Thermal pyrolysis method

Pyrolysis method involves thermal decomposition of suitable precursors to produce free radicals. Pyrolysis sources based on continuous molecular beam nozzles are well developed (for example, methyl6 8 and benzyl9). Recently, Chen and co-workers have pioneered a flash pyrolysis/supersonic jet technique to produce free radical beams (Fig. I).10 In this radical... 

Conventional thermal treatment methods, such as rotary kiln, rotary hearth furnace, or fluidized-bed furnace, are used for waste pyrolysis. Molten salt process may also be used for waste pyrolysis. 

The major limitation of the vacuum pyrolysis method appears to be thermal decomposition of less volatile diazo compounds during the pyrolysis. The vacuum pyrolysis method was unsuccessful for the preparation of 1-naphthyl diazomethane and 3,5-dichlorophenyldiazomethane. However, such diazo compounds could be prepared from the corresponding tosylhydrazone salts by pyrolysi s in ethylene glycol and extraction of the aryldiazomethane into... 

Thermal pyrolysis for upgrading plastic wastes is one of the better methods for recycling plastics in terms of its perspectives for industrial implementation. The conical spouted bed reactor proposed in this paper may be a solution to the problems arising in fluidized beds handling sticky solids, as particle agglomeration phenomena, which can cause defluidization. In order to avoid defluidization, experiments have been carried out in batch mode in the temperature range of 450-600 °C. A good performance of the reactor is proven under the conditions of maximum particle stickiness. 

The treatment methods for remediation of energetic materials from soils are divided on in situ and ex situ biological (bioremediation, phytoremediation, composting), in situ and ex situ physico-chemical (adsorption, oxidation, electrokinetic separation, extraction, solidification, reduction, soil washing), in situ and ex situ thermal (pyrolysis, desorption) [1]. Among the above described... 

As has been seen, competitive analytical systems correlating thermal and chemical behaviour are TG-MS, TG-FTIR, TG-GC, TG-GC-MS, etc. This list of techniques may easily be extended with various pyrolysis methods. 

In recent years, we have seen an explosive interest in nanomaterials, in particular in nanofibers, nanofilaments, and nanotubes of the very different chemical composition. The interest arises from the specific mechanical and physicochemical properties of these nano objects, which allow them to be used, for example, as specific adsorbents, catalyst supports, reinforcing components of composite materials, and so on. The most cited generic types of nanomaterials are carbon nanofilaments and nanotubes. Numerous methods for preparing these carbon materials are known. However, the simplest method seems to be thermal pyrolysis of various carbon contain ing precursors (e.g., carbon monoxide, saturated and unsaturated hydro carbons, etc.) in the presence of special catalysts that are typically nanosized particles of nickel, cobalt, iron metals, or their alloys with different metals. 

Dry methods and postcalcination methods The industrial micron sized R2O3 powder is commonly made by thermal pyrolysis of rare earth carbonates or oxalates at a temperature of 600-1000 °C. The dry methods usually result in fine powders with a relatively wide size distribution. After the sintering, the surface OH and other solvent related species are generally removed, therefore, the powder may exhibit better luminescence efficiency and longer decay time. Nano-sized rare earth oxide products could be obtained from finely selected precursors like hydroxides gels, premade nanostructures, through heat treatment, spray pyrolysis, combustion, and sol-gel processes. 

High-temperatnre pyrolysis and cracking of waste thermoplastic polymers, such as polyethylene, polypropylene and polystyrene is an environmentally acceptable method of recycling. These type of processes embrace both thermal pyrolysis and cracking, catalytic cracking and hydrocracking in the presence of hydrogen. Mainly polyethylene, polypropylene and polystyrene are used as the feedstock for pyrolysis since they have no heteroatom content and the liquid products are theoretically free of sulfur. 

The use of the direct thermal decomposition method has been fairly widespread, and the values obtained by it will be discussed in the appropriate sections of this book. The O - N bond in alkyl nitrates and nitrites, and the G N bond in nitromethane are among those whose dissociation energy has been measured by this method, but in view of the possible kinetic complexities which may be encountered, such as those already mentioned in connection with the pyrolysis of organic iodides (see Section 4.2.4) the values obtained are often at best only tentative. 

The fact that flame retardants and salts alter the kinetics, as well as the products, of the pyrolysis reactions is confirmed by the investigations of Tang and Neil involving thermogravimetric and differential thermal analysis methods (see Section 11,6 p. 446). These investi-... 

Knowledge of the effects of various independent parameters such as biomass feedstock type and composition, reaction temperature and pressure, residence time, and catalysts on reaction rates, product selectivities, and product yields has led to development of advanced biomass pyrolysis processes. The accumulation of considerable experimental data on these parameters has resulted in advanced pyrolysis methods for the direct thermal conversion of biomass to liquid fuels and various chemicals in higher yields than those obtained by the traditional long-residence-time pyrolysis methods. Thermal conversion processes have also been developed for producing high yields of charcoals from biomass. 

H-NMR Thermal Scanning Methods for Studying Oil Shale Pyrolysis... 

Pyrolysis reactions are one class of reactions that benefit from the use of an SCF solvent medium since the SCF can solubilize reacted products and remove them from the high-temperature zone, thus avoiding further thermal decomposition. The carbon formation that occurs at the high temperatures normally encountered in pyrolysis reactions can therefore be minimized. Improved yields, selectivities, and product separation have been attained in an SCF reaction medium, compared with conventional pyrolysis methods. There is no doubt that a sufficiently high temperature is needed to provide the thermal energy to break bonds in a pyrolysis reaction. But it is not necessary to operate at excessively high temperatures to increase the vapor pressure of the product materials because the SCF medium has the necessary solvent strength to dissolve the products and remove them from the reaction zone. 

The analytical scheme for these studies precluded measurement of water. Both pyrolysis methods evolve carbon monoxide and carbon dioxide in comparable amounts. However, plasma processing produces 43% hydrogen and 14% acetylene on a volume basis while thermal pyrolysis gases contain neither component. Instead, the major hydrocarbon generated in the thermal pyrolysis system is methane (38%), while saturated hydrocarbons are minor components in the plasma process. These differences illustrate that the nature of conventional pyrolysis reactions is radically different from the microwave plasma pyrolysis reactions. 

By exploiting the good dissolution properties of compressed gases in the supercritical state in a flow apparatus, thermal degradation of cellulose has been achieved without the secondary reactions and strong carbonization usual in conventional pyrolysis methods. Cellulose could be degraded to the extent of 98%. 

At the same time, there is a very interesting observation about indole and methylindole revealed by Py-GC/MS as products of thermal decomposition of tryptophan in egg white, because this amino acid is absent in animal glue and is usually lost in the acid hydrolysis workup common to conventional GC and HPLC. Also, there is a very detailed comparison between conventional techniques (Uke GC aud HPLC) and analytical pyrolysis methods in the end of the article. 

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