Explosive side reaction

Addition of anhydrous hydrogen chloride to vinylidene fluoride is reported to be accompanied by a hazardous (explosive) side reaction [53]. 

Centrifugal separators are used in many modem processes to rapidly separate the hydrocarbon and used acid phases. Rapid separation greatly reduces the amounts of nitrated materials in the plant at any given time. After an explosion in a TNT plant (16), decanters (or gravity separators) were replaced with centrifugal separators. In addition, rapid separation allows the hydrocarbon phase to be quickly processed for removal of the dissolved nitric acid, NO, etc. These dissolved materials lead to undesired side reactions. The organic phase generally contains some unreacted hydrocarbons in addition to the nitrated product. 

Hydrochloric acid may conveniently be prepared by combustion of hydrogen with chlorine. In a typical process dry hydrogen chloride is passed into a vapour blender to be mixed with an equimolar proportion of dry acetylene. The presence of chlorine may cause an explosion and thus a device is used to detect any sudden rise in temperature. In such circumstances the hydrogen chloride is automatically diverted to the atmosphere. The mixture of gases is then led to a multi-tubular reactor, each tube of which is packed with a mercuric chloride catalyst on an activated carbon support. The reaction is initiated by heat but once it has started cooling has to be applied to control the highly exothermic reaction at about 90-100°C. In addition to the main reaction the side reactions shown in Figure 12.6 may occur. 

Nitration Hazards arise from the strong oxidizing nature of the nitrating agents used (e.g. mixture of nitric and sulphuric acids) and from the explosive characteristics of some end products Reactions and side reactions involving oxidation are highly exothermic and may occur rapidly Sensitive temperature control is essential to avoid run-away... 

The kinetics and thermodynamics of the reaction, and of possible side reactions, need to be understood. The explosive potential of chemicals liable to exothermic reaction should be carefully appraised. 

Can hazards from the reaction be reduced by changing the relative concentration of reactants or other operating conditions Can side reactions produce toxic or explosive material, or cause dangerous fouling ... 

Common reaction rate v. temperature characteristics for reactions are illustrated in Figure 6.5. To avoid runaway conditions (Fig. 6.5a) or an explosion (Figure 6.5c), it may be essential to control the rate of addition of reactants and the temperature. The kinetics and thermodynamics of the reaction, and of possible side reactions, need to be understood. The explosive potential of chemicals liable to exothermic reaction should be carefully appraised. 

Can side reactions produce toxic or explosive material, or cause dangerous fouling ... 

These reactions take place in the inner zone of stars heavier than 15 solar masses. Hydrostatic carbon burning is followed by explosive neon burning at temperatures of around 2.5 x 109K. Under these conditions, phosphorus (31P) can be formed, although complex side reactions also occur. In comparison with the formation of... 

Lawrence (1996) summarized the answers of the experts and calculated the total scores for each parameter. According to this summary the most important parameters for inherent safety were inventory and toxicity. Other important factors were, in this order, chemical stability, temperature, pressure, flammability and explosiveness, which were considered to be essential by all experts. Also flash points and side reactions were quite important. 

In this thesis an inherent safety index for evaluating inherent safety in preliminary process design was presented. The inherent safety of a process is affected by both chemical and process engineering aspects. These have been dealt separately, since the index was divided into the Chemical Inherent Safety Index and the Process Inherent Safety Index. These two indices consist of several subindices which further depict specific safety aspects. The Chemical Inherent Safety Index describes the inherent safety of chemicals in the process. The affecting factors are the heat of the main reaction and the maximum heat of possible side reactions, flammability, explosiveness, toxicity, corrosiveness and the interaction of substances present in the process. The Process Inherent Safety Index expresses safety of the process itself. The subindices describe maximum inventory, maximum process temperature and pressure, safety of equipment and the safety of process structure. 

Poor to modest yields of trinitromethyl compounds are reported for the reaction of silver nitroform with substituted benzyl iodide and bromide substrates. Compounds like (36), (37), and (38) have been synthesized via this route these compounds have much more favourable oxygen balances than TNT and are probably powerful explosives." The authors noted that considerable amounts of unstable red oils accompanied these products. The latter are attributed to O-alkylation, a side-reaction favoured by an SnI transition state and typical of reactions involving benzylic substrates and silver salts. Further research showed that while silver nitroform favours 0-alkylation, the sodium, potassium and lithium salts favour C-alkylation." The synthesis and chemistry of 1,1,1-trinitromethyl compounds has been extensively reviewed. The alkylation of nitronate salts has been the subject of an excellent review by Nielsen." ... 

Agents for the drying of liquids must, of course, be chemically inert, as otherwise undesired side reactions could occur (e.g., styrene polymerizes explosively on contact with concentrated sulfuric acid at room temperature). 

Apart from the side reactions (39) and (40), others may occur which also result in the formation of explosive substances other than cyclonite. 

Nitration. All nitration reactions are potentially hazardous because of the explosive nature of the products and the strong oxidizing tendency, characteristic of the nitrating agent. The nitration reaction and the oxidation side reaction are highly exothermic. Therefore, these reactions may be extremely rapid and become uncontrollable. Close temperature control must be maintained (80,81). Sensitivity is enhanced by the presence of impurities, and rapid autocatalytic... 

In consequence of such drastic conditions of nitration several side reactions of oxidation and break-down processes take place, giving rise to the products mentioned above (trinitrobenzoic acid, trinitrobenzene, tetranitromethane). A decomposition reaction (p, 76) also gives off a large volume of carbon monoxide, which may form an explosive mixture with air. Several explosions of such mixtures have been described. 

For thiophene itself, conditions of type (1) tend to produce very fast reactions. However, work has shown that the explosively fast reaction with nitric acid-acetic acid, due to nitrosation, can be largely suppressed by using urea [71 JCS(B) 102] and sulfanilic acid would probably be even better in this respect [cf. 77JCS(P2)248, 77JCS(P2)1693]. Conditions (1) have therefore been confined mainly to deactivated thiophenes, with conditions (2) being preferred for activated thiophenes. It is believed that acetic anhydride suppresses side reactions preceeding via nitrosation under conditions (2) [71 JCS(B) 102]. 

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