Tech Blog

How to control the product quality of melamine

Melamine powder is a widely used organic chemical intermediate that appears as a white, odorless, and low-toxicity powder. Its appearance quality has almost no visual difference, so strict quality grading and process control are crucial to ensure compliance with industrial standards and final performance. This article summarizes mature methods for quality of melamine control based on long-term industrial production experience, covering key influencing factors and operational guidelines.

Why is the quality of melamine important?

Melamine powder comes in various grades and applications, and non-compliant products are often affected by excessive moisture, high ash content, discoloration, high turbidity, or impurities, resulting in economic losses. Stable, high-quality melamine directly enhances product competitiveness and reduces waste.

Low ash content and turbidity can prevent defects in transparent coatings and molded products.

Controlled Color (APHA) is crucial for white or light colored finished products.

The appropriate pH value can affect storage stability and compatibility with other chemicals.

Unqualified quality leads to:

Poor resin fluidity and gel time change
Final product discoloration or turbidity
Customer complaints and contract loss
Reduce prices to achieve

Quality indicators of melamine powder

Item	Premium Grade	First Class
Melamine Content, % ≥	99.8	99.0
Moisture, % ≤	0.1	0.2
Ash Content, % ≤	0.03	0.05
Color (APHA) ≤	20	30
Turbidity (Kaolin) ≤	20	30
pH Value	7.5–9.5	7.5–9.5
Appearance	White free‑flowing powder	White free‑flowing powder

8 key factors affecting the quality of melamine

1.Purity of urea

In the production of melamine powder, if there is too much oil and metal ions in the urea solution, it can cause the activated carbon bed in the carbon bed reactor to be penetrated, resulting in excessive product color. The oil content in the urea solution must be strictly controlled.

2.Process Circulating Water Volume

To ensure sufficient process circulation water volume corresponding to the reactor load, control the OAT at a lower level than the water volume. The optimal circulation amount must consider two factors: the melamine content in the solution of the rapid cooling section and the consumption of utilities. The optimal melamine concentration in the feed to the gas stripping tower is approximately 8% to 9%.

3.Ammonia dosage for purification system

It is necessary to strictly control the ammonia ratio in the purification system to maintain it at 12% to 14% to ensure the ammonia concentration in the refining system. If the ammonia concentration is too low, some undecomposed impurities will precipitate during crystallization, resulting in unqualified melamine. Excessive concentration can cause overpressure in the crystallizer.

4.Working status of online filters and carbon bed reactors

The functions of online filters and carbon bed reactors are to remove impurities and colored substances from melamine solutions. If performance decreases or the carbon rod is damaged, it will result in excessive chromaticity and produce unqualified melamine. Therefore, it is necessary to regularly inspect and replace the carbon rod.

5.Temperature of dryer

If the dryer temperature is too low, the product’s moisture content will be too high. The dryer temperature must be maintained above 80℃.

6.Quantity of CO₂ added to the second crystallizer of OAT

Adding carbon dioxide to the second crystallizer of OAT adjusts the solution’s pH. The optimal pH value for the feed is 7-7.5, which can be achieved by adjusting the CO₂ flow rate injected into the crystallizer.

7.Situation of filtrate in OAT filter

The turbidity of the filtrate indicates that the filtration effect of OAT is poor. There will be a large amount of OAT in the solution that has not been filtered out, leading to a high OAT content in the circulating process water and excessive turbidity in the product, resulting in unqualified products.

8.Non-process factors

If the airflow blower filter is misaligned or fails, impurities in the air will enter the system, producing small black spots that affect the appearance quality.

In addition, non-standard operations in packaging positions may also result in unqualified product inspections upon arrival. Melamine powder has hygroscopicity. Exposure to humid air can increase moisture content (over 0.1%), which later leads to clumping and poor flow.