A straight-run diesel hydrocracking method

Abstract

The invention discloses a straight-run diesel hydrocracking method. After the straight-run diesel is hydrorefined, the hydrocracking reaction effluent is separated by a hydrocracking catalyst bed containing a ZSM‑5@β composite molecular sieve to obtain a naphtha fraction; the obtained naphtha component is passed through a normal isomerization adsorption separation device to obtain a component rich in normal alkanes and rich in isoalkanes, and the component rich in normal alkanes can be directly used as a raw material for steam cracking to produce ethylene, while the component rich in isoalkanes can be used as a high-quality National VI gasoline blending component. In the present invention, a ZSM‑5@β composite molecular sieve with strong paraffin cracking and isomerization capabilities is selected as an acidic center, which can effectively isomerize and crack the paraffins in diesel into the naphtha component to produce high-octane gasoline.

Description

Technical Field

[0001] The invention relates to a straight-run diesel hydrocracking method, which is particularly suitable for the process of producing gasoline by diesel hydrocracking and can achieve the purpose of reducing the diesel-gasoline ratio in refineries. Background Art

[0002] In recent years, fuel oil consumption has continued to decline, diesel product sales have peaked, and my country's diesel-to-gasoline ratio has approached 0.8. The problem of excess and unsalable diesel products has seriously restricted the high-quality and sustainable development of oil refining companies. Hydrocracking technology can process raw materials such as naphtha, jet fuel, diesel, and wax oil, and convert them into ideal products. Diesel hydrocracking technology can effectively convert diesel fractions into gasoline components to achieve the purpose of reducing diesel. In addition, the National VI gasoline standard has stricter control over the aromatics and benzene content in gasoline products, with the aromatics content required to be no more than 35%, and the benzene content required to be no more than 0.8%. Therefore, the blending amount of gasoline components that rely on aromatics to maintain high octane numbers in the gasoline blending pool will be strictly limited, such as low-sulfur gasoline produced by catalytic gasoline adsorption desulfurization, and high-octane gasoline components produced by catalytic diesel hydrogenation conversion. In order to meet the National VI gasoline standard, the isoparaffin content in the gasoline component must be increased. Straight-run diesel has a low aromatic content and a high paraffin content. If the paraffins in straight-run diesel can be selectively isomerized and cracked into naphtha to produce gasoline components with high octane number and high isoparaffin content, it can not only change the isoparaffin content in the gasoline pool to meet national standards, but also effectively reduce the diesel-gasoline ratio, meet market demand, and improve the economic benefits of the enterprise.

[0003] There are many reports on catalytic diesel hydrogenation methods, but there are few reports on the production of high-octane gasoline by straight-run diesel hydrocracking units. CN 103865577 A discloses a method for producing light aromatics and clean fuel oil products from catalytic cracking diesel. The inventive method cuts the effluent after catalytic diesel hydrorefining, wherein the heavy fraction >355°C is deeply hydrocracking into light oil products; the light fraction oil obtained by cutting is extracted, and the alkane-rich raffinate oil is used as a clean diesel blending component; the aromatic-rich extracted oil is hydrocracking to produce light aromatics and clean gasoline blending components. This method can be based on the composition of high-quality hydrocarbons in the product, using a separation and precision processing method, but the aromatic and benzene content of the gasoline component produced is too high, and the blending amount is limited.

[0004] CN 1493665A discloses a medium-pressure hydrocracking and catalytic cracking combined process for producing low-sulfur diesel. The invention provides a diesel medium-pressure hydrocracking-catalytic cracking combined process, the middle distillate oil obtained by medium-pressure hydrocracking is used as FCC raw material, and ultra-low sulfur clean diesel components are produced in maximum quantity. This method mainly increases the production of middle distillate oil in maximum quantity, the gasoline yield is limited, the process flow is complicated, the operating cost is high, and it is impossible to significantly change the diesel and gasoline ratio of the whole plant. Summary of the invention

[0005] The technical problem to be solved by the present invention is how to selectively isomerize and crack the paraffins in straight-run diesel into naphtha, and produce high-quality gasoline blending components and ethylene cracking raw materials after normal isomerization separation.

[0006] A straight-run diesel hydrocracking method of the present invention comprises the following steps:

[0007] (1) providing a hydrofining reaction zone and a hydrocracking reaction zone, wherein the hydrofining reaction zone is filled with a hydrofining catalyst, and the hydrocracking reaction zone is filled with a hydrocracking catalyst containing a ZSM-5@β composite molecular sieve;

[0008] (2) After the straight-run diesel feedstock is mixed with hydrogen, it enters the hydrotreating reaction zone and contacts the hydrotreating catalyst to undergo desulfurization, denitrification and dearomatization reactions;

[0009] (3) The effluent from the hydrotreating reaction and optional supplemental hydrogen enter the cracking reaction zone, which usually includes 2 to 5 beds, for hydrocracking reaction;

[0010] (4) Separating the effluent from the hydrocracking reaction to obtain dry gas, liquefied gas, naphtha and diesel components; the initial distillation point of naphtha is 20~85℃, and the dry point is 165~210℃;

[0011] (5) The naphtha component obtained in step (4) is subjected to an n-isomerization adsorption separation unit to obtain a component rich in n-alkanes and a component rich in isoalkanes; the component rich in n-alkanes can be directly used as a raw material for steam cracking to produce ethylene, while the component rich in isoalkanes can be used as a high-quality National VI gasoline blending component.

[0012] Furthermore, the hydrotreating reaction zone and the hydrocracking reaction zone, the refining reaction zone and the cracking reaction zone may be arranged in one reactor or in two or more reactors.

[0013] Furthermore, the hydrorefining catalyst may be a conventional hydrorefining catalyst in the art, or may be prepared according to an existing patent method. Commercial hydrorefining catalysts that may be selected include FF-46, FF-56, FF-66, and FF-76 catalysts developed by Dalian Petrochemical Research Institute.

[0014] Furthermore, the hydrocracking catalyst includes a carrier, an active metal and a binder. The catalyst carrier contains a ZSM-5@β composite molecular sieve with a core-shell structure. The ZSM-5@β composite molecular sieve with a core-shell structure has a β molecular sieve as a core and a ZSM-5 molecular sieve as a shell, wherein the theoretical mass ratio of the β molecular sieve to the ZSM-5 molecular sieve is 1:2~1:10. The total silicon-aluminum ratio of the composite molecular sieve is 12~40, the infrared acid content is 0.2~1.5 mmol / g, the average pore diameter is 2.0~4.0 nm, and the specific surface area is 250~500 m 2 / g, pore volume is 0.08~0.30 cm 3 / g.

[0015] Furthermore, the hydrocracking carrier is a mixture of alumina or / and amorphous silicon aluminum and ZSM-5@β composite molecular sieve. The mass fraction of ZSM-5@β composite molecular sieve in the catalyst carrier is generally 5% to 60%. The binder is generally alumina or silicon oxide. The active metal component is at least one of Group VI, Group VII or Group VIII metals, metal oxides or metal sulfides, more preferably at least one of iron, chromium, molybdenum, tungsten, cobalt, nickel, their sulfides, or oxides. Based on the weight of the hydrocracking catalyst, the content of the active metal in terms of oxide is generally 6 to 40wt%.

[0016] Further, the preparation method of the ZSM-5@β composite molecular sieve is as follows:

[0017] (a) First, synthesize nanocrystalline seeds of β molecular sieve: use tetraethyl orthosilicate as silicon source (TEOS) and tetraethylammonium hydroxide (TEAOH) as template, stir and mix them in a mass ratio of 1:1~1:5 to form mixed solution I; use NaAlO2 as aluminum source and NaOH aqueous solution as reaction medium, NaAlO2:H2O: NaOH=1:100~200:0.05~1 (mass ratio), and stir the prepared mixed solution II at 15~35℃ for 2~4h. Then, pour mixed solution II into mixed solution I, and transfer the mixed solution of the two to a crystallization kettle, crystallize at 120~160℃ for 24~72h to obtain nanoscale β molecular sieve;

[0018] (b) Preparation of ZSM-5 molecular sieve synthesis emulsion: using tetraethyl orthosilicate as silicon source, tetrapropylammonium hydroxide (TPAOH) as template, adding water as dissolving medium, the mass ratio of the three is TEOS:H2O:TPAOH=1:1~3:1~5, and obtaining mixed solution III after full dissolution; using NaAlO2 as aluminum source, using aqueous solution of NaOH as reaction medium, NaAlO2:H2O:NaOH=1:1~10:0.5~2 (mass ratio), and stirring the prepared solution IV at 15~35℃ for 2~4h; adding solution III and β molecular sieve seed to solution IV and stirring for 2~4h; then transferring the mixed solution to a crystallization kettle, and crystallizing at 120~160℃ for 12~72h; filtering, washing and drying the crystallized product, and calcining at 400~600℃ for 4~10h to obtain Na-type ZSM-5@β composite molecular sieve;

[0019] (c) Using ammonium chloride aqueous solution as the ammonium exchange medium at an exchange temperature of 70-95°C, the Na-type ZSM-5@β composite molecular sieve obtained in step (b) is subjected to two ammonium exchanges and calcined at 400-600°C for 2-4 h to finally obtain an H-type ZSM-5@β composite molecular sieve.

[0020] Furthermore, in step (a), the silicon-aluminum ratio of the feed is 20-40.

[0021] Furthermore, the ratio of silicon to aluminum in step (b) is 10 to 40. The drying in step (b) refers to drying at 50 to 100° C. for 6 to 12 hours.

[0022] Furthermore, the straight-run diesel has an initial boiling point of 130-250°C, a final boiling point of 300-400°C, a sulfur content of 0.1wt%-1.5wt%, a nitrogen content of 0.01wt%-0.1wt%, and a density of 0.75-0.83 g / cm 3 , the aromatic content is 10wt%~25wt%.

[0023] Furthermore, the diesel component obtained in step (4) can be used as a blending component for National VI diesel, or as a raw material for steam cracking to produce ethylene, or can be circulated to the refining reaction zone or the cracking reaction zone for deep cracking to produce a high-octane gasoline component in maximum quantity.

[0024] Furthermore, the naphtha isomerization separation device described in step (5) adopts conventional knowledge in the art. The naphtha isomerization separation device generally includes an adsorption unit, a purge unit, and a desorption unit. The typical operating conditions of the adsorption unit are: pressure 0.1-1.5 MPa, temperature 150-350 °C, liquid phase volume space velocity 0.4-4 h -1, adsorption time 10 to 20 min. The typical operating conditions of the purge unit are: purge pressure 0.1 to 1.5 MPa, temperature 150 to 350 °C, volume space velocity 40 to 120 h -1 , purge time 5 to 10 min. The typical operating conditions of the desorption unit are: pressure 0.3 to 1.5 MPa, temperature 150 to 350 °C, volume space velocity 40 to 120 h -1 , desorption time is 5 to 10 min.

[0025] Furthermore, the reaction conditions in the hydrotreating reaction zone and the hydrocracking reaction zone are generally as follows: reaction pressure 5.0-15.0 MPa, preferably 6.0-12.0 MPa; average reaction temperature 280-430°C, preferably 310-420°C; hydrotreating volume space velocity 0.2-6.0 h -1 , preferably 0.5~2.0h -1 ; Hydrocracking volume space velocity is 0.6~10.0h -1 , preferably 1.0~2.0h -1 ; The volume ratio of hydrogen to oil is 400:1 to 1800:1, preferably 600:1 to 1000:1.

[0026] Furthermore, the separation in step (4) generally includes high-pressure gas-liquid separation, low-pressure gas-liquid separation and fractionation operations.

[0027] The applicant has found through research that the molecular sieve component plays a role in the cracking activity of the hydrocracking catalyst, and different types of molecules show different characteristics of hydrocarbon molecular cracking reactions. Generally speaking, the Y molecular sieve has good ring-opening selectivity for aromatics and cycloalkanes; the ZSM-5 molecular sieve has good cracking selectivity for alkanes and a high secondary cracking ratio; and the β molecular sieve has strong isomerization ability for alkanes. However, in the prior art, a single molecular sieve component cannot meet the requirements of efficiently and selectively cracking alkanes in diesel into naphtha. In the present invention, a ZSM-5@β composite molecular sieve with a core-shell structure is prepared by compounding the ZSM-5 molecular sieve and the β molecular sieve as a cracking active component for the hydrocracking process of straight-run diesel feedstock. The chain alkanes in the straight-run diesel directly undergo cracking reaction with the ZSM-5 cracking components in the shell layer, converting into smaller molecules, and then entering the β molecular sieve in the core layer for isomerization reaction, which can maximize the cracking of the chain alkanes in the straight-run diesel into naphtha and ensure that most of the chain alkanes in the naphtha are isoalkanes, so the octane number of the resulting naphtha can be significantly improved.

[0028] The straight-run diesel hydrocracking method provided by the present invention can be used in any hydrocracking field, and is particularly suitable for producing high-octane gasoline components by hydrocracking of straight-run diesel, which can significantly increase the isoparaffin content and octane number in the gasoline components, thereby achieving the purpose of reducing the diesel-gasoline ratio.

[0029] Compared with the prior art, the method of the present invention has the following beneficial effects:

[0030] 1. Using straight-run diesel as raw material for hydrocracking reaction, the resulting naphtha has a high content of chain alkanes. After normal isomerization separation, the resulting gasoline component has a high content of isoalkanes and can be directly used as a blending component for National VI gasoline. The component rich in normal alkanes can be directly used as a steam cracking raw material for ethylene.

[0031] 2. The ZSM-5@β composite molecular sieve with strong alkane cracking and isomerization capabilities is selected as the acid center, which can effectively isomerize and crack the alkanes in diesel into naphtha components to produce high-octane gasoline.

[0032] 3. According to the characteristics of hydrocarbon composition in straight-run diesel, suitable hydrocracking catalysts are selected, and according to the quality requirements of the products, the concept of molecular refining is adhered to to achieve the goal of optimal product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The present invention is a schematic diagram of the process flow of a straight-run diesel hydrocracking-adsorption separation combined unit. DETAILED DESCRIPTION

[0034] The straight-run diesel hydrocracking-adsorption separation combined process provided by the present invention is further described below in conjunction with the accompanying drawings. Many equipments are omitted in the drawings, such as pumps, heat exchangers, heating furnaces, air cooling and stripping towers, but they are well known to ordinary technicians in this field.

[0035] Combination Figure 1 The process flow of the hydrocracking-adsorption separation combined device of the present invention is described in detail as follows: the raw oil 1 is mixed with the mixed hydrogen 2 and enters the stage refining reactor 3, and desulfurization, denitrogenation and dearomatization reactions occur through the hydrorefining catalyst bed, and the refined oil 4 enters the hydrocracking reactor 5. The oil 6 generated by the hydrocracking reactor enters the separator 7, the gas discharged from the upper part passes through the desulfurization tower 8, and the obtained circulating hydrogen is pressurized by the circulating hydrogen compressor 9 and mixed with the new hydrogen 10, and the mixed hydrogen 2 enters the hydrorefining reactor. The liquid phase 11 separated at the bottom of the separator 7 enters the fractionation tower 12 to obtain the fractionation tower top gas 13, naphtha 14 and diesel 15. The diesel 15 can be extracted as a product, or it can be circulated to the refining or cracking reactor inlet. 14 Naphtha enters the normal isomerization adsorption separation unit, and after adsorption, purging and desorption engineering, the residual oil and desorbed oil are obtained. The residual oil is rich in isoparaffins, and the desorbed oil is rich in normal paraffins.

[0036] The straight-run diesel hydrocracking method provided by the present invention will be further described below in conjunction with the embodiments, but the present invention is not limited thereto.

[0037] Table 1. Properties of crude oil.

[0038]

[0039] Table 2 Industrial catalysts.

[0040]

[0041] Table 3 Evaluation conditions.

[0042]

[0043] The raw oil used in the following examples and comparative examples is straight-run diesel, and its properties are shown in Table 1. The first stage refining reactor is filled with FF-66 hydrofining catalyst, and the hydrocracking reactor is filled with hydrocracking catalyst. In the examples and comparative examples, the distillation range of naphtha is 65~205℃, and the distillation range of diesel is>205℃.

[0044] In this embodiment, three ZSM-5@β composite molecular sieves with different properties are synthesized, and the specific synthesis methods are as follows:

[0045] Composite molecular sieve 1

[0046] (1) First, a hydrocracking catalyst with ZSM-5@β composite molecular sieve as the acid center was prepared. The specific preparation method is as follows: (1) First, β molecular sieve seed crystals were synthesized, and the feed silicon-aluminum ratio was controlled to be 25. Tetraethyl orthosilicate (TEOS) was used as the silicon source, and tetraethylammonium hydroxide (TEAOH) was used as the template. The mixture was fully stirred and mixed in a mass ratio of 1:1.5 to form a mixed solution I; NaAlO2 was used as the aluminum source, and an aqueous solution of NaOH was used as the reaction medium. The mass ratio of NaAlO2, H2O and NaOH was 1:120:0.1. The prepared mixed solution II was stirred at 25°C for 3 h. Subsequently, the mixed solution II was poured into the mixed solution I, and the mixed solution of the two was transferred to a crystallization kettle and crystallized at 140°C for 48 h to obtain nano-scale β molecular sieve seed crystals. (2) Secondly, a ZSM-5 synthetic emulsion was prepared, and the feed silicon-aluminum ratio was controlled to be 25. Tetraethyl orthosilicate was used as silicon source, tetrapropylammonium hydroxide (TPAOH) was used as template, and a certain amount of water was added as dissolving medium. The mass ratio of the three was TEOS: H2O: TPAOH = 1:2:4. After the three were fully dissolved, it was recorded as mixed solution III. NaAlO2 was used as aluminum source, and NaOH aqueous solution was used as reaction medium. NaAlO2:H2O:NaOH=1:3:1.5 (mass ratio). The prepared solution IV was stirred at 25℃ for 3 h. Solution III and β molecular sieve seeds were added to solution IV and stirred for 3 h. Then the mixed solution was transferred to a crystallization kettle and crystallized at 130℃ for 36 h. The solution in the crystallization kettle was filtered, washed with water, and dried in an oven at 60℃ for 8 h. The dried solid was transferred to a muffle furnace and calcined at 500℃ for 6 h to obtain a Na-type ZSM-5@β composite molecular sieve. The aqueous solution of ammonium chloride was used as the ammonium exchange medium, and the exchange temperature was 85°C. The Na-type ZSM-5@β composite molecular sieve prepared above was subjected to two ammonium exchanges and calcined at 500°C for 3 h to finally obtain the H-type ZSM-5@β composite molecular sieve 1. The theoretical mass ratio of β molecular sieve to ZSM-5 molecular sieve in the composite molecular sieve 1 was 1:5, the infrared acid content was 0.45 mmol / g, the average pore size was 2.4 nm, and the specific surface area was 300 m 2 / g, pore volume is 0.18 cm 3 / g.

[0047] Composite molecular sieve 2

[0048] (1) First, a hydrocracking catalyst with ZSM-5@β composite molecular sieve as the acid center was prepared. The specific preparation method is as follows: (1) First, β molecular sieve seed crystals were synthesized, and the feed silicon-aluminum ratio was controlled to be 30. Tetraethyl orthosilicate (TEOS) was used as the silicon source, and tetraethylammonium hydroxide (TEAOH) was used as the template. The mixture was fully stirred and mixed in a mass ratio of 1:3 to form a mixed solution I; NaAlO2 was used as the aluminum source, and an aqueous solution of NaOH was used as the reaction medium. The mass ratio of NaAlO2, H2O and NaOH was 1:150:0.1. The prepared mixed solution II was stirred at 25°C for 3 h. Subsequently, the mixed solution II was poured into the mixed solution I, and the mixed solution of the two was transferred to a crystallization kettle and crystallized at 140°C for 48 h to obtain nano-scale β molecular sieve seed crystals. (2) Secondly, a ZSM-5 synthetic emulsion was prepared, and the feed silicon-aluminum ratio was controlled to be 35. Tetraethyl orthosilicate was used as silicon source, tetrapropylammonium hydroxide (TPAOH) was used as template, and a certain amount of water was added as dissolving medium. The mass ratio of the three was TEOS: H2O: TPAOH = 1:2:4. After the three were fully dissolved, it was recorded as mixed solution III. NaAlO2 was used as aluminum source, and NaOH aqueous solution was used as reaction medium. NaAlO2:H2O:NaOH=1:3:1.5 (mass ratio). The prepared solution IV was stirred at 25℃ for 3 h. Solution III and β molecular sieve seeds were added to solution IV and stirred for 3 h. Then the mixed solution was transferred to a crystallization kettle and crystallized at 130℃ for 36 h. The solution in the crystallization kettle was filtered, washed with water, and dried in a 60℃ oven for 8 h. The dried solid was transferred to a muffle furnace and calcined at 500℃ for 6 h to obtain a Na-type ZSM-5@β composite molecular sieve. The aqueous solution of ammonium chloride was used as the ammonium exchange medium, and the exchange temperature was 85°C. The Na-type ZSM-5@β composite molecular sieve prepared above was subjected to two ammonium exchanges and calcined at 500°C for 3 h to finally obtain the H-type ZSM-5@β composite molecular sieve 2. The theoretical mass ratio of β molecular sieve to ZSM-5 molecular sieve in the composite molecular sieve 2 was 1:6. The infrared acid content of the composite molecular sieve 2 was 0.35 mmol / g, the average pore size was 2.1 nm, and the specific surface area was 280 m 2 / g, pore volume is 0.15 cm 3 / g.

[0049] Composite molecular sieve 3

[0050] (1) First, a hydrocracking catalyst with ZSM-5@β composite molecular sieve as the acid center was prepared. The specific preparation method is as follows: (1) First, β molecular sieve seed crystals were synthesized, the feed silicon-aluminum ratio was controlled to be 40, tetraethyl orthosilicate (TEOS) was used as the silicon source, tetraethylammonium hydroxide (TEAOH) was used as the template, and the mixture was fully stirred and mixed in a mass ratio of 1:5 to form a mixed solution I; NaAlO2 was used as the aluminum source, and an aqueous solution of NaOH was used as the reaction medium. The mass ratio of NaAlO2, H2O and NaOH was 1:150:0.1, and the prepared mixed solution II was stirred at 25°C for 3 h. Subsequently, the mixed solution II was poured into the mixed solution I, and the mixed solution of the two was transferred to a crystallization kettle, and crystallized at 140°C for 48 h to obtain nano-scale β molecular sieve seed crystals. (2) Secondly, a ZSM-5 synthetic emulsion was prepared, and the feed silicon-aluminum ratio was controlled to be 40. Tetraethyl orthosilicate was used as silicon source, tetrapropylammonium hydroxide (TPAOH) was used as template, and a certain amount of water was added as dissolving medium. The mass ratio of the three was TEOS: H2O: TPAOH = 1:2:4. After the three were fully dissolved, it was recorded as mixed solution III; NaAlO2 was used as aluminum source, and NaOH aqueous solution was used as reaction medium. NaAlO2:H2O:NaOH = 1:3:1.5 (mass ratio), and the prepared solution IV was stirred at 25 ° C for 3 h. Solution III and β molecular sieve seeds were added to solution IV and stirred for 3 h, and then the mixed solution was transferred to a crystallization kettle and crystallized at 130 ° C for 36 h. The solution in the crystallization kettle was filtered, washed with water, and dried in a 60 ° C oven for 8 h. The dried solid was transferred to a muffle furnace and calcined at 500 ° C for 6 h to obtain a Na-type ZSM-5@β composite molecular sieve. The aqueous solution of ammonium chloride was used as the ammonium exchange medium, and the exchange temperature was 85°C. The Na-type ZSM-5@β composite molecular sieve prepared above was subjected to two ammonium exchanges and calcined at 500°C for 3 h to finally obtain the H-type ZSM-5@β composite molecular sieve 3. The theoretical mass ratio of β molecular sieve to ZSM-5 molecular sieve in the composite molecular sieve 3 was 1:6, the infrared acid content was 0.32 mmol / g, the average pore size was 2.2 nm, and the specific surface area was 260 m 2 / g, pore volume is 0.14 cm 3 / g.

[0051] Example 1

[0052] The H-type ZSM-5@β composite molecular sieve 1 synthesized by the above method and alumina are used as carriers, and the mass fraction of the H-type ZSM-5@β composite molecular sieve in the carrier is 10%; the active metals Ni and Mo are loaded, and the content of the active metals in the catalyst is 20wt%. After calcination at 500℃, the NiMo / ZSM-5@β-Al2O3 hydrocracking catalyst is obtained. The hydrocracking catalyst prepared above is loaded into the hydrocracking reactor, and the industrial hydrorefining catalyst FF-66 is loaded into the hydrorefining reactor. Using straight-run diesel as raw material, the process conditions in Table 3 are evaluated to obtain naphtha and diesel products. After the naphtha product passes through the normal isomerization separation device, the properties of all products are analyzed.

[0053] Example 2

[0054] The H-type ZSM-5@β composite molecular sieve 2 synthesized by the above method and alumina were used as carriers. The mass fraction of the H-type ZSM-5@β composite molecular sieve in the carrier was 15%, and the active metals Ni and Mo were loaded, and the active metal content was 25 wt%. After calcination at 500°C, the NiMo / ZSM-5@β-Al2O3 hydrocracking catalyst was obtained. The hydrocracking catalyst prepared above was loaded into the hydrocracking reactor, and the industrial hydrorefining catalyst FF-66 was loaded into the hydrorefining reactor. Using straight-run diesel as raw material, the process conditions in Table 3 were evaluated to obtain naphtha and diesel products. After the naphtha product passed through the normal isomerization separation device, the properties of all products were analyzed.

[0055] Example 3

[0056] The H-type ZSM-5@β composite molecular sieve 3 synthesized by the above method and alumina were used as carriers. The mass fraction of the H-type ZSM-5@β composite molecular sieve in the carrier was 20%, and the active metals Ni and Mo were loaded, and the active metal content was 25 wt%. After calcination at 500°C, the NiMo / ZSM-5@β-Al2O3 hydrocracking catalyst was obtained. The hydrocracking catalyst prepared above was loaded into the hydrocracking reactor, and the industrial hydrorefining catalyst FF-66 was loaded into the hydrorefining reactor. Using straight-run diesel as raw material, the process conditions in Table 3 were evaluated to obtain naphtha and diesel products. After the naphtha product passed through the normal isomerization separation device, the properties of all products were analyzed.

[0057] Example 4

[0058] The H-type ZSM-5@β composite molecular sieve 2 synthesized by the above method and alumina were used as carriers. The mass fraction of the H-type ZSM-5@β composite molecular sieve in the carrier was 30%, and the active metals Ni and W were loaded. The active metal content was 25 wt%. After calcination at 500 °C, the NiW / ZSM-5@β-Al2O3 hydrocracking catalyst was obtained. The hydrocracking catalyst prepared above was loaded into the hydrocracking reactor, and the industrial hydrorefining catalyst FF-66 was loaded into the hydrorefining reactor. Using straight-run diesel as raw material, the process conditions in Table 3 were evaluated to obtain naphtha and diesel products. After the naphtha product passed through the normal isomerization separation device, the properties of all products were analyzed.

[0059] Comparative Example 1

[0060] The industrial hydrocracking catalyst FC-14 was loaded into the hydrocracking reactor, and the industrial hydrofining catalyst FF-66 was loaded into the hydrofining reactor. Using straight-run diesel as the raw material, the process conditions in Table 3 were evaluated to obtain naphtha and diesel products. After the naphtha product passed through the normal isomerization separation unit, the properties of all products were analyzed.

[0061] Comparative Example 2

[0062] The industrial hydrocracking catalyst FC-76 was loaded into the hydrocracking reactor, and the industrial hydrofining catalyst FF-66 was loaded into the hydrofining reactor. Using straight-run diesel as the raw material, the process conditions in Table 3 were evaluated to obtain naphtha and diesel products. After the naphtha product passed through the normal isomerization separation unit, the properties of all products were analyzed.

[0063] Comparative Example 3

[0064] The industrial hydrocracking catalyst FC-52 was loaded into the hydrocracking reactor, and the industrial hydrofining catalyst FF-66 was loaded into the hydrofining reactor. Using straight-run diesel as the raw material, the process conditions in Table 3 were evaluated to obtain naphtha and diesel products. After the naphtha product passed through the normal isomerization separation unit, the properties of all products were analyzed.

[0065] Table 4 Experimental results of the examples.

[0066]

[0067] Table 5 Comparative test results.

[0068]

[0069] It can be seen from the experimental results of the comparative examples and the embodiments that, using the ZSM-5@β composite molecular sieve provided by the present invention as a carrier, at the same conversion rate, the naphtha produced by the hydrocracking of straight-run diesel has a high octane number, and after normal isomerization separation, the octane number of the residual oil rich in isomer components obtained can reach above 95, which is a high-quality National VI gasoline blending component. When the catalyst in Example 4 is used, the naphtha produced by the hydrocracking of straight-run diesel has a maximum octane number of 95.6 after normal isomerization separation.

Claims

1. A straight-run diesel hydrocracking method, characterized in that: The following steps are involved: (1) providing a hydrofining reaction zone and a hydrocracking reaction zone, wherein the hydrofining reaction zone is filled with a hydrofining catalyst, and the hydrocracking reaction zone is filled with a hydrocracking catalyst containing a ZSM-5@β composite molecular sieve; (2) The straight-run diesel feedstock is mixed with hydrogen and enters the hydrotreating reaction zone, where it comes into contact with the hydrotreating catalyst to undergo desulfurization, denitrogenation and dearomatization reactions; (3) The effluent from the hydrotreating reaction and optional supplemental hydrogen enter the hydrocracking reaction zone for a hydrocracking reaction. The hydrocracking reaction zone includes 2 to 5 beds. (4) The effluent from the hydrocracking reaction is separated to obtain dry gas, liquefied gas, naphtha and diesel components; the initial distillation point of naphtha is 20~85℃, and the dry point is 165~210℃; (5) The naphtha component obtained in step (4) is subjected to a normal-isomerization adsorption separation device to obtain a normal-alkane-rich component and an iso-alkane-rich component; The ZSM-5@β composite molecular sieve has a β molecular sieve as a core and a ZSM-5 molecular sieve as a shell; the theoretical mass ratio of the β molecular sieve to the ZSM-5 molecular sieve is 1:2-1:10; The total silicon-aluminum ratio of the ZSM-5@β composite molecular sieve is 12-40, the infrared acid content is 0.2-1.5 mmol / g, the average pore diameter is 2.0-4.0 nm, and the specific surface area is 250-500 m 2 / g, pore volume is 0.08~0.30 cm 3 / g; The mass fraction of the ZSM-5@β composite molecular sieve in the catalyst carrier is 5% to 60%.

2. The hydrocracking method according to claim 1, characterized in that: The hydrocracking catalyst comprises a catalyst carrier, an active metal and a binder. The catalyst carrier contains a ZSM-5@β composite molecular sieve with a core-shell structure.

3. The hydrocracking method according to claim 2, characterized in that: The content of the active metal in terms of oxide is 6-40wt%.

4. The hydrocracking method according to claim 1, characterized in that: The straight-run diesel has an initial distillation point of 130-250° C., a final distillation point of 300-400° C., and an aromatics content of 10wt%-25wt%.

5. The hydrocracking method according to claim 1, characterized in that: The diesel component obtained in step (4) is used as a National VI diesel blending component or a steam cracking raw material for ethylene production, or is recycled to the refining reaction zone or cracking reaction zone for deep cracking.

6. The hydrocracking method according to claim 1, characterized in that: The normal isomerization adsorption separation device includes an adsorption unit, a purge unit and a desorption unit. The operating conditions of the adsorption unit are: pressure 0.1-1.5 MPa, temperature 150-350 °C, liquid phase volume space velocity 0.4-4 h -1 , adsorption time 10-20 min; the operating conditions of the purge unit are: purge pressure 0.1-1.5 MPa, temperature 150-350 °C, volume space velocity 40-120 h -1 , purge time 5 to 10 min; the typical operating conditions of the desorption unit are: pressure 0.3 to 1.5 MPa, temperature 150 to 350 °C, volume space velocity 40 to 120 h -1 , desorption time is 5 to 10 min.

7. The hydrocracking method according to claim 1, characterized in that: The reaction conditions of the hydrotreating reaction zone and the hydrocracking reaction zone are: reaction pressure of 5.0-15.0 MPa, average reaction temperature of 280-430°C, volumetric space velocity of hydrotreating of 0.2-6.0 h -1 , the volume space velocity of hydrocracking is 0.6~10.0h -1 , the volume ratio of hydrogen to oil is 400:1 to 1800:

1.

8. The hydrocracking method according to claim 7, characterized in that: The reaction conditions of the hydrotreating reaction zone and the hydrocracking reaction zone are: reaction pressure of 6.0-12.0 MPa, average reaction temperature of 310-420°C, volumetric space velocity of hydrotreating of 0.5-2.0 h -1 , the volumetric space velocity of hydrocracking is 1.0~2.0h -1 , the volume ratio of hydrogen to oil is 600:1~1000:

1.

9. The hydrocracking method according to any one of claims 1 to 8, characterized in that: The ZSM-5@β composite molecular sieve is prepared by the following method: (a) Synthesis of nanocrystalline seeds of β molecular sieve: using tetraethyl orthosilicate as a silicon source and tetraethylammonium hydroxide as a template, the mixture is stirred and mixed in a mass ratio of 1:1-1:5 to prepare a mixed solution I; using NaAlO2 as an aluminum source and a NaOH aqueous solution as a reaction medium, a mixed solution II is prepared in a mass ratio of NaAlO2:H2O:NaOH of 1:100-200:0.05-1, and the prepared mixed solution II is stirred at 15-35°C for 2-4 hours; Subsequently, the mixed solution II is poured into the mixed solution I, and the mixed solution of the two is transferred to a crystallization reactor, and crystallized at 120-160° C. for 24-72 h to obtain nano-scale β molecular sieve seed crystals; (b) Preparation of ZSM-5 molecular sieve synthesis emulsion: Tetraethyl orthosilicate TEOS is used as a silicon source, tetrapropylammonium hydroxide TPAOH is used as a template, and water is added as a dissolving medium. The mass ratio of the three is TEOS:H2O:TPAOH = 1:1~3:1~5. After the three are fully dissolved, it is recorded as a mixed solution III; NaAlO2 is used as an aluminum source, and an aqueous NaOH solution is used as a reaction medium. A mixed solution IV is prepared according to the mass ratio of NaAlO2:H2O:NaOH of 1:1~10:0.5~2. The prepared mixed solution IV is stirred at 15~35°C for 2~4h; the mixed solution III and β molecular sieve seed crystals are added to the mixed solution IV and stirred for 2~4h, and then the mixed solution is transferred to a crystallization kettle and crystallized at 120~160°C for 12~72h; the solution in the crystallization kettle is filtered, washed with water, and then dried; the dried solid is transferred to a muffle furnace and calcined at 400~600°C for 4~10 h, obtain Na-type ZSM-5@β composite molecular sieve; (c) Using ammonium chloride aqueous solution as the ammonium exchange medium at an exchange temperature of 70-95 °C, the Na-type ZSM-5@β composite molecular sieve prepared above was subjected to two ammonium exchanges and calcined at 400-600 °C for 2-4 h to finally obtain the H-type ZSM-5@β composite molecular sieve.

10. The hydrocracking method according to claim 9, characterized in that: In step (a), the silicon-aluminum ratio of the feed is controlled to be 20-40, and in step (b), the silicon-aluminum ratio of the feed is controlled to be 10-40.

Images