REACTOR AND PROCESS FOR THE NON-CATALYTIC HIGH-PRESSURE SYNTHESIS OF MELAMINE FROM UREA

Abstract

COMBINED REACTOR FOR HIGH PRESSURE SYNTHESIS OF MELAMINE. Reactor for the non-catalytic high pressure synthesis of melamine from urea comprising an internal coaxial reaction zone (6) and an external reaction zone (7) wherein crude melamine is formed in the internal reaction zone and brought into contact with gaseous ammonia for separation in the external reaction zone, wherein a gaseous phase released in the external zone is collected in a gas collection chamber (12) above the reaction zones, wherein the molten crude melamine material is transferred from the internal zone to the external zone by means of a submerged liquid passage below the liquid level to provide a liquid seal between the chambers.

Description

1 / 17 “REACTOR AND PROCESS FOR THE NON-CATALYTIC HIGH-PRESSURE SYNTHESIS OF MELAMINE FROM UREA” Field of application

[0001] The invention relates to installations for the synthesis of melamine from urea. The invention relates, in particular, to reactors for the high-pressure synthesis of melamine. Previous Technique

[0002] Processes for the synthesis of melamine from urea are commonly classified as low-pressure catalytic processes and high-pressure non-catalytic processes. A low-pressure process is typically conducted at a pressure below 1 MPa; a high-pressure process is generally conducted at a pressure of at least 7 MPa and preferably in the range of 7 to 25 MPa. The low-pressure process and the high-pressure process are described in the literature, for example, Ullmann's Encyclopedia of Industrial Chemistry, 6th ed., vol. 21, p. 205.

[0003] Melamine production can be integrated with urea production, since urea is the raw material for melamine synthesis and melamine synthesis produces gases containing ammonia and carbon dioxide, which are the starting materials for urea production. Therefore, melamine can be produced in a facility called an integrated urea-melamine plant, including a melamine plant and a linked urea plant.

[0004] A known high-pressure melamine synthesis process essentially comprises three steps: a bulk conversion of urea into a molten, crude melamine material; a second removal step Petition 870240098256, dated 11 / 18 / 2024, page 12 / 45 2 / 17 of the carbon dioxide (CO2) contained in the melamine melt is removed by introducing gaseous ammonia and reducing the content of byproducts that are converted into melamine; a third stage during which the gases formed in the first two stages are washed or scrubbed with urea for subsequent recycling to the urea synthesis section. The three stages above are conventionally carried out in separate vessels called respectively the primary reactor, secondary reactor or stripping reactor, and scrubber.

[0005] A configuration with three separate pressure vessels, however, has disadvantages in terms of cost and complication.

[0006] Document WO 2015 / 124409 discloses a combined apparatus for the synthesis of melamine with an internal reaction space and an external reaction space arranged coaxially, wherein the internal reaction space acts as a primary reactor and the external reaction space acts as a secondary reactor. The internal reaction space is enclosed by an inner reactor casing. The reactor may include an upper cupola acting as a scrubber.

[0007] The coaxial reactor described above operates as follows. Bulk conversion of urea to melamine and the formation of crude melamine molten material occur in the inner reaction space; the crude melamine molten material formed in the inner space flows into the outer reaction space overflowing from the upper edge of the inner casing; in the outer reaction space, gaseous ammonia is added as a separation medium; the byproducts formed during bulk conversion are converted into melamine and Petition 870240098256, dated 11 / 18 / 2024, page 13 / 45 3 / 17 CO2 is removed along with the ammonia gas. Summary of the Invention

[0008] The invention aims to improve the aforementioned prior art of a combined reactor including an internal reaction space and an external reaction space arranged coaxially. More specifically, the invention aims to reduce the byproducts contained in the melamine removed from the reactor and thus increase its purity.

[0009] The present invention is based on the discovery that in a reactor with the above-described arrangement of internal and external coaxial reaction spaces, the gas mixture collected in the upper portion of the reactor and above the coaxial reaction spaces contains a significant amount of CO2 generated during the bulk conversion of urea to melamine that occurs in the internal reaction space. The applicant has found that this CO2 collected above the coaxial reaction spaces can diffuse into the external reaction space and affect its secondary conversion performance, namely the conversion of by-products to melamine and CO2 removal. If the conversion of by-products and / or the removal of CO2 are affected, the purity of the final product containing melamine is also affected.

[0010] Based on this finding, the above objective is achieved with a reactor and a process for the synthesis of melamine according to the claims.

[0011] In the inventive reactor and process, primary mass conversion and secondary conversion are carried out, respectively, in an inner reaction space and an outer reaction space arranged coaxially. The liquid melt mass of crude melamine formed in the reaction space Petition 870240098256, dated 11 / 18 / 2024, page 14 / 45 4 / 17 The internal reaction is transferred to the external reaction space through a passage which, during operation, is located below the liquid level of said molten melamine material.

[0012] Due to the immersed location described above of the melamine melt passage, a hydraulic seal is created between the inner reaction space and the outer reaction space. A differential pressure is established between the outer reaction space and the inner reaction space. In particular, the outer reaction space operates at a higher pressure than the inner reaction space. Molten melamine from the inner reaction space can flow into the outer reaction space creating a static head; this liquid head provides a hydraulic seal between the two reaction spaces.

[0013] Furthermore, and according to preferred embodiments, the outlet area for gas extraction from the outer reaction space can be reduced to increase the gas outlet velocity. Faster gas outlet increases the convective flux of the outlet gas; consequently, the diffuse transfer of gaseous carbon dioxide to the outer reaction zone is reduced.

[0014] The invention therefore has the following advantages: gaseous CO2 collected at the top of the reactor, above the coaxial reaction spaces, is substantially prevented from entering the external reaction space where secondary conversion is carried out; the available reaction volume is exploited to the maximum; the purity of the melamine obtained is increased because the conversion of by-products into melamine is no longer affected by the unwanted diffusion of CO2. Petition 870240098256, dated 11 / 18 / 2024, page 15 / 45 5 / 17 Description of Preferred Options

[0015] A reactor according to the invention generally includes an outer pressure enclosure; a urea inlet arranged to direct a urea feed to the first reaction zone; separation means arranged to separate the first reaction zone from the second reaction zone.

[0016] The reactor includes at least one communication port between the first reaction zone and the second reaction zone, said port being arranged to transfer the liquid raw melamine molten material formed in the first reaction zone to the second reaction zone, where the melamine molten material is further processed.

[0017] The Reactor additionally includes means for removing a product containing melamine from the bottom of the second reaction zone and means for removing melamine from the top of the gas containing ammonia and carbon dioxide from said second reaction zone.

[0018] The said communication port has a liquid intake section which, in operation, is located below the level of the molten liquid melamine material contained in the first reaction zone.

[0019] The inlet section of the communication port is therefore immersed in liquid molten melamine. A liquid head exists above said inlet section and, in operation, creates a hydraulic seal between the reaction zones.

[0020] The communication port may include a single passage or a plurality of passages. Petition 870240098256, dated 11 / 18 / 2024, page 16 / 45 6 / 17

[0021] Preferably, all liquid passages between the first reaction zone and the second reaction zone are located below the melamine melt liquid level in the first reaction zone, i.e., there is no liquid passage between said two zones at or above said liquid level.

[0022] Said liquid level can be defined by the upper edge of an inner reactor shell that divides the first reaction zone from the second reaction zone. In some embodiments, said liquid level can be defined by a transition between different portions of said inner shell, for example, a transition from a cylindrical portion to a conical portion. Consequently, the reactor can comprise one or more liquid passages located below said upper edge or transition of the inner shell.

[0023] In one embodiment, the means of separating the reaction zones include an inner envelope and a cover. Said inner envelope is coaxial to the outer pressure envelope of the reactor and is arranged to separate the two reaction zones in the radial direction, such that the first reaction zone is within the inner envelope and the second reaction zone is radially delimited between said inner envelope and the outer pressure envelope of the reactor. For example, the second reaction zone is an annular region between said inner envelope and the outer pressure envelope of the reactor.

[0024] The said cover may be located above the inner enclosure in a region of the reactor between the outer pressure enclosure and the inner enclosure. In addition Petition 870240098256, dated 11 / 18 / 2024, page 17 / 45 7 / 17 of this, said covering may include passages for removing the gaseous melamine effluent from the second reaction zone and a lower portion extending into the first reaction zone and below an upper edge of the inner casing.

[0025] In this embodiment, a liquid passage is formed between the lower portion of the cover and the inner casing. At the lower edge of the cover, in particular, an inlet section for the liquid is formed, which is below the level of the molten melamine material when, in operation, the internal reaction space is filled with liquid melamine.

[0026] More preferably, said lower portion of the cover may extend into the first reaction zone coaxially to an upper portion of the inner shell, so that an annular passage for the molten melamine material is enclosed between said lower portion of the cover and the upper portion of the inner shell. Shell.

[0027] Preferably, said inner casing is cylindrical and said lower portion of the cover is also cylindrical.

[0028] The passages for removing gaseous melamine effluents are preferably located in close proximity to the outer pressure enclosure. For example, said passages may include suitable orifices or slots.

[0029] In one embodiment, said separation means include an inner casing that is coaxial to the reactor pressure casing and includes a portion below a first radial distance from the pressure casing. Petition 870240098256, dated 11 / 18 / 2024, page 18 / 45 8 / 17 external and an upper portion at a second radial distance from the external pressure envelope that is shorter than said first radial distance, the upper portion therefore being closer to the external pressure envelope than the lower portion. The internal envelope also includes a transition portion that connects the lower portion with the upper portion.

[0030] A space for the removal of melamine gas effluent is defined between the outer pressure envelope and the upper portion of the inner pressure envelope. As the upper portion of the inner envelope is relatively close to the outer envelope, said annular space may have a small gas passage cross-section resulting in a high gas velocity with the advantages explained above. In particular, the convective flow is increased and the undesirable diffuse transfer of CO2 is reduced thanks to the high gas flow velocity in this annular space.

[0031] The lower portion of the inner casing may include passages for the molten melamine material from the first reaction zone to the second reaction zone, which are located below the level of the molten melamine material in operation.

[0032] The lower and upper portions of the inner envelope may be cylindrical; the transition portion may be conical or substantially conical.

[0033] In another embodiment, an inner enclosure dividing the two reaction zones from each other may have an upper portion configured to cover the second reaction zone in a sealed manner. Consequently, the reactor Petition 870240098256, dated 11 / 18 / 2024, page 19 / 45 9 / 17 includes suitable means for extracting the gas released in the second reaction zone, for example, including nozzles in the outer pressure envelope.

[0034] One advantage of this method is a physical separation of the gas in the first reaction zone from the gas in the second reaction zone, to avoid unwanted diffusion of CO2.

[0035] A process for the synthesis of melamine from urea according to the invention can be carried out in a reactor comprising a first reaction zone and a second reaction zone, wherein the second reaction zone is an annular zone arranged coaxially around the first reaction zone. The process includes:

[0036] feed fresh urea into the first reaction zone, where a molten raw melamine liquid material is formed with a non-catalytic high-pressure process;

[0037] transfer said molten melamine material from the first reaction zone to the second reaction zone for further processing;

[0038] remove a product containing melamine from the second reaction zone and remove top melamine from the gas containing ammonia and carbon dioxide from said second reaction zone;

[0039] wherein the molten raw melamine material flows from the first reaction zone to the second reaction zone through one or more communicating ports having a liquid inlet section in the first reaction zone that is located below the level of the molten material of Petition 870240098256, dated 11 / 18 / 2024, page 20 / 45 10 / 17 liquid melamine contained in the first reaction zone.

[0040] Further processing of the molten melamine material in the second reaction zone may include removing the molten melamine material with ammonia gas. The ammonia gas is then removed along with the carbon dioxide gas as melamine gas.

[0041] The invention is now better elucidated with the help of the drawings. Description of the Figures

[0042] Figure 1 is a cross-sectional diagram of a combined primary and secondary melamine reactor of the prior art.

[0043] Figure 2 is a detail of a combined reactor similar to that of Figure 1, modified according to a first embodiment of the invention.

[0044] Figure 3 is an enlarged detail of Figure 2.

[0045] Figure 4 illustrates another embodiment of the invention.

[0046] Figure 5 illustrates another embodiment of the invention. Detailed Description

[0047] Figure 1 illustrates a combined primary and secondary melamine reactor R with coaxial reaction chambers 6 and 7 separated by an enclosure 4.

[0048] In particular, Figure 1 illustrates the following details. external pressure vessel of the reactor (outer casing) central duct heating elements, for example, tubes Petition 870240098256, dated 11 / 18 / 2024, page 21 / 45 11 / 17 Heating inner casing inner zone of the first reaction chamber, delimited by central duct 2 peripheral zone of the first reaction chamber 7-second reaction chamber (annular reaction chamber) molten urea inlet molten urea feed toroidal distributor gaseous ammonia feed gas separation chamber open upper section of duct 2 with deflector 13a melamine liquid level during normal operation edge of inner casing 4 melamine outlet gaseous effluent discharge line

[0049] The inner casing 4 defines a first reaction chamber composed of an inner zone 5 delimited by the central duct 2 and a peripheral zone 6, outside the central duct 2, housing the heating tubes 3. A second reaction chamber 7, with a substantially annular shape, is delimited between said casing 4 and the outer casing 1.

[0050] In operation, the liquid melamine reaches the level indicated by line 14 and flows over the upper edge 15 of the inner casing 4 and into the annular chamber 7.

[0051] In annular chamber 7, liquid melamine is extracted by raising the gaseous ammonia introduced by the toroidal distributor 10 located in the lower portion of annular chamber 7. The purified melamine 16 Petition 870240098256, dated 11 / 18 / 2024, page 22 / 45 The 12 / 17 thus obtained (after removal) is discharged from the bottom of chamber 7; the gases released during the pickling process, containing predominantly CO2 and ammonia, are collected in chamber 12 and discharged through line 17.

[0052] This reactor in Figure 1 (prior technique) basically provides a primary conversion section in chambers 5 and 6 and a secondary extraction section in annular chamber 7. The crude melamine formed in chambers 5, 6 is transferred to chamber 7 for secondary processing (removal) by overflow from the inner casing 4.

[0053] Figure 2 illustrates a first embodiment of the invention. The same numbers from Figure 1 are used for clarity.

[0054] According to Figure 2, the reactor includes an annular chamber cover 7 20 which is tightly joined to the inner surface of the outer casing 1.

[0055] Preferably, the cover 20 has a first portion 21 attached to the outer wrapper 1, a second portion 22, a third portion 23.

[0056] The first portion 21 has one or more passages 24 for the outlet gas. Said passages 24 place the annular chamber 7 in gas communication with the gas collection chamber 12 above. The passages 24 may be orifices or slits and are preferably located in the vicinity of the outer casing 1.

[0057] The third portion 23, which is a lower portion of the covering 20, extends into the first reaction zone 6 and below the upper edge 15 of the inner envelope 4. In particular, the lower edge 25 of the covering 20 Petition 870240098256, dated 11 / 18 / 2024, page 23 / 45 13 / 17 (the lower edge of its portion 23) is below the edge 15 of the inner envelope 4.

[0058] The third portion 23 is distanced from the inner casing 4 so that a substantially annular passage 26 is enclosed between them. Said annular passage 26 provides a communication port for liquid melamine from reaction chamber 6 to reaction chamber 7.

[0059] In operation, the liquid melamine in chamber 6 will reach a level 14 above edge 15, due to the presence of the cover 20 and its portion 23. The height of the level 14 above edge 15 provides the driving force for the melamine liquid to flow through the submerged passage 26 to chamber 7. It can be noted that the passage 26 has an inlet section 26a that is submerged below the melamine level 14.

[0060] Liquid melamine forms a liquid seal preventing the gas released in the second chamber 7 from flowing back into the first chamber 6. Said gas is collected in the upper chamber 12 through passages 24. Additionally, the gas above chamber 6 is prevented from entering chamber 7 and diffusing into the liquid melamine contained therein.

[0061] The second chamber 7 is substantially separated from the gas collection chamber 12 by the cover 20, and gas passage between said two chambers is possible only through gas passages 24, which may be limited in number and act substantially unidirectionally from chamber 7 to chamber 12. Thus, the collection of a gaseous phase in the upper portion of the second chamber 7 and above the liquid is avoided. Consequently, the possible diffusion of CO2 is prevented. Petition 870240098256, dated 11 / 18 / 2024, page 24 / 45 14 / 17 gaseous in the liquid melamine contained in the second chamber 7 is avoided or greatly reduced.

[0062] Figure 4 illustrates an embodiment in which the separation between the first chamber 6 and the second chamber 7 is provided by an inner envelope 30 that is coaxial to the outer envelope 1 and replaces the inner envelope 4 described previously.

[0063] Said inner envelope 30 includes a lower portion 31, an upper portion 32 and a transition portion 33. The lower portion 31 is at a first radial distance d1 from the outer pressure envelope 1 and the upper portion 32 is at a second radial distance d2 from the same, wherein d2 is less than d1. The upper portion 32 is therefore closer to the outer pressure envelope 1.

[0064] An annular space 34 for removing melamine gas effluent is defined between the outer pressure envelope 1 and the upper portion 32 of the inner pressure envelope 30. Preferably, the distance d2 is small, so that the annular space 34 has a relatively small cross-section to increase the gas flow velocity in the space 34.

[0065] In the same way as the embodiment described previously, chambers 7 and 12 are substantially separated by the envelope 30 and gas communication is only possible through space 34. Due to the rapid gas flow in this space 34, the convective flow of gas exiting chamber 7 prevails over diffuse transfer and, therefore, the diffusion of CO2 into the liquid contained in chamber 7 is avoided or substantially reduced.

[0066] Transfer of crude melamine from Petition 870240098256, dated 11 / 18 / 2024, p. 25 / 45 15 / 17 chamber 6 to chamber 7 is provided by a series of submerged orifices 35 of the casing 30, more precisely of its lower portion 31. Each orifice 35 has an inlet section 35a which is also below the liquid level 14.

[0067] In operation, passages 35 are located below liquid level 14 in chamber 6. The maximum level to be reached by the liquid melamine may correspond, for example, to the transition between portions 31 and 33 of the casing 30.

[0068] Preferably, the lower and upper portions of the inner envelope 30 are cylindrical and the transition portion 33 is conical or substantially conical as illustrated.

[0069] Figure 5 illustrates another embodiment in which chambers 6 and 7 are separated by an inner casing 40 which includes: a lower portion 41 which radially separates said two chambers 6, 7 and an upper portion 42 configured to cover chamber 7 in a sealed manner. In this case, the gas released in chamber 7 is extracted through the nozzles 43 of the outer pressure casing 1. The molten melamine is transferred from chamber 6 to chamber 7 by a series of submerged orifices 44 with inlet sections 44a made in the lower portion 41 of said inner casing 40.

[0070] In this version of Figure 5, there is a physical separation between reaction zones 6 and 7 to prevent unwanted diffusion of CO2.

[0071] Nozzles 43 can be connected to a gas extraction line. In one embodiment, said gas extraction line can be provided with one or more flow control valves to regulate the pressure in chamber 7. Petition 870240098256, dated 11 / 18 / 2024, p. 26 / 45 16 / 17

[0072] In all embodiments (for example, embodiments in Figures 2 to 5) chamber 6 belongs to a first reaction zone which may also include an internal zone around the reactor axis delimited by a duct 5 as in Figure 1.

[0073] The invention in its various forms achieves the objectives stated above.

[0074] A liquid seal is established between chambers 6 and 7, thanks to the fact that the liquid passages for the molten melamine material traveling from inner chamber 6 to outer chamber 7 are below level 14 in chamber 6, i.e., a static head exists over the liquid inlet.

[0075] A pressure difference is also created between the two chambers 6 and 7, with the outer chamber 7 being at a higher pressure. Particularly, in the embodiments of Figures 2 to 4, the higher pressure in chamber 7 is due to a pressure difference (Delta-p) that is required for the gaseous ammonia to flow through the relatively small cross-section of the passages 24 or the annular space 34. In other words, it can be said that the pressure in chamber 7 is substantially equal to the pressure in chamber 12 plus the delta-p of the gaseous ammonia. In the embodiment of Figure 5, the pressure in chamber 7 can also be controlled by one or more flow regulating valves provided in an outlet gas extraction line connected to the nozzles 43.

[0076] Gaseous melamine effluents are extracted from external chamber 7, where the separation of the molten raw melamine material occurs. A better separation is also obtained between the exhaust gas and the liquid contained in the Petition 870240098256, dated 11 / 18 / 2024, page 27 / 45 17 / 17 outer chamber 7. The residence of a gaseous phase over the liquid in the outer chamber 7 and the unwanted diffusion of CO2 into the liquid are avoided. Thus, the conversion of 5 byproducts into melamine is facilitated, which ultimately results in better purity (lower byproduct content) of the melamine produced 16. Petition 870240098256, dated 11 / 18 / 2024, page 28 / 45

Claims

1 / 5 CLAIMS 1. Reactor for the non-catalytic high-pressure synthesis of melamine from urea, characterized in that it comprises an outer pressure shell (1), a first reaction zone (6) and a second reaction zone (7) contained in said outer shell (1), wherein the second reaction zone is an annular space arranged coaxially around the first reaction zone, wherein the reactor further includes: a urea inlet arranged to direct a urea feed into the first reaction zone, which is a zone for converting urea into a crude melamine melt; separation means arranged to separate the first reaction zone from the second reaction zone; at least one communication port (26, 35, 44) between the first reaction zone (6) and the second reaction zone (7) arranged to transfer the liquid crude melamine melt formed in the first reaction zone to the second reaction zone for further processing;at least one melamine outlet for removing a product containing purified melamine from the bottom of the second reaction zone and at least one gas passage (24, 34, 43) for removing the excess gaseous effluent of melamine containing ammonia and carbon dioxide from said second reaction zone (7); wherein said at least one communication port has a liquid inlet section (26a, 35a, 44a) which, in operation, is located below the level (14) of the liquid melamine melt contained in the first reaction zone, Petition 870260052975, dated 01 / 06 / 2026, page 6 / 19 2 / 5 said inlet section being immersed in the liquid melamine melt to create a hydraulic seal between the first reaction zone (6) and the second reaction zone (7).; 2. Reactor according to claim 1, characterized in that said separation means include an inner shell (4) and a cover (20), wherein: said inner shell is coaxial to the reactor pressure shell, arranged to separate the two reaction zones in a radial direction, such that the first reaction zone (6) is within the inner shell and the second reaction zone (7) is radially delimited between said inner shell (4) and the reactor's outer pressure shell (1); said cover (20) is located above the inner shell in the annular region between the outer pressure shell and said inner shell; wherein said cover has gas passages (24) to remove the melamine gas effluent from the second reaction zone; wherein said cover has a lower portion (23) that extends into the first reaction zone (6) and below an upper edge (15) of the inner shell (4).

3. Reactor, according to claim 2, characterized in that said lower portion (23) of the cover (20) extends into the first reaction zone coaxially to at least one upper portion of the inner shell, such that an annular passage (26) for the melamine melt is enclosed between said lower portion of the cover and the upper portion of the inner shell.

4. Reactor, according to claim 3, characterized in that said inner shell is cylindrical and said lower portion of the cover is also cylindrical.

5. Reactor, according to any one of claims 2 to 4, characterized in that said gas passages (24) of the cover for removing the melamine gas effluent are located in close proximity to the outer pressure shell (1).

6. Reactor, according to any one of claims 2 to 5, characterized in that said gas passages of the cover include orifices or slots.

7. Reactor, according to claim 1, characterized in that said separation means include an inner shell (30) that is coaxial to the pressure shell (1) of the reactor and includes: a lower portion (31) at a first radial distance from the outer pressure shell; an upper portion (32) at a second radial distance from the outer pressure shell that is less than said first radial distance, the upper portion being, therefore, closer to the outer pressure shell than the lower portion; a transition portion (33) connecting the lower portion with the upper portion.

8. Reactor, according to claim 7, characterized in that an annular space (34) for removing the melamine gas effluent is defined between the outer pressure shell and the upper portion of the inner pressure shell.

9. Reactor, according to claim 7 or 8, characterized in that said at least one communication port for the liquid raw melamine melt includes passages (35) provided in the lower portion (31) of said inner shell (30), which are located below the level (14) of the melt in operation.

10. Reactor, according to any one of claims 7 to 9, characterized in that the lower and upper portions of the inner shell are cylindrical and the transition portion is conical or substantially conical.

11. Reactor, according to claim 1, characterized in that said separation means include an inner shell (40) that is coaxial to the reactor pressure shell and includes: a lower portion (41) that radially separates the first reaction zone from the second reaction zone; an upper portion (42) configured to cover the second reaction zone in a sealed manner; wherein the reactor further includes nozzles (43) in the outer pressure shell to remove the melamine gaseous effluent from the second reaction zone.

12. Reactor, according to claim 11, characterized in that said lower portion (41) of the inner shell (40) includes submerged passages (44) for the melamine melt from the first reaction zone to the second reaction zone.

13. Reactor, according to any of the preceding claims, characterized in that it includes means for feeding gaseous ammonia to the second reaction zone.

14. Process for the synthesis of melamine from urea with a non-catalytic high-pressure process, Petition 870260052975, dated 01 / 06 / 2026, page 9 / 19 5 / 5 characterized in that the process is carried out in a reactor, as defined in claim 1, comprising a first reaction zone (6) and a second reaction zone (7), wherein the second reaction zone is an annular zone arranged coaxially around the first reaction zone, wherein the process includes: feeding fresh urea into the first reaction zone, wherein a liquid crude melamine melt is formed; transferring said crude melamine melt from the first reaction zone to the second reaction zone for further processing; removing a melamine-containing product from the bottom of the second reaction zone and removing excess gaseous melamine effluent containing ammonia and carbon dioxide from said second reaction zone;wherein the melamine melt is transferred from the first reaction zone to the second reaction zone through one or more passages located below the level of the liquid melamine melt contained in the first reaction zone; said one or more passages being in an immersed location to create a hydraulic seal between the first reaction zone (6) and the second reaction zone (7).

15. Process according to claim 14, characterized in that the further processing of the melamine melt carried out in the second reaction zone includes pickling the melamine melt with gaseous ammonia.

16. Process, according to claim 14 or 15, characterized in that the pressure in the second reaction zone (7) is greater than the pressure in the first reaction zone (6). Petition 870260052975, dated 01 / 06 / 2026, page 10 / 19

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