Chapter 10 - Contact Process (10.4) Flashcards
What are the raw materials of the contact process
Sulfur/sulfur dioxide
air
water
Where is sulfur and sulfur dioxide obtained from
Roasting of sulfide ores
or burning sulfur
Step 1 of the contact process
word and chemical eqn
Sulfur is burned in air
Sulphur + Oxygen –> Sulfur Dioxide
S (s) + O2 (g) —> SO2 (g)
Step 2 of the contact process
Sulfur dioxide is mixed with more air.
Step 3 of the contact process
catalyst name
temperature
word and chemical eqn
is this eqn reversible
Sulfur dioxide mixture with air passes over 4 beds of catalyst (pellets of Vanadium (V) oxide) at 450 deg Celsius to give sulfur trioxide.
Sulfur dioxide + Oxygen <—–> Sulfur Trioxide
2SO2 (g) + O2 (g) <—–> 2SO3 (g)
it is a reversible reaction
What happens to the unreacted sulfur dioxide in step 3
Recycled and passed over the beds of catalyst again to try and react and form sulfur trioxide.
How is the temperature of the catalyst maintained
Pipes of cold water are coiled around the beds of catalyst and constantly carry the excess heat out.
What is step 4 in the contact process
what does it give
formula
Sulfur trioxide gas is dissolved in concentrated sulfur acid.
This gives a thick fuming liquid called ‘Oleum”
H2S2O7
What is step 5 in the contact process
word eqn
chem eqn
Oleum is mixed with water to give sulfuric acid
H2O (l) + H2S2O7 (g) —-> 2H2SO4 (l)
why isnt sulfur trioxide directly reacted with water to form sulfuric acid
Extremely violent reaction and sulfuric acid is formed in a mist state, hence it is unsafe and not easy to collect.
What type of reaction is the forward reaction (endo or exo)
exo
What is the key reaction in the contact process
molecules
what is the forward
2SO2 (g) + O2 ⇌ 2SO3 (g)
3 molecules vs 2 molecules
—> exo
<— endo
What are the ideal conditions for the contact process
Low temp - since its exo
High pressure - since there are more molecules on the reactant side
Remove product to lower its concentration so more will form
both would shift the equilibrium to the right
What are the actual conditions for the contact process
450 deg Celsius - although the lower the temperature is, the higher the yield would be, the catalyst is necessary as well. Vanadium pentoxide activates at 400 deg Celsius and works better at higher temperatures. So 450 Deg Celsius is a compromise between speed and yield.
2 atm - Raising pressure more would cost more (pipes, storage, etc) and would be more unsafe. This pressure gives an acceptable yield.
Removal of sulfur trioxide - by dissolving it in sulfuric acid
catalyst - Vanadium pentoxide
Total yield of the contact process
over 99% since all unreacted reactants are recycled until they reach they react and become products.
