Tech Blog

Factors Affecting color of High Pressure Melamine

Melamine is a critical organic chemical intermediate widely used in resins, flame retardants, and construction materials. In high pressure melamine production (e.g., the 4th-generation technology from Eurotecnica), chromaticity is a key quality indicator that directly impacts product grade and market competitiveness—especially for export-oriented products. This article details root causes, data validation, and practical solutions for chemical plant operators, process engineers, and quality control professionals.

Overview of High Pressure Melamine & Chromaticity Significance

High-Pressure Process Advantages

The 4th-generation high pressure melamine process (adopted by Xinjiang Yihua) offers high product purity, continuous production, energy efficiency, and high automation—critical for large-scale industrial production.

Why Chromaticity Matters

Chromaticity reflects melamine’s internal purity; excessive chromaticity indicates impurities (e.g., metal ions from corrosion), reducing the quality of downstream products like melamine-formaldehyde resin.

Meeting national standard GB/T 9567-2016 is mandatory for domestic sales and exports—stable chromaticity ensures compliance and market acceptance.

Key Factors Affecting color of High Pressure Melamine

Through systematic testing and data analysis, three non-critical factors were ruled out, while system corrosion was confirmed as the root cause:

Non-Critical Factors (Minimal Impact)

Analytical Detection Process

Testing Method: Chromaticity is measured via the formaldehyde water dissolution test (GB/T 9567-2016), where formaldehyde pH is a potential variable.
Data Validation: When formaldehyde pH was stabilized at 2.9–3.0, melamine chromaticity fluctuated irregularly (8.65–16.11), indicating that the detection process did not cause high chromaticity.

Purification System

System Configuration: Carbon rods and carbon bed filters for decolorization.
Performance Verification: Newly replaced activated carbon had iodine adsorption value (1201 mg/g), phenol adsorption value (75 mg/g), and methylene blue adsorption value (120 mg/g)—all within standard ranges. The system reduced chromaticity from 31 (inlet) to 17 (outlet), confirming effective purification.

System OAT Content

OAT Role: Oxiaminothriazine (OAT) is a byproduct; excessive levels cause chromaticity/turbidity spikes.
Data Validation: Turbidity remained stable at ~1 NTU while chromaticity fluctuated (14.95–19.64), indicating low OAT content—no correlation with chromaticity.

Primary Factor: System Corrosion

Metal Ion Analysis in Melamine Products

		Cr	Ni	Zn	Cu	Ba	Mn
1 (Normal)	15.62	0.03	0.03	0.05	0.03	0.01	0.02
2 (High Chromaticity)	200.97	0.51	1.29	1.93	1.29	0.18	0.56

Critical Finding: Nickel content in high-chromaticity samples was 43x higher (1.29×10⁻⁶ vs. 0.03×10⁻⁶), with other metal ions also significantly elevated. Nickel’s corrosion resistance means high levels indicate severe equipment degradation.

Corrosion Tracking in System Equipment

Long-term monitoring of nickel content in key equipment showed a steady increase, with chromaticity rising proportionally (Figure 1):

Severely Corroded Equipment: Quench towers (nickel content up to 2.67×10⁻⁶), tail gas concentration towers (up to 1.85×10⁻⁶).
Correlation: Linear positive correlation between system nickel content and product chromaticity—higher corrosion = higher chromaticity.

Solutions to Reduce System Corrosion & Chromaticity

Equipment & Material Quality Control

Material Selection: Use corrosion-resistant materials for key equipment/pipelines; ensure welding with matching corrosion-resistant welding wires.
Installation Quality: Minimize defects and residual stress during processing/installation to reduce corrosion points.

Strengthen Corrosion Monitoring

Regular Testing: Conduct periodic equipment thickness measurements and nickel content analysis. Immediately investigate and address rising nickel levels or corrosion signs.
Key Equipment Focus: Prioritize monitoring quench towers and tail gas concentration towers (high corrosion risk).

Optimize Operating Parameters for Critical Equipment

Quench Tower

Control the middle-section water flow at 12 t/h.
Maintain middle-section water temperature at ~165℃.
Adjust the passivation airflow to 30–40 kg/h.
Keep the minimum liquid level at 40%.

Tail Gas Separator

Control the liquid level at 60% to avoid excessive effusion
in inlet pipelines.
Add 2 passivation air injection points at the inlet/outlet.

Tail Gas Concentration Tower

Maintain top temperature at 140–146℃.
Control the passivation air flow at 35 kg/h.

Wastewater Stripper

Stabilize the top temperature at 137–141℃.
Keep the bottom temperature at 162–165℃.

FAQ

Q1: Why does nickel content correlate with chromaticity?

A1: Nickel is released from corroded equipment (e.g., stainless steel components). Metal ions act as colorants, directly increasing melamine’s chromaticity—higher nickel = more intense discoloration.

Q2: Can purification systems remove metal ions from corrosion?

A2: No. Carbon-based purification systems primarily adsorb organic impurities rather than metal ions. Controlling corrosion at the source is the only effective solution.

Q3: How to quickly determine if chromaticity spikes are due to corrosion?

A3: Test melamine for nickel content. If nickel >0.5×10⁻⁶, corrosion is the root cause; investigate key equipment (quench towers, concentration towers) for degradation.

Q4: Does OAT content ever affect chromaticity?

A4: Only at extremely high levels (>5×10⁻⁶), which is rare in well-operated high-pressure processes. Stable turbidity (>1 NTU) indicates OAT-related chromaticity issues.

conclusion

For high pressure melamine powder, system corrosion is the dominant factor driving chromaticity fluctuations—metal ions (especially nickel) from corroded equipment directly degrade product color. Analytical detection, purification systems, and OAT content have negligible impacts.

By implementing strict material quality control, regular corrosion monitoring, and optimized operating parameters for critical equipment (quench towers, concentration towers), plants can effectively reduce corrosion, stabilize nickel content, and maintain low chromaticity. This ensures product quality meets national/export standards, enhancing market competitiveness. As high pressure melamine production scales, corrosion control will remain indispensable for consistent chromaticity and product reliability.