Enhancing Corrosion Inhibition Performance with 3-Diethylaminopropylamine

Enhancing Corrosion Inhibition Performance with 3-Diethylaminopropylamine

Introduction

Corrosion remains one of the most significant challenges in industrial infrastructure, particularly within sectors such as oil and gas, marine engineering, chemical processing, and power generation. The economic impact of corrosion is staggering—global estimates suggest annual losses exceed $2.5 trillion USD, representing approximately 3.4% of the world’s GDP (Koch et al., 2016). To mitigate this, corrosion inhibitors play a pivotal role by forming protective layers on metal surfaces, thereby reducing electrochemical degradation processes.

Among the diverse classes of organic corrosion inhibitors, amine-based compounds have demonstrated exceptional efficacy due to their electron-donating nitrogen atoms, which facilitate strong adsorption onto metallic substrates. One such compound, 3-Diethylaminopropylamine (DEAPA), has recently gained attention for its dual functionality as both a surfactant and a corrosion inhibitor. This article explores the molecular characteristics, inhibition mechanisms, performance parameters, and practical applications of DEAPA in enhancing corrosion resistance across various environments.

Chemical Structure and Physical Properties

3-Diethylaminopropylamine (CAS Number: 99-97-8) is an aliphatic tertiary amine with the molecular formula C₉H₂₂N₂. Its IUPAC name is N,N-diethylpropane-1,3-diamine. Structurally, it features a three-carbon backbone with a primary amine group at one end and a diethyl-substituted tertiary amine at the other. This bifunctional architecture enables versatile reactivity and surface interaction capabilities.

The molecule’s amphiphilic nature—possessing both hydrophilic (amine groups) and hydrophobic (alkyl chains)—allows it to act as a surface-active agent, promoting uniform dispersion in aqueous systems while enabling effective interfacial adsorption on metal surfaces.

Mechanism of Corrosion Inhibition

Corrosion in aqueous environments typically proceeds via electrochemical reactions involving anodic metal dissolution and cathodic hydrogen evolution or oxygen reduction. For iron and steel substrates, the general process can be summarized as:

Anode:
Fe → Fe²⁺ + 2e⁻

Cathode (acidic medium):
2H⁺ + 2e⁻ → H₂

In neutral or alkaline media, oxygen reduction dominates:
O₂ + 2H₂O + 4e⁻ → 4OH⁻

Organic inhibitors like DEAPA interfere with these reactions primarily through adsorption onto the metal surface, forming a barrier that impedes ion and electron transfer. Adsorption can occur via:

1. Physisorption: Electrostatic interaction between protonated amine groups (in acidic media) and negatively charged metal surfaces.
2. Chemisorption: Donation of lone pairs from nitrogen atoms to vacant d-orbitals of iron, forming coordinate covalent bonds.
3. Film formation: Aggregation into micellar structures or polymeric networks that cover large surface areas.

Studies using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization indicate that DEAPA predominantly acts as a mixed-type inhibitor, affecting both anodic and cathodic processes, though with a slight preference toward cathodic suppression (Zhang et al., 2020).

Performance Evaluation in Different Media

1. Acidic Environments (HCl Solutions)

Hydrochloric acid is widely used in industrial pickling and descaling operations, but it aggressively attacks carbon steel. DEAPA has shown high inhibition efficiency in such conditions.

A study conducted by Liu et al. (2021) evaluated DEAPA on Q235 carbon steel in 1 M HCl at temperatures ranging from 25°C to 60°C. Results are summarized below:

The decrease in efficiency at elevated temperature suggests partial desorption of the inhibitor, yet even under harsh conditions, DEAPA maintains over 89% protection. Thermodynamic analysis revealed negative values of ΔG°ads (−38.7 kJ/mol), indicating spontaneous and predominantly chemisorptive adsorption.

2. Neutral Chloride Solutions (Simulated Seawater)

Chloride-induced pitting corrosion is a major concern in offshore and marine applications. DEAPA was tested in a synthetic seawater solution (3.5% NaCl) using ASTM A36 steel.

Polarization data showed a shift in corrosion potential (Ecorr) from −680 mV (blank) to −610 mV (with 150 ppm DEAPA), accompanied by a significant reduction in corrosion current density (Icorr) from 4.2 μA/cm² to 0.67 μA/cm²—an inhibition efficiency of 84%.

The increase in polarization resistance (Rp) confirms the formation of a robust protective layer. Scanning electron microscopy (SEM) images revealed a smooth, homogeneous surface in inhibited samples, contrasting sharply with the deeply eroded morphology observed in control specimens.

3. Alkaline Cooling Water Systems

In closed-loop cooling systems, alkaline pH (8.5–9.5) is maintained to minimize scaling and general corrosion. DEAPA functions effectively in this regime due to its ability to remain unprotonated and interact via donor-acceptor mechanisms.

Field trials at a petrochemical plant in Shandong, China, introduced DEAPA at 25 ppm alongside zinc sulfate (5 ppm) as a synergistic treatment. Over six months, coupon weight loss measurements indicated a corrosion rate of 1.8 mpy for treated systems versus 8.3 mpy in untreated units—a 78.3% reduction.

Additionally, DEAPA exhibited biocidal properties against sulfate-reducing bacteria (SRB), reducing microbial counts by >90%, thus mitigating microbiologically influenced corrosion (MIC).

Synergistic Effects with Other Inhibitors

Combining DEAPA with other functional additives often enhances overall performance through cooperative interactions.

Notably, halide ions (especially I⁻) significantly boost DEAPA’s effectiveness by creating negatively charged sites on positively charged metal surfaces, facilitating stronger electrostatic attraction with protonated DEAPA molecules (Tang et al., 2019).

Surface Analysis and Characterization

Advanced analytical techniques have been employed to validate the adsorption behavior and film integrity of DEAPA.

X-ray Photoelectron Spectroscopy (XPS)

XPS analysis of mild steel after immersion in 1 M HCl with 200 ppm DEAPA revealed distinct N 1s peaks at 399.6 eV (free amine) and 401.8 eV (protonated amine), confirming both physisorption and chemisorption. An Fe 2p peak shift from 711.2 eV (unprotected) to 710.1 eV (protected) indicates reduced oxidation state, suggesting suppressed Fe²⁺ formation.

Atomic Force Microscopy (AFM)

AFM topography scans showed a dramatic reduction in surface roughness:

This near tenfold decrease in roughness confirms the formation of a dense, adherent protective layer.

Contact Angle Measurements

The wettability of the metal surface changed significantly upon DEAPA treatment. Untreated steel had a contact angle of ~65°, indicating hydrophilicity. After inhibitor application, the angle increased to ~105°, demonstrating hydrophobic character—a key indicator of effective surface coverage and water repellency.

Environmental and Safety Considerations

While DEAPA exhibits strong inhibition performance, its environmental footprint must be assessed. According to OECD 201 guidelines, DEAPA shows moderate toxicity to aquatic organisms:

• LC50 (96h, Danio rerio): 15.8 mg/L
• EC50 (48h, Daphnia magna): 12.3 mg/L

It is readily biodegradable (>60% in 28 days under aerobic conditions), reducing long-term ecological persistence. However, proper handling protocols are required due to its corrosive nature to eyes and skin (GHS Category 2).

Industrial formulations often encapsulate DEAPA in polymer matrices or use slow-release technologies to minimize dosage and environmental release.

Industrial Applications

Oilfield Acidizing

During matrix acidizing treatments, concentrated HCl is injected into wells to dissolve carbonate formations. DEAPA is added at 0.5–2% v/v to protect downhole tubulars. Field data from Daqing Oilfield (China National Petroleum Corporation) reported a 92% reduction in post-acidizing tubing failures when DEAPA was included in the formulation.

Boiler Water Treatment

In steam boilers operating above 100°C, DEAPA serves as an oxygen scavenger and pH buffer. Its volatility allows transport with steam, providing protection throughout the condensate system. It reacts with dissolved O₂ as follows:

4RNH₂ + O₂ → 2RN=NR + 4H₂O

This reaction pathway prevents oxygen pitting in return lines.

Concrete Reinforcement Protection

Carbonation and chloride ingress lead to depassivation of rebar in concrete. DEAPA-based migratory corrosion inhibitors (MCIs) are applied topically or incorporated into coatings. These low-molecular-weight amines diffuse through porous concrete and accumulate at the steel interface, restoring alkalinity and inhibiting rust propagation.

Laboratory tests at Tsinghua University showed that concrete specimens treated with DEAPA-containing sealers maintained chloride threshold levels 2.3 times higher than untreated controls after 180 days of exposure to 3.5% NaCl fog.

Comparative Performance with Other Amines

To contextualize DEAPA’s effectiveness, a comparative analysis with structurally related amines was conducted under identical test conditions (1 M HCl, 25°C, 200 ppm concentration):

DEAPA outperforms all counterparts due to its extended alkyl chain (enhancing hydrophobicity) and dual amine functionality (increasing binding sites). The diethyl substitution also increases electron density on the nitrogen, improving donor capacity.

Formulation and Dosage Guidelines

Optimal performance depends on correct formulation and dosing strategies. Below are recommended practices based on system type:

For batch processes, pre-filming procedures involving 2-hour immersion at double the operational dose are advised to ensure complete surface coverage before service initiation.

Challenges and Limitations

Despite its advantages, DEAPA presents certain limitations:

• Volatility: At elevated temperatures (>80°C), vapor loss may reduce residual concentration.
• Foaming: Due to its surfactant properties, foaming can occur in agitated systems; defoamers may be necessary.
• Compatibility: May react with strong oxidizers (e.g., hypochlorite) or precipitate with multivalent cations (Fe³⁺, Al³⁺).
• Color Development: Prolonged storage leads to yellowing due to oxidation, though this does not impair function.

Research is ongoing to develop DEAPA derivatives with improved thermal stability and reduced environmental impact, including quaternary ammonium variants and polymer-bound analogs.

Future Prospects and Research Directions

Emerging trends in corrosion science point toward smart, responsive inhibitor systems. DEAPA is being explored in stimuli-responsive nanocarriers, such as mesoporous silica nanoparticles (MSNs), which release the inhibitor only upon pH drop—a hallmark of localized corrosion onset.

Furthermore, computational modeling using density functional theory (DFT) has validated DEAPA’s high Fukui indices at nitrogen centers, predicting strong nucleophilic attack capability. Molecular dynamics simulations show favorable orientation parallel to the Fe(110) surface, maximizing contact area and adsorption energy.

Integration with IoT-based monitoring systems allows real-time adjustment of DEAPA dosing based on electrochemical noise and conductivity feedback, paving the way for autonomous corrosion management in critical infrastructure.

Conclusion (Omitted per Instruction)

(Note: As instructed, no concluding summary is provided.)