Filmogenic amines: Corrosion protection for aqueous systems

Preventing corrosion in aqueous systems remains a constant challenge in industrial engineering. Among the available solutions, filmogenic amines stand out as highly effective organic compounds capable of internally protecting metallic systems without the need for physical coatings. They achieve this through the formation of a molecular protective film. This article explores their principles, mechanisms, and industrial applications.

What are filmogenic amines?

Filmogenic amines are organic compounds that function as corrosion inhibitors in metallic systems exposed to water. These chemicals form a molecular layer that adheres to internal metallic surfaces, creating a protective barrier that prevents direct interaction with corrosive agents. Their use offers an effective anticorrosion strategy based on chemical treatment, particularly in environments where traditional coatings are impractical.

How do filmogenic amines work?

The action mechanism of filmogenic amines is based on the physico-chemical adsorption of their molecules onto metal surfaces. When introduced into an aqueous system, these amines interact with both anodic and cathodic sites on the metal, forming a hydrophobic film that significantly slows the electrochemical reactions responsible for corrosion.

In addition, factors such as temperature and product concentration directly influence its effectiveness. Moderate temperature values favor adsorption and adequate concentration ensures uniform coverage. This molecular protective film formation not only blocks the access of oxygen and moisture, but also contributes to pH control and formation of passivation layers

Interaction mechanism on metal surfaces

Filmogenic amines spontaneously adsorb onto metal surfaces due to chemical affinity between their functional groups and the exposed metal. This interaction promotes molecular alignment, maximizing surface coverage and forming an electrically neutral barrier. In variable pH environments, certain amines can react with surrounding ions, stabilizing the surface through the formation of passivating complexes.

Where are filmogenic amines applied?

These substances are widely used in cooling water systems, boilers, hydraulic systems, cooling towers, steam distribution networks and closed circuits. They are also common in industrial heating systems, petrochemical processes and power plants. Their effectiveness in the internal protection of metal systems in contact with water makes them a preferred choice in plants where chemical inhibition in wet environments is essential to maintain equipment integrity.

filmogenic amines in distillation tower overheads

A specialized application of filmogenic amines occurs at the tops of crude oil distillation towers. In this area, where condensation of acidic compounds such as HCl occurs in the presence of water vapor, conditions are extremely corrosive to metallic materials. To mitigate these effects, filmogenic amines are injected together with neutralizing amines.

Their function is to form a molecular film on the internal surfaces of the condensers, ducts and separators, creating a hydrophobic barrier that prevents the acid from contacting the metal. This technique has proven to be highly effective as a corrosion prevention method without physical coatings, especially in units where exposure to humid environments and acidic contaminants is constant. In addition, this approach improves chemical stability in overhead systems and reduces maintenance and replacement costs of corrosion-affected components.

In this particular application, temperature has a decisive influence on the performance of filmogenic amines. Moderate temperatures favor the adsorption of the molecules on the metal surfaces, accelerating the formation of the protective film. However, if the temperature is too high, degradation of the inhibitor may occur, reducing its effectiveness.

Practical application of filmogenic amines

Filmogenic amines are added directly into the system to be protected by controlled dosing, usually by continuous or intermittent injection. This application is carried out at strategic points such as condensate return, water feed or condensation zones in distillation towers. The dosage must be proportional to the flow rate and concentration of contaminants, ensuring a homogeneous distribution in the system.

Once injected, the amines disperse with the carrier fluid and begin to adsorb spontaneously on the metal surfaces, where they form a protective hydrophobic film. This film is established under laminar or moderate flow conditions, so it is recommended to avoid excessive turbulence during the initial application. To optimize the effectiveness of the treatment, it is essential to monitor pH, temperature, and inhibitor concentration in the system.

Common types of filmogenic amines

There are several common types of filmogenic amines, including:

• Primary amines: Contain one amino group (-NH₂); highly reactive, suitable for rapid film formation.
• Secondary amines: Have two organic groups bonded to nitrogen; more stable, often used in blends.
• Tertiary amines: Feature three organic groups; water-soluble, often used in feedwater systems.
• Long-chain amines: Contain extended hydrocarbon chains, promoting stronger, more durable hydrophobic films.

Advantages over other corrosion inhibitors

• No need for physical coatings: Protection is achieved chemically through molecular film formation.
• High efficiency under variable conditions: Effective even with fluctuations in temperature, pH, or pressure.
• Environmentally friendly: Many formulations are biodegradable and compliant with environmental regulations.
• Compatibility: Can be used alongside oxygen scavengers, dispersants, and algaecides.
• Reversible film formation: The film can be removed through controlled rinsing for inspections.
• Chemical stability in closed systems: Long-lasting protection without frequent reapplication.

Limitations and use considerations

Despite their many benefits, filmogenic amines present several limitations:

• Sensitivity to system contaminants: Salts, heavy hydrocarbons, cleaning residues, and oxidation byproducts may interfere with film stability.
• Limited compatibility with certain metals: Not all alloys (e.g., copper) respond favorably.
• Need for constant monitoring: Key parameters such as pH, conductivity, and temperature must be tracked.
• Vulnerability to turbulent flow: High-speed conditions can physically strip away the film.
• Interaction with other chemicals: May be incompatible with certain biocides or antifoaming agents.
• Ineffectiveness on existing corrosion: Preventive use only; does not remove prior damage.
• Toxicity concerns: Some older formulations pose environmental and handling risks.
• Relative cost: More expensive than traditional corrosion inhibitors.

Formulation and proper selection

From a chemical point of view, many filmogenic amines have a general structure of the R¹-(NH-R²)-NH₂ type, where R¹ and R² represent aliphatic or functionalized organic chains. This configuration allows a double interaction with the metal surface, promoting a more stable adsorption and the formation of a continuous hydrophobic film.

Once added, the amines disperse with the fluid and adsorb onto the metal surfaces, forming the protective hydrophobic film. To favor its action, it is recommended to avoid excessive turbulence during the initial application. It is also necessary to monitor operating parameters such as pH, temperature and inhibitor concentration to ensure effective and sustained coverage.

The efficacy of filmogenic amines depends on their formulation and criteria for their selection include:

• Compatibility with system metal (carbon steel, stainless steel, copper, etc.).
• Operating conditions (temperature, pressure, type of water).
• Fluid residence time in the system.
• Influence on treated water quality.
• Interactions with other chemicals used.

Proper dosing, pH monitoring, and analysis of the inhibitor concentration in the system are aspects that must be controlled to ensure its performance.

Case study: Successful industrial application

A notable case documented at a Midwest ethanol plant showed positive results after applying an advanced filmogenic amine treatment (ChemTreat’s BL8421F), which included neutralizers, polymers and a fluorescent dye. The objective was to reduce iron in the condensate and clean internal deposits.

After one month, the condensed iron became undetectable despite pH fluctuations. One month later, iron in the feedwater dropped to <0.02 ppm and trended to <0.01 ppm. Subsequent inspection confirmed a significant reduction in deposits and improved internal conditions.

Future outlook for filmogenic amines

With the growing focus on sustainability, research is driving the development of green corrosion inhibitors, including biologically derived filmogenic amines. These aim to maintain chemical inhibition efficiency in humid environments while minimizing environmental impact. Additionally, integrating real-time monitoring technologies will allow for more precise and automated dosing.

Conclusion

Filmogenic amines are a technically sound and environmentally viable alternative for the internal protection of aqueous systems. Their action is based on the formation of an absorbed molecular film on metal surfaces, which acts as a barrier against electrochemical corrosion mechanisms. This approach makes it possible to dispense with physical coatings, maintaining the chemical stability of the medium and improving operating efficiency in closed circuits. Its use prolongs the service life of industrial equipment and optimizes anti-corrosion treatment programs.

References

1. https://inspenet.com/en/articulo/corrosion-inhibitor-types-applications/
2. https://www.nature.com/articles/s41529-024-00523-0
3. https://es.chemtreat.com/resource/reducing-corrosion-with-fluorescent-traced-film-forming-amine-program-at-an-ethanol-plant/