Staged pyrolysis

One of the advantages of GFAAS is the direct analysis of solid samples without prior decomposition, this technique has been reviewed by Bendicho and de Loos-Vollebregt (1991). The solid samples can be introduced directly or as a slurry. Calibration can be with aqueous standards, synthetic solids, standard additions or with SRMs. SRMs have been used for calibration for solid sampling of plant material (Schmidt and Falk, 1987). Examples of the use of solid samples with ETAAS are shown in Table 9-4. In many cases a matrix modifier is used with the sample, this allows the matrix to be volatilised at the pyrolysis stage without analyte loss, particularly important with volatile analytes such as Cd and Pb. (Ure, 1990). 

A patented process has been developed for the production of electrode binder pitch from petroleum-based materials. Carbon anodes produced from the petroleum-based pitch and coke have been used successfully on a commercial scale by the aluminum industry. One stage of the process involves the pyrolysis of a highly aromatic petroleum feedstock. To study the pyrolysis stage of the process a small, sealed tube reactor was used to pyrolyze samples of feedstock. The progress of the reaction is discussed in terms of the formation of condensed aromatic structures, defined by selective solvent extraction of the reaction product. The pyrolysis of the feedstock exhibits a temperature-dependent induction period followed by reaction sequences that can be described by first-order kinetics. Rate constants and activation energies are derived for the formation of condensed aromatic structures and coke. 

A laboratory reactor system was constructed for the investigation of tar conversion under real fixed-bed conditions. The basic idea behind the reactor design was the spatial separation of primary pyrolysis and secondary tar reactions. A scheme of the system is shown in fig, 2. After the primary pyrolysis stage, the tar containing pyrolysis gas is swept to the conversion reactors where homogeneous and/or heterogeneous tar reactions can be investigated. 

Assuming different pyrolysis product distributions for almond shells according to the measurements of El Asri ct al. [5], Font et al. [12, 13], or Parodi et al. [14], different composition of the flue gases, in particular CO contents, have been predicted. It was found that the amount of char formed in the pyrolysis stage is of great importance. The fraction of fme particles that escape to the conical part of the reactor is of relevance for the CO production, but it doesn t affect the NO formation. The variation of the air splitting ratios between different blocks is of minor importance. 

Burchfield and his associates (12, 13, 14) reported a procedure involving reductive pyrolysis of the effluent gases whereby compounds containing chlorine, sulfur, or phosphorus form HCl, H2S, or PH3, respectively. By using an aluminum oxide scrubber following the pyrolysis stage, the system was specific for phosphorus. However, the detection system appears to be inferior to other available detectors for phosphorus and will probably have little or no use for this purpose. 

Figure 5.7.2. On-line Py-HPLC system which works in three stages A-B-A [96a], First stage A. pyrolysis. Stage B, flush the pyrolysing chamber and carry the analytes to the precolumn. Second stage A, the analytes are back flushed and sent to the analytical column.

ZHS (phr) ATH (phr) Pyrolysis stage Char oxidation stage Residue at 600°C ... 

In the pyrolysis stage, the ester, vaporised at 250°C, is mixed with steam at 600 C, in a weight ratio of 1/1. It resides for about 10 s in a furnace, where the temperature lies between 400 and 575°C. 

Samples in nano- or microgram amounts are introduced into the furnace in a form of solutions. These aliquots (10-30 xL) are dried and, before the atomization, are subjected to a preliminary p3Tolysis, which is aimed to remove (evaporate) more volatile matrix components from the sample. To achieve more efficient separation, 1-10 pg of one of the platinum group metals (most often, palladium) is added to the sample in the form of a nitrate solution. This additive serves as a chemical matrix modifier preventing evaporation of the analyte during the pyrolysis stage. 

Perhaps the shortest synthesis reported to date involves the acid-catalysed condensation of 2-ethylindole and 3-acetylpyridine to give the intermediate (177), which can be converted into ellipticine (173) by quaternization followed by pyrolysis (Scheme 27). Very high yields are quoted, although the final, pyrolysis stage is not completely regiospecific, and the yield obtained is clearly very sensitive to the experimental conditions. 

Moreover, inter- and intramolecular ester exchange reactions causing rearranged polyester sequences at the pyrolysis stage were also demonstrated to take place for aliphatics and aliphatic-aromatic polyesters" using Py-MS. 

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