What is oxygen inhibitor?

An oxygen inhibitor, also referred to as an oxygen scavenger, is a chemical substance used to reduce or remove dissolved oxygen from water or other fluids in various industrial processes. The primary purpose of an oxygen inhibitor is to prevent oxygen-induced corrosion, which can damage metal surfaces, reduce system efficiency, and shorten the lifespan of equipment, particularly in systems that involve water, steam, or other fluids that are in contact with metal components.

How Oxygen Inhibitors Work
Oxygen inhibitors work by either chemically reacting with dissolved oxygen or by forming protective layers on metal surfaces to prevent oxygen from interacting with them. Most oxygen inhibitors are reducing agents that donate electrons to oxygen, effectively neutralizing it. By removing dissolved oxygen, these inhibitors help protect metal parts, such as pipes, boilers, heat exchangers, and tanks, from corrosion, which is accelerated by the presence of oxygen.

Types of Oxygen Inhibitors
Chemical Oxygen Scavengers
These chemicals directly react with dissolved oxygen to neutralize it. The most common types include:

Sodium Sulfite (Na₂SO₃): Sodium sulfite is commonly used in boiler water treatment. It reacts with oxygen to form sodium sulfate (Na₂SO₄), thus preventing corrosion in steam boilers and cooling systems.

O₂+Na₂SO₃→Na₂SO₄

Hydrazine (N₂H₄): Hydrazine is a more powerful oxygen scavenger than sodium sulfite and is often used in high-pressure boiler systems. It reacts with oxygen to form nitrogen gas (N₂) and water (H₂O).

N₂H₄+O₂→N₂+2H₂O

Ascorbic Acid (Vitamin C): Ascorbic acid can also act as an oxygen scavenger, particularly in low-concentration applications. It reacts with dissolved oxygen, reducing it to water.

Sodium Bisulfite (NaHSO₃): Used in various industrial applications, sodium bisulfite also acts as a reducing agent, reacting with dissolved oxygen to prevent corrosion.

Catalytic Oxygen Scavengers
Catalytic oxygen scavengers do not directly remove oxygen themselves. Instead, they speed up the natural chemical reactions that remove oxygen. These systems are typically used in processes where a continuous removal of oxygen is required. For example, iron-based catalysts may be used in water treatment systems to enhance oxygen scavenging processes.

Organic Oxygen Scavengers
Organic compounds such as alkyl hydrazines (e.g., methylhydrazine, ethylhydrazine) are used in some specialized applications, particularly in situations where the scavenger needs to be biodegradable or have low toxicity. These compounds also react with dissolved oxygen but tend to be more specialized for certain industries, such as aerospace or military.

Applications of Oxygen Inhibitors
Boiler Water Treatment

Oxygen inhibitors are most commonly used in steam boiler systems to prevent oxygen corrosion. Oxygen in boiler water can lead to serious pitting corrosion, which can damage the boiler’s internal components, such as pipes, tubes, and heat exchangers. Oxygen scavengers are added to the feedwater or directly to the boiler water to remove dissolved oxygen before it can cause harm.
Cooling Systems

In industrial cooling systems (such as cooling towers and chillers), oxygen inhibitors prevent corrosion of metal components, such as pipes, pumps, and heat exchangers. This helps maintain the integrity of the system and reduces the need for expensive repairs and maintenance.
Oil and Gas Industry

Oxygen inhibitors are used in oil pipelines and water injection systems to prevent oxygen-induced corrosion. In oil refineries, oxygen scavengers can be used in the water used for enhanced oil recovery (EOR) to prevent corrosion of equipment and pipelines.
Food and Beverage Industry

In certain applications, such as water treatment for bottling plants or food processing, oxygen inhibitors are used to ensure that oxygen does not affect the quality or taste of the products. Oxygen scavengers can also help preserve the freshness of certain foods by removing oxygen in packaging.
Pulp and Paper Industry

Oxygen inhibitors are used in the pulp and paper industry to protect equipment and reduce corrosion in recovery boilers, evaporators, and other water systems that come in contact with oxygen.
Steam Generation and Power Plants

In power plants, oxygen inhibitors are used in steam generation systems to remove dissolved oxygen, which can otherwise lead to corrosion in turbine components, boilers, and other critical infrastructure.
Advantages of Using Oxygen Inhibitors
Corrosion Prevention

The main advantage of using oxygen inhibitors is their ability to prevent oxygen-induced corrosion, which can be a major issue in steam boilers, cooling systems, pipelines, and industrial equipment.
Extended Equipment Life

By preventing corrosion and scaling, oxygen inhibitors help extend the life of equipment, reducing the frequency of maintenance and the need for costly replacements.
Improved System Efficiency

Oxygen inhibitors help maintain system efficiency by preventing rust, scale, and fouling, which can reduce heat transfer efficiency and increase energy consumption in industrial systems.
Cost-Effective

The use of oxygen inhibitors is generally a cost-effective solution compared to the high cost of equipment repairs, downtime, or replacement due to corrosion damage.
Environmental Benefits

By using oxygen inhibitors, the potential for chemical leaching or environmental damage caused by corrosion products is reduced. For example, oxygen scavengers like sodium sulfite often form benign byproducts, such as sodium sulfate, that have relatively low environmental impact.
Challenges of Oxygen Inhibitors
Overdosing

Overdosing oxygen inhibitors can result in the buildup of unwanted byproducts (such as sodium sulfate), which may lead to scaling, fouling, or other operational issues in the system.
Toxicity and Safety Concerns

Some oxygen inhibitors, such as hydrazine, can be hazardous or toxic to humans and the environment, requiring careful handling, storage, and disposal. Hydrazine, in particular, is highly toxic and requires strict safety measures in its use.
Compatibility with Other Chemicals

Oxygen inhibitors need to be compatible with other water treatment chemicals, such as scale inhibitors, biocides, or pH regulators. In some cases, oxygen inhibitors may interfere with the effectiveness of other treatment agents.
Continuous Monitoring

To maintain the correct balance of oxygen inhibitor levels in the system, continuous monitoring is necessary. This ensures that the correct amount of inhibitor is used and that the dissolved oxygen levels remain low enough to prevent corrosion.
Environmental Concerns

Although oxygen inhibitors like sodium sulfite are relatively safe, excessive amounts can still lead to environmental concerns, especially if they enter natural water systems. Proper disposal of chemical byproducts is essential to avoid contamination.
Conclusion
Oxygen inhibitors are crucial chemicals used in various industries to prevent oxygen-induced corrosion, which can cause significant damage to equipment and infrastructure. By removing or neutralizing dissolved oxygen, these inhibitors help protect boilers, cooling systems, pipelines, and other industrial systems. While effective, their use requires careful monitoring and control to avoid overuse and ensure compatibility with other water treatment chemicals.