US4408046A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Process of preparing melamine
Assignee: DSM BV
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Filing: 1982-04-16
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Granted: 1983-10-04
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Expires: 2002-04-16
Abstract
Abstract An improved process for the preparation of melamine from urea or thermal decomposition products thereof. A melamine containing reaction mixture is cooled with an aqueous medium to form an aqueous product stream containing melamine and reaction by-products. Product melamine is separated from the aqueous product stream leaving a residual aqueous stream which is recycled into the process. A portion of this residual aqueous stream still containing reaction by-product is treated to remove by-products therefrom prior to being recycled to the process.
Inventors
- 👤 Rudolf van Hardeveld
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 07:49
CPC Classifications
C; C07; C07D; C07D251/00; C07D251/02; C07D251/12; C07D251/26; C07D251/40; C07D251/54; C07D251/56; C07D251/60
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
93 words
In a process for the preparation of melamine from urea or thermal decomposition products thereof wherein a reaction mixture is cooled with an aqueous medium to form an aqueous product stream containing melamine and reaction by-products, whereafter product melamine is separated from said aqueous product stream leaving a residual aqueous stream which is recycled into said process, the improvement wherein a portion of said residual aqueous stream still containing reaction by-products is separated from the remainder of such stream and is treated to remove by-products therefrom prior to being recycled to said process.
Claim 2
Dependent Claim
93 words
In a process for the preparation of melamine from urea or thermal decomposition products thereof wherein a reaction mixture is cooled with an aqueous medium to form an aqueous product stream containing melamine and reaction by-products, whereafter product melamine is separated from said aqueous product stream leaving a residual aqueous stream which is recycled into said process, the improvement wherein a portion of said residual aqueous stream still containing reaction by-products is separated from the remainder of such stream and is treated to remove by-products therefrom prior to being recycled to said process.
Claim 3
Dependent Claim
24 words
The process of claim 1 wherein the portion of said residual aqueous stream treated constitutes between about 5 and 50 percent of said stream.
Claim 4
Dependent Claim
24 words
The process of claim 2 wherein the portion of said residual aqueous stream treated constitutes between about 8 and 15 percent of said stream.
Claim 5
Dependent Claim
46 words
The process of claim 1, 2, or 3 wherein the portion of said residual aqueous stream is treated by lowering its pH to a level of between about 7.5 and 9.0 to form a precipitate of said by-products, and said precipitate is removed therefrom by filtration.
Claim 6
Dependent Claim
16 words
The process of claim 4 wherein said pH is lowered by the addition of carbon dioxide.
Claim 7
Dependent Claim
34 words
The process of claim 1 wherein the treated portion of said residual aqueous stream is recycled into said process as at least a part of said aqueous medium used for cooling said reaction mixture.
Claim 8
Dependent Claim
33 words
The process of claim 1 wherein the remainder of said residual aqueous stream is recycled into said process as at least a part of said aqueous medium used for cooling said reaction mixture.
Claim 9
Dependent Claim
46 words
The process of claim 1 wherein said reaction mixture is cooled with said aqueous medium to form an aqueous suspension of melamine particles, whereafter said suspension is diluted with recycled residual aqueous stream and said melamine particles substantially all dissolved to form said aqueous product stream.
Claim 10
Dependent Claim
19 words
The process of claim 8 wherein said suspension is diluted with the treated portion of said recycled aqueous stream.
Claim 11
Dependent Claim
20 words
The process of claim 8 wherein said suspension, after dilution, is heated to promote the dissolution of said melamine particles.
Claim 12
Dependent Claim
44 words
The process of claim 8, 9, or 10 wherein melamine is crystallized and removed from said aqueous product stream, and a portion of the residual aqueous stream thus formed, substantially free of solid melamine particles, is subjected to said treatment for removal of by-products.
Claim 13
Dependent Claim
21 words
The process of claim 11 wherein said aqueous prouduct stream is filtered prior to said crystallization to remove particles suspended therein.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1986-10-03 | 1987-04-04 | 1987-10-04 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1990-10-03 | 1991-04-04 | 1991-10-04 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1994-10-03 | 1995-04-04 | 1995-10-04 | $7700.00 | Window Closed / Lapsed |