Types of Pyrolyzers

The gas fluidized-bed reactor is the most efficient approach to pyrolysis. In this reactor the waste plastic is suspended around the heating medium and snbjected to pyrolysis by means of immersed heating tubes and gas-solid convective heat transfer. At present the only difficulty with this reactor is the problem of its structure. Fluidized-bed pyrolyzers have been designed for pyrolysis of waste tyre mbber in Taiwan and in Hangzon. A schematic apparatus of a fluidized-bed pyrolyzer is shown in Fignre 27.2. 

The reactor is constructed with a cylindrical colnmn and an expanded freeboard. The distributor is a perforated plate. An inert gas matrix composed primary of crystal sand, is used as the bed material. The blower supplies the inert gas for flnidization or the amount of air for partial combustion. A cyclone is used to collect fine particles. Sembbers serve to quench the off-gases and remove condensables that were withdrawn from reactors. 

The furnace has an adjustable rotation rate of 0.5-10 rpm. The kiln is heated externally. The sealing of rotary kilns is a difficult task, especially for a pyrolyzer. The internal pressure of the kiln is higher than atmospheric pressure. A special friction-type seal is required for a pyrolyzer operating at high temperature. Solid waste with different shapes, sizes, and heating values can be fed into rotary kilns in batches or continuously. 

The thermal cracking of waste plastic involves breaking of polymeric bonds by the effect of heat alone. The waste stream may comprise PP, PVC, PET, thermosetting plastic. 

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Heated-filament pyrolyzers are often used to analyze lignins (Kratzl et al. 1965, Lindberg et al. 1982, Obst 1983, Gardner et al. 1985, Faix et al. 1987, 1991, Funazukuri et al. 1987, Salo et al. 1989). In this type of analyzer, electric current is passed through a resistance ribbon or coiled wire, both made of platinum. The dissipation of power increases the temperature of the conductor. Heat-up and pyrolysis times are selected from an instrument control. Characteristic parameters of this type of pyrolyzer have been described by Wells et al. (1980) and Wampler and Levy (1987). 

Resistively heated filament pyrolyzers have been used for a long time in polymer pyrolysis [1], The principle of this type of pyrolyzer is that an electric current passing through a resistive conductor generates heat in accordance with Joule s law ... 

The true temperature of a sample heated using a filament pyrolyzer can be quite different from the above profile temperature, significantly lower temperatures being recorded inside the samples [4]. In order to obtain a correct Teq, modern equipment uses a feedback controlled temperature system (see e g. [5] for a more detailed description of this type of pyrolyzer). Several other procedures for a precise temperature control of the filament are available, such as the use of optical pyrometry or thermocouples [6, 7], Special pyrolysis systems that allow programmed heated rates at different time intervals also are available [8]. 

Some problems are inherent to this type of pyrolyzer. One such problem is that the set temperature and the actual temperature of the filament must be calibrated. The filament electrical resistance is part of the temperature controlling circuit. This resistance may modify in time, mainly in the systems where the sample is put directly on the filament. Because of this, the correspondence between the set operating temperature and the actual temperature will change during the life of the filament. Even in correctly operating instruments, problems may occur in achieving the Teq as precisely as the manufacturer may indicate [9]. 

A factor that must be considered with furnace pyrolyzers as well as with the other types of pyrolyzers is the achieving of short TRT values. A slow sample introduction in the hot zone of the furnace will end in a long TRT. A poor contact between the sample and the hot source may also lead to long TRT, most of the heat being transferred by radiation and convection and not by conduction. However, fairly short TRTs in furnace pyrolyzers were reported in literature [14, 15]. Also, in furnace pyrolyzers it is more common to see differences in the temperature between the furnace and the sample. Due to the poor contact between the sample and the hot source, the sample may reach a lower actual temperature than the temperature of the furnace wall. This may be the explanation why there were reported variations in the pyrolysis products in microfurnace systems as compared to the results obtained in inductively or filament heated pyrolyzers [16,17]. 

Comparisons between the results obtained using different pyrolyzers are not uncommon in literature [14, 41-43]. These comparisons have two objectives to assess the quality of the analytical results (reproducibility, sensitivity, etc.) of a certain type of pyrolyzer and to indicate how the results of one pyrolyzer can be compared to those of another type. 

When Py-GC/MS is used, the chemical composition of the sample is reconstructed on the basis of an interpretation of the molecular profile of the thermal degradation products of the original components, and on the recognition of specific molecular markers or of characteristic molecular patterns, which act as fingerprints of the pyrolyzed material. Py profiles are strongly dependent on the instrument type and the experimental parameters, particularly the Py temperature, types of pyrolyzer (microfumace. Curie point, resistively heated... 

Fired reactors contain tubes or coils in which an endothermic reaction within a stream of reac tants occurs. Examples include steam/ hydrocarbon reformers, catalvst-filled tubes in a combustion chamber pyrolyzers, coils in which alkanes (from ethane to gas oil) are cracked to olefins in both types of reac tor the temperature is maintained up to 1172 K (1650°F). 

Several types of experimental magnesium-air cells were tested. These cells varied in their size (the working area of the air electrodes used) [10]. The current-voltage curves of an experimental Mg-air cell with two air electrodes (Sair = 80 cm2) with pyrolyzed CoTMPP catalyst and sandwich-type Mg anode (MA8M06) operating in NaCl-electrolytes with different concentrations are presented by Figure 2. 

Although platinum is the metal of choice for PEM fuel cell cathodes, Paul Matter, Elizabeth Biddinger, and Umit Ozkan (Ohio State University) show that nonprecious metals will have to be developed for this type of fuel cell to become practical and widely used. Although few materials have the electrochemical properties needed to replace platinum, this review discusses candidates such as macrocycle compounds, non-marcrocyclic pyrolyzed carbons, conducting polymers, chalcogen-ides, and heteropolyacids. 

Thus, by shifting a methyl group from Si to N, the mechanism of transformation has been changed entirely. The products from pyrolysis of — [ NMe] — and —[MeHSiNHR— are quite different as clearly seen in Figure 4, which compares the 29Si NMR spectra for both materials pyrolyzed to 1000 °C. This is proof that polymer architecture can strongly influence the type of ceramic material produced on pyrolysis. 

The carbon materials attract the increasing interest of membrane scientists because of their high selectivity and permeability, high hydrophobicity and stability in corrosive and high-temperature operations. Recently many papers were published considering last achievements in the field of carbon membranes for gas separation [2-5]. In particular, such membranes can be produced by pyrolyzing a polymeric precursor in a controlled condition. The one of most usable polymer for this goal is polyacrylonitrile (PAN) [6], Some types of carbon membranes were obtained as a thin film on a porous material by the carbonization of polymeric predecessors [7]. Publications about carbon membrane catalysts are not found up to now. 

Pyrolysis may be performed using continuous-mode or pulse-mode instruments. In the first instance, the material must be introduced rapidly into the furnace at a predetermined temperature, which is maintained throughout the pyrolysis. Common modem pulse-mode instruments allow very rapid sample heating within a specified time. There are three different types of pulse-mode pyrolyzers ... 

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