PROCESS OF PREPARATION OF ANHYDROUS HYDRAZINE STARTING FROM HYDRAZINE HYDRATE

1. Process for the preparation of anhydrous hydrazine of high purity from hydrazine hydrate, comprising the following stages : a) dissolving in hydrazine hydrate, at a temperature from 50 to 100 degrees C, a quantity of caustic soda which causes the formation of two liquid phases, a heavy phase which is impoverished in hydrazine and a light phase which is enriched in hydrazine ; b) separating the light phase from the heavy phase ; c) passing the light phase over a cation exchange resin to remove the Na**+ ions contained in the said light phase ; and d) subjecting the deionized light phase to a purification operation by zone crystallization consisting in (i) filling an elongated tube with the impure light liquid phase, (ii) arranging around one of the extremities of the tube at least one sleeve with a short length compared with the length of the tube, this sleeve being cooled to a temperature within the crystallization or solidification region of the impure light liquid phase, so as to cause the formation of a solid crystallized plug in the region of the said extremity, (iii) moving the tube slowly with respect to the sleeve so as to cause the said plug to progress in the direction of the other extremity of the said tube, the previously crystallized portion in the tube melting again after passage of the sleeve, (iv) continuing the relative displacement of the tube and the sleeve until at least 0.4 times the length of the tube has travelled through the sleeve and, (v) collecting the purified melted liquid product which is behind the crystallized plug.