Product distributions of pyrolysis

Figure 6. Product distribution of pyrolysis of PP in He at 414°C , C% , ChH8 O, C2H6 A, C5H10 s 6> A, C6H12 O, C7H12...

Figure 5. Relative yields and product distributions of pyrolysis in inert atmosphere as functions of temperature, time, and heating rate...

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 phenol, the cresol isomers, and the dimethylphenols, major pyrolysis products in e Moscow wood sample, are probably also derived frt>m lignin precursors that have been altered through coalification reactions. Hatcher [fr] have shown that an increase is observed in the relative proportion of phenols and cresols as rank of coaHfred wood samples increases to subbituminous coal. Comparing the distribution of pyrolysis products from the Moscow wood to that of other coalified wood samples of Hatcher allows us to deduce that the... 

Because pyrolysis reactions do not occur at sharply defined temperatures, the heating rate has a marked effect on the nature and distribution of pyrolysis products, as summarized in Table 19.14. Solomon and coworkers conducted extensive work on the kinetics of coal devolatilization, and many reviews are available.36... 

These assumptions, together with the relevant thermal data, are of tremendous use in correlating and understanding the extraordinarily complicated product distributions of many pyrolysis reactions. 

The observed pyrolysis product distribution of PP is developed by a free radical mechanism [28, 29] which begins with the homolytic breakage of the polymer chain drawn in Scheme 12.3 where X represent a methyl group in this case. Primary macroradical 1 is formed only in the initial step, thus its decomposition plays a minor role in PP. Secondary macroradicals may decompose to propene by depolymerization reproducing 2, or... 

Recently the pyrolysis of polymer mixtures has become a focus of interest due to the increasing role of plastics recycling. Many researchers have investigated the thermal decomposition of various polymers in the presence of PVC. Kniimann and Bockhom [25] have studied the decomposition of common polymers and concluded that a separation of plastic mixtures by temperature-controlled pyrolysis in recycling processes is possible. Czegfny et al. [31] observed that the dehydrochlorination of PVC is promoted by the presence of polyamides and polyacrylonitrile however, other vinyl polymers or polyolefins have no effect on the dehydrochlorination. PVC generally affects the decomposition of other polymers due to the catalytic effect of HCI released. Even a few per cent PVC has an effect on the decomposition of polyethylene (PE) [32], HCI appears to promote the initial chain scission of PE. Day et al. [33] reported that PVC can influence the extent of degradation and the pyrolysis product distribution of plastics used in the... 

In summary, it was observed that the alumina catalyst increased the extent of pitch pyrolysis at long reaction times, accompanied by some changes in the product distribution. The pyrolysis reaction was found to be first order with respect to the pitch reactant. A compensation effect was observed in which the Arrhenius parameters Ea and A were found to vary with the residue weight, WR. This effect was explained in terms of a modified Arrhenius equation and of the increasing activation energy Ea associated with the less reactive molecular species. 

The product distribution of cy clohexane pyrolysis under given reaction conditions may depend on (he temperature and conversion. Taralas [3 concluded that the selcciivitics... 

Formation of sub-bituminous coal seems to involve O loss through conversion of dihydroxy phenolic units (catechols) to monohydroxy units (phenols and alkylphenols), as shown in Fig. 4.7, based on the simple distribution of pyrolysis products, which are dominated by phenol, ortho-cresol (2-methylphenol) and 2,4-dimethylphenol (Hatcher 1990). Oxygenated aliphatic structures (alkyl hydroxyls and ethers) seem to be absent. Figure 4.8 shows the types of units present at various stages of biochemical coalification, based on a random hgnin polymer. 

However, Goldstein examined the product distribution from pyrolysis of all cis-... 

Competitive hydrogen abstraction reactions by phenoxy and benzyl radicals on the a-or )8-carbon of PPE are the core reactions of the radical chain propagation (Scheme 7.2) in the thermal degradation of PPE and are the only reactions needed in the analytical kinetic model derived in Section 7.3.2.3 to calculate overall a/)8-selectivities. Because hydrogen abstractions are the rate-determining steps, effects of substituents on hydrogen abstraction have the most impact on overall product distributions and pyrolysis rates. 

Propane and propylene were first pyrolyzed separately to determine general trends in the product distribution. The typical product distributions of the pyrolysis of propane and propylene mixtures are given in Table 1. The product distributions when the major reactant was propane or propylene were similar to those when propane and propylene were separately pyrolyzed, respectively. 

An attempt was made to calculate the product distributions of propane pyrolysis on the basis of the reaction model considering both inhibition and acceleration effects observed in the pyrolysis of propane-propylene mixtures. The reaction model for propane pyrolysis used in this work is shown in Table 4. The rate constants given in Table 4 were measured in our previous works (3, 4). At the initial stage of propane pyrolysis, the formation of the primary products such as methane, ethylene and propylene is predominant but as the reaction proceeds, the consecutive decomposition of each product is also remarkable. Therefore, a reaction model was postulated which consisted of major stoichiometric reactions for propane (i) - (iv), for propylene (v), (vi) and... 

The thermal decomposition of propylene involves a series of primary and secondary reactions leading to a complex mixture of products. Studies showed that the distribution of pyrolysis products varies considerably with the pyrolysis conditions and the type of reactor used. There is agreement among the studies on propylene pyrolysis that the three major products of pyrolysis are methane, ethylene, and hydrogen. However, there is disagreement on the types and amounts of minor or secondary product species. Ethane, butenes, acetylene, methylacetylene, allene, and heavier aromatic components are reported in different studies, Laidler and Wojciechowski (1960), Kallend, et al. (1967), Amano and Uchiyama (1963), Sakakibara (1964), Sims, et al. (1971), Kunugi, et al. (1970), Mellouttee, et al. (1969), conducted at different conversion and temperature levels. Carbon was also reported as a product in the early work of Hurd and Eilers (1943) and in the more recent work of Sims, et al. (1971). 

FIGURE 13.45 Plot of product distribution of selected hydrocarbons as a function of temperature for bench-scale pyrolysis of a naphtha sample. (Reprinted with permission from Reference 112, Journal of Chromatographic Science, Copyright 1978, Preston Publications, A Division of Preston Industries, Inc.)... 

The nature and distribution of pyrolysis products from a particular sample critically depend largely on the pyrolysis temperature and the specific set of pyrolysis conditions (i.e. temperature rise time, sample size, pyrolyser geometry). Laser pyrolysers are practically the only type of radiative heating pyrolyser with certain applicability. A laser pyrolyser consists of five components (i) laser (ii) fibre optics (Hi) probe for sample introduction (iv) pyrolyser body, containing the pyrolysis chamber and (v) heater of the pyrolysis chamber with dedicated control unit. The laser beam can be focused onto a small spot of a sample to deliver the radiative energy. This provides a special way to pyrolyse only a small portion of a sample. Only the sample itself is... 

Ranzi S., Dente M., Pierucci S. and Biardi G. (1983) Initial Product Distribution from Pyrolysis of Normal and Branched Paraffins , Ind. Eng. Chem. Fundam. 22, 132-139. 

Distribution of pyrolysis products and specific compounds produced (particularly in the liquid fraction) can be greatly affected by the introduction of a catalyst to the pyrolysis reaction system. Catalytic pyrolysis, the main subject of this chapter, is not so different to standard pyrolysis but has a significant effect on pyrolysis products by enhancing potential biofuel or higher-value chemical production. Catalytic pyrolysis is covered in depth below. 

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