The gas stream that leaves the separation (distillation) unit is now rich in ethane. The next step is to make ethylene from ethane. This step is necessary since ethylene is the single unit (called monomer) that is used to generate the long polyethylene chain. This chain is what is used to produce garbage bags (The question of what is a polyethylene chain and how it is generated will be discussed later on).

Copyright, Shell Oil, 1996

Ethylene is generated by running the gas stream through a reactor. The reactor (pictured above), which is nothing more than a long pipe enclosed inside a furnace, is known as a thermal cracker. Its purpose is to heat up the ethane that is in the gas stream to a point where ethane starts to breakdown (crack) and form ethylene along with other gases (See the picture below).

The furnace is set at a temperature of 1900 degrees fahrenheit (1311K). The reactor needs to be this hot in order for any ethylene to form. The next stop is the purification unit.

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