Process for melamine purification

Patent metadata

Field	Value
Publication number	US-11840520-B2
Application number	US-202117368430-A
Country	US
Kind code	B2
Filing date	Jul 6, 2021
Priority date	Jul 22, 2016
Publication date	Dec 12, 2023
Grant date	Dec 12, 2023

Abstract

A process for the purification of a melamine melt ( 5 ) containing melamine and by-products, comprising the steps of: (a1) In quenching of said melamine melt; (a2) decomposition of by-products with alkali, providing an alkaline aqueous solution of melamine ( 26 ); (b) stripping of said alkaline aqueous solution of melamine ( 26 ); (c) crystallization of melamine with a first alkali-containing solution ( 6 b ) and separation of solid melamine ( 7 ) from a mother liquor ( 8 ); (d) treatment of said mother liquor, providing a waste water stream ( 11 ) containing carbonates; (e) decomposition of at least part of the carbonates contained in said waste water stream ( 11 ) into carbon dioxide and alkali, providing a second alkali-containing aqueous solution ( 30 ); (f) recycle of at least part of said alkali-containing aqueous solution ( 30 ) to at least one of said steps (a1), (a2) and (c).

First claim

What is claimed is:

1. A melamine purification section of a high-pressure melamine plant comprising:
a quencher, receiving a melamine melt containing melamine and by-products;
a decomposer, wherein at least part of said by-products are decomposed by means of alkali, providing an alkaline aqueous solution of melamine;
a stripper fed with said alkaline aqueous solution of melamine and with a stripping medium, providing a stripped melamine solution;
a crystallizer fed with said stripped melamine solution and a first alkali-containing aqueous solution, wherein melamine is separated from a melamine mother liquor;
a treatment unit for at least part of said mother liquor, providing an aqueous solution containing carbonates;
a decomposition unit of at least part of the carbonates contained in said aqueous solution into carbon dioxide and alkali, providing a second alkali-containing aqueous solution and a water stream;
at least one line for recycling at least a portion of said second alkali-containing aqueous solution provided by the decomposition unit to at least one of the quencher, the decomposer and the crystallizer.

2. A melamine purification section of a high-pressure melamine plant comprising:
a quenching/decomposition unit receiving a melamine melt containing melamine and by-products, wherein at least part of said by-products are decomposed by means of alkali, providing an alkaline aqueous solution of melamine;
a stripper fed with said alkaline aqueous solution of melamine and with a stripping medium, providing a stripped melamine solution;
a crystallizer fed with said stripped melamine solution and a first alkali-containing aqueous solution, wherein melamine is separated from a melamine mother liquor;
a treatment unit for at least part of said mother liquor, providing an aqueous solution containing carbonates;
a decomposition unit of at least part of the carbonates contained in said aqueous solution into carbon dioxide and alkali, providing a second alkali-containing aqueous solution and a water stream;
at least one line for recycling at least a portion of said second alkali-containing aqueous solution provided by the decomposition unit to at least one of the quenching/decomposition unit and the crystallizer.

3. The purification section according to claim 1 , wherein said decomposition unit is an electrolytic cell.

4. The purification section according to claim 1 , comprising one or more lines for recycling at least a portion of said water stream to said melamine plant.

Assignees

• Casale Sa

Inventors

• Scotto Andrea
• Gamba Simone

Classifications

• C07D251/62 Primary

  Purification of melamine · CPC title

• C07D251/60 Primary

  from urea or from carbon dioxide and ammonia · CPC title