Dsm N.v.

Dsm IP Assets B.v.

Tjay Tjien Tjioe

Hubertus J M Slangen

Jozef Hubert Meessen

Eric Grolman

David E Best

Michal Kuczynski

Henricus Antonius Maria Duisters

Veronika M L J Aarts

Reinier Franciscus Petrus Grimbergen

Koert Liekelema

Process for the preparation of melamine, comprising a first mixing step in which at least two melamine-containing flows, originating from at least two different processes for the preparation of melamine, are brought into contact with each other, with a mixture being formed. In one embodiment, at least one melamine-containing flow contains melamine from a low-pressure gas-phase process for the preparation of melamine and at least one melamine-containing flow contains melamine from a high-pressure liquid-phase process for the preparation of melamine.

Process for the preparation of melamine

Process for increasing the capacity of a urea plant comprising a compression section, a high-pressure synthesis section, a urea recovery section, in which a urea melt is formed, and optionally a granulation section, the capacity of the urea plant being increased by the additional installation of a melamine plant and the urea melt from the urea recovery section of the urea plant being fed wholly or partly to the melamine plant and the residual gases from the melamine plant being returned wholly or partly to the high-pressure synthesis section and/or the urea recovery section of the urea plant.

Process for increasing the capacity of a urea plant

The invention relates to a method for contacting molten urea with a gas stream that contains ammonia and/or carbon dioxide, in which use is made of an additional stream the temperature of which differs from the temperature of the molten urea and/or the gas stream. The additional stream preferably contains ammonia. The method is preferably part of a process for the preparation of melamine.

Method for contacting molten urea with a gas stream

Multicrystalline melamine powder having a specific area of from 0.7-5 m /g, content of oxygen-containing components of less than 0.7 wt %, an APHA colour less than 17 and a melam content higher than 1.5 wt %. The multicrystalline melamine powder may be used in amino-formaldehyde resins.

Crystalline melamine and its use in amino-formaldehyde resins

Method for preparing melamine from urea via a high-pressure process in which solid melamine is obtained by transferring the melamine melt to an expansion vessel where the melamine melt is cooled by incorporated ammonia. Excess ammonia gas is added to the melamine melt to produce a gas/liquid mixture having a mass ratio of at least 0.01. This two-phase mixture is then sprayed via a spraying means into an expansion vessel, the expansion vessel having an ammonia environment with a reduced ammonia pressure. The melamine melt is cooled and solidified by the expansion and evaporation of the incorporated ammonia to form melamine powder. The melamine melt is thereby directly converted into a melamine powder after which the melamine powder is cooled further and the ammonia pressure is released.

Method for preparing melamine

A method for the production of melamine from urea via a high-pressure non-catalytic process in which molten urea is reacted to produce melamine, carbon dioxide, and ammonia, the by-product gases are separated from the melamine melt, and the melamine melt is treated with ammonia in a liquid-filled column to remove dissolved carbon dioxide, the treated melamine melt being solidified to produce high-purity melamine. In the liquid-filled column, or bubble column, the melamine melt is treated with between 0.02 and 3 tons of ammonia per ton of melamine, the bubble column being operated at a pressure of between 1 and 40 MPa and at a temperature between the melting point of melamine at prevailing pressure and 450&deg; C., with the residence time of the melamine melt in the bubble column being between 1 minute and 10 hours.

Method for preparing melamine from urea via a high-pressure process in which solid melamine is obtained by transferring the melamine melt coming from the reactor to a vessel where the melamine melt is cooled with an evaporating cooling medium. The melamine melt comes from the melamine reactor at a temperature between the melting point of melamine and 450&deg; C. and is sprayed into a cooling vessel, via spraying means, having an ammonia environment with an increased ammonia pressure and cooled by means of an evaporating cooling medium to form melamine powder. The melamine melt is thereby converted into melamine powder having a temperature of 270&deg; C. or below after which the ammonia pressure is released and the melamine powder is cooled, at least for part of the cooling range, by the powder being set in motion mechanically and being cooled directly or indirectly and, if necessary, the melamine powder is cooled further.

Method for preparing melamine from urea via a high-pressure process in which solid melamine is obtained by transferring the melamine melt coming from the reactor to a vessel where the melamine melt is cooled with an evaporating cooling medium. The melamine melt comes from the melamine reactor at a temperature between the melting point of melamine and 450&deg; C. and is sprayed into a cooling vessel, via spraying means, and cooled by means of an evaporating cooling medium to form melamine powder. The cooling vessel has an ammonia environment with an increased ammonia pressure. The melamine melt is thereby converted into melamine powder having a temperature of between 200&deg; C. and the solidification point of melamine. The melamine powder is then cooled to a temperature below 200&deg; C. with the powder mechanically agitated and being cooled directly or indirectly, after which the ammonia pressure is released and, if necessary, the melamine powder is cooled further.

Process for the preparation of melamine from urea via a high-pressure process in which dry melamine powder is obtained by transferring the melamine melt leaving the reactor to a vessel in which the melamine melt is cooled by means of ammonia characterized in that the melamine melt is sprayed into a cooling vessel and cooled by droplets of evaporating liquid ammonia which is sprayed into the same cooling vessel at a pressure above 0.1 MPa and a temperature between 50&deg; C. and the melting point of the melamine in the cooling vessel.

Method for preparing melamine from urea via a high-pressure process in which solid melamine product is obtained directly from the melamine melt by transferring the melamine melt into a product cooling unit where it is cooled with ammonia. The melamine melt from the melamine reactor has a temperature between the melting point of melamine and 450&deg; C. and is sprayed, via spraying means, into a product cooling vessel containing an ammonia environment with an increased pressure, where the melamine melt solidifies to form melamine powder. The melamine powder, having a temperature of between 200&deg; C. and the solidification point of melamine, is maintained under an increased ammonia pressure for a contact time of between 6 seconds and 5 hours at a pressure. During this contact time, the powder melamine product may be maintained in the product cooling vessel, or a series of vessels, at a virtually constant temperature or may be cooled further to a temperature above 200&deg; C.

Multicrystalline melamine powder having the following properties:

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Sittard, Netherlands

Tjay Tjien Tjioe