Deflagration, peroxides

Deep fat frying, oil autoxidation, 623, 662 Deflagration, peroxides, 617 Degradation... 

Decomposition Hazards. The main causes of unintended decompositions of organic peroxides are heat energy from heating sources and mechanical shock, eg, impact or friction. In addition, certain contaminants, ie, metal salts, amines, acids, and bases, initiate or accelerate organic peroxide decompositions at temperatures at which the peroxide is normally stable. These reactions also Hberate heat, thus further accelerating the decomposition. Commercial products often contain diluents that desensitize neat peroxides to these hazards. Commercial organic peroxide decompositions are low order deflagrations rather than detonations (279). 

With regard to metals or oxides, the violence of reaction depends on concn of the performic acid as well as the scale and proportion of the reactants. The following observations were made (Ref 1) with additions of 2—3 drops of about 90% performic acid. Ni powder becomes violent Hg, colloidal Ag and Th powder readily cause explns. Zn powder causes a violent exp In immediately. Fe powder (and Si) are ineffective alone, but a trace of Mn dioxide promotes deflagration. Ba peroxide, Cu oxide, impure Or trioxide, Ir dioxide, Pb dioxide, Mn dioxide, and V pentoxide all cause violent decompn, sometimes accelerating to expin. Pb oxide, trilead tetraoxlde and Na peroxide all cause an immediate violent expin... 

Confinement volume plays a huge role but cannot be modelled. The solidity of the closure does not perform any role. So a sheet of paper placed on the test tube is enough to transform the deflagration decomposition process of benzoyl peroxide into a detonation, which pulverises the test tube (this accident happened to the author but proved to be unrepeatable during a later test). So it is not a transition -al effect of pressure increase that plays an aggravating roie. 

A drop of amine added to benzoyl peroxide is enough to cause a deflagration or a detonation of the peroxide, depending on to what extent the apparatus is confined. Phenylamine, N,N-dimethylaniline, N,N-dimethyl-p-toluidine react the same way. 

Barium peroxide had been used instead of potassium permanganate to purify acetic anhydride. Several operations had been carried out and the technicians had realised that this medium gives rise to mild deflagrations. During the last test a very violent detonation took place. It was thought that acetyl peroxide had formed. 

Benzoyl peroxide as a pure solid is classified as a deflagration hazard. When it is a solid containing about 30% water it is an intermediate fire hazard. As a paste (50% peroxide) it is a low fire or negligible hazard. See reference 18 for a definition of hazard classifications. Benzoyl peroxide containing 50% water will be purchased. It should be stored in a separate cool area, since all peroxides have short half-lives. 

Violence of reaction depends on concentration of acid and scale and proportion of reactants. The following observations were made with additions to 2-3 drops of ca. 90% acid. Nickel powder, becomes violent mercury, colloidal silver and thallium powder readily cause explosions zinc powder causes a violent explosion immediately. Iron powder is ineffective alone, but a trace of manganese dioxide promotes deflagration. Barium peroxide, copper(I) oxide, impure chromium trioxide, iridium dioxide, lead dioxide, manganese dioxide and vanadium pentoxide all cause violent decomposition, sometimes accelerating to explosion. Lead(II) oxide, lead(II),(IV) oxide and sodium peroxide all cause an immediate violent explosion. 

A published analytical procedure [1] for decomposing the sodium salt with ferrous-sulfate/peroxide in nitric acid at pH 2 led to deflagration or explosion dining the evaporation stage when applied to 10 g samples, but not with 5 g samples. Presence of sulfuric acid avoids the problem [2],... 

Confinement—Deflagration rates of substances such as azo compounds, peroxides, and certain lead oxides may accelerate by pressure increase, especially when the governing decomposition reaction is gas-phase controlled [28]. Initiation of a deflagration at the bottom or at the center of a closed or partially closed vessel may lead to an increase of eh deflagration rate by a factor of more than 100 in comparison with top initiation. Autocatalytic decomposition by a volatile catalyst is enhanced by confinement. 

Deflagration tests run under ambient pressure are relatively rudimentary. They provide information concerning only the propagation rate of deflagration after forced initiation. Examples of these tests are the UN deflagration test [143], dedicated to classification of organic peroxides, and the UN trough test [145], dedicated to classification of fertilizers. 

An example of the influence of pressure on the deflagration rate is shown in Figure 2.29 as obtained in testing with the constant pressure autoclave (CPA). An organic peroxide, f-butylperoxybenzoate (TBPB), was tested at several temperatures and pressures. It is clear from the data that the deflagra-... 

The liquid phase deflagration testing resulted in a temperature-concentration relation which divided the regimes at which the peroxide does and does not sustain a deflagration. This relation depended on the test tube diameter (2.5-cm and 7.6-cm tubes were used), and thus extrapolation of the diameter of interest is required. 

The results of a number of tests such as those described in Chapter 2 led to classifications for the peroxide group. These tests included the determination of the hazards of decomposition (deflagration and detonation), bum rate, fire hazard, and reactivity hazards. Five different classes were formulated, as listed in the NFPA 43B Hazard Class, from the test results. Emergency procedures have been established for these five classes. 

Concentrated organic peroxides, such as f-butyl peroxybenzoate (TBPB), have an F value of about 100 to 150 kj/kg. These compounds can produce a runaway ending in a deflagration. Dilution of the peroxide with the proper solvent will result in a considerable decrease of the F value because of the decrease in concentration of the active component and the decrease in the maximum temperature due to heating and evaporation of the solvent. 

Work on the deflagration hazards of organic peroxides has been done using a revised Time-Pressure test, to determine the characteristics of ignition sensitivity and violence of deflagration. Some correlation is evident between these characteristics and the AO content within each structurally based peroxide type. Also, for the same AO content, the nature of the characteristics appears to decrease hi the order diacyl peroxides, peroxyesters, dialkyl peroxides, alkylhydroperoxides [18],... 

H3N.CH2.CH2.NH2+Cr04+2H20 greenish-grey crysts, mp — dec-imp with evoln of water and deflagration nearly insol in w is stable in the dark. It can be prepd from ethylenediamine, chromic acid and 30% hydrogen peroxide Refs 1) Beil 4, 232 2) K.A. Hofmann, Ber... 

There is reason to believe that the measurement of burning rate should be of interest to the chemical industry. A number of materials that are handled can deflagrate, particularly if subjected to elevated temperature and pressure certain organic material containing nitrate, nitro, peroxide, and certain other oxidizing species are examples. It is important to know what these rates are and how they depend on temperature and/or pressure in order to know whether or not they constitute an industrial hazard. 

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