Radical formation hydrocarbon cracking

Thermal cracking is the breaking of a hydrocarbon carbon-carbon bond through the free-radical mechanism. Cracking may result in the formation of lower chained hydrocarbons, the original "cracked" hydrocarbon, or further cracking of the hydrocarbon to "soot. 

Formation Diffusion of C through Ni-crystal Nucleation and whisker growth with Ni-crystal at the top Slow polymerization of C Hm radicals on Ni-surface into encapsulating film Thermal cracking of hydrocarbon Deposition of C-precursors on catalyst... 

Tihe cracking of olefinic hydrocarbons has not been as well studied as the cracking of paraffins. V. V. Voevodsky theorized (25) that the allyl radicals, in addition to decomposition and addition to double bonds, can enter into disproportion with the starting olefin. The reaction results in the formation of diene and alkyl radicals of the type shown in Reaction 1 (Voevodsky Reaction)... 

The compounds we studied show that the theoretical Reaction 1 is almost never realized. At the same time the true cracking mechanism of olefinic hydrocarbons should include the formation of alkyl radicals. 

The mechanism of thermal degradation of plastics proceeds through a radical chain reaction pathway with hydrogen transfer steps. In secondary reactions, branched products were only formed as a result of the interaction between two radicals without any rearrangement reactions [48]. As a consequence, thermal cracking of polyolefins leads toward a broad distribution of hydrocarbons up to waxy products. More than 500 °C temperatures are needed to receive more oily products. In contrast, catalytic cracking takes place at lower temperatures and leads to the formation of smaller branched hydrocarbons. This catalytic cracking can potentially lower the costs and increase the yields of valuable products. 

As to the formation mechanism of carbon black, there are indications that the carbon particles are formed by recombination of smaller hydrocarbons (acetylene, ethylene and their radicals as well as aromatic cracking products). 

Free-radical mechanisms are also thought to be important in other significant organic reactions such as the cracking of hydrocarbon chains and the formation of polymers such as poly(ethene). 

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