US3686305A
Expired / Lapsed
US
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Method for synthesizing urea
Assignee: Mitsui Toatsu Chemicals Inc
•
Filing: 1969-02-19
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Granted: 1972-08-22
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Expires: 1989-02-19
Abstract
Abstract A process for synthesizing urea comprising reacting carbon dioxide and ammonia at urea forming temperatures and pressures to produce a reaction mixture containing urea, water, unreacted ammonium carbamate, gaseous carbon dioxide and gaseous ammonia, introducing said reaction mixture into a heat recovering zone to recover excess heat of reaction thereby condensing most of said gaseous carbon dioxide and gaseous ammonia contained in reaction mixture, and further reacting the reaction mixture from said heat recovering zone to form additional urea.
Inventors
- 👤 Eiji Otsuka
- 👤 Kazumichi Kanai
- 👤 Shigeru Inoue
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 06:50
CPC Classifications
C; C07; C07C; C07C273/00; C07C273/02; C07C273/04
Claims Analysis
Total Claims: 44
Claim 1
Independent Claim
35 words
removing heat while maintaining the temperature substantially the same as that of the first urea synthesizing zone from said first stream in a heat recovery zone to condense gaseous ammonia and carbon dioxide therein and
Claim 2
Dependent Claim
43 words
A process as claimed in claim 1 wherein 50 to 90 per cent by weight of the make-up ammonia and carbon dioxide is fed into said first urea synthesizing zone and the remaining portion thereof is mixed with said first reaction product stream.
Claim 3
Dependent Claim
46 words
removing heat from said first reaction product stream in a heat recovery zone to recover excess heat of reaction while maintaining the temperature substantially the same as that of the first urea synthesizing zone to condense most of said gaseous ammonia and said gaseous carbon dioxide,
Claim 4
Dependent Claim
36 words
further reacting said first reaction product stream from said heat recovery zone in a second urea synthesizing zone to form a urea synthesis effluent containing urea, excess ammonia, unreacted carbon dioxide, unreacted ammonium carbamate and water,
Claim 5
Dependent Claim
35 words
introducing said stream from the heat recovering zone into a second urea synthesizing zone for further reaction to form a urea synthesis effluent containing urea, excess ammonia, unreacted carbon dioxide, unreacted ammonium carbamate and water,
Claim 6
Dependent Claim
64 words
A process as claimed in claim 1 wherein said unreacted ammonium carbamate contained in said second stream is separated by distillation in the form of a gaseous mixture of ammonia and carbon dioxide, at least a part of said gaseous mixture is absorbed in an absorbent to form an absorbate containing ammonium carbamate, and said absorbate is recirculated to said first urea synthesizing zone.
Claim 7
Dependent Claim
32 words
reacting said condensed ammonia and carbon dioxide in said first stream in a second urea synthesizing zone to form a second reaction product stream containing additional urea, water and unreacted ammonium carbamate.
Claim 8
Dependent Claim
66 words
A process as claimed in claim 1 wherein said unreacted ammonium carbamate contained in said second reaction product stream is separated by distillation in the form of a gaseous mixture of ammonia and carbon dioxide, at least a part of said gaseous mixture is absorbed in an absorbent to form an absorbate containing ammonium carbamate, and said absorbate is mixed with saId first reaction product stream.
Claim 9
Dependent Claim
27 words
reducing the pressure of the resulting urea synthesis effluent from said second urea synthesizing zone to a pressure ranging from about 40 to about 100 kg/cm (gauge),
Claim 10
Dependent Claim
42 words
reducing the pressure of said urea synthesis effluent to a pressure ranging from about 40 to about 100 kg/cm2 (gauge) to separate therefrom most of the excess ammonia in the form of gaseous ammonia containing up to minute amounts of carbon dioxide,
Claim 11
Dependent Claim
45 words
subjecting said urea synthesis effluent depleted of excess ammonia to a high pressure distillation under a pressure from about 10 to about 30 kg/cm2 (guage) to distill out most of unreacted ammonium carbamate in the form of a gaseous mixture of ammonia and carbon dioxide,
Claim 12
Dependent Claim
49 words
subjecting said urea synthesis effluent having pressure reduced to a first high pressure distillation under a pressure from about 40 to about 100 kg/cm2 (gauge) to distill out excess ammonia and a part of unreacted ammonium carbamate in the form of a gaseous mixture of ammonia and carbon dioxide,
Claim 13
Dependent Claim
29 words
A process as claimed in claim 1 wherein said ammonia is preheated to a temperature of 50* to 150*C prior to being introduced into said first urea synthesizing zone.
Claim 14
Dependent Claim
49 words
A process as claimed in claim 1 wherein said urea-forming pressure is a pressure ranging from a pressure equal to the equilibrium pressure of said second reaction product stream at the outlet of said second urea synthesizing zone to a pressure of 30 kg/cm2 higher than said equilibrium pressure.
Claim 15
Dependent Claim
48 words
subjecting the effluent from the first high pressure distillation to a second high pressure distillation under a pressure from about 10 to about 30 kg/cm2 (gauge) to distill out most of the remaining unreacted ammonium carbamate in the form of a gaseous mixture of ammonia and carbon dioxide,
Claim 16
Dependent Claim
49 words
treating said gaseous mixture from said high pressure distillation in an absorbent selected from the group consisting of water, an aqueous solution of ammonia, an aqueous solution of urea, an aqueous solution of ammonium carbamate and an aqueous solution of ammonium carbamate and urea to form a first absorbate,
Claim 17
Dependent Claim
7 words
increasing the pressure of said first absorbate,
Claim 18
Dependent Claim
50 words
absorbing said gaseous mixture from the second high pressure distillation in an absorbent selected from the group consisting of water, an aqueous solution of ammonia, an aqueous solution of urea, an aqueous solution of ammonium carbamate and an aqueous solution of ammonium carbamate and urea, to form a first absorbate,
Claim 19
Dependent Claim
34 words
A process as claimed in claim 1 wherein said heat removed in step 2 is recovered by indirect heat exchange between said first reaction product stream and a stream of water to generate steam.
Claim 20
Dependent Claim
8 words
A urea synthesizing process with solution recycle comprising
Claim 21
Dependent Claim
7 words
increasing the pressure of said first absorbate,
Claim 22
Dependent Claim
32 words
absorbing in said first absorbate said minute amounts of carbon dioxide in said gaseous ammonia from the step 4 thereby forming a gaseous ammonia free of carbon dioxide and a second absorbate,
Claim 23
Dependent Claim
10 words
recirculating said second absorbate to said first urea synthesizing zone,
Claim 24
Dependent Claim
36 words
absorbing in said first absorbate carbon dioxide and a part of ammonia contained in said gaseous mixture from the first high pressure distillation thereby obtaining a gaseous ammonia free of carbon dioxide and a second absorbate,
Claim 25
Dependent Claim
8 words
A process as claimed in claim 8 wherein
Claim 26
Dependent Claim
25 words
condensing said gaseous ammonia free of carbon dioxide by mixing the same along with raw material liquid ammonia to produce high temperature liquid ammonia, and
Claim 27
Dependent Claim
10 words
recirculating said second absorbate to said first urea synthesizing zone,
Claim 28
Dependent Claim
25 words
A process as cLaimed in claim 9 wherein said concentrating step is conducted by evaporation employing the heat of absorption generated in absorbing step 16.
Claim 29
Dependent Claim
8 words
A urea synthesizing process with solution recycle comprising
Claim 30
Dependent Claim
24 words
condensing said gaseous ammonia free of carbon dioxide by mixing the same into raw material liquid ammonia to produce high temperature liquid ammonia, and
Claim 31
Dependent Claim
12 words
recirculating the thus obtained liquid ammonia to said first urea synthesizing zone.
Claim 32
Dependent Claim
58 words
said urea synthesis effluent after said high pressure distillation step 5 is subjected to a low pressure distillation at a gauge pressure of about 0 to about 5 kg/cm2 to distill out substantially all remaining unreacted ammonium carbamate in the form of a gaseous mixture of ammonia and carbon dioxide and result in an aqueous solution of urea,
Claim 33
Dependent Claim
12 words
recirculating the thus obtained liquid ammonia to said first urea synthesizing zone.
Claim 34
Dependent Claim
8 words
A process as claimed in claim 11 wherein
Claim 35
Dependent Claim
51 words
the urea synthesis effluent from said second high pressure distillation is subjected to a low pressure distillation at a gauge pressure of about 0 to about 5 kg/cm2 to distill out substantially all of the remaining unreacted ammonium carbamate in the form of a gaseous mixture of ammonia and carbon dioxide,
Claim 36
Dependent Claim
37 words
A process as claimed in claim 12 wherein said concentration is conducted by evaporation employing the heat of absorption generated in absorbing said gaseous mixture from said second high pressure distillation in said absorbate in step 7.
Claim 37
Dependent Claim
7 words
concentrating the resulting aqueous solution of urea,
Claim 38
Dependent Claim
14 words
crystallizing urea from the concentrated solution to form a mother liquor and urea crystals,
Claim 39
Dependent Claim
22 words
the resulting aqueous solution of urea is subjected to concentration and then to crystallization to separate a mother liquor from urea crystals,
Claim 40
Dependent Claim
35 words
A process as claimed in claim 1 wherein said heat removed in step 2. is recovered by indirect heat exchange between said first reacTion product stream and said second reaction product under a reduced pressure.
Claim 41
Dependent Claim
15 words
the gaseous mixture from said low pressure distillation is absorbed in said mother liquor and
Claim 42
Dependent Claim
18 words
absorbing the gaseous mixture from said low pressure distillation in said mother liquor to form an absorbate, and
Claim 43
Dependent Claim
13 words
absorbing said gaseous mixture from said high pressure distillation in the resulting absorbate.
Claim 44
Dependent Claim
16 words
the resulting absorbate is used for absorbing said gaseous mixture from said second high pressure distillation.
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) | 1975-08-22 | 1976-02-21 | 1976-08-22 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-08-22 | 1980-02-21 | 1980-08-22 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-08-22 | 1984-02-21 | 1984-08-22 | $7700.00 | Window Closed / Lapsed |