Melamine Manufacturing Process

Melamine is a white powder organic base which is mainly used to form resins with formaldehyde (MF) and formaldehyde-urea (MUF), extensively used as coatings for furniture, textiles and paper or as plastizers.

Melamine is obtained from Urea in two stages: First the urea decomposition to form isocyanic acid and ammonia, and afterwards a formation step yielding melamine and carbon dioxide. The overall process is endothermic.

Since urea is the feedstock for melamine manufacturing process, and ammonia by-product is obtained in the latter, the recycle of the off-gas to the Urea plant is arranged for efficient feedstock use:

The main characteristics of the continuous processes actually employed are listed in the following table:

High Pressure Synthesis HP	Low Pressure Synthesis LP
80-150 bar, 400ºC	<10 bar, 400ºC
No Catalyst	Al, Ti oxides
Reaction in Liquid phase	Reaction in Gas phase

The LP process in vapour phase is a catalytic process in which the decomposition of molten urea and the synthesis of melamine takes place in a fluidized catalytic reactor. The effluent is quenched with water (recovering the product in a slurry) or with cold gas, and the off gas is sent to the recovery and treatment unit. The slurry (in case of liquid quenching) is driven through a filter (to remove catalyst fines) and finally to a crystallization equipment, where the final product is obtained after a centrifuge and a dryer with a purity above 99,8%. In the following process flow diagram by Lurgi, the quenching is carried out with gas and therefore there is no drying unit:

Gas Quench LP Melamine by Lurgi.

The HP process in liquid phase (or Shortened Liquid Phase SLP) requires no catalyst, reaches similar purities as  in LP, and consists of a high pressure section, in which molten urea is converted to Melamine in the reactor followed by a quenching step and the recovering of the off gas through a stripper. In the low pressure section the hydrolyser and filtration lead to a crystallization unit from which the Melamine slurry is dried and stored.. The figure below shows schematically these steps:

Liquid Quench HP Melamine by Eurotecnica

The advantage of this process is that there are no concerns regarding the catalyst and fines, and that the dry off gas at high pressure enables it to be easily integrated in a Urea plant. Due to the high pressures involved, this technology is more suitable for low production capacities (Melaf-4, OCI, Geleen 30kton/a) whereas the low pressure process is preferred for large production capacity (Melaf-2, OCI, Geleen, 120 kton/a)

Carlos Arnaiz