CH410904A - Process for preventing corrosion in urea synthesis - Google Patents
Process for preventing corrosion in urea synthesisInfo
- Publication number
- CH410904A CH410904A CH847762A CH847762A CH410904A CH 410904 A CH410904 A CH 410904A CH 847762 A CH847762 A CH 847762A CH 847762 A CH847762 A CH 847762A CH 410904 A CH410904 A CH 410904A
- Authority
- CH
- Switzerland
- Prior art keywords
- nitrogen oxide
- dependent
- reactor
- synthesis
- urea
- Prior art date
Links
Classifications
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
- C23C8/24—Nitriding
- C23C8/26—Nitriding of ferrous surfaces
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/02—Apparatus characterised by being constructed of material selected for its chemically-resistant properties
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C273/00—Preparation of urea or its derivatives, i.e. compounds containing any of the groups, the nitrogen atoms not being part of nitro or nitroso groups
- C07C273/02—Preparation of urea or its derivatives, i.e. compounds containing any of the groups, the nitrogen atoms not being part of nitro or nitroso groups of urea, its salts, complexes or addition compounds
- C07C273/04—Preparation of urea or its derivatives, i.e. compounds containing any of the groups, the nitrogen atoms not being part of nitro or nitroso groups of urea, its salts, complexes or addition compounds from carbon dioxide and ammonia
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J2219/02—Apparatus characterised by their chemically-resistant properties
- B01J2219/0204—Apparatus characterised by their chemically-resistant properties comprising coatings on the surfaces in direct contact with the reactive components
- B01J2219/0236—Metal based
- B01J2219/024—Metal oxides
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/141—Feedstock
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Description
Verfahren zur Verhütung von Korrosionen bei der Harnstoffsynthese
Ziel der Erfindung ist die Verhütung von Korrosionen der Anlage aus rostfreiem Stahl bei der Harnstoffsynthese durch Passivierung der Innenfläche der Anlage.
Ein weiteres Ziel der Erfindung ist die Verhütung von Korrosionen des Reaktors aus rostfreiem Stahl bei der Harnstoffsynthese durch Nitrieren der Reak torinnenfläche.
Es ist bekannt, Harnstoff durch Erhitzen von Kohlendioxyd und Ammoniak bei Temperaturen von 17 (}-220 C und bei Drucken von 2W350 Atm. in Autoklaven aus rostfreiem Stahl herzustellen. Bei der Synthese treten aber Korrosionen des Autoklaven auf, weiche sich in einer starken Verfärbung der entstehenden Harnstofflösung zeigen.
Es ist auch bekannt, dass man zur Verhütung der Korrosion des Reaktors aus rostfreiem Stahl bei der Harnstoffsynthese aus Ammoniak und Kohlendioxyd Sauerstoff bzw. sauerstoffhaltige Gase wie z. R. Luft in kleinen Mengen dem Ausgangsgas zusetzt. Der entstehende Harnstoff ist dann rein weiss. Dieses Verfahren verlangt aber eine dauernde regelmässige Kontrolle der Sauerstoffzugabe, um einerseits die Korrosion durch Sauerstoffmangel, anderseits eine Trübung der erzeugten Harnstofflösung durch Sauerstoffüberschuss zu vermeiden.
Es wurde nun gefunden, dass die Korrosion bei der Harnstoffsynthese verhindert werden kann, wenn der Reaktor im Inneren mit einer dünnen Metall nitridschicht versehen wird.
Die Erfindung betrifft ein Verfahren zur Verhütung von Korrosionen im Inneren des Reaktors aus rostfreiem Stahl bei der Synthese von Harnstoff aus Ammoniak und Kohlendioxyd unter Druck und bei erhöhter Temperatur und ist dadurch gekennzeichnet, dass an der Reaktorinnenfläche eine dünne Metall- nitridschicht erzeugt wird.
Die Metallnitridschicht kann an der Innenfläche des Reaktors durch Einleiten von Stoffen, welche auf das Material des Reaktors oberflächlich nitrierend wirken, erzeugt werden. Vorzugsweise werden gasförmige Stoffe, wie z. B. Stickstoffoxydul, in den Reaktor frühestens vor und spätestens während der Synthese eingeleitet. Beim Erwärmen auf 170-220 C zersetzt sich das Stickstoffoxydul; der dabei frei werdende atomare Stickstoff bildet mit der Innenschicht des rostfreien Autoklaven eine dünne, geschlossene Nitridschicht, die den Werkstoff bei der Harnstoffsynthese vor Korrosionen schützt.
Im Gegensatz zu den bekannten Verfahren ist die Schutzwfrku'ng von langer Dauer, so dass auch bei nur intermittierender Zugabe des Passivierungsmitteis ein ausreichender Schutz des Reaktors gewährleistet ist.
Eine bevorzugte Ausführungsform der Erfindung besteht darin, dass man das Stickstoffoxydul dem Kohlendioxyd vor der Kompression zusetzt. Die Menge des zugesetzten Stickstoffoxyduls beträgt vorzugsweise 0,005-0,5 Vol.%, bezogen auf CO2.
Die Synthese findet zweckmässig in einem Autoklaven aus rostfreiem Stahl bei Drucken von 300 bis 350 Atm. und Temperaturen von l96208O C und einem Molverhältnis von CO2 zu NH3 wie 1 zu etwa 4,5 statt.
Beispiel 1
Ein Autoklav aus V4-A-Stahl wird mit flüssigem Ammoniak, das auf 600 C vorgewärmt wurde, und flüssigem KoSendioxyd im Molverhältnis 4,5 :1 beschickt. Im Autoklaven wird bei 320 Atm. unter dem Einfluss der exothermen Reaktion die Synthesetemperatur von 198-208 C erreicht. Dem Kohlendioxyd wird vor der Kompression 0,01-0,1 Vol. % gasförmiges Stickstoffoxydul zugesetzt. Nach dem Umsatz wird die Reaktionslösung unter Entspannung in einen Entgasungsapparat geführt, der bei 10 Atm. und 1000 C betrieben wird. Die Ausbeute an Harnstoff, bezogen auf CO2, beträgt 77%. Die erzeugte Harn stofflösung ist farblos und wasserklar.
Der daraus gewonnene Harnstoff enthält weniger als 1 ppm Eisen und ist deshalb für alle Verwendungszwecke geeignet.
Beispiel 2
2. Die Synthese wird unter denselben Bedingungen wie in Beispiel 1 durchgeführt, wobei aber der Stickstoffoxydulzusatz nach 6 Std. unterbrochen wird. Die anfallende Harnstofflösung ist 12 Std. nach der Unterbrechung des Sdckstoffoxydulzusatzes noch immer klar und farblos. Der daraus gewonnene Harnstoff ist rein weiss und enthält weniger als 1 ppm Eisen.
Process for the prevention of corrosion in urea synthesis
The aim of the invention is to prevent corrosion of the system made of stainless steel during urea synthesis by passivating the inner surface of the system.
Another object of the invention is to prevent corrosion of the stainless steel reactor during urea synthesis by nitriding the inner surface of the reactor.
It is known that urea can be produced from stainless steel by heating carbon dioxide and ammonia at temperatures of 17 (} -220 ° C. and at pressures of 2W350 atmospheres in autoclaves show the resulting urea solution.
It is also known that to prevent corrosion of the stainless steel reactor in the synthesis of urea from ammonia and carbon dioxide, oxygen or oxygen-containing gases such as. Usually air is added to the starting gas in small amounts. The resulting urea is then pure white. However, this process requires constant, regular monitoring of the addition of oxygen in order to avoid corrosion due to lack of oxygen on the one hand and turbidity of the urea solution generated due to excess oxygen on the other.
It has now been found that corrosion during urea synthesis can be prevented if the reactor is provided with a thin metal nitride layer on the inside.
The invention relates to a method for preventing corrosion inside the stainless steel reactor during the synthesis of urea from ammonia and carbon dioxide under pressure and at elevated temperature and is characterized in that a thin metal nitride layer is produced on the inner surface of the reactor.
The metal nitride layer can be produced on the inner surface of the reactor by introducing substances which have a surface nitriding effect on the material of the reactor. Preferably, gaseous substances, such as. B. nitrogen oxide, introduced into the reactor at the earliest before and at the latest during the synthesis. When heated to 170-220 C, the nitrogen oxide decomposes; The atomic nitrogen released in the process forms a thin, closed nitride layer with the inner layer of the rust-free autoclave, which protects the material from corrosion during urea synthesis.
In contrast to the known processes, the protective effect is of a long duration, so that sufficient protection of the reactor is ensured even with only intermittent addition of the passivating agent.
A preferred embodiment of the invention consists in adding the nitrogen oxide to the carbon dioxide before compression. The amount of nitrogen oxide added is preferably 0.005-0.5% by volume, based on CO2.
The synthesis takes place conveniently in a stainless steel autoclave at pressures of 300 to 350 atm. and temperatures of 196208O C and a mole ratio of CO2 to NH3 such as 1 to about 4.5 take place.
example 1
An autoclave made of V4-A steel is charged with liquid ammonia, which has been preheated to 600 ° C., and liquid carbon dioxide in a molar ratio of 4.5: 1. In the autoclave is at 320 atm. reached the synthesis temperature of 198-208 C under the influence of the exothermic reaction. Before compression, 0.01-0.1% by volume of gaseous nitrogen oxide is added to the carbon dioxide. After the conversion, the reaction solution is passed into a degassing apparatus, which is operated at 10 atm. and 1000 C is operated. The urea yield, based on CO2, is 77%. The urea solution produced is colorless and water-clear.
The urea obtained from it contains less than 1 ppm iron and is therefore suitable for all purposes.
Example 2
2. The synthesis is carried out under the same conditions as in Example 1, but the addition of nitrogen oxide is interrupted after 6 hours. The urea solution obtained is still clear and colorless 12 hours after the interruption of the addition of nitrogen oxide. The urea obtained from it is pure white and contains less than 1 ppm iron.
Claims (1)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CH847762A CH410904A (en) | 1962-07-12 | 1962-07-12 | Process for preventing corrosion in urea synthesis |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CH847762A CH410904A (en) | 1962-07-12 | 1962-07-12 | Process for preventing corrosion in urea synthesis |
Publications (1)
Publication Number | Publication Date |
---|---|
CH410904A true CH410904A (en) | 1966-04-15 |
Family
ID=4340970
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CH847762A CH410904A (en) | 1962-07-12 | 1962-07-12 | Process for preventing corrosion in urea synthesis |
Country Status (1)
Country | Link |
---|---|
CH (1) | CH410904A (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0089885A2 (en) * | 1982-03-23 | 1983-09-28 | L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude | Method of surface-hardening metallic parts |
-
1962
- 1962-07-12 CH CH847762A patent/CH410904A/en unknown
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0089885A2 (en) * | 1982-03-23 | 1983-09-28 | L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude | Method of surface-hardening metallic parts |
EP0089885A3 (en) * | 1982-03-23 | 1984-12-05 | L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude | Method of surface-hardening metallic parts |
US4531984A (en) * | 1982-03-23 | 1985-07-30 | L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude | Surface hardening process for metal parts |
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