System for producing 2, 6-dimethylnaphthalene

Abstract

A system for producing 2, 6-dimethylnaphthalene comprises a hydrogenation reactor, a second lifting pipe and a cutting fractionating tower, the second lifting pipe is provided with a diameter expanding section, catalytic diesel oil I enters the hydrogenation reactor through a diesel oil pipeline I for hydrotreating to obtain a hydrogenation product, the hydrogenation product enters the first lifting pipe, hydrogen atoms are removed from the diameter expanding section, and catalytic diesel oil II is obtained; 2, 6-dimethylnaphthalene is obtained after the catalytic diesel oil II passes through the cutting fractionating tower, the whole short process and high yield of 2, 6-dimethylnaphthalene production can be achieved, and the yield reaches 7%.

Description

Technical Field

[0001] The present invention relates to the technical field of preparing 2,6-dimethylnaphthalene, and specifically to a system for producing 2,6-dimethylnaphthalene. Background Art

[0002] 2,6-dimethylnaphthalene (2,6-DMN) is an important fine chemical product. After oxidation, it forms 2,6-naphthalenedicarboxylic acid (2,6-NDCA). 2,6-naphthalenedicarboxylic acid is used to synthesize polyethylene naphthalate (PEN) and liquid crystal polyester (LCP). Both have excellent properties, and their wide applications are limited by the production cost of 2,6-dimethylnaphthalene.

[0003] Currently, 2,6-dimethylnaphthalene is mostly synthesized from o-xylene and 1,3-butadiene. The synthesis method is as follows: using o-xylene and 1,3-butadiene as raw materials, 5-o-tolyl-2-pentene is synthesized through an alkylation reaction, then 1,5-dimethyltetralin is generated through a cyclization reaction, 1,5-dimethyltetralin is dehydrogenated to generate 1,5-dimethylnaphthalene and 1,6-dimethylnaphthalene. Finally, an isomerization reaction is carried out on 1,5-dimethylnaphthalene and 1,6-dimethylnaphthalene to produce 2,6-dimethylnaphthalene and its isomers. This synthesis process is very complex, the cost of the produced product is high, and the production capacity of its downstream products is limited.

[0004] Therefore, a method for extracting 2,6-dimethylnaphthalene from catalytic diesel has been proposed. The process flow of this method is as follows: catalytic diesel is rectified to obtain a narrow fraction, the narrow fraction is extracted with furfural at 40 - 50°C, and then separated. The mixed liquid of preliminarily enriched 2,6-DMN and furfural is subjected to vacuum distillation to take out the 2,6-DMN enriched fraction, which is frozen at -10 to -25°C for 2 - 5 hours. Then, the crystallized 2,6-DMN is centrifuged to obtain crude 2,6-DMN, and then recrystallized with absolute ethanol at -10 to -25°C to obtain 2,6-DMN. However, the recovery rate of 2,6-DMN obtained by this method is low, that is, the yield is low. Summary of the Invention

[0005] In order to solve the problem of low yield of extracting 2,6-dimethylnaphthalene from catalytic diesel in the prior art, the present invention provides a system for producing 2,6-dimethylnaphthalene, which can achieve a short process and high yield in the whole production of 2,6-dimethylnaphthalene, and the yield reaches 7%.

[0006] To achieve the above object, the specific solution adopted by the present invention is as follows: A system for producing 2,6-dimethylnaphthalene, comprising a hydrogenation reactor, a second riser pipe, and a cutting fractionating tower. The second riser pipe has a diameter-expanded section. Catalytic diesel I enters the hydrogenation reactor through diesel pipeline I for hydrogenation treatment to obtain a hydrogenation product. The hydrogenation product enters the second riser pipe and hydrogen atoms are removed in the diameter-expanded section to obtain catalytic diesel II. Catalytic diesel II is obtained 2,6-dimethylnaphthalene after passing through the cutting fractionating tower.

[0007] As an optimized solution of the above system for producing 2,6-dimethylnaphthalene: The top of the hydrogenation reactor is connected to a first riser pipe. The bottom of the first riser pipe is connected to a raw material pipeline for introducing poor-quality heavy oil. The poor-quality heavy oil is introduced into the first riser pipe to undergo a catalytic cracking reaction to obtain catalytic diesel I.

[0008] As another optimized solution of the above system for producing 2,6-dimethylnaphthalene: A first separation unit is provided between the first riser pipe and the hydrogenation reactor. The first separation unit includes a main settler and a main fractionating tower. The reaction products generated by the catalytic cracking reaction in the first riser pipe are sequentially separated by the main settler and fractionated by the main fractionating tower to obtain catalytic diesel I.

[0009] As another optimized solution of the above system for producing 2,6-dimethylnaphthalene: The outlet of the first riser pipe is connected to the main settler. The top of the main settler is connected to the bottom of the main fractionating tower through reaction oil and gas pipeline I. The catalytic diesel I outlet of the main fractionating tower is connected to the hydrogenation reactor through diesel pipeline I.

[0010] As another optimized solution of the above system for producing 2,6-dimethylnaphthalene: A regenerator is connected below the main settler. The deactivated catalyst in the first riser pipe enters the regenerator for regeneration after being separated by the main settler, and the regenerated catalyst enters the first riser pipe.

[0011] As another optimized solution of the above system for producing 2,6-dimethylnaphthalene: A second separation unit is provided between the second riser pipe and the cutting fractionating tower. The second separation includes a secondary settler and a secondary fractionating tower. The reaction products in the second riser pipe are sequentially separated by the secondary settler and fractionated by the secondary fractionating tower to obtain catalytic diesel II.

[0012] As another optimized solution of the above system for producing 2,6-dimethylnaphthalene: A regenerator is connected below the secondary settler. The deactivated catalyst in the second riser pipe enters the regenerator for regeneration after being separated by the secondary settler, and the regenerated catalyst enters the second riser pipe.

[0013] As another optimization solution for the above system for producing 2,6 - dimethylnaphthalene: The catalytic heavy diesel outlet of the cutting fractionating tower is connected to the top of the hydrogenation reactor through a heavy diesel pipeline, and the catalytic light diesel outlet of the cutting fractionating tower is connected to the diameter - expanding section through a light diesel pipeline, enabling the catalytic light diesel to enter the diameter - expanding section to break the side chains and combine with hydrogen atoms.

[0014] As another optimization solution for the above system for producing 2,6 - dimethylnaphthalene: The hydrogenation reactor is connected to the bottom of the second riser through a hydrogenation product pipeline, and the connection position of the hydrogenation product pipeline and the second riser is below the diameter - expanding section.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. The present invention provides a system for producing 2,6 - dimethylnaphthalene. First, catalytic diesel I is fed into the hydrogenation reactor for hydrogenation treatment, and hydrogen atoms are removed under certain conditions to obtain catalytic diesel II. Then, catalytic diesel II is fed into the cutting fractionating tower for fractionation to obtain 2,6 - dimethylnaphthalene. This system realizes a short - process and high - efficiency production of 2,6 - dimethylnaphthalene, reduces the production cost of 2,6 - dimethylnaphthalene, and improves the yield of 2,6 - dimethylnaphthalene.

[0017] 2. In the present invention, the catalytic light diesel enters the diameter - expanding section to break the side chains of long - branched - chain monocyclic aromatic hydrocarbons to generate alkylbenzenes and light olefins, and the light olefins combine with hydrogen atoms in the diameter - expanding section, improving the yield of 2,6 - dimethylnaphthalene; meanwhile, high - value - added alkylbenzenes can be by - produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic structural diagram of the system of the present invention;

[0019] Reference numerals: 1, raw material pipeline; 2, first riser; 3, main settler; 4, regenerator; 401, first regeneration pipeline; 402, second regeneration pipeline; 403, air pipeline; 5, reaction oil and gas pipeline I; 6, main fractionating tower; 7, diesel pipeline I; 8, catalytic gasoline pipeline I; 9, catalytic slurry pipeline I; 10, hydrogenation reactor; 11, hydrogenation product pipeline; 12, second riser; 1201, diameter - expanding section; 13, auxiliary settler; 14, reaction oil and gas pipeline II; 15, auxiliary fractionating tower; 16, catalytic gasoline pipeline II; 17, diesel pipeline II; 18, catalytic slurry pipeline II; 19, cutting fractionating tower; 20, product pipeline; 21, light diesel pipeline; 22, heavy diesel pipeline. DETAILED DESCRIPTION OF THE INVENTION

[0020] The technical solution of the present invention will be further elaborated in detail below in conjunction with specific embodiments. For parts that are not detailedly recorded and disclosed in the following embodiments of the present invention, they should all be understood as the prior art known or should be known to those skilled in the art.

[0021] Example 1

[0022] A system for producing 2,6 - dimethylnaphthalene, comprising a hydrogenation reactor 10, a second riser 12 and a cutting fractionation tower 19. The second riser 12 has an expanded diameter section 1201. The top of the hydrogenation reactor 10 is connected to a diesel pipeline I7. The bottom of the hydrogenation reactor 10 is connected to the bottom of the second riser 12 through a hydrogenation product pipeline 11, and the connection point of the hydrogenation product pipeline 11 and the second riser 12 is located below the expanded diameter section 1201. There is a hydrogenation catalyst in the hydrogenation reactor 10, so that catalytic diesel I enters the hydrogenation reactor 10 through the diesel pipeline I7 for hydrogenation treatment to obtain a hydrogenation product, and the hydrogenation product is rich in tetralin - like substances. The hydrogenation product enters the second riser 12 through the hydrogenation product pipeline 11 and hydrogen atoms are removed in the expanded diameter section 1201 to obtain catalytic diesel II. The catalytic diesel II is obtained as 2,6 - dimethylnaphthalene after passing through the cutting fractionation tower 19.

[0023] The reaction conditions in the hydrogenation reactor 10 are: the reaction temperature is 320 - 390 °C, the hydrogen partial pressure is 5.0 - 10.0 MPa, the volume space velocity is 0.5 - 1.5 h -1 , the hydrogen / oil volume ratio is 300 - 800. Under these reaction conditions and the conditions of the hydrogenation catalyst, the bicyclic aromatic hydrocarbons in the catalytic diesel are selectively hydrogenated and saturated to tetralin - like substances, that is, a hydrogenation product rich in tetralin - like substances is obtained; the hydrogenation catalyst has optimized hydrogenation saturation activity, that is, the hydrogenation catalyst has an active metal, and the content of the active metal is 12 w% - 30 w%, the active metal is mainly nickel, and other metals include one or several of cobalt, molybdenum or tungsten.

[0024] In the second riser 12: the hydrogenation product removes hydrogen atoms under the conditions of a temperature of 480 - 580 °C, a catalyst - to - oil ratio of 5 - 10, a pressure of 0.1 - 0.4 MPa and the action of a catalyst to obtain catalytic diesel II. The catalyst is a conventional catalytic cracking catalyst. The hydrogenation product selectively removes hydrogen atoms under the above conditions to generate catalytic diesel II rich in naphthalene - like substances. Specifically, hydrogen transfer occurs between tetralin - like molecules to generate 2,6 - dimethylnaphthalene and its isomers and alkylbenzenes. Among them, 2,6 - dimethyltetralin and its isomers in the tetralin - like substances remove hydrogen atoms to generate 2,6 - dimethylnaphthalene and its isomers, and the remaining tetralin - like substances combine with hydrogen atoms to generate alkylbenzenes, that is, hydrogen atom transfer occurs between tetralin - like substances. The short - process and high - efficiency production of 2,6 - dimethylnaphthalene are realized, the production cost of 2,6 - dimethylnaphthalene is reduced, and the yield of 2,6 - dimethylnaphthalene is increased; at the same time, high - value - added alkylbenzenes are by - produced.

[0025] In this embodiment, catalytic diesel I is obtained by catalytic cracking of inferior heavy oil. Specifically, the top of the hydrogenation reactor 10 is connected to a first riser 2, and the bottom of the first riser 2 is connected to a feed pipeline 1 for introducing inferior heavy oil. The inferior heavy oil is introduced into the first riser 2 to undergo catalytic cracking to obtain catalytic diesel I. The reaction temperature of the catalytic cracking reaction is 480 - 550 °C, the catalyst-oil ratio is 5 - 10, the reaction pressure is 0.1 - 0.4 MPa, the reaction time is 3 - 6 s, and the atomizing steam accounts for 3 - 8 w% of the feed amount.

[0026] A first separation unit is provided between the first riser 2 and the hydrogenation reactor 10. The first separation unit includes a main settler 3 and a main fractionating tower 6. The reaction products generated by the catalytic cracking reaction in the first riser 2 are separated by the main settler 3 in sequence and fractionated by the main fractionating tower 6 to obtain catalytic diesel I. The outlet of the first riser 2 is connected to the main settler 3, the top of the main settler 3 is connected to the bottom of the main fractionating tower 6 through a reaction oil and gas pipeline I5, and the catalytic diesel I outlet of the main fractionating tower 6 is connected to the hydrogenation reactor 10 through a diesel pipeline I7. The reaction products generated in the first riser 2 enter the main settler 3 to be separated into reaction oil and gas and deactivated catalyst. Among them, the reaction oil and gas enter the main fractionating tower 6 through the reaction oil and gas pipeline I5 for fractionation to obtain catalytic gasoline I, catalytic diesel I, and catalytic slurry I. A catalytic gasoline pipeline I8 and a circulation pipeline I9 are connected to the main fractionating tower 6. A separator is provided on the catalytic gasoline pipeline I8. That is, the catalytic gasoline is introduced into the separator through the catalytic gasoline pipeline I8 to separate out rich gas and sewage and then introduced into the absorption tower. A part of the fractionated catalytic slurry I enters its downstream system and another part of the catalytic slurry I re-enters the main fractionating tower 6 through the circulation pipeline I9.

[0027] A regenerator 4 is connected below the main settler 3. The deactivated catalyst in the first riser 2 enters the regenerator 4 for regeneration after being separated by the main settler 3, and the regenerated catalyst enters the first riser 2. Specifically, an inlet connected to the first riser 2 is provided at a position near the top on one side of the main settler 3. The bottom end of the main settler 3 is connected to the top end of the regenerator 4. The bottom of the regenerator 4 is connected to the bottom of the first riser 2 through a first regeneration pipeline 401, and an air pipeline 403 for introducing air into the regenerator 4 is connected to the bottom end of the regenerator 4. The deactivated catalyst separated by the main settler 3 enters the regenerator 4 for regeneration, and the regenerated catalyst enters the bottom of the first riser 2 through the first regeneration pipeline 401 and participates in the catalytic cracking reaction in the first riser 2.

[0028] The hydrogenated product enters the second riser 12 through the hydrogenated product pipeline 11, and hydrogen atoms are removed in the enlarged diameter section 1201 of the second riser 12. The reaction conditions in the enlarged diameter section 1201 of the second riser 12 are: temperature 480 - 580 °C, catalyst-oil ratio 5 - 10, pressure 0.1 - 0.4 MPa, and catalyst is introduced into the enlarged diameter section 1201, so that catalytic diesel I reacts in the second riser 12 to obtain reaction oil gas, and 2,6-dimethyltetralin and its isomers in tetralin remove hydrogen atoms to obtain 2,6-dimethylnaphthalene and its isomers. Specifically, a second separation unit is provided between the second riser 12 and the cutting fractionating tower 19. The second separation includes a secondary settler 13 and a secondary fractionating tower 15. The reaction products in the second riser 12 are separated by the secondary settler 13 in sequence and fractionated by the secondary fractionating tower 15 to obtain catalytic diesel II. The outlet of the second riser 12 is connected to the secondary settler 13. The top of the secondary settler 13 is connected to the bottom of the secondary fractionating tower 15 through the reaction oil gas pipeline II 14. The catalytic diesel II outlet of the secondary fractionating tower 15 is connected to the cutting fractionating tower 19 through the diesel pipeline II 17. The reaction products generated in the second riser 12 enter the secondary settler 13 to be separated into reaction oil gas and deactivated catalyst. Among them, the reaction oil gas enters the secondary fractionating tower 15 through the reaction oil gas pipeline II 14 for fractionation to obtain catalytic gasoline II, catalytic diesel II, and catalytic slurry II. A catalytic gasoline pipeline II 16 and a circulation pipeline II 18 are connected to the main fractionating tower 6. A separator is provided on the catalytic gasoline pipeline II 16. That is, catalytic gasoline is introduced into the separator through the catalytic gasoline pipeline II 16 to separate out rich gas and sewage and then introduced into the absorption tower. The fractionated catalytic slurry II is connected to the circulation pipeline I 9 through the circulation pipeline II 18.

[0029] A regenerator 4 is connected below the secondary settler 13. The deactivated catalyst in the second riser 12 enters the regenerator 4 for regeneration after being separated by the secondary settler 13, and the regenerated catalyst enters the second riser 12. Specifically, an inlet connected to the second riser 12 is provided at a position near the top on one side of the secondary settler 13. The bottom end of the secondary settler 13 is communicated with the top end of the regenerator 4. The bottom of the regenerator 4 is connected to the bottom of the second riser 12 through the second regeneration pipeline 402, and an air pipeline 403 for sending air into the regenerator 4 is connected to the bottom end of the regenerator 4. The deactivated catalyst separated by the secondary settler 13 enters the regenerator 4 for regeneration, and the regenerated catalyst enters the bottom of the second riser 12 through the second regeneration pipeline 402 and flows into the enlarged diameter section 1201 to participate in the reaction.

[0030] A product pipeline 20 for flowing out 2,6 - dimethylnaphthalene and its isomers is connected to the cutting fractionating tower 19. The catalytic diesel II is cut and fractionated in the cutting fractionating tower 19 to obtain 2,6 - dimethylnaphthalene and its isomers, catalytic light diesel, and catalytic heavy diesel. The catalytic diesel II is cut and fractionated to obtain 2,6 - dimethylnaphthalene and its isomers. The cutting and fractionating temperature of the catalytic diesel II is 255°C and 275°C, and 2,6 - dimethylnaphthalene and its isomers, catalytic light diesel, and catalytic heavy diesel are obtained.

[0031] The production of 2,6 - dimethylnaphthalene using the system described in Example 1 includes the following steps:

[0032] S1, The inferior heavy oil is fed into the first riser 2 through the raw material pipeline 11 for catalytic cracking reaction. The reaction temperature of the catalytic cracking reaction is 480 - 550°C, the catalyst - to - oil ratio is 5 - 10, the reaction pressure is 0.1 - 0.4 MPa, the reaction time is 3 - 6 s, and the atomizing steam accounts for 3 - 8 w% of the feed amount. The reaction products obtained from the catalytic cracking reaction are successively separated by the main settler 33 and fractionated by the main fractionating tower 6 to obtain catalytic diesel I;

[0033] S2, The catalytic diesel I is fed into the hydrogenation reactor 10 through the diesel pipeline I7 for hydrogenation treatment to obtain a hydrogenation product. The reaction temperature of the hydrogenation treatment is 320 - 390°C, the hydrogen partial pressure is 5.0 - 10.0 MPa, the volume space velocity is 0.5 - 1.5 h -1 , and the hydrogen - to - oil volume ratio is 300 - 800. Under these reaction conditions and the conditions of the hydrogenation catalyst, the bicyclic aromatic hydrocarbons in the catalytic diesel I are selectively hydrogenated and saturated to tetralin - like compounds, that is, a hydrogenation product rich in tetralin - like compounds is obtained; the hydrogenation catalyst has optimized hydrogenation saturation activity, that is, the hydrogenation catalyst has an active metal, and the content of the active metal is 12 w% - 30 w%, the active metal is mainly nickel, and the other metals include one or several of cobalt, molybdenum, or tungsten;

[0034] S3. The hydrogenated product is fed into the bottom of the second riser 12 through the hydrogenated product pipeline 11, and hydrogen atoms are removed in the diameter-expanded section 1201 to obtain a reaction product. The reaction product is separated by the auxiliary settler 13 and fractionated by the auxiliary fractionating tower 15 to obtain catalytic diesel II. The reaction temperature for the reaction occurring in the diameter-expanded section 1201 is 480-580 °C, the catalyst-oil ratio is 5-10, and the pressure is 0.1-0.4 MPa. The catalyst is a conventional catalytic cracking catalyst. The hydrogenated product selectively removes hydrogen atoms under the above conditions to generate catalytic diesel II rich in naphthalene. Specifically, hydrogen transfer occurs between tetralin molecules to generate 2,6-dimethylnaphthalene and its isomers and alkylbenzene. Among them, 2,6-dimethyltetralin and its isomers in tetralin remove hydrogen atoms to generate 2,6-dimethylnaphthalene and its isomers, and the remaining tetralin combines with hydrogen atoms to generate alkylbenzene, that is, hydrogen atom transfer occurs between tetralin. This realizes a short process and high efficiency for the production of 2,6-dimethylnaphthalene, reduces the production cost of 2,6-dimethylnaphthalene, and improves the yield of 2,6-dimethylnaphthalene; at the same time, high-value-added alkylbenzene is produced as a by-product.

[0035] Example 2

[0036] This example is an improved system for producing 2,6-dimethylnaphthalene based on Example 1. Its main steps are the same as those in Example 1. The improvement lies in that the catalytic heavy diesel outlet of the cutting fractionating tower 19 is connected to the top of the hydrogenation reactor 10 through the heavy diesel pipeline 22, that is, the catalytic heavy diesel enters the hydrogenation reactor 10 and is mixed with catalytic diesel I for hydrogenation treatment to obtain catalytic diesel II. The catalytic light diesel outlet of the cutting fractionating tower 19 is connected to the diameter-expanded section 1201 through the light diesel pipeline 21. The catalytic light diesel enters the diameter-expanded section 1201 through the light diesel pipeline 21. The long side-chain monocyclic aromatic hydrocarbons in the catalytic light diesel break the side chains to generate alkylbenzene and light olefins. The light olefins combine with hydrogen atoms in the diameter-expanded section 1201, further promoting the removal of hydrogen atoms from catalytic diesel II, thereby improving the yield of 2,6-dimethylnaphthalene and its isomers. At the same time, high-value-added alkylbenzene is produced.

[0037] The production of 2,6-dimethylnaphthalene using the system described in Example 2 includes the following steps:

[0038] S1-3 is the same as that in Example 1 for the production of 2,6-dimethylnaphthalene; in S4, the reaction product of the second riser 12 is separated by the secondary settler 13 and fractionated by the secondary fractionating column 15 to obtain catalytic heavy diesel and catalytic light diesel. The catalytic heavy diesel is mixed with catalytic diesel I and enters the hydrogenation reactor 10 for hydrogenation treatment. The catalytic light diesel enters the diameter-expanding section 1201 through the light diesel pipeline 21 to be mixed with the hydrogenation product to break its chain and combine with hydrogen atoms. Among them, the catalytic light diesel is rich in long-branched single-ring aromatic hydrocarbons. When the catalytic light diesel is introduced into the hydrogenation product, at a temperature of 480-580°C, a catalyst-oil ratio of 5-10, a pressure of 0.1-0.4 MPa, and under the action of a catalyst, the long-branched single-ring aromatic hydrocarbons break the side chains to form alkylbenzenes and light olefins. The catalyst is a conventional catalytic cracking catalyst. The light olefins can combine with hydrogen atoms to form alkanes, that is, the light olefins can undergo hydrogen transfer with 2,6-dimethyltetrahydronaphthalene, further increasing the yield of 2,6-dimethylnaphthalene. At the same time, alkylbenzenes with high added value are obtained.

[0039] Example 3

[0040] The properties of the inferior heavy oil used in this example are shown in Table 1. The inferior heavy oil undergoes a catalytic cracking reaction to obtain catalytic diesel I. The reaction temperature of the catalytic cracking reaction is 500°C, the catalyst-oil ratio is 5.5, the reaction pressure is 0.2 MPa, the reaction time is 3 s, and the atomizing steam accounts for 3 w% of the feed amount.

[0041] The catalytic diesel I is subjected to hydrogenation treatment to obtain a hydrogenation product. The reaction temperature of the hydrogenation treatment is 320°C, the hydrogen partial pressure is 5.0 MPa, the volume space velocity is 0.5 h -1 ⁻¹, the hydrogen / oil volume ratio is 300. The catalyst for the hydrogenation treatment is a hydrogenation catalyst. The hydrogenation catalyst has an active metal, and the content of the active metal is 12 w%. The active metal is mainly nickel, and the other metal is cobalt.

[0042] At a temperature of 500°C, a catalyst-oil ratio of 5.5, a pressure of 0.2 MPa, and under the action of a catalyst, the hydrogenation product removes hydrogen atoms to obtain catalytic diesel II. The catalyst is a conventional catalytic cracking catalyst.

[0043] The catalytic diesel II is cut and fractionated at a temperature of 255°C (low cut point) and 275°C (high cut point) to obtain 2,6-dimethylnaphthalene and its isomers. The yields of 2,6-dimethylnaphthalene and its isomers are shown in Table 3.

[0044] Example 4

[0045] The properties of the inferior heavy oil used in this example are shown in Table 1. The inferior heavy oil undergoes a catalytic cracking reaction to obtain catalytic diesel I. The reaction temperature of the catalytic cracking reaction is 500°C, the catalyst-oil ratio is 5.5, the reaction pressure is 0.2 MPa, the reaction time is 3 s, and the atomizing steam accounts for 3 w% of the feed amount.

[0046] The hydrotreated diesel I is subjected to hydrotreating to obtain a hydrotreated product. The reaction temperature of the hydrotreating is 320 °C, the hydrogen partial pressure is 5.0 MPa, the volume hourly space velocity is 0.5 h -1 , the hydrogen / oil volume ratio is 300, the catalyst for the hydrotreating is a hydrotreating catalyst. The hydrotreating catalyst has an active metal, and the content of the active metal is 12 w%, the active metal is mainly nickel, and the other metal is cobalt.

[0047] Under the conditions of a temperature of 500 °C, a catalyst / oil ratio of 5.5, a pressure of 0.2 MPa and in the presence of a catalyst, the hydrotreated product removes hydrogen atoms to obtain catalytic diesel II. The catalyst is a conventional fluid catalytic cracking catalyst.

[0048] The catalytic diesel II is fractionated at a temperature of 255 °C (low cut point) and 275 °C (high cut point) to obtain 2,6-dimethylnaphthalene and its isomers, catalytic light diesel and catalytic heavy diesel. The catalytic heavy diesel is mixed with the catalytic diesel I and subjected to hydrotreating to obtain a hydrotreated product. The catalytic light diesel is mixed with the hydrotreated product and reacts under the conditions of a temperature of 500 °C, a catalyst / oil ratio of 5.5, a pressure of 0.2 MPa and in the presence of a catalyst. The yields of 2,6-dimethylnaphthalene and its isomers are shown in Table 3.

[0049] Example 5

[0050] The properties of the inferior heavy oil used in this example are shown in Table 1. The inferior heavy oil undergoes a fluid catalytic cracking reaction to obtain catalytic diesel I. The reaction temperature of the fluid catalytic cracking reaction is 550 °C, the catalyst / oil ratio is 10, the reaction pressure is 0.4 MPa, the reaction time is 6 s, and the atomizing steam accounts for 8 w% of the feed amount.

[0051] The catalytic diesel I is subjected to hydrotreating to obtain a hydrotreated product. The reaction temperature of the hydrotreating is 390 °C, the hydrogen partial pressure is 10.0 MPa, the volume hourly space velocity is 1.5 h -1 , the hydrogen / oil volume ratio is 800, the catalyst for the hydrotreating is a hydrotreating catalyst. The hydrotreating catalyst has an active metal, and the content of the active metal is 30 w%, the active metal is mainly nickel, and the other metal is cobalt.

[0052] Under the conditions of a temperature of 580 °C, a catalyst / oil ratio of 10, a pressure of 0.4 MPa and in the presence of a catalyst, the hydrotreated product removes hydrogen atoms to obtain catalytic diesel II. The catalyst is a conventional fluid catalytic cracking catalyst.

[0053] Catalytic diesel II is fractionated at temperatures of 255 °C (low cut point) and 275 °C (high cut point) to obtain 2,6-dimethylnaphthalene and its isomers, catalytic light diesel, and catalytic heavy diesel. The catalytic heavy diesel is mixed with catalytic diesel I and subjected to hydrotreating to obtain a hydrotreated product. The catalytic light diesel is mixed with the hydrotreated product and reacted at a temperature of 580 °C, a catalyst-to-oil ratio of 10, a pressure of 0.4 MPa, and in the presence of a catalyst. The yields of 2,6-dimethylnaphthalene and its isomers are shown in Table 3.

[0054] Comparative example

[0055] To extract 2,6-dimethylnaphthalene from catalytic diesel, catalytic diesel and catalytic diesel I have the same properties and are both obtained by catalytic cracking of inferior heavy oil. The properties of the inferior heavy oil used in this example are shown in Table 1. The reaction temperature of the catalytic cracking reaction is 500 °C, the catalyst-to-oil ratio is 5.5, the reaction pressure is 0.2 MPa, the reaction time is 3 s, and the atomized steam accounts for 3 w% of the feed. The catalytic diesel is rectified to obtain a narrow fraction, and the narrow fraction is extracted with furfural at 40 - 50 °C and then separated. The mixed liquid of preliminarily enriched 2,6-DMN and furfural is subjected to vacuum distillation, and the 2,6-DMN enriched fraction is taken out, frozen at -10 to -25 °C for 2 - 5 h, and then the crystallized 2,6-DMN is centrifuged to obtain crude 2,6-DMN, and then recrystallized with absolute ethanol at -10 to -25 °C to obtain 2,6-DMN. The yield of 2,6-DMN obtained by this method is shown in Table 3.

[0056] Table 1 Heavy oil properties

[0057] Table 2 Main operating conditions

[0058] Table 3 Product distribution

[0059] According to Table 3, it can be seen that the yield of 2,6-dimethylnaphthalene in Examples 3 - 5 reaches more than 7 w%, and the yields of 2,6-dimethylnaphthalene in Examples 4 and 5 are greater than the yield of 2,6-dimethylnaphthalene in Example 3.

[0060] The foregoing description of the disclosed embodiments enables those skilled in the art to practice or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A system for producing 2,6-dimethylnaphthalene, comprising a hydrogenation reactor (10), a second riser (12) and a cutting fractionation column (19), characterized in that: The second riser (12) has a diameter-expanded section (1201). The catalytic diesel I enters the hydrogenation reactor (10) through the diesel pipeline I (7) for hydrogenation treatment to obtain a hydrogenated product. The hydrogenated product enters the second riser (12) and hydrogen atoms are removed in the diameter-expanded section (1201) to obtain catalytic diesel II. The catalytic diesel II is fractionated in the cutting fractionating tower (19) to obtain 2,6-dimethylnaphthalene.

2. The system for producing 2,6-dimethylnaphthalene according to claim 1, characterized in that: The top of the hydrogenation reactor (10) is connected to a first riser (2). The bottom of the first riser (2) is connected to a feed pipeline (1) for introducing inferior heavy oil. The inferior heavy oil is introduced into the first riser (2) to undergo a catalytic cracking reaction to obtain catalytic diesel I.

3. The system for producing 2,6 - dimethylnaphthalene according to claim 2, wherein: A first separation unit is arranged between the first riser (2) and the hydrogenation reactor (10). The first separation unit includes a main settler (3) and a main fractionating tower (6). The reaction products generated by the catalytic cracking reaction in the first riser (2) are sequentially separated by the main settler (3) and fractionated by the main fractionating tower (6) to obtain catalytic diesel I.

4. A system for producing 2,6-dimethylnaphthalene according to claim 3, characterized in that: The outlet of the first riser (2) is connected to the main settler (3). The top of the main settler (3) is connected to the bottom of the main fractionating tower (6) through a reaction oil and gas pipeline I (5). The catalytic diesel I outlet of the main fractionating tower (6) is connected to the hydrogenation reactor (10) through the diesel pipeline I (7).

5. The system for producing 2,6-dimethylnaphthalene according to claim 3, characterized in that: The regenerator (4) is communicated below the main settler (3). The deactivated catalyst in the first riser (2) enters the regenerator (3) for regeneration after being separated by the main settler (3), and the regenerated catalyst enters the first riser (2).

6. The system for producing 2,6-dimethylnaphthalene according to claim 1, characterized in that: A second separation unit is arranged between the second riser (12) and the cutting fractionating tower (19). The second separation includes a secondary settler (13) and a secondary fractionating tower (15). The reaction products in the second riser (12) are sequentially separated by the secondary settler (13) and fractionated by the secondary fractionating tower (15) to obtain catalytic diesel II.

7. The system for producing 2,6 - dimethylnaphthalene according to claim 6, wherein: The outlet of the second riser (12) is connected to the secondary settler (13). The top of the secondary settler (13) is connected to the bottom of the secondary fractionating tower (15) through a reaction oil and gas pipeline II (14). The catalytic diesel II outlet of the secondary fractionating tower (15) is connected to the cutting fractionating tower (19) through the diesel pipeline II (17).

8. The system for producing 2,6-dimethylnaphthalene according to claim 6, characterized in that: The regenerator (4) is communicated below the secondary settler (13). The deactivated catalyst in the second riser (12) enters the regenerator (4) for regeneration after being separated by the secondary settler (13), and the regenerated catalyst enters the second riser (12).

9. The system for producing 2,6-dimethylnaphthalene according to claim 1, characterized in that: The catalytic heavy diesel outlet of the cutting fractionating tower (19) is connected to the top of the hydrogenation reactor (10) through a heavy diesel pipeline (22). The catalytic light diesel outlet of the cutting fractionating tower (19) is connected to the diameter-expanded section (1201) through a light diesel pipeline (21) to make the catalytic light diesel break the chain and combine with hydrogen atoms in the diameter-expanded section (1201).

10. The system for producing 2,6-dimethylnaphthalene according to claim 1, characterized in that: The hydrogenation reactor (10) is connected to the bottom of the second riser (12) through a hydrogenation product pipeline (11), and the connection between the hydrogenation product pipeline (11) and the second riser (12) is located below the enlarged diameter section (1201).

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