Pyrolytic conversion

Chemical Analysis. The presence of siUcones in a sample can be ascertained quaUtatively by burning a small amount of the sample on the tip of a spatula. SiUcones bum with a characteristic sparkly flame and emit a white sooty smoke on combustion. A white ashen residue is often deposited as well. If this residue dissolves and becomes volatile when heated with hydrofluoric acid, it is most likely a siUceous residue (437). Quantitative measurement of total sihcon in a sample is often accompHshed indirectly, by converting the species to siUca or siUcate, followed by deterrnination of the heteropoly blue sihcomolybdate, which absorbs at 800 nm, using atomic spectroscopy or uv spectroscopy (438—443). Pyrolysis gc followed by mass spectroscopic detection of the pyrolysate is a particularly sensitive tool for identifying siUcones (442,443). This technique rehes on the pyrolytic conversion of siUcones to cycHcs, predominantly to [541-05-9] which is readily detected and quantified (eq. 37). 

Since that discovery a major aspect of our research effort has been to develop a method to account for this unwanted pyrolytic conversion of organic to elemental carbon. This report describes a combined thermal-optical instrument in which the reflectance of the filter sample is continuously monitored during the thermal analysis. Dod (14) have also reported a combustion... 

Figure 3. Analytical response. Peaks 1, 2, and the shaded portion of 3 correspond to organic C the unshaded portion of Peak 3 is elemental C. The shaded portion of Peak 3 constitutes the correction for pyrolytic conversion of organic to elemental C. Peak 4 is the calibration peak.

More complex substances, however, showed higher degrees of pyrolytic conversion. In aerosol samples collected from the combustion of distillate and residiaal oil, 31 and 25% respectively of the organic carbon underwent pyrolytic conversion to elemental carbon. Lesser amounts of conversion were observed for leaded and unleaded auto exhaust samples, and no conversion occurred in a diesel truck exhaust sample. Biological samples also showed large degrees of conversion e.g., 45% of the carbon associated with wood fiber was pyrolytically converted to elemental carbon. 

High degrees of conversion were also observed in ambient samples. In approximately 200 filters from 9 urban sites an average of 22% of the organic carbon was pyrolytically converted to elemental carbon. As a fraction of elemental carbon this corresponded to 23%. Thus, the correction for pyrolytic conversion is significant and cannot be neglected. 

The precision of the pyrolytic conversion correction has been assessed by repeated analysis of one high volume filter. For a filter with 36 pg/cm of organic carbon and 25 pg/cm of elemental carbon one standard deviation corresponded to 10% in both the organic and elemental modes. 

This criterion, which is product rather than precursor-property driven, is critical to the design and synthesis of new precursors. The need for high ceramic yields arises because of the excessive volume changes associated with pyrolytic conversion to ceramic materials. Scheme 1 illustrates these changes for a SiC precursor with an 80% ceramic yield of phase pure SiC (3.2 gml-1). Most precursors densities are close to 1 gml-1, whereas most Si ceramic densities range from 2.5 to 3.5 gml-1. 

Figure 9.1 Definitions of the various species used as starting materials and condensation products during pyrolytic conversion to ceramics.

At the same time there is an increase of carbon dioxide, carbon monoxide, methane, propene, and other gaseous components. The low-boiling components are carbon oxides and hydrocarbon while the higher-boiling components are esters. Mechanistically, the pyrolytic conversion of PMMA to its monomer is a radical process [24]. Two radicals are formed by the action of heat of the polymer chain (Scheme 24.1). 

Synthesis of Some Organosilicon Polymers and Their Pyrolytic Conversion to Ceramics... 

This chapter gives an introduction to the preceramic polymer route to ceramic materials and focuses on the reasons why this new approach was needed and on the chemical considerations important in its implementation, with examples from research on organosilicon polymers. Novel polysilazanes have been prepared by the dehydro-cyclodimerization reaction, a new method for polymerizing suitably substituted cyclooligosilazanes. The living polymer intermediate in this reaction has been used to convert Si-H-containing organosilicon polymers that are not suitable for pyrolytic conversion to ceramics into useful preceramic polymers. 

The Kinetics and Mechanism of Graphitization, D. B. Fischbach The Kinetics of Graphitization, A. Pacault Electronic Properties of Doped Carbons, Andre Marchand Positive and Negative Magnetoresistances in Carbons, P. Delhaes The Chemistry of the Pyrolytic Conversion of Organic Compounds to Carbon. E. Fitzer, K. Mueller, and W. Schaefer... 

Biomass Selection Criteria for Pyrolytic Conversion Processes... 

Based on this method, suitability of various biomass for pyrolytic conversion is studied and is found that based on the conqiosition of biomass, different biomass are suited for different applications such as carbonisation, liquefaction, gasification and making of char adsorbent. 

Only cellulose is the feedstock of pyrolysis process treated in the model. Cellulose mass consunq>tion represents the degree of the pyrolytic conversion. Figures 10 and 11 show the mass losing curves as pyrolysis proceeds for 2 ram and 10 mm particles respectively. As can be seen that cellulose density decreases all the way down to zero. The density in the outside surface layer decreases much faster than the center. It takes about 5s for the 2 mm cellulose particle to be devolatilized completely, and 60s for the 10mm particle. It also shown that devolatilization of cellulose particles proceeds layer by layer, which is more obvious for the outside layers and for the large particle. 

Final report (1999), Contract JOR3-CT96-0099, A novel approach for the integration of biomass pyrolytic conversion processes in existing markets of liquid fuels and chemicals. 

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