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WO1998017635A1 - Procede de synthese d'uree a partir d'ammoniaque et de dioxyde de carbone - Google Patents

Procede de synthese d'uree a partir d'ammoniaque et de dioxyde de carbone Download PDF

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Publication number
WO1998017635A1
WO1998017635A1 PCT/IT1997/000252 IT9700252W WO9817635A1 WO 1998017635 A1 WO1998017635 A1 WO 1998017635A1 IT 9700252 W IT9700252 W IT 9700252W WO 9817635 A1 WO9817635 A1 WO 9817635A1
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WO
WIPO (PCT)
Prior art keywords
carbamate
urea
ammonia
section
kpa
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/IT1997/000252
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English (en)
Inventor
Vincenzo Lagana'
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Eurotecnica Contractors and Engineers SpA
Original Assignee
Eurotecnica Contractors and Engineers SpA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Eurotecnica Contractors and Engineers SpA filed Critical Eurotecnica Contractors and Engineers SpA
Priority to AU46381/97A priority Critical patent/AU4638197A/en
Publication of WO1998017635A1 publication Critical patent/WO1998017635A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • 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
    • 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

Definitions

  • the present invention refers to an improved process for the urea manufacture from ammonia and carbon dioxide. More particularly the present invention is directed to a urea manufacturing process wherein carbamate, resulting as a by-product of the urea synthesis, is decomposed by stripping with ammonia to recover urea as well as to recycle the stripping section outcoming gases to the synthesis zone.
  • the urea synthesis processes nowadays in operation comprise a carbamate decomposition section located downstream of the synthesis zone in order to obtain, respectively, a urea solution to be possibly sent to further purification steps and a mixture of stripping gases consisting of ammonia, carbon dioxide and water to be recycled to the synthesis zone.
  • carbamate decomposition is obtained by reacting (stripping) carbamate with one of the reactants, (ammonia or carbon dioxide), or, in accordance to a more recent technology by consecutive carbamate strippings with both reactants. It has been suggested to carry out synthesis reaction and carbamate stripping essentially at same pressure to avoid pumping gas mixture coming out of the stripping section and recondensed in form of carbamate to the urea synthesis zone.
  • urea synthesis zone is operated at a pressure higher than the one existing in the stripping section. More particularly in the process according to the present invention the urea synthesis reaction is carried out with an ammonia to urea molar reaction in the range of 4 to 5, under a pressure in the range of 180 to 250.10 2 KPa and at a temperature of from 170 to 250°C, the stripping section operating with ammonia at a pressure comprised between 1 10 and 160.10 2 KPa.
  • the conversion to urea is higher than 70%, while in the conventional isobaric processes the conversion to urea does not reach 65%
  • the presently available centrifugal pumps used for carbamate recycling are quite reliable and do not exhibit any unreliability inconvenient as it was experienced in the past with reciprocating pumps.
  • High conversion obtained by the process according to the present invention allows to reduce steam consumption for the carbamate decomposition if compared with isobaric process steam consumption. Moreover by carrying out the ammonia stripping step at considerably lower pressure than the synthesis, and even lower than the one conventionally employed in isobaric stripping processes, carbamate decomposition is made easier leaving
  • Vapors coming out of the stripping section are mixed with carbamate liquid solution resulting from the carbamate decomposition section located downstream of the synthesis zone.
  • Said carbamate decomposition is well known in the art and generally operates at pressure lower than or equal to 22.10 2 KPa.
  • the recovered two-phase mixture is made to condense in a process section referred to as carbamate condensation section by operating essentially at the same pressure as the stripping section; resulting carbamate is recycled by means of a pump to the synthesis zone.
  • Carbamate condensation heat is partially employed to provide residual carbamate, still present in the urea solution coming out of the stripping section, with the necessary heat of decomposition, while the condensation heat of the carbamate decomposed in the latter step can be used for steam production.
  • the urea manufacturing process according to the present invention is specifically suitable for its integration with a melamine synthesis process starting from urea.
  • the melamine manufacturing process starting from urea yields, as by-products, ammonia, water and carbon dioxide which are condensed as a carbamate solution that has to be recycled back to urea synthesis zone.
  • the process of the present invention it is possible to recycle said carbamate solution without introducing into the urea synthesis reactor the water present in said solution.
  • aqueous carbamate solution is added to the product sent to the stripping section and then vapors are sent after condensation to the synthesis section, while water remains into the urea solution.
  • CO 2 coming from the plant battery limits is compressed at a pressure of 230.10 2 KPa by means of compressor 1 and is sent to the bottom of the urea synthesis reactor 2.
  • Both recycled carbamate through pump 3, and ammonia coming from pump 4 and preheated to a temperature of 90°C in preheated 5 enter the bottom of the reactor.
  • Reactor operates at a tot pressure of 226.10 2 KPa and a 195°C top temperature with a CO 2 conversion yield of
  • Liquid solution is discharged from reactor 2 trough valve 6 whereby its pressure is lowered to 130.10 2 KPa before entering stripper 7 operating at a pressure of 130.10 2 KPa.
  • Solution entering the top of the falling film type stripper is heated up to a temperature of 207°C by means of steam fed into the heating mantle;
  • the steam provides the necessary heat to decompose most of carbamate coming out of reactor 2.
  • the incompletely purified urea solution is expanded through valve 9 down to a pressure of 18.10 2 KPa to continue its purification, while effluent gases from the top section of stripper 7 enter the top section of carbamate condenser 10A through ejector 12 wherein said gases are thoroughly mixed with carbamate solution fed by pump 14 after having been preheated up to a temperature of 100°C by preheated 13.
  • Heat for this decomposition step is provided by carbamate condensation taking place in the pipes of carbamate condenser 10B.
  • urea solution enter evaporator 2 IB where vapor phase is sent to a first vacuum system 28, while urea solution is sent to final concentrator 23 operating at a pressure of 0.03.10 2 KPa and a temperature of 140 C C to obtain essentially pure urea at a concentration of 99.1%.
  • the heat necessary to reach said concentration is provided by 4.5.10 2 KPa steam condensing on the mantle side.
  • Molten urea contains a small amount of free ammonia that when mixed with cooling air would result in an environmental pollution when discharged into the atmosphere.
  • CO 2 is injected in the delivery side of molten urea pump 30. CO 2 will react with ammonia to yield carbamate and therefore will lower the ammonia emission level of the top of tower 31.
  • the two-phase liquid coming out of the mantle of evaporator 21 is sent to ammonia preheated 5 to condense further and then enters the bottom section of column 32 wherein a
  • EET R 6 carbamate liquid phase is formed in the bottom while pure gaseous ammonia exits from the upper part of the column.
  • Carbamate formation heat is removed by means of a pure ammonia reflux entering on top of column 32.
  • pump 14 the bottom carbamate enters the preheat er 13 wherein the preheating heat is provided by steam coming out of the top of separator 16; the mixed phase is sent to final condenser 25 together with carbamate solution 39 coming from a process condensate treatment section that has not been illustrated in the drawing.
  • Carbamate coming out of condenser 25 is collected in a reservoir 27 wherefrom carbamate is recycled by means of the pump 26 as illustrated above.
  • Gas phase ammonia coming out of the top of column 32 enters condenser 33 wherein ammonia is condensed and collected in a reservoir 34 wherefrom it is drawn by pump 35 which delivers ammonia both on top of column 31 as a reflux and to pump 4 that will send ammonia to reactor 2 after its preheating in heat exchanger 5.
  • Inert gases accumulated in reservoir 34 are saturated of ammonia at a temperature of 43°C and a pressure of 18.10 2 KPa: therefore before discharging to the atmosphere they are washed in column 36 with fresh ammonia coming from battery limits, typically at a temperature of -34°C to lower as much as possible their ammonia content.
  • melamine plant produces certain amounts of NH 3 , CO 2 , H 2 O gas which are condensed in the melamine plant itself, liquid carbamate obtained in such a way has to be recycled to urea plant in order to transform it into urea.
  • reactor yield is 71.5%
  • the outgoing solution having the following composition: NH 3 44125 kg/h 37.00% by weight
  • Carbamate solution content is 21634 kg/h.
  • Carbamate solution content is 30078 kg/h.
  • Solution coming out of the reactor at a pressure of 199.10 2 KPa is expanded down to a pressure of 13510 2 KPa, then is sent to stripper operating at a temperature of 205°C, and the purified solution has the following composition:
  • the 23.10 2 KPa saturated steam consumption is 11288 kg/h corresponding to 271 kg/t of urea.
  • the stripper out coming solution is expanded to a pressure of 18.10 2 KPa and is sent to the mantle of the carbamate condenser 10A wherein is heated up to a temperature of 160°C to decompose residual carbamate obtaining the following solution: NH 3 1249 kg/h 2.16% by weight
  • Solution coming out of the decomposition step under a pressure of 18.10 2 KPa is expanded down to a pressure of 4.5.10 2 KPa and is sent to carbamate condenser mautle 10B wherein the solution is heated up to a temperature of 138°C to decompose residual carbamate obtaining the following composition.
  • the heat necessary for carbamate decomposition is 1934000 kcal h and is provided by the condensation of the stripping outcoming vapors.
  • Stripping effluent gases are combined with carbamate solution coming out from the 18.10 2 KPa section and are condensed under a pressure of 134.10 2 KPa and a temperature of
  • Vapor coming out of the 18.10 2 KPa carbamate decomposition section and separator 15 are condensed in the mantle of evaporator 21 A wherein the urea solution is concentrated up to
  • Heat provided by vapor condensation is approximately 4250000 kcal/h while the remain heat necessary to concentrate urea solution up to 95% and corresponding to 2709000 kcal/h is provided by heated steam.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
  • Catalysts (AREA)

Abstract

Cette invention se rapporte à un procédé permettant de fabriquer de l'urée à partir de dioxyde de carbone et d'ammoniaque avec des taux de conversion élevés, ce procédé utilisant une section de synthèse de l'urée et une section d'élimination du carbamate obtenu comme sous-produit à l'aide de l'ammoniaque, le procédé se caractérisant en ce que la zone de synthèse de l'urée agit à une pression supérieure à la pression régnant dans la section d'élimination du carbamate.
PCT/IT1997/000252 1996-10-17 1997-10-16 Procede de synthese d'uree a partir d'ammoniaque et de dioxyde de carbone Ceased WO1998017635A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU46381/97A AU4638197A (en) 1996-10-17 1997-10-16 Process for the urea synthesis from ammonia and carbon dioxide

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
ITMI96A002152 1996-10-17
IT96MI002152A IT1290423B1 (it) 1996-10-17 1996-10-17 Procedimento per la sintesi di urea da anidride carbonica e ammoniaca

Publications (1)

Publication Number Publication Date
WO1998017635A1 true WO1998017635A1 (fr) 1998-04-30

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/IT1997/000252 Ceased WO1998017635A1 (fr) 1996-10-17 1997-10-16 Procede de synthese d'uree a partir d'ammoniaque et de dioxyde de carbone

Country Status (3)

Country Link
AU (1) AU4638197A (fr)
IT (1) IT1290423B1 (fr)
WO (1) WO1998017635A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2802559B1 (fr) 2012-01-09 2016-03-30 Saipem S.p.A. Procédé de synthèse de l'urée comprenant un flux de passivation au fond de la colonne de rectification

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1903117A1 (de) * 1968-01-23 1969-11-27 Sumitomo Chemical Co Verfahren zur Herstellung von Harnstoff
WO1983000861A1 (fr) * 1981-09-01 1983-03-17 Van Nassau, Petrus, Johannes, Marie Procede de preparation d'uree
EP0155735A1 (fr) * 1984-03-16 1985-09-25 Stamicarbon B.V. Procédé de préparation d'urée
EP0727414A1 (fr) * 1995-02-16 1996-08-21 SNAMPROGETTI S.p.A. Procédé de préparation d'urée à rendement élevé

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1903117A1 (de) * 1968-01-23 1969-11-27 Sumitomo Chemical Co Verfahren zur Herstellung von Harnstoff
WO1983000861A1 (fr) * 1981-09-01 1983-03-17 Van Nassau, Petrus, Johannes, Marie Procede de preparation d'uree
EP0155735A1 (fr) * 1984-03-16 1985-09-25 Stamicarbon B.V. Procédé de préparation d'urée
EP0727414A1 (fr) * 1995-02-16 1996-08-21 SNAMPROGETTI S.p.A. Procédé de préparation d'urée à rendement élevé

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2802559B1 (fr) 2012-01-09 2016-03-30 Saipem S.p.A. Procédé de synthèse de l'urée comprenant un flux de passivation au fond de la colonne de rectification

Also Published As

Publication number Publication date
IT1290423B1 (it) 1998-12-03
AU4638197A (en) 1998-05-15
ITMI962152A1 (it) 1998-04-17

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