Thermal oxidative decomposition processes

Thermal oxidative decomposition processes Furnace black is the newest but also overwhelmingly the predominant process. Liquid feedstock is atomized, sprayed into a flame inside a ceramic-lined furnace, and then quenched, cooled, and filtered. The process offers technical and economic advantages, with the facility to produce a wide range of types, with adjustment of particle size and specific surface area. Particle aggregation can also be controlled by addition of very small amounts of an alkali metal salt. Particle size ranges from 10 to 100 pm. Black made by this process has a very low bulk density and is difficult to handle in this form. It is therefore pelletized or further densified. Wet-pelleting enables carbon black to be converted with water... 

Thermal-oxidative decomposition Furnace black process Degussa gas black process Lamp black process Aromatic oils on coal tar basis or mineral oil, natural gas Coal tar distillates Aromatic oils on coal tar basis or mineral oil... 

The disadvantage of the methods employing plate or rod-shaped semifinished materials is to be seen in the processing requirement to heat up and cool the materials twice in the process. To ensure stability for both processing steps and later use, large amounts of expensive additives must be used to prevent thermal and thermal-oxidative decomposition of the matrix polymers. 

The thermal decomposition of polymers involves exothermic and endothermic processes. Comparisons of experimental results obtained in the presence and absence of oxygen revealed that a pure thermal decomposition was not usually accompanied by exothermic heat changes while, during thermal oxidative decompositions, intensive heat evolution was generally observed. 

Allylic hydroperoxides (3.11) formed from auto-oxidation at low temperatures (50-90 °C) and thermal oxidation during processing (130-190 °C) differ substantially in the rates of decomposition, and initiation of degradation processes ... 

The polymer is exposed to an extensive heat history in this process. Early work on transesterification technology was troubled by thermal—oxidative limitations of the polymer, especially in the presence of the catalyst. More recent work on catalyst systems, more reactive carbonates, and modified processes have improved the process to the point where color and decomposition can be suppressed. One of the key requirements for the transesterification process is the use of clean starting materials. Methods for purification of both BPA and diphenyl carbonate have been developed. 

The most intensive development of the nanoparticle area concerns the synthesis of metal particles for applications in physics or in micro/nano-electronics generally. Besides the use of physical techniques such as atom evaporation, synthetic techniques based on salt reduction or compound precipitation (oxides, sulfides, selenides, etc.) have been developed, and associated, in general, to a kinetic control of the reaction using high temperatures, slow addition of reactants, or use of micelles as nanoreactors [15-20]. Organometallic compounds have also previously been used as material precursors in high temperature decomposition processes, for example in chemical vapor deposition [21]. Metal carbonyls have been widely used as precursors of metals either in the gas phase (OMCVD for the deposition of films or nanoparticles) or in solution for the synthesis after thermal treatment [22], UV irradiation or sonolysis [23,24] of fine powders or metal nanoparticles. 

The plasma decomposition process is applicable to any hydrocarbon fuel, from methane to heavy hydrocarbons. Similar to oxidative plasma reforming, plasma decomposition processes fall into two major categories thermal and nonthermal plasma systems. 

The sample temperature is increased in a linear fashion, while the property in question is evaluated on a continuous basis. These methods are used to characterize compound purity, polymorphism, solvation, degradation, and excipient compatibility [41], Thermal analysis methods are normally used to monitor endothermic processes (melting, boiling, sublimation, vaporization, desolvation, solid-solid phase transitions, and chemical degradation) as well as exothermic processes (crystallization and oxidative decomposition). Thermal methods can be extremely useful in preformulation studies, since the carefully planned studies can be used to indicate the existence of possible drug-excipient interactions in a prototype formulation [7]. 

Measurements of thermal analysis are conducted for the purpose of evaluating the physical and chemical changes that may take place in a heated sample. This requires that the operator interpret the observed events in a thermogram in terms of plausible reaction processes. The reactions normally monitored can be endothermic (melting, boiling, sublimation, vaporization, desolvation, solid-solid phase transitions, chemical degradation, etc.) or exothermic (crystallization, oxidative decomposition, etc.) in nature. 

Superadiabatic partial oxidation (combustion) process is the thermal decomposition of HjS in HjS-rich waste streams to high-purity hydrogen and elemental sulfur (Slimane et al., 2002). In the superadiabatic combustion (SAC) process, some part of the HjS is combusted to provide the thermal energy required for the decomposition reaction, as indicated by the following two reactions ... 

Vanoppen et al. [88] have reported the gas-phase oxidation of zeolite-ad-sorbed cyclohexane to form cyclohexanone. The reaction rate was observed to increase in the order NaY < BaY < SrY < CaY. This was attributed to a Frei-type thermal oxidation process. The possibility that a free-radical chain process initiated by the intrazeolite formation of a peroxy radical, however, could not be completely excluded. On the other hand, liquid-phase auto-oxidation of cyclohexane, although still exhibiting the same rate effect (i.e., NaY < BaY < SrY < CaY), has been attributed to a homolytic peroxide decomposition mechanism [89]. Evidence for the homolytic peroxide decomposition mechanism was provided in part by the observation that the addition of cyclohexyl hydroperoxide dramatically enhanced the intrazeolite oxidation. In addition, decomposition of cyclohexyl hydroperoxide followed the same reactivity pattern (i.e., NaY < BaY... 

Ellis and coworkers studied the effect of lead oxide on the thermal decomposition of ethyl nitrate vapor.P l They proposed that the surface provided by the presence of a small amount of PbO particles could retard the burning rate due to the quenching of radicals. However, the presence of a copper surface accelerates the thermal decomposition of ethyl nitrate, and the rate of the decomposition process is controlled by a reaction step involving the NO2 molecule. Hoare and coworkers studied the inhibitory effect of lead oxide on hydrocarbon oxidation in a vessel coated with a thin fQm of PbO.P l They suggested that the process of aldehyde oxidation by the PbO played an important role. A similar result was found in that lead oxide acts as a powerful inhibitor in suppressing cool flames and low-temperature ignitions.P l... 

The second step (eq. 4.5) is a thermal oxidative process. This initiates the reaction of ZDDP with oxygen, and enhances the decomposition. Since oxygen and/or hydroperoxide is present in the oil, decomposition is not a pure thermal degradation. The main products on the surface are zinc polyphosphates with minor amounts of zinc sulfides. As the rubbing continues, the polyphosphate layer comes into closer contact with water in oil and is hydrolyzed to give short-chain polyphosphates (eq. 4.6). 

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