Process for the purification of melamine and relative equipment

1. An improved process for the purification of melamine obtained by synthesis from urea, comprising:

a) bringing raw melamine containing impurities of polycondensates and other by-products of the synthesis reaction, into solution, obtaining a solution/suspension in which the insoluble products are dispersed;

b) subjecting the solution/suspension thus obtained to treatment to remove the CO 2 dissolved, reducing its concentration to values lower than 0.5% by weight;

c) treating the solution/suspension obtained in step b), having a content of CO 2 lower than 0.5% by weight, with ammonia in a quantity ranging from 1 to 4% at a temperature ranging from 110 to 180° C.;

putting the solution leaving step c) in contact with a solid catalyst, under the same conditions as step c).

2. The process according to claim 1 , wherein the solid catalyst is a bed of activated carbon.

3. The process according to claim 1 , wherein phase b) for the removal of the CO 2 dissolved is effected by stripping with an inert gas.

4. The process according to claim 1 , further comprising a mechanical filtration of the solution leaving step c), before the treatment of step d).

5. The process according to claim 1 , further comprising a mechanical filtration of the solution leaving d).

6. The process according to claim 1 , wherein the solution leaving d) has a concentration of polycondensates lower than 100 ppm by weight.

7. The process according to claim 1 , wherein the solution/suspension obtained in b) is treated at a temperature of from 130 to 140° C.

8. The process according to claim 3 , wherein the inert gas is water vapor.

9. The process according to claim 1 , wherein during the treating (c) the amount of melamine hydrolyzed to form oxyaminotriazines is less than 1% by weight.

10. The process according to claim 1 , wherein the treating (c) is carried out in a column.

11. The process according to claim 1 , wherein the contacting after the treating (c) eliminates melamine polycondensates from the solution/suspension.

12. The process according to claim 1 , wherein the treating (c) converts over 70% of melamine polycondensates present in the solution/suspension into melamine.

13. The process according to claim 1 , wherein the treating (c) is carried out at a temperature of 110-130° C.

14. A process for purifying a melamine-containing composition, comprising:

(a) dissolving the melamine composition in water to form a first melamine solution comprising melamine, one or more melamine polycondensates and one or more by-products;

(b) reducing the concentration of CO 2 in the first melamine solution to an amount of lower than 0.5% by weight to form a reduced-CO 2 melamine solution;

(c) treating the reduced-CO 2 melamine solution with ammonia in an amount of from 1 to 9% by weight at a temperature of from 130 to 140° C. to form a melamine-ammonia solution;

(d) contacting the melamine-ammonia solution formed in (c) with an activated carbon bed;

wherein the treating (c) converts over 70% of the melamine polycondensates to melamine, and the contacting (d) eliminates melamine polycondensates from the melamine-ammonia solution.

15. The process according to claim 14 , wherein the loss of melamine due to hydolysis to form oxyaminotriazine is less than 1% by weight.