What Is the Contact Process?

Mary McMahon

The contact process is a method for the industrial production of sulfuric acid. It is the industry standard for production of this chemical in the purity and volume needed for manufacturing applications ranging from batteries to fertilizer production. Use of this process dates to the mid-1800s, when British chemists first developed it to meet the needs of the growing industrial revolution. After production in a chemical factory, sulfuric acid is ready for shipment to manufacturers and other facilities.

Scientist with beakers
Scientist with beakers

There are four stages in the production of sulfuric acid with the contact process. The first involves the production of sulfur dioxide, often by burning in a high oxygen environment. In the second step, more oxygen is added along with vanadium oxide, which acts as a catalyst to create sulfur trioxide in the next step. This creates a compound known as oleum that can be mixed with water to create sulfuric acid in the final step.

Companies can use this process to generate very large volumes of sulfuric acid. Technicians tightly control the conditions to keep the chemical as pure as possible. Contamination can impact the contact process or create problems with the finished chemical. For quality control purposes, the firm may periodically take samples from batches of sulfuric acid and test them to confirm they are free of contaminants and ready for use. Facilities may make a mixture of chemicals and it is important to keep them all at a high state of purity.

This chemical can be dangerous. Technicians need to be vigilant during the contact process and must package finished sulfuric acid with care to avoid injury. They use nonreactive containers to limit the risk of a problem during processing and shipping, and to ensure that the chemical will arrive intact at an end destination. For very large shipments, companies may fill tanker trucks or train cars and use these for the transport of their finished sulfuric acid.

The basics of the contact process remain consistent, but each factory may tweak the process slightly. It is possible to use different catalysts, and there are several ways to produce the initial sulfur dioxide. Companies also need to consider issues like the potential for pollution. Inadvertent release of chemicals during this process could result in the payment of fines or cleanup costs, or exposure to lawsuits from members of the public injured by chemicals. Measures like wastewater filtration and tight control of manufacturing facilities help limit pollution and keep surrounding communities safe.

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Discussion Comments


@everetra - It would be nice if we had alternatives to this corrosive chemical, given how an easy release could pollute and destroy the nearby environment. Perhaps there could be an ecologically friendly alternative. Industries rely too much on dangerous chemicals in my opinion.


@miriam98 - I think what you’re suggesting would mess up the contact process of sulfuric acid. One of the things they do before releasing it is that they check it to make sure that it’s not contaminated.

The deactivator solution you’re referring to would probably be a contaminant of sorts, and therefore render the sulfuric acid impure. What you really want is a canister that is tightly sealed so that the stuff never spills in the first place.


The manufacture of sulfuric acid is a dangerous business indeed. If you’ve ever seen what sulfuric acid can do, you know what I mean. It can burn holes very easily, and while it’s used for large scale industrial processes, it is also used in everyday things like batteries.

You can get a shock just holding a battery improperly and you definitely don’t want to keep an open or corroded battery around as it can burn you.

It would be neat if when they package the sulfuric acid in canisters that they had some way of “deactivating” it somehow. I’ve heard that some chemicals don’t do their thing unless an activator is dropped into them.

Perhaps you can do this with sulfuric acid, to make it inert, until such time as you needed it; then you can add the activator. That way if you accidentally spill it nothing will go wrong.

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