A method for hydrocracking kerosene

Abstract

The present invention discloses a method for hydrocracking kerosene. The method comprises: (1) in the presence of hydrogen, contacting kerosene with a first shape-selective cracking catalyst for a shape-selective cracking reaction; wherein the mass content of C7 + n-alkanes in the reaction product is controlled to be below 3.0%; (2) in the presence of hydrogen, contacting the reaction product of step (1) with a hydrocracking catalyst for a hydrocracking reaction; (3) separating the reaction product of step (2) to obtain an ethylene feedstock and a reforming feedstock. This method uses kerosene as a raw material for hydrocracking to produce chemical raw materials, and can greatly improve the yield and quality of chemical raw materials.

Description

Technical Field

[0001] The present invention belongs to the field of hydrocarbon oil hydrocracking, and particularly relates to a method for hydrocracking kerosene. Background Art

[0002] At present, optimizing the feedstock structure, deeply tapping the potential for integrated efficiency improvement, and increasing the proportion of light and low-grade feedstocks in ethylene cracking feedstocks are important tasks for Chinese steam cracking ethylene enterprises to reduce the production cost of olefins. Hydrocracking technology has the characteristics of strong feedstock adaptability, great flexibility in production operation and product scheme, and good product quality. It can directly convert various heavy and inferior feeds into high-quality jet fuels, diesel oils, lubricant base stocks, chemical naphtha, and tail oil steam cracking ethylene feedstocks urgently needed in the market, and has become one of the most important heavy oil deep processing processes in modern refining and petrochemical industries, and is increasingly widely used. With the current decrease in the demand for kerosene in the Chinese market, converting kerosene fractions into high-quality chemical raw materials has become a beneficial technical path for refining enterprises to optimize product structure and improve economic benefits.

[0003] CN201580070326.4 discloses a method for preparing LPG and BTX, including: a) subjecting a mixed hydrocarbon stream to a first hydrocracking in the presence of a first hydrocracking catalyst to prepare a first hydrocracking product stream; b) separating the first hydrocracking product stream to provide at least one light hydrocarbon stream containing at least C2 and C3 hydrocarbons, an intermediate hydrocarbon stream composed of C4 and / or C5 hydrocarbons, and a heavy hydrocarbon stream containing at least C6+ hydrocarbons, and c) subjecting the heavy hydrocarbon stream to a second hydrocracking in the presence of a second hydrocracking catalyst to prepare a second hydrocracking product stream containing BTX, wherein the second hydrocracking is more severe than the first hydrocracking, d) wherein, in the presence of a C4 hydrocracking catalyst, at least part of the intermediate hydrocarbon stream is subjected to C4 hydrocracking to prepare a C4 hydrocracking product stream, and the C4 hydrocracking is optimized for converting C4 hydrocarbons into C3 hydrocarbons.

[0004] CN201480037272.7 discloses a method for producing light olefin hydrocarbon compounds from a hydrocarbon feedstock, including the following steps: (a) feeding the hydrocarbon feedstock to a reaction zone for ring opening; (b) separating the reaction product generated from the reaction zone into an overhead stream and a side stream; (c) feeding the side stream from (b) to a gasoline hydrocracker (GHC) unit; (d) separating the reaction product of the GHC in step (c) into an overhead stream containing hydrogen, methane, ethane, and liquefied petroleum gas and a stream containing aromatic hydrocarbon compounds and a small amount of hydrogen and non-aromatic hydrocarbon compounds; (e) feeding the overhead stream from the gasoline hydrocracker (GHC) unit to a steam cracker unit.

[0005] The above method is mainly used for the production of LPG and BTX. At the same time, when producing ethylene raw materials, the content of n-alkanes in the ethylene raw materials is low, which will also result in a relatively low yield of trienes in the steam cracking ethylene plant. Therefore, it is of great significance to develop a hydrocracking method suitable for producing high-quality chemical raw materials from kerosene. Summary of the Invention

[0006] Aiming at the problems existing in the prior art, the object of the present invention is to provide a kerosene hydrocracking method. This method uses kerosene as a raw material for hydrocracking to produce chemical raw materials, which can significantly improve the yield and quality of chemical raw materials (i.e., ethylene raw materials and reforming raw materials).

[0007] The present invention provides a kerosene hydrocracking method, which uses kerosene as a raw material for hydrocracking to produce ethylene raw materials and reforming raw materials. The method includes:

[0008] (1) In the presence of hydrogen, kerosene is contacted with a first shape-selective cracking catalyst for shape-selective cracking reaction; wherein the mass content of C7 n-alkanes in the product of the first shape-selective cracking reaction is controlled to be below 3.0%. + The mass content of n-alkanes is controlled below 3.0%.

[0009] (2) In the presence of hydrogen, the reaction product of step (1) is contacted with a hydrocracking catalyst for hydrocracking reaction;

[0010] (3) The reaction product of step (2) is separated to obtain ethylene raw materials and reforming raw materials.

[0011] According to the present invention, in step (1), the first shape-selective cracking catalyst can be one or more catalysts.

[0012] According to the present invention, the composition of the first shape-selective cracking catalyst in step (1), based on the mass of the catalyst, includes:

[0013] a) 50.0% - 70.0% of molecular sieve; the molecular sieve is selected from one or more of ZSM-5 molecular sieve, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35 and ZSM-38 molecular sieves, preferably ZSM-5 molecular sieve;

[0014] b) 10% - 20% of at least one metal selected from Group VIB and Group VIII metals, calculated as oxides;

[0015] c) 10% - 40% of binder.

[0016] According to the present invention, preferably, component a) is ZSM-5 molecular sieve. Preferably, the SiO2 / Al2O3 molar ratio of the ZSM-5 molecular sieve is 40 - 60.

[0017] According to the present invention, preferably, the Group VIB metal in component b) is molybdenum and / or tungsten. The Group VIII metal in component b) is cobalt and / or nickel.

[0018] According to the present invention, preferably, the binder in component c) is preferably alumina.

[0019] According to the present invention, preferably, the composition of the first shape-selective cracking catalyst in step (1), based on the mass of the catalyst, comprises:

[0020] a) 50.0% to 70.0% of ZSM-5 molecular sieve;

[0021] b) 5.0% to 15.0% of molybdenum and / or tungsten, and 2.0% to 5.0% of cobalt and / or nickel, calculated as oxides;

[0022] c) 10% to 40% of binder.

[0023] According to the present invention, the specific surface area of the first shape-selective cracking catalyst in step (1) is 200 to 400 m 2 / g, and the pore volume is 0.25 to 0.45 mL / g.

[0024] According to the present invention, the preparation method of the first shape-selective cracking catalyst in step (1) can be prepared according to the conventional methods in the art. First, the molecular sieve and the binder are shaped, then dried and calcined, and then the metal components are loaded; the loading of the metal components is preferably the impregnation method.

[0025] According to the present invention, preferably, the mass content of C7 + n-alkanes in step (1) is controlled at 0.5 wt% to 3 wt%. As a non-limiting example, the mass content of C7 + n-alkanes in step (1) can be 0.1 wt%, 0.8 wt%, 1.2 wt%, 1.8 wt%, 2 wt%, 2.5 wt%, etc.

[0026] According to the present invention, the reaction pressure of the shape-selective cracking reaction in step (1) is 2.0 to 6.0 MPa, preferably 3.0 to 5.0 MPa.

[0027] According to the present invention, the reaction conditions of the shape-selective cracking reaction in step (1) are as follows: the average reaction temperature is 250 to 450 °C, preferably 300 to 400 °C; the liquid hourly space velocity is 0.1 to 15.0 h -1 , preferably 1.0 to 5.0 h -1 ; the hydrogen-oil volume ratio is 100:1 to 2500:1, preferably 400:1 to 2000:1.

[0028] According to the present invention, the mass content of n-alkanes in the kerosene in step (1) is 10% to 60%, preferably 20% to 50%. The kerosene may be straight-run kerosene, coking kerosene or other kerosene fractions with a relatively high content of n-alkanes.

[0029] According to the present invention, the mass content of cyclic hydrocarbons in the kerosene in step (1) is 30% to 80%, where the cyclic hydrocarbons are the sum of naphthenes and aromatics.

[0030] According to the present invention, the initial boiling point of the kerosene in step (1) is 100°C to 200°C, preferably 130°C to 180°C; the final boiling point is 210°C to 300°C, preferably 220°C to 280°C. The initial boiling point of the kerosene is at least 30°C to 150°C lower than the final boiling point, preferably 50°C to 100°C lower.

[0031] According to the present invention, the kerosene in step (1) may contain impurities such as sulfur, nitrogen, etc. According to actual needs, a hydrofining catalyst may be provided upstream of the first shape-selective cracking catalyst to remove impurities such as sulfur, nitrogen, etc. Among them, the nitrogen content in the reaction stream in contact with the first shape-selective cracking catalyst is preferably below 50 mg / kg, more preferably below 20 mg / kg. The hydrofining catalyst mentioned above may adopt a conventional hydrofining catalyst, which is mainly used for hydrodesulfurization, denitrification and other impurities. The hydrofining catalyst includes a carrier and a hydroactive metal. The carrier is an inorganic refractory oxide, generally selected from one or more of alumina, amorphous silica-alumina, silica or titanium oxide, etc.; the hydroactive metal includes Group VIB and / or Group VIII metal components. In the hydrofining catalyst, Group VIB is preferably selected from tungsten and / or molybdenum, and its content in the catalyst based on the mass of the oxide is 5% to 30%, preferably 10% to 20%; Group VIII is preferably selected from nickel and / or cobalt, and its content in the catalyst based on the mass of the oxide is 1% to 6%, preferably 1.5% to 5%.

[0032] According to the present invention, in the reaction product obtained in step (2), the mass ratio of the C6-C8 monocyclic cyclic hydrocarbons to the total cyclic hydrocarbons in the raw material is 0.30 to 0.50, preferably 0.35 to 0.45. The raw material is kerosene.

[0033] According to the present invention, the hydrocracking catalyst in step (2) includes at least two catalysts. Preferably, along the flow direction of the material, the hydrocracking catalysts are an isohydrocarbon conversion catalyst and a second shape-selective cracking catalyst in sequence; among them, the volume ratio of the isohydrocarbon conversion catalyst to the second shape-selective cracking catalyst is 1:1 to 6:1, preferably 2:1 to 4:1.

[0034] According to the present invention, the isohydrocarbon conversion catalyst in step (2) has the functions of ring-opening cracking of polycyclic cyclic hydrocarbons, selectively cracking the side chains of isohydrocarbons or cyclic hydrocarbons and retaining monocyclic cyclic hydrocarbons.

[0035] According to the present invention, in step (2), the isomerization hydrocarbon conversion catalyst, based on the mass of the catalyst, comprises:

[0036] k) The hydrogenation component content is 5 wt% to 40 wt%, preferably 10 wt% to 20 wt% in terms of oxide;

[0037] l) The cracking component content is 20 wt% to 80 wt%, preferably 30 wt% to 70 wt%;

[0038] m) The binder content is 5 wt% to 75 wt%, preferably 10 wt% to 50 wt%.

[0039] According to the present invention, preferably, the hydrogenation component in component k) comprises at least one of metals of Group VIB and / or Group VIII, metal oxides, and metal sulfides. Preferably, the hydrogenation component in component k) comprises at least one of metals, metal oxides, and metal sulfides of iron, chromium, molybdenum, tungsten, cobalt, and nickel.

[0040] According to the present invention, preferably, the cracking component in component l) comprises an acidic molecular sieve, preferably at least one of Beta zeolite and Y zeolite, more preferably Beta zeolite.

[0041] According to the present invention, preferably, the binder in component m) is alumina and / or silica.

[0042] According to the present invention, in step (2), the second shape-selective cracking catalyst, based on the mass of the catalyst, comprises:

[0043] o) 50.0% to 70.0% of molecular sieve; the molecular sieve is selected from one or more of ZSM-5 molecular sieve, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, and ZSM-38 molecular sieves, preferably ZSM-5 molecular sieve;

[0044] p) 10% to 20% of at least one selected from metals of Group VIB and Group VIII in terms of oxide;

[0045] q) 10% to 40% of binder.

[0046] According to the present invention, preferably, component o) is ZSM-5 molecular sieve. The SiO2 / Al2O3 molar ratio of the ZSM-5 molecular sieve is 40 to 60.

[0047] According to the present invention, preferably, the metal of Group VIB in component p) is molybdenum and / or tungsten. The metal of Group VIII in component b) is cobalt and / or nickel.

[0048] According to the present invention, preferably, the binder in component q) is preferably alumina.

[0049] According to the present invention, in step (2), the second shape-selective cracking catalyst, based on the mass of the catalyst, comprises:

[0050] o) 50.0% to 70.0% of ZSM-5 molecular sieve;

[0051] p) 5.0% to 15.0% of molybdenum and / or tungsten, and 2.0% to 5.0% of cobalt and / or nickel, calculated as oxides;

[0052] q) 10% to 40% of a binder.

[0053] According to the present invention, in step (2), the specific surface area of the second shape-selective cracking catalyst is 200 to 400 m 2 / g, and the pore volume is 0.25 to 0.45 mL / g.

[0054] According to the present invention, in step (2), the hydrocracking catalyst can be prepared by conventional methods in the art. First, the molecular sieve and the binder are shaped, then dried and calcined, and then the metal components are loaded; the preferred method for loading the metal components is the impregnation method.

[0055] According to the present invention, in step (2), the reaction pressure of the hydrocracking reaction is 2.0 to 6.0 MPa, preferably 3.0 to 5.0 MPa.

[0056] According to the present invention, in step (2), the reaction conditions of the hydrocracking reaction are as follows: the average reaction temperature is 250 to 450 °C, preferably 300 to 400 °C; the liquid hourly space velocity is 0.1 to 15.0 h -1 , preferably 1.0 to 5.0 h -1 ; the hydrogen-oil volume ratio is 100:1 to 2500:1, preferably 400:1 to 2000:1.

[0057] According to the present invention, preferably, the reaction effluent of step (2) is subjected to supplementary hydrorefining.

[0058] According to the present invention, preferably, the hydrocracking reaction in step (2) and the shape-selective cracking reaction in step (1) are carried out at the same pressure.

[0059] According to the present invention, in step (3), the reforming feedstock is heavy naphtha. The ethylene feedstock in step (3) includes ethane, propane, butane, and light naphtha. Heavy naphtha can be used as a reforming feedstock to produce BTX. The ethylene feedstock can be steam cracked to produce light olefins. Light olefins refer to olefins with four or fewer carbon atoms, especially ethylene, propylene, and butadiene.

[0060] According to the present invention, in the ethylene raw material obtained in step (3), based on the total mass of ethane, propane, butane and light naphtha, the normal paraffins account for 50% to 70%, preferably 55% to 65%. Based on the total mass of ethane, propane, butane and light naphtha, after entering the steam cracking to ethylene unit, the yield of trienes (including ethylene, propylene and butadiene) reaches more than 50%, and further can reach 50% to 60%. Generally, the operating conditions of the steam cracking to ethylene unit are as follows: reaction temperature 750°C to 900°C, reaction pressure 0.1 to 0.5 MPa, and water-oil mass ratio 0.2 to 0.6.

[0061] According to the present invention, preferably, the reforming raw material obtained in step (3) is subjected to supplementary hydrofining.

[0062] According to the present invention, the product obtained in step (3) further contains tail oil; the tail oil can be recycled to step (1) to contact and react with the first shape-selective cracking catalyst, and / or recycled to step (2) to contact and react with the hydrocracking catalyst.

[0063] Petroleum hydrocarbons have a complex composition, mainly including alkanes, cycloalkanes and aromatics, while high-quality ethylene raw materials are small-molecule normal paraffins, and reforming raw materials are monocyclic cycloalkanes and aromatics. The inventors have found through research that kerosene raw materials can selectively generate small-molecule normal paraffins with high selectivity by successively passing through the shape-selective cracking of straight-chain alkanes, the ring-opening cracking of polycyclic cyclic hydrocarbons, and the selective hydrocracking of long side chains on isoparaffins or cyclic hydrocarbons, while trying to retain monocyclic cyclic hydrocarbons, so as to efficiently enrich small-molecule normal paraffins in the ethylene raw material, and at the same time retain monocyclic cyclic hydrocarbons in the reforming raw material as much as possible to achieve efficient enrichment of high-quality reforming raw materials. In this way, the purpose of greatly improving the yields of chemical raw materials (i.e., ethylene raw materials and reforming raw materials) and the quality of ethylene raw materials and reforming raw materials can be achieved, thereby completing the present invention.

[0064] Compared with the prior art, the present invention has the following beneficial technical effects:

[0065] (1) In the hydrocracking method for producing chemical raw materials from kerosene of the present invention, the kerosene contacts and reacts with the first shape-selective cracking catalyst, mainly selectively cracking the normal paraffins in the raw material and the long straight chains of isoparaffins and cycloalkanes containing long straight chains to generate small-molecule normal paraffins, and controlling C7 in the reaction product +The content of n-alkanes is below 3.0%; the product of the shape-selective cracking reaction contacts with a hydrocracking catalyst with a specific grading (in the direction of the material flow, successively an isohydrocarbon conversion catalyst and a second shape-selective cracking catalyst) for reaction. The main reactions are to open the rings of polycyclic cyclic hydrocarbons and retain the monocyclic cyclic hydrocarbons, and further break the side chains in each hydrocarbon to generate small-molecule hydrocarbons. In this way, a large amount of linear alkanes in the raw material can be converted into gas and light naphtha components, that is, enriched in ethylene raw materials, while the monocyclic cyclic hydrocarbons are retained in the heavy naphtha fraction, that is, enriched in reforming raw materials. Through simple fractionation, the efficient separation of linear alkanes and cyclic hydrocarbons can be achieved. While increasing the production of high-quality ethylene cracking raw materials, the quality of heavy naphtha as a catalytic reforming feedstock is improved.

[0066] (2) The content of monocyclic cyclic hydrocarbons in the heavy naphtha obtained by the method of the present invention is high. As the feedstock for the catalytic reforming unit, the linear alkane cyclization and dehydrogenation unit in the catalytic reforming unit can be omitted, and the investment and energy consumption of the catalytic reforming unit can be greatly reduced. At the same time, since the hydrocracking reaction follows the carbocation reaction mechanism, the side-chain breaking reaction of cyclic hydrocarbons above C9 can be selectively realized, so that the C6-C8 cyclic hydrocarbons in the product have a high enrichment degree. After catalytic reforming and aromatics extraction, the BTX yield can be greatly increased.

[0067] (3) The present invention selectively converts the linear alkanes in kerosene into small-molecule alkanes. This process consumes a certain amount of hydrogen, but the light hydrocarbons also have a high hydrogen yield as the raw material for the ethylene unit. The lower the carbon number, the higher the hydrogen yield. Therefore, most of the hydrogen consumed in the hydrogenation process can be recovered after passing through the ethylene unit. At the same time, the light hydrocarbons as ethylene raw materials can greatly increase the yields of ethylene, propylene and butadiene, and extend the cleaning cycle of the ethylene unit, significantly improving the economic benefits of the unit. Detailed implementation mode

[0068] The functions and effects of the present invention will be further illustrated by the following examples, but the following examples do not limit the method of the present invention.

[0069] In the present invention, unless otherwise specified, % is the mass fraction.

[0070] The overall volumetric space velocity in the examples and comparative examples is the ratio of the volume of fresh feed to the total volume of the catalyst.

[0071] In the present invention, the first shape-selective cracking catalyst in each example is represented by Cat-A plus a number, such as Cat-A1, Cat-A2. The first shape-selective cracking catalyst is prepared by a conventional active metal saturation impregnation method, and the physical and chemical properties of the obtained catalyst are shown in Table 1.

[0072] In the present invention, the isoparaffin conversion catalysts in each example are denoted as Cat-B plus a number, such as Cat-B1, Cat-B2. The second shape-selective cracking catalyst is denoted as Cat-C plus a number, such as Cat-C1, Cat-C2. The physicochemical properties of the catalysts are shown in Table 2. In each example, the isoparaffin conversion catalyst and the second shape-selective cracking catalyst are prepared by a conventional active metal saturation impregnation method. Among them, the properties of the Beta zeolite used are as follows: the SiO2 / Al2O3 molar ratio is 30, the specific surface area is 350 m 2 / g, and the pore volume is 0.32 cm 3 / g. The properties of the Y zeolite used are as follows: the SiO2 / Al2O3 molar ratio is 15, the specific surface area is 400 m 2 / g, and the pore volume is 0.30 cm 3 / g. The physicochemical properties of the obtained catalysts are shown in Table 2.

[0073] In the present invention, the feedstock oil in each example uses kerosene as the raw material, and its main properties are shown in Table 3.

[0074] In the present invention, the distillation range of light naphtha is the liquid component with a boiling point less than 60 °C, and the distillation range of heavy naphtha is 60 - 175 °C.

[0075] In the present invention, the yield of ethylene feedstock refers to the mass ratio of ethane, propane, butane, and light naphtha in the hydrocracking product to the fresh feedstock (kerosene) for hydrocracking. The yield of heavy naphtha refers to the mass ratio of heavy naphtha in the hydrocracking product to the fresh feedstock for hydrocracking.

[0076] Examples 1 - 4

[0077] The hydrocracking method described above includes the steps of:

[0078] (1) In the presence of hydrogen, kerosene is contacted with the first shape-selective cracking catalyst for a shape-selective cracking reaction; and the mass content of C7 + n-alkanes in the reaction product is controlled;

[0079] (2) In the presence of hydrogen, the reaction product of step (1) is contacted with the hydrocracking catalyst for a hydrocracking reaction; along the flow direction of the material, the hydrocracking catalyst is successively the isoparaffin conversion catalyst and the second shape-selective cracking catalyst.

[0080] (3) The product of step (2) is separated to obtain ethylene feedstock, reforming feedstock, and tail oil; the reforming feedstock is heavy naphtha; the ethylene feedstock includes ethane, propane, butane, and light naphtha; the tail oil is recycled to the hydrocracking reaction zone in step (2).

[0081] The process conditions and hydrocracking effects in each example are shown in Table 4.

[0082] Comparative Example 1

[0083] The difference from Example 1 is that the feedstock directly contacts and reacts with the hydrocracking catalyst. The process conditions and hydrotreating effects in this example are shown in Table 4.

[0084] Comparative Example 2

[0085] The difference from Example 1 is that in step (1), the content of C7 + n - paraffin in the reaction product is controlled to be 4%. The process conditions and hydrotreating effects in this example are shown in Table 4.

[0086] Table 1 Physicochemical properties of the first - shape - selective cracking catalyst

[0087] Catalyst Cat-A1 Cat-A2 <![CDATA[Pore volume, cm 3 / g]]> 0.35 0.45 <![CDATA[Specific surface area, m 2 / g]]> 300 200 Catalyst composition ZSM-5, wt% 50 70 Mo, wt% 15 5 Ni, wt% 5 5 Binder 30 20 <![CDATA[SiO2 / Al2O3 molar ratio of ZSM-5]]> 40 60

[0088] Table 2 Physicochemical properties of the hydrocracking catalyst

[0089] Catalyst properties Cat-B1 Cat-B2 Cat-C1 Cat-C2 <![CDATA[Pore volume, cm 3 / g]]> 0.35 0.35 0.35 0.35 <![CDATA[Specific surface area, m 2 / g]]> 300 300 300 300 Catalyst composition Beta, wt% 50 - - - Y, wt% - 50 - - <![CDATA[MoO3, wt%]]> 10 10 15 5 NiO, wt% 5 5 2 5 Aluminum oxide, wt% 35 35 30 20 ZSM-5, wt% - - 53 70

[0090] Table 3 Main properties of the feedstock

[0091] Name of feedstock oil Kerosene <![CDATA[Density (20 °C) / kg·m -3 > 788.3 Distillation range / °C (ASTM D86) IBP / 10% 162 / 184 30％ / 50％ 196 / 205 70％ / 90％ 215 / 231 95% / EBP 238 / 246 Normal paraffin, wt% 24 Cyclic hydrocarbon, wt% 42 Nitrogen content, mg / kg 20

[0092] Table 4 Process conditions and hydrotreating effects of each example

[0093]

[0094]

[0095] Continued Table 4

[0096]

[0097] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A kerosene hydrocracking process, comprising: (1) In the presence of hydrogen, kerosene is contacted with a first shape-selective cracking catalyst for shape-selective cracking reaction; Among them, the mass content of C7 in the reaction product + in the normal paraffin is controlled below 3.0%; (2) In the presence of hydrogen, the reaction product of step (1) is contacted with a hydrocracking catalyst for hydrocracking reaction; (3) The reaction product of step (2) is separated to obtain ethylene feedstock and reforming feedstock; In step (2), the hydrocracking catalyst comprises at least two catalysts; along the material flow direction, the hydrocracking catalysts are an isoparaffin conversion catalyst and a second shape-selective cracking catalyst in sequence; Heavy naphtha is used as reforming feedstock to produce BTX; Ethane, propane, butane and light naphtha are used as ethylene feedstock to produce light olefins; In the obtained ethylene feedstock, based on the total mass of ethane, propane, butane and light naphtha, the normal paraffin hydrocarbons account for 55% - 70%; The composition of the first shape-selective cracking catalyst in step (1), based on the mass of the catalyst, comprises: a) 50.0% - 70.0% of molecular sieve; the molecular sieve is selected from one or more of ZSM-5 molecular sieve, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35 and ZSM-38 molecular sieves; b) 10% - 20% of at least one metal selected from Group VIB and Group VIII metals, calculated as oxides; c) 10% - 40% of binder; The isoparaffin conversion catalyst in step (2), based on the mass of the catalyst, comprises: k) The content of hydrogenation component is 5wt% - 40wt% calculated as oxides; l) The content of cracking component is 20wt% - 80wt%; m) The content of binder is 5wt% - 75wt%; Component l) The cracking component includes at least one of Beta molecular sieve and Y molecular sieve; The second shape-selective cracking catalyst in step (2), based on the mass of the catalyst, comprises: o) 50.0% - 70.0% of molecular sieve; the molecular sieve is selected from one or more of ZSM-5 molecular sieve, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35 and ZSM-38 molecular sieves; p) 10% - 20% of at least one metal selected from Group VIB and Group VIII metals, calculated as oxides; q) 10% - 40% of binder.

2. The method according to claim 1, wherein In the reaction product obtained in step (2), the mass ratio of C6 - C8 monocyclic cyclic hydrocarbons to the total mass of cyclic hydrocarbons in the reaction product is 0.30 - 0.

50.

3. The method according to claim 2, wherein In the reaction product obtained in step (2), the mass ratio of C6 - C8 monocyclic cyclic hydrocarbons to the total mass of cyclic hydrocarbons in the reaction product is 0.35 - 0.

45.

4. The method according to claim 1, wherein In step (2), the volume ratio of the isoparaffin conversion catalyst to the second shape-selective cracking catalyst is 1:1 - 6:

1.

5. The method according to claim 4, characterized in that In step (2), the volume ratio of the isoparaffin conversion catalyst to the second shape-selective cracking catalyst is 2:1 - 4:

1.

6. The method according to claim 1, characterized in that The isoparaffin conversion catalyst in step (2), based on the mass of the catalyst, comprises: k) The content of hydrogenation component is 10wt% - 20wt% calculated as oxides; l) The content of cracking component is 30wt% - 70wt%; m) The content of the binder is 10 wt% to 50 wt%; Component l) The cracking component includes Beta zeolite.

7. The method according to claim 1 or 6, characterized in that, In step (2), the zeolite of the second shape-selective cracking catalyst is ZSM-5 zeolite.

8. The method according to claim 1, characterized in that, In step (1), the zeolite in the first shape-selective cracking catalyst is ZSM-5 zeolite.

9. The method according to claim 1 or 8, characterized in that, The specific surface area of the first shape-selective cracking catalyst described in step (1) is 200-400 m 2 / g, and the pore volume is 0.25-0.45 mL / g.

10. The method according to claim 1, wherein C7 in step (1) + The mass content of the n-alkane is controlled at 0.5 wt% to 3 wt%.

11. The method according to claim 1, characterized in that The reaction conditions of the shape-selective cracking reaction described in step (1) are as follows: the average reaction temperature is 250~450°C; and / or, the liquid hourly space velocity is 0.1~15.0 h -1 ; and / or, the hydrogen-oil volume ratio is 100:1~2500:

1.

12. The method according to claim 11, wherein The reaction conditions of the shape-selective cracking reaction described in step (1) are as follows: the average reaction temperature is 300 to 400 °C; and / or, the liquid hourly space velocity is 1.0 to 5.0 h -1 ; and / or, the hydrogen-oil volume ratio is 400:1 to 2000:

1.

13. The method according to claim 1 or 11, characterized in that, In step (1), the reaction pressure of the shape-selective cracking reaction is 2.0 to 6.0 MPa.

14. The method according to claim 13, wherein In step (1), the reaction pressure of the shape-selective cracking reaction is 3.0 to 5.0 MPa.

15. The method according to claim 1, characterized in that In step (1), the mass content of n-alkanes in the kerosene is 10% to 60%; and / or, the mass content of cyclic hydrocarbons in the kerosene is 30% to 80%; and / or, the initial boiling point of the kerosene is 100 °C to 200 °C; the final boiling point is 210 °C to 300 °C.

16. The method according to claim 15, wherein In step (1), the mass content of n-alkanes in the kerosene is 20% to 50%; and / or, the initial boiling point of the kerosene is 130 °C to 180 °C; the final boiling point is 220 °C to 280 °C.

17. The method according to claim 1, wherein The reaction conditions for the hydrocracking reaction in step (2) are as follows: the average reaction temperature is 250 - 450 °C; and / or, the liquid hourly space velocity is 0.1 - 15.0 h -1 ; and / or, the hydrogen-oil volume ratio is 100:1 - 2500:

1.

18. The method according to claim 17, wherein The reaction conditions of the hydrocracking reaction in step (2) are as follows: the average reaction temperature is 300~400°C; and / or, the liquid hourly space velocity is 1.0~5.0 h -1 ; and / or, the hydrogen-oil volume ratio is 400:1~2000:

1.

19. The method according to claim 1 or 17, characterized in that, In step (2), the reaction pressure of the hydrocracking reaction is 2.0 to 6.0 MPa.

20. The method according to claim 19, wherein In step (2), the reaction pressure of the hydrocracking reaction is 3.0 to 5.0 MPa.

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