2. Production of Sulfuric Acid
Sulfuric acid is made in several stages from SO2,
obtained from the oxidation of sulphur or collection of
SO2 from the smelting of sulfide ores such as copper,
zinc or lead.
SO2(g) SO3(g) H2SO4(aq)
In the following slides we will break down this
process into three main steps.
3. 1. Furnace or Burner (Only necessary if raw sulfur is used)
Air is cleaned by electrostatic precipitation, dried then heated
to approx. 600oC.
Pure (liquid) sulphur is sprayed under pressure into the furnace,
reacting with the oxygen in the air. The product is sulphur
dioxide
S(l) + O2(g) SO2(g)
4. 2. The converter
The converter contains trays or layers of porous pellets of a
catalyst, vanadium (V) oxide (V2O5). The sulphur dioxide reacts with
more air to form sulphur trioxide. This reaction is reversible and
reaches an equilibrium. It is also an exothermic reaction and the
temperature will rise to over 600oC. The mixture is continuously
cooled to 400oC between each tray.
2SO2(g) + O2(g) 2SO3(g)
As the temperature rises the equilibrium shifts to the left (not
forming SO3). To counter this the gases are allowed to cool
slightly before they pass over the next layer of catalyst, by
carefully controlling the process almost all sulphur dioxide is
converted to sulphur trioxide
5. 3. The absorption tower
In practice the sulphur trioxide dissolves almost completely and
is bubbled through concentrated sulfuric acid (that contains
relatively little water) to form 98% sulfuric acid, known as
Oleum (H2S2O7)
Sulphur trioxide will dissolve in water to form our final goal of
sulfuric acid. However it is violently exothermic and usually
results in a mist of sulfuric acid droplets that are very difficult
to control.
a) SO3(g) + H2SO4(l) H2S2O7(l)
b) H2S2O7(l) + H2O(l) H2SO4(l)
6. Waste products
Most of the “waste” heat is recovered and used to heat
water, in this way much of the energy can be reused.
Because of this many sulfuric acid plants are co-located
with other industrial processes.
Great care needs to be taken with the waste gases that are
formed. There will be small amounts of sulphur dioxide,
sulphur trioxide, sulfuric acid and possibly particle sulphur,
all of which must be removed to prevent environmental
damage. There is a double absorption method that can be
used to prevent SO2 emissions. After a first round of
processing through the converter, any SO2 that was not
converted into SO3, can be collected and passed back
through. SO2 that is released into the atmosphere can
cause acid rain and respiratory irritants.
9. Uses of Sulfuric Acid
The amount of sulfuric acid produced by a company is
often an indicator of a countries industrial activity.
Annual worldwide production is 170 million tonnes!
Transport and storage of sulfuric acid is hazardous, so
most of the acid produced is used by alternate
manufactures close to the production site.
Sulfuric acid is highly corrosive and burns skin and eyes.
For a large spill, the acid is treated with a natural hard
substances such as clay or sand, then slowly diluted with
water and finally neutralised with a base.
The main use of sulfuric acid Australia is for fertiliser.
