Intermediate Topic 477 of 1102 Kinetics & Equilibrium
Contact Process
Industrial production of sulfuric acid via SO2 oxidation over vanadium pentoxide catalyst.
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In-depth explanation of Contact Process
The contact process is the industrial method for making sulfuric acid, based on the catalytic oxidation of sulfur dioxide to sulfur trioxide, 2SO2 + O2 <-> 2SO3. The reaction is run at about 450 degrees C and near atmospheric pressure over a vanadium(V) oxide catalyst, and equilibrium limits the conversion, so several catalyst beds with intermediate cooling are used. Sulfur trioxide is not simply dissolved in water, because that produces a dangerous acid mist; instead it is absorbed in concentrated sulfuric acid to form oleum, which is then diluted to give the final acid. Overall conversion of about 99.5 percent is achieved in practice.
Going deeper: Contact Process
Key ideas: Steps: burn sulfur or roast sulfide ores to SO2, purify the gas to avoid catalyst poisons such as arsenic, oxidize over V2O5 at about 450 degrees C, absorb SO3 in 98 percent H2SO4 to give oleum, H2S2O7, then dilute. Reaction delta H is about -197 kJ per mol of O2 consumed, so the temperature is a compromise, and pressure is kept near 1 to 2 atm because yield is already high.
Common mistakes and connections: Students often say SO3 is dissolved directly in water or that high pressure is essential. Direct absorption in water gives a mist of acid droplets that is hard to condense. The equilibrium yield falls on heating because the reaction is exothermic, and the catalyst is used to restore rate. Links to Le Chatelier, catalysts and the Ostwald process as a comparable industrial synthesis.
Visualization of Contact Process
Equilibrium conversion of SO2 to SO3 falls as temperature rises, so the process uses about 450 C with a V2O5 catalyst and several cooled beds (approximate data). The interactive lesson shows this as a live animation or chart.
Worked example and use case
Passing SO2 and air over hot V2O5 in several beds gives about 99.5 percent conversion to SO3.
Frequently asked questions about Contact Process
What is Contact Process?
Industrial production of sulfuric acid via SO2 oxidation over vanadium pentoxide catalyst.
Is Contact Process a beginner, intermediate or advanced topic?
Contact Process is a intermediate topic in Kinetics & Equilibrium. It builds on the vocabulary of beginner topics in this area.
What should I learn before Contact Process?
Study these earlier topics in Kinetics & Equilibrium first: Effect of Temperature on Equilibrium, Effect of Catalyst on Equilibrium, Haber Process.
What comes after Contact Process?
The next topics in Kinetics & Equilibrium are Ostwald Process and Equilibrium and Free Energy.
Can I practise Contact Process with quizzes?
Yes. The interactive lesson includes a self-check question on Contact Process, and the Kinetics & Equilibrium quiz draws on every topic in this area.
Where Contact Process fits in Kinetics & Equilibrium
Contact Process is topic 58 of 91 in Kinetics & Equilibrium.