Nitroglycerine in spent acid

Fig. 9. Solubility of nitroglycerine in spent acid, according to Klassen and Humphrys [25].

The stronger the acid concentration, the higher the degree of nitration and the larger is the yield. An excess of acids establishes equilibria that favour a more complete reaction. The surplus must not be too large, however, since nitroglycerine is slightly soluble in spent acid and this may considerably decrease the yield of... 

The addition of water to detain nitroglycerine in the spent acid not only increases the solubility of nitroglycerine in the acid, it also alters the equilibrium of the reaction between dinitroglycerine, nitroglycerine and acid in such a way that dinitroglycerine does not undergo further nitration and the trinitrate is not formed (Renner and Helle [28]). 

In this arrangement the nitrator-separator of the Nathan system was combined with settlers of improved design so as to achieve a more precise separation of the nitroglycerine and spent acid. This settler is reminiscent of the Nathan nitrator (Figs. 34 and 35). 

In practice the nitrating conditions most frequently applied are those which permit the composition of the spent acids after nitration to approximate to the mixture My Naoiim [22] has established the solubility of nitroglycerine in mixed acids composed of ingredients resembling approximately the mixture M3 (Table 10),... 

Originally, nitroglycerine was manufactured by batch process. This represented a significant hazard because literally tons of product and spent acid were maintained for several hours at elevated temperatures. In an attempt to reduce the hazard, the operation was changed from batch to continuous, a process in which the glycerine and nitrating mixture were separately fed into a reaction chamber. In this way, the residence time was reduced to several seconds, which obviously resulted in a safer operation. 

Heat of nitration of glycerin. Suppose we wish to estimate the heat evolved in nitrating 1 mole of glycerin with mixed acid. To simplify this illustrative example we will assume initial mixture — 1 mole glycerin/3 moles 100% nitric acid/6 moles 100% sulfuric acid final mixture -1 mole nitroglycerin completely separated from the spent acid which is now diluted by 3 moles of water the entire heat of dilution is due to 3 moles water dissolving in 6 moles of 100% sulfuric acid. Thus... 

The quantitative effect of various additives on the rate of separation of nitroglycerine from spent add has been determined by Moisak and Grigoryev [15]. They found that in the presence of 0.5% ferric sulphate or lead sulphate, the separation rate is halved. Further, they established that the separation rate is related to the composition of the spent acid. The maximum rate of separating was achieved by using add composed as follows ... 

After separation of the nitroglycerine, the following remain in the spent acid nitroglycerine, dinitroglycerine, mixed esters of sulphuric and nitric arid. The two latter esters react slowly with the nitric arid contained in the waste arid to form further nitroglycerine, which floats on the surface of the arid. 

There is a further method of obtaining nitroglycerine from the spent acid if the main product is separated immediately after nitrating. Nitration is commonly performed at the temperature of 25 - 30°C. The waste acid is cooled after nitration is complete, to the temperature of 15°C or less, and as a result a part of the nitroglycerine which was dissolved in the acid is separated. 

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. 

Originally 2% of water were added to the spent acid and this prevented the separation of nitroglycerine at temperatures from 10 to 15°C. Nevertheless in 1906 a tank filled with this dilute spent acid exploded while being transported. Further experiments showed that nitroglycerine can separate from acid diluted in that way if its temperature falls below 10°C. Addition of 5% water was therefore introduced, to prevent separation of nitroglycerine even at a temperature of 0°C. At the present time this procedure is widely used with new methods of nitration including continuous processes. 

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. 

The remainder of the spent acid is allowed to separate in the usual way and normally yields a maximum of 0.1% emulsified nitroglycerine. Instead of afterseparation, water can of course be added to prevent separation. 

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