Process for preparing hydrazine hydrate with pyrazoline recycling
The present invention relates to an improved process for preparing hydrazine hydrate from the azine of methyl ethyl ketone obtained from methyl ethyl ketone by oxidizing ammonia with hydrogen peroxide in the presence of an activator, characterized in that it comprises a step of recycling the pyrazoline-class heterocycles purge.
1. A process for preparing hydrazine hydrate, comprising the following steps:
(a) reacting ammonia, hydrogen peroxide and methyl ethyl ketone in the presence of a solution comprising at least one activator to form an azine;
(b) treating the reaction mixture from step (a) to isolate:
an aqueous phase comprising the at least one activator; and
an organic phase comprising the azine and optionally unreacted methyl ethyl ketone;
(c) optionally recycling the aqueous phase to step (a) after optional treatment;
(d) washing the organic phase;
(e) distilling the washed organic phase to recover the azine;
(f) hydrolyzing the azine to give hydrazine hydrate and regenerated methyl ethyl ketone, with pyrazoline-class heterocycles being purged;
(g) optionally recycling the methyl ethyl ketone obtained in step (f) to step (a); and
(h) recycling the pyrazoline-class heterocycles purge obtained in step (f) to one at least of steps (a), (b), (c), (d) or (g).
2. The process as claimed in claim 1 , wherein the pyrazoline-class heterocycles purge obtained in step (f) is recycled to one at least of steps (c), (d) or (g).
3. The process as claimed in claim 1 , wherein the pyrazoline-class heterocycles purge obtained in step (f) is recycled to the organic phase washing step (d).
4. The process as claimed in claim 3 , wherein the pyrazoline-class heterocycles purge is sufficient to perform the organic phase washing, without addition of water.
5. The process as claimed in claim 1 , wherein the pyrazoline-class heterocycles purge is carried out by withdrawal.
6. The process as claimed in claim 1 , wherein the recycling step (h) is carried out continuously.
7. The process as claimed in claim 1 , wherein the pyrazoline-class heterocycles are 3,5-diethyl-5-methylpyrazoline and 3,4,5-trimethyl-5-ethylpyrazoline.
8. The process as claimed in claim 1 , wherein the azine hydrolysis and methyl ethyl ketone regeneration step (f) is performed in a packed or tray distillation column.
9. The process as claimed in claim 8 , wherein the amount of pyrazoline-class heterocycles is not more than 5% by weight relative to the total weight of the liquid phase on the trays of the column or in the parts of the column at which the amount is at its maximum.
10. The process as claimed in claim 1 , wherein the activator is acetamide.