Ethene: Production and Properties

Ethene, which is more commonly known as ethylene, is one of the main components of all plastics. It is the most produced carbon based chemical in the world. Most of this substance is produced in oil refineries using fractional distillation of crude oil.

Structure

The molecule is the simplest of the family of organic molecules known as the alkene series. It consists of two Carbon atoms that share a double bond, meaning a total of four electrons are holding the two Carbons together. Each Carbon also has two Hydrogen atoms bonded to it. Carbon requires eight electrons in its outer shell to achieve stability and Hydrogen requires two. This results in the structure shown below. Note that both structures represent the same molecule. The first shows the electrons. The second has pairs of electrons replaced with sticks.

One of the two bonds between the Carbons can be broken which allows other atoms or functional groups to be added to the molecule. This is how a wide range of chemicals that are in every day use are produced. These are called addition reactions since the extra chemicals are added to the molecule.

Ethanol

The first example of this is the industrial production of ethanol. This is obtained by adding a water molecule to ethene. The water molecule is split in two parts, as is one of the bonds between the two carbon atoms. The two parts of the water molecule are then added, one to each half of the broken C-C bond. The result is ethanol.

1,2-Dichloroethane

Also known as Ethylene Dichloride, this chemical is produced by reacting Ethene with Chlorine gas, Cl2. The reaction process is exactly the same as for the production of ethanol. The Cl2 molecule is split in two parts, each consisting of one Chlorine atom. The Carbon-Carbon double bond has one one of its bonds broken and a Chlorine atom is attached to each Carbon.

Production

Ethene is produced primarily from its alkane cousin, Ethane. Ethane is extracted from natural gas through fractional distillation. Ethane can also be extracted from longer oil hydrocarbon molecules by breaking them up in a process called cracking.

In reality the gases and oil molecules are somewhat mixed and the process described below for the treatment of Ethane also occurs to some longer molecules at the same time.

Steam Cracking

Ethane is exposed to super heated steam at 850 degrees celsius. While the gas is only exposed to these conditions for a very brief time, it is sufficient to knock two Hydrogen atoms off the ethane molecule. This results in each Carbon atom in Ethane having one free electron each. These then re-form into another single bond, giving the double bond between the two Carbon atoms.