DE1135482B - Process for the production of melamine - Google Patents

Description

GERMAN

PATENT OFFICE

St 17602 IVd / 12p

REGISTRATION DATE: MARCH 21, 1961

NOTICE
THE REGISTRATION
AND ISSUE OF THE
EDITORIAL: AUGUST 30, 1962

The invention relates to an improved method for producing melamine by heating Urea and / or one of the products resulting from the thermal decomposition of urea such. B. Biuret.

As is known, melamine is produced by heating urea under pressure - the partial pressure of NH ₃ and CO _{2 being a} minimum of 70 at and the temperature 300 to 450 ° C - in the presence of a catalyst such as phosphoric acid or phosphorus pentoxide or salts of Phosphoric acid in an amount of 0.1 to 10 mol percent, calculated on the starting material (U.S. Patent 2550 659).

It is also known to use urea as a starting material in the production of MeI-amine, which in the presence of NH ₃ and SO ₂ at temperatures of 200 to 360 ° C under an NH ₃ pressure of 14 to 70 atm and in the presence of a catalyst is heated, which consists of an oxide, salt or an acid of at least one element from the group consisting of phosphorus, arsenic or antimony in an amount of 0.01 to 10 percent by weight, calculated on the reactants (see U.S. Patent 2 902488).

It is also known that boron and boron compounds, such as boric acid, boron oxide, boron fluoride, metaborate and boron phosphate, as catalysts, significantly promote _{the production of melamine on the basis of urea, NH 3} and SO _{2 (US Pat. No. 2,857,381).}

A disadvantage of these known methods of preparation is that the reaction is always under proportionally high pressure is to be carried out, which places high demands on the apparatus have to.

It has now been found that melamine can also be produced at normal atmospheric pressure if urea and / or a product formed by thermal decomposition of urea, such as, for. B. Biuret, heated to a temperature of a minimum of 220 ° C in the presence of NH ₃ and in contact with a catalyst consisting of boron phosphate or aluminum phosphate. Normal atmospheric pressure should be understood here as a pressure of 1 at in addition to the pressure required to overcome the usual resistances in the apparatus and the lines. Usually this pressure will not exceed 1 at.

It has been mentioned earlier that melamine can be produced at atmospheric pressure by heating urea in the presence of NH _3. Process for the production of melamine

Applicant:
Stamicarbon NV, Heerlen (Netherlands)

Representative: Dr. F. Zumstein,

DipL-Chem. Dr. rer. nat. E. Assmann

and Dipl.-Chem. Dr. R. Koenigsberger,

Patent Attorneys, Munich 2, Bräuhausstr. 4th

Claimed priority:
Netherlands of March 23, 1960 (No. 249 75Oi

Johannes Joseph Steggerda, Geleen (Netherlands),
has been named as the inventor

could, if this heating takes place in the presence of a porous solid with a large internal surface area of 180 to 650 m ² / g, as z. B. is the case with silica gel (see UK Patent 767,344).

The catalysts used according to the invention do not have a large internal surface; the latter is 16 m ² / g for boron phosphate (BPO ₄ ) and 54 m ² / g for aluminum phosphate.

For the preparation, one can best use a method according to which the starting material is _{fed to a catalyst bed held by NH 3} in a fluidized bed, while the gases formed therein are then passed through a fixed catalyst bed. The ratio of NH ₃ to urea can be, for example, 1.5 to 5 m ^{3 of} NH ₃ per kg of urea, and the amounts by weight of catalyst in the fixed bed are, for. B. 10 to 20 times larger than in the fluidized bed.

The melamine yield is 90% of the theoretically possible amount.

209 638/399

Claims (1)

PATENT CLAIM: Process for the production of melamine, by heating urea and / or a product obtained by thermal decomposition of urea, characterized in that the heating in the presence of a catalyst consisting of boron phosphate or aluminum phosphate at atmospheric pressure and in the presence of ammonia and while maintaining a temperature at a minimum of 220 ° C. A priority document was displayed when the registration was announced. © 209 638/399 8.62