Patent GB-761920-A (GB)
Title: Improvements in or relating to the dehydration of hydrazine by azeotropic distillation
IPC: C01B21/16
Filed: 1954-06-10
Abstract: <PICT:0761920/III/1> In a process for the dehydration of hydrazine by azeotropic distillation using aniline as water-entrainer, the anhydrous hydrazine-aniline mixture withdrawn from the base of the azeotrope still is distilled in a second still from which anhydrous hydrazine is obtained as distillate and aniline is withdrawn as bottoms, the major portion of this aniline is returned to the azeotrope still while the remainder is distilled with water in a third still to give a distillate comprising an aniline phase and a water phase, at least part of the aniline phase is passed to the azeotrope still, while water containing non-volatile impurities but free from aniline is withdrawn from the base of the third still. That part of the condensed aniline-water azeotrope obtained as distillate from the azeotrope still and not returned as reflux thereto is advantageously used as source of water for the third still.  The water withdrawn from the base of the third still may contain hydrazine, and it is preferably passed to the evaporator used to volatilize the volatile components of the Raschig synthesis liquor.  The synthesis liquor is introduced through line 11 to evaporator 10; and vapours of hydrazine and water are evolved through line 13 to enter hydrate still 12. Water vapour is taken off from the head of still 12. Hydrazine-water mixture is withdrawn from reboiler 20, and is passed through line 22 to azeotrope still 23, which is heated by reboiler 34.  Aniline is fed to still 23 through lines 24, 25, 26; and vapours of an aniline-water azeotrope are taken off overhead and condensed in condenser-separator 28.  The condensate separates into a water phase and an aniline phase.  A portion of both phases of the condensate are returned to still 23 as reflux, while the balance of the condensate is passed through line 30 to aniline-recovery still 32.  Hydrazine-aniline mixture is withdrawn from reboiler 34 and is fed through line 36 to still 37. Anhydrous hydrazine is obtained as distillate from still 37, and is taken off as product through line 41.  Aniline, which may contain 1 to 10 per cent hydrazine depending upon the operation of still 37, is withdrawn from reboiler 43 through line 45.  The major portion of this aniline is recycled to azeotrope still 23 through line 26, while the remainder is passed through line 31 to aniline recovery still 32.  In still 32 all the aniline and a portion of the water contained in the feed are taken overhead as an aniline-water azeotrope to condenser-separator 47.  The condensate separates into an aniline phase and a water phase.  All the water phase is returned to still 32 as reflux, and the aniline phase is recycled to the azeotrope still through line 25. Condensers 28 and 47 may be replaced by a common condenser-separator of sufficient size to handle the aniline-water azeotrope both from still 23 and from still 32.  The aqueous liquid withdrawn from reboiler 49 through line 52 is passed to evaporator 10.  Salt and other involatile impurities are withdrawn from the evaporator through line 14.  Specifications 756,004 and 761,919 are referred to.