Olefins interconversion cycle

Olefins interconversion cycle olefin carbon pool ... 

So, the ethylene production does correlate with coke presence, in particular with aromatics formation as far as the diffusion limitations are not significant. However, it seems that the majority of ethylene is not always formed directly from MeOH [115]. The aromatics and other coke species could be the products of the conversion of primary carbenium ions, which are mobile and could equilibrate each other [28]. This may explain the isotopic distribution in products and retained coke molecules and the coexistence of aromatics and carbenium ions [28], In addition to the coproduction of ethylene with aromatics in olefins interconversion cycle, formation of ethylene via alkylation-dealkylation of methyl aromatics with heavy olefins or with the equivalent carbenium ions like ethyP, propyP, and butyP could be an option. The alkyl aromatics with the side chain length of two carbons or longer are not stable in the pore and dealkylates on the acid sites due to too long residence time and steric hindrances. This may lead to formation of ethylene, other olefins, and alkylaromatics with different structure, namely PMBs [129]. In other words, the ethylene is formed via interaction of the carbenium ions like ethyP, propyP, and butyP formed from MeOH or heavy olefins with aromatics and other coke precursors followed by cracking and in a less extent by a direct alkylation of PMBs with methanol. The speculation is based properly on analysis of the prior arts and is not contradictory with the concept of the aromatic cycle for ethylene formation. 

The fact that ZSM-22 does not produce a lot of ethylene and propylene is explained by a suppression of both aromatic/coke and olefins interconversion cycles on this catalyst. SAPO-34 favors aromatic/coke cycle and limits the olefins cycle. On the contrary,... 

As illustrated in Scheme 6, there are two general methods which imply thiyl radicals in multistep radical reactions. In the first approach (thiol as a coreactant) the thiyl radicals add to the substrate to form an initial radical which undergoes a radical cyclization to give the final radical. Hydrogen abstraction from the thiol gives the desired product and thiyl radical, thus completing the cycle of this chain reaction. In the second approach (thiyl radical as a catalyst) the initial thiyl radical adduct proceeds through a multistep reaction and the final radical terminates via ejection of the thiyl radical. The prototype of this approach is the Z)-(E) interconversion of olefins mentioned above. 

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