PROCESS FOR PREPARING HYDRAZINE HYDRATE IN THE PRESENCE OF AN ANTI-FOAMING AGENT

1 . A process for preparing hydrazine hydrate, comprising a step of hydrolyzing an azine in a distillation column in the presence of at least one silicone of the polydialkylsiloxane, polydiarylsiloxane or polyalkyl-arylsiloxane formula.

2 . The process according to claim 1 , characterized in that the silicone is selected from the polydimethylsiloxanes, polydiphenylsiloxanes, polymethylphenylsiloxanes and polyethylphenylsiloxanes

3 . The process according to claim 1 or 2 , characterized in that the silicone has a viscosity of between 5 and 1,000,000 cSt, preferably between 50 and 100,000 cSt, and more particularly between 80 and 10,000 cSt at 25° C.

4 . The process according to any one of the preceding claims , characterized in that the silicone is a polydimethylsiloxane.

5 . The process according to any one of the preceding claims , characterized in that the silicone is in the form of an aqueous emulsion.

6 . The process according to any one of the preceding claims , characterized in that the silicone is introduced at the head of the distillation column, with the water introduced into the column for hydrolysis.

7 . The process according to any one of the preceding claims , characterized in that the silicone is introduced in a content ranging from 1 ppm to 5000 ppm by weight relative to the azine, preferably between 5 ppm and 4000 ppm by weight relative to the azine.

8 . The process according to any one of the preceding claims , characterized in that the azine is methyl ethyl ketone azine or dimethyl ketone azine, preferably the azine is methyl ethyl ketone azine.

9 . The process according to any one of the preceding claims , characterized in that the process comprises:

a step of reacting ammonia, hydrogen peroxide and ketone in the presence of a solution comprising at least one activator to form an azine in a working solution, prior to the hydrolysis step defined in the preceding claims .

10 . The process according to claim 9 , characterized in that it comprises the following steps:

separating the azine from the working solution;

regenerating the working solution by bringing it to at least 130° C. whilst removing the reaction water and the water supplied by the hydrogen peroxide dilution water in the form of a stream containing water, ammonia, ketone and CO 2 ;

passing the stream obtained in the preceding step through a stripping column, in the presence of at least one silicone as defined in any one of claims 1 to 5 , as an anti-foaming agent.

11 . The use of at least one silicone as defined in any one of claims 1 to 5 as an anti-foaming agent in an azine hydrate preparation process.

12 . The use according to claim 11 , characterized in that the silicone is introduced into the distillation column allowing the hydrolysis of an azine.

13 . The use according to claim 11 or 12 , characterized in that the silicone is introduced into an ammonia stripping column fed by a flow from the step of regenerating the working solution recovered after the ammonia, hydrogen peroxide and ketone reaction step to form the azine.