Chemistry only
The word alcohol is most commonly associated with alcoholic drinks,
unfortunately most alcohols are toxic and are definitely
not suitable as drinks. The one alcohol
which is less harmful is ethanol, although it still causes many people to do very silly things when
taken in excess! Ethanol has been made for thousands of years as an alcoholic drink in
a process called fermentation.
As an example consider how beer is made.
To make beer, barley or sometimes oat grains are allowed to
start germinating by being placed in water. After a few days natuarlly
occurring enzymes
break down the starch present in the grains into the sugar maltose. This process is called malting. The
germinated barley grains are then dried by hot air .
These dried grains are often called
malt. Hops are then added to give the beer its bitter taste and aroma.
The barley grains are then lightly crushed in a process called milling and
finally the grains are transferred to large
tanks filled with hot water where the starch in the barley grains is converted into
simple sugars by natuarlly occuring
enzymes present in the barley. These simple sugars
dissolve in the water to form a solution which is often called "sweet wort".
This sweet wort is then transferred to copper vessels where it is boiled. The left over grains, often called brewers grains are
sold as animal or cattle feed.
Once the sweet wort solution has cooled, it is transferred into large fermenatation
tanks where the yeast is added. Yeast is a
natural fungus which will
produce an enzyme called zymase which will convert the simple sugars in the solution into carbon dioxide gas and the
alcohol ethanol. This is fermentation.
The fermentation process is slow and can take days or even weeks. Fermentation is a natural process, it is a form of anaerobic respiration. An equation for fermentation is:
Alcohol (ethanol) used in alcoholic drinks such as beer, wine and spirits is made by fermentation. However alcohol can also be made a method called direct hydration. Using this method produces alcohol very quickly and being the only substance made there is no waste and no costs are needed in separating out unwanted substance. It is also a continuous process whereas traditional fermenatation is a batch process. This makes direct hydration much more cost effective and more efficient, however is a non-renewable process since the ethene needed for it comes from crude oil.
Alcohol used for industrial purposes such as solvents and in sanitisers will be made by the direct hydration method rather than fermentation. Direct hydration involves adding steam across the C=C in an alkene molecule, usually ethene. The reaction is shown below. A catalyst (phosphoric acid) and a high temperature (3000C) and high pressure (65 atmospheres) are both needed to get this reaction to occur smoothly.
Equations for this reaction are: