Laboratory-scale thermal-decomposition

Polyfluoroparafins, fluorocarbons, and other perfluoro denvatives show remarkable heat stability They are usually stable at temperatures below 300 C Thermal decomposition at 500-800 °C, however, causes all possible splits in the molecules and produces complex mixtures that are difficult to separate For preparative purposes, only pyrolyses that do not yield complicated mixtures of products are of interest [7] The pyrolytic reacpons of polyfluoro and perfluoro derivatives, when carried out at 500-11 Ofl °C, represent the most useful route to preparative generation of perfluoroolefins on the laboratory scale [7]... 

On the laboratory scale, pure BF3 is best made by thermal decomposition of a diazonium tetrafluo-... 

Laboratory and industrial-scale processes show that acetylene is one intermediate in carbon formation in the combustion of petroleum hydrocarbons. This is not only a result of thermal decomposition but a part of the complex of reactions occurring in the oxidation system. Steps resulting in the immediate production of acetylene seem to be molecular decomposition of molecules, or free radicals, or dehydrogenation, followed by combination or addition of oxygen. Peroxide formation may occur also. These reactions may be a general source of the hydrocarbon flame bands. 

Thermal decompositions (pyrolyses) and catalysed reactions in the vapour phase are widely used large-scale industrial techniques. These vapour phase reactions often lead to more economic conversions than the smaller batchwise laboratory methods, because relatively inexpensive catalyst preparations (compared to the often expensive reagents required in laboratory procedures) may be used, and because the technique lends itself to automated continuous production. In undergraduate laboratory courses the technique has not achieved widespread use. The discussion below of the various apparatus designs, to meet a range of experimental conditions, may be regarded as an introduction to this topic. 

For laboratory-scale use, the preparation of carbon monoxide is best accomplished by the thermal decomposition of formic acid or sodium formate ... 

Methods for laboratory-scale production of s-diazadiborines have not yet been developed. Azidoboranes were reported to give good yields of s-diazadiborine compounds either by controlled photolytic decomposition in inert solvents or by controlled thermal decomposition without solvents 54,178)... 

On a laboratory scale, O2 can be prepared by decomposition of certain oxygen-containing compounds. Heavy metal oxides, such as HgO, are not thermally stable and are fairly easily decomposed ... 

AB. For example, in diglyme and monoglyme AB is not entirely decomposed at 85 °C even after 9 and 25 h, respectively. Dixon and coworkers [86] reported that AB in monoglyme (0.14 M) releases only 0.05equiv H2 at 60 °C after 24h. As expected, the H2 release can be fast at higher temperatures, the complete conversion of AB into borazine (BHNH)3 requires less than 3h at 130-140°C [85]. Wideman and Sneddon [87] used the thermal decomposition of AB in solution for the laboratory scale preparation of borazine. For this purpose, solid AB was added slowly, over the course of 3 h, to tetraglyme at 140-160 °C. Borazine was removed from the reaction mixture, trapped at —78 °C, and isolated, resulting in a 67% yield. 

Conversion of the as-deposited film into the crystalline state has been carried out by a variety of methods. The most typical approach is a two-step heat treatment process involving separate low-temperature pyrolysis ( 300 to 350°C) and high-temperature ( 550 to 750°C) crystallization anneals. The times and temperatures utilized depend upon precursor chemistry, film composition, and layer thickness. At the laboratory scale, the pyrolysis step is most often carried out by simply placing the film on a hot plate that has been preset to the desired temperature. Nearly always, pyrolysis conditions are chosen based on the thermal decomposition behavior of powders derived from the same solution chemistry. Thermal gravimetric analysis (TGA) is normally employed for these studies, and while this approach seems less than ideal, it has proved reasonably effective. A few investigators have studied organic pyrolysis in thin films by Fourier transform infrared spectroscopy (FTIR) using reflectance techniques. - This approach allows for an in situ determination of film pyrolysis behavior. 

Thermal decomposition of diazonium borofluorides (G. Balz and G. Schlemann). This procedure is also applicable to aromatic fluorine compounds, particularly on the laboratory scale (e.g., p-fluorotoluene). 

The conventional membrane architecture (CA), the one where the catalyst is placed within the wall of the membrane, is the most studied on the laboratory scale and most frequently reported in the literature. However, the application of the conventional architecture to H2S decomposition is limited by the current ceramic membrane thermal stability [72] and a mismatch between the membrane performance, in terms of flow through and the heat flux, which could be applied to the catalytic tubes. Such imbalance would, from an engineering point of view, require a large and impractical heat transfer surface. 

It should be recognized that there is no unique temperature at which thermal decomposition starts. The term thermal decomposition temperature is often used however, whether a decomposition reaction is detected or leads to a hazardous situation at a particular temperature depends on the heat lost from the system. The thermal decomposition temperature will, therefore, be markedly different on the plant and laboratory scale. 

Purification or refining of rare earths. The separation of rare earths from thorium can be performed in different ways depending on the production scale. Small laboratory-scale methods used first the fractional crystalhzation of nitrates, followed by the fractional thermal decomposition of nitrates. Pilot-scale separation can be achieved by ion exchange. Large commercial-scale separation is based only on the solvent-extraction process of an aqueous nitrate solution with n-tributyl phosphate (TBP) dissolved in kerosene. 

Initiator decomposition can be triggered in a variety of ways. The most conunon method for industrial free radical polymerization is thermal initiation (typically using azo or peroxy initiating species), while photoinitiation is more popular for laboratory scale kinetic studies. In either case. Equation 1.6 describes the decomposition of initiator into two radical species, which may or may not have equal reactivities, depending on the choice of initiator [1,2]. The concentration of initiator can then be calculated by ... 

No process can be made one hundrend percent safe. However, one can identify hazards and, if the hazard is severe, avoid such a chemical or process, or if the hazard is moderate, take precautions that minimize the risk. Safety hazards can be divided into four categories thermal instability, toxicity, flammability, and explosiveness. Typically the in-house safety laboratory measures the decomposition temperature of all reagents, intermediates, solvents, distillation residues and evaporation residues, and any exotherms associated with the decomposition, so that one stays well below these temperatures in the process. The heat of reactions is measured to ensure adequate cooling capacity of the reactor before scaling up a reaction. This minimizes the risk of runaway reactions. 

During the vacuum fractional distillation of bulked residues (7.2 t containing 30-40% of the bis(hydroxyethyl) derivative, and up to 900 ppm of iron) at 210-225°C/445-55 mbar in a mild steel still, a runaway decomposition set in and accelerated to explosion. Laboratory work on the material charged showed that exothermic decomposition on the large scale would be expected to set in around 210-230°C, and that the induction time at 215°C of 12-19 h fell to 6-9 h in presence of mild steel. Quantitative work in sealed tubes showed a maximum rate of pressure rise of 45 bar/s, to a maximum developed pressure of 200 bar. The thermally induced decomposition produced primary amine, hydrogen chloride, ethylene, methane, carbon monoxide and carbon dioxide. 

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