High-molecular-weight olefin formation

Steam cracking reactions are highly endothermic. Increasing temperature favors the formation of olefins, high molecular weight olefins, and aromatics. Optimum temperatures are usually selected to maximize olefin production and minimize formation of carhon deposits. 

P9-20p The formation of high-molecular-weight olefins, for example. 

The olefins that undergo metathesis include most simple and substituted olefins cycHc olefins give linear high molecular-weight polymers. The mechanism of the reaction is beheved to involve formation of carbene complexes that react via cycHc intermediates, ie, metaHacycles. Industrial olefin metathesis processes are carried out with soHd catalysts (30). 

Olefins participate in a variety of oxidation reactions which lead to the formation of carbonyl compounds, gums, and high-molecular-weight deposits... 

Fuel olefins have been implicated as the primary cause of deposits in gasoline fuel injectors and carburetors. High-boiling-point, high-molecular-weight aromatic components have also been shown to contribute to intake system deposit and gum formation. Once formed, other compounds in the fuel can adhere to these deposits to form an amorphous-type deposit. 

Metallocene Catalysts. Higher a-olefins can be polymerized with catalyst systems containing metallocene complexes. The first catalysts of this type (Kaminsky catalysts) include metallocene complexes of zirconium such as biscyclopentadienylzirconium dichloride, activated by methylaluminoxane. These catalysts polymerize a-olefins with the formation of amorphous atactic polymers. Polymers with high molecular weights are produced at decreased temperatures and have rubber-like properties. 

Polymerization is a process in which similar molecules (usually olefins) are linked to form a high-molecular-weight product such as the formation of polyethylene from ethylene... 

The formation of viscous liquids containing polymeric polysulfides from the reaction of sulfur with a number of olefinic hydrocarbons has been reported (16). Blight, Currell, and their colleagues have analytically characterized the sulfur—DCP system and have shown that the increase in viscosity for the sulfur-DCP solutions at 140°C is caused by the formation of high-molecular-weight polysulfides (17). Also as reaction time proceeds, the molecular weight of the polysulfides increases (17). 

In studies with propylene. Increasing isobutane-to-olefin ratio suppressed the formation of high-molecular-weight residue, indicating a substantial reduction in the role of olefin polymerization to large ions. 

The oligomerization of olefins is an exothermic consecutive reaction, which benefits from the application of CD for enhanced selectivity to intermediate products. Catalytic distillation plays a particularly important role in enhancing the catalyst lifetime because in situ separation reduces the undesirable high-molecular-weight oligomers or polymers, which will form coke and deactivate the catalyst. The use of reaction heat for distillation also reduces the formation of hot spots and catalyst deactivation due to sintering. 

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