Hoffmann Urea Process

CO(NH2)2 + NaOCl + 2 NaOH — NH2-NH2 + NaCl + Na2C03 + H20 (18.6) Urea Hypochlorite Hydrazine 

As in the Raschig process, aqueous caustic reacts with chlorine to make sodium hypochlorite solution. The urea solution is prepared by dissolving urea in water with the addition of steam to provide the heat needed for the endothermic dissolution. The temperature is kept at about 5°C for 43 percent urea solution. Glue is added at a ratio of 0.5g/Uter of solution to inhibit side reactions. The urea and hypochlorite solutions are added to the hydrazine reactor at a ratio of 1 4, and the reaction temperature is allowed to rise to 100°C. The crude product contains approximately 35 g N2H4/liter and can be refined in the same steps as used for the Raschig process. 

This process is not being operated in 2001 although it has operated commercially in the past. Compared with the standard Raschig process, it was the most economical method for low production levels. However rapid growth in plant size made it obsolete132. 

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Commercial production of hydrazine from its elements has not been successful. However three processes are available for the commercial production of hydrazine 1) The Raschig Process, 2) The Raschig/Olin Process, 3) The Hoffmann (urea) Process, 4) Bayer Ketazine Process, and 5) the Peroxide process from Produits Chimiques Ugine Kuhlmann (of France). 

Hoffmann (Urea) Process. The overall reaction proceeds in liquid phase as ... 

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