The Separation of Pyrolysis Products

3 The Thermal Decomposition of SiMe4 1.3.1 The Separation of Pyrolysis Products 

Apart from traces of SiH and Me2SiH2, the gaseous mixtures formed in the pyrolysis consist of the following compounds in the given ratios [18]  

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Because of the outstanding performance of modern quartz capillary columns, the gas chromatographic separation of lignin pyrolysis products is easily achieved. Generally, nonpolar or medium polarity columns are used the selection of the stationary phase is less important than for conventional packed columns. For the separation of pyrolysis products from wood or lignin a modified dimethylpolysiloxane liquid phase (e.g., SE-54 or OV-1701) should be used. 

Similar observations existed in the separation of pyrolysis products of MeSiCl3 by molecular distillation. A solid yellow-brown substance was obtained which produced a honeylike melt at 260 °C, an average molecular weight of 900, and the following elemental composition Si 29.7% C 16.3% H 2.2% Cl 48.7%. It is evident that here again a mixture of carbosilanes containing Si—Cl groups exists. 

Chromatogram received from the separation of pyrolysis products. 

In order to obtain reproducible results and characteristic pyrograms, one must define the optimal experimental parameters, which must then be strictly standardized, as the thermal degradation of a polymer is often sensitive to even minor changes in the pyrolysis conditions. Apart from the cell type, the determining experimental parameters are (1) the pyrolysis temperature and time, (2) the sample size and shape, (3) the nature and velocity of the carrier gas and (4) the chromatographic separation conditions. Let us now consider in greater detail the effect of the above factors on the yield of pyrolysis products and the specificity of pyrolysis. 

Py-GC employing various detection systems is the technique usually used to qualitatively and quantitatively analyse major components and low-level additives in polymers [1-3]. The technique utilises thermal energy to break down polymers to monomers and small oligomers. The mixture of pyrolysis products is directly passed into a gas chromatograph (GC) for separation. However, there are numerous low-level co-monomers and additives that may not be appropriately separated at the same time as the major monomers. These low-level co-monomers and additives frequently appear with poor peak shape under the chromatographic conditions established for analysis of the major monomers hence the interest in combining this technique with MS (such as a polar additive in a non-polar capillary colnmn). Additionally, these peaks may have been overlooked because they exist as converted products in the chromatogram after the pyrolysis-induced reaction (such as vinyl acetate converted to acetic acid). 

The depropanizer bottoms are further processed in the debutanizer for separation of C4 product from light pyrolysis gasoline. The debutanizer operates at a moderate pressure of 0.4 to 0.5 MPa, and is a conventional fractionator with steam heated reboilers and water cooled condensers. 

It appears, then, that there is a general, meaty aroma, common to cooked beef, pork, and lamb (and probably poultry), attributable to the pyrolysis of the mixture of low molecular weight nitrogenous and carbonyl compounds extracted from the lean meat by cold water. But the aromas of roast beef, roast pork, roast lamb, and roast chicken are unmistakably different. The chemical composition of the muscular fat deposits of these animals differ appreciably, and it is to these lipid components that we must look to account for the specific flavor differences. Heating the carefully separated fat alone does not give a meaty aroma at all, much less an animal-specific one. It is the subsequent reactions of pyrolysis products of nonlipid components that give the characteristic aromas and flavors of roasted meats (20). 

Quantification of Pyrolysis Products. The pyrolysis must be performed separately ( off-line approach, see Fig. 4.7.5), and the products are trapped completely so that an internal standard can be added. Accurate quantification of the pyrolysis products is achieved using a gas chromatograph equipped with a flame ionization detector (Faix et al. 1987). Fluoranthene is a suitable internal standard as it elutes from the column after the last detectable lignin pyrolysis product (trans-sinapyl alcohol). 

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