US3723430A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method for reclamation of melamine waste gas
Assignee: Nissan Chemical Corp
•
Filing: 1970-10-28
•
Granted: 1973-03-27
•
Expires: 1990-10-28
Abstract
Abstract Method for utilization of melamine waste gas in high pressure liquid phase melamine synthesis using urea or urea-thermal decomposition product as initial material, - characterized by synthesizing urea under the melamine synthesis pressure directly from melamine waste gas obtained as by-product in the synthesis or, depending on the case, with water or aqueous ammonium carbonate solution added thereto, and introducing the obtained lower pressure urea synthesis solution into decomposing stage of main urea synthesis.
Inventors
- 👤 R Kokubo
- 👤 K Yokomichi
- 👤 Y Takakuwa
- 👤 K Takahashi
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 21:46
CPC Classifications
C; C07; C07D; C07D251/00; C07D251/02; C07D251/12; C07D251/26; C07D251/40; C07D251/54; C07D251/56; C07D251/60; C07D251/28
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
32 words
then passing the urea synthesis solution reaction product obtained from the low pressure urea synthesizing reactor into an ammonium carbamate decomposition stage used in combination with a high pressure urea synthesis tower.
Claim 2
Dependent Claim
23 words
The method of claim 1, in which water or aqueous ammonium carbonate solution is also added to said low pressure urea synthesizing reactor.
Claim 3
Dependent Claim
39 words
The method of claim 1 in which excess ammonia is separated by distillation from said reactant product obtained in said low pressure urea synthesizing reactor prior to the introduction of said reactant product into the ammonium carbamate decomposition stage.
Claim 4
Dependent Claim
40 words
The method of claim 1, in which said ammonium carbamate decomposition is preliminarily effected by making use of heat generated within the low pressure urea synthesizing reactor, prior to introduction of said reactant product into the ammonium carbamate decomposition stage.
Claim 5
Dependent Claim
24 words
The process of claim 1 in which the pressure in the melamine reactor and in the low pressure urea synthesizing reactor are 80-150 Kg/cm2.
Claim 6
Dependent Claim
31 words
The process of claim 5, in which the pressure in the ammonium carbamate decomposition stage is 15-20 Kg/cm2 and the pressure in the high pressure urea synthesis tower is 180-300 Kg/cm2.
Claim 7
Dependent Claim
24 words
Method of reclamation of melamine waste gas as claimed in claim 1 in which the low pressure urea synthesis temperature is more than 160*C.
Claim 8
Dependent Claim
25 words
Method for reclamation of melamine waste gas as claimed in claim 7 in which MH3/CO2 (mol) in the composition of melamine waste gas is 2-6.
Claim 9
Dependent Claim
35 words
Method for reclamation of melamine waste gas as claimed in claim 7 in which in case of low pressure urea synthesis from melamine waste gas alone, a pressure of at least 130 Kg/cm2 is maintained.
Claim 10
Dependent Claim
36 words
Method for reclamation of melamine waste gas as claimed in claim 7 in which some addition of water is needed when low pressure urea synthesis is carried out at a pressure of less than 130 Kg/cm2.
Claim 11
Dependent Claim
63 words
Method for reclamation of melamine waste gas as claimed in claim 7 in which separation of excess ammonia from low pressure urea synthesis solution is carried out under the same pressure as the pressure of the first decomposition stage in main urea synthesis and the obtained ammonia is cooled and condensed to be reused in liquidified form as added ammonia in melamine synthesis.
Claim 12
Dependent Claim
115 words
Method for reclamation of melamine waste gas produced in high pressure liquid phase melamine synthesis using urea or urea-thermal decomposition product as initial material, -characterized by separating said melamine waste gas from the melamine synthesis solution under the same pressure as the melamine synthesis pressure, synthesizing urea under the melamine synthesis pressure directly from the obtained melamine waste gas, or depending on the case, with addition of water or aqueous ammonium carbonate solution, separating excess ammonia from the resulting low pressure urea synthesis solution, introducing the low pressure urea synthesis solution deprived of excess ammonia into the first decomposition stage of urea synthesis, and the separated excess ammonia being recycled to the melamine synthesis system.
Claim 13
Dependent Claim
23 words
Method for reclamation of melamine waste gas as claimed in claim 12 in which the urea is synthesized directly from melamine waste gas.
Claim 14
Dependent Claim
27 words
Method for reclamation of melamine waste gas as claimed in claim 12 in which the urea is synthesized with addition of water from the melamine waste gas.
Claim 15
Dependent Claim
30 words
Method for reclamation of melamine waste gas as claimed in claim 12 in which the urea is synthesized with addition of aqueous ammonium carbonate solution from the melamine waste gas.
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) | 1976-03-26 | 1976-09-25 | 1977-03-27 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-03-26 | 1980-09-25 | 1981-03-27 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-03-26 | 1984-09-25 | 1985-03-27 | $7700.00 | Window Closed / Lapsed |