Pyrolysis distributions

Step 4 of the thermal treatment process (see Fig. 2) involves desorption, pyrolysis, and char formation. Much Hterature exists on the pyrolysis of coal (qv) and on different pyrolysis models for coal. These models are useful starting points for describing pyrolysis in kilns. For example, the devolatilization of coal is frequently modeled as competing chemical reactions (24). Another approach for modeling devolatilization uses a set of independent, first-order parallel reactions represented by a Gaussian distribution of activation energies (25). 

Table 4. Product Distribution for the Occidental Flash Pyrolysis Process...

After brief discussion of the state-of-the-art of modern Py-GC/MS, some most recent applications for stixictural and compositional chai acterization of polymeric materials are described in detail. These include microstixictural studies on sequence distributions of copolymers, stereoregularity and end group chai acterization for various vinyl-type polymers such as polystyrene and polymethyl methacrylate by use of conventional analytical pyrolysis. 

Interest in the mechanism and product distribution of thermal and photochemical transformations of aryl azides led to the isolation of some nitrogen-containing derivatives of heptafulvalene. Based on elemental analysis and spectroscopic data it has been suggested tentatively that the compound isolated following vapor-phase pyrolysis of azidopentafluoro-... 

The carbon number distribution of technical secondary alkanesulfonates determined by pyrolysis gas chromatography and mass spectrometry (GC-MS) is shown in Fig. 13 together with the corresponding carbon number pattern of the raw material paraffins obtained by GC [16]. Pyrolysis was performed in a crucible-modified SGE pyrojector after covering the mixture with quartz wool. The presence of up to 10 wt % of disulfonates in technical alkanesulfonates is demonstrated by fast atom bombardment and mass spectrometry (FAB-MS) (Fig. 14) [24],... 

FIG. 13 Carbon number distribution of alkanemonosulfonates by pyrolysis gas chromatography (GC)/mass spectrometry (paraffin raw material by GC). 

Another chromatographic method is pyrolysis/gas-liquid chromatography. The sample is mixed with P205 and heated to 400°C. This technique yields the chain length distribution of the fatty acids initially used [107],... 

Similar results are obtained from incineration of polymeric materials with octabromo- and pentabromodiphenyl ether (refs. 11,12). The temperature with the maximum PBDF-yield depends on the kind of polymeric matrix. All three bromo ethers 1-2 give the same isomer distribution pattern with preference for tetrabrominated dibenzofiirans. The overall yield of PBDF is lower for incineration of pentabromobiphenyl ether 2, 4 % at 700°C compared to 29 % for ether 1 at 500 °C (ref. 12). The preferred formation of tetrabrominated fiirans observed at all temperatures cannot be a result of thermodynamic control of the cyclisation reaction it is likely due to the special geometry of the furnaces. One explanation is that a spontaneous reaction occurs at approximately 400°C while the pyrolysis products are transferred to the cooler zones of the reactor details can be found elsewhere (ref. 12). 

Industrial Engineering Chemistry Research 37, No.7, July 1998, p.2582-91 POLYETHYLENE PYROLYSIS THEORY AND EXPERIMENTS FOR MOLECULAR WEIGHT DISTRIBUTION KINETICS Sezgi N A Cha W S Smith J M McCoy B J California,University... 

Chemical vapor deposition (CVD) of carbon from propane is the main reaction in the fabrication of the C/C composites [1,2] and the C-SiC functionally graded material [3,4,5]. The carbon deposition rate from propane is high compared with those from other aliphatic hydrocarbons [4]. Propane is rapidly decomposed in the gas phase and various hydrocarbons are formed independently of the film growth in the CVD reactor. The propane concentration distribution is determined by the gas-phase kinetics. The gas-phase reaction model, in addition to the film growth reaction model, is required for the numerical simulation of the CVD reactor for designing and controlling purposes. Therefore, a compact gas-phase reaction model is preferred. The authors proposed the procedure to reduce an elementary reaction model consisting of hundreds of reactions to a compact model objectively [6]. In this study, the procedure is applied to propane pyrolysis for carbon CVD and a compact gas-phase reaction model is built by the proposed procedure and the kinetic parameters are determined from the experimental results. 

The catalytic pyrolysis of R22 over metal fluoride catalysts was studied at 923K. The catalytic activities over the prepared catalysts were compared with those of a non-catalytic reaction and the changes of product distribution with time-on-stream (TOS) were investigated. The physical mixture catalysts showed the highest selectivity and yield for TFE. It was found that the specific patterns of selectivity with TOS are probably due to the modification of catalyst surface. Product profiles suggest that the secondary reaction of intermediate CF2 with HF leads to the formation of R23. 

The effect of TOS on the product distribution during the pyrolysis of R22 over CU-AIF3 catalyst is shown in Fig. 3. The amoimt of halogen ion trapped in NaOH solution was determined by IC. The concentration of Cl formed during the pyrolysis of R22 was higher than the concentration of F at all TOS. This result is a consequence of the facile cleavage of the C-Cl bond in comparison to the C-F bond. Bond dissociation energy for the C-element of R22 is followed by the order C-C1[Pg.235]

Fig. 3. Product distribution with 70S during the pyrolysis of R22 over Cu-AlFj catalyst.

Thus, we considered a number of examples of application of the sensor technique in experiments on heterogeneous recombination of active particles, pyrolysis and photolysis of chemical compounds in gas phase and on the surface of solids, such as oxides of metals and glasses. The above examples prove that, in a number of cases, compact detectors of free atoms and radicals allow one to reveal essential elements of the mechanisms of the processes under consideration. Moreover, this technique provides new experimental data, which cannot be obtained by other methods. Sensors can be used for investigations in both gas phase and adsorbed layers. This technique can also be used for studying several types of active particles. It allows one to determine specific features of distribution of the active particles along the reaction vessel. The above experiments demonstrate inhomogeneity of the reaction mixture for the specified processes and, consequently, inhomogeneity of the... 

Product distribution for propane pyrolysis. [From Schutt, Chemical Engineering Progress, 50 (415), 1954. Used with permission.]... 

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