Denitration of spent acid

Fig. 27. Recovery (denitration) of spent acid (according to W. de C. Crater [29]).

The nitrating mixture is prepared from fresh concentrated nitric acid, 55% regenerated nitric acid (from the denitration of spent acid), and 96% sulphuric acid recovered by distillation. The mixture of acids is fed into the nitrator from a metering tank through a vacuum started siphon. Toluene is conveyed to the nitrator from another metering tank by means of compressed nitrogen. Air is considered as too dangerous to use, because the explosibility of mixtures of toluene vapour with air. 

RECOVERY OF SPENT ACIDS Denitration of spent acid NG... 

FIG, 6S. Denitration of spent acid of NG, NC, NT. (Courtesy Adolf Plinkc Sohnc l>-6 80 Bad Homburg.)... 

The denitration of spent acids offers some en ironmcntal problems. The major one being the escape of nitrous fumes from the denitration columns. According to Bcrkman (13) they can be introduced to a solution of sodium hydroxide to obtain sodium nitrate and nitrate aqueous solution. Tlie same... 

Generally, therefore, the spent acid remaining after manufacturing nitroglycerine and similar nitric esters undergoes denitration. The spent acid should be stored in lead tanks, and before passing on to the denitration tower, any separated nitroglycerine is skimmed from the surface by means of an aluminium ladle. 

TNT Mid then sent to denitration. Excess of spent acid from dinitration (14) is (Eluted to separate dissolved nitro compounds Mid also sent to denitration. 

DDNP see Dinitrodiazophcnol Deflagration of explosives in coal m nes 524.557 fill, 417-JlV) condition of Shot-firing 524 (in 40h> Denitration by electrochemical reduction of l.l.l trinitroeihanc 228 Dcniiriiiion of spent acids, environmental problems of 435-436 nt.R 332.610... 

The solubility of dinitrotriethylene glycol in the spent acid is exceptionally high amounting to 8-9%. Denitrating such an acid can be hazardous in view of the presence of such a large amount of an explosive substance. Separation takes place slowly and lasts over half an hour. This is an added hazard, since dinitro-triglycol readily decomposes in the presence of spent acid. It is therefore necessary to add water to the spent acid before the oily explosive material is separated, and the residual spent acid is transferred to the denitration unit. The separated oil is washed twice with water, then with a sodium carbonate solution and finally with water. A sample of washed and neutralized triethylene glycol dinitrate should withstand the heat test for 20 min at 82°C. 

After mixing the two solutions, the temperature is raised to 50-55°C and maintained thus for 40 min. The presence of crystals in the semi-liquid mixture results in a violet colour which gradually changes to grey and then to yellow. Nitration is judged to be complete when the colour turns pale-yellow. The contents of the nitrator are then cooled to 20°C and the product is filtered off on a vacuum filter. Spent acid (1290 parts) is drawn off, y of it returning to nitration and y going to denitration. 

The cyclonite was then washed with water and after neutralizing the residual acid with a 5% solution of sodium carbonate it was recrystallized. Initially, cyclonite was crystallized from nitrobenzene. However this proved to be dangerous due to the high boiling point of the solvent after a plant had been destroyed by an explosion, crystallization from acetone was adopted. The spent acid is denitrated, and KHSO ... 

In order to make use of the spent acid it must undergo denitration, which consists in separating the nitric add from the sulphuric acid. The spent acid should be denitrated as soon as possible after the supplementary separation of nitroglycerine. 

According to its size a plant for denitrating spent acid may have a daily output from 5 to 25 tons of acid. 

The denitration system works satisfactorily only for spent acid from the nitration of glycerine and similar alcohols. In spent acid from trinitrotoluene production the high content of dissolved nitrated hydrocarbons causes an excessive reduction of nitric arid at the top of the denitrating tower. Thus spent acid from the nitration... 

The spent acid leaves the separator from below to flow via a siphon, the height of which can be automatically controlled, to a diluter (6) where 1-2% water is added and then to a spent add mixer (8). Dilute spent acid is pumped to tank (9), and is used for displacement of nitroglycerine from the nitrator and separator after nitration has finished. Most of the dilute acid is sent to denitration. 

The nitration process was performed in the usual equipment, controlling the temperature, which should not exceed 25°C, by cooling with a 35% sodium nitrate solution, the temperature of which was — 15°C. Under these conditions nitration lasted about 25 min. When the nitration was completed, the contents of the nitrator were cooled down to 15°C and transferred to a separator. The separation was accomplished within 7 min and the spent acid was immediately sent to the denitration unit. Special care had to be taken to ensure that no spent add remained in the tank, because decomposition of the residual dinitrodiethylene glycol may start within a few hours. None the less such decomposition is less hazardous than that of nitroglycerine, since dinitrodiethylene glycol produces a spontaneous explosion only in the instance when the tank is confined. 

After the cotton has been removed from the nitration tank (Fig. 135) the composition of the acid in the tank is adjusted so that in quantity and strength of it remains unchanged throughout. The waste acid from the centrifuge is low in nitric acid. The regeneration of this spent acid by addition of oleum and fresh nitric acid is uneconomic. Spent acid is denitrated. 

In the TNT manufg industry, the acid recovery house is equipped to operate a separate process called "denitration or "acid recovery . During the mono-nitration process, the monomix acid becomes progressively weaker in HNOa and richer in water, so that the mono-waste acid resulting after nitration is complete contains only 4% of actual HNOa. The mono-waste acid also contains such a high percentage of water that it cannot be fortified economically as can the bi-and tri-spent acids. It is necessary, therefore, for economic reasons to recover H2S04 HNOa by distillation... 

Detoluation. Another characteristic feature of this method was the extraction of higher nitrated toluene derivatives, dissolved in the spent acids. The latter were conveyed to denitration and distillation (concentration) only after the nitro compounds present in them had been extracted with nitrotoluene, an operation which was called detoluation . Primarily it consisted in stirring the spent acids, heated to 75-80°C with a quantity of crude MNT, amounting to one quarter of the acid volume. A slight amount of nitrotoluene became nitrated due to the presence of the unreacted HN03 in the spent acid. 

Later the detoluation operation was combined with partial nitration of MNT to DNT, by adding to the spent acid a certain quantity of nitric acid from the recovery operation (denitration). 

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