Can DEHA be used at high temperatures?

Diethylhydroxylamine (DEHA) is an effective oxygen scavenger and metal passivator used primarily in boiler water treatment. Its performance at high temperatures depends on several factors:

1. Temperature Limits of DEHA

Effective Range:

Optimal Performance: 60–150°C (140–300°F) – Works efficiently in low- to medium-pressure boilers.

Upper Limit: Up to 200°C (392°F) for short-term exposure, but effectiveness decreases due to thermal decomposition.

Beyond 200°C: Not recommended; decomposes rapidly, losing oxygen-scavenging ability.

2. Comparison with Other Oxygen Scavengers

Oxygen Scavenger Max Temp (°C) Notes

DEHA 150–200 Best for low/medium-pressure boilers.

Hydrazine (N₂H₄) 300+ High-pressure boilers, but toxic.

Carbohydrazide 250 Less toxic, slower reaction than DEHA.

Erythorbic Acid 120 Low-temp systems only.

3. Key Considerations for High-Temp Use

Boiler Pressure:

<900 psi (60 bar): DEHA is suitable.

>900 psi: Switch to hydrazine alternatives (e.g., carbohydrazide).

Reaction Speed:

DEHA reacts faster at >100°C, but decomposes if overheated.

Passivation:

Forms protective magnetite (Fe₃O₄) layer on steel, but high temps may disrupt this process.

4. Recommended Dosage at High Temperatures

Normal Conditions (60–150°C): 0.1–0.5 mg/L per 1 mg/L dissolved O₂.

Near Upper Limit (150–200°C): Increase dosage by 20–30% to compensate for thermal loss.

5. Advantages & Limitations

Pros Cons

Non-toxic (safer than hydrazine). Less effective above 200°C.

Fast reaction with O₂. Not suitable for ultra-high-pressure boilers.

Passivates metals (reduces corrosion). May decompose into volatile byproducts.

6. Alternatives for Extreme Temperatures

>200°C: Use carbohydrazide or hydroquinone-based scavengers.

>300°C: Hydrazine (where permitted) or catalyzed sulfite blends.

Conclusion

DEHA is effective up to 150–200°C, making it suitable for low- and medium-pressure boilers. For high-pressure/high-temperature systems (>200°C), switch to more stable alternatives like carbohydrazide. Always monitor residual DEHA and oxygen levels to ensure optimal performance.

Recommendation:

For <150°C: DEHA is ideal (safe, efficient).

For 150–200°C: Use DEHA with increased dosing.

For >200°C: Choose a high-temp oxygen scavenger.