Pyrolysis, types Filament pyrolyser

A third type of pyrolyser sometimes utilizes a filament heated by its own electrical resistance. The most effective pyrolysers of this type use an initial pulse of heating at a high voltage to produce a high current and rapid heating to the pyrolysis temperature, i.e. 700°C in 12 ms, followed by reduction to an accurately controlled maintenance voltage to maintain the pyrolysis temperature. 

Resistively heated filament pyrolysers were used for a long time in polymer pyrolysis [9], A schematic drawing of a common filament pyrolyser is shown in Figure 4.1.1. The principle of this type of pyrolyser is that an electric current passing through a resistive conductor generates heat in accordance with Joule s law ... 

There are several advantages of the resistively heated filament pyrolysers compared to other types. They can achieve very short TRT values, the temperature range is large, and Teq can be set at any desired value in this range. Several commercially available instruments are capable of performing programmed pyrolysis, and autosampling capability is also available (such as the CDS AS-2500). 

In the pyrolytic reactors of the first group, the sample is pyrolysed on a filament (coil) rapidly heated by a current. This type of pyrolytic cell is also known as a cell with a filament or a filament-type cell. The heated coil is placed in a continuous-flow chamber whose walls have a temperature that normally does not exceed that of the subsequent chromatographic separation of the pyrolysis products. When working with such cells, the... 

Fig. 3.3B shows an induction-heating pyrolyser with a filament made of a ferromagnetic material. This arrangement provides for rapid heating of the filament with the sample to a temperature corresponding to the Curie point of the filament material, which is in fact the pyrolysis temperature. Fig. 3.3C shows various types of filaments on which samples are placed and pyrolysed. 

Curie-point pyrolysis involves placing the sample wire into a radio frequency field that induces eddy currents in the ferromagnetic material and causes a temperature rise. When the wire reaches the Curie-point temperature, it becomes paramagnetic and stops inducting power. The temperature at which the wire stabilizes (the Curie point) is a function of the type of metal. For example, the Curie points of cobalt, iron, and nickel are 1128, 770, and 358°C, respectively. Wires made from alloys of these metals produce intermediate temperatures. For example, the commonly used nickel-iron wire has a Curie point of 510°C. Differences between filament and Curie-point pyrolyzers depend on the pyrolysates examined and may be obscured by other instrumental differences, including the design of the transmission system to the detector. 

In the chemical data systems - filament coil type pyrolyser, Pyro-probe 122.the polymer samples are held in a quartz tube that is inserted into the platinum coil. If pyrolyses are to be conducted at slow rates the pyrolyser is interfaced to a sample concentration (Model 320, Chemical Data Systems) which collected the pyrolysates on a Tenax filled trap. In this way polymer samples can be processed for minutes or hours at slow heating rates and the pyrolysates collected for a single gas chromatographic analysis. When the pyrolysis is complete, the trap is pulse heated and backflushed with the carrier gas. The desorbed pyrolysates are transferred to a gas chromatograph (Model 3700 Varian or equivalent) equipped with a 50 m x 0.25 mm i.d. SE-54 capillary column (Quadrex). 

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