Pyrolysis, types Curie point pyrolyser

It should be noted that all of the above-described pyrolytic devices suffer from a serious drawback. Although relatively good reproducibility of the results can be attained on the same device, devices of the same model from the same manufacturer often show poor reproducibility. Until about 1970 it was considered that the best reproducibility as regards the composition of the pyrolysis products could be achieved on a Curie-point pyrolyser [77]. However, a comparative study of the results obtained in 18 laboratories on the same sample, conducted by the Py—GC subgroup of the Chromatography Discussion Group of the Institute of Petroleum in London, has shown that Curie-point cells are characterized by the same scatter of data as cells of the other types [78]. 

On- and off-line PyGC-MS approaches were discussed by Boon [708]. The first directly coupled PyGC-MS system, using a Curie-point pyrolyser, was described by Simon et al. [762]. The use of flash pyrolysis has increased dramatically with introduction of fused silica GC columns. In PyGC-MS the type of ionisation mode is usually either El or CL Electron impact ionisation at the normal ionising voltage (70 eV) causes extensive fragmentation. 

A Py-GC study [7] with pyrolysis done at 500° C showed numerous peaks corresponding to the isoprene dimers, trimers. .. up to hexamers eluting in clusters of peaks. The separation was done on a methyl silicone 5% phenyl silicone type column with FID detection. The results from a Py-GC/MS study [8] where natural rubber was pyrolysed at 580° C in a Curie point Py-GC/MS on-line system showed similar results. The TIC trace of the pyrolysate with the separation done on a 60 m Carbowax column, 0.32 mm i.d., 0.25 pm film thickness, with the temperature gradient of the GC oven between 40°... 

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. 

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