Heat of nitration

Many nitrated products are explosives, including DNT, TNT, and nitroglycerine (NG). At least some mononitroaromati.es can also be exploded under certain conditions (20). Because of the high heats of nitration, mnaway reactions followed by severe explosions have occurred in industrial batch nitrators. To rniiiimi2e these potential ha2ards, the compositions of the feed acids and reaction conditions are currently better controlled than formerly. 

In a commercial unit, a spray nitrator (39) is operated adiabaticaHy. The Hquid HNO feed is sprayed direcdy into the hot and preheated propane feed. The heat of nitration provides the heat to vaporize the HNO and to preheat it to the desired temperature for nitration. At one time, several spray nitrators were operated in series, with additional HNO being sprayed into each nitrator (32). In such an arrangement, the optimum propane HN02 ratios did not occur, and considerable amounts of nitroparaffins degraded. 

The spent acid compn is 12.6/70.8/16.6 nitric acid/sulfuric acid/water, or 83.4% total acid and 15.1% nitric acid based on total acid. The total heat of reaction AHt = AHn + AHj where AHn is the heat of nitration, ie, the heat of... 

Additional total heats of nitration quoted by Urbatfski (but without details of how they are obtained) are ... 

Several exptl studies are quoted for the heat of nitrating one OH group. On a per mole basis these range from 1.7 to 2.lkcal/mole. However, Miles (Ref 44) computes a lower value, 1.2kcal( mole, on the basis of accurately determined heats of combustion of NC... 

RDX. Gilpin Winkler (Ref 38b) measured a heat of nitration of — 88.0kcal/mole of hexa-mine for the reaction of hexamine with 97.5% nitric acid. They also obtained a value of — 140kcal/mole of hexamine for the formation of RDX from hexamine and Bachmann reagents (acetic anhydride, acetic acid, ammonium nitrate and nitric acid). Incidentally, Gilpin Winkler interpret their results to mean that hexamine dinitrate is an intermediate in the direct nitrolysis of hexamine to give RDX, while hexamine mononitrate is an intermediate in the Bachmann process of producing RDX... 

Other methods of prepn include the heating of nitrates, as for Na20 of carbonates, as for CaO or of hydroxides, as for MgO. Of course, many inorganic oxides occur in nature as ores. Examples of these are Fe203, Fe304 and Sn02 For individual methods of prepn, see under the selected inorgenic oxides described below... 

Urbariski (Ref 35) gives the total heat of nitration as —9l7.4kcal/kg of phenol... 

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... 

According to the British data the heat of nitration of 1 kg of hexamine to cyclonite is 277 kcal/kg. According to the German data (Schnurr [38]) it is about 500 kcal/kg. 

Gilpin and Winkler [51] report the following heats of nitration when cyclonite is prepared in different ways ... 

Dunning, Millard and Nutt [50] published a graph (Fig. 16) showing the relation between the heat of nitration of hexamine to cyclonite and the concentration of... 

According to information from different sources the heat of nitration of glycerol to nitroglycerine varies from 120 to 170 kcal per 1 kg of glycerine. 

Heat of nitration. During O-nitration of cellulose heat is evolved. Wilson, in 1937 [81] first carried out measurements of the thermal effects of this reaction with both nitric acid-water, and mixed acid. 

Final percentage of nitrogen % Total heat evolved during nitration Heat developed due to the change in acid composition Heat of absorption by nitrocellulose Heat of nitration (and —A Hn kcal/mole HNO3)... 

Kagawa [82] established that the heat of nitrating cellulose to 10.4% N is 77.5 cal per 1 g. cellulose, from which he calculated the heat of nitrating one —OH group to be 2.11 kcal. Calvet and Dhers-Pession [83] reported a value of 2.0 0.2 kcal. 

Kunz et al. [79a] determined the heat of nitration of pulverized cellulose at 0°C with nitric acid. They found it be 61.6 cal per 1 g cellulose or 1.696 kcal per one nitrated OH group. 

The heat of nitration has been also calculated from the heat of combustion of nitrocellulose (Miles [8]), as 1.17 kcal per one hydroxyl group. Measurements of the heat of combustion are extremely accurate, hence this value appears to be close to the actual value although it differs considerably form the values obtained by direct measurement by earlier authors. 

Temperature coeffident of nitration. Experiments have shown that in a moderate range, e.g. from 0 to 45°C, temperature affects the degree of nitration very little. A decrease in temperature usually results in some decrease in degree of nitration on a technical scale, where nitration time is limited, but this is because equilibrium is not reached, and the rate of the reaction is the governing factor. From a knowledge of the heat of nitration it should be possible to predict the course of the reaction from the known equation ... 

Thermochemical data are available (Ref 2) on the heats of combustion and formation for all five isomers, on the heats of nitration from various Dinitrotoluenes for the 23,4-, 2,4,5-, and 2,3,6-isomers, and on the heats of crystn for the 2,3,4- and 2,4,5-isomers. Data are also available (Ref 1) on the shock sensitivities of all of the isomers except 2,3,6-, and on the rates of decompn at 140° of the 23,4-, 2,4,5-, and 23,5-isomers. The detonation pressure and the temp coefficient of decompn between 140 and 180° have been measured for the 2,4,5-isomer 2,3,4- and 2,4,5-TNT form addition compds ( 7r-complexes ) at 1 1 molar ratio with several polycyclic aromatic hydrocarbons (naphthalene, acenaphthene, fluorene, phenanthrene and anthracene) (Ref 2). 2,4,5-TNT forms complexes with 4-aminozaobenzene, 4-aminoacetophenone, bis (2 hydroxy ethyl) amine, and tris (2-hydroxy-ethyl) amine (Ref 1). The first two have a 1 1 molar ratio, the third 1 2, and the fourth 2 1. Upon heating, the two 4-amino compds react with replacement of the 5-nitro group, as discussed below... 

In the adiabatic mononitrobenzene (MNB) process, benzene is nitrated in the presence of a large volume of mixed acid, such that the total heat of nitration and dilution is absorbed by the acid as sensible heat. The process utilizes this energy in a vacuum sulphuric acid evaporator to reconcentrate the spent acid, which is then returned to the nitration section. 

On the basis of the above values, Gamer and Abemethy [50] have calculated the corresponding heats of nitration (Table 45, Fig. 50). They have also determined the heats of crystallization, viz., for nitrobenzene they found a value of 2.78 kcal/mole, and for m- dinitrobenzene, 4.87 kcal/mole. 

Fig 50. Heats of formation of nitro derivatives of benzene and toluene (a) and heats of nitration of benzene and toluene (b) in kcal/mole. (Garner and Abernethy [50]). 

From these data Gamer and Abemethy have calculated the heats of nitration of toluene (Fig. 50 p. 261) ... 

The same authors have calculated the heat of nitration of mono- to di-nitrotoluene. 

Heat of nitration. The heat of conversion of dinitrotoluene to trinitrotoluene, calculated from the heats of formation of the reactants and of the reaction products... 

Heat of nitration. Heats of direct conversion of dinitrotoluenes to trinitrotoluenes are listed in Table 78 (after Gamer and Abemethy [3]). 

Rinkenbach [36] determined the heats of formation and heats of nitration from his measurements of heats of combustion of nitronaphthalenes. The heats of combustion of these compounds measured by Badoche [37] are in agreement with the values reported by Rinkenbach (Table 97). 

As the inert gas passes through the system, it becomes humidified, removing the water of reaction from the reaction mixture. Most of the energy required for the gas humidification comes from the heat of nitration. The wet gas is condensed and the inert gas is recycled to the nitrator. The condensed organic phase is recycled to the nitrator while the aqueous phase is sent to effluent treatment. The reaction mixture is phase separated and the sulfuric acid is returned to the nitrator. 

Heat of nitration of glycerin. Suppose we wish to estimate the heat evolved in nitrating... 

---