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Making Ethanol.

What is Ethanol?

Ethanol is an alcohol with the molecular formula C2H5OH
(see also the structural formula).
Ethanol is not a hydrocarbon because the molecule
contains oxygen as well as hydrogen and carbon.

Ethanol is a colourless liquid which boils at 78 °C.
It is completely miscible with water.
This means that it mixes with water in any quantity.
Ethanol is a neutral liquid.

How can Ethanol be Made?

Ethanol can be made by the fermentation
of a sugar solution (in a batch process)
by the reaction of ethene with steam in the presence
of phosphoric acid (in a continuous process, see below).

What is a Continuous Process?

A continuous process means that reactants are constantly being
put in at one end of the reaction vessel and products are
constantly being taken out at the other end of the reaction vessel.

Adding the components of water across the double bond
of ethene is called the hydration of ethene. The reaction
is carried out at a high temperature and a high pressure.

ethene       +      steam Phosphoric acid as a Catalyst      ethanol  
C2H4(g)       +      H2O(l)      arrow          C2H5OH(l)

See a comparison of the batch process
with the continuous process below.

Process Reaction Renewable Resource? Rate of Reaction Product
Batch Process Fermentation Yes - Sugar Cane Slow Ethanol / Water mixture
Continuous Process Hydration of Ethene No - Crude Oil Fast Pure Ethanol

Industry would rather use a continuous process than
a batch process because of the fast production of a
pure product. In some countries it may be more
practical to use a batch process - see the next page.

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