Patent GB-626926-A (GB)
Title: Recovery of acetic acid in the production of nitramine explosives
IPC: C07C51/487
Filed: 1945-05-11
Abstract: <PICT:0626926/IV (b)/1> Acetic acid which is present together with ammonium nitrate, nitric acid and residual nitramine explosives in the spent reaction liquor resulting from the manufacture of nitramine explosives, is recovered by adding sulphuric acid to said liquor so that the latter contains from 5 to 10 per cent by weight of sulphuric acid, heating the resultant mixture to a temperature below 112 DEG C. to effect fume-off, during which the ammonium nitrate and nitric acid are decomposed, and thereafter recovering the acetic acid by distillation of the fumed-off mother-liquor in the presence of an amount of sulphuric acid equal to 15 to 40 per cent by weight of the total mixture during which the residual nitramine explosives are destroyed.  The process is especially applicable to the recovery of acetic acid from the mother liquor obtained in the manufacture of cyclonite by heating together hexamine, preferably dissolved in glacial acetic acid, and nitric acid, ammonium nitrate and acetic anhydride at above about 35 DEG  C. or by treating paraformaldehyde with ammonium nitrate and acetic anhydride above about 35 DEG  C. Thus, the slurry comprising cyclonite and homocyclonite resulting from the first method is cooled, treated with ammonia to neutralize nearly all the nitric acid and then filtered.  The filtrate is next led into a fume-off chamber 10 together with sulphuric acid via lines 20 and 21, to fill the hydraulic legs 22 and 23 and nearly fill the chamber 10 to provide a mixture containing 5-10 per cent sulphuric acid. The mixture is heated to fume-off temperature, generally 106 DEG  C., and then prewarned filtrate and sulphuric acid in 95 : 5 ratio are continuously fed in.  The fume-off gases are led away through conduit 25.  The fumed-off liquor passes into the upper of a series of horizontal boiling tubes 11, each provided with dams 28, and flows down in sequence to the bottom tube and thence to storage tank 34.  The acetic acid vapours distilling from each tube are led through pressure equalizing line 31 and entrainer separator 12 to a condenser 13 and the condensed acid is collected in tank 32.  The temperature and sulphuric acid concentration vary from 120 DEG  C. and 15 per cent respectively at the upper tubes to 140 DEG  C. and 40 per cent at the bottom.  The residual acid in tank 34 may be recycled to the fume-off chamber.  The cyclonite filtered from the initial slurry may be treated with hot water to remove water-soluble and water-hydrolysable impurities.  The residual nitramine explosives in the fumedoff mother-liquor may also be decomposed by distilling the liquor from a sulphuric acid/acetic acid mixture containing 15 to 40 per cent by weight sulphuric acid maintained at 120 DEG  to 140 DEG C.; for example, fumed-off liquor containing 5.4 per cent sulphuric acid is distilled through a 40 : 60 sulphuric acid/acetic acid mixture using a reflux ratio of 0 : 1.  Graphical representations are given illustrating both the rate of destruction of cyclonite in boiling fumed-off mother-liquor sulphuric acid mixtures and the composition-boiling data for acetic acid-sulphuric acid mixtures.