What Is Involved in Making Sulfuric Acid?

The process of making sulfuric acid has been discussed in ancient texts since the first century AD, with many variations on methods. What is involved in the process depends on the purpose of the finished product. For the first several centuries of industrial production, sulfur and potassium nitrate were burned together and combined with steam to create a weak sulfuric acid. Modern methods of industrial sulfuric acid production involve combining sulfur and oxygen with heat, while using vanadium oxide as a catalyst. Nearly all industrial grade applications use this process, known as the contact process, for making sulfuric acid.

Originally known as oil of vitriol, many ancient texts refer to sulfuric acid as a naturally occurring mineral. Through the centuries, numerous methods for artificially creating sulfuric acid have been developed. While each method produces sulfuric acid, the concentration levels differ. Most methods center around heating sulfur or various sulfur derivatives with other elements, then combining the final product with water.

Based on a 17th century method developed by a Dutch chemist, the English inventor John Roebuck refined the original industrial method, known as the lead chamber process. Using sulfur and potassium nitrate, better known as saltpeter, Roebuck developed a method for burning the two minerals in a lead chamber filled with steam. Although less concentrated than modern sulfuric acid, this method was the standard for making sulfuric acid in large quantities until the 19th century. Refinements to the process over two centuries helped to purify the final product and increase concentration to 78 percent.

Increasing demands for various dyes and other industrial applications necessitated more concentrated sulfuric acid. As such, methods for making sulfuric acid in higher concentrations emerged during the Industrial Revolution. Dry distilling methods allowed iron disulfide, through several stages of heating and decomposition, to produce iron oxide and sulfur trioxide. Adding water to the sulfur trioxide produced a variety of sulfuric acid concentrations.

Simplistic methods for making sulfuric acid are less involved than industrial methods. Children are often taught how to make weak sulfuric acid in chemistry class experiments. Such methods involve a simple process, much like the original lead chamber process. Rather than using a lead chamber, these teaching lessons often use a Bunsen burner, a copper end cap, some sodium nitrate, some sulfur, and a plastic soda container as a reactor.

Heat is used to melt the sulfur and sodium nitrate in the copper end cap. Once sufficiently burned, the copper apparatus is placed inside a plastic container partially filled with water. Over time, the container fills with various gas byproducts, which are absorbed into the water to create sulfuric acid. Typically, the process takes a few hours to complete, unlike industrial processes that finish faster due to a more involved process.