Question

Describe the contact process for the production of sulfuric acid.

Short answer

The contact process produces sulfuric acid by oxidizing sulfur dioxide to sulfur trioxide and absorbing it in water.

Step-by-step solution

Understanding the Basics

The contact process is an industrial method used to produce sulfuric acid. It involves converting sulfur dioxide (SO₂) into sulfur trioxide (SO₃), which is then used to make sulfuric acid.

Producing Sulfur Dioxide

Sulfur dioxide is produced by burning sulfur or roasting sulfide ores. The equation is: \[ \text{S} + \text{O}_2 \rightarrow \text{SO}_2 \] or \[ \text{4FeS}_2 + \text{11O}_2 \rightarrow \text{2Fe}_2\text{O}_3 + \text{8SO}_2 \].

Converting SO₂ to SO₃

The sulfur dioxide is oxidized to sulfur trioxide using a vanadium(V) oxide catalyst at about 450°C and 1-2 atm. The reaction is: \[ 2\text{SO}_2 + \text{O}_2 \rightarrow 2\text{SO}_3 \].

Absorbing SO₃ and Producing H₂SO₄

Sulfur trioxide is absorbed in concentrated sulfuric acid to produce oleum, which is then mixed with water to form sulfuric acid, as represented by: \[ \text{H}_2\text{SO}_4 + \text{SO}_3 \rightarrow \text{H}_2\text{S}_2\text{O}_7 \] and \[ \text{H}_2\text{S}_2\text{O}_7 + \text{H}_2\text{O} \rightarrow 2\text{H}_2\text{SO}_4 \].

Key concepts

Sulfur Dioxide Production

Sulfur dioxide (\(\text{SO}_2\)) is a crucial starting point in the Contact Process for manufacturing sulfuric acid. This compound is typically generated by burning elemental sulfur in the presence of oxygen, resulting in the reaction: \(\text{S} + \text{O}_2 \rightarrow \text{SO}_2\). Alternatively, it can also be produced by roasting metallic sulfide ores, such as iron sulfide (\(\text{FeS}_2\)). Here, the chemical reaction proceeds as follows: \(\text{4FeS}_2 + \text{11O}_2 \rightarrow \text{2Fe}_2\text{O}_3 + \text{8SO}_2\).
The generation of sulfur dioxide is an essential step because it acts as the primary building block for further chemical transformations in sulfuric acid production. The process involves controlled conditions to ensure an efficient conversion rate. It's a relatively straightforward step, laying the groundwork for following reactions.

Sulfur Trioxide Conversion

Once sulfur dioxide is created, the next major step in the Contact Process is converting it to sulfur trioxide (\(\text{SO}_3\)). This oxidation process requires a catalyst to speed up the reaction under specific conditions. The conversion reaction is as follows: \(2\text{SO}_2 + \text{O}_2 \rightarrow 2\text{SO}_3\).
For this conversion to occur efficiently, it is essential to maintain a temperature of about 450°C and a pressure of 1-2 atmospheres. The presence of a catalyst, particularly vanadium(V) oxide, proves vital in facilitating this reaction. This step is crucial as the obtained \(\text{SO}_3\) is the intermediate needed for further processing into sulfuric acid.
A high conversion rate of \(\text{SO}_2\) to \(\text{SO}_3\) is desired because it maximizes efficiency and ensures that most of the sulfur feed is ultimately transformed into sulfuric acid.

Vanadium(V) Oxide Catalyst

In the Contact Process, the use of a vanadium(V) oxide catalyst is essential for the successful conversion of sulfur dioxide to sulfur trioxide. This catalyst is preferred for several reasons:

• It provides a lower energy pathway for the reaction, allowing it to occur swiftly and more efficiently.
• The operating conditions with vanadium(V) oxide, such as a temperature of about 450°C, are optimal for maximizing conversion without decomposing the product.
• The catalyst is relatively cost-effective and long-lasting, making it ideal for large-scale industrial applications.

Vanadium(V) oxide serves as a reliable agent in the balance between speed and efficiency of the reaction. It ensures that the transformation of sulfur dioxide to sulfur trioxide can be performed on an industrial scale with minimum waste and maximum yield.
This catalyst plays a pivotal role in the Contact Process, emphasizing its importance as a bridge between raw material and final product.

Oleum Production

The final phase in the Contact Process involves the safe absorption of sulfur trioxide into concentrated sulfuric acid to create oleum, also known as fuming sulfuric acid. This substance is represented by the chemical equation: \(\text{H}_2\text{SO}_4 + \text{SO}_3 \rightarrow \text{H}_2\text{S}_2\text{O}_7\). Oleum's production is crucial because it allows for the subsequent safe handling and conversion of \(\text{SO}_3\) into sulfuric acid.
The resulting oleum is then cautiously mixed with water to produce more sulfuric acid, as represented by: \(\text{H}_2\text{S}_2\text{O}_7 + \text{H}_2\text{O} \rightarrow 2\text{H}_2\text{SO}_4\). This step is vital because it ensures the efficient and controlled manufacture of sulfuric acid.
Through these reactions, the \(\text{SO}_3\) formed in the previous steps is effectively and safely turned into sulfuric acid, completing the Contact Process. Thus, oleum production not only offers a method to manage sulfur trioxide but also maximizes sulfuric acid production.