods, The liquid water aniline mixture may be separated from the solid iron oxide iron hydroxide sludge by steam distillation, vacuum distillation, filtration, centrifugation or siphoning. For example the finished reduction product may be neutralized with a small amount of sodium carbonate (about equal to the amount of hydrochloric acid in the charge) and allowed to settle. Most of aniline and some water siphoned off and the residual aniline is separated from the sludge by steam distillation. The sludge consisting of ferric oxide, water and small amount of ferric oxide is dumped and may be marketed after drying.

The water aniline mixture from the reducer is run to a separator where the lighter aniline separates and is withdrawn from the upper. The top layer, which contains 3 to 5% aniline, is partially distilled until the aniline content in the water is low. The residual aniline water is returned to the reducer for subsequent runs. The aniline in the distillate is separated by decantation and the water layer is redistilled to obtain the remaining aniline. An alternate procedure is to extract aniline from the aniline water with nitrobenzene.

The aniline streams from the separator and decanter are united and vacuum distilled to yield purified aniline. The yield based on nitrobenzene is approximately 95% by weight.

MECHANISM OF BECHAMP REDUCTION