Cracking polymerization

A modem petroleum refinery is a complex system of chemical and physical operations. The cmde oil is first separated by distillahon into fractions such as gasoline, kerosene, and fuel oil. Some of the distillate fractions are converted to more valuable products by cracking, polymerization, or reforming. The products are treated to remove undesirable components, such as sulfur, and then blended to meet the final product specifications. A detailed analysis of the entire petroleum production process, including emissions and controls, is obviously well beyond the scope of this text. 

All refining operations may be classed as either conversion processes or separation processes. In the former, the feed undergoes a chemical reaction such as cracking, polymerization, or desulfurization. Separation processes take advantage of differences in physical properties to split the feed into two or more different products. Distillation, the most common of all refinery separation processes, uses differences in boiling points to separate hydrocarbon mixtures. 

The alkylation reaction is complicated by the occurrence of minor side reactions such as cracking, polymerization, hydrogen transfer, etc. However, of major importance is the formation of polyalKylated products. The first alkyl group formed activates the aromatic nucleus so that the second alkylation proceeds more readily than the first and so on at least until steric hindrance intervenes, although hexaethylbenzene is quite readily formed. 

The kiln consists of four operating zones, a vaporization, cracking, polymerization and carburization zone. The remaining residues are transported out of the system by a screw flight. 

Butene-1 is a by-product of petroleum cracking. Polymerization with Ziegler-Natta catalysts produces a mixture of it- and at-PB. Alternatively, c/s-or /rnn5-butene-2 can be used as starting material, since both of these isomerize to butene-1 before polymerization when certain catalyst systems are used. 

Not many commercial processes of this type are available, but such reactions probably occur along with other reactions such as cracking, polymerization, and alkylation but cannot be recognized because of the other reactions and because of the difficulty in identif3dng the hydrocarbon products. 

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