Method for preparing melamine
AssigneeDsm N.V.
InventorTjay T. Tjioe
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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.
Claims19
Method for preparing melamine comprising reacting urea in the melt, separating the resulting melamine melt from gaseous products formed in the reaction, treating said melamine melt in a column with ammonia in order to remove the carbon dioxide dissolved in the melamine melt, the amount of ammonia used in the melt being between 0.02 and 3 tons per ton of melamine, the column being operated at a pressure of between 1 and 40 MPa and the temperature in the column being between the melting point of melamine at prevailing pressure and 450° C., and the residence time of the melamine melt in the column being between 1 minute and 10 hours, and wherein said column is a bubble column filled with a packing or divided into a plurality of compartments or provided with both packed regions and a plurality of compartments, and wherein the bubble column has a liquid hold-up of a least 35%, said liquid hold-up being defined as:
- liquid hold-up = (dynamic liquid volume in stripping zone) (column volume in stripping zone) .
Dependencies are inferred from the claim text.