Pyrolysis residual stability

Figure 14.5. Fatty acids patterns of soils under long-term monoculture, (a) Lipid extract of soil under maize, unfertilized, after derivatization with tetramethylammonium hydroxide determined by conventional gas chromatography/mass spectrometry (GC/MS) in comparison to direct, in-source pyrolysis-field ionization mass spectrometry (Py-FIMS) without derivatization (Jandl et al., unpublished), (b) Py-FIMS of lipid extract of soil under rye, farmyard manure (FYM) treatment, compared to solid extraction residue, both directly measured without derivatization. Reprinted from Marschner, B., Brodowski, S., Dreves, A., et al. (2008). How relevant is recalcitrance for the stabilization of organic matter in soils Journal of Plant Nutrition and Soil Science 171, 91-110, with permission from Wiley-VCH.

The thermal stability of the polymers and the yield of carbonized residues in pyrolysis increase with the relative number of aromatic groups per repeat unit of the main macromolecular chain. 

Isomerism of the substitution of aromatic rings affects the thermal stability of the polymer and the formation of carbonized residue in pyrolysis. Meta-isomers are less stable and yield less coke than para-isomers. 

The production of plastics also involves the use of potentially harmful chemicals under the name of stabilizers or colorants. Many of these stabilizers/additives have not undergone environmental risk assessment and their impact on human health and the environment is currently uncertain and doubtful. Phthalates, as additives, are widely used in the manufacturing of PVC products, and risk assessments of the effects of phthalates on the environment are currently being carried out. Recent research for the Community Recycling Network casts doubt on whether pyrolysis and gasification are the right processes for dealing with the residual municipal waste. 

The transformation of plant detritus into stabilized humic substances is one of the most complex and least understood biogeochemical processes in the carbon cycle (Stevenson, 1994). Traditionally, decomposition and humification of plant residues was thought to be dominated by the mineralization of labile materials, while more recalcitrant aromatic compounds accumulate in the soil. The application of modem analytical techniques—including solid-state NMR spectroscopy, pyrolysis gas chromatography, and degradative chemical techniques—to the study of decomposition and humification has significantly altered this simple view of carbon transformation in the soil (Baldock et al., 1997 Kogel-Knabner, 1997). 

A number of studies were done to assess thermal stability of aromatic polyesters. Some of these studies describe flash pyrolysis [27-32]. Some studies are dedicated to slow thermal degradation in an inert atmosphere, and others describe the decomposition in specific conditions such as in the presence of humidity or in the presence of catalysts [33]. For example, thermal decomposition of poly(butylene terephthalate) was significantly influenced by the presence of water vapor, and the amount of the residues decrease with increasing the partial pressure of water in the atmosphere [34]. In another study, thermal stability of some small molecule phthalate esters was studied [35]. The results can be used for inferring information on the thermal stability of related polymers. The influence of substitution on the p-carbon atom was evaluated on compounds such as bis(2-aminobutyl) phthalate, bis(2-nitrobutyl) phthalate, bis(2,4-diphenylbutyl) phthalate, and dineopentyl phthalate. Only the phenyl groups were found to improve the heat resistance by the obstruction of the planar configuration necessary for the c/s-elimination and the hindrance of the formation of a six-membered cyclic transition state. 

Recent experiments show that carbaboranes are stable at 500—600 °C for an hour, but at higher temperatures pyrolysis occurs to give H2, CH4, and an insoluble polymeric residue of approximate composition Ci.9H8 9B10. In the presence of water, decomposition occurs at a lower temperature.90 Introduction of phenyl groups on the C atoms of the carbaborane nucleus lowers the thermal stability. 

---