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
• • 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
  • B01J10/00—Chemical processes in general for reacting liquid with gaseous media other than in the presence of solid particles, or apparatus specially adapted therefor
  • B01J10/002—Chemical processes in general for reacting liquid with gaseous media other than in the presence of solid particles, or apparatus specially adapted therefor carried out in foam, aerosol or bubbles
• • 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
  • B01J19/0053—Details of the reactor
• • 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
  • B01J19/0053—Details of the reactor
  • B01J19/006—Baffles
• • 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
  • B01J3/00—Processes of utilising sub-atmospheric or super-atmospheric pressure to effect chemical or physical change of matter; Apparatus therefor
  • B01J3/03—Pressure vessels, or vacuum vessels, having closure members or seals specially adapted therefor
• • 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
  • B01J2219/00049—Controlling or regulating processes
  • B01J2219/00162—Controlling or regulating processes controlling the pressure
• • 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
  • B01J2219/00049—Controlling or regulating processes
  • B01J2219/00164—Controlling or regulating processes controlling the flow
• • 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
  • B01J2219/00049—Controlling or regulating processes
  • B01J2219/00182—Controlling or regulating processes controlling the level of reactants in the reactor vessel
• • 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
  • B01J2219/00761—Details of the reactor
  • B01J2219/00763—Baffles
  • B01J2219/00765—Baffles attached to the reactor wall
  • B01J2219/00777—Baffles attached to the reactor wall horizontal
• • 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
  • B01J2219/18—Details relating to the spatial orientation of the reactor
  • B01J2219/185—Details relating to the spatial orientation of the reactor vertical
• • 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
  • B01J2219/19—Details relating to the geometry of the reactor
  • B01J2219/194—Details relating to the geometry of the reactor round
  • B01J2219/1941—Details relating to the geometry of the reactor round circular or disk-shaped
  • B01J2219/1943—Details relating to the geometry of the reactor round circular or disk-shaped cylindrical
• • 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
  • Y02P20/50—Improvements relating to the production of bulk chemicals
  • Y02P20/582—Recycling of unreacted starting or intermediate materials

Definitions

• the present invention refers to a process for the urea manufacture using ammonia and carbon dioxide as starting materials.
• the invention refers also to a reactor particularly useful to carry out the process. Background art It is known that the synthesis of urea from ammonia and carbon dioxide passes through the preparation of carbamate, it is therefore necessary to separate urea from the reaction mixture and to recycle the unreacted carbamate to the urea synthesis reactor.
• the urea synthesis reaction takes place with liquid ammonia and gaseous carbon dioxide in presence of a recycled carbamate solution under a pressure ranging between 120xl0 2 and 400xl0 2 Kpa at a temperature in the range of 150 to 220°C wherein reactants and recycled carbamate solution are concurrently injected from the bottom while urea together with carbamate and the excess reactants are recovered from the top of the reactor in order to be subsequently treated for the urea separation.
• the processes wherein the reactants are fed concurrently to the reactor have several disadvantages all due to reduced reaction yield.
• the density of the starting reaction mixture consisting of liquid ammonia, gaseous carbon dioxide and recycled carbamate solution, increases when going toward the top of the reactor because of the urea formation from liquid ammonia and gaseous carbon dioxide.
• Such a urea formation inhibits the reaction mixture from rising and promotes the establishing of a back-mixing which negatively affects the reaction yield.
• the reactant concentration reduction due to the urea formation does not promote the increase of the urea yield in the final reaction step. It has to be taken into account that CO 2 fed as a reactant contains a certain amount of inert gases that has to be removed.
• a further object of the present invention is a reactor that can be usefully employed in the process of the present invention.
• the objects of the present invention are attained with a urea synthesis process starting from ammonia and carbon dioxide carried out under a pressure of 120xl0 2 to 400x10 2 KPa and a temperature of 140 to 215°C in a reactor in which gaseous CO 2 is fed in the bottom of the reactor while liquid ammonia and recycled carbamate aqueous solution are fed from the top of the reactor, and going downward the reactor, they meet in countercurrent rising gaseous CO 2 .
• Reactor behaviour is similar to the one of an adsorbing column.
• the reactor is equipped with means promoting a good contact between the going down liquid phase and the rising gaseous phase, said means consisting of filling- type materials or devices similar to distillation column trays.
• liquid- vapour contact promoting means consist of essentially cylindrical shaped bottom open trays arranged along the reactor axis, said trays being provided with holes or opening in their side surfaces to allow the liquid to pass through, while upper base surface consisting of a net or perforated plate allows the gaseous CO 2 to go upward after having overcome the pressure of the descending liquid seal.
• Liquid reactants consisting of ammonia and carbamate aqueous solution can be fed to the reaction through a single line in the upper part of the reactor or through separate lines.
• carbamate is preferably fed at a lower level than liquid ammonia which is fed in the upper practicable part of the reactor.
• the process according to the present invention in which the reaction takes place in a reactor in which the gaseous reactants are fed in countercurrent with respect to the liquid reactants has the following advantages over the conventional processes: - CO 2 , being the lightest phase goes upward to the top of the reactor, whilst NH 3 and carbamate mixture, being the heaviest phase and having the tendency to increase its density because of the urea formation, goes downward to the bottom of the reactor; any risk to establishing the undesired back-mixing is therefore avoided; - The reaction takes always place in presence of an excess of either reactants, therefore increasing the relevant yield.
• the reactor may be equipped with means which improve the close contact between descending liquid phase and rising gaseous phase.
• the reactor may be provided with internal device forcing liquid and gaseous phase to proceed through fixed routes; said devices could be filling-type materials or baffles.
• Fig. 1 is a reactor scheme useful to carry out the process according to the invention.
• Fig. 2 represents in detail a preferred device to be placed inside of the reactor to improve the countercurrent operations of the process of the invention.
• reactor 1 is comprised of a vertical column which may be operated under high pressure and at high temperature according to the practice of carrying out urea synthesis process.
• the pressure and temperature values may be respectively 120xl0 2 to 140xl0 2
• the reactor volume will be such as to allow a sufficient reaction time to perform the urea synthesis reaction.
• the reaction time may preferably be comprised between 15 and 90 minutes depending on the process operating conditions.
• CO 2 which may include small amount of gases not taking part to the reaction, such as H 2 , N 2 , O 2 , CH), CO, A, hereinafter referred to as inert gases, is fed to the lower part of the reactor 1 through line 2, at such a distance from the outlet of the obtained solution 3 as to allow this latter to get free from most therein dissolved gases and complete the urea formation reaction in the unperturbed zone 19 of the reactor bottom.
• inert gases is fed to the lower part of the reactor 1 through line 2, at such a distance from the outlet of the obtained solution 3 as to allow this latter to get free from most therein dissolved gases and complete the urea formation reaction in the unperturbed zone 19 of the reactor bottom.
• inert gases is fed to the lower part of the reactor 1 through line 2 through line 2, at such a distance
• liquid ammonia is fed through line 5 which is located at such a distance from the carbamate inlet line 4 as to allow liquid ammonia to adsorb most of CO 2 contained into the inert gases, so that a gas mixture is obtained which is practically free from CO 2 .
• a level control device 6 is provided whose regulating valve acts on the urea solution coming out from the bottom of the reactor and maintains such a liquid level on top of the reactor as to keep the solution inside of the reactor for a sufficient residence time to form urea.
• the higher portion 7 of the reactor above the solution seal will be occupied by the mainly ammonia saturated inert gases that are removed from the liquid phase.
• Such a gaseous phase is vented out of the reactor through the pressure regulating valve 8 driven by the pressure control device 9 installed on top of the reactor 1 in order to keep the desired operating conditions. Therefore the liquid entering the reactor through line 4 moves down by gravity in the direction of arrow 10 and ammonia fed through 5 starts reacting with the residual CO 2 moving toward the top of the reactor with inert gases in the direction of the arrow 1 1. During the descent of the liquid along the reactor, urea formation starts, then free ammonia meets a continuous increasing CO 2 concentration and the heat of the reaction heats the solution promoting therefore the urea synthesis reaction.
• Devices 12 are provided inside of the reactor improving the contact between moving down liquids and rising gases.
• Fig. 2 illustrates a partial cross-section perspective view of a device particularly suitable to ensure the countercurrent carrying out of the process according to the invention in the reactor 1 of fig.1.
• elements corresponding to the ones of fig. 1 are identified by the same numeric reference.
• the device of fig. 2 will be referred as "tray".
• a tray 12 of cylindrical shape has a base diameter which corresponds to 80 to 90% of the inner diameter of the reactor or column 1.
• the cylindrical tray height will be typically lower than the base diameter, but it will be at least 250 mm.
• Tray 12 is kept in its position by means of the plate 16 fixed to the inside wall of reactor or column 1.
• the cylindrical portion 13 of tray 12 is provided with a multiplicity of holes 14 where the moving down liquid phase passes through, while the gas phase pass through the perforated horizontal portion 15 of tray 12.
• the horizontal plate 15, being perforated or consisting of a suitably sized net, will improve the separation between the rising gas phase 17 and the descending liquid phase 18.

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

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

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Citations (2)

• 1996
  • 1996-07-23 IT IT96MI001530A patent/IT1283483B1/it active IP Right Grant
• 1997
  • 1997-07-22 AU AU38626/97A patent/AU3862697A/en not_active Abandoned
  • 1997-07-22 WO PCT/IT1997/000180 patent/WO1998003477A1/en active Application Filing
  • 1997-07-22 CN CN97198138A patent/CN1079394C/zh not_active Expired - Fee Related
  • 1997-07-22 CA CA002265459A patent/CA2265459A1/en not_active Abandoned

Patent Citations (2)

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