Abstract: Multicrystalline melamine powder having a specific area of from 0.7-5 m2/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.

Abstract: 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.

Abstract: 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° C., with the residence time of the melamine melt in the bubble column being between 1 minute and 10 hours.

Abstract: The invention relates to multicrystalline melamine powder having the following properties:

Abstract: Process for the preparation of melamine comprising a reaction step, a gas/liquid separation step in which a melamine melt is separated from off-gases, a stripping step and a cooling step, in which the stripping step is carried out at a pressure of between 5 MPa and 17 MPa and a temperature of between 330° C. and 450° C. and in which the melamine melt obtained in the preceding steps is pressurised in the cooling step to a pressure of between 15 and 35 MPa, with the pressure in the cooling step being higher than the pressure in the stripping step and with the temperature in the cooling step being adjusted between the melting point of the urea melt at the prevailing pressure and 365° C.

Abstract: 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.

Abstract: 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° C., with the residence time of the melamine melt in the bubble column being between 1 minute and 10 hours.

Abstract: 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° 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° 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.

Abstract: 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° 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° C. and the solidification point of melamine. The melamine powder is then cooled to a temperature below 200° 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.

Abstract: 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° C. and the melting point of the melamine in the cooling vessel.

Abstract: 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° 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° 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° C.

Abstract: Multicrystalline melamine powder having the following properties:specific surface area: 0.7-5 m.sup.2 /glevel of oxygen-containing components <0.7 wt %color APHA less than 17melamine: >98.5 wt %melam: <1.3 wt %Multicrystalline melamine powder obtainable via a high-pressure process in which solid melamine is obtained by the melamine melt being transferred to a vessel where the melamine melt is cooled with an evaporating cooling medium, the melamine melt having a temperature between the melting point of melamine and 450.degree. C. being treated with 0.1-15 mol of ammonia per mole of melamine and then being sprayed via spraying means and cooled with an evaporating cooling medium within a vessel in an ammonia environment at an ammonia pressure of 0.1-25 MPa, the melamine melt being converted into melamine powder having a temperature between 200.degree. C. and the solidification point of melamine, the melamine powder then being cooled to a temperature below 50.degree. C.

Abstract: Cadmium is removed from an acid, phosphate-containing aqueous medium with the aid of an anion exchanger, in which process, during the removal, iodide or bromide ions are present in a quantity of 100-6000 ppm calculated with respect to the acid phosphate-containing aqueous medium.